Can supervise: YES
Qin, C, Ni, W, Tian, H, Lu, L & Liu, RP 2019, 'Radio over Cloud (RoC): Cloud-Assisted Distributed Beamforming for Multi-class Traffic', IEEE Transactions on Mobile Computing.View/Download from: Publisher's site
IEEE Cloud has yet to be applied to computationally intensive radio signal processing, due to closely coupled computing tasks resulting from interference. This paper presents a new cloud-assisted joint beamforming architecture, where computations are decoupled for individual wireless users and pipelined for cloud execution, using Difference of Convex (DC), l1-norm approximations, and dual decompositions. User-specific tasks are constructed and aligned with the cloud to leverage computation reuses and minimize overhead. The time-complexity is dramatically improved to support networks with tens to hundreds of base stations and users, without compromising the sum rate and quality-of-service. Further, the superiority of DC to the state-of-the-art Weighted Minimum Mean Square Error (WMMSE) in terms of convex relaxation is observed and discussed. Corroborated by simulations, the reason is revealed as WMMSE aggressively increases the data rate at interim stages, hence adversely interacting with l1-norm approximation and reducing the feasible solution regions at later stages.
Wu, K, Ni, W, Su, T, Liu, RP & Guo, YJ 2019, 'Efficient angle-of-arrival estimation of lens antenna arrays for wireless information and power transfer', IEEE Journal on Selected Areas in Communications, vol. 37, no. 1, pp. 116-130.View/Download from: UTS OPUS or Publisher's site
© 1983-2012 IEEE. Antenna design and angle-of-arrival (AoA) estimation are critical to the efficiency of wireless information and power transfer. The AoA estimation is challenging for energy-efficient lens antenna arrays (LAAs), due to discrete sets of fixed discrete Fourier transform (DFT) beams. This paper presents a novel fast and accurate approach for the AoA estimation of LAAs. The key idea is that we prove the two differential outputs of three adjacent lens beams, referred to as 'DFT beam differences (DBDs),' that are the strongest at the two sides of an AoA. They are easy to identify and robust to noises, and their powers are proved to provide an accurate estimate of the AoA. Another important aspect is a new beam synthesis technique which produces different beam widths based on DFT beams and practical 1-bit phase shifts in real time. As a result, the angular region containing the AoA can exponentially narrow down, and the two strongest DBDs can be quickly identified. The proposed approach can operate in coupling with successive interference cancellation to estimate the AoAs of multiple paths. Simulations show that the proposed approach is able to outperform the state of the art by orders of magnitude in terms of accuracy. The power transfer efficiency can be dramatically improved.
Wang, X, Zha, X, Ni, W, Liu, RP, Guo, YJ, Niu, X & Zheng, K 2019, 'Game Theoretic Suppression of Forged Messages in Online Social Networks', IEEE Transactions on Systems, Man, and Cybernetics: Systems, pp. 1-11.View/Download from: Publisher's site
Yuan, C, Tao, X, Li, N, Ni, W, Liu, RP & Zhang, P 2019, 'Analysis on Secrecy Capacity of Cooperative Non-Orthogonal Multiple Access with Proactive Jamming', IEEE Transactions on Vehicular Technology, vol. 68, no. 3, pp. 2682-2696.View/Download from: Publisher's site
© 1967-2012 IEEE. This paper analyzes the secrecy capacity of a cooperative relaying system using non-orthogonal multiple access (NOMA). A new cooperative NOMA scheme is proposed, where the source actively sends jamming signals while the relay is forwarding, thereby enhancing the security of intended communication links. Closed-form expressions for the ergodic secrecy rate are derived in the presence of an eavesdropper. Asymptotic approximate expressions for the ergodic secrecy rate are established in high signal-to-noise ratio (SNR) regime, which provides insights on secure NOMA transmission. Numerical results reveal the critical condition, under which NOMA is able to outperform orthogonal multiple access (OMA) in terms of secrecy rate. The proposed NOMA scheme can improve the secrecy rate by about 78.1rm%.
Ren, C, Lyu, X, Ni, W, Tian, H & Liu, RP 2019, 'Distributed Online Learning of Fog Computing under Nonuniform Device Cardinality', IEEE Internet of Things Journal, vol. 6, no. 1, pp. 1147-1159.View/Download from: Publisher's site
© 2014 IEEE. Processing data around the point of capture, fog computing can support computationally demanding Internet-of-Things (IoT) services. Distributed online optimization is important given the size of IoT, but challenging due to time variations of random traffic and nonuniform connectivity (or cardinality) of edge servers and IoT devices. This paper presents a distributed online learning approach to asymptotically minimizing the time-average cost of fog computing in the absence of the a-priori knowledge on traffic randomness, for light-weight, and delay-tolerant application scenarios. Stochastic gradient descent is exploited to decouple the optimizations between time slots. A graph matching problem is then formulated for every time slot by decoupling and unifying the nonuniform cardinalities, and solved in a distributed manner by developing a new linear (1/2)-approximation method. We prove that the optimality loss resulting from the distributed approximate graph matching method can be compensated and diminish by increasing the learning time. Corroborated by simulations, the proposed distributed online learning is asymptotically optimal and superior to the state of the art in terms of throughput and energy efficiency.
Xiao, C, Zeng, J, Ni, W, Su, X, Liu, RP, Lv, T & Wang, J 2019, 'Downlink MIMO-NOMA for Ultra-Reliable Low-Latency Communications', IEEE Journal on Selected Areas in Communications, vol. 37, no. 4, pp. 780-794.View/Download from: UTS OPUS or Publisher's site
© 2019 IEEE. With the emergence of the mission-critical Internet of Things applications, ultra-reliable low-latency communications are attracting a lot of attentions. Non-orthogonal multiple access (NOMA) with multiple-input multiple-output (MIMO) is one of the promising candidates to enhance connectivity, reliability, and latency performance of the emerging applications. In this paper, we derive a closed-form upper bound for the delay target violation probability in the downlink MIMO-NOMA, by applying stochastic network calculus to the Mellin transforms of service processes. A key contribution is that we prove that the infinite-length Mellin transforms resulting from the non-negligible interferences of NOMA are Cauchy convergent and can be asymptotically approached by a finite truncated binomial series in the closed form. By exploiting the asymptotically accurate truncated binomial series, another important contribution is that we identify the critical condition for the optimal power allocation of MIMO-NOMA to achieve consistent latency and reliability between the receivers. The condition is employed to minimize the total transmit power, given a latency and reliability requirement of the receivers. It is also used to prove that the minimal total transmit power needs to change linearly with the path losses, to maintain latency and reliability at the receivers. This enables the power allocation for mobile MIMO-NOMA receivers to be effectively tracked. The extensive simulations corroborate the accuracy and effectiveness of the proposed model and the identified critical condition.
© 2017 Stretchable fiber-shaped supercapacitors (SFSSs) with high energy density and high-voltage output are becoming increasingly critical for powering wearable electronics. However, challenges still exist in the pursuit of combination of mechanical stretchability and excellent electrochemical performance due to the limitation of the fiber electrode. Here we circumvent these problems by developing a new type of 'internal tandem' stretchable fiber-shaped supercapacitors based on high crystalline 'all-in-one' polymer fiber. This polymer fiber has the combined properties of high conductivity, high flexibility, high specific capacitance and wide electrochemical window that can simultaneously function as electrical conductive wire and as energy storage electrode in an assembled device. The symmetric assembled tandem SFSS groups (T-SFSSs) are fabricated without the use of metal wire and additional welding connection showing tunable voltage output, tailored capacitance and outstanding stretchablility. The resulting T-SFSS assemblies consisting of 8 serially connected cells display high-voltage output of 12.8 V, ultrahigh energy density of 41.1 W h cm2 at power density of 3520 W cm2 and remarkable stretchability of up to 400% without obvious capacitance degradation. This work provides a new family of flexible fiber electrode and novel concept designs of flexible power systems that could be threaded or integrated into wearable and portable electronics.
Huang, L, Guan, Q, Cheng, J, Li, C, Ni, W, Wang, Z, Zhang, Y & Wang, B 2018, 'Free-standing N-doped carbon nanofibers/carbon nanotubes hybrid film for flexible, robust half and full lithium-ion batteries', Chemical Engineering Journal, vol. 334, pp. 682-690.View/Download from: Publisher's site
© 2017 Elsevier B.V. The development of flexible electronics requires the power sources with matchable flexibility, robust mechanic property, as well as high power and energy density that would maintain the durability of flexible electronics during use. Herein, newly designed free-standing N-doped carbon films with hierarchical structure of carbon nanofibers and carbon nanotubes (CNFs/CNTs hybrids) are prepared via a simple electrospinning process. This interconnected hybrid film displays high conductivity and excellent flexibility. As a free-standing and binder-free anode material, the CNFs/CNTs hybrid electrode can achieve a reversible capacity of 1099.5 mAh g1 at a current density of 0.05 A g1 with superior rate capabilities and excellent cyclic stability. What's more, utilizing the CNFs/CNTs hybrid film as the electrode, this assembled highly flexible half and full batteries also show attractive performances and can easily light up a group of 12 light emission diodes at flat and various bending positions, making it possible to be applied in the flexible electronic devices.
Qin, C, Ni, W, Tian, H, Liu, RP & Guo, YJ 2018, 'Joint Beamforming and User Selection in Multiuser Collaborative MIMO SWIPT Systems with Non-negligible Circuit Energy Consumption', IEEE Transactions on Vehicular Technology, vol. 67, no. 5, pp. 3909-3923.View/Download from: UTS OPUS or Publisher's site
IEEE Multi-antenna beamforming has potential to improve the efficiency of simultaneous wireless information and power transfer (SWIPT). Existing designs are focused on the downlink of multiple-input-single-output under the assumption of single-antenna users and negligible energy consumption in users' circuitry, despite the fact that using multiple antennas on the user side can further improve system efficiency. In this paper, novel multiuser collaborative multiple-input-multiple-output (MIMO) SWIPT systems are studied under the assumption of non-negligible circuit energy consumption. Particularly, we convexify and maximize the uplink sum rate of active users, while maintaining the quality of service (QoS) of their downlink data. The beamformers and durations of both links, and the power splitting factors of individual users are jointly optimized, using semidefinite programming and golden search. Further, the selection of active users is optimized, where all users are assumed to be active in the beginning and those detrimental to the sum-rate maximization are continually deactivated. Evident from simulations, the proposed approaches can eliminate the need for computationally prohibitive combinatorial integer programming at a marginal cost of the sum rate.
Ni, W, Zhang, A, Fang, Z, Abolhasan, M, Liu, RP & Guo, YJ 2018, 'Analysis of Finite Buffer in Two-Way Relay: A Queueing Theoretic Point-of-View', IEEE Transactions on Vehicular Technology, vol. 67, no. 4, pp. 3690-3694.View/Download from: UTS OPUS or Publisher's site
IEEE The impact of a finite relay buffer on the throughput of two-way relay is analyzed from a new queueing theoretic point-of-view. Distinctively from recent Markov model based analyses, the proposed queueing theoretic analysis is able to infer closed-form expressions, shed valuable insights, and point out limitations in existing analyses based on Markov models. Validated by simulations, our queueing theoretic analysis reveals that the throughput is increasingly insusceptible to the size of the relay buffer, as the buffer enlarges. Moreover, locking the relay in transmitting XORed packets can hardly improve the throughput, especially under balanced channel conditions. This is due to the fact that the relay queues are stabilized non-empty and hence, XORed packets are forwarded in most cases.
Li, K, Ni, W, Duan, L, Abolhasan, M & Niu, J 2018, 'Wireless Power Transfer and Data Collection in Wireless Sensor Networks', IEEE Transactions on Vehicular Technology, vol. 67, no. 3, pp. 2686-2697.View/Download from: UTS OPUS or Publisher's site
© 1967-2012 IEEE. In a rechargeable wireless sensor network, the data packets are generated by sensor nodes at a specific data rate, and transmitted to a base station. Moreover, the base station transfers power to the nodes by using wireless power transfer (WPT) to extend their battery life. However, inadequately scheduling WPT and data collection causes some of the nodes to drain their battery and have their data buffer overflow, whereas the other nodes waste their harvested energy, which is more than they need to transmit their packets. In this paper, we investigate a novel optimal scheduling strategy, called EHMDP, aimin g to minimize data packet loss from a network of sensor nodes in terms of the nodes' energy consumption and data queue state information. The scheduling problem is first formulated by a centralized MDP model, assuming that the complete states of each node are well known by the base station. This presents the upper bound of the data that can be collected in a rechargeable wireless sensor network. Next, we relax the assumption of the availability of full state information so that the data transmission and WPT can be semidecentralized. The simulation results show that, in terms of network throughput and packet loss rate, the proposed algorithm significantly improves the network performance.
Ma, X, Liang, J, Liu, R, Ni, W, Li, Y, Li, R, Ma, W & Qi, C 2018, 'A Survey on Data Storage and Information Discovery in the WSANs-Based Edge Computing Systems.', Sensors (Basel, Switzerland), vol. 18, no. 2.View/Download from: UTS OPUS or Publisher's site
In the post-Cloud era, the proliferation of Internet of Things (IoT) has pushed the horizon of Edge computing, which is a new computing paradigm with data are processed at the edge of the network. As the important systems of Edge computing, wireless sensor and actuator networks (WSANs) play an important role in collecting and processing the sensing data from the surrounding environment as well as taking actions on the events happening in the environment. In WSANs, in-network data storage and information discovery schemes with high energy efficiency, high load balance and low latency are needed because of the limited resources of the sensor nodes and the real-time requirement of some specific applications, such as putting out a big fire in a forest. In this article, the existing schemes of WSANs on data storage and information discovery are surveyed with detailed analysis on their advancements and shortcomings, and possible solutions are proposed on how to achieve high efficiency, good load balance, and perfect real-time performances at the same time, hoping that it can provide a good reference for the future research of the WSANs-based Edge computing systems.
Lai, W, Ni, W, Wang, H & Liu, RP 2018, 'Analysis of Average Packet Loss Rate in Multi-Hop Broadcast for VANETs', IEEE Communications Letters, vol. 22, no. 1, pp. 157-160.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Multi-hop relay can effectively improve the average packet loss rate (PLR) of vehicular ad hoc networks within a particular zone of interest. Challenges arise from analyzing the average PLR affected by distributed relay selections, which depend on the mobility of vehicles, the wireless channel conditions, and media access control (MAC). In this letter, we propose an average PLR analysis model taking into account the above three factors. However, the closed-form expression for the average PLR is intractable mainly due to the multiple integral of the joint distance distribution integrating with the channel conditions and vehicle mobility. An explicit expression for the upper bound of the average PLR is obtained by using Taylor series expansion, Holder's inequality, and the relay probability relaxation, which can facilitate the selection of the parameters at the physical and MAC layers for a better PLR. Simulation results validate our analyses.
Zou, S, Tang, Y, Ni, W, Liu, RP & Wang, L 2018, 'Resource multi-objective mapping algorithm based on virtualized network functions: RMMA', APPLIED SOFT COMPUTING, vol. 66, pp. 220-231.View/Download from: UTS OPUS or Publisher's site
Khan, AA, Abolhasan, M & Ni, W 2018, 'An evolutionary game theoretic approach for stable and optimized clustering in vanets', IEEE Transactions on Vehicular Technology, vol. 67, no. 5, pp. 4501-4513.View/Download from: UTS OPUS or Publisher's site
© 1967-2012 IEEE. Discovering and maintaining efficient routes for data dissemination in vehicular ad hoc networks (VANETs) has proven to be a very challenging problem. Clustering is one of the control protocols used to provide efficient and stable routes for data dissemination. However, the rapid changes in network topology in VANETs creates frequent cluster reformation, which can seriously affect route stability. We propose a novel evolutionary game theoretic (EGT) framework to automate the clustering of nodes and nominations of cluster heads, to achieve cluster stability in VANETs. The equilibrium point is proven analytically and the stability is also tested using Lyapunov function. The performance of the proposed evolutionary game is empirically investigated with different cost functions using static and mobile scenarios. The simulation results demonstrate the effectiveness and robustness of our proposed EGT approach for different populations and speeds, thus reducing the overhead of frequent cluster reformation in VANETs.
Zha, X, Ni, W, Wang, X, Liu, RP, Guo, YJ, Niu, X & Zheng, K 2018, 'The impact of link duration on the integrity of distributed mobile networks', IEEE Transactions on Information Forensics and Security, vol. 13, no. 9, pp. 2240-2255.View/Download from: UTS OPUS or Publisher's site
© 2005-2012 IEEE. A major challenge in distributed mobile networks is network integrity, resulting from short link duration and severe transmission collisions. This paper analyzes the impact of link duration and transmission collisions on a range of on-the-fly authentication protocols, which operate based on predistributed keys and can instantly verify and forward messages. All unexpired messages within a link duration can be verified retrospectively, once the keys are matched on-the-air. We develop a new general 4D Markov model which, apart from the first three dimensions modeling a cycle of the protocols, is able to unprecedentedly capture unexpired messages between cycles in the fourth dimension. Validated by simulation, our analysis reveals that the on-the-fly authentication is efficient under short link duration, but is susceptible to transmission collisions. The authentication requires holistic cross-layer designs of retransmission and rekeying. The proposed model is able to facilitate the design of the protocol parameters, which allows the protocols to significantly outperform the state of the art.
Yuan, X, Feng, Z, Xu, W, Ni, W, Zhang, JA, Wei, Z & Liu, RP 2018, 'Capacity Analysis of UAV Communications: Cases of Random Trajectories', IEEE Transactions on Vehicular Technology, vol. 67, no. 8, pp. 7564-7576.View/Download from: UTS OPUS or Publisher's site
© 1967-2012 IEEE. This paper analyzes the link capacity between autonomous unmanned aerial vehicles (UAVs) with random three-dimensional (3-D) trajectories. This is distinctively different from existing works typically under the assumption of either two-dimensional (2-D) or deterministic trajectories, and particularly interesting to applications such as surveillance and air combat. The key idea is that we geometrically derive the probability distributions of the UAV-to-UAV (U2U) distances which, by exploiting the Jensen's inequality, can be translated to the closed-form bounds for the capacity between UAVs, and between UAVs and ground stations. Another important aspect is that we extrapolate the idea to dense UAV networks, and analyze the impact of network densification, imperfect channel state information, and interference from ground transmitters on the capacity. Corroborated by simulations, our analysis shows that a U2U link with random 2-D trajectories is superior in terms of capacity due to its short average link distance. It is also revealed that a UAV-to-ground link can incur substantially lower capacity than a U2U link even in the case the 3-D coverage of the UAVs is the same, as the result of its longer average link length.
Wireless Sensor Networks (WSNs) have been the preferred choice for the
design and deployment of next generation monitoring and control systems
. In these networks, the sensor nodes forward their sensed data towards a
centralized base station. The neighboring nodes frequently sense correlated
data and forward towards the base station, using disjoints multiple paths .
As a result, the area around the base station becomes congested with all the
traffic converging towards it. Apart from packet lost due to congestion, a
significant number of packets are lost due to interference, packet collision,
node failure and transmission errors . For a successful monitoring of the
deployed environment, the critical data collected by the sensor nodes need to
be reliably and effectively delivered to the base station. Given the error-prone
nature of the wireless links, ensuring reliable transmission of data from
resource-constrained sensor nodes towards the base station continues to be
one of the major challenges in the field of WSNs . Retransmission and
redundancy are classified as the two main approaches to achieve data transmission reliability in WSNs. However, retransmission and redundancy techniques perform better when using hop-by-hop transmission approach as
compared to end-to-end transmission. Using hop-by-hop approach introduces
in-node processing overhead and incurs high overall latency in reporting data
to the base station. As a result, hybrid approaches need to be adopted to ensure highly reliable and effective data transmission towards the base stations in WSNs.
The specific objective of this special issue is to collect high quality research
articles with solid background in both theoretical and practical aspects of reliability and effectiveness for WSNs. This special issue focuses on various
topics pertaining to reliable and effective communication such as, fault-tolerance, energy-efficiency, topology control, load-balancing, propagation pathloss, co-channe...
Lin, SJ, Yu, JG, Ni, W & Liu, RP 2018, 'Decoupling 5G Network Control: Centralised Coordination and Distributed Adaptation', INTERNATIONAL JOURNAL OF COMPUTERS COMMUNICATIONS & CONTROL, vol. 13, no. 2, pp. 192-204.View/Download from: UTS OPUS
Cui, Q, Gu, Y, Ni, W, Zhang, X, Tao, X, Zhang, P & Liu, RP 2018, 'Preserving Reliability of Heterogeneous Ultra-Dense Distributed Networks in Unlicensed Spectrum', IEEE Communications Magazine, vol. 56, no. 6, pp. 72-78.View/Download from: UTS OPUS or Publisher's site
© 1979-2012 IEEE. This article investigates the prominent dilemma between capacity and reliability in heterogeneous ultra-dense distributed networks, and advocates a new measure of effective capacity to quantify the maximum sustainable data rate of a link while preserving the quality of service of the link in such networks. Recent breakthroughs are brought forth in developing the theory of the effective capacity in heterogeneous ultra-dense distributed networks. Potential applications of the effective capacity are demonstrated on the admission control, power control, and resource allocation of such networks, with substantial gains revealed over existing technologies. This new measure is of particular interest to ultra-dense deployment of the emerging 5G wireless networks in the unlicensed spectrum, leveraging the capacity gain brought by the use of the unlicensed band and the stringent reliability sustained by 5G in future heterogeneous network environments.
Ismaiel, B, Abolhasan, M, Ni, W, Smith, D, Franklin, D & Jamalipour, A 2018, 'Analysis of effective capacity and throughput of polling-based device-to-device networks', IEEE Transactions on Vehicular Technology, vol. 67, no. 9, pp. 8656-8666.View/Download from: UTS OPUS or Publisher's site
© 1967-2012 IEEE. Next-generation wireless networks will give rise to heterogeneous networks by integrating multiple wireless access technologies to provide seamless mobility to mobile users with high-speed wireless connectivity. Device-to-device (D2D) communication has proven to be a promising technology that can increase the capacity and coverage of wireless networks. The D2D communication was first introduced in long-term evolution advanced (LTE-A) and has gained immense popularity for the offloading traffic using the licensed and unlicensed band. Challenges arise from resource allocation, provision of quality-of-service (QoS), and the quantification of capacity in an unlicensed band due to the distributed nature of Wi-Fi. In this paper, we propose an analytical performance model for the scalable MAC protocol (SC-MP) in which a resource allocation mechanism is based on the IEEE 802.11 point coordinated function to access the Wi-Fi channel for voice and video/multimedia traffic. In the SC-MP, D2D communication is applied to further offload the video/multimedia traffic. In particular, this paper establishes a three-state semi-Markovian model to derive a closed-form expression of effective capacity in terms of transmission rate and quality-of-service. Further, the SC-MP is analytically modeled using the four-state traditional Markov model to derive the saturation throughput. The analytical results are validated through simulations, hence, proving the appropriateness of the model.
Li, W, Liu, BM, Liu, D, Liu, RP, Wang, P, Luo, S & Ni, W 2018, 'Unified Fine-grained Access Control for Personal Health Records in Cloud Computing.', IEEE journal of biomedical and health informatics.View/Download from: UTS OPUS or Publisher's site
Attribute-based encryption has been a promising encryption technology to secure personal health records (PHRs) sharing in cloud computing. PHRs consist of the patient data often collected from various sources including hospitals and general practice centres. Different patients' access policies have a common access sub-policy. In this paper, we propose a novel attribute-based encryption scheme for fine-grained and flexible access control to PHRs data in cloud computing. The scheme generates shared information by the common access sub-policy which is based on different patients' access policies. Then the scheme combines the encryption of PHRs from different patients. Therefore, both time consumption of encryption and decryption can be reduced. Medical staff require varying levels of access to PHRs. The proposed scheme can also support multi-privilege access control so that medical staff can access the required level of information while maximizing patient privacy. Through implementation and simulation, we demonstrate that the proposed scheme is efficient in terms of time. Moreover, We prove the security of the proposed scheme based on security of the ciphertext-policy attribute-based encryption scheme.
Zhang, X, Lv, T, Ni, W, Cioffi, JM, Beaulieu, NC & Guo, YJ 2018, 'Energy-efficient caching for scalable videos in heterogeneous networks', IEEE Journal on Selected Areas in Communications, vol. 36, no. 8, pp. 1802-1815.View/Download from: UTS OPUS or Publisher's site
© 1983-2012 IEEE. By suppressing repeated content deliveries, wireless caching has the potential to substantially improve the energy efficiency (EE) of the fifth-generation communication networks. In this paper, we propose two novel energy-efficient caching schemes in heterogeneous networks, namely, scalable video coding (SVC)-based fractional caching and SVC-based random caching, which can provide on-demand video services with different perceptual qualities. We derive the expressions for successful transmission probabilities and ergodic service rates. Based on the derivations and the established power consumption models, the EE maximization problems are formulated for the two proposed caching schemes. By taking logarithmic approximations of the l0-norm, the problems are efficiently solved by the standard gradient projection method. Numerical results validate the theoretical analysis and demonstrate the superiority of our proposed caching schemes, compared to three benchmark strategies.
Wei, Z, Wang, L, Zhuo, M, Ni, W, Wang, H & Ma, J 2018, 'Layered tin sulfide and selenide anode materials for Li- and Na-ion batteries', Journal of Materials Chemistry A, vol. 6, no. 26, pp. 12185-12214.View/Download from: Publisher's site
© 2018 The Royal Society of Chemistry. Layered tin sulfides have attracted great interest as high-capacity anode materials in Li-ion batteries (LIBs) and Na-ion batteries (NIBs). In this review, we focus on the recent research progress in the area of design and synthesis of tin sulfide and selenide (SnS, SnS 2 , SnSe, and SnSe 2 ) based anode materials for LIBs and NIBs. After a brief introduction of the energy concerns and the development prospects of LIBs and NIBs, we further detailed the properties and advantages of tin sulfide and selenide based anode materials for LIBs and NIBs. Besides the material structure design and optimization, the underlying mechanism and theoretical analysis for improved electrochemical performance are also presented. Additionally, comparison of tin sulfides and selenides is also provided. Innovative strategies that have demonstrated the effectiveness of enhancing the performance of tin sulfide and selenide based anode materials for LIBs and NIBs are summarized. We hope that this timely review can shed light on the research and development of tin sulfides and selenides as high-performance anode materials which are not only a good supplement to the material pool of commercialized LIBs, but also help facilitate the development of low-cost and sustainable NIBs for stationary energy storage in the future.
Li, S, Ni, W, Sung, CK & Hedley, M 2018, 'Recent advances on cooperative wireless localization and their application in inhomogeneous propagation environments', Computer Networks, vol. 142, pp. 253-271.View/Download from: UTS OPUS or Publisher's site
© 2018 Elsevier B.V. In this survey, we review recent advances on cooperative localization techniques and identify critical challenges in realistic cooperative localization systems. Particularly, we focus on the inhomogeneity of radio propagation environments, which has substantial impact on the accuracy of positioning systems that assume a homogeneous propagation model. Popular cooperative localization algorithms based on maximum-likelihood estimation, convex relaxation and optimization, and message passing are surveyed, with more emphasis placed on Received Signal Strength (RSS) based approaches due to their potential application in low cost devices. It is shown that most existing algorithms are based on the assumption of a propagation environment with a priori known spatially invariant propagation models. The extension of existing algorithms to capture the inhomogeneity of propagation environments are studied.
Gu, Y, Cui, Q, Chen, Y, Ni, W, Tao, X & Zhang, P 2018, 'Effective Capacity Analysis in Ultra-Dense Wireless Networks with Random Interference', IEEE Access, vol. 6, pp. 19499-19508.View/Download from: UTS OPUS or Publisher's site
© 2013 IEEE. Ultra-dense networks (UDNs) provide a promising paradigm to cope with exponentially increasing mobile traffic. However, a little work has to date considered unsaturated traffic with Quality-of-Service (QoS) requirements. This paper presents a new cross-layer analytical model to capture the unsaturated traffic of a UDN in the presence of QoS requirements. The effiective capacity (EC) of the UDN is derived, taking into account small-scale channel fading and possible interference. Key properties of the EC are revealed. The amount of traffic impacts EC of the UDN due to the sophisticated interactions among small base stations operating in the same frequency. The maximization of total EC is formulated as a non-cooperative game in this paper. The best-response function is derived, iteratively searching the Nash equilibrium point. System simulation results indicate that our proposed model is accurate. The simulations also show the maximum allowed arrival rate with the QoS guarantee, compared with the full interference model.
Zhang, Y, Cui, Q, Ni, W & Zhang, P 2018, 'Energy-Efficient Transmission of Hybrid Array With Non-Ideal Power Amplifiers and Circuitry', IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 17, no. 6, pp. 3945-3958.View/Download from: UTS OPUS or Publisher's site
Li, Y, Guan, Q, Cheng, J, Ni, W & Wang, B 2018, 'Carbon-coated hollow CoO microporous nanospheres synthesized by CoF2 as the intermediates as anode materials for lithium-ion batteries', Ionics, vol. 24, no. 6, pp. 1587-1594.View/Download from: Publisher's site
© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. Uniformly carbon-coated hollow CoO microporous nanospheres have been successfully synthesized by the facile hydrothermal method using CoF2 as the intermediates and glucose as the carbon source. The whole synthesis process can avoid using the toxic surfactant additives and tedious post-processing. The glucose-derived carbon not only suppresses the aggregation of CoO nanoparticles, but also plays an important role on the stabilization of hollow CoO microporous nanosphere structure. The specific structure can largely improve the electronic conductivity and accommodate the volume change of CoO electrode in the electrochemical processes. When used as anode materials of lithium ion batteries, the hollow CoO/C microporous composites exhibit exceptionally high-rate performances, high-specific capacity, and improved cycle performances. This study may provide a new approach for the synthesis of carbon-coated hollow microporous architecture electrode for high-performance batteries.
Li, B, Cheng, J, Wang, Z, Li, Y, Ni, W & Wang, B 2018, 'Highly-wrinkled reduced graphene oxide-conductive polymer fibers for flexible fiber-shaped and interdigital-designed supercapacitors', Journal of Power Sources, vol. 376, pp. 117-124.View/Download from: Publisher's site
© 2017 Elsevier B.V. Flexible supercapacitors have attracted great interest due to outstanding flexibility and light weight. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) fibers have the great potential in using as electrodes for flexible supercapacitors due to the good flexibility. However, the reported conductivity and specific capacitance of these PEDOT: PSS fibers are not very high, which limit their electrochemical performances. In this work, composite fibers of reduced graphene oxide(rGO)-PEDOT: PSS with a highly-wrinkled structure on the surface and pores inside are prepared by wet spinning. The fibers with different ratios of graphene to PEDOT:PSS show a distinctly enhanced conductivity up to ca. 590 S·cm1 and high strength up to ca. 18.4 MPa. Meanwhile, the composite fibers show an improved electrochemical performances, including a high specific areal capacitance of 131 mF cm2 and high specific areal energy density of 4.55 Wh·cm2. The flexible supercapacitors including fiber-shaped supercapacitors and interdigital designed supercapacitors not only could work in different bending states without obvious capacitance decay, but also have small leakage current. The interdigital design can further improve the performances of composite fibers with high capacitance and high utilization compared with traditional parallel connected structure.
Lu, L, Wang, T, Ni, W, Li, K & Gao, B 2018, 'Fog Computing-Assisted Energy-Efficient Resource Allocation for High-Mobility MIMO-OFDMA Networks', Wireless Communications and Mobile Computing, vol. 2018.View/Download from: UTS OPUS or Publisher's site
© 2018 Lingyun Lu et al. This paper presents a suboptimal approach for resource allocation of massive MIMO-OFDMA systems for high-speed train (HST) applications. An optimization problem is formulated to alleviate the severe Doppler effect and maximize the energy efficiency (EE) of the system. We propose to decouple the problem between the allocations of antennas, subcarriers, and transmit powers and solve the problem by carrying out the allocations separately and iteratively in an alternating manner. Fast convergence can be achieved for the proposed approach within only several iterations. Simulation results show that the proposed algorithm is superior to existing techniques in terms of system EE and throughput in different system configurations of HST applications.
Li, W, Ni, W, Liu, D, Liu, RP & Luo, S 2018, 'Unified Ciphertext-Policy weighted attribute-based encryption for sharing data in cloud computing', Applied Sciences (Switzerland), vol. 8, no. 12.View/Download from: UTS OPUS or Publisher's site
© 2018 by the authors. With the rapid development of cloud computing, it is playing an increasingly important role in data sharing. Meanwhile, attribute-based encryption (ABE) has been an effective way to share data securely in cloud computing. In real circumstances, there is often a mutual access sub-policy in different providers' access policies, and the significance of each attribute is usual diverse. In this paper, a secure and efficient data-sharing scheme in cloud computing, which is called unified ciphertext-policy weighted attribute-based encryption (UCP-WABE), is proposed. The weighted attribute authority assigns weights to attributes depending on their importance. The mutual information extractor extracts the mutual access sub-policy and generates the mutual information. Thus, UCP-WABE lowers the total encryption time cost of multiple providers. We prove that UCP-WABE is selectively secure on the basis of the security of ciphertext-policy weighted attribute-based encryption (CP-WABE). Additionally, the results of the implementation shows that UCP-WABE is efficient in terms of time.
Sutton, G, Zeng, J, Liu, R, Ni, W, Nguyen, D, Jayawickrama, B, Huang, X, Abolhasan, M & Zhang, Z 2018, 'Enabling Ultra-Reliable and Low Latency Communications through Unlicensed Spectrum', IEEE Network, vol. 32, no. 2, pp. 70-77.View/Download from: UTS OPUS or Publisher's site
In this article, we aim to address the question of how to exploit the unlicensed spectrum to achieve URLLC. Potential URLLC PHY mechanisms are reviewed and then compared via simulations to demonstrate their potential benefits to URLLC. Although a number of important PHY techniques help with URLLC, the PHY layer exhibits an intrinsic trade-off between latency and reliability, posed by limited and unstable wireless channels. We then explore MAC mechanisms and discuss multi-channel strategies for achieving low-latency LTE unlicensed band access. We demonstrate, via simulations, that the periods without access to the unlicensed band can be substantially reduced by maintaining channel access processes on multiple unlicensed channels, choosing the channels intelligently, and implementing RTS/CTS.
Lyu, X, Tian, H, Ni, W, Zhang, Y, Zhang, P & Liu, RP 2018, 'Energy-Efficient Admission of Delay-Sensitive Tasks for Mobile Edge Computing', IEEE Transactions on Communications, vol. 66, no. 6, pp. 2603-2616.View/Download from: UTS OPUS or Publisher's site
© 1972-2012 IEEE. Task admission is critical to delay-sensitive applications in mobile edge computing, but is technically challenging due to its combinatorial mixed nature and consequently limited scalability. We propose an asymptotically optimal task admission approach which is able to guarantee task delays and achieve (1 - )-approximation of the computationally prohibitive maximum energy saving at a time-complexity linearly scaling with devices. is linear to the quantization interval of energy. The key idea is to transform the mixed integer programming of task admission to an integer programming (IP) problem with the optimal substructure by pre-admitting resource-restrained devices. Another important aspect is a new quantized dynamic programming algorithm which we develop to exploit the optimal substructure and solve the IP. The quantization interval of energy is optimized to achieve an [O(),O(1/)]-tradeoff between the optimality loss and time complexity of the algorithm. Simulations show that our approach is able to dramatically enhance the scalability of task admission at a marginal cost of extra energy, as compared with the optimal branch and bound method, and can be efficiently implemented for online programming.
Wu, K, Ni, W, Su, T, Liu, RP & Guo, YJ 2018, 'Fast and Accurate Estimation of Angle-of-Arrival for Satellite-Borne Wideband Communication System', IEEE Journal on Selected Areas in Communications, vol. 36, no. 2, pp. 314-326.View/Download from: UTS OPUS or Publisher's site
© 1983-2012 IEEE. Accurate estimation of angle-of-arrival (AoA) is critical to wideband satellite communications, but is susceptible to receive noises and can be ambiguous due to space/cost-effective hybrid antenna array designs with localized analog phased subarrays. As a matter of fact, there has yet to be an unambiguous estimator even for narrow-band systems. This paper proposes a new design of subarray-specific time-varying phase shifts, which enables unambiguous and noise-tolerant estimation of AoA in localized hybrid arrays. Particularly, the new phase shifts deliver deterministic phase changes in the cross-correlations of receive signals between subarrays, and enable the cross-correlations to be coherently accumulated across subarrays and sub-carriers to eliminate ambiguities and tolerate noises. Another important contribution of the paper is that we optimize the frequency interval for coherent accumulation across sub-carriers, leveraging between estimation errors, and accumulation gains. Evident from simulations, our approach is able to dramatically improve the estimation accuracy by orders of magnitudes with significantly reduced requirements of complexities and training symbols, as compared with the state of the art. The approach is robust against noises, with estimation errors asymptotically achieving a rigorously developed lower bound.
Wu, K, Ni, W, Su, T, Liu, RP & Guo, YJ 2018, 'Robust Unambiguous Estimation of Angle-of-Arrival in Hybrid Array With Localized Analog Subarrays', IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 17, no. 5, pp. 2987-3002.View/Download from: UTS OPUS or Publisher's site
Lyu, X, Ren, C, Ni, W, Tian, H & Liu, RP 2018, 'Distributed Optimization of Collaborative Regions in Large-Scale Inhomogeneous Fog Computing', IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, vol. 36, no. 3, pp. 574-586.View/Download from: UTS OPUS or Publisher's site
Lyu, X, Ni, W, Tian, H, Liu, RP, Wang, X, Giannakis, GB & Paulraj, A 2018, 'Distributed Online Optimization of Fog Computing for Selfish Devices With Out-of-Date Information', IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 17, no. 11, pp. 7704-7717.View/Download from: UTS OPUS or Publisher's site
Lyu, X, Ren, C, Ni, W, Tian, H, Liu, RP & Guo, YJ 2018, 'Multi-Timescale Decentralized Online Orchestration of Software-Defined Networks', IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, vol. 36, no. 12, pp. 2716-2730.View/Download from: UTS OPUS or Publisher's site
Ismaiel, B, Abolhasan, M, Ni, W, Smith, D, Franklin, D, Dutkiewicz, E, Krunz, MM & Jamalipour, A 2018, 'PCF-based LTE Wi-Fi aggregation for coordinating and offloading the cellular traffic to D2D network', IEEE Transactions on Vehicular Technology, vol. 67, no. 12, pp. 12193-12203.View/Download from: UTS OPUS or Publisher's site
© 2018 IEEE. Device-to-device (D2D) communication is a promising technology towards 5G networks. D2D communication can offload traffic using licensed/unlicensed band by establishing a direct communication between two users without traversing the base station or core network. However, one of the major challenges of D2D communication is resource allocation and guaranteeing quality-of-service (QoS). In this paper, we establish an optimal queuing scheduling and resource allocation problem for three-tier heterogeneous network based on LTE Wi-Fi aggregation, to offload voice/multimedia traffic from licensed band to unlicensed band using scalable MAC protocol (SC-MP) under various static delay constraints. The access mechanism used for Wi-Fi in SC-MP is point coordination function, which further offloads the multimedia traffic using D2D communication in unlicensed band. Resource allocation and optimal joint queuing scheduling problems are formulated with diverse QoS guarantee between licensed and unlicensed band to minimize the bandwidth of licensed band. Furthermore, an iterative algorithm is proposed to express the nonconvex problem as a series of subproblems based on block coordinate descent and difference of two convex functions (D.C) program. We have simulated the proposed scheme using two scenarios: Voice traffic using licensed band and voice traffic using both licensed and unlicensed band, whereas multimedia traffic uses unlicensed band for both the scenarios. The simulation results show that both the schemes perform better than the existing scheme and scenario 2 outperforms scenario 1.
Abolhasan, M, Abdollahi, M, Ni, W, Jamalipour, A, Shariati, N & Lipman, J 2018, 'A Routing Framework for Offloading Traffic from Cellular Networks to SDN-based Multi-Hop Device-to-Device Networks', IEEE Transactions on Network and Service Management, vol. 15, no. 4, pp. 1516-1531.View/Download from: UTS OPUS or Publisher's site
IEEE Device-to-Device (D2D) Communications are set to form an integral part of future 5G wireless networks. D2D communications have a number of benefits such as improving energy efficiency and spectrum utilization. Until now much of the D2D research in LTE and 5G-type network scenarios have focused on direct (one-hop) communications between two adjacent mobile devices. In this paper, we propose a new routing framework called Virtual Ad hoc Routing Protocol (VARP). This framework introduces significant advantages such as better security, lower routing overheads, and higher scalability, when compared to conventional ad hoc routing protocols. It also reduces traffic overhead in LTE networks using multi-hop D2D communications under management of a SDN-controller. Further, it enables the development of various types of routing protocols for different networking scenarios. To this end, a source-routing based protocol was developed on top of VARP, referred to as VARP-S. We present a detailed analytical study of routing overhead in the VARP-S protocol, as compared to overhead analysis of our previous proposed Hybrid SDN Architecture for wireless distributed networks (HSAW)IEEENetworkMehran. Our results show that VARP-S, compared to HSAW, achieves higher network scalability and lower power consumption for mobile nodes.
Ni, W, Abolhasan, M, Hagelstein, B, Liu, RP & Wang, X 2017, 'A New Trellis Model for MAC Layer Cooperative Retransmission Protocols', IEEE Transactions on Vehicular Technology, vol. 66, no. 4, pp. 3448-3461.View/Download from: UTS OPUS or Publisher's site
Shi, S, Ni, W & Liu, RP 2017, 'Performance analysis of XOR two-way relay with finite buffers and instant scheduling', IET COMMUNICATIONS, vol. 11, no. 4, pp. 507-513.View/Download from: UTS OPUS or Publisher's site
Qin, C, Ni, W, Tian, H & Liu, RP 2017, 'Joint Rate Maximization of Downlink and Uplink in Multiuser MIMO SWIPT Systems', IEEE Access, vol. 5, pp. 3750-3762.View/Download from: UTS OPUS or Publisher's site
© 2013 IEEE. Beamforming has the potential to improve the efficiency of simultaneous wireless information and power transfer (SWIPT) systems. Existing beamforming techniques have been focused on the downlink of SWIPT systems. In this paper, we optimize the beamformers and transmit duration to maximize the weighted sum rate of both the downlink and uplink in a multiuser multiple-input multiple-output (MIMO) SWIPT system. Specifically, we formulate and transform the problem into a weighted sum mean square error minimization, conduct difference of convex programming to decouple the downlink and uplink, and convert the problem to quadratic programming (QP), which can be solved iteratively in a centralized fashion. We also decentralize the QP problem using dual decompositions, and reduce the time-complexity without compromising the data rate. Moreover, our algorithms are extended to the case under imperfect channel state information. Confirmed by simulations, the proposed decentralization can dramatically reduce the time-complexity by orders of magnitude. The scalability of the proposed approach can be substantially enhanced to support medium to large networks.
Zha, X, Ni, W, Zheng, K, Liu, RP & Niu, X 2017, 'Collaborative Authentication in Decentralized Dense Mobile Networks With Key Predistribution', IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY, vol. 12, no. 10, pp. 2261-2275.View/Download from: UTS OPUS or Publisher's site
Qin, C, Ni, W, Tian, H & Liu, RP 2017, 'Fronthaul Load Balancing in Energy Harvesting Powered Cloud Radio Access Networks', IEEE Access, vol. 5, pp. 7762-7775.View/Download from: UTS OPUS or Publisher's site
© 2013 IEEE. Enhanced with wireless power transfer capability, cloud radio access network (C-RAN) enables energy-restrained mobile devices to function uninterruptedly. Beamforming of C-RAN has potential to improve the efficiency of wireless power transfer, in addition to transmission data rates. In this paper, we design the beamforming jointly for data transmission and energy transfer, under finite fronthaul capacity of C-RAN. A non-convex problem is formulated to balance the fronthaul requirements of different remote radio heads (RRHs). Norm approximations and relaxations are carried out to convexify the problem to second-order cone programming (SOCP). To improve the scalability of the design to large networks, we further decentralize the SOCP problem using the alternating direction multiplier method (ADMM). A series of reformulations and transformations are conducted, such that the resultant problem conforms to the state-of-The-Art ADMM solver and can be efficiently solved in real time. Simulation results show that the distributed algorithm can remarkably reduce the time complexity without compromising the fronthaul load balancing of its centralized counterpart. The proposed algorithms can also reduce the fronthaul bandwidth requirements by 25% to 50%, compared with the prior art.
Wu, G, Liu, RP, Ni, W, Sutton, GJ & Xu, P 2017, 'Modeling Channel Switching and Contention Control in Vehicular Networks', IEEE Access, vol. 5, pp. 23102-23110.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. In vehicular networks, multi-channel operation standard IEEE 1609.4 is designed for vehicular communications across multiple channels. It has been revealed that such multi-channel operations may result in high contention in vehicular communications. However, existing analytical models are unable to capture the dynamic characteristic during channel switching. We develop a novel Markov model that takes into account the dynamic contention behavior during channel switching. In particular, our model reveals the high contention caused by the burst arrivals, which are the results of multi-channel operations. To combat such performance decline, we propose two solutions, a centralized equal-spaced algorithm and a distributed random-spaced algorithm. The key idea is to disperse the burst packet arrivals across the available timeframe in order to alleviate contention. Our model, validated by simulations, accurately characterizes the high contention caused by multi-channel operations. Our results demonstrate our proposed solutions can effectively mitigate packet collision, enhance reliability, and improve system throughput during the multi-channel operations.
Cui, Q, Gu, Y, Ni, W & Liu, RP 2017, 'Effective Capacity of Licensed-Assisted Access in Unlicensed Spectrum for 5G: From Theory to Application', IEEE Journal on Selected Areas in Communications, vol. 35, no. 8, pp. 1754-1767.View/Download from: UTS OPUS or Publisher's site
© 1983-2012 IEEE. License-assisted access (LAA) is a promising technology to offload dramatically increasing cellular traffic to unlicensed bands. Challenges arise from the provision of quality-of-service (QoS) and the quantification of capacity, due to the distributed and heterogeneous nature of LAA and legacy systems (such as Wi-Fi) coexisting in the bands. In this paper, we develop new theories of the effective capacity to measure LAA under statistical QoS requirements. A new four-state semi-Markovian model is developed to capture transmission collisions, random backoffs, and lossy wireless channels of LAA in distributed heterogeneous network environments. A closed-form expression for the effective capacity is derived to comprehensively analyze LAA. The four-state model is further abstracted to an insightful two-state equivalent which reveals the concavity of the effective capacity in terms of transmit rate. Validated by simulations, the concavity is exploited to maximize the effective capacity and effective energy efficiency of LAA, and provide significant improvements of 62.7% and 171.4%, respectively, over existing approaches. Our results are of practical value to holistic designs and deployments of LAA systems.
Zhou, Y, Ni, W, Zheng, K, Liu, RP & Yang, Y 2017, 'Scalable Node-Centric Route Mutation for Defense of Large-Scale Software-Defined Networks', Security and Communication Networks, vol. 2017.View/Download from: UTS OPUS or Publisher's site
© 2017 Yang Zhou et al. Exploiting software-defined networking techniques, randomly and instantly mutating routes can disguise strategically important infrastructure and protect the integrity of data networks. Route mutation has been to date formulated as NP-complete constraint satisfaction problem where feasible sets of routes need to be generated with exponential computational complexities, limiting algorithmic scalability to large-scale networks. In this paper, we propose a novel node-centric route mutation method which interprets route mutation as a signature matching problem. We formulate the route mutation problem as a three-dimensional earth mover's distance (EMD) model and solve it by using a binary branch and bound method. Considering the scalability, we further propose that a heuristic method yields significantly lower computational complexities with marginal loss of robustness against eavesdropping. Simulation results show that our proposed methods can effectively disguise key infrastructure by reducing the difference of historically accumulative traffic among different switches. With significantly reduced complexities, our algorithms are of particular interest to safeguard large-scale networks.
Fang, Z, Ni, W, Liang, F, Shao, P & Wu, Y 2017, 'Massive MIMO for Full-Duplex Cellular Two-Way Relay Network: A Spectral Efficiency Study', IEEE Access, vol. 5, pp. 23288-23298.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. This paper presents the new analysis of the applications of massive multiple-input-multiple-output (MIMO) in full-duplex (FD) cellular two-way relay networks, and sheds valuable insights on the interactions between massive MIMO, and relay and duplex modes. Practical scenarios are considered, where massive MIMO is deployed at the base station and the relay station. Based on generic relay modes, namely, antenna-selection-based decode-and-forward (DF) relay and signal-space alignment based amplify-and-forward (AF) relay, closed-form expressions for the asymptotic signal-to-interference-plus-noise ratios (SINRs) are derived. The difference between AF and DF in the FD mode is quantified, and so is that between FD and half-duplex (HD) under the two relay modes. With massive MIMO, the superiority of DF in the FD mode is confirmed in terms of spectral efficiency. The sufficient conditions for the FD mode to outperform the HD mode are identified. The effectiveness of massive MIMO in terms of self-loop interference cancellation and inter-user interference suppression is proved. All these insightful findings are corroborated by simulations.
Chen, X, Ni, W, Chen, T, Collings, IB, Wang, X & Guanacos, GB 2017, 'Real-Time Energy Trading and Future Planning for Fifth Generation Wireless Communications', IEEE Wireless Communications, vol. 24, no. 4, pp. 24-30.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Future 5G cellular networks, equipped with energy harvesting devices, are uniquely positioned to interoperate with smart grid, due to their resemblance in scale and ubiquity. New interoperable functionalities, such as real-time energy trading and future planning, are of particular interest to improve productivity, but extremely challenging due to the physical characteristics of wireless channels and renewable energy sources, as well as time-varying energy prices. Particularly, a priori knowledge on future wireless channels, energy harvesting, and pricing is unavailable in practice. In this scenario, simple but efficient Lyapunov control theory can be applied to stochastically optimize energy trading and planning. Simulations demonstrate that Lyapunov control can approach the offline optimum which is obtained under the ideal assumption of full a priori knowledge, leading to 65 percent reduction of the operational expenditure of 5G on energy over existing alternatives.
Saadat, A, Ni, W & Vesilo, R 2017, 'Collaborative Spectrum Sharing Through Non-Collaborative Gaming for Next-Generation Small Cells', IEEE Access, vol. 5, pp. 10182-10192.View/Download from: UTS OPUS or Publisher's site
© 2013 IEEE. Existing spectrum-sharing schemes either allow the secondary-network users (SUs) to utilize the spectrum when primary-network users (PUs) remain idle, or require the SUs to coordinate with the PUs, causing signaling overhead. In this paper, we propose a game-theoretic spectrum-sharing scheme, which enables the SUs and PUs to utilize the spectrum simultaneously, without compromising the quality of service (QoS) of the PUs and ensuring reduced signaling overhead. We formulate a multi-priority non-cooperative power-control game by considering a scenario where multiple small cell base stations belonging to either the primary network or secondary network utilize the available spectrum resources at the same time. The base stations are empowered to adjust their transmit powers in an automated manner based on measured interference, until their transmit powers are stabilized. As a key idea, a game parameter, dynamic price coefficient, is designed to give the primary network priority over the secondary network for accessing the spectrum. We determine appropriate bounds for the game parameters to ensure the existence and uniqueness of the Nash equilibrium of the proposed game. Furthermore, we propose a novel dual-mode solution to reduce the real-time signaling overhead between the networks, by minimizing the information exchange during the game required to reach an equilibrium point. Extensive simulation results are presented to prove the convergence of the game to a Nash equilibrium, along with a throughput performance analysis.
Cheng, J, Gu, G, Ni, W, Guan, Q, Li, Y & Wang, B 2017, 'Graphene oxide hydrogel as a restricted-area nanoreactor for synthesis of 3D graphene-supported ultrafine TiO2nanorod nanocomposites for high-rate lithium-ion battery anodes', Nanotechnology, vol. 28, no. 30, pp. 1-9.View/Download from: UTS OPUS or Publisher's site
© 2017 IOP Publishing Ltd. Three-dimensional graphene-supported TiO2nanorod nanocomposites (3D GS-TNR) are prepared using graphene oxide hydrogel as a restricted-area nanoreactor in the hydrothermal process, in which well-distributed TiO2nanorods with a width of approximately 5 nm and length of 30 nm are conformally embedded in the 3D interconnected graphene network. The 3D graphene oxide not only works as a restricted-area nanoreactor to constrain the size, distribution and morphology of the TiO2; it also work as a highly interconnected conducting network to facilitate electrochemical reactions and maintain good structural integration when the nanocomposites are used as anode materials in lithium-ion batteries. Benefiting from the nanostructure, the 3D GS-TNR nanocomposites show high capacity and excellent long-term cycling capability at high current rates. The 3D GS-TNR composites deliver a high initial charge capacity of 280 mAh g-1at 0.2 C and maintain a reversible capacity of 115 mAh g-1, with a capacity retention of 83% at 20 C after 1000 cycles. Meanwhile, compared with that of previously reported TiO2-based materials, the 3D GS-TNR nanocomposites show much better performance, including higher capacity, better rate capability and long-term cycling stability.
Cui, Q, Zhang, Y, Ni, W, Valkama, M & Jantti, R 2017, 'Energy Efficiency Maximization of Full-Duplex Two-Way Relay with Non-Ideal Power Amplifiers and Non-Negligible Circuit Power', IEEE Transactions on Wireless Communications, vol. 16, no. 9, pp. 6264-6278.View/Download from: UTS OPUS or Publisher's site
© 2002-2012 IEEE. In this paper, we maximize the energy efficiency (EE) of full-duplex (FD) two-way relay (TWR) systems under non-ideal power amplifiers (PAs) and non-negligible transmission-dependent circuit power. We start with the case where only the relay operates full duplex and two timeslots are required for TWR. Then, we extend to the advanced case, where the relay and the two nodes all operate full duplex, and accomplish TWR in a single timeslot. In both cases, we establish the intrinsic connections between the optimal transmit powers and durations, based on which the original non-convex EE maximization can be convexified and optimally solved. Simulations show the superiority of FD-TWR in terms of EE, especially when traffic demand is high. The simulations also reveal that the maximum EE of FD-TWR is more sensitive to the PA efficiency, than it is to self-cancellation. The full FD design of FD-TWR is susceptible to traffic imbalance, while the design with only the relay operating in the FD mode exhibits strong tolerance.
Yang, D, Ni, W, Cheng, J, Wang, Z, Li, C, Zhang, Y & Wang, B 2017, 'Omnidirectional porous fiber scrolls of polyaniline nanopillars array-N-doped carbon nanofibers for fiber-shaped supercapacitors', Materials Today Energy, vol. 5, pp. 196-204.View/Download from: UTS OPUS or Publisher's site
© 2017 Elsevier Ltd Rolled-up fiber scrolls with outer omnidirectional porous and inner hierarchical porous structure have been fabricated as electrodes of fiber-shaped supercapacitors (FSCs) by polymerizing polyaniline (PANi) nanopillars onto hierarchical 3D interconnected porous N-doped carbon nanofibers scrolls (PANi-HCNFs). The as-prepared fiber-shaped PANi-HCNFs electrode materials used for all solid-state FSCs display excellent electrochemical performance with a high specific capacitance of 339.3 F g1(85.1 mF cm1) and specific mass energy density of 11.6 Wh kg1(areal energy density of 4.28 Wh cm2). Meanwhile, PANi-HCNFs show good cycling stability with capacity retention of 74.2% after 3000 cycles at 0.5 A g1. The superior electrochemical performance can be attributed to the combining of PANi nanopillars array on the 3D interconnected conducting network with the outer omnidirectional porous and inner hierarchical porous composite structure. This unique composite structure can provide high specific surface area, enabling the effective transport of electrolyte to the inner region of the composite fiber. The backbones of N-doped carbon nanofibers form abundant interconnected conductive network and offer multiple electronic transfer paths. Meanwhile, introducing nanostructured PANi nanopillars array into the carbon matrix can improve higher energy density and provide better cycling stability.
Yang, D, Ni, W, Cheng, J, Wang, Z, Wang, T, Guan, Q, Zhang, Y, Wu, H, Li, X & Wang, B 2017, 'Flexible three-dimensional electrodes of hollow carbon bead strings as graded sulfur reservoirs and the synergistic mechanism for lithium–sulfur batteries', Applied Surface Science, vol. 413, pp. 209-218.View/Download from: UTS OPUS or Publisher's site
© 2017 Elsevier B.V. Three-dimensional (3D) flexible electrodes of stringed hollow nitrogen-doped (N-doped) carbon nanospheres as graded sulfur reservoirs and conductive frameworks were elaborately designed via a combination of the advantages of hollow structures, 3D electrodes and flexible devices. The as-prepared electrodes by a synergistic method of electrospinning, template sacrificing and activation for Li–S batteries without any binder or conductive additives but a 3D interconnected conductive network offered multiple transport paths for electrons and improved sulfur utilization and facilitated an easy access to Li+ingress/egress. With the increase of density of hollow carbon spheres in the strings, the self-supporting composite electrode reveals an enhanced synergistic mechanism for sulfur confinement and displays a better cycling stability and rate performance. It delivers a high initial specific capacity of 1422.6 mAh g1at the current rate of 0.2C with the high sulfur content of 76 wt.%, and a much higher energy density of 754 Wh kg1and power density of 1901 Wh kg1, which greatly improve the energy/power density of traditional lithium–sulfur batteries and will be promising for further commercial applications.
Cui, Q, Yuan, T & Ni, W 2017, 'Energy-efficient two-way relaying under non-ideal power amplifiers', IEEE Transactions on Vehicular Technology, vol. 66, no. 2, pp. 1257-1270.View/Download from: UTS OPUS or Publisher's site
© 2016 IEEE. Energy efficiency (EE) is crucial to many batterypowered relay applications. Maximizing EE is challenging due to non-convex structures resulting from non-ideal power amplifiers (PAs) and non-negligible circuit power. We formulate such non-convex problems to maximize the EE of two-way relay systems, where the transmit power and duration of all participating nodes are jointly optimized. The intrinsic connection between the optimal transmit power and duration is established through our derived necessary conditions of the optimality. It enables us to reformulate the non-convex problems to problems with rigorously proved convexity in the vicinities of the optimal transmit duration and to solve the problems using simple convex search. Simulation results show that the EE gain of our approach is substantial, compared with the state of the art, when the traffic demand is low or unbalanced in the two link directions. The gain enlarges as the imbalance of traffic demand grows.
Lei, WW, Li, H, Shi, LY, Diao, YF, Zhang, YL, Ran, R & Ni, W 2017, 'Achieving enhanced hydrophobicity of graphene membranes by covalent modification with polydimethylsiloxane', Applied Surface Science, vol. 404, pp. 230-237.View/Download from: UTS OPUS or Publisher's site
© 2017 Elsevier B.V. In this study, the graphene oxide was covalently modified by amino terminated polydimethylsiloxane (PDMS) through amidation reaction. And the membranes of the graphene oxide (GO), reduced graphene oxide (RGO) and PDMS-covalently modified graphene were prepared respectively by a vacuum filtration method, and the wettability of these membranes were investigated. Infrared spectroscopy, Raman, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetry analysis combined with dispersion ability indicated that PDMS chains were successfully grafted on the surface of graphene oxide sheets. The morphology of the prepared membranes had smooth surface and well-stacked structure in the cross-section indicated by the scanning electron microscope and EDS-mapping. The contact angle measurements indicated that the PDMS-modified graphene membrane with water contact angle 129.5° showed increased hydrophobicity compared with GO and RGO membranes.
Guan, Q, Cheng, J, Li, X, Ni, W & Wang, B 2017, 'Porous CoF2Spheres Synthesized by a One-Pot Solvothermal Method as High Capacity Cathode Materials for Lithium-Ion Batteries', Chinese Journal of Chemistry, vol. 35, no. 1, pp. 48-54.View/Download from: UTS OPUS or Publisher's site
Up to now, there are rare reports of CoF2spheres used as high capacity cathode materials. Herein, porous CoF2spheres were synthesized and studied as cathode materials for LIBs. The porous CoF2spheres were synthesized by a facile one-pot solvothermal method using a safe and inexpensive ammonium fluoride as the fluorine sources. The nature of the synthesis can avoid using corrosive fluorine sources and additional high-temperature thermal treatment. The structure, morphologies and electrochemical performance of the samples obtained at different reaction times and solvothermal temperatures were investigated. The results show that the CoF2spheres obtained at 200 ï¿½C for 20 h show better electrochemical performances, including a high initial discharge capacity, good capacity retention and high Coulombic efficiency. It can deliver a high initial discharge capacity of 537.8 mA*h*g1and keep 127.4 mA*h*g1after 30 cycles used as cathode materials for lithium-ion batteries. The good electrochemical performances may be attributed to good crystallinity, porous structure and relatively intermediate sphere size.
Wang, Z, Cheng, J, Ni, W, Gao, L, Yang, D, Razal, JM & Wang, B 2017, 'Poly(3,4-ethylene-dioxythiophene)-poly(styrenesulfonate) glued and graphene encapsulated sulfur-carbon film for high-performance free-standing lithium-sulfur batteries', Journal of Power Sources, vol. 342, pp. 772-778.View/Download from: UTS OPUS or Publisher's site
© 2017 Elsevier B.V. A novel free-standing composite film electrode for Li-S battery is investigated. This novel electrode consists of polyvinylpyrrolidone-coated hollow sulfur microspheres (PVPS) that are homogeneously confined within the conductive composite matrix of graphene and poly(3,4-ethylene-dioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS). The characteristic large surface area and wrinkled surface of graphene sheets allow the formation of a conductive layer on the surface of PVPS to suppress the polysulfide dissolution and accommodate the volumetric expansion of sulfur. The addition of PEDOT-PSS also enhances the adhesion between the PVPS and the graphene surface, the overall conductivity of the electrode, and the charge transportation during the charging and discharging processes. The best electrode performances are achieved for a composite film cathode with a sulfur content of about 63.9%, which delivers an initial specific capacity of around 1060 mAh g1at 0.1 C. This electrode also displays an excellent capacity retention of 75% after 500 cycles at 1C, corresponding to a capacity decay of only 0.05% per cycle.
Lyu, X, Ni, W, Tian, H, Liu, RP, Wang, X, Giannakis, GB & Paulraj, A 2017, 'Optimal schedule of mobile edge computing for internet of things using partial information', IEEE Journal on Selected Areas in Communications, vol. 35, no. 11, pp. 2606-2615.View/Download from: UTS OPUS or Publisher's site
© 1983-2012 IEEE. Mobile edge computing is of particular interest to Internet of Things (IoT), where inexpensive simple devices can get complex tasks offloaded to and processed at powerful infrastructure. Scheduling is challenging due to stochastic task arrivals and wireless channels, congested air interface, and more prominently, prohibitive feedbacks from thousands of devices. In this paper, we generate asymptotically optimal schedules tolerant to out-of-date network knowledge, thereby relieving stringent requirements on feedbacks. A perturbed Lyapunov function is designed to stochastically maximize a network utility balancing throughput and fairness. A knapsack problem is solved per slot for the optimal schedule, provided up-to-date knowledge on the data and energy backlogs of all devices. The knapsack problem is relaxed to accommodate out-of-date network states. Encapsulating the optimal schedule under up-to-date network knowledge, the solution under partial out-of-date knowledge preserves asymptotic optimality, and allows devices to self-nominate for feedback. Corroborated by simulations, our approach is able to dramatically reduce feedbacks at no cost of optimality. The number of devices that need to feed back is reduced to less than 60 out of a total of 5000 IoT devices.
Lyu, X, Tian, H, Ni, W, Liu, RP & Zhang, P 2017, 'Adaptive Centralized Clustering Framework for Software-Defined Ultra-Dense Wireless Networks', IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, vol. 66, no. 9, pp. 8553-8557.View/Download from: UTS OPUS or Publisher's site
Li, K, Ni, W, Wang, X, Liu, RP, Kanhere, SS & Jha, S 2016, 'Energy-Efficient Cooperative Relaying for Unmanned Aerial Vehicles', IEEE Transactions on Mobile Computing, vol. 15, no. 6, pp. 1377-1386.View/Download from: UTS OPUS or Publisher's site
Wang, X, Ni, W, Zheng, K, Liu, RP & Niu, X 2016, 'Virus Propagation Modeling and Convergence Analysis in Large-Scale Networks', IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY, vol. 11, no. 10, pp. 2241-2254.View/Download from: UTS OPUS or Publisher's site
Abolhasan, M, Maali, Y, Rafiei, A & Ni, W 2016, 'Distributed Hybrid Coverage Hole Recovery in Wireless Sensor Networks', IEEE Sensors Journal, vol. 16, no. 23, pp. 8640-8648.View/Download from: UTS OPUS or Publisher's site
Coverage Holes (CHs) can compromise the reliability and functionality of wireless sensor networks (WSNs). The recovery of CHs is challenging, especially in distributed applications where sensors have little knowledge about other sensors' actions. We propose a new game theoretic approach for recovering the CHs in a distributed manner. The key idea is that we formulate a potential game between the sensors, where each mobile sensor in the network only depends on local knowledge of its neighbouring nodes and takes CH recovery actions recursively with global convergence. An appropriate combined action of physical relocation and sensing range adjustment can be taken by each sensor to reduce the CHs in an energy-efficient way. Simulation results show that the proposed game theoretic approach is able to substantially increase network lifetime and maintain network coverage in the presence of random damage events, as compared to the prior counterpart(s).
Zhang, JA, Ni, W, Cheng, P & Lu, Y 2016, 'Angle-of-Arrival Estimation Using Different Phase Shifts Across Subarrays in Localized Hybrid Arrays', IEEE Communications Letters, vol. 20, no. 11, pp. 2205-2208.View/Download from: UTS OPUS or Publisher's site
© 1997-2012 IEEE. Angle-of-arrival (AoA) estimation, even for a single arriving signal, in a localized hybrid array is challenging and time-consuming due to a phase ambiguity problem. Subarrays use the same phase shifting values conventionally to exploit cross correlation between them. This results in the requirement of scanning multiple angles over excessively long periods to resolve the phase ambiguity problem. In this letter, we propose an approach which allows subarrays to use different phase shifts per estimation and can resolve the ambiguity problem by directly estimating the desired AoA parameter. This can potentially speed up the estimation and improve the estimation performance significantly. Simulation results are provided to demonstrate the effectiveness of the proposed approach.
Shi, S, Ni, W, Liu, RP & Li, S 2016, 'Performance analysis of two-way MAC layer network coding under finite relay buffer and non-negligible signalling overhead', Wireless Communications and Mobile Computing, vol. 16, no. 18, pp. 3230-3243.View/Download from: UTS OPUS or Publisher's site
Copyright © 2016 John Wiley & Sons, Ltd. Two-way exclusive OR (XOR) relay can enable hidden nodes to exchange data with low delays and high data rate, while keeping signal processing simple. In this paper, we analyse practical two-way XOR relaying systems, where finite relay buffer, non-negligible signalling overhead, and lossy wireless channels are all captured. A two-layer model is developed to characterise such practical two-way relay systems, which is then reformulated into a Markov process after we project and combine inter-layer state transitions of the two-layer model. Using Markov techniques, we evaluate the steady state probabilities of the Markov process and, in turn, the key performance measures of two-way XOR relaying, such as throughput, delay, and packet loss. The accuracy of our model is validated by simulations. Our model can also be used as an online tool to configure the buffer resources, adapting to wireless channel conditions and signalling requirements. Copyright © 2016 John Wiley & Sons, Ltd.
Ma, J, Ni, W, Yin, J, Liu, RP, Yuan, Y & Fang, B 2016, 'Modeling Mobile Cellular Networks Based on Social Characteristics', INTERNATIONAL JOURNAL OF COMPUTERS COMMUNICATIONS & CONTROL, vol. 11, no. 4, pp. 480-492.View/Download from: Publisher's site
Nan, Z, Chen, T, Wang, X & Ni, W 2016, 'Energy-Efficient Transmission Schedule for Delay-Limited Bursty Data Arrivals under Nonideal Circuit Power Consumption', IEEE Transactions on Vehicular Technology, vol. 65, no. 8, pp. 6588-6600.View/Download from: Publisher's site
© 2015 IEEE. This paper develops a novel approach to obtain energy-efficient transmission schedules for delay-limited bursty data under nonideal circuit power consumption. Assuming a priori knowledge of packet arrivals, deadlines, and channel realizations, we show that the problem can be formulated as a convex program. For both time-invariant and time-varying fading channels, it is revealed that the optimal transmission between any two consecutive channel or data state changing instants, termed epoch, can only take one of the three strategies: i) no transmission; ii) transmission with an energy-efficiency (EE)-maximizing rate over part of the epoch; or iii) transmission with a rate greater than the EE-maximizing rate over the whole epoch. Based on this specific structure, efficient algorithms are then developed to find the optimal policies that minimize the total energy consumption with low complexity. The proposed approach can provide the optimal benchmarks for practical schemes designed for transmissions of delay-limited data arrivals and can be employed to develop efficient online scheduling schemes, which require only causal knowledge of data arrivals and deadline requirements.
Yuan, D, Li, B, Cheng, J, Guan, Q, Wang, Z, Ni, W, Li, C, Liu, H & Wang, B 2016, 'Twisted yarns for fiber-shaped supercapacitors based on wetspun PEDOT:PSS fibers from aqueous coagulation', Journal of Materials Chemistry A, vol. 4, no. 30, pp. 11616-11624.View/Download from: Publisher's site
© The Royal Society of Chemistry 2016. Recently, fiber-shaped yarn supercapacitors (YSCs) have attracted extensive attention due to their merits of small volume, high flexibility and potential to be woven in textiles for future wearable electronics. PEDOT:PSS possesses properties of high-redox capacitance, high conductivity and high intrinsic flexibility, so PEDOT:PSS yarn electrodes are quite promising in the field of YSCs. However, to the best of our knowledge, twisted yarns based on wetspun PEDOT:PSS fibers for fiber-shaped YSCs have not been reported. Herein, we develop a new coagulation bath with CaCl2 in aqueous solution for preparing meter-long PEDOT:PSS fibers. The PEDOT:PSS fibers with good mechanical properties can be easily woven, sewed, knotted and braided as the YSC electrode. The PEDOT:PSS fiber-based YSCs show a high areal capacitance of 119 mF cm-2 and areal energy density of 4.13 W h cm-2. Meanwhile, the all-solid-state YSCs are flexible and robust enough to tolerate the long-term and repeated bending without an obvious capacitance drop.
Ni, W, Yang, D, Cheng, J, Li, X, Guan, Q & Wang, B 2016, 'Gel-type polymer separator with higher thermal stability and effective overcharge protection of 4.2 v for secondary lithium-ion batteries', RSC Advances, vol. 6, no. 58, pp. 52966-52973.View/Download from: Publisher's site
© 2016 The Royal Society of Chemistry. Overcharge protection by electroactive polymer composite separators is an alternative solution for the alleviation of safety concerns of rechargeable Li or Li-ion batteries. The use of gel-type electrolyte with less free organic solvent may benefit the safety performance as well as provide enhanced thermostability. Herein, a kind of gel-type polymer electrolyte separator, prepared by a facile electroactive conducting polymer solution dip-coating method, for effective overcharge protection of Li-ion batteries with enhanced thermal stability and electrochemical safety due to the introduction of heat-resistant polyfluorene end-capped with polysilsesquioxane, may be beneficial for solution of the Li-ion battery safety problem.
Chen, X, Ni, W, Wang, X & Sun, Y 2016, 'Optimal Quality-of-Service Scheduling for Energy-Harvesting Powered Wireless Communications', IEEE Transactions on Wireless Communications, vol. 15, no. 5, pp. 3269-3280.View/Download from: Publisher's site
© 2016 IEEE. In this paper, a new dynamic string tautening algorithm is proposed to generate the most energy-efficient off-line schedule for delay-limited traffic of transmitters with non-negligible circuit power. The algorithm is based on two key findings that we derive through judicious convex formulation and resultant optimality conditions, specifies a set of simple but optimal rules, and generates the optimal schedule with a low complexity of O(N2) in the worst case. The proposed algorithm is also extended to on-line scenarios, where the transmit schedule is generated on-the-fly. Simulation shows that the proposed algorithm requires substantially lower average complexity by almost two orders of magnitude to retain optimality than general convex solvers. The effective transmit region, specified by the tradeoff of the data arrival rate and the energy harvesting rate, is substantially larger using our algorithm than using other existing alternatives. Significantly more data or less energy can be supported in the proposed algorithm.
Wu, D, Chen, W & Ni, W 2016, 'Software implementation of BeiDou B1I code generator using Matlab/Simulink', Recent Patents on Computer Science, vol. 9, no. 1, pp. 74-80.
© 2016 Bentham Science Publishers. Conventional Matlab implementation of software ranging code generator requires code shifts to produce the ranging codes assigned to different satellites. Unfortunately, it is unable to implement software BeiDou B1I code generator using this method, because the B1I code shifts are unknown. Based on the generator revealed in BeiDou Interface Control Document (BICD), a software generator is implemented by using Simulink blocks in conjunction with Matlab programs in this paper. The Simulink blocks enable the generator to compute the BeiDou B1I code shifts, as well as reducing the complexity of the implementation. Simulation results show that the implementation is feasible and reliable. All B1I code shifts are calculated, which can be used for both software and hardware implementation in the future. Patents describing a wide range of applications based on the BeiDou system have also been proposed and implemented.
Ni, W, Cheng, J, Li, X, Guan, Q, Qu, G, Wang, Z & Wang, B 2016, 'Multiscale sulfur particles confined in honeycomb-like graphene with the assistance of bio-based adhesive for ultrathin and robust free-standing electrode of Li-S batteries with improved performance', RSC Advances, vol. 6, no. 11, pp. 9320-9327.View/Download from: Publisher's site
© The Royal Society of Chemistry 2016. Carbon/sulfur composites are attracting extensive attention due to their improved performances for Li-S batteries. Herein, a hierarchical ultrathin but robust graphene composite membrane, which includes an inherent carbon framework and the embedded sulfur multi-sized particles, is facilely in situ and one-pot synthesized with the assistance of bio-based surfactant/adhesive for flexible cathode without current collectors. It shows better cycling stability and higher specific capacity of 823 mA h g -1 over 100 cycles at 0.5C with a high sulfur content of 61 wt% in the electrode. The introduction of biosurfactant and interfacial adhesion enhanced the flexibility and strength of the thinner composite membrane in addition to the increased specific capacity, which may show promising potential for better flexible and wearable electronic devices.
Li, X, Li, X, Cheng, J, Yuan, D, Ni, W, Guan, Q, Gao, L & Wang, B 2016, 'Fiber-shaped solid-state supercapacitors based on molybdenum disulfide nanosheets for a self-powered photodetecting system', Nano Energy, vol. 21, pp. 228-237.View/Download from: Publisher's site
© 2016 Elsevier Ltd. Solid-state fiber supercapacitors (SCs) that meet the requirements of high performance, flexibility, durability and wearer comfort are promising power sources for wearable electronics. The bottleneck in this field is how to develop devices with combined advantages of high specific capacitance, excellent flexibility and high conductivity. Here we report a novel flexible all-solid-state fiber SC by using Ti/TiO 2 /MoS 2 coaxial fiber electrodes that consist of MoS 2 nanosheets grown on titanium wires by a TiO 2 buffer layer assisted hydrothermal growth strategy. The symmetrical supercapacitor achieved a specific capacitance of 230.2 F g -1 (70.6 F cm -3 ), an energy density of 2.70 Wh kg -1 (4.98 mWh cm -3 ) and a power density of 530.9 W kg -1 (977.4 mW cm -3 ). Remarkably, the flexible and mechanically stable fiber SCs show outstanding processability in well-controlled ways, including being assembled into a stretchable, spring-shaped device and knitted into the fabric to lighten light-emitting diodes. In addition, the fiber SCs have been integrated in a self-powered photodetecting system and power the ultraviolet (UV) photodetector steadily, demonstrating that the fiber SCs can be easily integrated into future sustainable self-sufficient sensor networks.
Wang, Z, Cheng, J, Li, X, Ni, W, Yuan, D & Wang, B 2016, 'In situ synthesized single-crystalline LiMn2O4 embedded in carbon nanotube films as free-standing cathodes for Li-ion batteries', RSC Advances, vol. 6, no. 26, pp. 22061-22068.View/Download from: Publisher's site
© The Royal Society of Chemistry 2016. Single-crystalline LiMn2O4 nanoparticles embedded in a carbon nanotube film (LMO-CF-in situ), which serves as a binder-free and self-standing cathode for lithium ion batteries (LIBs), is synthesized by an in situ hydrothermal reaction followed by heat treatment. The single-crystalline LiMn2O4 particles with a diameter of about 200-400 nm are homogeneously distributed and entrapped in the mechanically robust and highly conductive carbon nanotube (CNT) scaffolds, which not only improves the energy density by eliminating the use of conventional metal current collectors, polymer binders and conductive additives, but also effectively alleviates the aggregation of LiMn2O4 nanoparticles. The as-synthesized LMO-CF-in situ electrode exhibits attractive rate capability with an 86.2% retention of the capacity at 1C achieved at 5C, excellent cycling stability with an 82.1% specific capacity retention after 300 cycles at 1C and high coulombic efficiency of nearly 100%.
Yuan, D, Cheng, J, Qu, G, Li, X, Ni, W, Wang, B & Liu, H 2016, 'Amorphous red phosphorous embedded in carbon nanotubes scaffold as promising anode materials for lithium-ion batteries', Journal of Power Sources, vol. 301, pp. 131-137.View/Download from: Publisher's site
© 2015 Elsevier B.V. All rights reserved. Amorphous red phosphorus/carbon nanotubes (ARPC) composites are prepared by planetary ball-milling technique with the pre-milling red phosphorus processes, consisting of uniformly distributing amorphous red phosphorus embedding in a three-dimensional conductive scaffold of interconnected carbon nanotubes (CNTs). Combining the three-dimensional conductive network with the amorphous red phosphorus can not only alleviate the volumetric change in the charging/discharging processes, but also provide conductive network for electron transport and dramatically improve the specific capacity, cycling stability and rate capability of the composite electrode. The ARPC composites deliver a high initial charge capacity of 2133.4 mAh g-1 at a current density of 0.05 C and maintain a reversible capacity of 998.5 mAh g-1 with a high Coulombic efficiency of approximately 99% after 50 cycles. Meanwhile, the composite can maintain high specific capacities of 1993.8 mAh g-1, 1896.9 mAh g-1, 1546.8 mAh g-1 and 816.6 mAh g-1 at 0.01 C, 0.05 C, 0.1 C and 0.5 C, respectively. Compared with that of the ball-milled amorphous red phosphorus with or without CNTs, the pre-milled ARPC composites show much better electrochemical performances.
Saadat, A, Ni, W, Vesilo, R & Cui, Q 2016, 'An Evolutionary Game Theoretic Framework for Femtocell Radio Resource Management (vol 14, pg 6365, 2015)', IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 15, no. 12, pp. 8610-8612.View/Download from: Publisher's site
Hagelstein, B, Abolhasan, M, Franklin, D, Ni, W & Safaei, F 2016, 'Analytic Performance Model for State-Based MAC Layer Cooperative Retransmission Protocols', IEEE Transactions on Mobile Computing, vol. 15, no. 1, pp. 32-44.View/Download from: UTS OPUS or Publisher's site
COOPERATIVE retransmission is a well-established technique
for improving wireless network capacity . Its
effectiveness is strongly dependent on the choice of relay
selection algorithm, as this determines both the probability
of retransmission success and the probability of collisions
between simultaneous retransmission attempts. Consequently,
relay selection algorithm design remains an open
area of research.
Lin, S, Ni, W, Tian, H & Liu, RP 2015, 'An Evolutionary Game Theoretic Framework for Femtocell Radio Resource Management', IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 14, no. 11, pp. 6365-6376.View/Download from: UTS OPUS or Publisher's site
Wang, H, Liu, RP, Ni, W, Chen, W & Collings, IB 2015, 'VANET Modeling and Clustering Design Under Practical Traffic, Channel and Mobility Conditions', IEEE TRANSACTIONS ON COMMUNICATIONS, vol. 63, no. 3, pp. 870-881.View/Download from: UTS OPUS or Publisher's site
Huang, L, Cheng, J, Qu, G, Li, X, Hu, Y, Ni, W, Yuan, D, Zhang, Y & Wang, B 2015, 'Porous carbon nanofibers formed in situ by electrospinning with a volatile solvent additive into an ice water bath for lithium-sulfur batteries', RSC Advances, vol. 5, no. 30, pp. 23749-23757.View/Download from: Publisher's site
© The Royal Society of Chemistry 2015. The in situ formation of polyacrylonitrile (PAN) nanofibers with a porous structure was achieved by electrospinning ternary PAN/N,N-dimethylformamide (DMF)/chloroform (CHCl3), and ternary PAN/DMF/tetrahydrofuran (THF) solution systems into a glass dish filled with ice water. These porous carbon nanofibers (pCNFs) are both mesoporous and microporous, and attained high specific surface areas without the requirement of physical or chemical activation, which is mainly due to the in situ evaporation of the volatile solvent additive and the dissolution of the solvent in the ice water bath. The synthesis process is simple and versatile. The effects of the precursor components, precursor concentration and the collection method on the morphology and size distribution of the fibers have been investigated. The obtained pCNFs with porous structures and large surface areas were then utilized as conductive matrices for sulfur (S) to form pCNFs/S nanocomposites. Electrochemical measurements show that the pCNFs/S nanocomposite can deliver 400 and 340 mA h g-1 after 50 cycles and 100 cycles at 0.5 C, corresponding to 80.1% and 68% capacity retention with a high Coulombic efficiency, respectively.
Li, H, Shi, LY, Cui, W, Lei, WW, Zhang, YL, Diao, YF, Ran, R & Ni, W 2015, 'Covalent modification of graphene as a 2D nanofiller for enhanced mechanical performance of poly(glutamate) hybrid gels', RSC Advances, vol. 5, no. 105, pp. 86407-86413.View/Download from: Publisher's site
© The Royal Society of Chemistry. Graphene-based materials usually require defined functionalization for biological applications in order to control their physical/colloidal properties and to introduce additional capabilities. Here, poly(glutamate), a competitive polypeptide, is covalently grafted onto the graphene oxide two-dimensional (2D) structure through the combination of amidation reaction and ring-opening polymerization as the nanofiller of a hybrid polypeptide-based organogel with enhanced mechanical performance. The morphologies of the hybrid gels reveal that the modified graphene nanostructures may act as nanoscale skeletons, interfacial adhesives in the hybrid gels with nanofibrous 3D network nanostructures.
Qu, G, Cheng, J, Li, X, Huang, L, Ni, W, Wang, Z & Wang, B 2015, 'Graphene-Enveloped Poly(N-vinylcarbazole)/Sulfur Composites with Improved Performances for Lithium-Sulfur Batteries by a Simple Vibrating-Emulsification Method', ACS Applied Materials and Interfaces, vol. 7, no. 30, pp. 16668-16675.View/Download from: Publisher's site
© 2015 American Chemical Society. (Figure Presented) We prepared the Poly(N-vinylcarbazole)/sulfur@reduced graphene oxide (PVK/S@RGO) composites via a facile vibrating-emulsification synthesis method, which consist of the composites cores of large sulfur particles integrated into PVK conductive network and the conducting shell of reduced graphene oxide sheets. The PVK in the composites plays multiple roles in different processes. In preparation processes, PVK functions as dispersants to prevent sulfur particles from aggregating into excessively large size. And in the cycling test, PVK could play as additional electroactive binders and barriers to reinforce the electrode stability, accommodate volume change and reduce polysulfides shuttling. The resulting PVK/S@RGO composites containing 71 wt % sulfur exhibit excellent cycling performance and rate properties with a high discharge capacity of 843.5 mA h g-1 and a charge capacity retention of 77% (only 0.07% capacity degradation per cycle) from 20th to 400th at 1 C, corresponding to an average Coulombic efficiency of over 94%.
Li, X, Wang, Z, Zhang, Z, Chen, L, Cheng, J, Ni, W, Wang, B & Xie, E 2015, 'Light Illuminated -Fe2O3/Pt Nanoparticles as Water Activation Agent for', Scientific Reports, vol. 5.View/Download from: Publisher's site
The photoelectrochemical (PEC) water splitting is hampered by strong bonds of H2O molecules and low ionic conductivity of pure water. The photocatalysts dispersed in pure water can serve as a water activation agent, which provides an alternative pathway to overcome such limitations. Here we report that the light illuminated -Fe2O3/Pt nanoparticles may produce a reservoir of reactive intermediates including H2O2, OH, OH+ and H+ capable of promoting the pure water reduction/oxidation half2reactions at cathode and highly photocatalytic2active TiO2/In2S3/AgInS2 photoanode, respectively. Remarkable photocurrent enhancement has been obtained with -Fe2O3/Pt as water activation agent. The use of -Fe2O3/Pt to promote the reactivity of pure water represents a new paradigm for reproducible hydrogen fuel provision by PEC water splitting, allowing efficient splitting of pure water without adding of corrosive chemicals or sacrificial agent.
Guan, Q, Cheng, J, Li, X, Wang, B, Huang, L, Nie, F & Ni, W 2015, 'Low temperature vacuum synthesis of triangular CoO nanocrystal/graphene nanosheets composites with enhanced lithium storage capacity', Scientific Reports, vol. 5.View/Download from: Publisher's site
CoO nanocrystal/graphene nanosheets (GNS) composites, consisting of a triangular CoO nanocrystal of 2~20 nm on the surface of GNS, are synthesized by a mild synthetic method. First, cobalt acetate tetrahydrate is recrystallized in the alcohol solution at a low temperature. Then, graphene oxide mixed with cobalt-precursor followed by high vacuum annealing to form the CoO nanocrystal/ GNS composites. The CoO nanocrystal/GNS composites exhibit a high reversible capacity of 1481.9 m Ah g-1 after 30 cycles with a high Coulombic efficiency of over 96% when used as anode materials for lithium ion battery. The excellent electrochemical performances may be attributed to the special structure of the composites. The well-dispersed triangular CoO nanocrystal on the substrate of conductive graphene can not only have a shorter diffusion length for lithium ions, better stress accommodation capability during the charge-discharge processes and more accessible active sites for lithium-ion storage and electrolyte wetting, but also possess a good conductive network, which can significantly improve the whole electrochemical performance.
Chen, X, Ni, W, Wang, X & Sun, Y 2015, 'Provisioning Quality-of-Service to Energy Harvesting Wireless Communications', IEEE COMMUNICATIONS MAGAZINE, vol. 53, no. 4, pp. 102-109.View/Download from: Publisher's site
Gu, G, Cheng, J, Li, X, Ni, W, Guan, Q, Qu, G & Wang, B 2015, 'Facile synthesis of graphene supported ultralong TiO2 nanofibers from the commercial titania for high performance lithium-ion batteries', Journal of Materials Chemistry A, vol. 3, no. 12, pp. 6642-6648.View/Download from: Publisher's site
© The Royal Society of Chemistry. Novel nanocomposites consisting of two-dimensional graphene nanosheets and ultralong TiO2 nanofibers are fabricated via a simple one-pot hydrothermal reaction using commercial TiO2 particles as inorganic precursors. Complex chemical synthesis processes and high cost precursors can be avoided. When used as anodes of lithium ion batteries, the obtained nanocomposites exhibit a superior rate capability and an excellent long-term cycling stability. The nanocomposites maintain a charge capacity of 85 mA h g-1 at 20 C, while the TiO2 nanofibers fail when cycled at 5 C. The nanocomposites also demonstrate an excellent cycling stability with a charge capacity of 92 mA h g-1 after 1000 cycles at 10 C, approximately three times the capacity of the TiO2 nanofibers. The superior electrochemical performance can be attributed to the hybrid structure of the graphene nanosheets and the ultralong TiO2 nanofibers. The graphene nanosheets provide highly electronically conductive pathways and work as protected layers to keep the active material integrated during charging/discharging processes. The ultralong TiO2 nanofibers with high specific surface area have a short ion diffusion distance and provide more accessible sites. By combining the advantages of the graphene nanosheets and TiO2 nanofibers, the nanocomposites exhibit obviously improved electrochemical performances. This journal is
Huang, L, Cheng, J, Li, X, Yuan, D, Ni, W, Qu, G, Guan, Q, Zhang, Y & Wang, B 2015, 'Sulfur quantum dots wrapped by conductive polymer shell with internal void spaces for high-performance lithium-sulfur batteries', Journal of Materials Chemistry A, vol. 3, no. 7, pp. 4049-4057.View/Download from: Publisher's site
© The Royal Society of Chemistry 2015. Lithium-sulfur batteries are promising candidates for the next generation of energy storage systems due to the high specific capacity of the sulfur cathode (1675 mA h g-1) and their low cost. However, the intrinsic insulating properties of sulfur, the dissolution of polysulfides, and the huge volume expansion during cycling still hinder their practical application. We introduced the electroactive polymer poly(N-vinylcarbazole) (PVK) into the lithium-sulfur system as a conductive matrix and sulfur reservoir. Using a facile two-step dissolution-precipitation treatment, novel core-shell sulfur quantum dot/PVK (SQD/PVK) nanocomposites were synthesized, in which a large number of SQDs (about 5 nm in size) with plenty of internal void spaces were encapsulated in the PVK shell. The sulfur core consisted of uniformly dispersed SQDs and large void spaces, which formed effective transportation pathways for both electrons and ions among the SQDs. They also acted as a buffer zone to accommodate the volume expansion during cycling and facilitated wetting of the electrolyte. The conducting PVK shell coated on the surface of the sulfur core can restrain dissolution of the polysulfide and suppress the shuttle effect. Galvanostatic testing showed that this SQD/PVK nanocomposite maintained a specific capacity of 687.7 mA h g-1 after 200 cycles at 0.5 C, corresponding to an 89.7% capacity retention with only 0.05% capacity degradation per cycle. Even after long-term cycling, the electrode could still deliver 488.6 mA h g-1 at a rate of 0.5 C after 600 cycles and 443.9 mA h g-1 at 0.75 C after 500 cycles.
Ni, W, Cheng, J, Li, X, Gu, G, Huang, L, Guan, Q, Yuan, D & Wang, B 2015, 'Polymeric cathode materials of electroactive conducting poly(triphenylamine) with optimized structures for potential organic pseudo-capacitors with higher cut-off voltage and energy density', RSC Advances, vol. 5, no. 12, pp. 9221-9227.View/Download from: Publisher's site
© The Royal Society of Chemistry 2015. For electrochemical capacitors or supercapacitors, pseudo-capacitors via fast surface reactions are able to store/harvest more electrical energy when compared with electrochemical double layer capacitors (EDLCs) using an ion adsorption route. A combination of pseudo-capacitive materials, including oxides, nitrides and polymers, as well as understanding the charge storage mechanism and the development of advanced nanostructures with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. Electroactive polymeric cathodes with designed structures via electrospinning (without polymeric additives) and surfactant-free precipitation polymerization routes were herein fabricated for the abovementioned goals. The as-prepared polymeric active materials show an electrochemical capacitance of around 200 F g-1 with a higher cut-off voltage up to 4.2 V and an energy density up to 370 Wh kg-1 and power density up to 34 kW kg-1 in an organic electrolyte system.
Ni, W, Collings, IB, Wang, X, Liu, RP, Kajan, A, Hedley, M & Abolhasan, M 2015, 'Radio Alignment for Inductive Charging of Electric Vehicles', IEEE Transactions on Industrial Informatics, vol. 11, no. 2, pp. 427-440.View/Download from: UTS OPUS or Publisher's site
To maximize power transfer for inductively charging electric vehicles (EVs), charger and battery coils must be aligned. Wireless sensors can be installed to estimate misalignments; however, existing ranging techniques cannot satisfy the precision requirements of the misalignment estimation. We propose a high-precision wireless ranging and misalignment estimation scheme, where high precision is achieved by iteratively measuring, estimating, and aligning the coils. Another key aspect is to convert the nonconvex misalignment estimation to a more tractable problem with a convex objective. We develop a conditional gradient descent method to solve the problem, which performs gradient descent (or conditional gradient descent on the boundary of the search space) and projects out-of-boundary points back into the space. Employing experimentally validated models, we show that our scheme can achieve 92% of the efficiency of perfectly aligned coils in 90% of operations, and tolerate correlated distance measurement errors. In contrast, the prior art is susceptible to correlation, undergoing a significant efficiency degradation of 18.5%.
Ni, W, Abolhasan, M, Collings, I, Lipman, J, Wang, X & Tao, M 2015, 'Graph Theory and Its Applications to Future Network Planning: Software-Defined Online Small Cell Management', IEEE Wireless Communications Magazine, vol. 22, no. 1, pp. 52-60.View/Download from: UTS OPUS or Publisher's site
Network planning is facing new and critical challenges due to ad hoc deployment, unbalanced and drastically varying traffic demands, as well as limited backhaul and hardware resources in emerging small cell architectures. We discuss the application of graph theory to address the challenges. A clique-based software-defined online network management approach is proposed that captures traffic imbalance and fluctuation of small cells and optimally plans frequencies, infrastructures, and network structure at any instant. Its applications to three important small cell scenarios of cloud radio, point-to-point microwave backhaul, and interoperator spectrum sharing are demonstrated. Comparison studies show that in each of the scenarios, this new approach is able to significantly outperform conventional static offline network planning schemes in terms of throughput and satisfaction levels of small cells with regard to allocated bandwidths. Specifically, the throughput can be improved by 155 percent for the cloud radio scenario and 110.95 percent for the microwave backhaul scenario. The satisfaction level can be improved by 40 percent for interoperator spectrum sharing.
Abolhasan, M, lipman, J, Ni, W & Hagelstein, B 2015, 'Software-Defined Wireless Networking: Centralised, Distributed, or Hybrid?', IEEE Network: the magazine of global information exchange, vol. 29, no. 4, pp. 32-38.View/Download from: UTS OPUS or Publisher's site
Scalability is a key issue in large scale WDNs, such as vehicular networks and device-to-device networks. To address the issue, this article extends the SDN concept, and presents a new network architecture that eliminates the need of multi-hop flooding for route discovery, thereby enabling WDNs to scale. The key idea of the new architecture is to split network control and data forwarding by using two separate frequency bands. Another important aspect of the architecture is that computational complexity of routing is split between the SDN controller and the forwarding nodes, thereby allowing nodes to make distributed routing decisions. As a result, network control of the new architecture has a hybrid structure, which improves the operability and scalability of large scale WDNs. Our case study shows that the new architecture is able to substantially improve scalability and reliability of WDNs, especially in mobile environments.
Ni, W, Liu, RP, Biswas, J, Wang, X, Collings, IB & Jha, SK 2014, 'Multiuser MIMO Scheduling for Mobile Video Applications', IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 13, no. 10, pp. 5382-5395.View/Download from: UTS OPUS or Publisher's site
Ni, W, Collings, IB, Wang, X & Liu, RP 2014, 'MULTI-HOP POINT-TO-POINT FDD WIRELESS BACKHAUL FOR MOBILE SMALL CELLS', IEEE WIRELESS COMMUNICATIONS, vol. 21, no. 4, pp. 88-96.View/Download from: UTS OPUS or Publisher's site
Ni, W, Collings, IB, Liu, RP & Chen, Z 2014, 'Relay-Assisted Wireless Communication Systems in Mining Vehicle Safety Applications', IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, vol. 10, no. 1, pp. 615-627.View/Download from: UTS OPUS or Publisher's site
He, T, Wang, X & Ni, W 2014, 'Optimal chunk-based resource allocation for OFDMA systems with multiple BER requirements', IEEE Transactions on Vehicular Technology, vol. 63, no. 9, pp. 4292-4301.View/Download from: Publisher's site
© 2014 IEEE. In wireless orthogonal frequency-division multiple-access (OFDMA) standards, subcarriers are grouped into chunks, and a chunk of subcarriers is made as the minimum unit for subcarrier allocation. We investigate the chunk-based resource allocation for OFDMA downlink, where data streams contain packets with diverse bit-error-rate (BER) requirements. Supposing that adaptive transmissions are based on a number of discrete modulation and coding modes, we derive the optimal resource-allocation scheme that maximizes the weighted sum of average user rates under the multiple BER requirements and total power constraints. With proper formulation, the relevant optimization problem is cast as an integer linear program (ILP), and it is shown that the optimal strategy for this problem can be obtained through Lagrange dual-based gradient iterations with fast convergence and low computational complexity per iteration. Furthermore, a novel online algorithm is developed to approach the optimal strategy without knowing the statistics of the intended wireless channels a priori. The proposed approach is also generalized to utility maximization of average user rates to leverage the total throughput and fairness among users. Numerical results are provided to gauge the performance of the proposed schemes.
Ni, W, Cheng, J, Shi, L, Li, X, Wang, B, Guan, Q, Huang, L, Gu, G & Li, H 2014, 'Integration of Sn/C yolk-shell nanostructures into free-standing conductive networks as hierarchical composite 3D electrodes and the Li-ion insertion/extraction properties in a gel-type lithium-ion battery thereof', Journal of Materials Chemistry A, vol. 2, no. 45, pp. 19122-19130.View/Download from: Publisher's site
© the Partner Organisations 2014. A novel style of Sn/C yolk-shell nanospheres integrated into nanofibrous 3D electric conducting structures as free-standing materials for potential applications such as new-generation anode structures for gel-type lithium-ion batteries via the design principle of inhibiting the aggregation of tin nanoparticles, buffering the occurring volume strain, and the flexible conductive networks.
Li, X, Zhang, Z, Chen, L, Liu, Z, Cheng, J, Ni, W, Xie, E & Wang, B 2014, 'Cadmium sulfide quantum dots sensitized tin dioxide-titanium dioxide heterojunction for efficient photoelectrochemical hydrogen production', Journal of Power Sources, vol. 269, pp. 866-872.View/Download from: Publisher's site
CdS quantum dots (QDs)-sensitized branched TiO2/SnO2 heterojunction (B-SnO2 NF-CdS) with suitable combination of band gap and band alignment constitutes a promising architecture for photoanode for H2 generation. This novel structure combines the conflicting advantageous features of slow interfacial electron recombination, long electron life time, fast electron transport and visible light absorption. Remarkable photocurrent density of 3.40 mA cm-2 at zero bias (vs. standard calomel electrode) has been obtained in a three electrode configuration, more than two times as large as that of TiO2-CdS photoanode. The B-SnO2 NF-CdS yields a high maximum applied bias photon-to-current efficiency (ABPE) of 2.18% at an applied bias of 0.316 V vs. reversible hydrogen electrode (RHE), indicating excellent hydrogen generation performance at low bias. Moreover, on the basis of experimental results, we ascribe the remarkable "dark current/voltage" to the effect of primary cell. The influence of the primary cell on PEC hydrogen production is discussed. © 2014 Elsevier B.V. All rights reserved.
Guan, Q, Cheng, J, Wang, B, Ni, W, Gu, G, Li, X, Huang, L, Yang, G & Nie, F 2014, 'Needle-like Co3O4 anchored on the graphene with enhanced electrochemical performance for aqueous supercapacitors', ACS Applied Materials and Interfaces, vol. 6, no. 10, pp. 7626-7632.View/Download from: Publisher's site
We synthesized the needle-like cobalt oxide/graphene composites with different mass ratios, which are composed of cobalt oxide (Co3O 4 or CoO) needle homogeneously anchored on graphene nanosheets as the template, by a facile hydrothermal method. Without the graphene as the template, the cobalt precursor tends to group into urchin-like spheres formed by many fine needles. When used as electrode materials of aqueous supercapacitor, the composites of the needle-like Co3O4/graphene (the mass ratio of graphene oxide(GO) and Co(NO3)2·6H 2O is 1:5) exhibit a high specific capacitance of 157.7 F g -1 at a current density of 0.1 A g-1 in 2 mol L -1 KOH aqueous solution as well as good rate capability. Meanwhile, the capacitance retention keeps about 70% of the initial value after 4000 cycles at a current density of 0.2 A g-1. The enhancement of excellent electrochemical performances may be attributed to the synergistic effect of graphene and cobalt oxide components in the unique multiscale structure of the composites. © 2014 American Chemical Society.
Ni, W, Wang, B, Cheng, J, Li, X, Guan, Q, Gu, G & Huang, L 2014, 'Hierarchical foam of exposed ultrathin nickel nanosheets supported on chainlike Ni-nanowires and the derivative chalcogenide for enhanced pseudocapacitance', Nanoscale, vol. 6, no. 5, pp. 2618-2623.View/Download from: Publisher's site
Foamlike nickel hierarchical structures of ultrathin nanosheets supported on thin wires composed of nanoparticles are prepared by a facile one-pot synthesis via controlled nucleation and growth process. By further sulfidation, the sulfide derivative of loose porous fibrous structure shows a high electrochemical capacity for potential pseudocapacitor applications. © 2014 The Royal Society of Chemistry.
Pan, P, Zheng, B, Song, R & Ni, W 2014, 'Feed back load analysis for broadcast channels with zero-forcing beamforming', IET COMMUNICATIONS, vol. 8, no. 18, pp. 3326-3332.View/Download from: Publisher's site
Ni, W, Collings, IB & Liu, RP 2013, 'Decentralized User-Centric Scheduling with Low Rate Feedback for Mobile Small Cells', IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, vol. 12, no. 12, pp. 6106-6120.View/Download from: UTS OPUS or Publisher's site
The ubiquitous Ethernet has great potential to become an easy-to-install cost-effective backhaul solution for mobile small cells. However, limited Ethernet bandwidth is a practical constraint. Not only is small cell capacity limited by Ethernet bandwidth, but also the synchronization between cells can be substantially compromised. In this article we discuss small cells with Ethernet backhaul, focusing on two practical and important aspects: backhaul bandwidth requirements and tolerance to synchronization errors. The aspects become challenging in indoor small cell applications where the cells need to cooperatively suppress strong interference, producing a large amount of backhaul traffic. To address the challenges, we introduce a new distributed scheme of cooperative small cells over Ethernet. Exploiting a soft information combining technique, the scheme allows the signals of cooperative cells to be combined at aggregate switches along their backhaul paths, reducing backhaul traffic in Ethernet and distributing computational complexity. Our case study shows that the distributed scheme can reduce small cell backhaul traffic by 64 percent, compared to a conventional centralized approach. It is also tolerant to a large frequency error of ±4.6 ppm in a ¿freerun¿ state where synchronization is lost. Given the substantially reduced backhaul traffic, the new distributed scheme is able to support three times the cooperative small cells of the conventional centralized approach. © 1979-2012 IEEE. © 2013 IEEE.
Small cells are an emerging approach to improving hotspots throughput in cellular networks. Unfortunately, they cannot be deployed in a large scale under current cellular architectures, because of a severe interference problem and inefficient use of spectrum. We propose a new small-cell architecture which reconfigures topologies and frequency bands, adapting to changing traffic demands and interference-mitigating requirements. The new architecture consists of distributed small-cell nodes (SCN) and co-located baseband units (BBU), and adaptively switches the connections between the SCNs and BBUs. The BBUs can even be shared among multiple SCNs that use different frequency bands. Our architecture requires fewer BBUs, and the spectrum and energy utilization is significantly more efficient compared with current architectures. Simulations show that the new architecture is able to increase the spectrum utilization by 23.5%, and improve the network satisfaction regarding traffic demands by 144.2% for small cells covering 0.5 km2. Our architecture can also reduce the investment and energy consumption of the BBUs by up to 40%. © 1983-2012 IEEE.
Ni, W, Collings, IB & Liu, RP 2012, 'Relay Handover and Link Adaptation Design for Fixed Relays in IMT-Advanced Using a New Markov Chain Model', IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, vol. 61, no. 4, pp. 1839-1853.View/Download from: UTS OPUS or Publisher's site
Ni, W & Collings, IB 2012, 'Adaptive adjacent-frequency interference mitigation in multi-hop point-to-point FDD wireless backhaul networks', IEEE Communications Letters, vol. 16, no. 12, pp. 1988-1991.View/Download from: Publisher's site
Adjacent-frequency interference is a critical problem in point-to-point (PTP) frequency division duplex (FDD) wireless backhaul networks. It prevents existing methods from adaptively allocating frequencies to the PTP links, reducing spectrum utilization. We propose a new algorithm which mitigates the interference and enables the frequencies to be allocated adapting to changing traffic demands. Our algorithm is developed on a new recursive guard band adjusting technique. Simulations show that our algorithm is able to improve spectrum utilization by 33%, compared to the prior art, and enhance the network satisfaction regarding allocated bandwidth by over 173%. © 1997-2012 IEEE.
Ni, W, Chen, Z, Suzuki, H & Collings, IB 2011, 'On the performance of semi-orthogonal user selection with limited feedback', IEEE Communications Letters, vol. 15, no. 12, pp. 1359-1361.View/Download from: Publisher's site
The sum rates of MIMO broadcast channels degrade because of channel quantization errors (CQE), when semi-orthogonal user selection and zero-forcing beamforming (SUS-ZFBF) are used. To study this degradation, impractically many users have been assumed in the state-of-the-art. We derive two new bounds (i.e., upper and lower) to quantify the degradation for a practical number of users (i.e., K 100). Validated by simulations, the new bounds show that the degradation is marginal (<3%) from using non-optimal quantization methods. Our bounds also reveal that, for a given overall overhead, increasing quantization bits and reducing users per SUS-ZFBF process is able to substantially improve the sum rate. © 2006 IEEE.
Sun, QF, Dai, MY, Chen, W, Ding, JG, Ni, W & Xu, DZ 2008, 'The relationship between T cell subsets and secondary bacterial infection and prognosis of patients with chronic severe hepatitis B', Zhonghua gan zang bing za zhi = Zhonghua ganzangbing zazhi = Chinese journal of hepatology, vol. 16, no. 2, pp. 146-147.
Rafiei, A, Abolhasan, M, Franklin, DR, Safaei, F, Smith, S & Ni, W 2017, 'Cooperative recovery of coverage holes in WSNs via disjoint spanning trees', 2017, 11th International Conference on Signal Processing and Communication Systems, ICSPCS 2017 - Proceedings, International Conference on Signal Processing and Communication Systems, IEEE, Gold Coast, QLD, Australia, pp. 1-10.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Large scale coverage holes (CHs) resulting from correlated node failures, can significantly degrade quality of service and also jeopardise the integrity of WSNs. In the absence of centralised control, the distributed relocation of deployed nodes becomes a promising solution especially in harsh and hostile environments. In this paper, a distributed method is proposed that enables a network to partially or entirely repair itself through a collection of distributed movements of disjoint spanned trees (DS-Trees) towards the CHs. DS-Trees are spanned based on the nodes distances from the CHs, which are autonomously perceived by the nodes and their one-hop neighbours. DS-Trees around the CHs are spanned in a downstream style outwards from the holes, as nodes select their parents based on the minimum distance to the CH from their neighbours; nodes then decide whether or not to follow the movements of their DS-Trees parents. To examine the efficiency of the proposed model, its performance is compared with two Voronoi-based and one force-based node relocation algorithms. Results show that the proposed DS-Tree model either outperforms or matches the alternative approaches across a wide range of scenarios.
Khan, AA, Abolhasan, M & Ni, W 2018, '5G next generation VANETs using SDN and fog computing framework', CCNC 2018 - 2018 15th IEEE Annual Consumer Communications and Networking Conference, IEEE Annual Consumer Communications & Networking Conference, IEEE, Las Vegas, NV, USA, pp. 1-6.View/Download from: Publisher's site
© 2018 IEEE. The growth of technical revolution towards 5G Next generation networks is expected to meet various communication requirements of future Intelligent Transportation Systems (ITS). Motivated by the consumer needs for variety of ITS applications, bandwidth, high speed and ubiquity, researches are currently exploring different network architectures and techniques, which could be employed in Next generation ITS. To provide flexible network management, control and high resource utilization in Vehicular Ad-hoc Networks (VANETs) on large scale, a new hierarchical 5G Next generation VANET architecture is proposed. The key idea of this holistic architecture is to integrate the centralization and flexibility of Software Defined Networking (SDN) and Cloud-RAN (CRAN), with 5G communication technologies, to effectively allocate resources with a global view. Moreover, a fog computing framework (comprising of zones and clusters) has been proposed at the edge, to avoid frequent handovers between vehicles and RSUs. The transmission delay, throughput and control overhead on controller are analyzed and compared with other architectures. Simulation results indicate reduced transmission delay and minimized control overhead on controllers. Moreover, the throughput of proposed system is also improved.
Liu, R 2017, 'A Decoupled 5G Network Control Framework: Distributed Adaptation and Centralized Coordination', IEEE Globecom Workshops, IEEE, Singapore, Singapore.View/Download from: UTS OPUS or Publisher's site
A promising and cost-e ective way to connect massively and densely deployed 5G smallcells is through existing Internet infrastructure. However, severe delays of hundreds of milliseconds over Internet and signi cantly increased complexity due to massive networks impose critical challenges to 5G network control. Traditional centralized network control can neither cope with such delays nor scale to massive networks. Excessive inter-smallcell interfer- ence would occur. We introduce a new 5G network control structure which is tolerant to the severe delay and massive network scale. The key idea is to decouple delay-sensitive power control from the delay-tolerant channel assignment. The delay-sensitive power control can be decentralized, and formulated as a non-cooperative game. As a result, timely control with stringent delay requirements is eliminated. The delay-tolerant channel assignment is modelled as an evolutionary clustering game, so that the control complex- ity can be distributed among the smallcells and becomes practically acceptable. Performance studies show that the new decoupled 5G network control is e ective for timely interference mitigation. The stability and scalability of the new 5G network control are also demonstrated.
Zhou, Y, Ni, W, Zheng, K, Liu, RP & Yang, Y 2018, 'Node-centric route mutation for large-scale SDN based on 3D earth mover's distance model', 2017 17th International Symposium on Communications and Information Technologies, ISCIT 2017, pp. 1-6.View/Download from: Publisher's site
© 2017 IEEE. Exploiting software-defined networking techniques, randomly and instantly mutating routes can disguise strategically important infrastructure, and protect the integrity of data networks. Route mutation has been to date formulated as NP-complete constraint satisfaction problems where feasible sets of routes need to be generated with exponential computational complexities, limiting algorithmic scalability to large-scale networks. In this paper, we propose a novel node-centric route mutation method which interprets route mutation as a signature matching problem. We formulate the route mutation problem as a three-dimensional earth mover's distance (EMD) model and solve it by using a binary branch and bound method. Considering the scalability, we further propose a heuristic method yields significantly lower computational complexities with marginal loss of robustness against eavesdropping. Simulation results show that our proposed methods can effectively disguise key infrastructure by reducing the difference of historically accumulative traffic among different switches. With significantly reduced complexities, our algorithms are of particular interest to safeguard large-scale networks.
Chen, X, Wang, X, Ni, W & Collings, IB 2017, 'Two-way energy trading and online planning for fifth-generation communications with renewables', 2017 23rd Asia-Pacific Conference on Communications: Bridging the Metropolitan and the Remote, APCC 2017, Asia-Pacific Conference on Communications, Perth, WA, Australia, pp. 552-557.View/Download from: Publisher's site
© 2017 University of Western Australia. Future fifth-generation (5G) cellular networks, equipped with energy harvesting devices, are uniquely positioned to closely interoperate with smart grid. New interoperable functionalities are discussed in stochastic two-way energy trading and online planning to improve efficiency and productivity. Challenges lie in the unavailability of a-priori knowledge on future wireless channels, energy pricing and harvesting. Lyapunov optimization techniques are utilized to address the challenges and stochastically optimize energy trading and planning. Particularly, it is able to decouple the optimization of energy trading and planning during individual time slots, hence eliminating the need for joint optimization across a large number of slots.
Saadat, A, Ni, W & Vesilo, R 2017, 'Spectrum sharing in femtocell based networks using an equal priority power control game', 2017 17th International Symposium on Communications and Information Technologies, ISCIT 2017, International Symposium on Communications and Information Technologies, Cairns, QLD, Australia, pp. 1-6.View/Download from: Publisher's site
© 2017 IEEE. In order to keep pace with the recent proliferation of wireless services and mobile applications, efficient and flexible radio spectrum utilization needs to be ensured in next-generation mobile networks. In this regard, we present a game-Theoretic spectrum-sharing scheme, by considering coexistence of a set of femtocells, belonging to multiple networks, in a coverage area where all cells have an equal priority of accessing the spectrum. We formulate a non-cooperative transmit-power-control game, in which all the femtocells share the spectrum by adjusting their transmit powers according to the interference, until the transmit power is stabilized. We prove that a Nash equilibrium exists for the proposed non-cooperative game, verify that it is unique and highlight the role of specific game parameters in this regard. A novel dual-mode solution is proposed for implementation of the game, which ensures that an equilibrium point can be reached having minimum coordination among the network elements. Finally, we present simulation results to show that the game converges to a Nash equilibrium and provide a throughput performance analysis.
Sung, CK, Li, S, Hedley, M, Nikolic, N & Ni, W 2018, 'Skew log-normal channel model for indoor cooperative localization', IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, Personal, Indoor, and Mobile Radio Communications, IEEE, Montreal, QC, Canada, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. The performance of cooperative localization using received signal strength (RSS) benefits from accurate radio channel modeling. While log-normal shadowing is commonly used to model the relationship between RSS and range, the RSS error distribution in indoor environments has been observed to be neither normal nor symmetric. In this paper, we propose a skew log-normal channel model, which includes the standard log-normal model as a special case. We further propose an algorithm for using this model for RSS based cooperative localization. The algorithm was evaluated using data from an electro-magnetic simulation of an aircraft cabin, and was shown to generate more accurate node locations compared to the use of log-normal shadowing in the same localization algorithm.
Ismaiel, B, Abolhasan, M, Smith, D, Ni, W & Franklin, D 2017, 'Scalable MAC protocol for D2D communication for future 5G networks', 2017 14th IEEE Annual Consumer Communications and Networking Conference, CCNC 2017, 2017 14th IEEE Annual Consumer Communications & Networking Conference, IEEE, Las Vegas, NV, USA, pp. 542-547.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Device-to-device communication (D2D) will be an integral part of 5G wireless networks. Device-to-Device (D2D) communication provide the additional resources to the cellular users for spatially reusing licensed/unlicensed spectrum by establishing direct communication. Although, D2D communication is gaining significant attention towards offloading traffic in heterogeneous networks in licensed band, no attention has been given to offload traffic in an unlicensed band in a centralized manner. However, a major challenge of D2D communication is managing resources in an efficient manner in a heterogeneous network. This paper will direct a new approach to D2D Communication and will present a scalable MAC protocol for D2D communications based on Point Coordination Function (PCF) access mechanism. The importance of PCF access mechanism is that it operates in a centralized manner and highly suitable for the dense environment, hence, can create a centralized control in a distributive manner. In this article, we propose an innovative three tier 5G architecture for D2D communication, which will offload cellular traffic from the cellular network to the WLAN in a dense environment. Moreover, we will present a new centralized scalable MAC protocol for D2D communication between WLAN users, based on the IEEE 802.11 Point Coordination Function (PCF) access mechanism. Our simulation results show that the proposed MAC scheme can increase the capacity of the network and perform better relative to the legacy Distributed coordination Function (DCF) defined in IEEE 802.11.
Wu, W, Liu, RP, Ni, W, Kaafar, D & Huang, X 2017, 'AC-PROT: An Access Control Model to Improve Software-Defined Networking Security', Proceedings of the 85th IEEE Vehicular Technology Conference, IEEE Vehicular Technology Conference, IEEE, Sydney, Australia, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
The logically-centralized controllers have largely operated as the coordination points in software-defined networking(SDN), through which applications submit network operations to manage the global network resource. Therefore, the validity of these network operations from SDN applications are critical for the security of SDN. In this paper, we analyze the mechanism that generates network operations in SDN, and present a fine-grained access control model, called Access Control Protector(AC-PROT),that employs an attribute-based signature scheme for network applications. The simulation result demonstrates that AC-PROT can efficiently identify and reject unauthorized network operations generated by applications.
Li, W, Ni, W, Liu, D, Liu, RP, Wang, P & Luo, S 2017, 'Fine-Grained Access Control for Personal Health Records in Cloud Computing', Proceedings of the 95th IEEE Vehicular Technology Conference, IEEE Vehicular Technology Conference, IEEE, Sydney, NSW, Australia, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. This paper presents a novel access control scheme for personal health record(PHR) data in cloud computing. The scheme utilizes attribute-based encryption(ABE), hash function and symmetric encryption to realize a fine-grained, multi- privilege access control to PHR. The patients can share their PHR with medical staff from various departments with different privileges securely. The experimental results show the efficiency of our scheme in terms of running-time, communication cost and storage overhead.
Ismaiel, B, Abolhasan, M, Smith, D, Ni, W & Franklin, D 2017, 'A Survey and Comparison of Device-to-Device Architecture Using LTE Unlicensed Band', IEEE Vehicular Technology Conference, IEEE Vehicular Technology Conference, IEEE, Sydney, NSW, Australia, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Due to the rapid increase in data traffic, one of the solutions provided by mobile operators is to operate Long Term Evolution (LTE) in the unlicensed 5GHz band, as the licensed spectrum is becoming scarce. Mobile operators can expand their network capacity by operating LTE in the unlicensed band at lower cost when compared with using other licensed bands. Device to Device (D2D) communication, proven to be another effective way to enhance the capacity of a network, enables direct data exchange of localized traffic of users in proximity. Applying D2D communication to LTE unlicensed 5GHz band will further improve the network performance and user experience. In this article, we will discuss the new type of solutions that have been proposed for LTE operating in an unlicensed 5GHz band that includes; LTE-Unlicensed (LTE-U), LTE-License Assisted Access (LTE-LAA), LTE WiFi Link Aggregation (LWA), and MuLTEfire. We will discuss the important features along with their advantages and disadvantages and compare these technologies as well. We simulate LTE-LAA, LWA and MuLTEfire technologies in the presence of Wi-Fi hotspot and compare their results. Furthermore, we apply D2D communication to these technologies and from the results we conclude that MuLTEfire can increase the throughput drastically but network saturates quickly. Whereas, applying D2D communication with LWA is beneficial for a scalable network as it will not only increase the network throughput but will increase the network capacity as well.
Wu, G, Liu, RP, Ni, W & Xu, P 2017, 'Modeling CCH Switch to SCH in IEEE 802.11p/WAVE Vehicular Networks', IEEE Vehicular Technology Conference, IEEE Vehicular Technology Conference, IEEE, Sydney, NSW, Australia, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Packet collision and packet delay are considered to be critical for safety applications in vehicular networks. This paper designs a new analytical model to evaluate the performance of channel switching for IEEE 802.11p/WAVE in vehicular networks. Under this model, it explicitly expresses the WAVE channel switching, and constructs contention window size and number of vehicles as packet collision probability and packet delay time function of variables. Finally, we evaluate accuracy of the designed model of collision caused by channel switching and transmission delay in vehicular networks. The results show that the model could analyzes perfectly packet collision which is caused by channel switching and packet delay in vehicular networks.
Rafiei, A, Abolhasan, M, Franklin, DR, Safaei, F, Smith, S & Ni, W 2017, 'Effect of the number of participating nodes on recovery of WSN coverage holes', 2017 27th International Telecommunication Networks and Applications Conference, ITNAC 2017, International Telecommunication Networks and Applications Conference, IEEE, Melbourne, VIC, Australia, pp. 1-8.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Coverage holes (CHs) due to the correlated node failures, if not appropriately addressed in a timely manner, not only disrupt network's operation but also can compromise its integrity. In the absence of centralised control, distributed node relocation can be an effective solution to recover CHs. Relocation algorithms that mainly applied to all nodes to address networks' coverage and unbalanced deployments problems, are not efficient as participating nodes beyond a certain distance and depth from the CHs do not significantly contribute to recovery of CHs. Here, the effects of the number of participating nodes and movement iterations on recovery of CHs are examined in two Voronoi-based and one force-based node relocation algorithms.
Lin, S, Yu, J, Ni, W & Liu, R 2017, 'Radio Resource Management for Ultra-Dense Smallcell Networks: A Hybrid Spectrum Reuse Approach', Proceedings of the 85th IEEE Vehicular Technology Conference, IEEE Vehicular Technology Conference, IEEE, Sydney, NSW, Australia, pp. 1-7.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Smallcells have great potential to enhance cellular networks, complementing macrocells. Severe interference may occur, as smallcells are expected to be deployed and operated uncoordinatedly. However, existing resource management methods require significant overhead to suppress interference. We propose a new resource management approach which is able to mitigate the cross-tier and co-tier interference with substantially reduced overhead. The key idea is to categorize the smallcells into two regions based on a judiciously designed cross-tier interference criterion. Smallcells in the high-interference zone occupy orthogonal radio resources with the macrocell; smallcells in the other zone can reuse the resources that the macrocell is using. Another crucial aspect is that we formulate the resource sharing between the macrocell and smallcells in the low-interference zone to a multi-agent Q-learning process which assigns adequate transmit power levels in a decentralized manner to suppress the co/cross-tier interference. As a result, our approach is able to reduce the outage probabilities of macrocell users significantly to 0%, respectively, in a dense smallcell deployment (200 smallcells), as evidenced by simulation results.
Li, K, Ni, W, Duan, L, Abolhasan, M & Niu, J 2017, 'SWPT: A Joint-Scheduling Model for Wireless Powered Sensor Networks', 2017 IEEE Global Communications Conference, GLOBECOM 2017 - Proceedings, 2017 IEEE Global Communications Conference, IEEE, Singapore, Singapore, pp. 1-6.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. In a rechargeable wireless sensor network, the data packets are generated by sensor nodes at a specific data rate, and transmitted to a base station. Moreover, the base station transfers power to the nodes by using Wireless Power Transfer (WPT) to extend their battery life. However, inadequately scheduling WPT and data collection causes some of the nodes to drain their battery and have their data buffer overflow, while the others waste their harvested energy, which is more than they need to transmit their packets. In this paper, we investigate a novel optimal scheduling strategy, called Scheduled WPT (SWPT), aiming to minimize data packet loss from a network of wireless powered sensor nodes by jointly considering the sensor nodes' energy consumption and data queue state information. The scheduling problem is formulated by a MDP model, assuming that the complete states of each sensor node are well known by the base station. This presents the best effort performance of the scheduling that can be collected in a wireless powered sensor network. The simulation results show that, in terms of network throughput and packet loss rate, the proposed scheduling model significantly improves the network performance.
Zha, X, Wang, X, Ni, W, Liu, RP, Guo, YJ, Niu, X & Zheng, K 2017, 'Analytic model on data security in VANETs', Proceedings of the 2017 17th International Symposium on Communications and Information Technologies, ISCIT 2017, International Symposium on Communications and Information Technologies, IEEE, Cairns, QLD, Australia, pp. 1-6.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Fast-changing topologies and uncoordinated transmissions are two critical challenges of implementing data security in vehicular ad-hoc networks (VANETs). We propose a new protocol, where transmitters adaptively switch between backing off retransmissions and changing keys to improve success rate. A new 3-dimensional (3-D) Markov model, which can analyze the proposed protocol with symmetric or asymmetric keys in terms of data security and connectivity, is developed. Analytical results, validated by simulations, show that the proposed protocol achieves substantially improved resistance against collusion attacks.
Lai, W, Ni, W, Wang, H & Liu, RP 2017, 'Decentralized relaying and performance analysis in vehicular ad hoc networks', IEEE Vehicular Technology Conference, Vehicular Technology Conference, IEEE, Toronto, ON, Canada, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
© 2017 IEEE. Vehicular Ad Hoc Networks (VANET) is an important network technology. Relay communication can effectively improve the connectivity and coverage of VANET, especially in distributed environments. Challenges arise from intense collision resulting from inherently synchronized relays. In this paper, we propose a decentralized relay scheme without collecting neighbor nodes' information. Particularly, we design a new score function to prioritize the relays based on their reception quality from source and channel conditions towards intended destination. A closed-form expression for packet delivery ratio (PDR) is derived based on time-out probabilities. Our analyses, validated by simulations, show that the proposed scheme, in terms of PDR, is much better than DAFMAC protocol.
Lin, S, Ni, W, Tian, H, Liu, R & Liu, B 2015, 'Game Theoretic Approach for Smallcell Resource Management', 2015 IEEE Globecom Workshops (GC Wkshps) Proceedings, IEEE Globecom Workshops (Gc Workshops), IEEE, San Diego, CA.View/Download from: UTS OPUS or Publisher's site
Smallcells can provide high-quality radio coverage in indoor environment. However, resource management and interference mitigation are key challenges, resulting from the heterogeneous backhaul and the uncoordinated nature of smallcells. We propose a new game theoretic approach, where the transmit power of smallcells evolve in a distributed manner, adapting to traffic demands and mitigating interference. The key idea is to formulate smallcells' clustering as an evolutionary game, where the smallcells independently switch to less interfered clusters. At every evolutionary stage, a non-cooperative game is cast to balance the transmit powers within each cluster. Limited signalling is exchanged between the clusters, adjusting future evolution. Compared to the prior art, simulations show that our approach can improve the network throughput by 10.2%.
Zha, X, Ni, W, Liu, R, Zheng, K & Niu, X 2015, 'Secure Data Transmission and Modelling in Vehicular Ad Hoc Networks', 2015 IEEE Globecom Workshops (GC Wkshps) Proceedings, IEEE Globecom Workshops (Gc Workshops), IEEE, San Diego, CA.View/Download from: UTS OPUS or Publisher's site
Data security is crucial to safety-related vehicular applications. Critical challenges of unstable topologies and the collisions of uncoordinated data transmissions arise, due to the mobile and distributed nature of vehicular ad-hoc networks (VANETs). We propose a new secure transmission protocol for VANETs, where the transmitter can adaptively switch between backing off transmissions to alleviate collisions, as well as changing keys, to increase success rate with matched keys. We also develop a new 3-dimensional (3-D) Markov model to characterize the protocol. Security analyses are carried out. Interesting insights and useful guidelines to adequately distribute keys among mobile vehicular nodes are also provided.
Ma, J, Ni, W, Yin, J, Lin, S, Cui, H, Liu, RP & Fang, BX 2015, 'Modelling social characteristics of mobile radio networks', 2015 IEEE International Conference on Communication Workshop, ICCW 2015, IEEE International Conference on Communication Workshop, IEEE, London, UK, pp. 1575-1580.View/Download from: UTS OPUS or Publisher's site
© 2015 IEEE. Mobile communications are increasingly contributing to the Internet traffic. Users move within cellular networks and generate traffics of different types. In this paper, we propose to categorize cellular base stations from multiple dimensions. Key social characteristics of the base stations are jointly considered, including traffic fluctuation, user non-determinacy, temporal homogeneity and usage diversity. Our categorization is based on spectral clustering, which is able to leverage the multiple social characteristics. The results of the categorization indicate different application environments and scenarios. We further establish social models with important parameters derived for each of the categories. The applications to energy efficient wireless networks are studied. The proposed model is of practical value to facilitate designing, simulating, and evaluating network deployment.
Shi, S, Ni, W, Liu, RP, Li, S & Tian, J 2014, 'A new hybrid ARQ protocol for two-way relay networks', International Symposium on Wireless Personal Multimedia Communications, WPMC, International Symposium on Wireless Personal Multimedia Communications, IEEE, Sydney, NSW, Australia, pp. 646-651.View/Download from: UTS OPUS or Publisher's site
© 2014 National Institute of Information and Communicatio. In order to improve the throughput, robustness and resource utilization of relay network, we develop a new high-efficiency and stable two-way relay system with double antenna relay node, which employs combining Maximum Likelihood(ML) detection and Network Coding during access and broadcast stage respectively. It is not sensitive to link asymmetry compare with physical network coding(PNC), and can improve throughput by 50% compare with traditional three time slot relay network. This paper also employs and develops a novel automatic repeat request(ARQ) strategy to retransmit the corrupt packet, by using combination at the receiver, the users can recover the corrupt packet with negligible retransmission overhead. Numerical analysis and simulation results demonstrate that our proposed system can get a remarkable throughput improvement.
Lin, S, Tian, H, Ni, W & Liu, R 2014, 'Broker based bipartite matching game for resource management in femtocell networks', International Symposium on Wireless Personal Multimedia Communications, WPMC, International Symposium on Wireless Personal Multimedia Communications, IEEE, Sydney, NSW, Australia, pp. 579-583.View/Download from: UTS OPUS or Publisher's site
© 2014 National Institute of Information and Communicatio. Femtocells have great potential to enhance home cellular access and improve macrocell network efficiency by offload local traffic. However, dense deployment imposes critical challenges to resource management (i.e., interference mitigation and sub-channels allocation).In this paper, to formulate this resource management of femtocell, we propose broker based many-to-many bipartite matching game and develop a new distributed solution to the game. The key idea of our solution is that we propose clustering strategy to decompose the many-to-many matching game into several parallel cluster-based many-to-one matching sub-games. Then, for each sub-problem, we develop a cluster based fairness guaranteed matching algorithm (CFGM), which is able to guarantee intra-cluster fairness. Simulation results show that CFGM outperforms its counterparts, which guaranteeing statistical fairness.
Lin, S, Ni, W, Tian, H & Liu, RP 2015, 'Evolutionary radio resource management in distributed femtocell networks', 2015 22nd International Conference on Telecommunications, ICT 2015, IEEE International Conference on Telecommunications, IEEE, Sydney, NSW, Australia, pp. 168-173.View/Download from: UTS OPUS or Publisher's site
© 2015 IEEE. Femtocells are an integrating part of future cellular systems, where radio resource management is a challenge due to unbalanced backhaul delays and the hotspot nature of femtocells. We propose a new game theoretic framework, where the channel allocation and transmit powers evolve in a distributed manner, adapting to femtocells' topology and traffic demands. The key idea is to cast femtocells' clustering as an evolutionary game, where the femtocells independently switch to less interfered clusters. Within each cluster, we design a non-cooperative game to implement power control in the absence of centralized coordination. Simulations show that our approach is effective for timely interference mitigation and reliable topology management. The stability and scalability of our approach are also demonstrated.
Saadat, A, Fang, G & Ni, W 2015, 'A two-tier evolutionary game theoretic approach to dynamic spectrum sharing through Licensed Shared Access', Proceedings - 15th IEEE International Conference on Computer and Information Technology, CIT 2015, 14th IEEE International Conference on Ubiquitous Computing and Communications, IUCC 2015, 13th IEEE International Conference on Dependable, Autonomic and Secure Computing, DASC 2015 and 13th IEEE International Conference on Pervasive Intelligence and Computing, PICom 2015, pp. 6-11.View/Download from: Publisher's site
© 2015 IEEE. In this paper, we propose a two-tier evolutionary game for dynamic spectrum sharing nsing Licensed Shared Access (LSA) to serve the additional capacity needs of Mobile Network Operators (MNOs). The proposed algorithm ensures fair and demand-driven allocation of spectrum resources to LSA licensees, guaranteeing spectrum availability for licensees unlike previous spectrum sharing techniques. Moreover, we extend the evolutionary game by modeling the dynamic price adjustment strategies adopted by incumbents achieving an improved total gain for the incumbents. We prove the stability of the proposed evolutionary algorithm using Lyapunov stability criteria. Additionally! we perform simulations to prove convergence and stability of the evolutionary algorithm, and highlight the effects of dynamic parameters offered by incumbents such as price on overall average licensee payoff.
He, T, Wang, X & Ni, W 2015, 'Utility maximization for chunk-based OFDMA systems with multiple BER requirements', 2014 International Workshop Technical Committee on Communications Quality and Reliability, CQR 2014.View/Download from: Publisher's site
© 2014 IEEE. In wireless orthogonal frequency division multipleaccess (OFDMA) standards, subcarriers are grouped into chunks and a chunk of subcarriers is made as the minimum unit for subcarrier allocation. We investigate the chunk-based resource allocation for OFDMA downlink, where data streams contain packets with diverse bit-error-rate (BER) requirements. Supposing that adaptive transmissions are based on a number of discrete modulation and coding modes, we propose the optimal resource allocation scheme that maximizes a utility function of average user rates. With proper formulation, the relevant optimization problem is cast as an mixed-integer program, and it is shown that the optimal strategy for this problem can be obtained through Lagrange dual-based gradient iterations with fast convergence and low computational complexity per iteration. Furthermore, a novel on-line algorithm is developed to approach the optimal strategy without knowledge of intended wireless channels a priori. Numerical results show that the proposed optimal chunk allocation schemes with different -fair utility functions can nicely trade off total network throughput for fairness among users.
Li, K, Ni, W, Wang, X, Liu, RP, Kanhere, SS & Jha, S 2015, 'EPLA: Energy-balancing packets scheduling for airborne relaying networks', IEEE International Conference on Communications, IEEE International Conference on Communications, IEEE, London, UK, pp. 6246-6251.View/Download from: UTS OPUS or Publisher's site
© 2015 IEEE. Airborne relaying is of potential to extend wireless sensor networks (WSN) to human-unfriendly terrains. Challenges arise due to lossy airborne channels and limited battery of unmanned aerial vehicles (UAVs). We propose an energy-efficient relaying scheme to overcome the challenges. A swarm of UAVs are deployed to listen to remote sensors from distributed locations, improving packet reception over lossy channels. UAVs report their reception qualities to the base station where the optimal schedule with guaranteed success rates and balanced energy consumption can be generated. Such scheduling is an NP-hard binary integer programming. We develop a suboptimal solution by decoupling the processes of energy balancing and data rate adjustment. Simulations confirm that, in terms of network yield, our method is indistinguishable to the NP-hard optimal solution, 15% higher than greedy algorithms. Our method can reduce the complexity by orders of magnitude, and extend network lifetime by 33%.
Biswas, J, Ni, W, Liu, RP, Collings, IB & Jha, SK 2014, 'Low complexity user pairing and resource allocation of heterogeneous users for uplink virtual MIMO system over LTE-A network', 2014 IEEE Wireless Communications and Networking Conference (WCNC), IEEE Wireless Communications and Networking Conference, IEEE, Istanbul, Turkey, pp. 1903-1908.View/Download from: UTS OPUS or Publisher's site
© 2014 IEEE. Virtual Multiple-Input Multiple-Output (MIMO) is a promising uplink technology that can meet the throughput demand of Long-Term Evolution-Advanced (LTE-A) systems. However, the complexity of scheduling virtual MIMO is a challenge; existing virtual MIMO is therefore limited to best effort applications. We investigate the resource allocation and scheduling problem in a heterogeneous virtual MIMO system where delay sensitive applications are present. The goal is to maximize the system throughput while maintaining delay bound for delay sensitive traffic. To tackle the complexity challenge, we propose two low-complexity suboptimal algorithms, where the key idea is to reduce the search space and iteratively minimize the rate loss respectively. Simulation results show that the rate loss minimization based heuristic algorithm converges to within 99% of the optimal throughput on average and maintains delay bound for delay sensitive users. It also achieves almost the same fairness performance as the optimal solution.
Wang, H, Liu, RP, Ni, W, Chen, W & Collings, IB 2014, 'A new analytical model for highway inter-vehicle communication systems', 2014 IEEE International Conference on Communications, ICC 2014, IEEE International Conference on Communications, IEEE, Sydney, NSW, Australia, pp. 2581-2586.View/Download from: UTS OPUS or Publisher's site
In Vehicular Ad Hoc Networks (VANETs), vehicles along highways can be grouped into clusters. The design of VANET clusters (i.e., size and geographical span) depends on the packet collision in MAC layer, the wireless channel conditions in PHY layer, and the mobility of the vehicles. Existing works investigated these effects separately. In this paper, we present a comprehensive analysis that combines these three important factors into one model. In particular, we model an unsaturated VANET cluster with a Markov chain by introducing an idle state. The wireless channel fading and vehicle mobility are integrated by explicitly deriving the joint distribution of inter-vehicle distances. Closed-form expressions of network performance measures, i.e., packet loss probability and system throughput, are derived. The proposed analytic model, validated by simulations, is able to accurately characterize VANET performance. Our model can be applied to the design of VANET clusters, and reveals a number of insights that provide guidelines for VANETs design and management. © 2014 IEEE.
Nan, Z, Wang, X & Ni, W 2014, 'Energy-efficient transmission of delay-limited bursty data packets under non-ideal circuit power consumption', 2014 IEEE International Conference on Communications, ICC 2014, pp. 4957-4962.View/Download from: Publisher's site
This paper develops a novel approach to energy-efficient transmission schedule for delay-limited bursty data arrivals under non-ideal circuit power consumption. Assuming aprior knowledge of packet arrivals and deadlines, an efficient algorithm is proposed to find the optimal policy that minimizes the total energy consumption, with a low computational complexity. It is revealed that the optimal data departure for the general nonideal circuit-power case can be obtained by simply adjusting the ideal-case data departure in accordance to an energy efficiency (EE) maximizing rate value. The proposed approach provides optimal benchmark for all the practical schemes, and can be employed to develop efficient online scheduling schemes which assume only causal knowledge of the data arrival and deadline realizations. © 2014 IEEE.
Zhang, JA, Ni, W, Matthews, J, Sung, C-K, Huang, X, Suzuki, H & Collings, I 2014, 'Low latency integrated point-to-multipoint and e-band point-to-point backhaul for mobile small cells', Communications Workshops (ICC), 2014 IEEE International Conference on, IEEE International Conference on Communications, IEEE, Sydney, NSW, Australia, pp. 592-597.View/Download from: UTS OPUS or Publisher's site
Wireless backhaul is one of the main challenges in small cell deployment. Current wireless backhaul systems have one or more limitations on capacity, link distance and supporting line-of-sight (LOS) links. In this paper, we propose a novel two-tier small-cell backhaul architecture which provides a future-proof, powerful, flexible and scalable solution by using aggregation nodes and integrating sub-6GHz point-to-multipoint (P2MP) and point-to-point E-band links. In the bottom tier of the proposed architecture, local small cells are connected to an aggregation node by P2MP and low-cost mega bits per second (Mbps) E-band links; in the top tier, aggregation nodes are inter-connected by LOS giga bits per second (Gbps) E-band links. PHY and higher layer protocols, which integrate the three different links into a comprehensive solution, are introduced. Designs of devices used in the architecture, which are being developed in CSIRO, are provided. Novel techniques that have been developed for achieving low-latency are detailed. Simulation results show that the backhaul latency can be as low as a few microseconds when only E-band backhaul links are involved.
Biswas, J, Liu, RP, Ni, W, Collings, IB & Jha, SK 2013, 'Joint channel and delay aware user scheduling for multiuser MIMO system over LTE-A network', IEEE International Workshop on Quality of Service, IWQoS, IEEE/ACM International Symposium on Quality of Service (IWQoS), IEEE, Montreal, QC, Canada, pp. 129-136.View/Download from: UTS OPUS or Publisher's site
Existing mobile video applications are continuously driving up the demand for throughput and better quality of service (QoS) for future Long Term Evolution-Advanced (LTE-A) networks. Multi-User Multiple-Input Multiple-Output (MU-MIMO) is one of the most promising technologies that would meet the throughput demand. Unfortunately, existing MU-MIMO schemes do not consider metrics such as delay, and therefore, cannot meet the QoS requirement of delay sensitive applications, such as mobile video. We propose a new cross-layer MU-MIMO scheduling algorithm, which is referred to as joint channel and delay aware user scheduling (CDAUS), satisfies both the throughput and delay requirements. The key idea of the CDAUS algorithm is to select users to form MU-MIMO based on the delay requirements of individual users, as well as their channel correlations. The priority of the users is carefully designed to leverage their delay and throughput. Simulation results show that the proposed CDAUS algorithm is able to reduce the average delay by up to 30% with a marginal 2% sacrifice of throughput, compared to previous work. It also reduces delay variations and improves fairness among the users. © 2013 IEEE.
He, T, Wang, X & Ni, W 2013, 'Optimal chunk-based resource allocation for OFDMA systems with multiple BER requirements', ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, pp. 4774-4778.View/Download from: Publisher's site
We investigate the chunk-based resource allocation for OFDMA downlink, where data streams contain packets with diverse bit-error-rate (BER) requirements. Supposing adaptive transmissions based on a number of discrete modulation and coding modes, we derive the optimal scheme that maximizes the weighted sum of average user rates under the multiple BER and total power constraints. With the relevant optimization problem cast as an integer linear program, we show that the optimal strategy can be obtained through Lagrange dual-based gradient iterations with fast convergence and low computational complexity per iteration. Furthermore, a novel on-line algorithm is developed to approach the optimal strategy without knowledge of intended wireless channels a priori. © 2013 IEEE.
Ni, W & Collings, IB 2012, 'A new adaptive frequency allocation algorithm in multi-hop point-to-point FDD backhaul networks for metro cells', 2012 International Symposium on Communications and Information Technologies, ISCIT 2012, pp. 187-192.View/Download from: Publisher's site
Wireless point-to-point (PTP) FDD backhaul networks have great potential to be applied to metro cells. Unfortunately, their current spectrum utilization is very low because of static frequency allocation. We propose a new adaptive allocation algorithm, which dramatically improves the spectrum utilization and enables the networks to be practically applied to metro cells. Our algorithm adapts to dramatically changing metro-cell traffic, and eliminates co-channel interference and adjacent frequency interference between backhaul links. On a particular practical case study, simulations show that the new adaptive algorithm is able to enhance the network satisfaction regarding allocated bandwidths by over 161%, compared to the state of the art. It also improves the spectrum utilization by 33%. © 2012 IEEE.
Ni, W & Collings, IB 2012, 'A New Base Station Control Switch for Metro Cells', 2012 IEEE 23RD INTERNATIONAL SYMPOSIUM ON PERSONAL INDOOR AND MOBILE RADIO COMMUNICATIONS (PIMRC), IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), IEEE, Sydney, AUSTRALIA, pp. 1174-1178.
Egan, M, Collings, IB, Ni, W & Sung, CK 2011, 'User scheduling for the broadcast channel using a sum-rate threshold', IEEE International Conference on Communications.View/Download from: Publisher's site
In this paper, we present a novel user selection scheme for the broadcast channel (BC) using zero-forcing (ZF) precoding with optimal power control. Our scheme is based on a threshold that sets a minimum acceptable sum-rate. In order to design the threshold, we develop a new approximation of the sum-rate and derive simple design rules for the threshold with complexity constraints. We also extend the scheme so that users with differing quality of service (QoS) demands can be accommodated. Simulations show our scheme performs close to the exhaustive search algorithm, but with significantly reduced complexity. Moreover, it significantly reduces the outages compared to non-threshold based low complexity scheduling schemes. © 2011 IEEE.
Wireless decode-and-forward (DF) relay networks suffer from severe latency due to multi-hop propagation. When hybrid ARQ (HARQ) is employed, the latency leads to the throughout degradation of individual HARQ processes because of the decreased number of retransmissions of unsuccessful packets in a given time. We propose two new distributed cooperative HARQ protocols to not only reduce latency but also optimize throughput in both forward and reverse DF links. Additional selection diversity from multiple packets is exploited to compensate for the throughput loss stemming from the less powerful source in the reverse DF link. Based on the 1st hop reception quality, each relay station (RS) independently forwards the packet in such a manner that, from the perspective of the destination, one of the three cooperative relaying modes is effectively formed with the highest instantaneous throughput: spatial multiplexing (SM), space-time transmit diversity (STTD) and unicast (UC). The maximal throughput can be achieved with minimal latency. The superiority of the proposed approaches has been demonstrated in terms of the optimal spectral efficiency and significant reduction in latency. Compared to the centralized approaches, the reduction is up to 40% at high signal-to-noise ratio (SNR) and the throughput of individual HARQ processes increases as a result. © 2010 IEEE.
Ni, W, Chen, Z, Collings, IB & Suzuki, H 2010, 'Sum-rate scheduling of decode-and-forward broadcast channel with limited-feedback', IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, pp. 2460-2465.View/Download from: Publisher's site
In wireless dual-hop decode-and-forward (DF) relaying networks, multiple relay stations (RS) and users construct a multiple-in-multiple-out (MIMO) broadcast channel (BC). Due to unpredictable decoding failure, scheduling the transmission for the decode-and-forward broadcast channel (DFBC) should depend on not only channel qualities but also the availability of errorless data at individual RSs. Based on the reception qualities of RSs and channel quality information (CQI), we propose a new centralized scheduling scheme to maximize the sum rate of the DFBC. An exact closed-form expression for the sum rate is derived to analyze the new scheme. Simulations demonstrate that the derived closed-form expression is able to quantify the proposed scheduling method accurately. It is also revealed that extra cooperative diversity can be exploited by employing the increased number of RSs, thereby improving sum rate. ©201 0 IEEE.
Ni, W, Chen, Z & Collings, IB 2010, 'Hybrid ARQ Based Cooperative Relaying in Wireless Dual-Hop Networks', 2010 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, 2010 IEEE International Conference on Communications, IEEE, Cape Town, SOUTH AFRICA.
Ni, W, Chen, Z, Suzuki, H & Collings, IB 2010, 'Performance Analysis of Scheduling in Decode-and-Forward Broadcast Channel with Limited-Feedback', 2010 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE GLOBECOM 2010, IEEE Global Telecommunications Conference (GLOBECOM 2010), IEEE, Miami, FL.
Ni, W, Wang, H & Li, Z 2009, 'Centralized proportional fair (PF) scheduling with concurrent transmission enabled in wireless multi-hop OFDMA networks', IEEE Wireless Communications and Networking Conference, WCNC.View/Download from: Publisher's site
The paper proposes the scheduling method to not only implement the proportional fairness between terminal users but also improve spectral efficiency by enabling concurrent transmission (CT) in wireless multi-hop OFDMA networks. The overhead reduction of channel quality information (CQI) is presented in coupling with the proposed scheduling and hereafter its performance with the reduced CQI is discussed. Simulation results illustrate the proposed scheme outperforms the prior art on both spectral efficiency and fairness. © 2009 IEEE.
By constructing the cliques of the compatibility graph, the heuristic spectrum sharing (SS) method is proposed to enable opportunistic frequency reuse between two networks possessing the adjacent bands in the centralized manner. With the method, the minimal satisfaction of cells is maximized and the spectral utilization is improved. However, the method suffers the prohibitive complexity, especially if the number of cells is large. To cope with the complexity, the suboptimal SS method has been developed with the same principle. Simulations reveal that the suboptimal SS method can provide similar performance in terms of spectral utilization and minimal satisfaction to the heuristic solution.
Ni, W, Zou, W & Wang, H 2008, 'Modeling of spatially cross-correlated shadow fading in distributed radio access networks', IEEE International Conference on Communications, pp. 4472-4476.View/Download from: Publisher's site
Spatial cross-correlation is an important feature in distributed radio access networks (D-RAN) and has strong impacts on their performance. In this paper, a two-step method of modeling the spatially correlated shadowing is proposed. At the first step, the coefficients of the shadow-fading (SF) expression are calculated by exploiting the statistical characteristics of spatial cross-correlation, and then at the second step, the value of individual shadow fading is worked out with the coefficients. Simulations demonstrates that the novel model of spatially correlated shadow fading is reasonable and of great importance to verify signal processing techniques in D-RAN. ©2008 IEEE.