Portrait of Professor Jiangzhou Wang

Professor Jiangzhou Wang

Professor of Telecommunications

About

Professor Jiangzhou Wang (王江舟教授) is a professor and the former Head of the School of Engineering and Digital Arts at the University of Kent. He has published over 300 papers in international journals and conferences in the area of wireless mobile communications. He has written/edited three books. His awards and honours include: 

  • Fellow of Royal Academy of Engineering (英国皇家工程院院士)
  • Fellow of IEEE
  • Fellow of IET
  • IEEE Distinguished Lecturer (2013 - 2014)
  • Recipient of the Best Paper Award at IEEE Globecom2012, California
  • Conference organizing chair, including Executive Chair of IEEE ICC2015, London, and Technical Program Chair of IEEE ICC2019, Shanghai
  • Editor or guest editor for a number of international journals, including IEEE Transactions on Communications (1998 - 2013)

Research interests

Professor Wang's research interests are in the area of wireless mobile communications, including

  • Massive MIMO and beamforming technologies
  • Cloud radio access networks (C-RAN) and distributed antenna systems (DAS)
  • Multiple access techniques, including NOMA and OFDMA
  • Device to device communications (D2D)
  • Vehicular communications (V2X)
  • Emergency communications
  • Machine learning for mobile communications
  • Drone communications   

Teaching

  • EL677 Digital Communications
  • EL827 Advanced Communications Theory
  • EL872 Wireless Mobile Communications

Publications

Article

  • Daghal, A., Zhu, H. and Wang, J. (2018). Content Delivery Analysis in Multiple Devices to Single Device Communications. IEEE Transactions on Vehicular Technology [Online]. Available at: https://doi.org/10.1109/TVT.2018.2865012.
    Content caching at mobile user devices (UDs) utilizing device to device (D2D) communications is a promising technology to enhance the performance of mobile networks, in terms of latency, throughput, energy consumption, and so on. In this paper, a novel method of content delivery using multiple devices to single device (MDSD) communications through D2D links is presented. In this method, the Zipf distribution with exponent shape parameter is adopted to model the content caching popularity for the analysis of the achievable signal to interference plus noise ratio (SINR). In order to investigate the advantage of the proposed MDSD method, firstly, a closedform expression of the outage probability is theoretically derived for a single D2D communication to evaluate the success of content delivery to a reference UD. Secondly, the expression of the outage probability for MDSD communication is derived, where the outage probability is modeled as a function of content caching popularity, the density of UDs, and the size of cooperative area. The research work is further extended to address the frequency reuse among different UDs in one cell, where a frequency band factor is introduced, and the optimal radius of the cooperative area is introduced and analysed. The analytical results, validated by the simulation results, show that the outage probability decreases drastically when the popularity of the content increases, or the radius of the cooperative area increases. Using the given closed-form expression of the outage probability, the area spectral efficiency (ASE) of the system is presented. Furthermore, the results show that as the frequency band factor increases, the outage probability decreases, as well as the ASE decreases. Finally, it is shown that the MDSD outperforms the single D2D-based method.
  • Liu, J. et al. (2018). Achievable rates for full-duplex massive MIMO systems with low-resolution ADCs/DACs under imperfect CSI environment. EURASIP Journal on Wireless Communications and Networking [Online] 2018:1-12. Available at: https://doi.org/10.1186/s13638-018-1242-y.
    We investigate the uplink and downlink achievable rates of full-duplex (FD) massive multi-input multi-output (MIMO)
    systems with low-resolution analog-digital converters/digital-to-analog converters (ADCs/DACs), where maximum
    ratio combining/maximum ratio transmission (MRC/MRT) processing are adopted and imperfect channel state
    information (CSI) is assumed. In this paper, the quantization noise is encapsulated as an additive quantization noise
    model (AQNM). Then, employing the minimum mean-square error (MMSE) channel estimator, approximate
    expressions of the uplink and downlink achievable rates are derived, based on the analysis of the quantization error,
    loop interference (LI), and the inter-user interference (IUI). It is shown that the interference and noise can be
    eliminated by applying power scaling law properly and increasing the number of antennas. Moreover, given the
    number of antennas, it is found that the uplink and downlink approximate achievable rates will converge to a
    constant when the number of quantization bit tends to infinity. Therefore, the system performance that can be
    improved by increasing ADC/DAC resolution is limited, implying that it is reasonable to adopt low-resolution
    ADCs/DACs in FD massive MIMO systems.
  • Albasry, H., Zhu, H. and Wang, J. (2018). In-band Emission Interference in D2D-enabled Cellular Networks: Modelling, Analysis, and Mitigation. IEEE Transactions on Wireless Communications [Online]. Available at: https://doi.org/10.1109/TWC.2018.2866833​.
    Next generation network is considered as a device to device (D2D)-enabled system. The overlay in-band scheme can be used by the cellular user equipments (CUEs) and D2D user equipments (DUEs) to send data. The cellular and D2D links experience the in-band emission interference (IEI) from the DUEs that use the adjacent frequencies. This paper models the IEI impact by using the stochastic geometry and analytically investigates this impact on cellular and D2D links. The IEI intercell and IEI intra-cell are separately assessed, and the expected D2D resource block (DRB) reuse factor is evaluated. Further, distance-density based (DDB) strategy is proposed to mitigate the IEI by controlling the number and location of served DUEs for each DRB. Also, optimal power allocation (OPA) algorithm is proposed by calculating the optimal DUEs transmission power profile that mitigates IEI and maximizes the DUEs sum rate. The performance is improved significantly for the proposed methods. The application scenario is identified for each mitigation method.
  • Wan, S. et al. (2018). Power Allocation Strategy of Maximizing Secrecy Rate for Secure Directional Modulation Networks. IEEE Access [Online]. Available at: https://doi.org/10.1109/ACCESS.2018.2815779.
    In this paper, given the beamforming vector of confidential messages and artificial noise (AN) projection matrix and total power constraint, a power allocation (PA) strategy of maximizing secrecy rate (Max-SR) is proposed for secure directional modulation (DM) networks. By the method of Lagrange multiplier, the analytic expression of the proposed PA strategy is derived. To confirm the benefit from the Max-SRbased PA strategy, we take the null-space projection (NSP) beamforming scheme as an example and derive its closed-form expression of optimal PA strategy. From simulation results, we find the following facts: in the medium and high signal-to-noiseratio (SNR) regions, compared with three typical PA parameters such β = 0:1, 0:5, and 0:9, the optimal PA shows a substantial SR performance gain with maximum gain percent up to more than 60%. Additionally, as the PA factor increases from 0 to 1, the achievable SR increases accordingly in the low SNR region whereas it first increases and then decreases in the medium and high SNR regions, where the SR can be approximately viewed as a convex function of the PA factor. Finally, as the number of antennas increases, the optimal PA factor becomes large and tends to one in the medium and high SNR region. In other words, the contribution of AN to SR can be trivial in such a situation.
  • Wang, J. et al. (2018). A Machine Learning Framework for Resource Allocation Assisted by Cloud Computing. IEEE Network [Online] 32:144-151. Available at: https://doi.org/10.1109/MNET.2018.1700293.
    Conventionally, the resource allocation is formulated as an optimization problem and solved online with
    instantaneous scenario information. Since most resource allocation problems are not convex, the optimal solutions
    are very difficult to be obtained in real time. Lagrangian relaxation or greedy methods are then often employed,
    which results in performance loss. Therefore, the conventional methods of resource allocation are facing great
    challenges to meet the ever-increasing QoS requirements of users with scarce radio resource. Assisted by cloud
    computing, a huge amount of historical data on scenarios can be collected for extracting similarities among scenarios
    using machine learning. Moreover, optimal or near-optimal solutions of historical scenarios can be searched offline
    and stored in advance. When the measured data of current scenario arrives, the current scenario is compared with
    historical scenarios to find the most similar one. Then, the optimal or near-optimal solution in the most similar
    historical scenario is adopted to allocate the radio resources for the current scenario. To facilitate the application
    of new design philosophy, a machine learning framework is proposed for resource allocation assisted by cloud
    computing. An example of beam allocation in multi-user massive multiple-input-multiple-output (MIMO) systems
    shows that the proposed machine-learning based resource allocation outperforms conventional methods.
  • Wang, J. et al. (2018). Frequency Reuse of Beam Allocation for Multiuser Massive MIMO Systems. IEEE Transactions on Wireless Communications [Online]. Available at: https://doi.org/10.1109/TWC.2018.2793227.
    Abstract—Massive multiple-input-multiple-output (MIMO)
    has become a promising technique to provide high-data-rate
    communication in fifth-generation (5G) mobile systems, thanks to
    its ability to form narrow and high-gain beams. Among various
    massive MIMO beamforming techniques, the fixed-beam scheme
    has attracted considerable attention due to its simplicity. In this
    paper, we focus on a fixed-beam based multiuser massive MIMO
    system where each user is served by a beam allocated to it. To
    maximize the sum data rate, a greedy beam allocation algorithm
    is proposed under the practical condition that the number of
    radio frequency (RF) chains is smaller than the number of users.
    Simulation results show that our proposed greedy algorithm
    achieves nearly optimal sum data rate. As only the sum data rate
    is optimized, there are some “worst-case” users who could suffer
    from strong inter-beam interference and thus experience low
    data rate. To improve the individual data rates of the worst-case
    users while maintaining the sum data rate, an adaptive frequency
    reuse scheme is proposed. Simulation results corroborate that our
    proposed adaptive frequency reuse strategy can greatly improve
    the worst-case users’ data rates and the max-min fairness among
    served users without sacrificing the sum data rate.
  • Yu, H. et al. (2018). GPI-Based Secrecy Rate Maximization Beamforming Scheme for Wireless Transmission With AN-Aided Directional Modulation. IEEE Access [Online] 6:12044-12051. Available at: https://doi.org/10.1109/ACCESS.2018.2812180.
    In a directional modulation network, a general power iterative (GPI) based beamforming
    scheme is proposed to maximize the secrecy rate (SR), where there are two optimization variables required to
    be optimized. The �rst one is the useful precoding vector of transmitting con�dential messages to the desired
    user while the second one is the arti�cial noise (AN) projection matrix of forcing more AN to eavesdroppers.
    In such a secure network, the paramount problem is how to design or optimize the two optimization variables
    by different criteria. To maximize the SR (Max-SR), an alternatively iterative structure (AIS) is established
    between the AN projection matrix and the precoding vector for con�dential messages. To choose a good
    initial value of iteration process of GPI, the proposed Max-SR method can readily double its convergence
    speed compared to the random choice of initial value. With only four iterations, it may rapidly converge to
    its rate ceil. From simulation results, it follows that the SR performance of the proposed AIS of GPI-based
    Max-SR is much better than those of conventional leakage-based and null-space projection methods in the
    medium and large signal-to-noise ratio (SNR) regions, and its achievable SR performance gain gradually
    increases as SNR increases.
  • Hu, J. et al. (2018). Covert Communication Achieved by A Greedy Relay in Wireless Networks. IEEE Transactions on Wireless Communications [Online]. Available at: https://doi.org/10.1109/TWC.2018.2831217.
    Covert wireless communication aims to hide the very
    existence of wireless transmissions in order to guarantee a strong
    security in wireless networks. In this work, we examine the
    possibility and achievable performance of covert communication
    in amplify-and-forward one-way relay networks. Specifically, the
    relay is greedy and opportunistically transmits its own information
    to the destination covertly on top of forwarding the source’s
    message, while the source tries to detect this covert transmission
    to discover the illegitimate usage of the resource (e.g., power,
    spectrum) allocated only for the purpose of forwarding the
    source’s information. We propose two strategies for the relay to
    transmit its covert information, namely rate-control and powercontrol
    the transmission schemes, for which the source’s detection
    limits are analysed in terms of detection error probability and the
    achievable effective covert rates from the relay to destination are
    derived. Our examination determines the conditions under which
    the rate-control transmission scheme outperforms the powercontrol
    transmission scheme, and vice versa, which enables the
    relay to achieve the maximum effective covert rate. Our analysis
    indicates that the relay has to forward the source’s message
    to shield its covert transmission and the effective covert rate
    increases with its forwarding ability (e.g., its maximum transmit
    power).
  • Pan, C. et al. (2018). User-centric C-RAN Architecture for Ultra-dense 5G Networks: Challenges and Methodologies. IEEE Communications Magazine [Online] 56:14-20. Available at: http://dx.doi.org/10.1109/MCOM.2018.1700483.
    Ultra-dense networks (UDN) constitute one of the most promising techniques of supporting the fifth generation (5G) mobile system. By deploying more small cells in a fixed area, the average distance between users and access points can be significantly reduced, hence a dense spatial frequency reuse can be exploited. However, severe interference is the major obstacle in UDNs. Most of the contributions investigate the interference by designing distributed algorithms based on cooperative game theory. This paper advocates the application of dense user-centric cloud radio access network (CRAN) philosophy to UDNs, thanks to the recent development of cloud computing techniques. Under dense C-RAN architectures, centralized signal processing can be invoked for supporting Coordinated Multiple Points Transmission/Reception (CoMP). We summarize the main challenges in dense usercentric C-RANs. One of the most challenging issues is the requirement of the global CSI for the sake of cooperative transmission. We investigate this requirement by only relying on partial channel state information (CSI), namely, on inter-cluster large-scale CSI. Furthermore, the estimation of the intracluster CSI is considered, including the pilot allocation and robust transmission. Finally, we highlight several promising research directions to make the dense user-centric C-RAN become a reality, with special emphasis on the application of the ‘big data’ techniques.
  • Ye, Z. et al. (2018). Tradeoff Caching Strategy of Outage Probability and Fronthaul Usage in Cloud-RAN. IEEE Transactions on Vehicular Technology [Online] 67. Available at: http://dx.doi.org/10.1109/TVT.2018.2797957.
    In this paper, tradeoff content caching strategy is proposed to jointly minimize the cell average outage probability and fronthaul usage in cloud radio access network (Cloud-RAN). At first, an accurate closed form expression of the outage probability conditioned on the user’s location is presented, and the cell average outage probability is obtained through the composite Simpson’s integration. The caching strategy for jointly optimizing the cell average outage probability and fronthaul usage is then formulated as a weighted sum minimization problem, which is a nonlinear 0-1 integer problem. Two heuristic algorithms are proposed to solve the problem. Firstly, a genetic algorithm (GA) based approach is proposed. Numerical results show that the performance of the proposed GA-based approach with significantly reduced computational complexity is close to the optimal performance achieved by exhaustive search based caching strategy, and the GA-based approach can improve the performance by up to 47.5% on average than the typical probabilistic caching strategy. Secondly, in order to further reduce the computational complexity, a mode selection approach is proposed. Numerical results show that this approach can achieve near-optimal performance over a wide range of the weighting factors through a single computation.
  • Li, J. et al. (2017). Downlink Spectral Efficiency of Distributed Massive MIMO Systems with Linear Beamforming under Pilot Contamination. IEEE Transactions on Vehicular Technology [Online] 67:1130-1145. Available at: https://doi.org/10.1109/TVT.2017.2733532.
    In this paper, the downlink spectral efficiency of multi-cell multi-user distributed massive MIMO systems with linear beamforming is studied in the presence of pilot contamination. According to the levels of effective channel gain information at user side, we provide the lower bound and upper bound on user ergodic achievable downlink rate. Due to the different access distance from each user to different remote antenna units, the entries of user channel vectors are no longer identically distributed in distributed massive MIMO systems, which makes the spectral efficiency analysis challenging. Using the properties of Gamma distributions together with the approximate methods for non-isotropic vectors, we derive tractable but accurate closed-form expressions for the rate bounds with maximum ratio transmission (MRT) and zero-forcing (ZF) beamforming in distributed massive MIMO systems. Based on these expressions, user ultimate achievable rates are also given when the ratio of the total number of transmit antennas to the number of users goes to infinity. It is shown that MRT and ZF beamforming achieve the same ultimate rate no matter what levels of effective channel gain information at user side. Numerical results show that ZF achieves better performance gain and faster convergence speed than MRT. When the coherence interval is large, the downlink beamforming training scheme is more preferable for the distributed massive MIMO systems.
  • Hu, J. et al. (2017). Artificial-Noise-Aided Secure Transmission with Directional Modulation based on Random Frequency Diverse Arrays. IEEE Access [Online]. Available at: http://dx.doi.org/10.1109/ACCESS.2017.2653182.
    In this paper, a random frequency diverse array based directional modulation with artificial noise (RFDA-DMAN)
    scheme is proposed to enhance physical layer security of wireless communications. Specifically, we first design the RFDADM-
    AN scheme by randomly allocating frequencies to transmitantennas, thereby achieving two-dimensionally (i.e., angle and
    range) secure transmissions, and outperforming the state-of-theart one-dimensional (i.e., angle) phase array (PA) based DM
    scheme. Then we derive the closed-form expression of a lower bound on the ergodic secrecy capacity (ESC) of our RFDA-DMAN scheme. Based on the theoretical lower bound derived, we further optimize the transmission power allocation between the useful signal and artificial noise (AN) in order to improve the ESC. Simulation results show that 1) our RFDA-DM-AN scheme achieves a higher secrecy capacity than that of the PA based DM scheme, 2) the lower bound derived is shown to approach the ESC as the number of transmit antennas N increases and precisely matches the ESC when N is sufficiently large, and 3) the proposed optimum power allocation achieves the highest ESC of all power allocations schemes in the RFDA-DM-AN.
  • Huseyin, H., Zhu, H. and Wang, J. (2017). Performance of Non-orthogonal Multiple Access (NOMA) with a Novel Asynchronous Interference Cancellation Technique. IEEE Transactions on Communications [Online]. Available at: https://doi.org/10.1109/TCOMM.2016.2640307.
    The non-orthogonal multiple access (NOMA) allows one subcarrier to be allocated to more than one user at the same time in an orthogonal frequency division multiplexing (OFDM) system. NOMA is a promising technique to provide high throughput due to frequency reuse within a cell. In this paper, a novel interference cancellation (IC) technique is proposed for asynchronous NOMA systems. The proposed IC technique exploits a triangular pattern to perform the IC from all interfering users for the desired user. The bit error rate (BER) and capacity performance analysis of an uplink NOMA system with the proposed IC technique is presented, along with the comparison to orthogonal frequency division multiple access (OFDMA) systems. The numerical and simulation results show that the NOMA with the proposed asynchronous IC technique outperforms the OFDMA. It is also shown that employing iterative IC provides significant performance gain for NOMA and the number of required iterations depends on the modulation level and the detection method.With hard-decision, two iterations are sufficient, however with soft-decision, two iterations are enough only for low modulation level, and more iterations are desirable for high modulation level.
  • Pan, Y. et al. (2017). On Consideration of Content Preference and Sharing Willingness in D2D Assisted Offloading. IEEE Journal on Selected Areas in Communications [Online] 35:978-993. Available at: http://dx.doi.org/10.1109/JSAC.2017.2680938.
    Device-to-device (D2D) assisted offloading heavily depends on the participation of human users. The content preference and sharing willingness of human users are two crucial factors in the D2D assisted offloading. In this paper, with consideration of these two factors, the optimal content pushing strategy is investigated by formulating an optimization problem to maximize the offloading gain measured by the offloaded traffic. Users are placed into groups according to their content preferences, and share content with intergroup and intragroup users at different sharing probabilities. Although the optimization problem is nonconvex, the closed-form optimal solution for a special case is obtained, when the sharing probabilities for intergroup and intragroup users are the same. Furthermore, an alternative group optimization (AGO) algorithm is proposed to solve the general case of the optimization problem. Finally, simulation results are provided to demonstrate the offloading performance achieved by the optimal pushing strategy for the special case and AGO algorithm. An interesting conclusion drawn is that the group with the largest number of interested users is not necessarily given the highest pushing probability. It is more important to give high pushing probability to users with high sharing willingness.
  • Wu, L. et al. (2017). Channel Estimation for Multicell Multiuser Massive MIMO Uplink Over Rician Fading Channels. IEEE Transactions on Vehicular Technology [Online]:1-1. Available at: http://dx.doi.org/10.1109/TVT.2017.2698833.
    Pilot contamination (PC) is a major problem in massive multiple-input multiple-output (MIMO) systems. This paper proposes a novel channel estimation scheme for such a system in Rician fading channels. First, the possible angle of arrivals (AOAs) of users served by a base station (BS) are derived by exploiting the channel statistical information, assuming a traditional pilot structure, where the pilots for the same-cell users are orthogonal but are identical for the same-indexed users from different cells. Although with this pilot structure the channel state information (CSI) derived contains CSI from other-cell users caused by PC, the line-of-sight (LOS) component of the desired user is PC-free when the number of antennas equipped at the BS is large. Then, based on the AOAs and the contaminated CSI, the LOS component of each user served by a BS is estimated, and data are detected by using the derived LOS components. Finally, the decoded data are used to update the CSI estimate via an iterative process. The achievable spectral efficiency of the proposed scheme is analyzed in detail, and simulation results are presented to compare the performance of the proposed scheme with that of three existing schemes.
  • Pan, C. et al. (2017). Joint Precoding and RRH selection for User-centric Green MIMO C-RAN. IEEE Transactions on Wireless Communications [Online] 16:2891-2906. Available at: http://ieeexplore.ieee.org/document/7880689/.
    This paper jointly optimizes the precoding matrices and the set of active remote radio heads (RRHs) to minimize the network power consumption (NPC) for a user-centric cloud radio access network (C-RAN), where both the RRHs and users have multiple antennas and each user is served by its nearby RRHs. Both users’ rate requirements and per-RRH power constraints are considered. Due to these conflicting constraints, this optimization problem may be infeasible. In this paper, we propose to solve this problem in two stages. In Stage I, a low-complexity user selection algorithm is proposed to find the largest subset of feasible users. In Stage II, a low-complexity algorithm is proposed to solve the optimization problem with the users selected from Stage I. Specifically, the re-weighted l1-norm minimization method is used to transform the original problem with non-smooth objective function into a series of weighted power minimization (WPM) problems, each of which can be solved by the weighted minimum mean square error (WMMSE) method. The solution obtained by the WMMSE method is proved to satisfy the Karush-Kuhn-Tucker (KKT) conditions of the WPM problem. Moreover, a low-complexity algorithm based on Newton’s method and the gradient descent method is developed to update the precoder matrices in each iteration of the WMMSE method. Simulation results demonstrate the rapid convergence of the proposed algorithms and the benefits of equipping multiple antennas at the user side. Moreover, the proposed algorithm is shown to achieve near-optimal performance in terms of NPC.
  • Pan, C. et al. (2017). Joint User Selection and Energy Minimization for Ultra-Dense Multi-channel C-RAN with Incomplete CSI. IEEE Journal on Selected Areas in Communications [Online] 35:1809-1824. Available at: http://dx.doi.org/10.1109/JSAC.2017.2710858.
    This paper provides a unified framework to deal with the challenges arising in dense cloud radio access networks (C-RAN), which include huge power consumption, limited fronthaul capacity, heavy computational complexity, unavailability of full channel state information (CSI), etc. Specifically, we aim to jointly optimize the remote radio head (RRH) selection, user equipment (UE)-RRH associations and beam-vectors to minimize the total network power consumption (NPC) for dense multi-channel downlink C-RAN with incomplete CSI subject to per-RRH power constraints, each UE’s total rate requirement, and fronthaul link capacity constraints. This optimization problem is NP-hard. In addition, due to the incomplete CSI, the exact expression of UEs’ rate expression is intractable. We first conservatively replace UEs’ rate expression with its lower-bound. Then, based on the successive convex approximation (SCA) technique and the relationship between the data rate and the mean square error (MSE), we propose a single-layer iterative algorithm to solve the NPC minimization problem with convergence guarantee. In each iteration of the algorithm, the Lagrange dual decomposition method is used to derive the structure of the optimal beam-vectors, which facilitates the parallel computations at the Baseband unit (BBU) pool. Furthermore, a bisection UE selection algorithm is proposed to guarantee the feasibility of the problem. Simulation results show the benefits of the proposed algorithms and the fact that a limited amount of CSI is sufficient to achieve performance close to that obtained when perfect CSI is possessed.
  • Wu, L. et al. (2016). Polarity Information Coded Flip-OFDM for Intensity Modulated Systems. IEEE Communications Letters [Online]:1-1. Available at: http://doi.org/10.1109/LCOMM.2016.2579625.
    A polarity-information-coded flip orthogonal frequency division multiplexing (PIC-flip-OFDM) is proposed for intensity modulation/direct detection (IM/DD) optical communications in this letter. In the proposed scheme, the modulated signals in the frequency domain are not constrained to have Hermitian symmetry. The real and imaginary parts of the timedomain complex signals are separated, and the polarities of the real and imaginary parts are jointly encoded and modulated. The transmit strategy and the receive algorithm of the proposed scheme are analyzed in detail. The major advantage of the proposed scheme is that its spectral and optical power efficiencies are higher than existing schemes, which is validated in simulation.
  • Wang, D. et al. (2016). An overview of transmission theory and techniques of large-scale antenna systems for 5G wireless communications. Science China Information Sciences [Online]. Available at: http://doi.org/10.1007/s11432-016-0278-5.
    To meet the future demand for huge traffic volume of wireless data service, the research on the fifth generation (5G) mobile communication systems has been undertaken in recent years. It is expected that the spectral and energy efficiencies in 5G mobile communication systems should be ten-fold higher than the ones in the fourth generation (4G) mobile communication systems. Therefore, it is important to further exploit the potential of spatial multiplexing of multiple antennas. In the last twenty years, multiple-input multiple-output (MIMO) antenna techniques have been considered as the key techniques to increase the capacity of wireless communication systems. When a large-scale antenna array (which is also called massive MIMO) is equipped in a base-station, or a large number of distributed antennas (which is also called large-scale distributed MIMO) are deployed, the spectral and energy efficiencies can be further improved by using spatial domain multiple access. This paper provides an overview of massive MIMO and large-scale distributed MIMO systems, including spectral efficiency analysis, channel state information (CSI) acquisition, wireless transmission technology, and resource allocation.
  • Pan, C. et al. (2016). Pricing-Based Distributed energy-efficient beamforming for MISO interference channels. IEEE Journal on Selected Areas in Communications [Online]. Available at: http://dx.doi.org/10.1109/JSAC.2016.2544602.
    In this paper, we consider the problem of maximizing the weighted sum energy efficiency (WSEE)
    for multi-input single-output (MISO) interference channels (ICs). Various 5G networks, such as the
    heterogeneous networks (HetNets), multicell networks, can be modeled as ICs. To solve this problem, we
    develop a low-complexity distributed beamforming algorithm based on pricing mechanism. Specifically,
    each user updates its price information and broadcasts it to all the other users. Having collected
    all these prices, each user solves its beam-vector problem with low-complexity. We then provide
    the sequential updating of the algorithm along with the proof for its convergence. We also provide
    an implementation method of the proposed distributed algorithm with limited information exchange.
    An alternative centralized algorithm based on the gradient projection method is also developed to
    serve as a performance benchmark for the proposed distributed algorithm. Numerical results show
    that our algorithm converges much faster than the existing algorithms, but yields similar performance
    or better performance. Also, in some special scenarios, the proposed algorithm with limited information
    exchange is even better than the full information exchange algorithm due to its reduced backhaul power
    consumption.
  • Zhang, Y. et al. (2016). Channel Estimation for Massive MIMO-OFDM Systems by Tracking the Joint Angle-Delay Subspace. IEEE Access [Online]. Available at: http://dx.doi.org/10.1109/ACCESS.2016.2634025.
    In this paper, we propose joint angle-delay subspace based channel estimation in single cell for broadband massive multiple-input and multiple-output (MIMO) systems employing orthogonal frequency division multiplexing (OFDM) modulation. Based on a parametric channel model, we present a new concept of the joint angle-delay subspace which can be tracked by the low-complexity low-rank adaptive filtering (LORAF) algorithm. Then, we investigate an interference-free transmission condition that the joint angle-delay subspaces of the users reusing the same pilots are non-overlapping. Since the channel statistics are usually unknown, we develop a robust minimum mean square error (MMSE) estimator under the worst precondition of pilot decontamination, considering that the joint angle-delay subspaces of the interfering users fully overlap. Furthermore, motivated by the interference-free transmission criteria, we present a novel low-complexity greedy pilot scheduling algorithm to avoid the problem of initial value sensitivity. Simulation results show that the joint angle-delay subspace can be estimated effectively, and the proposed pilot reuse scheme combined with robust MMSE channel estimation offers significant performance gains.
  • Wei, H. et al. (2016). Mutual Coupling Calibration for Multiuser Massive MIMO Systems. IEEE Transactions on Wireless Communications [Online] 15:606-619. Available at: http://doi.org/10.1109/TWC.2015.2476467.
    Massive multiple-input multiple-output (MIMO) is a promising technique to greatly increase the spectral efficiency and may be adopted by the next generation mobile communication systems. Base stations (BSs) equipped with large-scale antennas can serve multiple users simultaneously by exploiting the downlink precoding in time division duplex (TDD) mode. However, channel state information (CSI) of uplink transmissions cannot be simply used for downlink precoding, because the gain mismatches of the transceiver radio frequency (RF) circuits disable the channel reciprocity. In this paper, we focus on antenna calibration for massive MIMO systems with maximal ratio transmit (MRT) precoding to solve the channel nonreciprocity problem. A new calibration method, called mutual coupling calibration, is proposed by using the effect of mutual coupling between adjacent antennas. By exploiting this method, the BS can perform the calibration without extra hardware circuit and users' involvement. We also build up the model of calibration error and derive the closed-form expressions of the ergodic sum-rates for evaluating the impact of calibration error on system performance. Simulation results verify the high calibration accuracy of the proposed method and show the significant improvement of system performance by performing antenna calibration.
  • Wang, J. et al. (2016). Low-Complexity Beam Allocation for Switched-Beam Based Multiuser Massive MIMO Systems. IEEE Transactions on Wireless Communications [Online]:1-1. Available at: http://doi.org/10.1109/TWC.2016.2613517.
    This paper addresses the beam allocation problem in a switched-beam based massive multiple-input-multiple-output (MIMO) system working at the millimeter wave (mmWave) frequency band, with the target of maximizing the sum data rate. This beam allocation problem can be formulated as a combinatorial optimization problem under two constraints that each user uses at most one beam for its data transmission and each beam serves at most one user. The brute-force search is a straightforward method to solve this optimization problem. However, for a massive MIMO system with a large number of beams N, the brute-force search results in intractable complexity O(NK), where K is the number of users. In this paper, in order to solve the beam allocation problem with affordable complexity, a suboptimal low-complexity beam allocation (LBA) algorithm is developed based on submodular optimization theory, which has been shown to be a powerful tool for solving combinatorial optimization problems. Simulation results show that our proposed LBA algorithm achieves nearly optimal sum data rate with complexity O(K logN). Furthermore, the average service ratio, i.e., the ratio of the number of users being served to the total number of users, is theoretically analyzed and derived as an explicit function of the ratio N=K.
  • Wei, H. et al. (2016). Impact of RF mismatches on the performance of massive MIMO systems with ZF precoding. Science China Information Sciences [Online] 59:1-14. Available at: http://doi.org/10.1007/s11432-015-5509-1.
    Thanks to the channel reciprocity, the time division duplex (TDD) operation is more preferred in massive multiple-input multiple-output (MIMO) systems. Avoiding the heavy feedback of downlink channel state information (CSI) from the user equipment (UE) to the base station (BS), the uplink CSI can be exploited for the downlink precoding. However, due to the mismatches of the radio frequency (RF) circuits at both sides of the link, the whole communication channels are usually not symmetric in practical systems. This paper is focused on the RF mismatches at the UEs and the BS for the multi-user massive MIMO systems with zero forcing (ZF) precoding. The closed-form expressions of the ergodic sum-rates are derived for evaluating the impact of RF mismatches on the system performance. Theoretical analysis and simulation results show that the RF mismatches at the UEs only lead to a negligible performance loss. However, it is imperative to perform reciprocity calibration at the BS, because the RF mismatches at the BS contribute to the inter-user interference (IUI) and result in a severe system performance degradation.
  • Yang, C. et al. (2015). When ICN meets C-RAN for HetNets: an SDN approach. IEEE Communications Magazine [Online] 53:118-125. Available at: http://doi.org/10.1109/MCOM.2015.7321980.
    With ever growing mobile Internet and the explosion of its applications, users are experiencing abundant services from different content providers via different network service providers in the heterogeneous network. The information-centric network (ICN) advocates getting rid of the current host-centric network protocol because information dissemination rather than end-to-end communication contributes to the majority of today's network traffic. Furthermore, it is better for network entities to converge as a whole in order to take advantage of open, scalable, and smart traffic transmission. The cloud radio access network is one of the emerging architecture evolutions on the wireless side for easier infrastructure deployment and network management. Therefore, when the information-centric network meets the C-RAN in the Het-Net, it is worthwhile and consequential to integrate ICN protocol with C-RAN architecture to achieve more efficient communication and information management. Moreover, SDN has been recognized as another promising architecture evolution to achieve the flexibility and reconfigurability of dense HetNets; its inherent advantage lies in global uniform control of the wired network. Thus, any of ICN, C-RAN and SDN is the complementary to the others. In this article, we contribute to a fresh proposal for and elaboration of the integration of the ICN, CRAN, and SDN for the HetNet to achieve a win-win situation. The vision of the proposed system is demonstrated, followed by the advantages and challenges. We further present a hybrid system in a large-scale wireless heterogeneous campus network.
  • Wang, J. (2015). Performance Analysis of Multi-Antenna Hybrid Satellite-Terrestrial Relay Networks in the Presence of Interference. IEEE Transactions on Communications [Online] 63. Available at: http://dx.doi.org/10.1109/TCOMM.2015.2474865.
    Abstract—The integration of cooperative transmission into
    satellite networks is regarded as an effective strategy to increase
    the energy efficiency as well as the coverage of satellite communications.
    This paper investigates the performance of an amplifyand-
    forward (AF) hybrid satellite-terrestrial relay network
    (HSTRN), where the links of the two hops undergo Shadowed-
    Rician andRayleigh fadingdistributions, respectively.By assuming
    that a single antenna relay is used to assist the signal transmission
    between the multi-antenna satellite and multi-antenna
    mobile terminal, and multiple interferers corrupt both the
    relay and destination, we first obtain the equivalent end-to-end
    signal-to-interference-plus-noise ratio (SINR) of the system. Then,
    an approximate yet very accurate closed-form expression for the
    ergodic capacity of the HSTRN is derived. The analytical lower
    bound expressions are also obtained to efficiently evaluate the
    outage probability (OP) and average symbol error rate (ASER)
    of the system. Furthermore, the asymptotic OP and ASER expressions
    are developed at high signal-to-noise ratio (SNR) to reveal
    the achievable diversity order and array gain of the considered
    HSTRN. Finally, simulation results are provided to validate of the
    analytical results, and show the impact of various parameters on
    the system performance.
  • Pan, C. et al. (2015). Weighted Sum Energy Efficiency Maximization in Ad Hoc Networks. IEEE Wireless Communications Letters [Online] 4:233-236. Available at: http://doi.org/10.1109/LWC.2015.2401580.
    In this letter, we propose a distributed adaptive-pricing algorithm aimed at solving the weighted sum energy efficiency (EE) maximization problem in ad hoc networks. It is theoretically proven that the proposed distributed algorithm strictly converges to the Karush-Kuhn-Tucker (KKT) point of the problem. Significant performance enhancement is observed by numerical results with fast convergence. Moreover, it is shown that the proposed algorithm degrades gracefully when decreasing overhead of information exchange.
  • Pan, C. et al. (2015). Totally Distributed Energy-Efficient Transmission in MIMO Interference Channels. IEEE Transactions on Wireless Communications [Online] 14:6325-6338. Available at: http://doi.org/10.1109/TWC.2015.2452908.
    In this paper, we consider the problem of maximizing the energy efficiency (EE) for multiple-input–multiple-output (MIMO) interference channels (ICs), subject to the per-link power constraint. To avoid extensive information exchange among all links, the optimization problem is formulated as a noncooperative game, where each link maximizes its own EE. We show that this game always admits a Nash equilibrium (NE) and the sufficient condition for the uniqueness of the NE is derived for the case of large enough maximum transmit power constraint. To reach the NE of this game, we develop a totally distributed EE algorithm, in which each link updates its own transmit covariance matrix in a completely distributed and asynchronous way. Some players may update their solutions more frequently than others or even use the outdated interference information. The sufficient conditions that guarantee the global convergence of the proposed algorithm to the NE of the game have been given as well. We also study the impact of the circuit power consumption on the sum EE performance of the proposed algorithm in the case when the links are separated sufficiently far away. Moreover, the tradeoff between the sum EE and the sum spectral efficiency (SE) is investigated with the proposed algorithm under two special cases: 1) low transmit power constraint regime; and 2) high transmit power constraint regime. Finally, extensive simulations are conducted to evaluate the impact of various system parameters on the system performance.
  • Xin, Y. et al. (2015). Area Spectral Efficiency and Area Energy Efficiency of Massive MIMO Cellular Systems. IEEE Transactions on Vehicular Technology [Online] 65:3243-3254. Available at: http://doi.org/10.1109/TVT.2015.2436896.
    This paper investigates the performance of massive
    multiple input multiple output (MIMO) cellular systems with
    pilot contamination. We derive a closed-form approximation of
    the area spectral efficiency (ASE) for uplink multi-cell multiuser
    massive MIMO systems by using an uniformly distributed
    user location model. Considering a practical power consumption
    model, we obtain the area energy efficiency (AEE) in a cell. The
    theoretical results of ASE and AEE can be used to investigate
    some system parameters of massive MIMO cellular system, such
    as the number of antennas at the base station, the number of
    users, and the number of symbols over which the channel remains
    constant. We also study the optimal pilot-to-data power ratio
    (PDPR) for both ASE maximization and AEE maximization.
  • Xu, P. et al. (2015). Analysis and Design of Channel Estimation in Multicell Multiuser MIMO OFDM Systems. IEEE Transactions on Vehicular Technology [Online] 64:610-620. Available at: http://dx.doi.org/10.1109/TVT.2014.2322654.
    This paper investigates the uplink transmission in multicell multiuser multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. The system model considers imperfect channel estimation, pilot contamination (PC), and multicarrier and multipath channels. Analytical expressions are first presented on the mean square error (MSE) of two classical channel estimation algorithms [i.e., least squares (LS) and minimum mean square error (MMSE)] in the presence of PC. Then, a simple H-infinity (H-inf) channel estimation approach is proposed to have good suppression to PC. This approach exploits the space-alternating generalized expectation–maximization (SAGE) iterative process to decompose the multicell multiuser MIMO (MU-MIMO) problem into a series of single-cell single-user single-input single-output (SISO) problems, which reduces the complexity significantly. According to the analytic results given herein, increasing the number of pilot subcarriers cannot mitigate PC, and a clue for suppressing PC is obtained. It is shown from the results that the H-inf has better suppression capability to PC than classical estimation algorithms. Its performance is close to that of the optimal MMSE as the length of channel impulse response (CIR) is increased. By using the SAGE process, the performance of the H-inf does not degrade when the number of antennas is large at the base station (BS).
  • Alade, T., Zhu, H. and Wang, J. (2015). Uplink Spectral Efficiency Analysis of In-Building Distributed Antenna Systems. IEEE Transactions on Wireless Communications [Online] 14:4063-4074. Available at: http://doi.org/10.1109/TWC.2015.2416235.
    Providing high data rate wireless transmissions has been difficult in indoor environments, particularly in multi-floor buildings. One way to achieve high data rate wireless transmissions is to reduce the radio transmission distance between the transmitter and the receiver by using distributed antenna systems (DASs) and employing frequency reuse. However, due to the reuse of the limited available spectrum, co-channel interference can severely degrade system capacity. In this paper, the uplink spectral efficiency of an in-building DAS with frequency reuse is studied, where remote antenna units (RAUs) deployed on each floor throughout the building are connected to a central unit (CU) where received signals are processed. The impact of co-channel interference on system performance is investigated by using a propagation channel model derived from multi-floor, in-building measurement results. The proposed scheme exploits the penetration loss of the signal through the floors, resulting in frequency reuse in spatially separated floors, which increases system spectral efficiency and also reduces co-channel interference. A comparative analysis with conventional co-located antenna deployment at the floor center is provided. Location based RAU selection and deployment options are investigated. System performance is evaluated in terms of location-specific spectral efficiency for a range of potential mobile terminal (MT) locations and various in-building propagation characteristics.

Book section

  • Wang, J. et al. (2017). Integrating Optical Tweezers, DNA Tightropes, and Single-Molecule Fluorescence Imaging: Pitfalls and Traps. in: Single-Molecule Enzymology: Nanomechanical Manipulation and Hybrid Methods. Elsevier, pp. 171-192. Available at: https://doi.org/10.1016/bs.mie.2016.08.003.
    Fluorescence imaging is one of the cornerstone techniques for understanding how single molecules search for their targets on DNA. By tagging individual proteins, it is possible to track their position with high accuracy. However, to understand how proteins search for targets, it is necessary to elongate the DNA to avoid protein localization ambiguities. Such structures known as "DNA tightropes" are tremendously powerful for imaging target location; however, they lack information about how force and load affect protein behavior. The use of optically trapped microstructures offers the means to apply and measure force effects. Here we describe a system that we recently developed to enable individual proteins to be directly manipulated on DNA tightropes. Proteins bound to DNA can be conjugated with Qdot fluorophores for visualization and also directly manipulated by an optically trapped, manufactured microstructure. Together this offers a new approach to understanding the physical environment of molecules, and the combination with DNA tightropes presents opportunities to study complex biological phenomena.

Conference or workshop item

  • Sabbagh, R., Pan, C. and Wang, J. (2018). Pilot Allocation and Sum-Rate Analysis in Cell-Free Massive MIMO Systems. in: 2018 IEEE International Conference on Communications (ICC). IEEE. Available at: https://doi.org/10.1109/ICC.2018.8422575.
    This paper deals with the challenging issue of the unaffordable channel training overhead in the dense cell-free massive multi-input multi-output (MIMO) system when a high number of users are being simultaneously served. By adopting the user-centric cluster method, a dynamic pilot reuse (DPR) scheme is proposed to allow a pair of users to share a single pilot sequence. Specifically, the proposed reuse scheme is achieved with the objective of maximizing the uplink achievable sum-rate subject to users' signal to interference plus noise ratio (SINR) requirements and pilot resources constraints. On this basis, the SINR expression is derived for any user sharing its pilot with another by utilizing both minimum mean squared error (MMSE) detection and channel estimation. A low complexity pilot reuse algorithm is then developed based on the separation distance between users. The iterative grid search (IGS) method is employed to find the threshold that can be utilized in the proposed algorithm to maximize the sum-rate. Finally, simulation results are presented to show the effectiveness of the DPR scheme with the optimized threshold in terms of the uplink achievable sum-rate.
  • Alade, T. and Wang, J. (2018). Indoor Distributed Antenna Systems for Multi-Storey Buildings. in: 2018 IEEE 87 th Vehicular Technology Conference (VTC Spring). IEEE. Available at: https://doi.org/10.1109/VTCSpring.2018.8417676.
    One of the main targets of the fifth generation (5G) mobile communication systems and beyond is providing high data rate wireless transmissions and ubiquitous coverage to users. To support increasing subscriber populations in indoor environments, indoor wireless communication systems are required, but frequency spectrum allocations are limited and requires reuse of the limited spectrum. In order to design efficient and reliable indoor communication systems, a thorough understanding of the reuse distance is vital. This paper investigates a number of important issues associated with indoor radio propagation and frequency reuse planning in multi-storey buildings employing indoor distributed antenna system (DAS), where distributed remote antenna units (RAUs) supported by a central unit (CU) communicate with mobile equipment (MEs). In the DAS, co-channel interference caused by frequency reuse is a restraining factor as the frequency reuse distances are generally smaller. The effect of different reuse distances, penetration losses, pathloss exponents, and co-channel interference on spectral efficiency is analysed and performance evaluated over a wide range of potential ME locations.
  • Wang, J., Gomes, N. and Wang, J. (2018). Adaptive Frequency Reuse for Beam Allocation Based Multiuser Massive MIMO Systems. in: 2018 IEEE International Conference on Communications (ICC). IEEE. Available at: https://doi.org/10.1109/ICC.2018.8422264.
    Massive multiple-input-multiple-output (MIMO) is a promising technique to provide high-data-rate communication in fifth-generation (5G) mobile systems, thanks to its ability to form narrow and high-gain beams. Among various massive MIMO beamforming techniques, the fixed-beam scheme has attracted considerable attention due to its simplicity. In this paper, we focus on a fixed- beam based multiuser massive MIMO system where each user is served by a beam allocated to it. As the directions of fixed beams are predetermined and the users are randomly distributed, there could be some ``worst-case'' users, located at the edge of its serving beam, suffering from strong inter-beam interference and thus experiencing low data rate. To improve the individual data rates of the worst-case users while maintaining the sum data rate, an adaptive frequency reuse scheme is proposed. Simulation results corroborate that our proposed adaptive frequency reuse strategy can greatly improve the worst-case users' data rates without sacrificing the sum data rate.
  • Albasry, H., Zhu, H. and Wang, J. (2018). The Impact of In-Band Emission Interference in D2D-Enabled Cellular Networks. in: IEEE Globecom 2017. IEEE. Available at: http://dx.doi.org/10.1109/GLOCOM.2017.8254841.
    The overlay in-band device to device (D2D) scheme can be used by cellular user equipments (CUEs) and D2D user equipments (DUEs) to transmit the uplink and D2D data in the channel. The CUEs experience in-band emission interference (IEI) from the DUEs that transmit D2D signals in the adjacent channels. This paper investigates the IEI impact in D2D-enabled cellular networks and evaluates the cellular system performance by deriving the coverage probability and average data rate of typical CUE under different DUEs densities. Further, the intra-cell IEI and inter-cell IEI are separately examined to calculate the dominating interference in the system. Moreover, we propose density-based strategy (DBS) to mitigate IEI in D2D-enabled networks and evaluate the data rate gain. The reduction percentage of DUEs that can be served for each time slot is derived as a trade-off metric of the strategy. The results show the IEI impact is significant and should be considered to evaluate the system performance accurately. We evaluate the IEI impact by changing the DUEs density and DUEs transmission power. Additionally, a remarkable result finds that the intra-cell and inter-cell IEI dominate the typical CUE coverage probability similarly at low DUEs density, whilst at high DUEs density the intra-cell IEI does. The DBS results depict the remarkable improvement of the typical CUE data rate and define the upper bound of the data rate that can be achieved by DBS.
  • Raoof, R., Zhu, H. and Wang, J. (2018). Pilot Allocation and Sum-rate Analysis in Distributed Massive MIMO Systems. in: 2017 IEEE 86th Vehicular Technology Conference: VTC2017-Fall. IEEE. Available at: http://dx.doi.org/10.1109/VTCFall.2017.8288013.
    In distributed massive multi-input multi-output (DM-MIMO) systems, orthogonal pilot sequences are generally utilized to acquire the channel state information (CSI). However, this highly restricts the number of users simultaneously served. In this paper, a pilot reuse within a single cell DM-MIMO system is proposed to serve more users than the available pilot sequences. The reuse in this strategy is applied so that maximum achievable sum-rate is satisfied with the constraint of predefined pilot resource. On this basis, two users in different subcells separated by a large distance and satisfying a specific signal to interference plus noise ratio (SINR) level can share the same pilot sequence. An expression for SINR is derived for any pair of users who use the same pilot. Based on this expression, an algorithm is proposed to choose which pairs of users are able to use the same pilot with the constraint of satisfying the minimum SINR required for these users. The simulation results demonstrate that the uplink achievable sum-rate for the proposed strategy is higher than both cases when no pilot reuse or random pilot reuse are considered.
  • Ali, W. et al. (2018). An Expedited Predictive Distributed Antenna System Based Handover Scheme for High-Speed Railway. in: IEEE Globecom 2017. IEEE. Available at: http://dx.doi.org/10.1109/GLOCOM.2017.8254579.
    High-speed train has drawn considerable attention and become one of the most preferable conveyance mechanism. Each year the manufacture corporations reach a higher speed record which is expected to attain 1000 km/h by 2021 using hyperloop one technology. Moving at such a high speed results in a high handover (HO) rate which makes it challenging for high speed railway (HSR) mobile wireless communication to preserve steady link performance. Employing distributed antenna systems (DASs) along with the two-hop architecture, this paper proposes a fast predictive HO algorithm. In this strategy, the serving cell starts the HO preparation phase in advance by inferring the train current location. Issuing the HO preparation phase in advance reduces the HO latency and reduces the HO command failure probability as well. Lower HO command failure probability means lower HO failure probability which could greatly improve the end-users quality of services (QoS). The analytical results show that the proposed scheme performs better compared with the conventional HO scheme.
  • Khadka, A. et al. (2018). Cooperative Transmission Strategy Over Users’ Mobility for Downlink Distributed Antenna Systems. in: IEEE Globecom 2017. IEEE. Available at: http://dx.doi.org/10.1109/GLOCOM.2017.8254565.
    Previously, a scheme in [1] is proposed for the outdated channel state information (CSI) problem, for data transmission in time division duplex (TDD) systems. In user movement environment, the actual channel of data transmission at downlink time slot is different from the estimated channel due to channel variation. In this paper the effect of different user mobility on TDD downlink multiuser distributed antenna system is investigated. An efficient autocorrelation based feedback interval technique is proposed and updates CSI at less cost of the downlink time slots. In the proposed technique, the frequency of CSI feedback for different users is proportional to their speed. Cooperative clusters are formed to maximize sum rate where channel gain based antenna selection and user clustering based on SINR threshold is applied to reduce computational complexity. Numerical results show that sum rate superiority of the proposed scheme over the user mobility.
  • Hu, J. et al. (2018). Covert Communication in Wireless Relay Networks. in: IEEE Globecom 2017. IEEE. Available at: http://dx.doi.org/10.1109/GLOCOM.2017.8254008.
    Covert communication aims to shield the very existence of wireless transmissions in order to guarantee a strong security in wireless networks. In this work, for the first time we examine the possibility and achievable performance of covert communication in one-way relay networks. Specifically, the relay opportunistically transmits its own information to the destination covertly on top of forwarding the source’s message, while the source tries to detect this covert transmission to discover the illegitimate usage of the recourse (e.g., power, spectrum) allocated only for the purpose of forwarding source’s information. The necessary condition that the relay can transmit covertly without being detected is identified and the source’s detection limit is derived in terms of the false alarm and miss detection rates. Our analysis indicates that boosting the forwarding ability of the relay (e.g., increasing its maximum transmit power) also increases its capacity to perform the covert communication in terms of achieving a higher effective covert rate subject to some specific requirement on the source’s detection performance.
  • Daghal, A., Zhu, H. and Wang, J. (2018). Performance analysis of Mobile Content Delivery in Multiple Devices to Single Device Communication. in: IEEE Globecom 2017. IEEE. Available at: http://dx.doi.org/10.1109/GLOCOM.2017.8254839.
    In wireless communication networks, caching and delivering popular content via the device to device (D2D) communication has recently been proposed as an exciting and innovative technology in order to offload network data traffic. In this paper, a novel method of content delivery using multiple devices to the single device (MDSD) communication via D2D links is presented. An expression of the outage probability (Pout) is analytically derived and validated by simulation to determine the success of the content delivery to the user equipment (UE). Zipf distribution with exponent shape parameter p is adopted to model the UE requests and content caching popularity which affects the achievable link data rate (Ra). The results show that Pout decreases as the popularity of the content increases. Meanwhile, MDSD improves the UE experience in terms of Pout substantially compared to the single D2D link based method.
  • Mahbas, A., Zhu, H. and Wang, J. (2018). Mobility Management in Small Cell Networks. in: IEEE Globecom 2017. IEEE. Available at: http://dx.doi.org/10.1109/GLOCOM.2017.8254570.
    The cell sojourn time and the handoff rate are considered as the main parameters in the mobility management of the cellular systems. In this paper, we address the mobility management in a two-tier heterogeneous network (HetNet) and propose a framework to study the impact of different system parameters on the handoff rate and the small cell sojourn time. In the proposed framework, the overlapping coverage among the small cells and the number of overlaps on the path of a reference user equipment (UE) are derived to obtain the actual time that the reference UE spends in each small cell during its movement from the starting point to the destination point. The results show the accuracy of the analysis in this paper in comparison to the analysis when ignoring the impact of the overlaps. The results also show the importance of considering the overlaps among the small cells in dense HetNets.
  • Pan, Y. et al. (2017). Content Offloading via D2D Communications Based on User Interests and Sharing Willingness. in: IEEE ICC2017. Institute of Electrical and Electronics Engineers (IEEE). Available at: http://dx.doi.org/10.1109/ICC.2017.7996627.
    As a promising solution to offload cellular traffic, device-to-device (D2D) communication has been adopted to help disseminate contents. In this paper, the D2D offloading utility is maximized by proposing an optimal content pushing strategy based on the user interests and sharing willingness. Specifically, users are classified into groups by their interest probabilities and carry out D2D communications according to their sharing willingness. Although the formulated optimization problem is nonconvex, the optimal solution is obtained in closed-form by applying Karush-Kuhn-Tucker conditions. The theoretical and simulation results show that more contents should be pushed to the user group that is most willing to share, instead of the group that has the largest number of interested users.
  • Ali, W. et al. (2017). Distributed antenna system based frequency switch scheme evaluation for high-speed railways. in: 2017 IEEE International Conference on Communications (ICC). Institute of Electrical and Electronics Engineers (IEEE), pp. 1-6. Available at: https://doi.org/10.1109/ICC.2017.7996443.
    High-speed railway (HSR) has witnessed a huge growth globally, and now is reaching a maximum speed of 575 km/h. This record of speed makes mobile communications difficult for HSR since the handover (HO) frequency increases which results in a high loss of connectivity. Based on distributed antenna systems (DASs), this paper utilizes the two-hop network architecture for HSR broadband wireless communication systems. With the target of achieving high system capacity, superior transmission reliability, and consequently high-quality broadband wireless communication service for passengers in HSR. Moreover, a Frequency Switch (FSW) scheme is proposed for the two-hop network architecture to alleviate the frequent HO issue in traditional HSR wireless communication systems where HO generally happens between the successive remote antenna units (RAUs) connecting to the same central unit (CU) control. The FSW scheme provides mobility robustness signalling process that guarantees a successful frequency switching instead of HO, and reduces the probability of radio link failure (RLF) compared to HO process in traditional HSR systems, where the HO failure (HOF) rate is about 21%. The analytical results show that the proposed scheme outperforms traditional HO schemes.
  • Mahbas, A., Zhu, H. and Wang, J. (2017). The Optimum Rate of Inter-Frequency Scan in Inter-Frequency HetNets. in: IEEE International Conference on Communications (ICC) 2017. Institute of Electrical and Electronics Engineers (IEEE). Available at: http://dx.doi.org/10.1109/ICC.2017.7996442.
    Inter-frequency scan (IFS) is a process carried out by the terminals to discover the small cells (SCs) in the interfrequency heterogeneous networks (HetNets) prior to offload them to the discovered SCs. The IFS has a great impact on the quality of service, the energy efficiency and the spectral efficiency in the cellular systems. In this paper, a framework is presented to model and evaluate the impact of IFS on the system performance by using the stochastic geometry. The energy efficiency is derived as performance metric to obtain the optimum value of the IFS rate (optimum number of scans per unit time) by taking into consideration the trade-off in the offloading process between the power consumption and exploiting the system resources efficiently. Considering the energy consumption for performing IFSs along with the energy consumption for maintaining the uplink transmission will help to find the optimum value of IFS rate that achieves the best energy efficiency. The analysis and results show that the optimum IFS rate depends on different system parameters such as SCs’ density, terminal’s speed and the transmit power of the SCs (SCs’ coverage).
  • Pan, C. et al. (2017). Joint Precoding and RRH selection for Green MIMO C-RAN. in: Global Communications Conference (GLOBECOM), 2016 IEEE. Institute of Electrical and Electronics Engineers (IEEE). Available at: http://dx.doi.org/10.1109/GLOCOM.2016.7841930.
    This paper jointly optimizes the precoding matrices and the set of active remote radio heads (RRHs) to minimize the network power consumption for a cloud radio access network (C-RAN) where both the RRHs and users all have multiple antennas. Both users’ rate requirements and per-RRH power constraints are considered. Due to these conflicting constraints, this optimization problem may be infeasible. We propose to solve this problem with two phases. In Phase I, a new approach is proposed to check the feasibility of the original problem. If the feasibility is guaranteed, in Phase II, a low-complexity algorithm is proposed to solve the original optimization problem. Simulation results demonstrate the rapid convergence of the proposed algorithms and the benefits of equipping multiple antennas at the user side.
  • Ye, Z. et al. (2017). Outage Probability and Fronthaul Usage Tradeoff Caching Strategy in Cloud-RAN. in: IEEE ICC2017. Institute of Electrical and Electronics Engineers (IEEE). Available at: http://dx.doi.org/10.1109/ICC.2017.7996856.
    In this paper, optimal content caching strategy is proposed to jointly minimize the cell average outage probability and fronthaul usage in cloud radio access network (Cloud-RAN). An accurate closed form expression of the outage probability conditioned on the user’s location is presented, and the cell average outage probability is obtained through the composite Simpson’s integration. The caching strategy for jointly optimizing the cell average outage probability and fronthaul usage is formulated as a weighted sum minimization problem, which is a nonlinear 0-1 integer NP-hard problem. In order to deal with the NP-hard problem, at first, two particular caching placement schemes are investigated: the most popular content (MPC) caching scheme and the proposed location-based largest content diversity (LB-LCD) caching scheme. Then a genetic algorithm (GA) based approach is proposed. Numerical results show that the performance of the proposed GA-based approach with significantly reduced computational complexity is close to the optimal performance achieved by exhaustive search based caching strategy.
  • Xin, Y. et al. (2016). Area Spectral Efficiency and Energy Efficiency Analysis in Downlink Massive MIMO Systems. in: 2015 IEEE 82nd Vehicular Technology Conference (VTC2015-Fall). pp. 1-5. Available at: https://doi.org/10.1109/VTCFall.2015.7390846.
    We consider the downlink multi-user multi-cell massive MIMO systems, assuming that the number of antennas at base station (BS) and the number of users are large. Our system model accounts for channel estimation, pilot contamination, and uniformly random user location distribution. We derive the approximation of area spectral efficiency (ASE) with regularized zero-forcing (RZF) precoding technique which are proven to be accurate via simulation results. With a realistic power consumption model considering not only transmit power but also the fundamental power for operating the circuit at transmitter and receiver, we analyze the performance of area energy efficiency (AEE). Finally, based on the proposed power consumption model, we determine the optimal number of antennas at BS aimed at maximizing AEE when transmit power is given.
  • Khadka, A. et al. (2015). Cooperative transmission strategy for downlink distributed antenna systems over time-varying channel. in: IEEE Globecom2015,.. Available at: http://dx.doi.org/10.1109/GLOCOM.2014.7417837.
    The channel state information (CSI) is used to optimise data transmission in time division duplex (TDD) systems, which is obtained at the time of channel estimation. The actual channel of data transmission at downlink time slot is different from the estimated channel due to channel variation in user movement environment. In this paper the impact of different user mobility on TDD downlink multiuser distributed antenna system is investigated. Based on mobility state information (MSI), an autocorrelation based feedback interval technique is proposed and updates CSI and mitigate the performance degradation imposed by the user speed and transmission delay. Cooperative clusters are formed to maximize sum rate and a channel gain based antenna selection and user clustering based on SINR threshold is applied to reduce computational complexity. Numerical results show that
    the proposed scheme can provide improved sum rate over the non cooperative system and no MSI knowledge. The proposed technique has good performance for wide range of speed and suitable for future wireless communication systems.
  • Haci, H., Zhu, H. and Wang, J. (2015). A novel interference cancellation technique for non-orthogonal multiple access (NOMA). in: IEEE Globecom2015.. Available at: http://dx.doi.org/10.1109/GLOCOM.2014.7417128.