Meng Zhang

Joint Optimization in Bidirectional Multi-User Multi-Relay MIMO Systems: Non-Robust and Robust Cases

This paper studies the precoder design of bidirectional networks in which each node is equipped with multiple antennas. In contrast to the conventional model of bidirectional relay networks, this paper considers a more general scenario, i.e., a multi-user multi-relay network. First, by assuming that perfect channel state information (CSI) is available, we investigate the precoding design for the relays and users to minimize the sum mean squared error (MSE) and the maximum of single users MSE, respectively. Then, we consider a more practical scenario where CSI estimation error is taken into account. By means of alternating optimization approach, we decompose the main problem into several decoupled subproblems with tractable solutions. It is shown that, in both the perfect and imperfect CSI cases, the proposed precoding algorithms outperform the existing solutions in terms of MSE and bit-error-rate (BER) performance.

Relaying Robust Beamforming for Device-to-Device Communication With Channel Uncertainty

In this letter, we study robust beamforming design in the scenario that user equipments (UEs) relay the messages from a base station (BS) to a destination UE out of the cellular networks, which is considered as a high-priority device-to-device (D2D) scenario in the 3rd Generation Partnership Project (3GPP) Long-Term-Evolution (LTE) standardization. We assume that another D2D UE, which receives data from another D2D transmission group, coexists in the network, and it is interfered by D2D relay UEs. Moreover, the channel links between D2D relay UEs and the interfered UE are supposed to suffer from Gaussian errors due to low accuracy of channel estimation. Our optimization objective is to minimize the total transmission power at the BS and D2D relay UEs, while satisfying the signal-to-interference-plus-noise ratio (SINR) requirement of the destination D2D receiver and keeping the probability of low SINR event of the interfered D2D receiver smaller than a predefined threshold. Finally, we present the joint BS and D2D relay UE beamforming design, the effectiveness of which is verified by computer simulations.

QoS-Based Source and Relay Secure Optimization Design with Presence of Channel Uncertainty

In this letter, we study relay-aided networks with presence of single eavesdropper. We provide joint beamforming design of the source and relay that can minimize the overall power consumption while satisfying our predefined quality-of-service (QoS) requirements. Additionally, we investigate the case that the channel between relay and eavesdropper suffers from channel uncertainty. Finally, simulation results are provided to verify the effectiveness of our algorithm.

Correlated shadow fading for cellular network system-level simulations with wrap-around

In system-level simulations, it is vital to appropriately model spatially correlated shadow fading, especially the auto-correlation, so as to emulate realistic scenarios. However, as the size of the network increases, the complexity of the straightforward approach involving the Cholesky decomposition grows exponentially. Alternatively, low-complexity oriented schemes to generate correlated shadow fading value (SFV) maps for large networks are more preferable. However, the existing schemes do not consider wrap-around, which should be taken into account in the generation of SFV maps to facilitate user equipment (UE) mobility simulation and avoid the reduced interference in the outer-rim region. In order to prevent discontinuous shadow fading across the border of the simulated area and the wrap-around area, new methods to efficiently generate SFV maps are required. In this paper, a novel scheme to generate SFV maps with wrap-around is proposed, and its significant accuracy is analysed using computer simulations.

Secrecy capacity optimization in coordinated multi-point processing

In this paper, we will consider a coordinated multipoint (CoMP) transmission system which accords with the current Long Term Evolution-Advanced (LTE-A) system and the 5th generation wireless system (5G). This paper will consider two different circumstances, one concerning the condition that transmitters knows exactly which user will be wiretapped; the other concerning the condition that transmitters have no knowledge about the wiretapped users index. Accordingly, we provide the corresponding precoding strategies and simulation results to verify the effectiveness of our proposed algorithms.

Leakage-Based Robust Beamforming for Multi-Antenna Broadcast System With Per-Antenna Power Constraints and Quantized CDI

In this paper, we investigate the robust beamforming schemes for a multi-user multiple-input-single-output (MU-MISO) system with per-antenna power constraints and quantized channel direction information (CDI) feedback. Our design objective is to maximize the expectation of the weighted sum-rate performance by means of controlling the interference leakage and properly allocating the power among user equipments (UEs). First, we prove the optimality of the non-robust zero-forcing (ZF) beamforming scheme in the sense of generating the minimum amount of average inter-UE interference under quantized CDI. Then we derive closed-form expressions of the cumulative density function (CDF) of the interference leakage power for the non-robust ZF beamforming scheme, based on which we adjust the leakage thresholds and propose two robust beamforming schemes under per-antenna power constraints with an iterative process to update the per-UE power allocations using the geometric programming (GP). Simulation results show the superiority of the proposed robust beamforming schemes compared with the existing schemes in terms of the average weighted sum-rate performance.

Sum Secrecy Rate Maximization for Relay-Aided Multiple-Source Multiple-Destination Networks

This paper studies a multiple-source multiple-destination network with the presence of multiple eavesdroppers, in which an amplify-and-forward (AF) relay is used to bridge the communication between the source–destination pairs to overcome the long-distance attenuation. Considering the physical-layer security issues, we aim to maximize the sum secrecy rate subject to the relay power constraint and the quality-of-service (QoS) requirements for legitimate user equipment. First, we propose an algorithm based on the monotonic optimization and the semidefinite programming (MO-SDP). Simulation results show that our proposed MO-SDP algorithm exhibits almost the same performance as the optimal solution. To alleviate the problem of high complexity associated with the MO-SDP algorithm, we then propose an alternative solution based on the null-space (NuS) relay precoding, the complexity of which is significantly reduced, and it yields a semiclosed-form expression for the solution. Moreover, the performance of the proposed NuS algorithm is evaluated via simulations, and the performance of the NuS algorithm and that of the MO-SDP algorithm are shown to converge at the high signal-to-noise ratio (SNR) region.

Two-Hop Co-Located Robust Precoding Design in Radio SWIPT Relay Networks

—This paper studies the two-hop co-located transmission architecture that incorporates simultaneous wireless information and power transfer in radio relay networks. Joint robust precoding design of the information and power transfer that can minimize the overall relays’ power consumption while satisfying our predefined quality-of-service and energy-harvest requirements is provided. By using SemiDefinite Relaxation technique, the non-convex initial problem can be converted to be convex. Additionally, the dual problem of the relaxed problem is investigated, and the closed-form optimal solutions of the relaxed problem can be achieved by our proposed method. Finally, approximate solutions show the effectiveness of our proposed robust precoding design.

Probabilistic-Constrained Simultaneous Wireless Information and Power Transfer for Multiple-Relay Networks

Simultaneous Wireless Information and Power Transfer (SWIPT) potentially offers great convenience to prolong the lifetime of energy-constrained nodes in wireless networks. This paper considers multiple-relay network that incorporates SWIPT where the Base Station (BS) communicates with the user through the help of multiple single-antenna relays. A relay beamforming and energy harvest design is proposed to maximize the probability of the Signal-to-Noise-Ratio (SNR) of the user larger than a pre-defined threshold while not violating the power constraint of relays and guaranteeing the energy of the user received from probabilistic perspective. Then, we use S-lemma transform probabilistic-constrained problem into non- probability. An iteration-based algorithm is devised to solve this problem. Simulation results verify the effectiveness of the proposed scheme, which can achieve better tradeoff between the power consumption of relays and the users SNR.

Bit allocation strategy among users in coordinated multi-cell systems with limited feedback

In this paper, we propose a novel bit allocation strategy in coordinated multi-cell systems with limited feedback. Multi-cell cooperation technique is an effective way to improve the system throughput and especially the performance of the cell edge users. In a Coordinated Multi-Point (CoMP) system, the rate loss caused by quantization error of Channel State Information (CSI) is minimized considering two aspects of the channels. Firstly, as the physical conditions and constraints of different users are not identical, appropriately allocating feedback bits to users based on their channels can achieve higher throughput. Secondly, in a Coordinated Beamforming/Coordinated Scheduling (CB/CS) system, each user has a serving channel to the serving base station and an interfering channel to the coordinated base station. The user needs to partition its available bits between the two channels. Thus, we study a global bit allocation strategy that can minimize the rate loss from that of the full CSI circumstance. From our simulation results, we prove that the proposed bit allocation strategy achieves higher per-cell sum-rate compared with the equal bit allocation strategy.