Niwei Wang

MIMO Beamforming Designs With Partial CSI Under Energy Harvesting Constraints

In this letter, we investigate multiple-input multiple-output (MIMO) communications under energy harvesting (EH) constraints. In our considered EH system, there is one information transmitting (ITx) node, one traditional information receiving (IRx) node and multiple EH nodes. EH nodes can transform the received electromagnetic waves into energy to enlarge the network operation life. When the ITx node sends signals to the destination, it should also optimize the beamforming/precoder matrix to charge the EH nodes efficiently simultaneously. Additionally, the charged energy should be larger than a predefined threshold. Under the EH constraints, in our work both minimum mean-square-error (MMSE) and mutual information are taken as the performance metrics for the beamforming designs at the ITx node. In order to make the proposed algorithms suitable for practical implementation and have affordable overhead, our work focuses on the beamforming designs with partial CSI and this is the distinct contribution of our work. Finally, numerical results are given to show the performance advantages of the proposed algorithms.

Ergodic secrecy rate of two-user MISO interference channels with statistical CSI

This paper considers a two-user multiple-input single-output (MISO) interference channel with confidential messages (IFC-CM), where the beamforming vectors at the two transmitters are jointly optimized using the closed-form Pareto-optimal parameterization. We prove that artificial noise cannot improve the secrecy rate performance, and coordinated beamforming is secrecy-rate optimal which is achieved by agreeing on the parameters between the two transmitters. We analyze the feasible set of the beamforming parameters that guarantees positiveness of the secrecy rates when the transmitters know only statistical CSI, and then analysis in the ergodic secrecy rate region is discussed. More importantly, we derive the closed form of the ergodic secrecy rates and illustrate the Pareto-optimal structure of the beamforming vectors.摘要本文考虑两用户多输入单输出的带有安全信息的干扰信道, 采用闭式帕累托最优参数法来联合优化发送端的波束成形向量。 其次, 证明加入人为噪声不能提高安全速率, 且对发送端参数的一致性调整可获得协作波束成形的最优安全速率。 当发送端已知信道的统计信息时, 通过分析波束成形参数的可行集来保证安全速率的正定性, 进而得到遍历安全速率域。 最后, 提出遍历安全速率的闭式解, 并阐明波束成形向量的帕累托最优解的结构。

A robust and distributed design for coordinated downlink beamforming for secure MISO interference channels

In this paper, we address the optimization problems of downlink coordinated beamforming over the K-user multiple-input single-output interference channel with confidential messages. Our design objective is to minimise the total transmit power subject to the constraints of individual signal-to-interference plus noise ratio and equivocation rates. For the case with perfect channel state information CSI, by deriving the equivalent forms for the signal-to-interference plus noise ratio and the secrecy constraints, the optimization problem is reformulated as a second-order cone programme problem. Then, an optimal distributed algorithm using the partial Lagrangian duality is discussed. In addition we extend the analysis to the imperfect CSI scenario with bounded ellipsoidal errors, the centralised algorithm has been proposed by solving a semi-definite programme with the help of rank relaxation, whereas the distributed robust algorithm is devised by using ADMM. Finally, the simulation results have shown that with perfect CSI, the centralised and distributed algorithms have nearly the same performance, but in the case of imperfect CSI, the centralised algorithm shows a slightly better performance. Copyright

A QoE-based cell range expansion scheme in heterogeneous cellular networks

Deploying low-power nodes (LPNs) overlaid with Macro cells is a promising strategy to improve the coverage and capacity of cellular systems. Meanwhile, cell range expansion (CRE) scheme is proposed to select a proper serving base station (BS) for users between Macro eNodeBs and LPNs, and then offloading of traffic from Macro cell is made. In this paper, first, we introduce the LPNs deployment strategy and its activation criteria in the heterogeneous system. Then, a quality of experience (QoE)-based CRE scheme to adjust the coverage area of LPNs adaptively is proposed. Different from the existing CRE schemes, the QoE values for different users with different services are considered when the users try to select an appropriate serving BS. Finally, simulation results demonstrate that the proposed scheme can improve cell edge user experience for various services as well as overall system performance.创新点本文主要研究了LTE-Advanced系统异构网络中低功率节点的部署问题以及部署完成后小区选择算法的设计。小区范围扩展(CRE)方案提出的目的是将部分用户接入到邻近的低功率节点所在的小区, 从而降低宏小区的负载量。本文首先介绍了异构网络中低功率节点的部署和激活准则, 然后提出了一种基于用户体验质量的自适应CRE算法。该算法综合考虑了不同业务下的用户对功率以及用户体验质量的不同需求, 从用户需求角度出发, 设计了一种新的小区范围扩展算法。最后, 仿真结果验证了所提算法在用户体验质量和系统吞吐量两方面的性能要求, 说明了所提算法的可行性和有效性。

An Energy-Efficient Dense PicoStation Deployment and Power Control Strategy for Heterogeneous Networks

Deploying PicoStations in traditional Macro-cellular networks, especially in hot-spot areas, is a promising strategy to boost system throughput and enhance indoor coverage. However, PicoStations’ introduction brings some new problems, such as severe interference and energy consumption, which may result in performance degradation. In order to improve energy efficiency, throughput fairness and PicoStation coverage, a practical energy-efficient dense PicoStation deployment and power control algorithm is proposed. The proposed scheme maximizes both the number of active PicoStations that can achieve the required capacity and the sum cell capacity under individual capacity constraints in two steps. Finally, simulation results demonstrate that the proposed algorithm outperforms the traditional cell capacity maximum scheme in terms of user fairness and energy saving.

Secrecy Balancing over Two-User MISO Interference Channels with Rician Fading

This paper considers a 2-user multiple-input single-output (MISO) interference channel with confidential messages (IFC-CM), in which the Rician channel model is assumed. The coordinated beamforming vectors at the two transmitters have the similar parameterizations as those for perfect CSI, which could be optimized jointly and achieved by agreeing on the real parameters between the two users. Our main contribution is that a quadratic relationship between the two real-valued parameters can be derived for the Rician channel to reach the ergodic secrecy rate balancing point. Simulation results present the secrecy performance over the 2-user MISO IFC-CM scenario.

Robust Filter-and-forward Beamforming Design for Two-way Multi-antenna Relaying Networks

In this paper, we investigate a robust filter-and-forward (FF) beamforming design for two-waymulti-antenna relaying networks, where multiple relays assist two terminals to exchange information. With Gaussian distributed channel errors, the proposed robust beamforming design aims at maximizing the signal-to-interference-plus-noise-ratio (SINR) under individual transmit power constraints at each relay. Exploiting the elegant convex optimization mathematical tools, the optimization problem can be efficiently solved. Finally, simulation results demonstrate that the proposed robust beamformer reduces the sensitivity of the two-way multi-antenna relay networks to channel estimation errors, and outperforms the algorithm with estimated channels only. Moreover, the length of robust beamformer also influences the system performance.

A QoE-based jointly subcarrier and power allocation for multiuser multiservice networks

Quality of experience (QoE) is widely applied to reflect user’s satisfaction of the network service, which exactly conforms to the user-centric concept in 5G. In this paper, we propose a QoE-based subcarrier and power allocation algorithm for the downlink transmission of a multiuser multiservice system. For the subcarrier allocation algorithm, the rate proportional fairness factor is defined to ensure the fairness between users. Based on different QoE models of three services, i.e., file down (FD), video streaming and voice over internet protocol (VOIP), a multi-objective optimization method is exploited to allocate the power resource by minimizing the total power consumption and maximizing the mean opinion score (MOS) value of users simultaneously. Simulation results indicate that the proposed algorithm has less power consumption and higher QoE performance than the traditional proportional fairness (PF) algorithm. In addition, the proposed algorithm can achieve nearly the same fairness performance as the PF algorithm. Moreover, when the number of subcarriers becomes larger, the power assumption will be less but with little influence on both the QoE and fairness performances.创新点为了有效的提升无线通信系统的能源效率和整体性能, 本文提出了一种基于用户体验质量的高 能效的频率功率分配算法。针对多业务多用户网络系统中存在的各方面性能不均衡性以及系统 具有较高能耗的问题, 分别对无线通信系统中的频谱资源和功率资源进行优化分配。本文的 创新点在于利用多目标优化技术, 同时实现了优化系统能效, 用户平均QoE和用户公平性的目标。

Low complexity LMMSE beamforming design for uplink virtual MIMO systems

In this paper, the beamforming designs for uplink virtual MIMO systems are investigated. In such systems, the most challenging difficulty in beamforming designs comes from the fact that the nodes consisting the virtual MIMO are subjected to individual power constraints or named per-antenna power constraints instead of sum power constraints. The instinct individual power constraints for virtual MIMO prohibit the derivation for closed-form solutions. Although in existing works, it has been revealed that under per-antenna power constraints the design problems are still convex and can be efficiently solved using some famous convex optimization tools such as semidefinite programming (SDP). Unfortunately, it is far from desired for practical implementations. In our work, linear minimum mean square error (LMMSE) beamforming is designed under per-antenna power constraints. Exploiting the hidden convexity, an iterative solution is proposed, which has clear structure and well-suited for virtual MIMO communications e.g, the uplink of Machine-to-Machine (M2M)communications in cellular networks. Finally, simulation results demonstrate the advantages of the proposed design.