多中继放大转发协作通信中的功率分配和中继位置联合优化

文章研究了多中继放大转发协作分集系统中的功率分配和中继位置联合优化问题。利用信道的统计状态信息,在总功率一定的条件下,以最大化系统的信道容量为目标,推导了多中继和选择中继两种模型下基于高信噪比近似的联合优化算法的闭式解。理论分析和仿真验证表明,提出的算法大大提高了传统的等功率分配方案下系统的性能。     

中继增强的无线蜂窝多小区系统的联合调度与功率控制算法

针对采用全局频率复用的中继增强的无线蜂窝多小区系统,该文考虑多种通信模式并存的混合场景,提出了一种干扰感知的联合资源分配策略。以最大化系统总吞吐量为目标,同时考虑小区间干扰对中继节点与移动站点的影响,以及基站与中继节点各自的发射功率约束。为了降低计算复杂度,针对用户与中继节点配对问题提出了一种基于小区间干扰的调度算法;针对功率控制问题分别提出了一种基于符号规划的最优功率分配算法和一种次优的最小能耗功率分配算法。仿真结果表明,该文所提算法逼近最优资源分配,在系统吞吐量与能量效率等性能方面具有显著优势。     

无人机辅助无蜂窝大规模MIMO中的空地协同调度

无蜂窝大规模多输入多输出(multiple-input multiple-output,MIMO)技术采用大量接入点(access point,AP)为地面用户提供高效的通信服务,但在有高速移动用户的场景中,会加剧对信道状态信息的依赖。为了减少导频资源的消耗,提出了一种综合无人机(unmanned aerial vehicle,UAV)辅助通信和无蜂窝大规模MIMO通信的双系统架构,该架构能够预测高速移动用户的轨迹,利用无人机为其提供可靠通信;进一步提出了基于深度强化学习(deep reinforcement learning,DRL)的无人机轨迹设计和地面用户调度方案,在满足各类约束的前提下实现系统总和速率最大化。仿真结果表明,与现有方案相比,所提方案能够有效提升系统容量。     

蜂窝通信中的多用户协作分集

协作分集技术是一种新型的空间分集技术,它通过使多个具有单天线的终端共享彼此的天线,达到获得多天线分集增益的目的.协作分集技术能够提高系统的容量,降低系统的误码率.本文主要介绍了协作分集的概念分类,以及在多用户协作条件下的系统模型.     

多无人机辅助通信中用户匹配与频谱资源联合优化方法

针对多无人机作为空中基站为地面设备提供临时服务的动态频谱分配问题,主要考虑无人机与地面用户匹配、子信道分配和功率分配三个方面。为了保证用户通信的公平性,在考虑频谱复用和共信道干扰的情况下,以最大化地面用户最小传输速率为目标,提出了一种用户匹配与频谱资源联合优化算法来解决上述混合整数非线性优化问题,通过聚类算法优化无人机与地面用户的最佳匹配,通过块坐标下降法迭代优化子信道分配和功率分配。仿真实验分析表明,提出的求解方法可以有效提升用户的传输速率,保证用户通信公平性。     

频率选择性信道下多节点放大转发协作通信中的信道估计方法

针对频率选择性信道下基于正交频分复用(OFDM,orthogonal frequency division multiplexing)技术的多节点放大转发(AF,amplify-and-forward)协作通信,提出了一种基于训练序列的最小二乘信道估计方法,推导出其均方误差性能的下界并给出了相应的最优训练序列方案.同时,该方法选取经功率分配优化后具有恒幅特性的Chu序列作为训练序列,实现了多节点AF协作通信中信道估计的最小均方误差.仿真结果证实了该信道估计方法在多节点AF协作通信环境下的有效性以及所提最优训练序列方案在系统性能上的优越性.     

Joint optimization of source and relay precoding in non‐regenerative MIMO relay systems

We investigate the problem of precoding optimization in an amplify‐and‐forward multiple‐input‐multiple‐output relay system. Most reported works on this problem focus chiefly on the design of relay precoder without simultaneously optimizing the direct link. In this paper, we propose a method for joint source/relay precoder design, taking both direct and relay links into account. Our design is based on maximizing the mutual information (MI) under limited transmission power constraints at the source and relay, respectively. We first formulate a constrained optimization problem before relaxing the original cost function for tractability and derive a MI lower bound. This elaborate bound can asymptotically approach the exact expression of MI in an iterative fashion. In contrast to previous strategies, we then prove that the optimal structure of the source and relay precoders jointly convert the multiple‐input‐multiple‐output relay channel into a bank of single‐input‐single‐output relay channels without having to assume a beamforming structure to simplify the derivation. Specifically, the linear precoding design problem degenerates into power loading among multiple single‐input‐single‐output relay channels. Applying standard Lagrange technique results in a scalar convex optimization, and it can be readily solved by iterative water filling. Numerical examples demonstrate that the proposed scheme, either exploiting partial or full channel state information, significantly outperforms the existing methods. Copyright © 2012 John Wiley & Sons, Ltd.     

On the capacity of MIMO relay channels

We study the capacity of multiple-input multiple- output (MIMO) relay channels. We first consider the Gaussian MIMO relay channel with fixed channel conditions, and derive upper bounds and lower bounds that can be obtained numerically by convex programming. We present algorithms to compute the bounds. Next, we generalize the study to the Rayleigh fading case. We find an upper bound and a lower bound on the ergodic capacity. It is somewhat surprising that the upper bound can meet the lower bound under certain regularity conditions (not necessarily degradedness), and therefore the capacity can be characterized exactly; previously this has been proven only for the degraded Gaussian relay channel. We investigate sufficient conditions for achieving the ergodic capacity; and in particular, for the case where all nodes have the same number of antennas, the capacity can be achieved under certain signal-to-noise ratio (SNR) conditions. Numerical results are also provided to illustrate the bounds on the ergodic capacity of the MIMO relay channel over Rayleigh fading. Finally, we present a potential application of the MIMO relay channel for cooperative communications in ad hoc networks.     

Peroformance analysis of decode-and-forward MIMO relay channels with OSTBCs

Performance analysis is presented for multiple-input multiple-output(MIMO) relay channels employing transmit antenna diversity with orthogonal space-time block codes(OSTBCs),where the source and the destination are equipped with Ns and Nd antennas,and communicate with each other with the help of a multiple-antenna relay operating in decode-and-forward(DF) mode.Over independent,not necessarily identical Rayleigh fading channels,exact closed-form symbol error rate(SER) expressions are derived for various digi...     

MIMO中继下行通信系统中的多目标优化设计

针对通信系统中系统功率消耗和接收信号均方误差(MSE)存在冲突关系,无法同时达到性能最优的情况,采用多目标优化(MOO)框架联合优化系统功率消耗和接收信号MSE.文中考虑两跳的多入多出(MIMO)放大转发(AF)中继下行通信系统.联合优化形成的多目标优化问题是非凸且难以直接求解的,为此,提出一种基于帕累托最优策略的资源分配方法,该方法采用加权切比雪夫法,并引入中继预编码矩阵的一般结构和Schur补引理将优化问题转化为SDP问题.仿真结果验证了所提出方法的有效性,表明其具有更好的性能,同时也给出了系统功耗和MSE性能之间的帕累托最优边界.     

Outage performance of MIMO relay channels with maximal ratio transmission

The outage performance of a multiple-input multiple-output (MIMO) relay system over slow frequency-nonselective fading channels, where maximal ratio transmission is adopted at both the source and relay transmitters whereas maximal ratio combining is used at relay and destination receivers, is investigated. A closed-form expression for the outage probability is presented. Numerical results are presented to verify the analysis.     

Power optimization for maximum channel capacity in MIMO relay system

Introducing multiple-input multiple-output (MIMO) relay channel could offer significant capacity gain.And it is of great importance to develop effective power allocation strategies to achieve power efficiency and improve channel capacity in amplify-and-forward relay system.This article investigates a two-hop MIMO relay system with multiple antennas in relay node (RN) and receiver (RX).Maximizing capacity with antenna selection (MCAS) and maximizing capacity with eigen-decomposition (MCED) schemes are proposed to efficiently allocate power among antennas in RN under first and second hop limited scenarios.The analysis and simulation results show that both MCED and MCAS can improve the channel capacity compared with uniform power allocation (UPA) scheme in most of the studied areas.The MCAS bears comparison with MCED with an acceptable capacity loss, but lowers the complexity by saving channel state information (CSI) feedback to the transmitter (TX).Moreover, when the RN is close to RX, the performance of UPA is also close to the upper bound as the performance of first hop is limited.     

Joint Tx-Rx beamforming design for multicarrier MIMO channels: a unified framework for convex optimization

This paper addresses the joint design of transmit and receive beamforming or linear processing (commonly termed linear precoding at the transmitter and equalization at the receiver) for multicarrier multiple-input multiple-output (MIMO) channels under a variety of design criteria. Instead of considering each design criterion in a separate way, we generalize the existing results by developing a unified framework based on considering two families of objective functions that embrace most reasonable criteria to design a communication system: Schur-concave and Schur-convex functions. Once the optimal structure of the transmit-receive processing is known, the design problem simplifies and can be formulated within the powerful framework of convex optimization theory, in which a great number of interesting design criteria can be easily accommodated and efficiently solved, even though closed-form expressions may not exist. From this perspective, we analyze a variety of design criteria, and in particular, we derive optimal beamvectors in the sense of having minimum average bit error rate (BER). Additional constraints on the peak-to-average ratio (PAR) or on the signal dynamic range are easily included in the design. We propose two multilevel water-filling practical solutions that perform very close to the optimal in terms of average BER with a low implementation complexity. If cooperation among the processing operating at different carriers is allowed, the performance improves significantly. Interestingly, with carrier cooperation, it turns out that the exact optimal solution in terms of average BER can be obtained in closed form.     

Joint relay selection and opportunistic physical layer network coding for two-way relay channels

Wireless Networks - Physical layer network coding can significantly increase the throughput of two-way relay networks. However, fading phenomenon usually causes great asymmetry between two multiple...     

Joint precoding and power allocation for multiuser transmission in MIMO relay networks

This paper proposes a joint precoding and power allocation strategy to maximize the sum rate of multiuser multiple‐input multiple‐output (MIMO) relay networks. A two‐hop relay link working on amplify‐and‐forward (AF) mode is considered. Precoding and power allocation are designed jointly at the base station (BS). It is assumed that there are no direct links between the BS and users. Under individual power constraints at the BS and relay station, precoders designed based on zero forcing, minimum mean‐square error and maximum ratio transmission are derived, respectively. Optimal power allocation strategies for these precoders are given separately. To demonstrate the performance of the proposed strategies, we simulate the uncoded bit error rate performance of the underlined system. We also show the difference of the sum rate of the system with the optimal power allocation strategies and with average power transmission. The simulation results show the advantages of the proposed joint precoding and power allocation strategies as expected. Copyright © 2011 John Wiley & Sons, Ltd.     

频率选择性信道下的MIMO收发机联合设计

研究了频率选择性信道下非块传输多天线系统的线性空间收发机联合设计问题,提出了基于最小均方误差准则(MMSE)的联合最优收发算法.为了避免MMSE算法所需要的收发机迭代计算,还给定MMSE接收机、提出了一种低复杂度的串行搜索迫零(ZF-SS)发射预编码,它能够采用多天线提供的空间资源减小或消除多径信道带来的符号间干扰.仿真分析表明,MMSE算法和ZF-SS算法在高信噪比下的性能明显优于现有的基于特征值的波束形成算法.