协同中继传输处理技术研究

协同通信技术能够有效抵抗信道衰落、提高系统容量、扩大系统覆盖范围,广泛应用于蜂窝移动网络,无线传感器网络,及车到车通信等。特别是协同中继传输协议,已经成为近年来研究的热点。虽说目前有关协同中继传输协议的研究已经取得了一些成果,但是很多中继传输协议都有各自的局限性及不足之处。因此,对协同中继传输处理技术进行更深一步的探讨和研究是十分必要的。文章对现有的各种中继传输协议进行归纳总结,并指出其优缺点以及中继传输协议的研究方向。     

基于部分协作检测的 MIMO 中继系统

为了降低多输入多输出（MIMO）中继传输系统中中继节点进行信号处理和转发的运算复杂度,提升系统整体性能,在全检测转发（FDF）技术的基础之上,提出了一种基于树的遍历的部分协作检测（CPD）算法,采用本算法的中继节点只转发部分信噪比较高的信息流,不仅降低了中继转发的负担同时还去除了一些经历了深度衰落的信号。仿真结果显示,和国外同类典型研究相比较,中继节点的负担大大降低,同时传输系统的性能有了明显提升。     

一种采用复合中继激励的协作下行传输机制

为了解决现有中继激励机制中长期回报存在不确定性,以及即时回报导致资源利用效率降低的问题,该文针对协作下行通信系统提出一种复合中继激励机制(CCRI)。首先利用链路不平衡产生的瓶颈,将第1跳链路超过第2跳的数据速率部分作为即时回报,用于中继节点自身数据的传输;同时针对即时回报量不足,过量或瓶颈存在于第1跳导致即时回报失效的情况,采用基于比例公平的长期回报作为补充,进一步调整中继节点的调度权重。仿真结果表明,所提机制能够给予中继节点合理的回报,并实现系统频谱效率和生存时间,以及中继能量效率的改善。     

基于分布式中继选择的自适应协作传输方案

协作分集通过使网络用户共享彼此天线以形成虚拟多天线阵列,可以显著提高网络容量,然而针对网络拓扑的动态变化与无线传输的时变特性,仅靠协作分集并不能十分有效地解决这些问题,必须结合考虑相应的自适应传输策略.本文提出动态网络环境中协作中继的最佳选择准则,在此基础上给出最佳协作中继的分布式选择协议.根据协作中继与源节点间的无线信道质量,进一步提出一种自适应协作传输方案,以有效抵抗多用户网络环境中的无线衰落.此外,对自适应协作传输方案的误码性能,在瑞利衰落信道下进行相应的理论分析,得到了系统误比特率的解析表达式,据此给出数值仿真实验以进行性能比较.结果表明:相对于传统协作分集而言,本文提出的自适应协作传输方案获得了进一步的性能增益,误比特率显著下降.     

协同安全传输系统中最佳中继选择技术研究

对于中继不可信的多中继协同传输模型,主要针对如何构建协同安全系统,即利用人工干扰实现系统安全时的协同策略问题.协同系统构建完成后,又考虑了各中继节点间如何进行功率分配来提高系统安全性问题.分别采用等功率分配与最佳功率分配的方式,分析了不同中继节点分布场景下,最佳中继节点选择.结果表明,采用人工干扰的方式能够保证系统的安全传输,最佳中继的选择能够提高系统的安全性能.     

协同信道空时优化MIMO无线传输系统

该文提出一种基于虚拟信道的空时优化多输入多输出(MIMO)无线传输系统。通过在发射端产生不同的空时虚拟信道,与实际空间无线信道级联,构成系统的整体传输信道即协同空分信道。系统可以根据接收端的反馈信息采用模拟退火算法来优化虚拟信道,改善误码率(BER)性能。利用虚拟信道方法,可以使一根MIMO发射天线在同一时间、同一频段传输多路叠加合并后的数据信号,从而可以使发射的不同数据信号的总路数超过发射天线的数量,突破了现有MIMO系统在同一时间、同一频段最多只能发射与发射天线数量相等的不同数据信号的传统方式,可以显著提高系统的频谱效率。仿真结果和基于ZC706和AD9361硬件平台的微波暗室实际测试结果充分验证了新MIMO系统的有效性。     

An Energy-Efficient Relay Selection Strategy Based on Optimal Relay Location for AF Cooperative Transmission

In this paper, an energy-efficient optimal relay selection strategy which is jointly optimized with the energy-efficient optimal power allocation scheme for AF cooperative transmission is proposed. The relay selection criterion is the distance from the potential relay to the corresponding optimal relay locations where the minimum transmission power of the source, the relay or their total can be achieved. In order to determine the optimal relay locations, a universal algorithm with low computational complexity and easy implementation is also presented. Simulations are conducted to validate our theoretical analysis. The results show that with the relay selected by the proposed strategy, the cooperative transmission can achieve considerably high energy-efficiency.     

Opportunistic Relay Selection in Cooperative Systems With Dirty-Paper Coding

This paper investigates an optimization of the conventional relay selection for multirelay environments. In contrast with previously reported selection schemes, where a selected relay accesses the channel in a dedicated cooperative slot, the proposed scheme recovers the bandwidth loss of the half-duplex constraint by allowing two relays to simultaneously access the channels. Based on an appropriate dirty-paper coding (DPC) technique among relays, the proposed scheme enables a relay to establish communication with the destination at the same time that another relay forwards the data from the source. It is proven that the interplay between relay selection and the superposition DPC weight factor provides a tradeoff between relaying and new data performance. Hence, an appropriate codesign of the superposition DPC parameter and opportunistic relay selection can achieve efficient communication for the new data without affecting the relaying performance. The proposed scheme is compared with conventional relaying approaches, and its enhancements are provided through theoretical studies and numerical results.      

Differential Modulation and Relay Selection With Detect-and-Forward Cooperative Relaying

In this paper, we consider the bit error rate (BER) performance analysis of a cooperative relay communication system with differential modulation and selective relaying, where the best relay is selected to forward the signals from the source to the destination. The advantage of differential modulation is that it allows noncoherent detection without requiring the full channel-state information (CSI), as obtaining CSI in a cooperative communication system at each node is a complicated and costly task. We consider a simple detect-and-forward (DetF) relay system and take into account the effect of imperfect detection at the relay. We derive the average bit error probability of the DetF relay scheme by using the closed-form relay link signal-to-noise ratio (SNR). Based on the analysis, we show that the proposed system with $N$ relay nodes and the simple relay selection can achieve a total diversity gain of $N + 1$. The BER performance of the system is also evaluated by simulation. It is shown that the analysis matches well with the simulation results.      

Performance Analysis of OSTBC Transmission in Amplify-and-Forward Cooperative Relay Networks

A performance analysis is presented for amplify-and-forward (AF) cooperative relay networks employing transmit antenna diversity with orthogonal space-time block codes (OSTBCs), where multiple antennas are equipped at the transmitter. We develop a symbol-error-rate (SER) and outage performance analysis for OSTBC transmissions with and without cooperative diversity over flat Rayleigh fading channels. We first derive exact probability density functions (pdf's) and cumulative distribution functions (cdf's) for the system SNR without direct transmission with an arbitrary number of transmit antennas and then present the exact closed-form SER and outage probability expressions. Next, we derive the moment-generating function (MGF) for the overall system SNR with direct transmission and present the exact SER and outage probability with joint transmit antenna diversity and cooperative diversity. The theoretical analysis is validated by simulations, which indicate an exact match between them. The results also show how the transmit antenna diversity and the cooperative diversity affect the overall system performance.      

Worst-Case Robust MIMO Transmission With Imperfect Channel Knowledge

In this paper, we consider robust transmit strategies, against the imperfectness of the channel state information at the transmitter (CSIT), for multi-input multi-output (MIMO) communication systems. Following a worst-case deterministic model, the actual channel is assumed to be inside an ellipsoid centered at a nominal channel. The objective is to maximize the worst-case received signal-to-noise ratio (SNR), or to minimize the worst-case Chernoff bound of the error probability, thus leading to a maximin problem. Moreover, we also consider the QoS problem, as a complement of the maximin design, which minimizes the transmit power consumption and meanwhile keeps the received SNR above a given threshold for any channel realization in the ellipsoid. It is shown that, for a general class of power constraints, both the maximin and QoS problems can be equivalently transformed into convex problems, or even further into semidefinite programs (SDPs), thus efficiently solvable by the numerical methods. The most interesting result is that the optimal transmit directions, i.e., the eigenvectors of the transmit covariance, are just the right singular vectors of the nominal channel under some mild conditions. This result leads to a channel-diagonalizing structure, as in the cases of perfect CSIT and statistical CSIT with mean or covariance feedback, and reduces the complicated matrix-valued problem to a scalar power allocation problem. Then we provide the closed-form solution to the resulting power allocation problem.     

基于聚类的无线传感网络的合作MIMO传输方案

Wireless sensor network is becoming more and more popular in recent years, but energy-constrained characteristic of sensor nodes is one of the critical issues that we must consider in system design. In this paper, a cluster-based virtual V-BLAST transmission scheme is proposed to achieve energy savings for energy-constrained wireless sensor networks. In the proposed scheme, instead of using cluster member as cooperative nodes, multiple cluster heads cooperate to form virtual antenna array so that V-BLAST based virtual MIMO transmission can be implemented. Based on the communication energy consumption model, a way to optimize the parameters for the scheme is given. In addition, detailed simulation is performed to evaluate the performance of the proposed scheme for both densely and sparsely deployed sensor networks. Theoretical analysis and simulation results verify the energy efficiency of the proposed scheme.     

On the Gaussian MIMO Relay Channel With Full Channel State Information

This paper addresses the problem of source and relay transmit covariance optimization on the Gaussian MIMO relay channel with full channel state information (CSI), i.e., assuming perfect knowledge of all channels. For full-duplex relaying, we show that the cut-set bound on capacity can be computed as the solution of a convex problem, thus providing a tighter bound than previously published. For time division duplex (TDD) relaying, both upper and lower bounds on capacity are derived, and the transmit covariance matrices are optimized for decode-and-forward (DF) strategies with either partial or full decoding at the relay. A generic procedure is introduced to formulate these problems into a standard convex form, and to solve them efficiently. Suboptimum precoders are also proposed which have a specific matrix structure that either leads to a closed-form expression or at least reduces the dimension of the optimization problem. Practical aspects related to transmit power constraints and CSI availability are then discussed. Finally, simulations in a cellular downlink scenario show that the partial DF strategy can achieve a rate very close to capacity for realistic values of the source to relay SNR, and that the rate loss due to suboptimum precoder structures remains small for typical antenna configurations.      

多天线系统中多中继传输的时间分配和功率分配优化方法

本文考虑单小区内的两个中继使用解码转发的方法为两个用户提供下行数据的场景,基站和中继配置多根天线,用户配置单天线。两中继使用相同的频率资源同时为两个用户提供服务。为减小两中继同时向两用户传输时产生的干扰,中继到用户的传输采用协作干扰避免的策略;相应的基站到中继的传输采用多用户空分复用的传输策略。本文在时间分配和功率分配两个方面对上述两跳传输过程进行了优化,提出了两跳传输最优的时间分配策略。由于功率分配最优化问题难以求解,本文提出了一种匹配链路容量的次优功率分配方法,并对其进行简化以降低复杂度。通过仿真可以看出,简化的功率分配方法与匹配链路容量的功率分配性能很接近;所提出的时间分配和功率分配方案可以获得有效的性能提升。      

MIMO解码转发双向中继系统中的传输策略与中断概率分析

在多输入多输出(MIMO)解码转发(DF)双向中继系统中,分别设计了两种信道状态信息(CSI)情况下的系统传输策略,并推导了系统中断概率的闭合表达式.当已知完全CSI时,采用(最大比发送-最大比接收)MRT-MRC技术设计波束形成和合并向量;当未知完全CSI时,设计了基于有限反馈的传输策略,并采用随机向量量化和Grassmann两种码本进行数值仿真验证.仿真结论显示,所设计的双向中继传输策略的中断概率性能明显优于其他策略,所推导的闭合表达式能准确地表征系统中断概率性能.     

MIMO协同中继系统中的最大似然合并解调算法

协同中继系统通过合并解调不同路径的信号副本,得到比非协同系统更优的误码性能。传统的合并解调算法将合并解调过程分开处理,性能较差。该文针对多输入多输出（MIMO）放大转发协同中继系统,基于最大似然（ML）准则,提出了在目的节点对来自源节点和中继节点的信号进行合并解调的新算法。该算法首先对来自源节点和中继节点的信号进行ML合并,然后采用传统的MIMO最大似然检测完成信号的解调。分析与仿真结果表明,与最大比合并（MRC）等算法相比,在不同调制方式和信道条件下,所提算法均获得了显著的性能增益,且高阶调制下的复杂度低。      

WSN中一种基于能量效率的协同中继传输方案

本文针对分簇无线传感器网络,提出了一种基于能量效率的协同中继传输方案,该方案中源簇头根据源到邻簇头之间的信道状态信息选择最优中继节点;协同传输数据时,目的节点接收到两个时隙的信号后进行最大比合并,并根据设定的接收信噪比门限范围在确认帧中给中继节点反馈功率调整信息,以减少重传次数或降低中继节点的发射功率,在不增加开销的情况下可以减少系统总的能量消耗。文章利用概率密度函数推导了基于部分信道状态信息选择中继协同的误符号率闭式表达式,最后通过蒙特卡洛仿真进行了验证。结果表明:误符号率的理论推导值与仿真值一致,在相同的接收信噪比门限时,本文所提方案能够明显提高系统的能效性。      

多跳协同中继网络下物理层安全传输方案

针对多跳中继传输系统的信息安全传输问题,提出了一种基于全双工模式下多节点协作干扰(FD-MCJ)的物理层安全传输方案.该方案利用通信网络中的中继节点发送干扰信号恶化窃听节点的接收性能,同时中继节点根据信道状态信息(Channel State Information,CSI)自适应的选择两种情况下的安全传输方案.本文首先...