一种基于嵌套晶格码的MIMO中继多用户矢量预编码设计

针对多输入多输出(MIMO)中继多用户系统的多址传输问题,为了提高系统可达速率和误码率性能,该文利用嵌套晶格码具有可达加性高斯白噪声信道容量的特性,设计一种基站和中继联合预编码的方法。基站端的嵌套晶格码结合矢量扰动(VP)预编码,以控制发送信号的功率。由于矢量扰动预编码和嵌套晶格码都存在相同的模运算步骤,因此在中继端的模运算抑制噪声功率的同时消除了冗余矢量。接着实现中继联合迫整数预编码方法,这种基站/中继混合预编码技术能够控制等效噪声功率,实现对蜂窝用户的有效信号传输。更进一步地,在给出整系数矩阵和扰动矢量矩阵的计算方法后,以最大化系统可达速率为目标对基站和中继的功率实现最优分配。实验结果表明,该方案在可达速率和误码性能方面优于现有方案。     

双向MIMO中继网络中采用信道独立预编码的自干扰消除技术

双向中继网络在提高频谱效率的同时会引入额外的自干扰,本文针对放大转发（AF）模式下双向多输入多输出（MIMO）中继网络中的自干扰抵消问题,从消除信道估计误差引入的剩余自干扰着手,提出一种采用信道独立预编码的盲干扰抵消（BIC）方案。新方案在源节点对信息进行行空间预编码,从而构建不依赖于MIMO信道矩阵的期望信号子空间和自干扰子空间,实现未知信道状态下自干扰抵消和期望信号分离,从而消除非理想信道估计带来的剩余自干扰信号。在此基础上,以最大化有效信噪比为目标设计最佳预编码,通过推导可达和速率的闭合表达式,分析不同方案下信道估计误差对可达和速率的影响。仿真结果表明,新方案在不同的信道估计误差下,能够实现完美自干扰消除,其检测性能和容量均优于基于信道估计的自干扰消除方案。      

网络-信道联合编码的DmF协作通信技术

提出了一种采用网络-信道编码的解调前传(DmF)协作通信方案.与译码前传(DF)相比,DmF协作方式在中继处只对信号进行解调而非译码,因此,大大降低了中继节点的复杂度.在由两个用户、一个中继节点和一个基站组成的通信模型中,采用LDPC信道编码与网络编码结合的方式,构造了一种DmF协作传输方式.在基站处,通过构造的H矩阵对来自两用户及中继的信号进行联合译码.仿真结果表明:所给方案的性能优于非协作方式及无网络编码的协作通信方式,随着信噪比的增加这种优势会更加明显;另外,DmF的性能与DF的非常接近,但其设备复杂度却大大降低,因此DmF比DF方式更具实用性.同时,该方案在降低设备复杂度、减少延迟、有效对抗无线信道慢衰落、提高通信性能及频谱利用率等方面都是非常有效的.     

菱形中继网络中基于叠加训练的信道估计技术研究

针对放大转发(Amplify-and-Forward, AF)模式下的菱形中继网络,为了高效获取级联和单跳链路信道状态信息(Channel State Information, CSI),本文提出基于叠加训练的信道估计方案,以消除多址接入干扰和训练间互干扰为目标,进行最优的多训练序列设计。新方案将中继训练叠加到源训练序列上,通过对中继识别符号以及中继训练组进行联合优化设计,设计了一种基于频域循环移位的正交扩展序列组生成算法。为了消除非高斯复合噪声对单跳信道估计造成的严重干扰,提出了一种中继噪声消除算法。通过两路中继链路获取的信息副本,能够在端节点实现分集合并,有效提高符号检测性能。仿真实验对比了同类型的信道估计方案,分析验证了方案的有效性。      

基于双向MIMO中继系统的一种预编码策略

为了克服已有的双向MIMO中继系统模型中预编码技术计算量大的缺点,提出了一种基于双向MIMO系统的三时段预编码策略,给出了该策略的模型和算法。该模型的中继节点预均衡各信道状态信息影响(CSI)后将合并信号分时段发送给不同通信节点,简化了传统中继转发矩阵对多信道信息的联合设计。理论计算和仿真结果表明,该策略在性能和复杂度之间得到了良好的折衷     

一种空间相关MIMO信道下的空时预编码方案

在实际的多输入多输出（MIMO：Muhiple Input Multiple Output）移动通信系统中，信道的空间相关性通常会使得现有的空时编码方案难以获得最佳的误码性能。为了解决该问题，本文提出了一种适用于MIMO空间相关信道的空时预编码方案。该方案在完成对发射信号的空时编码后，针对发射天线的空间相关矩阵设计了合理的预编码矩阵，进而能够在保证分集增益的前提下克服相关信道的不利影响。仿真结果证实，该方案能够在一定程度上有效提高整个系统的误码性能。     

有限反馈MIMO下行系统中基于黄金码的传输方案与解码方法

针对有限反馈多输入多输出下行系统,结合黄金码与预编码技术,提出一种新的预编码设计准则、码字选择方案及新的传输方案和相应的低复杂度解码方法。事实上,在充分利用黄金码能够克服信道深度衰落这一特性的基础上,对所选预编码码字进行重新构造,得到一个二重预编码矩阵,将其作为发送信号,从而能够实现线性解码。与此同时,针对传统的MIMO下行系统传输方案提出了ML和MMSE的联合解码方法,使其能通过一个门限值动态地调节解码复杂度。数值仿真结果证明了本文所提方案性能的优越性。     

MIMO多中继系统中基于不完全信道状态信息的预编码算法研究

针对配置多个中继节点的多输入多输出（Multiple-input Multiple-Output,MIMO）系统,提出一种不完全信道状态信息（Imperfect channel state information,CSI）下基于最小均方误差（Minimum Mean-Squared Error,MMSE）准则的预编码设计方案,该方案综合考虑各个节点天线之间的相关性及信道估计误差。由于各个中继端预编码矩阵之间可视为相互独立,故将约束优化问题转化为若干半正定规划问题,继而通过内点法或CVX工具箱求解预编码矩阵,然后采用求导法推导出接收端处理矩阵。最后利用迭代算法交替迭代来联合优化预编码矩阵和接收端处理矩阵,直到算法收敛。仿真结果表明,与未能综合考虑各个节点的预编码算法相比,本文提出的算法能明显改善系统BER性能。      

基于两阶段的毫米波大规模MIMO低复杂度混合预编码算法

针对现有基于矩阵分解的混合预编码算法信道容量有损和算法复杂度高的问题,本文提出了一种基于两阶段的低复杂度混合预编码算法.该算法分为获取最优全数字预编码器和求解混合预编码器两部分.首先,本文联合奇异值分解(Singular Value Decomposition,SVD)与注水算法以容量无损的要求设计最优全数字预编码矩阵.其次,为了降低搜索超完备矩阵列的复杂度,提出两阶段混合预编码(Two?Stage Hybrid Precoding,TS?HP)算法求解混合预编码矩阵.第一阶段,根据天线阵列响应矩阵的相关性获取模拟预编码矩阵备选集;第二阶段,利用贪婪搜索对备选集进行搜索构建混合预编码矩阵.仿真结果表明,所提算法能够有效改善系统性能,降低复杂度.     

MIMO中继系统中预编码的级联算法

在两跳MIMO中继通信系统的预编码相关研究中,提出了一种级联预编码算法,该算法把两跳系统的预编码分解成两个独立的部分,从而把预编码问题转化成为求源节点到中继节点的预编码过程以及中继节点到目的节点的过程。本文使用MMSE准则,在简化迭代算法复杂度的同时,与一种只在中继节点进行联合优化的算法进行比较,由仿真可以看出,本文算法有一定的性能提升。     

Robust Tomlinson-Harashima Precoding for Two-Way Relaying

Most of the non-linear transceivers, which are based on Tomlinson-Harashima (TH) precoding and have been proposed in the literature for two-way relay systems, assume perfect channel state information (CSI). In this paper, a novel and robust TH precoding scheme has been investigated for two-way relay systems, with multiple antennas at the transceiver and relay nodes. We assume imperfect CSI and the channel uncertainty is bounded by a spherical region. The minimum mean square error at the destinations is used as the design criterion and we develop an iterative method to solve this nonconvex problem to obtain TH precoding matrices at the transmitter, linear precoding matrix at the relay and linear equalizer at the destination nodes, where each subproblem is convex. Simulations are provided to evaluate the performance and to validate the efficiency of the proposed scheme.

     

Precoding and decoding design for two-way MIMO AF multiple-relay system

In this paper, a joint precoding and decoding design scheme is proposed for two-way Multiple-Input Multiple-Output (MIMO) multiple-relay system. The precoding and decoding matrices are jointly optimized based on Minimum Mean-Square-Error (MMSE) criteria under transmit power constraints. The optimization problem is solved by using a convergent iterative algorithm which includes four sub-problems. It is shown that due to the difficulty of the block diagonal nature of the relay precoding matrix, sub-problem two cannot be solved with existing methods. It is then solved by converting sub-problem two into a convex optimization problem and a simplified method is proposed to reduce the computational complexity. Simulation results show that the proposed scheme can achieve lower Bit Error Rate (BER) and larger sum rate than other schemes. Furthermore, the BER and the sum rate performance can be improved by increasing the number of antennas for the same number of relays or increasing the number of relays for the same number of antennas.     

Joint Source/Relay Precoder Design in Nonregenerative Cooperative Systems Using an MMSE Criterion

This paper considers transmitter precoding in an amplify-and-forward cooperative system where multiple antennas are equipped at the source, the relay, and the destination. Existing methods for the problem only consider the design of the relay precoder. To further improve the performance, we include the source precoder into the design. Using a minimum-meansquare- error (MMSE) criterion, we propose a joint source/relay precoder design method, taking both the direct and relay links into account. It is shown that the MMSE is a highly nonlinear function of the precoding matrices, and a direct minimization is not feasible. To facilitate analysis, we propose to design the precoders toward first diagonalizing the MSE matrix of the relay link. This imposes certain structural constraints on both precoders that allow us to derive an analytically tractable MSE upper bound. By conducting minimization with respect to this bound, the solution can be obtained by an iterative water-filling technique.     

Efficient Beamforming by SLNR Maximization for Dual-Hop Relay Assisted MIMO Network

Relay beamforming is a key signal processing technique to mitigate interference in single and multiuser multiple input and multiple output (MIMO) wireless communication networks. In MIMO relay networks interference cancellation is an essential task of the study to get optimal network capacity. In this paper, the problem of interference resulted from leakage signal from desired signal for intended antenna, which causing interference to other antennas of the same user with multiple antennas is tackled. The criterion of signal to leakage plus noise ratio (SLNR) maximization is considered to design a vector by vector relay downlink precoding based on Fukunaga Koontz transform. This can control the interference among multiple antennas and maximize SLNR. However, matched filter beamforming is utilized at the relay receiving side that can increase output signal to noise ratio at the relay node. The channel state information of both the channel between source to relay and relay to destination is assumed at the relay node. The effectiveness of the proposed technique is studied and compared with conventional relay precoding techniques. Simulation is carried out in MATLAB environment using ideal channel conditions. This study demonstrates that, the proposed scheme for relay assisted MIMO networks can improve overall system performance in terms of ergodic capacity.     

一种基于预编码的AF多中继协作通信系统信道估计方法

针对瑞利平坦衰落信道下AF多中继协作通信系统,提出了一种基于预编码的分段式信道估计方法.该方法分两个阶段对S-R和R-D两个链路的信道状态信息进行估计,利用在中继端进行预编码,使中继节点可同时向目的节点发送训练序列.仿真结果表明,提出的方法可有效地估计出两段链路的信道状态信息,减小了训练时隙的开支,缩短了信道估计时间.     

Orthogonal superimposed training design for block transmission over frequency‐selective fading channels

Channel estimation for single‐carrier block transmission over frequency‐selective fading channel using superimposed training is addressed. A novel affine precoding model based on orthogonal polyphase sequence set is designed to decouple channel estimation from symbol detection. The orthogonal constraints on the training and precoding matrices ensure the separation of superimposed signals and accurate channel estimation with less training overheads as compared with time‐multiplexed scheme. Simulation results show that the proposed scheme exhibits good performance and outperforms another data‐dependent superimposed training scheme, especially for compact constellations or channel with long delay‐spread. Copyright © 2014 John Wiley & Sons, Ltd.     

Precoder Design for Non-Regenerative MIMO Relay Systems

This paper studies the precoder design for a 3-node non-generative MIMO relay channel, taking the direct link transmission into consideration. We first look into the scenario where precoding is only performed at the relay. Our analytical approach enables a relay precoding design to achieve better ergodic capacity than the precoding design to achieve a lower bound of the capacity reported in earlier works. We next propose an iterative algorithm to perform joint precoding design at both the source and the relay. To reduce the computation complexity of the iterative algorithm, a two-step algorithm is then developed. Our numerical results show that under some circumstances, capacity gain can be achieved by performing precoding at both the source and the relay compared to the case where precoding is performed at the relay only. The efficiency of the proposed two-step algorithm is verified since it achieves roughly identical capacity as the iterative joint precoding scheme.     

Physical-layer network coding in k-users MIMO-Y two-way relay channels

In order to exchange information among k users using the technology of physical-layer network coding in the multiple input multiple output Y two-way relay channels,the GSA-GSA scheme was proposed,using the technology of general signal alignment during the uplink and the downlink.The signals were exchanged between every source node align in a transformed subspace,rather than the direct subspace.This was realized by jointly designing the precoding matrices at all source nodes and the processing matrix at the relay.The constraints of the number of sending and receiving antennas and the sum rate of proposed scheme were analyzed.In simulation,it can figure out that the proposed scheme needs fewer antennas in the whole system and can improve the achievable system sum rate under the same SNR and degrees of freedom.     

一种前向放大中继通信系统中的有限反馈中继预编码方案

 本文首先给出了前向放大中继通信系统中,在给定QoS要求下的最优中继预编码矩阵的设计. 进而,针对实际通信系统中反馈信道带宽的限制,给出了一种有限反馈中继预编码码本的设计方案. 计算机仿真表明,本文所提新码本有限反馈中继预编码方案的系统性能随着反馈比特数的增加接近完全反馈下的系统性能,且在相同反馈比特数下的系统容量和误码率均明显优于将传统MIMO通信系统中的Grassmannian码本或随机码本直接应用于中继预编码的有限反馈方案.