Lattice-reduction-aided MMSE precoding for correlated MIMO channels and performance analysis

The lattice-reduction (LR) has been developed to improve the performance of the zero-forcing (ZF) precoder in multiple input multiple output (MIMO) systems. Under the assumptions of uncorrelated flat fading channel model and perfect channel state information at the transmitter (CSIT), an LR-aided ZF precoder is able to collect the full transmit diversity. With the complex LenstraLenstra-Lova′sz (LLL) algorithm and limited feedforward structure, an LR-aided linear minimum-mean-square-error (LMMSE) precoder for spatial correlated MIMO channels and imperfect CSIT is proposed to achieve lower bit error rate (BER). Assuming a time division duplexing (TDD) MIMO system, correlated block flat fading channel and LMMSE uplink channel estimator, it is proved that the proposed LR-aided LMMSE precoder can also obtain the full transmit diversity through an analytical approach. Furthermore, the simulation results show that with the quadrature phase shift keying (QPSK) modulation at the transmitter, the uncoded and coded BERs of the LR-aided LMMSE precoder are lower than that of the traditional LMMSE precoder respectively when E b / N0 is greater than 10 dB and 12 dB at all correlation coefficients.     

大规模MIMO系统中分布式压缩感知LMMSE信道估计

大规模多输入多输出(multiple input multiple output, MIMO)系统中，信道估计算法复杂度随着基站侧天线数量的增加而急剧增加, 针对需要在信道估计算法复杂度与算法性能之间进行折中的问题，提出分布式压缩感知线性最小均方误差(distributed compressed sensing linear minimum mean square error, DCS-LMMSE)算法。该算法利用信道的空时共稀疏性, 首先根据先验支撑集信息将接收信号分为密集部分和稀疏部分, 然后分别采用不同的算法进行初始信道估计, 最后采用奇异值分解代替信道相关矩阵求逆进一步降低DCS-LMMSE算法复杂度。所提算法与传统线性最小均方误差算法相比明显地降低了计算复杂度。仿真结果表明, 所提算法与纯压缩感知稀疏信道估计算法相比具有更好的性能。     

MC-CDMA系统中基于粒子群算法的多用户检测

提出了一种频率选择性信道下使用多天线分集接收的多载波码分多址(MC-CDMA)系统中基于粒子群算法(PSO)的多用户检测(MUD).当采用多天线分集接收时,各个天线接收的信号经历了相互独立的衰落,导致不同天线分支对应的匹配度函数相互独立.为解决多天线分集接收的多目标优化问题,提出了虚拟Pareto前端的概念,并使粒子按照Pareto优化准则进行速度和位置更新.仿真结果表明,所提方案获得了增强的开发和探索能力,其性能优于常规粒子群算法和多目标遗传算法.     

OFDM水声通信中基于压缩传感的稀疏信道估计

针对正交频分复用(orthogonal frequency division multiplexing, OFDM)水声通信中常规的最小均方（least square, LS）信道估计方法需要大量训练导频且得不到较高估计精度的问题,提出了一种基于压缩传感原理的OFDM稀疏水声信道估计方法。该方法首先以正交短时傅里叶基构成的训练波形为OFDM的导频来“感知”信道,然后利用压缩传感技术的稀疏重构算法来对信道进行重构。〖JP2〗基于实测水声信道的仿真结果表明,在相同估计精度前提下,基于压缩传感的信道估计方法较常规的LS算法所需训练导频数得到大幅度减小,传输效率得以提高,且对噪声的鲁棒性增强,较好地适应了双扩展稀疏水声信道,尤其适用于动平台OFDM水声通信系统。     

Hybrid pilots assisted channel estimation algorithm for MIMO-OFDM systems

Abstract: A hybrid pilots assisted channel estimation algorithm for multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems under low signal-to-noise ratio (SNR) and arbitrary Doppler spread scenarios is proposed. Motivated by the dissatisfactory performance of the optimal pilots (OPs) designed under static channels over multiple OFDM symbols imposed by fast fading channels, the proposed scheme first assumes that the virtual pilot tones superimposed at data locations over specific subcarriers are transmitted from all antennas, then the virtual received pilot signals at the corresponding locations can be obtained by making full use of the time and frequency domain correlations of the frequency responses of the time varying dispersive fading channels and the received signals at pilot subcarriers, finally the channel parameters are derived from the combination of the real and virtual received pilot signals over one OFDM symbol based on least square (LS) criterion. Simulation results illustrate that the proposed method is insensitive to Doppler spread and can effectively ameliorate the mean square error (MSE) floor inherent to the previous method, meanwhile its performance outmatches that of OPs at low SNR region under static channels.     

基于嵌入式码流UEP的有噪信道图像传输方法

针对基于嵌入式码流不等差错保护(unequal error protection, UEP)的有噪信道图像传输,提出了一种码率分配方案(rate allocation scheme, RAS)边信息编码传输方法,分析了其实际可达最优传输性能。首先,给出了考虑RAS边信息传输的信源建模、系统性能评价和最优RAS求解方法。然后,进一步证明了最优RAS具有码率分段的形式,提出了一种有效的基于游程长度编码的压缩编码方法。最后,采用所提出的边信息编码传输方法,分析了不同传输策略下的图像传输方法实际可达最优性能,可得到相应的系统设计准则。     

Equivalent Joint Space-Time Multiuser Detection for Uplink ISI-Corrupted Multicarrier CDMA Systems with Arbitrary Antenna Arrays

The multicarrier code division multiple access (MC-CDMA) systems without cyclic prefix (CP) hold a fine spectral efficiency though they are unavoidably corrupted by the intersymbol interference (ISI) over the finite impulse response (FIR) channel. We call MC-CDMA systems without CP the ISI-corrupted MC-CDMA systems in some sense. Considering the fact that combining antenna arrays with so-called ISI-corrupted MC-CDMA systems is advantageous in suppressing cochannel interference in cellular communication systems, this paper investigates ISI-corrupted MC-CDMA systems with base station antenna arrays. Joint space-time multiuser detection (MUD) schemes for DS-CDMA systems with antenna arrays have drawn much attention recently. Based upon them, we can derive the equivalent joint spatial-temporal MUD scheme for ISI-corrupted MC-CDMA systems with antenna arrays. In order to achieve this goal, an equivalent space-time estimation method of uplink vector channel is first derived for the ISI-corrupted MC-CDMA syste     

在衰减信道中基于最小贝叶斯风险的检测算法

针对实际检测过程中本地检测器至融合中心传输信道的非理想性,提出了基于两种非理想信道模型的分布式检测算法:第一种为融合中心已知非理想信道的瞬时状态信息;第二种为融合中心已知非理想信道的统计特性。通过最小化平均贝叶斯风险来设计本地检测器和融合中心的优化判决算法,其判决形式都可简化为似然比判决。最后通过仿真表明第二种模型的检测性能略低于第一种模型,但其计算量却大大降低。     

考虑渠道碳排放差异的零售商渠道选择策略

考虑由制造商、零售商和具有低碳环保意识的消费者组成的供应链,其中零售商主导供应链,并在纯实体渠道、纯网络渠道和双渠道三种策略中进行选择.本文建立考虑渠道间碳排放差异和销售成本差异的供应链决策模型,研究零售商的最优渠道选择策略.研究发现:实体渠道与网络渠道的单位碳排放差异是影响零售商渠道选择策略的重要因素之一.特别地,给定其他因素,随着实体渠道相对于网络渠道的单位碳排放水平增加,零售商应依次选择纯实体渠道、双渠道、纯网络渠道.而渠道间碳排放差异对零售商渠道选择策略的影响也会受到渠道间销售成本差异的调节.进一步分析零售商最优定价决策发现:当零售商选择双渠道策略时,随着实体渠道相对于网络渠道单位碳排放水平的增加,零售商应降低实体渠道销售价格,而最优网络渠道销售价格依赖于渠道间碳排放差异的大小.同时,零售商可通过开通新渠道来影响制造商的最优批发价格,从而增加零售商自身的利润.     

#br# 基于POMDP的机载网络信道接入策略研究

针对机载网络随机竞争类媒介接入控制(medium access control,MAC)协议在网络负载较重时性能下降严重、接入门限值设置缺乏理论依据和多优先级业务服务质量无法有效支持等问题,提出一种基于部分可观测马尔可夫决策过程的信道接入策略。在以不同优先级分组占用信道代价作为目标函数的基础上建立动态规划方程,采用状态空间压缩方法对问题求解进行简化,得到各优先级分组间理论近似最优接入门限值的数学表达式,可为不同优先级分组的接入决策过程提供理论依据并实现接入冲突的有效控制。仿真结果表明,该算法能够有效提高数据传输的时延、成功概率等性能,满足军事航空通信中数据传输的实时性和可靠性需求。     

可重构智能表面通信系统的渐进信道估计方法

针对现有可重构智能表面(reconfigurable intelligent surface,RIS)的信道估计方法中反射系数为随机配置而导致接收端信噪比较低的问题,提出一种配置特定反射系数的渐进式信道估计方法.该方法利用非完整信道状态信息(channel state information,CSI)计算出当前时刻下的...     

基于不完全信道信息的MIMO双向中继系统线性预编码算法#br#

针对配置两个通信节点的多输入多输出双向中继系统,提出一种基于不完全信道状态信息的预编码设计方案,该方案综合考虑信道估计误差与信道反馈延迟的情况。在中继发射功率受限的条件下,以最小均方误差为准则设计以预编码矩阵为变量的优化问题,提出矩阵分解和联合迭代两种线性预编码算法。矩阵分解法通过矩阵分解推导得到中继矩阵的闭式解;联合迭代法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,直到算法收敛数。仿真结果表明,随着信噪比由0到25 dB逐渐增大,与现有方案相比,矩阵分解法能有效地降低系统的误比特率,联合迭代法能获得最佳的系统性能提升。     

LTE-A中的SLNR联合校准多用户多流波束赋形方案

提出了一种长期演进项目的后续演进（long term evolution-advanced, LTE-A）中的信漏噪比联合校准多用户多流波束赋形方案。基于信漏噪比准则进行波束赋形消除多用户间干扰,实现LTE A下的多用户多流波束赋形传输;建立信道校准机制,补偿实际通信系统中的射频增益影响,恢复信道互易性,提升实际通信系统中的误码率性能。在适用于LTE-A的空间信道扩展模型(spatial channel model extension, SCME)信道环境下进行了仿真,仿真结果表明,该方法相比常用的基于信干噪比准则的块对角化方案误码率性能有明显提升,且能在存在射频增益影响的非理想环境中恢复信道互易性,提升系统传输性能。     

Evolutionary algorithm based index assignment algorithm for noisy channel

A globally optimal solution to vector quantization (VQ) index assignment on noisy channel, the evolutionary algorithm based index assignment algorithm (EAIAA), is presented. The algorithm yields a significant reduction in average distortion due to channel errors, over conventional arbitrary index assignment, as confirmed by experimental results over the memoryless binary symmetric channel (BSC) for any bit error.     

水声信道非线性均衡的研究

对浅海信道传输的声信号进行深入分析,在对判决反馈均衡(DFE)算法进行分析的基础上,对稀疏权DFE均衡器信道估计的均方误差(MSE)、信道的稀疏估计等进行了分析研究,并对信道进行了稀疏化估计,对全阶均衡器和稀疏权均衡器进行了仿真,证明对非线性均衡器结构进行稀疏化是可行的,降低了算法复杂性,并使由此造成的性能下降限定在一定的范围内。     

Toeplitz矩阵有限等距特性研究

在压缩感知热潮的影响下,观测矩阵的有限等距特性（restricted isometry property, RIP）也受到广泛关注。大多数理论研究表明高斯随机矩阵是满足RIP特性的,但由于其存储成本较高,物理实现较复杂,在实际使用中托普利兹（Toeplitz）随机矩阵由于可以使用快速离散傅里叶变换实现而受到青睐。该文将图论中点均匀着色定理和盖尔圆盘定理应用于压缩感知中,对托普利兹观测矩阵的RIP特性进行了证明,证明结果表明,由服从某种特定概率分布的项构造的Toeplitz矩阵以较大概率满足有限等距特性。最后,对最小二乘算法（least square,LS）、线性最小均方误差（linear minimum mean square error,LMMSE）算法和高斯观测矩阵的压缩感知算法以及Toeplitz观测矩阵的压缩感知算法进行了对比分析,Toeplitz观测矩阵的压缩感知算法在性能方面要优于高斯观测矩阵的压缩感知算法和传统算法,运算复杂度方面要优于高斯随机矩阵,为压缩感知实现无失真地重构原始信号提供了理论和应用参考。     

基于WIA-PA的无线总线多信道调度算法

针对无线总线替代有线总线所带来的网络实时性和吞吐量下降的问题,充分利用无线信道提供的众多信道,在媒体接入控制(media access control, MAC)层提出了一种多信道调度算法。该算法在星型拓扑下将每个通信周期分为载波侦听多路访问(carrier sense multiple access,CSMA)阶段和时分多址(time division multiple access,TDMA)阶段。在CSMA阶段,基于不同优先级的灵活接入使得节点间发生碰撞的可能性大大降低。在TDMA阶段,基于全局队列的最早截止时间优先(earliest deadline first, EDF)调度使得信道利用率明显提高。仿真结果表明:提出的多信道MAC调度算法可以有效提高网络的实时性和吞吐量。     

Improved H-infinity channel estimator based on EM for MIMO-OFDM systems

H-infinity estimator is generally implemented in timevariant state-space models,but it leads to high complexity when the model is used for multiple input multiple output with orthogonal frequency division multiplexing (MIMO-OFDM) systems.Thus,an H-infinity estimator over time-invariant system models is proposed,which modifies the Krein space accordingly.In order to avoid the large matrix inversion and multiplication required in each OFDM symbol from different transmit antennas,expectation maximization (EM) is developed to reduce the high computational load.Joint estimation over multiple OFDM symbols is used to resist the high pilot overhead generated by the increasing number of transmit antennas.Finally,the performance of the proposed estimator is enhanced via an angle-domain process.Through performance analysis and simulation experiments,it is indicated that the proposed algorithm has a better mean square error (MSE) and bit error rate (BER) performance than the optimal least square (LS) estimator.Joint estimation over multiple OFDM symbols can not only reduce the pilot overhead but also promote the channel performance.What is more,an obvious improvement can be obtained by using the angle-domain filter.     

SC-FDE系统中基于UW的联合信道估计均衡算法

针对基于特殊字(unique word, UW)帧结构的单载波频域均衡(single carrier frequency domain equalization, SC-FDE)系统提出一种联合信道估计噪声预测最小均方误差-残留码间干扰消除(minimum mean square error-residual intersymbol interference cancellation, MMSE-RISIC)均衡算法。该算法包括噪声预测MMSE-RISIC均衡算法与基于UW的噪声消除时域信道估计算法, 并将频域均衡算法与信道估计算法相结合。最后,利用华北地区300 km的9径散射链路参数进行仿真, 结果表明基于UW的噪声消除时域信道估计算法较基于UW的时域信道估计算法总体性能有所提高, 当误码率为10^-2时信噪比大约有1.2 dB的性能增益; 联合信道估计噪声预测MMSE-RISIC均衡算法相比改进MMSE-RISIC均衡算法性能也有提高, 当误码率为10^-2时信噪比大约有3.2 dB的性能增益。     

基于差分编码调制的多址中继网络编码方法

现有多址接入中继信道（multiple-access relay channel,MARC）的网络编码技术多采用非差分调制,相干解调时会产生相位模糊。引用差分调制可克服此问题,但解调性能会损失约2.5 dB。为了弥补此损失,文中提出一种基于差分调制的比特交织编码调制迭代译码（bit-interleaved coded modulation scheme with iterative decoding,BICM-ID）方法。利用外信息转移图分析比较了两种编码（卷积码和低密度校验（low density parity check,LDPC）码）结合差分正交幅度调制（differential quadrature amplitude modulation,DQAM）在格雷和改进集合分割（modified set partitioning, MSP）映射下的性能,并做仿真对比。结果表明,对于差分调制,格雷映射比MSP映射更优。对于格雷映射,卷积码比LDPC码更优,有0.7dB的增益,且复杂度更低。