MIMO信道的GBDB模型及其信道容量分析

针对非频率选择性Rice衰落MIMO移动信道，建立GBDB模型，并推导出新的MIMO系统的GBDB模型的空时联合相关函数。新的GBDB模型统一现有的多种MIMO信道模型，新的空时联合相关函数综合考虑了无线衰落信道收发两端的多普勒扩展、非均匀角度扩展以及平均发射与到达方向，综合考虑了收发端天线阵的配置。最后基于新的空时联合相关函数，分析了非均匀散射参数以及Rice分布参数变化对MIMO信道统计容量的影响。     

频率选择性衰落MIMO信道容量分析

随着传输速率越来越高,信号所占用的带宽越来越宽,实际信道呈现出频率选择性衰落特性.根据频率选择性衰落信道特性,建立了频率选择性衰落MIMO信道模型,采用频域和时域的方法研究了在频率选择性衰落下,发射端已知和未知信道状态信息的MIMO信道容量,并给出了相关的仿真结果.研究结果表明:在相同发射功率和传输带宽下,MIMO系统可以不牺牲信号带宽而显著提高信道的容量,并且天线数量和输入信噪比的大小对信道容量具有不同的影响.研究结果为如何提高频率选择性衰落环境下MIMO信道容量提供了依据.     

MIMO信道在巷道中的GBDB模型分析

多输入多输出(MIMO)技术可以有效减弱无线传输多径衰落现象。建立矿井巷道环境下MIMO信道的三维GBDB模型,推导了该模型的空时相关函数,并对矿井下MIMO信道容量进行了数值仿真。结果表明,矿井巷道中的空间相关性对MIMO系统容量的影响很大,增加接收端天线数量、增大天线间距可以大幅度提高系统的信道容量。     

MIMO系统在空时二维相关莱斯快衰落信道下的性能

与准静态独立的瑞利衰落信道模型相比较,在MIMO(Multi-Input Multi-Output)系统中,实际信道更趋向于空时相关莱斯快衰落。考虑到MIMO系统的收发分集优势以及收发两端天线阵列的空时相关性,在简单论述了MIMO系统和信道模型的基础上,该文利用多变量统计学理论,推导出MIMO系统在空时相关莱斯快衰落信道下平均成对差错概率上界的闭合表达式,并探讨了信道特性对系统性能的影响,然后给出相应仿真结果。     

频率选择性衰落信道下STBC—DFDM系统的性能

本文将基于平衰落信道提出的空时块编码（STBC）方案应用到OFDM系统中,理论分析和仿真证明在理想信道估计下这种STBC-OFDM系统在频率选择性信道下能够获得对应的STBC在平衰落信道下的性能。     

频率选择性衰落信道中的空时分组编码系统性能研究

空时分组码（STBC）由于具有较高的分集增益和简单的编译方法，从而得到普遍关注。但是它只适于频率平坦信道，而实际的信道多为频率选择性信道。丈中将考虑两种适用于频率选择性信道的空时分组码系统方案：OFDM-STBC和SC／FDE-STBC方案，即考虑空时分组码与正交频分复用或单载波频域均衡结合。通过对OFDM-STBC和SC／FDE-STBC系统性能仿真结果的比较和分析，表明SC／FDE-STBC方案要优于OFDM-STBC方案。此外，文中也给出一些细致的仿真性能的观察。     

频选衰落MIMO信道的Turbo均衡

针对Turbo编码频选慢衰落MIMO信道,提出基于滑窗式概率数据辅助(Probabilistic Data Association)的软输出判决反馈均衡和软输入软输出Turbo信道解码器间迭代处理的Turbo均衡算法。充分利用已获得的信息,实现信道均衡与信道解码的迭代更新,克服传统判决反馈均衡器误差传播的缺陷。仿真表明,该系统经3次迭代就可获得较为满意的符号间干扰消除效果。     

频率选择性衰落OFDM的半盲信道估计算法研究

从系统性能分析和设计的角度详细地研究了基于无线HIPERLAN2通信协议的OFDM(orthogonal frequency division multiplexing，正交频分多路复用技术)系统信道估计与均衡的一种半盲算法，提出了结合直接法和Cholesky分解法的切换盲算法。这种半盲算法综合了全盲算法得到的信息与已知导频符号，充分利用了原发信号的统计特性和OFDM帧结构中插入的导频符号，克服了全盲和导频训练序列存在的问题^[6,7]，且不需额外的带宽。仿真结果表明，在误比特率和收敛性方面，该算法比现有的主要三种全盲算法有更好的收敛和抗干扰特性。     

Rayleigh衰落信道中选择性分集合并的性能分析及其实现

文章首先对两路相互独立Rayleigh衰落信道的选择性合并方法的中断概率及差分、相干检测误码率的性能进行了分析,在此基础上进一步分析了两路相关Rayleigh衰落信道下的选择性合并方法的中断概率及差分、相干检测的误码率的性能,并仿真出了各种情况下的性能曲线。最后,给出了四路选择性合并方法的具体实现电路。     

频率选择性衰落信道GMSK误码性能分析

通过对数字移动信道脉冲响应时延展宽包络 ( PDSP)波形的研究 ,分析了GMSK调制下的脉冲时延展宽包络与误码率之间的变化关系 ,建立了两者之间关系的理论模型和计算机仿真模型 ,同时给出了在四种较为典型的 PDSP作用下 ,GMSK误码率特性的计算机仿真结果。     

Adaptive quantization for fading channels with feedback

The effect of the presence of a feedback channel on the transmission of information was first considered by Shannon, who showed that the capacity of a memoryless channel is not increased by the existence of a feedback link even if the feedback link is noiseless. Later it was shown that the information on a feedback channel can be used to improve considerably the performance of channel coding. In this work we study the transmission of an information source through a fading channel with feedback, modeled by a finite-state channel in the Gilbert-Elliot sense. We show that by employing the feedback information in the quantizer design for this finite-state channel, one can achieve lower overall distortion compared to the case where feedback is not available. The feedback channel is used to estimate the channel state using a hidden Markov model, and a quantizer matched to the channel state is chosen based on this information.     

Multiuser adaptive transmission technique for time-varying frequency-selective fading channels

This paper proposes an efficient multiuser adaptive modulation and coding (AMC) scheme that considers inevitable feedback delay by employing short-term and long-term channel state information (CSI) in time-varying frequency-selective fading channels. By taking the statistic of the true signal-to-noise ratio (SNR) at a given predicted SNR value into account, the required transmit power to meet the target packet-error-rate (PER) can be obtained and used for user selection, power allocation, and modulation and coding set (MCS) selection. In addition, a simple and useful approximation method of obtaining the required transmit power is proposed. The performance of the proposed scheme is shown to be much better than that of conventional schemes without considering the feedback delay or the prediction error. The proposed scheme can also reduce the feedback resource while maintaining the system throughput by allocating different feedback resources to different users according to their prediction error variances.     

空时编码多载波码分多址MIMO系统下行频率选择性信道盲估计

基于子空间方法的无线信道盲估计由于其算法的固有特性,使得估计结果与实际信道之间存在一个不确定复系数,无法得到无线信道的精确估计。在利用子空间分解方法对空时编码多输入多输出MC-CDMA系统下行频率选择性信道盲估计的基础上,利用发射符号的有限码集特性,将单载波系统下的模糊复系数盲辨识方法推广到多载波多输入多输出系统,从而得到信道的精确估计。Monte-Carlo仿真表明,在信噪比较低的情况下,本方法的信道估计误差仍然较小。     

Achievable information rates and coding for MIMO systems over ISI channels and frequency-selective fading channels

We propose a simulation-based method to compute the achievable information rates for general multiple-input multiple-output (MIMO) intersymbol interference (ISI) channels with inputs chosen from a finite alphabet. This method is applicable to both deterministic and stochastic channels. As an example of the stochastic MIMO ISI channels, we consider the multiantenna systems over frequency-selective fading channels, and quantify the improvement in the achievable information rates provided by the additional frequency diversity (for both ergodic and nonergodic cases). In addition, we consider the multiaccess multiantenna system and present some results on the achievable information-rate region. As for the deterministic MIMO ISI channels, we use the binary-input multitrack magnetic recording system as an example, which employs multiple write and read heads for data storage. Our results show that the multitrack recording channels have significant advantages over the single-track channels, in terms of the achievable information rates when the intertrack interference is considered. We further consider practical coding schemes over both stochastic and deterministic MIMO ISI channels, and compare their performance with the information-theoretical limits. Specifically, we demonstrate that the performance of the turbo coding/decoding scheme is only about 1.0 dB away from the information-theoretical limits at a bit-error rate of 10/sup -5/ for large interleaver lengths.     

Performance analysis and design of STBCs for frequency-selective fading channels

In this paper, space-time block-coded transmission over frequency-selective fading channels is investigated. A lower bound for the pairwise error probability for optimum detection is given. Also, an approximation for the bit-error rate is derived and compared with simulation results for maximum-likelihood sequence estimation (MLSE) for the GSM/EDGE (Enhanced Data Rates for GSM Evolution) system. Furthermore, a novel design rule for space-time block codes (STBCs) for frequency-selective fading channels is provided. A corresponding code is designed and shown to yield higher performance than Alamouti's code. It is demonstrated that for fading channels with L independent impulse response coefficients, STBCs designed for the flat fading channel can achieve at most a diversity order of (N/sub T/+L-1)N/sub R/ if N/sub T/ transmit antennas and N/sub R/ receive antennas are used. On the other hand, the maximum diversity order employing the proposed code design rule is LN/sub T/N/sub R/.     

On the design of space-time and space-frequency codes for MIMO frequency-selective fading channels

The authors introduced an algebraic design framework for space-time coding in flat-fading channels . We extend this framework to design algebraic codes for multiple-input multiple-output (MIMO) frequency-selective fading channels. The proposed codes strive to optimally exploit both the spatial and frequency diversity available in the channel. We consider two design approaches: The first uses space-time coding and maximum likelihood decoding to exploit the multi-path nature of the channel at the expense of increased receiver complexity. Within this time domain framework, we also propose a serially concatenated coding construction which is shown to offer a performance gain with a reasonable complexity iterative receiver in some scenarios. The second approach utilizes the orthogonal frequency division multiplexing technique to transform the MIMO multipath channel into a MIMO flat block fading channel. The algebraic framework is then used to construct space-frequency codes (SFC) that optimally exploit the diversity available in the resulting flat block fading channel. Finally, the two approaches are compared in terms of decoder complexity, maximum achievable diversity advantage, and simulated frame error rate performance in certain representative scenarios.     

一种针对频率选择性MIMO信道的新型空时分层迭代检测算法

本文针对FS-BLAST算法中的误码扩散问题提出了一种新的分层迭代方法：部分最大似然分层迭代（MLIC）算法。FS-BLAST由于采用了干扰对消的方案,不可避免的产生了误码扩散问题。在本文中,提出了一种新的部分最大似然分层迭代方案,它在分层迭代算法中引入最大似然的概念,是最大似然检测和分层迭代算法的折衷。从实验仿真中,可以看出,这种改进的算法比传统的FS-BLAST和已有的迭代算法具有更好的系统性能。     

Service provided by fading MIMO channels: a deterministic perspective

In this paper, we study the channel service process of a multiple‐input multiple‐output (MIMO) system over an independent and identically distributed (i.i.d.) fading channel. One key problem of communication over fading MIMO channels is what kind of service the MIMO channel can provide. In this paper, this problem is investigated in terms of channel service process. Assuming that the channel state information is available at the receiver, the channel service process S(t) is defined as the integral of the instantaneous channel capacity over a time interval of length t, which specifies the service provided by the channel during the period. Using the characteristic function approach and the infinitely divisible law, it is proved that the channel service process S(t) is a deterministic linear function of time t, other than any curve form or a stochastic process. Specifically, , where is a constant equal to the corresponding ergodic capacity. This result has two implications: (i) i.i.d. fading MIMO channels can support a constant rate traffic stream of rate without higher layer transmission delay; (ii) the ergodic capacity is the actual transmission capacity of the fading channel, other than only a statistical average value. Copyright © 2012 John Wiley & Sons, Ltd.