瑞利衰落信道下的网格酉空时调制的研究

酉空时是一种多天线系统信号调制方案,可以在不知道信道状态下进行解调。文中将网格编码与酉空时星座结合运用,性能仿真证明了网格酉空时调制系统非常适合无信道状态信息的无线通信系统,网格编码在一定程度上改进了系统的比特误码率性能。将网格编码下的酉空时调制与未编码的酉空时调制进行对比,结果显示在10^-4的比特误码率下可以得到10～15dB的编码增益。     

Bruhat分解、Weyl群在酉空时码中的应用

运用了Bruhat分解和Weyl群概念基础上,通过搜寻最大平均欧氏距离的方法,提出了一种新的差分全分集酉子群调制方式,给出了基于四天线系统酉子群的PSK酉空时码近似优化,并列举了若干PSK酉时空编码的实例。仿真表明,在准静态瑞利衰落信道下,近似酉空时优化码相对于循环码性能更为优异。     

差分酉空时调制

总结了差分酉空时调制的原理和编译码方法。差分酉空时调制是多输入多输出（MIMO）无线通信中不需要信道信息的一种调制方法,它的性能比相干检测接收差3dB。文中首先介绍了酉空时调制的基本原理和在各种信噪比下的信号星座图的设计原则;然后在此基础上介绍了不需要信道信息的差分酉空时调制;最后介绍了差分酉空时调制的最新进展,指出了其研究方向。     

一种新颖的基于子矩阵交织的差分酉空时调制

差分酉空时调制(DUSTM)是一种应用于时变衰落信道下的多天线调制方法。该方法在慢衰落信道下无需知道信道状态信息而能获得全发送分集增益。但是,在快速衰落信道下,其性能明显恶化并且呈现出较高的误码平层。该文通过在差分酉空时调制中引入矩阵分割和子矩阵交织等操作提出了一种基于子矩阵交织的差分酉空时调制(SMI-DUSTM)方案,并对其性能进行了分析。性能分析和相应的计算机仿真证明了SMI-DUSTM 不仅能够继承DUSTM在慢衰落信道下的优点,而且在快速衰落信道下能够保持良好的系统性能。     

无需信道估计的一种简单的差分分集OFDM传输方式

空时码在近几年得到了普遍关注,但空时码的应用通常都假定信道具有非频率选择性衰落特性,同时还假定信道状态也是已知的,这些都极大地限制了空时码的应用。该文给出了一种未知频率选择性衰落信道下的差分分集调制方法。应用正交频分复用技术的基本原理,把一个频率选择性衰落信道转换成了多个并行平坦衰落信道。在此基础上,给出了一种无需信道估计的简单的时空频分集结构.仿真结果表明,这种结构在频率选择性衰落信道中无需信道估计就能得到很好的结果.     

BICM在差分跳频系统中的应用

将比特交织编码调制(BICM)技术应用于差分跳频(DFH)通信系统,在加性白高斯噪声(AwGN)信道及频率非选择性瑞利慢衰落信道下,对采用无迭代译码及迭代译码的系统比特误码率(BER)上界进行了理论推导及数值仿真验证,并与传统的差分跳频系统的性能进行了比较.其数值仿真结果表明:采用BICM技术的差分跳频系统,可以在不增加跳频带宽及译码复杂度的情况下,利用最优卷积码增大了其G函数网格图的最小自由距离.同时对于可用频率数为16的无迭代译码BICM/DFH,当BER为10-1时,在瑞利信道下相对于CHESS系统而言,其性能改善可达6dB.若采用迭代译码,则当BER为10-1时,其性能相对于无迭代译码可进一步改善3,dB.     

酉空时调制系统中基于多符号差分检测的软检测器

该文设计了一种适用于差分酉空时调制体制的低复杂度软检测算法。该算法基于多符号差分检测,为软判决译码模块提供编码比特的对数似然比信息。仿真表明,在通常容许的误码范围内,采用所提出的软检测算法构建的差分酉空时调制系统比原硬判决系统节省2～4dB的信号功率,并解除了基于单符号差分检测的软检测算法在快衰落信道下的错误平层。     

具有低复杂度的 LDPC 已编码非相干酉空时调制系统设计简

提出一种克服无线信道瑞利衰落和高斯白噪声干扰的非相干编码调制MIMO系统方案。纠错码采用IEEE 802.16e中的非规则QC-LDPC码,非相干调制采用基于三角函数的酉空时调制(SC-USTM)。在接收端,推导出SC-USTM的最大后验概率（MAP）解调算法;为了降低复杂度,构造了SC-USTM的双解调器方案;为了改善双解调的性能,在置信传播（BP）迭代解码器和MAP解调器之间引入了迭代反馈机制。仿真实验表明LDPC已编码SC-USTM的MIMO系统比未编码USTM的MIMO系统在 误码率时,性能改善15~17 dB,并且整个系统具有较低的计算复杂度。     

基于遗传搜索和有限反馈的酉阵设计

在MIMO系统中,酉阵主要应用于差分空时调制（DUSTM）及有限反馈预编码两个方面。DUSTM主要应用于无法获得信道状态参数（CSI）情况下,而有限反馈预编码则应用于完全或部分可获得CSI情况下。文中提出了一种基于实型＂频率＂系数的遗传搜索方法,即使在系统维数很大的情况下,运用该方法获得酉阵设计的码字性能优于由整型＂频率＂系数穷举搜索而获得的码字。     

空时编码在瑞利衰落信道下的性能分析

以正交空时分组码为例讨论了空时编码技术的性能特征。给出了各种STC-OFDM系统的BER性能。理论分析和仿真结果表明,STBC-OFDM系统在频率选择性的瑞利衰落信道下,性能优于其它STC-OFDM系统。     

Performance of trellis-coded CPM with iterative demodulation anddecoding

Interleaved trellis-coded systems with full response continuous-phase modulation (CPM) are considered. Upper bounds on the bit-error rate performance are derived for coherent detection on the additive white Gaussian noise and flat Rayleigh fading channels by considering the trellis code, interleaver, and CPM modulator as a serially concatenated convolutional code. A coherent receiver that performs iterative demodulation and decoding is shown to provide good bit error performance. Finally, a noncoherent iterative receiver is proposed and is shown to perform close to the coherent iterative receiver     

Design, analysis, and performance evaluation for BICM-ID withsquare QAM constellations in Rayleigh fading channels

We consider bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth-efficient transmission over Rayleigh fading channels. We propose the design criteria that utilize a large Hamming distance inherited in a low-rate code and a new labeling technique designed specifically for fading channels. This results in a large coding gain over noniterative coded modulation and performance close to that of “turbo” coded modulation with less complexity. We also show that BICM-ID designed for fading channels usually has a very good performance over the additive white Gaussian noise (AWGN) channel while the converse is difficult to achieve. When combined with signal space diversity, diversity order can be improved to twice the diversity order of conventional BICM-ID; therefore, the code complexity can further be reduced while maintaining the same level of performance. Specifically, with the bandwidth efficiency of 2 bits/s/Hz over Rayleigh fading channels, a bit error rate (BER) of 10^-6 can be achieved with 16-QAM, a four-state rate 1/2 code at E_b/N₀ of about seven dB. We also derive performance bounds for BICM-ID with and without signal space diversity over Rayleigh fading channels, which can be easily extended for other types of fading channels     

移动通信系统中空时格码的改进设计

本文根据空时格玛在快瑞利衰落信道下的成对错误概率上界，得出不同发射天线的码设计具有独立性，进而提出一种改进的快瑞利衰落信下空时格码的设计准则，当信道衰落快慢介于准静态和快瑞利衰落之间时，空时格码的设计方法也可做相应的改进，分析及仿真结果表明，由改进方法设计的空时格码比由传统方法得出的具有更优的性能。     

慢变平坦衰落信道下空时码设计准则的改进

对用于慢变平坦瑞利衰落信道的空时码设计准则进行了研究。考察了不同长度的首事件差错概率，并基于这些概率推出误帧率的上界，进而提出一种使误帧率的上界最小化的新准则。另外，证明了空时码的几何一致性并使用该特性大大地减少了空时码搜索的复杂度。依据该准则搜索得到一些新码，并与现有好码进行性能比较。     

Information theoretic considerations for coded modulation overfading channels

We compute the random coding error exponent for coded modulation transmitted over a flat, memoryless, Rayleigh fading channel. In addition, estimates of code lengths required to achieve a certain error probability are determined and compared to those required for the additive white Gaussian noise channel. Finally, the effect of receiver antenna diversity is also considered as a method to compensate for fading and is shown to have a significant, positive impact on the error exponent. The results we obtain represent an information theoretic view that complements the existing literature on the performance of coded modulation over fading channels with receiver diversity     

Performance analysis on LDPC-Coded systems over quasi-static (MIMO) fading channels

In this paper, we derive closed form upper bounds on the error probability of low-density parity-check (LDPC) coded modulation schemes operating on quasi-static fading channels. The bounds are obtained from the so-called Fano- Gallager?s tight bounding techniques, and can be readily calculated when the distance spectrum of the code is available. In deriving the bounds for multiple-input multiple-output (MIMO) systems, we assume the LDPC code is concatenated with the orthogonal space-time block code as an inner code. We obtain an equivalent single-input single-output (SISO) channel model for this concatenated coded-modulation system. The upper bounds derived here indicate good matches with simulation results of a complete transceiver system over Rayleigh and Rician MIMO fading channels in which the iterative detection and decoding algorithm is employed at the receiver.     

An adaptive multiuser detector for DS‐CDMA systems in multipath fading channels

In this paper, we investigate the performance of an adaptive multistage detection scheme for direct‐sequence code‐division multiple‐access (DS‐CDMA) systems. The first stage consists of an adaptive multiuser detector which is based on the linear constrained minimum variance (LCMV) criterion. The interference cancellation (IC) occurs in the second stage. The performance of the iterative receiver over both flat and frequency‐selective fading channels is investigated and compared to the single‐user bound. In all cases, and under heavy system loads with near‐far problems, the iterative receiver is shown to offer substantial performance improvement and large gain in user‐capacity relative to the standard LCMV. In flat‐fading channels, our results show that the performance of the iterative detector is very close to the single‐user bound. For the frequency‐selective channel, this performance is noted to be in the order of 1 dB far from the single‐user bound. Copyright © 2007 John Wiley & Sons, Ltd.     

An Exact Error Probability Analysis of OFDM Systems with Frequency Offset

In this paper, we derive exact closed form bit error rate (BER) or symbol error rate (SER) expressions for orthogonal frequency division multiplexing (OFDM) systems with carrier frequency offset (CFO). We consider the performance of an OFDM system subject to CFO error in additive white Gaussian noise (AWGN), frequency flat and frequency selective Rayleigh fading channels. The BER/ SER performances of BPSK and QPSK modulation schemes are analyzed for AWGN and frequency-flat Rayleigh fading channels while BPSK is considered for frequency-selective Rayleigh fading channels. Our results can easily be reduced to the respective analytical error rate expressions for the OFDM systems without CFO error. Furthermore, the simulation results are provided to verify the accuracy of the new error rate expressions.     

On channel parameter estimation in a space-time bit-interleaved-coded modulation system for multipath DS-CDMA uplink with receive diversity

In this paper, we consider iterative space-time multiuser detection and channel parameter estimation in a bit-interleaved coded modulation scheme for asynchronous direct-sequence code division multiple access (DS-CDMA) transmission over frequency selective, slowly fading channels. Accurate estimation of the channel parameters is critical as it has great impact on the overall BER performance. We present an iterative space-time multiuser (STMU) turbo detection and estimation scheme, based on space alternating generalized expectation maximization (SAGE) algorithm. This algorithm operates on the coded symbols by exchanging soft information between the detector and the estimator. We show through computer simulations that the proposed low complexity STMU receiver considerably outperforms conventional estimation schemes and achieves excellent performance, both in terms of BER and estimation error variance. Finally, we will consider different mapping strategies and investigate their impact on the performance and complexity of the estimator.     

Error performance of interleaved trellis-coded PSK modulations incorrelated Rayleigh fading channels

The authors derive an exact and easily computed expression for the pairwise error event probability of interleaved coded PSK modulations transmitted over channels with correlated Rayleigh flat fading and additive white Gaussian noise. Both coherent and differential detection are considered. In the case of coded DPSK, it is found that full interleaving does not necessarily provide the best error performance, especially when the fading is relatively fast and when the autocorrelation function of the channel fading process exhibits an oscillating behavior. For coherent detection or for differential detection in channels with relatively slow fading, increasing the interleaving depth always improves the error performance. In these cases, an interleaving depth equivalent to one-fifth to one-quarter the duration of a fade cycle is almost as good as full interleaving