正交空时分组码在瑞利衰落信道下的性能分析

基于典型的多输入—多输出无线通信系统,推导了在瑞利衰落信道下正交空时分组码的瞬时接收信噪比和抗噪声性能的一般表达式,并在MATLAB环境中对不同发送天线、接收天线、调制方式、传输速率下正交空时分组码的误码率性能进行了仿真与结果比较分析,得出误码率性能与分集增益、编码速率、比特传输率和调制方式存在内部关联。     

空时码在Rician衰落信道下性能分析

基于Alamouti提出的BPSK调制下空时分组码在Rayleigh衰落信道中的简单分集方案。推导出多发射和多接收天线系统中正交空时分组码在Rician衰落信道的BPSK调制下的比特差错率的最小距离球界,并推广到在高阶调制下衰落信道中系统符号差错率的性能。仿真分析和比较了空时分组码的多天线系统中发射和接收天线分集增益,以及信道相关参数的变化对系统误比特性能的影响。     

非理想信道估计对STBC性能的影响

信道估计误差对空时分组码(STBC)解码性能的影响依然值得进一步的研究,通过讨论STBC在仅有不完整信道估计时的解码性能,首先建立系统分析模型,然后进行理论分析和模拟,并同接收分集的性能作比较.仿真结果表明,在非相关空间衰落的多散射环境中,STBC提供了一种有效的町获得空间分集增益的简单发射分集方案,但信道估计误差对其解码性能有较大的影响.     

卷积编码与MT-CDMA相结合的通信系统性能分析

简要介绍了卷积编码与MT-CDMA相结合的通信系统的理论基础,从理论上分析了MT-CDMA在瑞利衰落信道下的误码性能,并从仿真的角度论证了编码后的MT-CDMA较未编码的MT-CDMA在频率选择性衰落信道下误码率能得到显著改善。     

发射分集系统中正交空时分组码的研究

分析了空时分组码在实际应用中较空时格码的优势.以Alamouti发射分集方案为例简要介绍了空时分组码的编译码方法.针对带来性能优势的信号正交性设计,进行了详细的讨论.对瑞利衰落信道下,针对不同天线配置和不同调制方式条件下的空时分组码进行了性能仿真.     

一种新的准正交空时分组码设计

根据正交设计理论,当发送天线数大于2时,不存在可以获得完全分集增益和全速率的复正交空时分组码。对空时分组码采用准正交设计,能够保证数据以全速率传输,但是会使其误码性能降低。本文根据矩阵正交理论提出了一种新的全速率准正交空时分组码并给出了一种基于QR分解的最大似然译码方法。仿真结果表明,本文方案与已有典型的准正交空时分组码相比,具有更好的误码性能。     

基于MATLAB的信道编码仿真

本文分析了线性分组码和卷积码的编译码原理,然后通过MATLAB的sumilink仿真模块对二进制对称信道和高斯白噪声信道在汉明码编码下进行仿真分析;根据误码率曲线图对信道性能的特点进行比较分析.结果表明:汉明码的误码率会随着信噪比的升高而降低,而卷积码在信噪比较大时误码率明显降低.     

瑞利衰落信道最大比合并的误码率改进新方法

通过分析瑞利衰落信道模型,以及BPSK在最大比合并瑞利衰落信号下的误码率解析结果,提出了在最大比合并之前添加自动增益控制模块,弥补接收过程带来的信噪比损失,从而改善误码率性能。通过Matlab数值仿真的方法,证明采用在最大比合并之前添加自动增益控制过程的分集接收策略能有效地改善瑞利衰落对无线信道传输信号的影响。     

双向中继系统中断概率下界优化及分集增益

主要研究了瑞利衰落信道下基于放大转发策略的双向中继系统的中断性能及分集性能。首先利用信源节点信噪比间的关系和调和不等式对信噪比的范围进行优化,得到新的中断概率下界,仿真结果表明Monte Carlo仿真得到的中断概率接近新得到的中断概率下界;同时证明了多中继存在时,基于最大最小互信息准则的双向中继系统仍然取得全分集增益且能够优化中断概率下界。     

空时码不对称调制方法研究

提出了空时编码不对称调制方案。软件分析了比特交织空时编码调制系统在Rayleigh衰落信道下的成对错误概率上界。对于常用的几种映射方案,采用不对称调制星座图,可以增大汉明距离为1的调制符号间的最小欧氏距离,从而提高系统的编码增益和分集增益,降低成对错误概率的上界。理论分析和仿真结果表明,不对称调制星座图改善了比特交织空时编码调制系统在Rayleigh信道下的性能,并且没有牺牲频谱效率和增加系统复杂性的代价。     

发射分集MC-CDMA系统空时多用户检测

该文研究了在频率选择性瑞利衰落信道中的同步多载波码分多址(MC-CDMA)系统上行链路,在移动终端处使用两个发射天线,采用基于空时分组码的发射分集,基站采用分集天线接收。考虑对应于子载波的衰落系数是信道冲激响应的离散傅里叶变换,给出了采用发射分集和接收分集的MC-CDMA系统上行链路信号模型。研究了采用发射分集和接收分集的MC-CDMA系统的解相关多用户检测、最小均方误差(MMSE)多用户检测,进行联合的多用户检测和空时码解码。仿真结果验证了上述模型及算法的有效性。     

Performance improvement of QO-STBC over time-selective channel for wireless network

Signal detection for vehicle-to-vehicle and wireless network application has motivated new design for conditions in which channel is time-selective fading. Since the physical layer (PHY) forms the foundation of the communication protocol stack, the performance of this layer affects all high layers of the system stack. Quasi-orthogonal space-time block code (QO-STBC) can provide full rate transmission and partial diversity under low decoding complexity. Previous papers on QO-STBC assume that the channels are slow fading or remain static over the length of the codeword. However, time-selective channels do exist, and in this case, the decoder proposed in Jafarkhani (2001) cannot be used to achieve a proper error performance. In order to mitigate the severe performance degradation, the zero forcing (ZF) and minimum mean square error (MMSE) decoders are employed in this paper. We also propose a zero forcing interference cancellation decision-feedback equalizer (ZF-IC-DFE) and a minimum mean-square error interference cancellation decision-feedback equalizer (MMSE-IC-DFE) via Cholesky factorization of the channel Gram matrix after performing interference cancellation. By feeding back past decisions on previously detected symbols, DFE schemes can achieve an additional performance gain compared to their corresponding linear decoders.     

几种空时码容量对比

贝尔实验室提出的分层空时（layered space-time code,LSTC）主要基于空分复用思想,它的主要目的是提高系统频谱效率;而其它空时码（space-time code,STC）,如空时分组码（space-time block code,STBC）、空时格码（space-time trellis code,STTC）等主要基于发射分集。它们主要利用空间分集带来的增益,包括分集增益和编码增益来对抗无线信道的各种衰落。本文从信道容量角度评估各种空时编码的性能,同时将其和相同收发天线数下多输入输出（Multiple input multiple output,MIMO）系统的信道容量进行对比。     

不同信道条件下MIMO空时编码技术的特性分析

为了分析多输入多输出（ MIMO）空时编码技术在不同信道条件下的性能优劣,研究了无线信道的衰落统计特性,对比了在Rayleigh信道、Rician信道和Nakagami信道条件下,正交频分复用空时块编码（ STBC-OFDM）、垂直空时分层码（ V-BLAST）及空时格型码（ STTC）的系统误码率。通过仿真分析结果表明：STBC-OFDM系统在衰减指数为5的Nakagami信道条件,系统误码率最低,Rician信道次之,Rayleigh信道最高,而且当系统误码率为10－3时,其所需的信噪比（ SNR）分别为7,9,11 dB;但对于V-BLAST和STTC系统,随着信噪比的增加,不同的信道条件对系统误码率的影响各有优劣。     

Variable energy adaptation for asynchronous CDMA communications over slowly fading channels

In this paper, a detailed theoretical analysis of variable energy adaptation in an asynchronous code division multiple access (A-CDMA) system is discussed. Rayleigh and Rician frequency-selective slowly fading channels are considered. The receiver, capable of measuring the received signal energy-to-noise ratio, provides the transmitter with the necessary signal-to-noise ratio measurement to control the transmitter energy through a noise-free feedback channel. System parameters such as fading margin and mean transmitter energy gain are calculated for both Rayleigh and Rician fading channels as a function of the probability of error specification and the probability of unsatisfactory operation.     

一种接近于Shannon限的级联BCM码

给出一种新的级联分组调制（ＢＣＭ）码,其中内码选用带宽有效的ＢＣＭ码,外码采用ＲＳ码,在高斯信道中的仿真结果表明,这种码字在误码率为１０＾－６时较近乎相同带宽利用率下的未编码ＱＰＳＫ系统有５．３ｄＢ的编码增益,距离Ｓｈａｎｎｏｎ限只有０．５ｄＢ;在Ｒａｙｌｅｉｇｈ衰落信道中,误码率为１０＾－５时较未编码ＱＰＳＫ系统的编码增益可达到２０ｄＢ,距离无信道状态信息时的信道截止速率Ｒ０限为４．２ｄＢ,且译     

Performance analysis of MIMO systems with arbitrary number transmit antenna selection and OSTBC in the presence of imperfect CSI

In this paper, the performance analysis of MIMO systems with arbitrary number transmit antenna selection (TAS) and orthogonal space-time block coding (STBC) in Rayleigh fading channels for imperfect channel state information (CSI) is presented. For the performance analysis, the moment generating function of the system effective SNR as well as its upper and lower bounds are derived. Then, accurate and approximate expressions of bit error rate (BER) of MIMO-TAS-STBC with MPSK and MQAM are further derived. Using the approximate BER formula and imperfect CSI, an adaptive antenna selection scheme is developed for minimizing the BER. The diversity gain and coding gain are analyzed at high SNR. The results indicate that the MIMO-TAS-STBC for imperfect CSI can only achieve partial diversity order KN and the coding gain is affected by K, N, code rate, modulation pattern, and channel correlation coefficients, when K transmit antennas are selected and N receive antennas are used. Simulation results show that the theoretical analysis matches the simulation result well, and the approximate expressions are close to the accurate ones but have a lower complexity.     

Adaptive rate coding using convolutional codes for asynchronous code division multiple access communications over slowly fading channels

This paper presents a method of code rate adaptation using punctured convolutional codes for direct sequence spread spectrum communication systems over slowly fading channels. A blind channel estimation technique is used to estimate the nature of the multi-user channel at the detector (before the decoder). The path gains obtained from the channel estimation technique are used to adapt the code rates. Punctured codes derived from a specific rate 1/2 (M = 4) mother code are used to provide error protection corresponding to the actual channel state. The upper and lower bounds on the bit error probability and the upper bound on the error event probability are derived for hard-decision and soft-decision decoding over Rayleigh and Rician fading channels. The throughput gains obtained using the adaptive scheme and the performances of the punctured codes are studied.