QPSK调制解调通信系统仿真实现

本文用Matlab仿真通信系统的四相相移键控（QPSK）调制及相关解调,分析数字信号在AWGN信道和Rayleigh衰落信道巾的传输。仿真实现在AWGN信道与Rayleigh信道下的传输差错特性,包括仿真的结果与理论计算的结果。     

Turbo-TCM系统中几种交织器的性能研究

研究了Turbo码与网格编码调制(TCM)相结合的Turbo-TCM技术,将Turbo码中三类奇偶交织器的设计分别应用到Turbo-TCM中,并在Awgn信道和Rayleigh衰落信道下,对采用三种不同交织方式、不同帧长Turbo-TCM的性能进行了仿真。仿真结果表明,短帧条件下,Awgn信道中采用确定性奇偶交织器的Turbo-TCM性能最优,而Rayleigh衰落信道中三种交织方式的Turbo-TCM性能相近。长帧条件下,Awgn信道和Rayleigh衰落信道中,基于随机奇偶交织器的Tur-bo-TCM性能最优。     

DWDM中色散条件下基于两种模型SRS效应的功率转移研究

在DWDM系统中受激喇曼散射（SRS）效应是一种重要的非线性效应。将巩稼民的无色散条件下N信道的SRS效应模型和Singh_Hudiara模型分别加入色散走离,采用＂时域分步法＂对多信道、长距离传输中的＂色散＂以及SRS效应所带来的影响进行仿真。通过对这两种模型的功率转移仿真图对比,得出信号功率的变化随着信道波长的增加而线性增长的结论。这对SRS研究有着重要的意义。     

编码64DAPSK信号的软输出解调

基于子载波采用64DAPSK调制的OFDM系统,提出了卷积编码64DAPSK信号的软输出解调方法。仿真结果表明,在AWGN信道、平坦Rayleigh衰落信道和多径Rayleigh衰落信道下,前向纠错编码采用速率3/4的punctured卷积码时,与64DAPSK信号的硬输出解调译码方法相比,系统的误比特性能可改善约2dB。文章提出的新方法同样适用于采用卷积编码64DAPSK调制的其它系统。     

卫星衰落信道分析与建模

在研究分析传统Rayleigh信道和Rice信道抽头时延模型的基础上,采用两条多径路线代替传统模型,提出一个具有确定数学表达式的简化卫星信道模型,只需对该模型中的两个参数取适当的取值,就可以得到不同的衰落强度和衰落中心频率的卫星信道.理论和仿真结果表明,当时延τ=.63ns,β=0.75时,可以获得的最大衰落幅度为10...     

MC-CDMA系统存在频偏时的性能分析

多载波码分多址(MC-CDMA)是把正交频分复用(OFDM)和码分多址(CDMA) 结合起来的新一代移动通信系统.详细构建了一个MC-CDMA 系统的数学模型,并给出了载频偏移和多径信道存在时的矩阵-向量表示模型.在此系统模型的基础上,分析了频偏对MC-CDMA系统多用户检测器性能的影响.MATLAB仿真显示了MC-CDMA系统对频偏极为敏感,当经历多径Rayleigh信道时,系统只能忍受较小的频偏.     

高信道数FBG色散补偿器的设计

随着密集波分复用(DWDM)技术向着高信道数方向发展,色散对光纤通信的限制也日趋严重.然而传统的色散补偿器只能补偿各信道色散值相同的情况.利用离散剥层法与遗传算法相结合的方法可以设计补偿各信道色散为任意值的色散补偿器.通过遗传算法对各信道插入相位的优化,可以使N信道的最大折射率调制幅度为单信道的√N倍,极大减小了折射率调制幅度对信道数的限制.     

基于2-FSK／4-PSK调制的BICM系统

文中提出一种基于2-FSK／4-PSK调制的比特交织编码调制系统（BICM）。理论分析和计算机仿真表明无论在AWGN信道或是Rayleigh衰落信道下，通过合理控制2-FSK／4-PSK调制，BICM系统的性能都有所提高，且在衰落信道下新系统将达到基于8PSK调制的BICM-ID系统多次迭代的效果。     

一种改进型的无线信道模型研究

本文引入Clarke参考模型,采取了一种改进型的瑞利衰落信道模型作为单径瑞利衰落信道的仿真模型,并用MATLAB编程仿真实现.该技术有助于对移动通信系统电磁干扰的研究.     

差分跳频信号抗多音干扰性能仿真分析

CHESS电台采用了差分跳频技术,可以实现短波频段内高速率数据传输。在分析差分跳频信号的生成过程以及对信号进行检测的原理的基础上,构建了差分跳频通信系统仿真模型,对AWGN信道和Rayleigh信道下差分跳频信号与常规跳频信号的抗多音干扰能力进行了仿真分析。结果表明,差分跳频信号具有较强的抗多音干扰能力。     

Some block- and trellis-coded modulations for the Rayleigh fadingchannel

The error performance of a modulation code over a channel depends on several distance parameters and the path multiplicity of the code. For the AWGN channel, the error performance of a modulation code depends mainly on its minimum squared Euclidean distance and path multiplicity. For the Rayleigh fading channel, however, the error performance of a modulation code depends strongly on its minimum symbol distance, minimum product distance, and path multiplicity. It depends on the minimum squared Euclidean distance in a lesser degree. This paper is concerned with the construction of block and trellis MPSK modulation codes for the Rayleigh fading channel. In each construction, the distance parameters are chosen to achieve good error performance with reduced decoding complexity     

Capacity of AM-PSK on partially coherent fading channels

This paper presents numerical capacity curves for two discrete complex channels: (1) a slow-fading Rayleigh channel with discrete carrier tracking by a phase-locked loop (PLL), where the PLL SNR is proportional to the fading amplitude squared, and (2) a fast-fading Rician channel with carrier phase estimation for the line-of-sight path only. Both channel models assume independent fading of successively received symbols. Capacity calculations are performed for equiprobable signaling with 8-ary and 16-ary amplitude-modulated phase-shift-keyed (AM-PSK) constellations. On the Rayleigh channel, the AM-PSK constellations give gains between 2 and 9 dB over PSK, at SNRs between 5 and 40 dB. For the Rician channel, AM-PSK gives a capacity gain over PSK of up to 0.75 bit at high SNR     

Maximum Log-Likelihood Function-Based QAM Signal Classification over Fading Channels

In this paper, we propose a modulation classification algorithm for M-ary QAM signals in Rician and Rayleigh fading channels. The developed algorithms are based on the maximum log-likelihood functions, which are derived from received signals. First of all, we derived the amplitude PDF of M-ary QAM signal over flat and slowly Rayleigh and Rician fading channel, then we developed the log-likelihood functions and then the decision functions for classification. To demonstrate the performance of the proposed classifier, we give an example to classify the 16/32 QAM signals. Results indicate that the performance of classifier is heavily dependent on the severity of channel fading. When channel is AWGN, which means that there exists only one path (may be specular path) between transmitter and receiver, and the Rician factor k, approaches infinity in this case, henceforth, the performance is the best. The performance, however, is degraded with the decrease of k, and finally the classifier performs worst when channel becomes Rayleigh. Further performance improvement can be achieved by increasing the length of record.     

A Theoretical Method for Estimating Performance of Reed-Solomon Codes Concatenated with Orthogonal Space-Time Block Codes

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Variable dwell-time code acquisition for direct-sequencespread-spectrum systems on time-variant Rayleigh fading channels

Variable dwell-time code acquisition based on multiple-dwell or sequential linear tests is investigated for direct-sequence spread-spectrum systems on time-variant Rayleigh fading channels. Unlike in the conventional additive white Gaussian noise channels, the channel memory incurred by fading renders the exact analysis of the acquisition systems extremely difficult, if not impossible. In this paper, a novel method is developed to evaluate the mean acquisition time of the acquisition systems very accurately. The effects of Rayleigh fading are evaluated, and comparisons are made between double-dwell and sequential linear tests. Numerical results show that Rayleigh fading may result in 1-4-dB loss in performance, and the sequential linear test can outperform double-dwell test by a margin of 1-2 dB. The analytical results are verified by computer simulations     

旋转星座下匙孔信道的四元素准正交空时分组码研究

提出了一种基于匙孔信道的旋转四元素准正交空时分组码(QQOSTBC-CR,Constellation Rotation Quaternion Quasi-Orthogonal Space Time Block Code),该码可以通过极化天线进行发射和接收,设计出发射天线数为8的QOSTPBC-CR,并对N＝8的情况进行成对译码,最后与匙孔信道下传统旋转准正交空时分组码(QOSTBC CR,Constellation Rotation Quasi Orthogonal Space Time Block Code)、准正交空时分组码(QOSTBC,Quasi Orthogonal Space Time Block Code)以及瑞利信道下QQOSTBC-CR进行了仿真比较.结果表明:对4个发射天线的情况,当BER＝10(-3)时,BPSK和QPSK调制下本文所提QQOSTBC-CR分别比QOSTBC-CR有4.5dB和7dB的增益,分别比瑞利信道下QQOSTBC-CR有-4dB和-3dB的增益.     

采用两条支路分集接收的相关瑞利衰落信道容量

本文研究采用两条支路最大比合并(MRC)或选择合并(SC)分集接收的相关瑞利衰落信道理论容量推导恒定发射功率自适应M进制正交幅度调制(M-QAM)的频谱效率,并将它们与独立同分布瑞利信道理论容量进行比较,其结果对收发信机之间无视距分量路径、接收机上分集天线之间的距离小于半个波长的无线通信系统设计具有指导作用.     

基于OFDM技术的短波电台系统研究

OFDM（正交频分复用）技术是一种多载波数字调制技术,在无线多径衰落信道下具有较好的传输特性,文中设计短波电台系统采用了OFDM技术来对克服多径衰落带来的干扰,并且给出了系统的设计方案。利用Simulink建模,并在瑞利衰落信道和高斯信道下进行了仿真,结果显示出性能上有较大的改进。     

On the use of interference suppression to reduce intermodulationdistortion in multicarrier CDMA systems

This paper presents a coded multicarrier direct-sequence code-division multiple-access (DS-CDMA) system that, by the use of a minimum mean-squared-error receiver, achieves frequency diversity (instead of path diversity as in a conventional single-carrier RAKE DS-CDMA) and has the ability to suppress the intermodulation distortion and partially compensate for the signal distortion introduced by a nonlinear amplifier at the transmitter. A frequency-selective Rayleigh fading channel is decomposed into M frequency-nonselective channels, based on the channel coherence bandwidth. A rate 1/M convolutional code, after being interleaved, is used to modulate M different DS-CDMA waveforms. The new system is shown to effectively combat intermodulation distortion in the presence of multiple-access interference