Comment on “closed-form SER expressions for star MQAM in frequency non-selective Rician and Nakagami- channels”

An explicit expression is derived for the symbol error rate (SER) of the star MQAM system considered by Ioannis and Aris [Closed-form SER expressions for star MQAM in frequency non-selective Rician and Nakagami-m channels. Int J Electron Commun AEU 2005;59:417–20].     

带有分集的RS码非相干混合DS-SFH扩频通信系统性能分析

本文针对部分带宽噪声干扰、多址干扰和高斯白噪声等多种干扰以及Ｒｉｃｉａｎ信道衰落存在环境下,编码与非编码的异步非相干ＭＦＳＫ调制混合ＤＳ－ＳＦＨ扩频通信系统性能进行了分析、计算和比较。本文分析的编码为前向纠错编码,包括ＲＳ（Ｎ,Ｋ）码,带有分集的ＲＳ（Ｎ,Ｋ）码。与此同时分析和讨论了分集、Ｒｉｃｉａｎ衰落以及部分带宽噪声干扰、多址干扰等对系统性能的影响,得到一些重要结果。     

去除磁共振成像图像莱斯噪声的加权扩散

针对各向同性扩散易于造成图像边缘等特征区域的模糊以及相干增强扩散易于在图像背景区域内产生伪条纹的问题,提出了一种根据磁共振成像（MRI）图像莱斯噪声分布特点来对其进行降噪的加权扩散算法。该算法以MRI图像背景区域的莱斯噪声方差作为区分MRI图像背景区域和感兴趣的边缘特征区域二者特征差异的阈值。基于该阈值,该算法构造了一个加权函数,并用该函数对各向同性扩散和相干增强扩散进行加权。加权函数根据图像在不同结构区域的变化,自适应地调整两种扩散的权值,从而充分发挥两种扩散的优势并克服各自的不足。实验结果表明,该算法在峰值信噪比（PSNR）及平均结构相似度（MSSIM）的评价上优于一些经典算法。因此,该算法的降噪及保护、增强边缘的能力更为优越。     

发射分集系统在空间相关莱斯快衰落信道下的性能

采用空时编码的发射分集系统的性能分析是当前移动通信研究领域的热点问题。相对准静态独立的瑞利衰落信道模型而言,空间相关莱斯快衰落信道更适用于实际情况。但由于在空间相关莱斯快衰落情况下,发射分集系统的性能分析比较复杂,因此关于这方面的论文较少。本文利用多变量统计学理论,得到发射分集系统在空间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,并详细说明了信道特性对系统性能的影响。最后给出了仿真结果。     

Performance Analysis of LDPC on Rician Fading Channels

This paper analyzes and simulates the performance of irregular low-density parity check (LDPC) codes on Rician fading channels. The authors also modified the brief propagation decoding algorithm, proved the symmetry and showed the stability conditions of the channels, and calculated the Shannon limits on Rician channels in this paper. By using Visual C++ programming to simulate the performance, the result indicates that when code length N = 3,072 and code rate R = 1/3, the difference with the Shannon limit is about 2 dB. Therefore, the performance of LDPC is also very effective on all kinds of channels, including the Rician kind. Translated from Journal of Beijing University of Posts and Telecommunications, 2004, 27(2): 48–53 (in Chinese)     

非频率选择性莱斯慢衰落信道中M元正交信号的接收

本文推导出了非频率选择性莱斯慢衰落信道中Ｍ元正交信号的相干接收机与非相干接收机的误比特率计算公式，并给出了一些数值结果。最后，对相干接收机和非相干接收机的性能进行了比较     

非选择性Rician衰落信道中A—T接收机的性能

本文给出了在Ｒｉｃｉａｎ衰落信道中一种抗多址干扰单用户检测接收机［１］的比特误码率特性。结果表明，当系统实际正使用用户数不大于系统的最大设计用户数时，这种接收机的误码率与系统内正使用用户数的相关性不大     

Packet-by-Packet Adaptive Scheme for Video Coding and Transmission Over Wireless IP Networks Using Rate-Compatible Punctured Turbo (RCPT) Codes

In this paper, we consider real-time video coding and transmission over packet-switched wireless IP networks, such as WLAN, using RCPT codes and joint source-channel coding (JSCC) with concentration on a packet-by-packet adaptive scheme. We present a systematic design methodology to enable the applicability of JSCC techniques. The performance of H.263+ video coding and transmission over wireless channel modeled as slow Rician fading channels using this approach is studied. Results indicate that a packet-by-packet adaptive RCPT-JSCC approach is of significant advantage for real-time video applications and leads to more acceptable video delivery quality over interference-limited and time-varying wireless networks.     

基于海面散射的莱斯MIMO信道容量研究

通过相关莱斯信道模型对海面散射水声多入多出(MIMO)信道容量进行了研究。从Helmholtz-Kirchhoff积分和Fresnel近似出发,得到海面散射信号的空间相关性,由于信道的协方差矩阵不可以表示成发射相关矩阵和接收相关矩阵的Kronecker积,通过Monte Carlo仿真研究了莱斯因子、接收信噪比和空间相关性对MIMO信道容量的影响。从对outage capacity和信道容量的CCDF(Complementary Cumulative Distribution Function)的仿真计算结果可以看出,莱斯衰落的MIMO信道容量并不总是小于瑞利衰落MIMO信道容量,当信道的空间相关性较大和接收信噪比较小时,由于信道的衰落作用将起主要作用,对于较小的收发阵元数,以非衰落的直达信号为主的莱斯MIMO信道容量将大于瑞利衰落的MIMO信道容量。     

Performance analysis of cooperative network over Nakagami and Rician fading channels

This paper presents an analysis on the performance of single‐relay and multiple fixed‐relay cooperative network. The relay nodes operate in amplify‐and‐forward (AF) mode and transmit the signal through orthogonal channels. We consider maximal‐ratio combining at the destination to get the spatial diversity by adding the received signals coherently. The closed‐form moment‐generating function (MGF) for the total equivalent signal‐to‐noise ratio (SNR) is derived. The exact expressions of symbol‐error rate, outage capacity, and outage probability are obtained using the closed‐form MGF for single‐relay and multiple‐relay cooperative network with M‐ary phase shift keying (M‐PSK) and M‐ary quadrature amplitude modulation (M‐QAM) over independent and non‐identical Nakagami‐m channels and Rician fading channels. The approximated closed‐form expression of ergodic capacity is derived for both Nakagami‐m and Rician fading channels. The performance of the system is analyzed at various relay locations. The theoretical results are then compared with the simulation results obtained for binary PSK, quadrature PSK, and 16‐QAM modulation schemes to verify the analysis. Here, the expressions derived can be easily and more efficiently used to compute the performance parameters than doing Monte Carlo simulations. It is shown that cooperation is significant only for low K values for Rician by plotting cooperation gain versus K. The results show that the cooperative network performs best when the relay is located in the middle of source to destination link, at lower SNR values, and the performance of the system is worst if the relay is located closer to the source than to the destination. Copyright © 2013 John Wiley & Sons, Ltd.