PPM多级编码调制的硬判决迭代解调译码

针对脉冲位置调制(PPM)与多级编码结合中的错误传播问题,利用多阶段译码原理的"链式规则",提出一种基于迭代的解调译码方法,给出了8-PPM多级编码调制的硬判决迭代算法。仿真分析表明,迭代解调译码方法可以改善错误传播现象,降低系统的误码率;在相同迭代次数下,信道衰减越大,该译码方法获得的增益越明显。综合考虑性能改善效果及成本,M阶编码调制系统的迭代次数宜选M次以内。     

大气无线光信道下基于光子计数的迭代译码性能

为了克服大气无线光信道中光强闪烁带来的长突发错误,本文提出了一种基于光子计数的迭代译码方案,并分析基于大气无线光信道下的译码性能.仿真结果表明,本方案不仅提高了系统的抗突发错误性能,并且与传统的信道交织+级连码方案相比,具有不引入信道交织时延和易于硬件实现的优点.     

非平稳信道下LDPC码低复杂度滑窗置信传播联合信道估计与译码算法

随着移动通信应用场景的持续增多,非平稳信道成为越来越常见的传输环境,而非平稳信道下的可靠传输依赖于准确的信道估计。基于信源编码中用于信源参数估计和信源相关性估计的滑窗置信传播(SWBP)算法,该文提出一种非平稳信道下LDPC码的联合信道估计与译码(JCED)算法;同时,分别基于交叉熵和离散傅里叶变换提出两种在每轮JCED迭代中自适应设置滑窗长度的快速算法。仿真结果表明,在无导频辅助的前提下,所提算法具有接近理想信道估计下置信传播译码的性能以及高效率、低复杂度、强鲁棒性和不导致错误平层等优点。     

非平稳信道下LDPC码低复杂度滑窗置信传播联合信道估计与译码算法

随着移动通信应用场景的持续增多,非平稳信道成为越来越常见的传输环境,而非平稳信道下的可靠传输依赖于准确的信道估计.基于信源编码中用于信源参数估计和信源相关性估计的滑窗置信传播(SWBP)算法,该文提出一种非平稳信道下LDPC码的联合信道估计与译码(JCED)算法;同时,分别基于交叉熵和离散傅里叶变换提出两种在每轮JCED迭代中自适应设置滑窗长度的快速算法.仿真结果表明,在无导频辅助的前提下,所提算法具有接近理想信道估计下置信传播译码的性能以及高效率、低复杂度、强鲁棒性和不导致错误平层等优点.     

Turbo编码OFDM系统中一种判决反馈的WLMS信道跟踪算法

在Turbo译码时对信息位和校验位都进行MAP译码,避免了传统基于译码再编码判决反馈信道估计和跟踪算法中反馈信号重构时的错误传播问题,降低了反馈信号的错误概率,提高了信道估计和跟踪的性能,解决了在信道变化较快条件下文献[8]提出的维纳LMS(WLMS)算法信噪比门限过高的问题。仿真结果表明,算法性能接近理想判决反馈时的性能限,与直接判决反馈的维纳LMS算法相比,在系统误比特率为10~(-4)条件下系统性能约提高2dB。     

瑞利信道下基于Turbo-BICM-ID的DFT-S-OFDM性能研究

为了提升DFT-S-OFDM系统在瑞利信道下的传输性能,采用位交织编码调制迭代译码方案(BICM-ID)、旋转映射(R-QAM)和Turbo码等技术,设计了基于Turbo-BICM-ID的DFT-S-OFDM系统。给出了系统原理框图,对编码调制系统的解调译码迭代算法进行了推导,对系统进行了Matlab仿真验证。仿真结果表明,与传统的卷积码设计方案相比,该设计方案在误码率为10-5时,可以获得5.7 d B的增益改善,同时可以获得更低的错误平层,有效地改善了DFT-S-OFDM系统在瑞利信道下的性能。     

基于振荡迭代的修正BP译码算法

针对中高信噪比(SNR)下低密度奇偶校验(LDPC)译码错误振荡迭代不收敛,提出了基于置信传播(BP)算法的修正LDPC译码算法,即软值归零BP算法。该算法通过将振荡迭代的变量节点传递的外信息置零,减少错误信道消息对迭代译码的影响,较大地改善了译码性能。而且,还给出了振荡迭代节点的判定准则,提高了振荡迭代节点判定的准确性。仿真结果表明,在中高信噪比区且译码迭代次数相同的情况下,该算法能比BP算法获得更好的译码性能。     

基于符号的LDPC码在OFDM水声通信仿真

低密度奇偶校验码(LDPC)具有结构简单、编码增益高、在高斯信道下接近香农限的性能和可并行译码等特点,是当前通信领域研究的热点。水下有限带宽、多径时变和高噪声等特点的信道使信号在传输时,产生的突发和随机错误使系统误码率较高,通信质量难以保证。提出基于符号的LDPC码的OFDM水声通信系统,利用基于符号的迭代编译码算法可有效纠正突发和随机错误,且与高阶调制结合可以提高水下有限频谱利用率。仿真结果表明:基于符号的LDPC码相比传统主流的Turbo码和卷积码,能以更低信噪比达到正交频分复用水声通信系统误码率的要求。     

基于电力线通信的LDPC码分层译码算法研究

针对电力线信道多径延迟效应和脉冲噪声影响问题,建立了基于电力线的LDPC-OFDM系统模型.并基于该模型,对低密度奇偶校验码(LDPC)的译码算法进行深入研究.基于最小和置信传播(Belief Propagation,BP)译码算法原理,改进分层和积译码算法,提出一种基于修正因子的分层最小和对数似然比译码算法.仿真结果表明,该算法译码复杂度低,迭代收敛速度快,能够有效降低电力线LDPC-OFDM系统的误码率(BER),提高传输效率.     

LDPC码的不可检测译码错误分析

纠错性能良好的LDPC码同时具有良好的检错性能。本文介绍了LDPC码的不可检测译码错误概率上限，讨论了不可检测译码错误与码参数的关系，提出对于特定构造的LDPC码，在基于AWGN信道传输和置信传播迭代译码时，可以应用迭代过程中连续消息的密度进化来分析不可检测译码错误概率，并给出了一些短码长高码率情况下的仿真结果。     

Performance of joint source–channel decoding with iterative bit combining and detection

A joint source–channel decoding scheme (JSCD) with iterative bit combining (IBC) is proposed, which exploits two types of a priori information. The first one is the a priori bit probabilities obtained from source statistics, and the second is the channel a priori probabilities obtained from saved extrinsic information of previous transmissions. The JSCD-IBC scheme also incorporates iterative detection as both a stopping criteria and mechanism for triggering retransmissions. This adds an implicit adaptivity to the system and prevents excess iterations/retransmissions from being effected. The performance of the JSCD-IBC scheme is evaluated with four different iterative detection schemes and also two different types of variable length codes, Huffman and reversible variable length codes. Simulation results show that a significant performance gain in terms of bit error rate, throughput, and number of iterations can be achieved with the JSCD-IBC scheme as compared to a separate decoding scheme.     

一种抗多径效应的非相干无人机测距方案

多径效应是造成无人机测控系统可用性降低的重要原因之一。为了降低多径效应对无人机（UAV）测控系统的影响,提出了一种非相干测距技术方案。该方案利用了单载波频域均衡（SC-FDE）技术以及优化遥控帧与伪码速率关系及发送位置的方法,降低了机上测距数据下传误码率,同时提高了机上采样精度。经仿真验证,在反射路径信号比直达路径小6 dB且信噪比大于7 dB时,系统的测距精度满足无人机测控系统的指标要求。     

RS（16,12）缩短码编译码原理及性能分析

在各类数字通信系统以及计算机存储和运算系统经常利用差错控制编码降低误码率,提高通信质量,满足对数据传输通道可靠性的要求。RS码是一种性能优良的前向纠错码,具有同时纠正随机错误和突发错误的能力,它的构造特点决定了其非常适合于纠正突发性错误。文中在阐述RS系统码编译码原理的基础上,提出了RS（16,12）缩短码的编译码方法,利用MATLAB对R S（16,12）缩短码在高斯信道和瑞利信道条件下的纠错能力进行仿真,并分析其纠错性能。     

Performance evaluation of HDAF relaying systems for pilot and data symbol burst transmission over quasi‐static Rayleigh fading channels

This paper analyzes averaged symbol error probabilities of burst transmission consisting of pilot and data symbols for hybrid adaptive decode‐or‐amplify‐forward (HDAF) relaying systems. Under the assumption of quasi‐static Rayleigh fading channels with independent and non‐identically distribution, we consider a channel estimation scheme based on pilot symbols and show how channel estimation error affects received signal‐to‐noise ratio (SNR) and symbol error probability (SEP). Firstly, all the possible detection error‐events are presented for all the relay nodes, and their probabilities are derived as forms related with data symbol burst transmission. For the given error event, we analyze the conditional SEP as an exact form and then, the averaged SEP (ASEP) is approximately derived as a closed‐form. The simulation results verify that our derived ASEP expression is accurate over all the regions of SNR. Utilizing the proposed expressions, we can evaluate ASEP performance of HDAF relay systems easily and fast. Copyright © 2015 John Wiley & Sons, Ltd.     

无人机测控信道衰落特性及其抑制方式

分析了无人机测控信道模型以及由小规模衰落带来的非频率选择性衰落、频率选择性衰落与时间选择性衰落的产生机理及特性,并针对这3种衰落进行了抑制方法分析,指出OFDM、交织与编码以及空间分集是无人机测控中值得重点研究的抗衰落技术.     

Multiuser receiver scheme for full‐rate space–time coded CDMA system with imperfect estimation

By introducing a full‐rate space–time coding (STC) scheme, a synchronous CDMA (code division multiple access) system with full‐rate STC is given, and the corresponding uplink performance is investigated in Rayleigh fading channel with imperfect estimation. Considering that existing STC‐CDMA system has high decoding complexity, low‐complexity multiuser receiver schemes are developed for perfect and imperfect estimations, respectively. The schemes can make full use of the complex orthogonality of STC to reduce the high decoding complexity of the existing scheme, and have linear decoding complexity compared with the existing scheme with exponential decoding complexity. Moreover, the proposed schemes can achieve almost the same performance as the existing scheme. Compared with full‐diversity STC‐CDMA, the given full‐rate STC‐CDMA can achieve full data rate, low complexity, and partial diversity, and form efficient spatial interleaving. Thus, the concatenation of channel coding can effectively compensate for the performance loss due to partial diversity. Simulation results show that the full‐rate STC‐CDMA has lower bit error rate (BER) than full‐diversity STC‐CDMA systems under the same system throughput and concatenation of channel code. Moreover, the system BER with imperfect estimation are worse than that with perfect estimation due to the estimation error, which implies that the developed multiuser receiver schemes are valid and reasonable. Copyright © 2010 John Wiley & Sons, Ltd.     

基于信道编码及空时编码级联的两用户协同分集

传统协同分集通过使网络中各单天线用户共享彼此天线,形成虚拟多天线阵列来实现空间分集,使得体积和功耗受限的网络终端也能获得分集增益,然而这并没有将信道编码和空时编码结合起来以使系统得到编码增益。为了能够获得编码增益来进一步改善系统性能,本文提出了一种基于信道编码和分布式空时分组码级联方式下的两用户协同分集方案,并且在准静态的瑞利衰落信道下对系统误码性能进行了理论推导和系统仿真,给出了误比特率的上限解析表达式。在协同用户间信道存在噪声的情况下,我们分别对CRC-DSTBC和CC-DSTBC级联下的发射方案进行了性能分析和系统仿真。仿真结果表明:即使协同用户间的信道存在噪声,本文所提出的协同分集方案与传统协同分集相比,不但获得了分集增益,同时也得到了编码增益,系统误比特率大大降低,从而显著提高了系统性能,并且这也和理论分析相吻合。     

Bit error probability of distributed Turbo coded relay systems over quasi-static Rayleigh fading channels

As is known, distributed Turbo coding (DTC) performs close to the theoretic outage probability bound of a relay channel when correct decoding is assumed at the relay. However, decoding error is inevitable in practical fading channels due to the error-prone feature of radio channels, and the decoding error propagation in DTC scheme will severely degrade the error performance of the relay system. As a result, it is necessary to evaluate the error performance of the DTC scheme in multi-hop relaying wireless systems in practical fading channels. Moreover, the theoretical method of analysis provides an effective tool for obtaining the error performance besides lengthy simulations. In this article, the concept of equivalent signal-to-noise ratio (SNR) of the two-hop relay channel and the method of computing equivalent SNR are developed, and then the upper bound on the bit error probability (BEP) of DTC relay systems is analyzed by use of Turbo code's distance spectrum, the concept of uniform interleaver, the limit-before-averaging technique, and the union bound method. Both theoretical analysis and numerical simulation are implemented for relay systems with DTC scheme over quasi-static Rayleigh fading channels. The results show that the upper bound approaches the simulation results in the medium to high SNR region.     

一种基于大数逻辑判决和信道响应的HARQ算法

为了克服无线信道时变和多径衰落对信号传输的影响,全球微波互联接入(WiMAX)系统采用混合自动重传请求(HARQ)技术以提高数据传输的可靠性,确保服务质量。传统的非合并HARQ算法处理比较简单,内存需求较少,但是重传次数多,系统吞吐量低;合并译码HARQ算法能够有效减少重传次数,提高系统吞吐量,但是运算复杂度和内存需求较大。针对已有算法存在的不足,提出了一种基于大数逻辑判决(MLD)和信道冲激响应功率(CSI)的HARQ合并译码算法—MLD-CSI。该算法综合运用择多判决法则和择优选择法则,在接收端对多次重传的接收信号进行合并译码。分析和仿真结果表明,在时变和多径信道环境下,所提算法与MRC合并算法相比,几乎不损失系统的误码率和吞吐量性能,且运算复杂度和内存需求显著降低,非常适用于实际系统。      

Hybrid block-convolutional rate-½ coding strategy forconstant envelope (CE)Q2PSK

The authors address the problem of trellis coding on multidimensional signal space for incorporation into a 4D quadrature-quadrature phase-shift keying (Q²PSK) communication system. A low-complexity rate-½ hybrid block-convolutional coding scheme is proposed, to be utilised in a constant envelope (CE)Q²PSK system configuration. The encoder and decoder designs have been structured to facilitate simple implementation with standard components. The bit error rate performance of the proposed coding scheme is studied by means of simulation on a non-frequency selective Rician fading channel assuming coherent detection. The benefits of the use of channel state information (CSI) in conjunction with maximum-likelihood Viterbi decoding are also considered