空间相关莱斯衰落信道下基于部分信道信息的多用户预编码与调度算法

在空间相关的莱斯衰落信道模型下,针对多用户MIMO(Multiple-Input Multiple-Output)系统潜在的多用户分集增益和空间分集增益,该文提出了一种基于部分信道信息的多用户预编码与调度算法。结合部分瞬时信道信息和统计信息,利用约束最大似然估计对各用户信道矢量进行估计,然后利用估计的各用户信道调度多个用户进行预编码。仿真结果表明,该方案以较少的反馈开销,获得了较大的性能增益。     

Polar码在OFDM系统中应用研究

Polar码是2007年由ErdalArikan基于信道极化理论提出的一种新的信道编码方法。在理论上,它能够达到信道容量,并且有着较低复杂度的编译码算法。由于Polar码出现不久,其相关应用研究报道较少。OFDM（Orthogonal Frequency Division Multiplexing）即正交频分复用技术将信道分成若干正交子信道,将高速数据信号转换成并行的低速子数据流,调制到每个子信道上进行传输。本文研究Pola鸸在OFDM系统中的应用,讨论在OFDM系统中Polar码的译码迭代次数、码长、码率以及系统输入信噪比（SignaltoNoiseRatio,SNR）等因素对信号传输的影响。通过性能仿真说明在一定条件下译码迭代次数增加,和码率减小,都能使Polar—OFDM系统的性能更好。     

相关莱斯信道下最大比合并的性能分析

相关莱斯信道下最大比合并的性能分析在现有的文献中很少见。该文提出了一种线性变换的方法以及借助于一定的数学工具,获得了相关莱斯信道下最大比合并后输出信号信噪比的概率密度函数,并且在此基础上得到了频移键控与相移键控相干检测与非相干检测在相关莱斯信道下的误比特率封闭表达式。     

一种基于Polar码的可抗差错图像传输方法

Polar码是第一种理论上被严格证明能达到香农限的信道编码方法。结合Polar码的构造特点,提出了一种基于Polar码的可抗差错的图像传输方法,将传输图像进行离散变换后获取的频率分量与Polar码极化后信道的可靠性一一对应,然后进行编码传输。仿真结果表明,新构造的图像传输系统,能以较少的信息完成图像传输,同时达到较高的传输质量,具有良好的可抗差错性和较高的传输效率。     

卫星通信系统中可变码率LDPC码设计方法

提出了一种基于准循环置换扩展的卫星通信系统可变码率LDPC码设计方法.分析了卫星通信信道的Loo模型及莱斯分布简化模型以计算置信传播解码算法中反映信道特征的初始消息密度,然后使用离散密度进化和粒子群优化在莱斯信道下搜索有较高噪声门限的度分布对,接着利用PEG方法构造具有双对角线结构、围长大于4的基本矩阵,从而确保构造的LDPC码性能较高,最后通过准循环置换扩展基本矩阵得到了多种码率的LDPC码.仿真结果表明,在中低度遮蔽情况下莱斯分布简化模型能很好地近似Loo模型,设计的LDPC码具有线性的编码复杂度,易于工程实现,且性能优良.     

低莱斯因子信道分集接收技术研究

由于低莱斯因子信道存在着多径传播,在信道上经多径传播后的接收信号是衰减和时延都随时间变化的各路径信号的合成,所以接收信号会发生衰落和产生码间干扰。针对低莱斯因子信道中衰落和码间干扰的影响,提出了带内三重频率分集接收实现方式,给出了采用带内三重频率分集的调制器和解调器的原理框图。最后对调制解调器进行了性能测试,并得到了比较理想的实验结果。     

莱斯多径衰落信道下OFDM系统的容量方差分析

方差是系统容量的一个重要参数,可以用来估计通信系统的中断容量。该文研究了正交频分复用（OFDM）系统在莱斯衰落信道下的容量方差。首先该文建立了多径莱斯信道的模型并且定义了多径莱斯信道的莱斯因子,基于此信道模型推出了一个OFDM系统容量方差新的数学表达式,此表达式以OFDM系统的子载波数、信噪比、信道的多径时延等为参数。基于此表达式,计算机仿真和数值计算研究了信噪比、多径数目、莱斯因子对OFDM系统容量方差的影响。结果表明:计算机仿真和数值计算基本吻合,验证了所推导数学表达式的正确性;系统容量方差与信噪比成正比,与莱斯因子和信道的多径数目成反比。另外,该文以积分的形式给出了任意两个相关莱斯随机变量的联合概率密度函数。      

无线信道中的Polar码协商

近年来,无线通信物理层安全逐渐成为一个研究热点,而密钥协商是物理层密码技术的关键部分。针对无线信道特征密钥提取技术中获得的信道特征不完全一致的问题,论文提出了一种基于Polar码的逆向密钥协商方案。合法用户(Alice和Bob)分别通过信道估计获得自已的原始密钥,然后Bob对原始密钥进行Polar码逆编码,并将冻结位信息传输给Alice。在冻结位及其位置信息的基础上,Alice进行Polar码译码后,再通过Polar的编码,获得与Bob一致的密钥序列。仿真结果表明基于Polar码的密钥协商协议,密钥的一致性得到显著提升,且与同等条件下的基于低密度奇偶校验码协商协议相比,可获得更高的纠错成功率。      

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。     

基于PD-CNN的Polar码译码算法

针对传统Polar码译码算法在相关噪声信道下性能严重下降的问题,提出了一种基于前置预判-卷积神经网络（Prior Decision-Convolutional Neural Networks,PD-CNN）的译码算法。通过前置预判深度优化CNN,使其准确地估计信道噪声并使残余噪声尽可能遵循高斯分布,再根据残余噪声分布统计更新出可靠的似然比信息。分析了不同译码算法对不同码率Polar码在不同噪声相关强度下的译码性能,并与本文所提出的译码算法进行对比。仿真结果表明:在相关噪声信道下,当误码率为10-5时,本文所提出的译码算法与标准置信度传播算法相比可获得约2.5 Bd的增益。此外,在高信噪比时,与置信度传播-卷积神经网络算法相比,本文提出的译码算法具有相同的性能,但复杂度更低,译码延迟最大可减少42%。      

Performance of parallel and serial concatenated codes on fading channels

The performance of parallel and serial concatenated codes on frequency-nonselective fading channels is considered. The analytical average upper bounds of the code performance over Rician channels with independent fading are derived. Furthermore, the log-likelihood ratios and extrinsic information for maximum a posteriori (MAP) probability and soft-output Viterbi algorithm (SOVA) decoding methods on fading channels are developed. The derived upper bounds are evaluated and compared to the simulated bit-error rates over independent fading channels. The performance of parallel and serial codes with MAP and SOVA iterative decoding methods, with and without channel state information, is evaluated by simulation over independent and correlated fading channels. It is shown that, on correlated fading channels, the serial concatenated codes perform better than parallel concatenated codes. Furthermore, it has been demonstrated that the SOVA decoder has almost the same performance as the MAP decoder if ideal channel state information is used on correlated Rayleigh fading channels.     

非规则LDPC码在RICE信道中的性能分析

本文对非规则LDPC码在RICE信道的性能进行了分析和仿真,修正了BP译码算法,证明了RICE信道满足对称性,给出了RICE信道译码稳定性条件,推导出了RICE信道的Shannon容量限,采用VC编程对码长N=49512和3072进行了仿真,同时与同码长的Turbo码进行了比较;仿真结果表明LDPC码在码长N＝49512、码率R＝1/3时,与Shannon限相差1dB以内、在低信噪比时其性能优于Turbo码,以及LDPC码本身有很好的交织特性和抗衰落的能力;这进一步表明了LDPC码在包括RICE信道在内的各种信道中的性能都是非常优良的.     

Concatenated coding performance for FSK modulation ontime-correlated Rician fading channels

We present an analytical method for evaluating the performance of noninterleaved concatenated codes over channels modeled as a nonfrequency selective correlated Rician fading channel with a known power spectral density. The main idea is to model the communication system from the modulator input to the demodulator output as a finite state channel (FSC) model, and apply powerful enumeration techniques to such a discrete channel in order to gain useful information on the system performance. The concatenated scheme makes use of two codes; Reed-Solomon codes are employed for the outer code, and binary block codes are used as the inner code. Next, the method is extended to study the effect on the performance when an interleaving with finite depth is incorporated into the communication system. A comparison between symbol and bit interleaving is made. Finally, we study the potential gain produced when channel information is passed on to the outer decoder in the form of an erasure symbol. In all cases, analytical expressions for the probability of the number of error symbols produced by the FSC model were obtained in terms of a coefficient in a formal power series. This is an interesting alternative approach with respect to computer simulations     

Bandwidth efficient coding for fading channels: code constructionand performance analysis

The authors apply a general method of bounding the event error probability of TCM (trellis-coded modulation) schemes to fading channels and use the effective length and the minimum-squared-product distance to replace the minimum-free-squared-Euclidean distance as code design parameters for Rayleigh and Rician fading channels with a substantial multipath component. They present 8-PSK (phase-shift-keying) trellis codes specifically constructed for fading channels that outperform equivalent codes designed for the AWGN (additive white Gaussian noise) channel when v⩾5. For quasiregular trellis codes there exists an efficient algorithm for evaluating event error probability, and numerical results which demonstrate the importance of the effective length as a code design parameter for fading channels with or without side information have been obtained. This is consistent with the case for binary signaling, where the Hamming distance remains the best code design parameter for fading channels. The authors show that the use of Reed-Solomon block codes with expanded signal sets becomes interesting only for large value of E_s/N₀, where they begin to outperform trellis codes     

一种基于增强奇偶校验码级联极化码的新型编译码方法

极化码作为一种纠错码,具有较好的编译码性能,已成为5G短码控制信道的标准编码方案。但在码长较短时,其性能不够优异。提出一种基于增强奇偶校验码级联极化码的新型编译码方法,在原有的奇偶校验位后设立增强校验位,对校验方程中信道可靠度较低的信息位进行双重校验,辅助奇偶校验码在译码过程中对路径进行修剪,以此提高路径选择的可靠性。仿真结果表明,在相同信道、相同码率码长下,本文提出的新型编译码方法比循环冗余校验(cyclic redundancy check,CRC)码级联极化码、奇偶校验(parity check,PC)码级联极化码误码性能更优异。在高斯信道下,当码长为128、码率为1/2、误码率为10-3时,本文提出的基于增强PC码级联的极化码比PC码级联的极化码获得了约0.3 dB增益,与CRC辅助的极化码相比获得了约0.4 dB增益。     

An improved construction algorithm of polar codes based on the frozen bits

In order to improve the problems that the minimum hamming weight(MHW) of the polar codes of the traditional Gaussian approximation(GA) construction is small and its performance is not good enough, an improved channel construction algorithm of polar codes based on frozen bits is proposed by combining the construction of the Reed-Muller(RM) code to effectively increase the MHW and analyzing the correcting and checking functions of the frozen bits in the successive cancellation list(SCL) decoding. ...     

Space-time trellis codes over rapid rayleigh fading channels with channel estimation?part ii: performance analysis and code design for non-identical channels

We consider the maximum likelihood (ML) receiver design, performance analysis and code design for space-time trellis codes (STTC) over non-identical, rapid fading channels with imperfect channel state information (CSI). The exact pairwise error probability (PEP) and PEP bounds for the ML receiver are obtained. A new code design criterion exploiting the statistical information of the channel estimates is proposed, which can minimize the performance loss caused by channel estimation error. New codes are obtained via an iterative search algorithm with reduced complexity. Under actual channel estimation conditions, our codes perform better than the existing codes in the literature which are designed on the assumption of identical channels, and perfect CSI at the receiver. More performance gain can be achieved by our codes when the degree of imbalance among the links is higher.     

A novel bit mapping scheme for high-order polar coded modulation systems

In order to improve the spectrum efficiency of the high-order polar coded modulation systems, the polar code is used as the component code of the bit-interleave coded modulation (BICM) system, a novel bit mapping scheme is proposed considering of the channel polarization and successive cancellation (SC) decoding principle of polar codes as well as the unequal protection of equivalent channels by modulator. In this scheme, the frozen bits on the unreliable split channel are allocated to the equivalent channel with the low protection of the modulator, while the equivalent channels with the high protection are used to transmit the information bits. Thus, the error-correcting performance of polar codes is improved. Compared with some bit mapping schemes, the proposed bit mapping scheme only needs to divide and choose the parameters of the split channels reliability measurement, the complexity does not increase obviously, and simulation results show that the proposed scheme has the better performance under the quadrature amplitude modulation (QAM) modulation based on the Gray mapping.     

极化码的参数捷变技术及性能仿真

极化码是首个能够从理论上证明接近信道容量的纠错码,于2016年11月和低密度奇偶校验码一并作为第5代移动通信的标准。针对极化码特有的蝶形结构采用Trellis对其进行了重新描述,详细分析了串行抵消列表译码算法。同时,基于密度进化理论给出了极化码的码参数捷变技术,能够在不改变编译码器硬件结构与程序的情况下实时、快速地改变编译码参数。仿真结果表明,在编码参数近似相同的情况下极化码的性能要优于低密度奇偶校验码。     

Coding for Frequency-Hopped Spread-Spectrum Communication with Partial-Band Interference--Part I: Capacity and Cutoff Rate

The performance of optimal codes on frequency-hopped channels with partial-band interference is investigated. The performance measures considered are channel capacity and cutoff rate. Worst-case partial-band Gaussian noise interference is assumed with the interference independent of the transmitted signal. The capacity and cutoff rate are calculated as a function of the signal-to-noise ratio. We consider soft decision receivers and hard decision receivers with and without side information. Optimal code rates are found for each of the above cases. The required signal-to-noise ratio for reliable communication when codes are used is determined as a function of the code rate.