多脉冲位置调制卫星光通信中时钟抖动对比特错误概率影响

多脉冲位置调制(MPPM)是基于脉冲位置调制(PPM)的改进形式,已成为卫星光通信中高效调制方式。针对存在背景辐射、大气湍流、热噪声的卫星光通信信道,研究了远场激光脉冲展宽机理和时钟抖动对系统的影响。提出基于格雷码的MPPM联合编码调制方式减小时钟抖动和码间干扰影响,应用星座图设计了基于格雷码(7,2)MPPM映射方法,在相同传输带宽下(7,2)MPPM的传输效率超过16PPM的2倍。分析泊松信道下基于格雷编码的(7,2)MPPM字符错误概率和比特错误概率(BEP)。结果表明,采用格雷编码MPPM可以有效抵御定时误差并降低系统比特错误概率。     

高效纠错编码技术在无线光通信中的性能分析

在介绍无线光通信信道及系统模型的基础上,推导了无线光通信未编码系统和RS编码系统在已知信道边信息条件下的平均误码率,从接收光功率和对数振幅起伏方差方面对RS码编码系统和Turbo编码系统的性能进行比较.仿真结果表明,采用编码方案可以有效地改善大气湍流对通信链路性能的恶化,Turbo码编码方案比RS码编码方案能更好地抗大气湍流干扰.     

基于Turbo码的无线光通信副载波误码性能分析

介绍了湍流信道条件下光强闪烁的对数正态分布模型,结合大气信道特点,在不同光强闪烁效应下,对比分析了几种未编码大气激光通信副载波系统的误码性能。采用Turbo码性能限分析了基于Turbo编码的无线光通信副载波调制系统误码性能,并对Turbo编码前后系统误比特性能进行了对比。仿真结果表明,二进制相移键控(BPSK)误码性能优于其它几种副载波调制,同时Turbo码技术在较强光强闪烁指数下能够获得较大的编码增益,可以有效地提高系统的抗干扰能力。     

大气湍流光PPM通信系统中LDPC码的置信传播译码

对大气弱湍流光PPM通信系统中LDPC码的BP 解码算法进行了研究,提出了相应系统模型下的解码算法.通过理论分析和大量计算机仿真,结果表明:采用LDPC的大气弱湍流光PPM通信系统比未编码的大气弱湍流光PPM通信系统的性能好,但是系统的BER性能随着PPM的时隙数的增加而增大.     

基于H-PPM的可见光通信系统RS编码性能分析

为了改善复杂交通环境下湍流信道的光强闪烁对信号的影响,研究了大气湍流光强闪烁的系统模型,并且针对PPM和DPIM等调制方法存在的问题,提出一种新型的无线光通信调制方法——头脉冲位置调制(head pulse position modulation,H-PPM)。根据湍流信道的特点,推导出基于H-PPM的可见光通信系统未编码时与RS(Reed-Solomon)码纠错后的误时隙率公式。数值仿真曲线证明,当系统误码率为10-10时,RS(15, 7)纠错码可以提高约18 dB的编码增益。由此可得,采取H-PPM调制和RS编码相结合可提高信号的质量,更有利于复杂交通环境下的可见光通信。     

雾对大气激光通信系统的影响及克服方法

分析了雾产生的原因、相关数学模型及其对大气激光通信系统的影响.为了克服雾对无线光通信链路的影响,将LDPC码作为信道编码应用到大气激光通信系统中,并结合置信传播迭代译码算法和副载波PSK强度调制方案,在有雾的大气信道中进行了仿真.仿真结果表明：LDPC码具有优越的纠错能力,并获得了较大的编码增益,该方案可以满足大气激光通信系统的需要.     

雾对大气激光通信系统的影响及克服方法

分析了雾产生的原因、相关数学模型及其对大气激光通信系统的影响.为了克服雾对无线光通信链路的影响,将LDPC码作为信道编码应用到大气激光通信系统中,并结合置信传播迭代译码算法和副载波PSK强度调制方案,在有雾的大气信道中进行了仿真.仿真结果表明:LDPC码具有优越的纠错能力,并获得了较大的编码增益,该方案可以满足大气激光通信系统的需要.     

低密度奇偶校验码在光通信中的性能

低密度奇偶校验码(LDPC)不仅有逼近香农限的良好性能, 而且译码复杂度较低, 结构灵活, 是近年信道编码领域的研究热点, 在光通信系统中有广泛的应用前景。针对非规则Tanner图上构造的低密度奇偶校验长码具有良好的性能, 以及其在光通信系统中的应用, 构造了几种LDPC码, 并采用置信传播(BP)译码, 在加性高期白噪声(AWGN)信道、二相移相键空(BPSK)调制下进行了计算机仿真。根据规则LDPC码和非规则LDPC码的误码率(BER)和FER曲线, 对规则码和非规则LDPC码在编译码方面以及性能方面作了分析和比较, 进而对构造在光通信系统中具有实用价值的LDPC码提出了看法。通过理论分析与仿真结果表明LDPC 码型具有良好的性能, 可以节省硬件开销, 比较适用于光通信系统中, 可作为超强前向纠错码型的候选码。     

基于低密度奇偶校验码的超强前向纠错码设计

光纤中的传输效应(如色散、偏振模色散(PMD)和非线性效应等)会严重影响传输速率和传输距离的进一步提高。因而有必要研究性能更好的新超强前向纠错(Super-FEC) 码型,使其在光通信系统中获得更高的编码增益和更好的纠错性能。简单介绍了低密度奇偶校验(LDPC)码, 然后提出光通信系统中一种基于LDPC码的超强前向纠错(Super-FEC)码型,构造了冗余度为6.68%的新颖LDPC(3969,3720)码, 并给出超强FEC码型的仿真结果。通过与RS(255,239)及BCH(3860,3824)+BCH(2040,1930)进行对比分析, 还分析与探讨了新LDPC码型的编译码电路的设计实现问题。通过理论分析与仿真结果表明这种超强 FEC 码型具有良好的性能, 可以节省硬件开销, 比较适用于光通信系统中, 可作为超强 FEC 码型的候选码。     

光通信系统中基于有限域的LDPC码的构造(英文)

基于有限域中域特征提出一种新型LDPC码的构造法.所构造LDPC码的校验矩阵由基于有限域循环置换矩阵的阵列组成,可以有效地降低编译码复杂度.针对光通信的特点,构造出适合于光传输系统的且具有高码率和高编码增益的码字.仿真结果表明:本文构造的码率为93.7%的LDPC(3780,3542)码与其它几种构造法构造出的具有相同码率的码字相比具有更高的编码增益,更适合应用于光通信系统中.     

A novel construction algorithm of the LDPC code for high-speed long-haul optical transmission systems

According to the transmission characteristics of high-speed long-haul optical transmission system, the main construction method of Low-Density Parity-Check (LDPC) code for optical transmission system is presented and a novel construction algorithm of LDPC code is proposed, the theoretical analysis shows that the parity check matrix of the LDPC code constructed by the proposed construction algorithm has no four-girth phenomenon, this is also theoretically proved out. Both the novel LDPC(3969,3720) code with 6.69% redundancy and the novel LDPC(8281,7920) code with 4.56% redundancy for optical transmission systems are constructed by using the presented construction method and proposed construction algorithm. The simulation results show that the net coding gain (NCG) of the two novel LDPC codes at the eighteenth iteration for the BER of 10^?12 are respectively 1.63 dB and 1.49 dB more than that of the RS(255,239) code in ITU-T G.975. Moreover, the decoding of the LDPC code in the hardware can parallel be implemented, so the decoding speed of the two novel LDPC codes are very rapid, the complexities of implementing the two novel LDPC codes, compared with the concatenated codes in ITU-T G.975.1, are relatively lower, furthermore, the hardware overhead and storage space can relatively be saved and the computation complexity can be reduced in implementing the hardware in the future. As a result, the two novel LDPC codes can better be suitable for high-speed long-haul optical transmission systems.     

Closed-form BER analysis of variable weight MPPM coding under gamma-gamma scintillation for atmospheric optical communications

In this paper, the performance of the variable weight multiple pulse-position modulation (MPPM) coding technique in an atmospheric optical communication environment under gamma-gamma optical scintillation is analyzed, proposing a closed-form expression for the average bit error rate (BER). This study is based on a hyperexponential fitting of the conditional BER in absence of turbulence fluctuations, leading to closed-form expressions that characterize the behavior of this nonlinear coding scheme. Finally, conditional and average BER expressions proposed here are corroborated with Monte Carlo simulations results.     

Performance analysis and design of quasi-cyclic LDPC codes for underwater magnetic induction communications

Magnetic induction (MI) communication is an effective scheme for underwater wireless communication. In this paper, we aim to design an underwater MI communication system based on Quasi-cyclic LDPC (QC-LDPC) codes. Firstly, for a given QC-LDPC code used in underwater MI communication, we propose a novel algorithm to evaluate its performance, which is named as underwater magnetic induction protograph (UWMIP) extrinsic information transfer algorithm. Furthermore, we present a differential evolution UWMIP (DE-UWMIP) algorithm, which incorporates the differential evolution method and the UWMIP algorithm. By this algorithm, we search the optimized QC-LDPC codes with best distance threshold. Simulation results show that the proposed algorithm is effective and provide a good guidance to design the underwater MI communication system.     

低密度奇偶校验码的性能分析与水下通信验证

在ADSP-BF561上实现了低密度奇偶校验码的编码算法。为解决编码复杂度高的问题,将校验矩阵变换后存入数据空间。为节省存储空间,采用压缩算法,并提出相应的编码算法,没有增加复杂度。对不同码率的低密度奇偶校验码在不同信道中的性能进行仿真分析。将不同码率的低密度奇偶校验码应用于水声通信系统进行浅海试验,结果表明低密度奇偶校验码能提高通信系统的鲁棒性,码率越低性能越好。当解码前符号信噪比在7～8dB时,可达到近似无误码的通信性能。     

High-efficiency Gaussian key reconciliation in continuous variable quantum key distribution

Efficient reconciliation is a crucial step in continuous variable quantum key distribution. The progressive-edge-growth(PEG) algorithm is an efficient method to construct relatively short block length low-density parity-check(LDPC) codes. The qua-sicyclic construction method can extend short block length codes and further eliminate the shortest cycle. In this paper, by combining the PEG algorithm and quasi-cyclic construction method, we design long block length irregular LDPC codes with high error-correcting capacity. Based on these LDPC codes, we achieve high-efficiency Gaussian key reconciliation with slice recon-ciliation based on multilevel coding/multistage decoding with an efficiency of 93.7%.     

Spherical reconciliation for a continuous-variable quantum key distribution

Information reconciliation is a significant step for a continuous-variable quantum key distribution(CV-QKD) system.We propose a reconciliation method that allows two authorized parties to extract a consistent and secure binary key in a CV-QKD protocol,which is based on Gaussian-modulated coherent states and homodyne detection.This method named spherical reconciliation is based on spherical quantization and non-binary low-density parity-check(LDPC) codes.With the suitable signal-to-noise ratio(SNR) and code rate of non-binary LDPC codes,spherical reconciliation algorithm has a high efficiency and can extend the transmission distance of CV-QKD.