A new probability decoding scheme based on genetic algorithm for FEC codes in optical transmission systems

Based on the genetic algorithm(GA),a new genetic probability decoding(GPD) scheme for forward error correction(FEC) codes in optical transmission systems is proposed.The GPD scheme can further offset the quantification error of the hard decision by making use of the channel interference probability and statistics information to restore the maximal likelihood transmission code word.The theoretical performance analysis and the simulation result show that the proposed GPD scheme has the advantages of lower decoding complexity,faster decoding speed and better decoding correction-error performance.Therefore,the proposed GPD algorithm is a better practical decoding algorithm.     

光通信中基于BCJR的BCH译码算法研究

首先从理论上分析了硬判决译码算法和软判决译码算法的性能然后对BCH(Bose,Ray-Chaudhuri,Hocquenghem)码的网格结构以及BCJR(Bahl,Cocke,Jelinek and Raviv)算法进行了详细地分析及推导。实验结果表明,在光信道环境中,在误比特率为10-5时,当仅提高最小汉明距离码率相同或者仅减小码率最小汉明距离相同时,BCJR算法相对于硬判决译码算法的编码增益分别在之前的编码增益基础上又增加了0.15dB和0.25dB。因此设计级联码方案时,应尽可能选择纠错能力较大的内码。此外也可以采用适当增加内码的冗余度相应减小外码的冗余度的方法,在获得更高的编码增益的同时保证整个系统的带宽利用率不变。     

A novel decoding algorithm based on the hierarchical reliable strategy for SCG-LDPC codes in optical communications

An effective hierarchical reliable belief propagation （HRBP） decoding algorithm is proposed according to the struc- tural characteristics of systematically constructed Gallager low-density parity-check （SCG-LDPC） codes. The novel decoding algorithm combines the layered iteration with the reliability judgment, and can greatly reduce the number of the variable nodes involved in the subsequent iteration process and accelerate the convergence rate. The result of simulation for SCG-LDPC（3969,3720） code shows that the novel HRBP decoding algorithm can greatly reduce the computing amount at the condition of ensuring the performance compared with the traditional belief propagation （BP） algorithm. The bit error rate （BER） of the HRBP algorithm is considerable at the threshold value of 15, but in the sub- sequent iteration process, the number of the variable nodes for the HRBP algorithm can be reduced by about 70% at the high signal-to-noise ratio （SNR） compared with the BP algorithm. When the threshold value is further increased, the HRBP algorithm will gradually degenerate into the layered-BP algorithm, but at the BER of 10-7 and the maximal iteration number of 30, the net coding gain （NCG） of the HRBP algorithm is 0.2 dB more than that of the BP algo- rithm, and the average iteration times can be reduced by about 40% at the high SNR. Therefore, the novel HRBP de- coding algorithm is more suitable for optical communication systems.     

一种改进的无线光通信LDPC码译码算法

针对无线光通信中低密度奇偶校验码(LDPC)置信传播(BP)译码算法复杂度高及置信度振荡造成译码错误等缺点,基于对数BP算法提出了一种改进的译码算法。改进的译码算法在校验节点运算时,判断输入到校验节点消息的最小值与某个门限的大小,根据比较结果,分别用消息最小值或若干个最小值进行运算,在损失很少性能的情况下降低了运算复杂度;同时在比特节点采用振荡抵消处理运算,提高了算法的性能增益。最后在对数正态分布湍流信道模型下,分别对比特充分交织和交织深度为16的情况进行了仿真实验。仿真结果表明,改进的译码算法与BP算法相比,大幅度降低了计算复杂度,而且译码性能有一定的优势,收敛速度损失很少;而相对于最小和算法,改进的算法虽然译码复杂度有所增加,但误码率性能有明显的优势,并且收敛速度也优于最小和算法。因此,改进的译码算法是无线光通信中LDPC码译码算法复杂度和性能之间一个较好的折中处理方案。     

A novel RS BTC coding scheme for optical communications

A novel Reed Solomon(RS) block turbo code(BTC) coding scheme of RS(63,58)×RS(63,58) for optical communications is proposed.The simulation results show that the net coding gain(NCG) of this scheme at the sixth iteration is more than that of other coding schemes at the third iteration for the bit error rate(BER) of 10-12.Furthermore,the novel RS BTC has shorter component code and rapider encoding and decoding speed.Therefore,the novel RS BTC coding scheme can be better used in high-speed long-haul optical communication systems,and the novel RS BTC can be regarded as a candidate code of the super forward error correction(super-FEC) code.Moreover,the encoding/decoding design and implementation of the novel RS BTC are also presented.     

A novel construction scheme of QC-LDPC codes based on the RU algorithm for optical transmission systems

A novel lower-complexity construction scheme of quasi-cyclic low-density parity-check (QC-LDPC) codes for optical transmission systems is proposed based on the structure of the parity-check matrix for the Richardson-Urbanke (RU) algorithm. Furthermore, a novel irregular QC-LDPC(4 288, 4 020) code with high code-rate of 0.937 is constructed by this novel construction scheme. The simulation analyses show that the net coding gain (NCG) of the novel irregular QC-LDPC(4 288,4 020) code is respectively 2.08 dB, 1.25 dB and 0.29 dB more than those of the classic RS(255, 239) code, the LDPC(32 640, 30 592) code and the irregular QC-LDPC(3 843, 3 603) code at the bit error rate (BER) of 10-6. The irregular QC-LDPC(4 288, 4 020) code has the lower encoding/decoding complexity compared with the LDPC(32 640, 30 592) code and the irregular QC-LDPC(3 843, 3 603) code. The proposed novel QC-LDPC(4 288, 4 020) code can be more suitable for the increasing development requirements of high-speed optical transmission systems.     

Soft decoding in optical systems

We consider the application of concatenated codes with interleaver and iterative decoding to optical communication systems. We show how to obtain the optimum log-likelihood ratio to be provided to the soft decoder in the optical channel environment, and compare the performance of a decoder using it with the one employing a Gaussian approximation of the optical channel. Simulation results refer to practical turbo-product codes, and encompass the effect of quantization on the log-likelihood ratio. The results show that the Gaussian assumption in computing the log-likelihood ratio for the optical channel leads to significant losses.     

多元LDPC码串行译码算法在光纤通信中的应用

将串行BP译码算法用在多元LDPC码中,降低了在光纤传输系统中的译码延时.详细介绍了在多元LDPC码中的串行BP译码算法和光纤通信系统的仿真模型.给出了在采用串行BP算法的LDPC译码器中,译码最大迭代数量对译码性能的影响,比较了采用传统的BP算法扣串行BP算法时LDPC译码器的性能.结果表明,采用串行BP算法确实能够提升LDPC译码器的收敛速度.     

基于量子遗传算法的自由曲面离轴反射光学系统设计

针对自由曲面离轴反射光学系统的初始结构较少、优化过程复杂的问题,提出了一种基于量子遗传算法的离轴反射光学系统设计方法,即采用量子遗传算法结合像差理论得到高像质的初始光学系统结构,再对其离轴化处理并引入自由曲面,进而设计得到自由曲面离轴反射光学系统。该方法可以方便、快捷地为自由曲面离轴反射光学系统提供像质良好、特定布局的初始结构。以离轴三反系统为例,采用该方法设计了一套工作在可见光波段、视场大小为10°×4°、F数为2的主三镜一体化的自由曲面离轴三反系统。仿真结果表明,该离轴三反系统视场较大、结构紧凑、成像质量良好,其最大RMS波像差为0.0485 λ (λ=0.6328 μm),全视场的调制传递函数（MTF）在50 lp/mm处大于0.9,且一体化集成结构有利于简化系统的对准及装调。     

A soft-output decoding algorithm for concatenated systems

In order to fully utilize the SDD (soft-decision decoding) capacity of the outer codes in a concatenated system, reliability information on the inner decoder outputs (called soft outputs) needs to be provided to the outer decoder. This paper shows that a modified MAP algorithm can be effectively and accurately used to generate such information. In the course of the presentation, a metric based on the reliability information is proposed for the outer decoder. This metric has the Euclidean metric on AWGN channels as its special case, which leads to the concept of generalized SDD (GSDD). Several practical concerns regarding the proposed soft-output decoder are addressed through theoretical analysis and simulation: the effect of finite decoding depth, computational complexity, range overflow, and scaling. Comparisons to previous work on soft-output decoders are made     

Low-density parity check codes and iterative decoding for long-haul optical communication systems

A forward-error correction (FEC) scheme based on low-density parity check (LDPC) codes and iterative decoding using belief propagation in code graphs is presented in this paper. We show that LDPC codes provide a significant system performance improvement with respect to the state-of-the-art FEC schemes employed in optical communications systems. We present a class of structured codes based on mutually orthogonal Latin rectangles. Such codes have high rates and can lend themselves to very low-complexity encoder/decoder implementations. The system performance is further improved by a code design that eliminates short cycles in a graph employed in iterative decoding.     

一种以备份信息为基础的译码新方法

提出了一种新的译码方法———"备份信息"译码方法,该方法在编码的"备份信息"全集中适当选取子集并加以组合,最终形成判决量进行译码。此方法在保证误码率基本不变的情况下大大减少了译码复杂度。计算机仿真表明这种译码方法在短码译码上有较好的性能。     

An algorithm for global optimization of optical communication systems

We present a global optimization algorithm especially appropriate for the optimization of optical communication systems. It is independent of external parameters and converges to the global optimum, considerably reducing the simulation time. The algorithm is used to optimize the fiber launch powers and dispersion map of a single-channel OOK, DPSK and DQPSK at several data rates.     

FSO MIMO系统中迭代译码算法的研究

自由空间光通信（FSO）系统是一种新型的宽带接入系统,结合了光纤通信与微波通信的优点。但是FSO系统容易受到环境和天气状态的影响,把多输入多输出（MIMO）技术应用于FSO系统中可以有效改善大气对激光波束的影响,提高系统性能。文中主要研究了FSO-MIMO系统的空时译码问题,结合传统的一些译码算法,把Turbo码的迭代译码思想应用于FSO MIMO的空时译码中,分析了一种基于马尔科夫链蒙特卡洛（MCMC）算法的迭代译码方法。     

一种基于量化预处理的低复杂度LDPC译码算法

为了降低低密度奇偶校验(Low Density Parity Check,LDPC)码译码算法的复杂度,提出了一种基于量化预处理的LDPC迭代大数逻辑译码算法。该算法在迭代译码过程中,校验节点采用基于伴随式的信息处理方式,避免了外信息的计算;同时,变量节点基于回传的伴随式信息进行可靠度偏移大小的计算,并结合与当前码位相对应的调制映射信息进行可靠度偏移方向的设计。迭代更新时,变量节点采用基于信息匹配的可靠度更新规则。迭代前的量化预处理能避免实数乘法运算进入迭代过程,使其只涉及整数加法操作和逻辑操作。仿真结果表明,在保持译码性能的前提上,所提算法具有更低的译码复杂度。     

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%。      

基于RADIX-4的Turbo码全并行译码算法

针对Turbo码全并行译码算法译码迭代次数多、硬件消耗大的问题,提出了一种基于RADIX-4的改进译码算法.将译码算法中状态转移图的相邻两步状态合并为一步计算,译码时以"比特对"的形式操作进行迭代.在保留译码最大并行度同时,译码计算单元使用量减少一半,显著降低了Turbo码全并行译码算法的运算复杂度和存储开销.仿真结果...     

A new Reed-Solomon code decoding algorithm based on Newton'sinterpolation

A Reed-Solomon code decoding algorithm based on Newton's interpolation is presented. This algorithm has as main application fast generalized-minimum-distance decoding of Reed-Solomon codes. It uses a modified Berlekamp-Massey algorithm to perform all necessary generalized-minimum-distance decoding steps in only one run. With a time-domain form of the new decoder the overall asymptotic generalized-minimum-distance decoding complexity becomes O(dn), with n the length and d the distance of the code (including the calculation of all error locations and values). This asymptotic complexity is optimal. Other applications are the possibility of fast decoding of Reed-Solomon codes with adaptive redundancy and a general parallel decoding algorithm with zero delay     

A new sequential decoding algorithm based on branch metric

A new sequential decoding algorithm with an adjustable threshold and a new method of moving through the decoding tree is proposed. Instead of the path metric of the conventional sequential decoding algorithms, the proposed algorithm uses a branch metric based on maximum-likelihood criterion. Two new parameters, the jumping-back distance and going-back distance, are also introduced. The performance of the algorithm for long constraint length convolutional codes is compared to those of the other sequential decoding algorithms and the Viterbi algorithm. The results show that the proposed algorithm is a good candidate for decoding of convolutional codes due to its fast decoding capability and good bit error rate (BER) performance. This work was supported in part by the Research Foundation at Karadeniz Technical University under Grant 2004.112.004.01 and 2005.112.009.2.     

基于遗传算法的异构系统多副本容错调度算法

针对异构系统中基于多副本机制的容错调度方法忽略调度makespan、任务间依赖与系统链路失效及严格调度方式调度makespan较长问题,首先提出通用调度方式下同时考虑节点和链路失效的可靠性计算方法;然后给出该通用调度问题的0-1整数规划模型;接着提出可靠性意识多副本任务通用调度(RAMD_TGS, reliability-aware multi-duplication task general scheduling)算法,通过遗传算法种群进化来搜索副本映射节点和开始执行时间。实验表明该算法不仅满足可靠性要求,而且与严格调度方式相比能进一步减小调度makespan,该算法资源占用开销也是可接受的。