基于Polar码的速率兼容调制方案设计

提出了一种基于Polar码的速率兼容调制（rate compatible modulation,RCM）联合设计方案,用于提高无线通信频谱利用率.相应地设计了基于置信度传播（belief propagation,BP）和软抵消（soft cancellation,SCAN）的接收端高效联合迭代译码算法.根据该算法可通过优化变量节点对数似然比（log-likelihood ratio,LLR）信息迭代方式以及采用限制译码符号上限的改进措施,提高译码过程的稳定性与时效性.与距离优化的级联低密度奇偶校验（low-density parity-check codes,LDPC）码RCM方案对比结果表明,提出的高效联合迭代译码算法在低信噪比（signal noise ratio,SNR）下有更低的译码复杂度,并且具有更优的吞吐量和误码率性能.因此,本文所提方案适合在恶劣信道条件下的无线传输.     

迭代检测算法在比特交织编码调制系统中的比较研究

迭代检测技术不仅局限于在传统的级联码系统中的应用,还可用于解决现代数字通信中的许多检测／译码问题。随着Turbo码的出现,人们对迭代译码算法进行深入研究,并提出一些简化译码算法。比特交织编码调制及迭代检测（bit—interleaved coded modulation with iterative decoding,BICMID）是一种高效数据传输系统。比特交织和迭代译码是BICM—ID系统具有卓越性能的关键因素,译码算法的选择不仅影响接收机的性能,也决定了系统的复杂度。文中研究迭代译码算法对BICM—ID系统性能的影响,分析各种译码算法的计算复杂度。仿真结果表明log-APP算法有好的性能同时复杂度也高,简化的译码算法能降低译码器的复杂度,但会带来一定的性能损失;随着信道条件的改善,算法简化带来的性能损失也随之减小。     

Belief Propagation List Decoding for Polar Codes: Performance Analysis and Software Implementation on GPU

Belief propagation(BP) decoding outputs soft information and can be naturally used in iterative receivers. BP list(BPL) decoding provides comparable error-correction performance to the successive cancellation list(SCL) decoding. In this paper, we firstly introduce an enhanced code construction scheme for BPL decoding to improve its errorcorrection capability. Then, a GPU-based BPL decoder with adoption of the new code construction is presented. Finally, the proposed BPL decoder is tested on NVID...     

极化码的多比特译码算法研究

针对极化码的连续消除列表（successive cancellation list,SCL）译码算法的高时延问题,提出了基于对数似然比的多比特SCL（multi-bit SCL,MSCL）译码算法,可以在一个判决时刻同时译出多个码字比特,在不损失译码性能的前提下,将译码时延由3N-2个时钟降为4N/M-2个时钟,相比于现有的多比特SCL译码算法,MSCL译码算法具有更低的路径度量值计算复杂度。为了降低循环冗余校验（cyclical redundancy check, CRC）辅助的SCL（CRC aided SCL,CA-SCL）译码算法的译码时延以及存储空间,提出了分段CRC辅助的MSCL（segmented CRC-aided MSCL,SCA-MSCL）译码算法,并提出了分段信息码字长度修正算法,来保证在信息位索引集A不变的前提下,实现每一分段结尾处对应的信息位索引能够被M整除。SCA-MSCL算法可以借助多个CRC判决来尽可能早地输出译码码字,从而减少译码器的存储空间以及译码时延。     

RS码与LDPC码的联合迭代译码

针对RS码与LDPC码的串行级联结构,提出了一种基于自适应置信传播(ABP)的联合迭代译码方法.译码时,LDPC码置信传播译码器输出的软信息作为RS码ABP译码器的输入;经过一定迭代译码后,RS码译码器输出的软信息又作为LDPC译码器的输入.软输入软输出的RS译码器与LDPC译码器之间经过多次信息传递,译码性能有很大提高.码长中等的LDPC码采用这种级联方案,可以有效克服短环的影响,消除错误平层.仿真结果显示:AWGN信道下这种基于ABP的RS码与LDPC码的联合迭代译码方案可以获得约0.8 dB的增益.     

基于VHDL的TPC译码器设计

Turbo乘积码是一种性能卓越的前向纠错码,具有译码复杂度低,且在低信噪比时可以获得近似最优的性能。介绍基于Chase算法的Turbo乘积码软入软出（SISO）迭代译码算法,提出基于VHDL硬件描述语言的TPC译码器设计方案,并在FPGA芯片上进行了仿真和验证。仿真结果证明该译码器有很大的实用性和灵活性。     

比特交织随机分层空时码的Turbo检测—译码方法

对于一种采用比特交织的随机分层结构的空时码,提出了一种应用Turbo原理的迭代检测-译码方法,新方法基于软干扰消除的BLAST检测和卷积码的SISO（softinput soft output）译码,通过交换检测器和译码器之间的软信息,为迭代处理提供新的软信息.新方法大大提高了系统的性能,计算机仿真结果和计算复杂度分析显示了新方法的应用潜力.     

三维TPC译码器的设计及FPGA实现

Turbo乘积码（TPC）是一种性能优秀的纠错编码方法,它具有译码复杂度低、译码延时小等优点,且在低信噪比下可以获得近似最优的性能。介绍了基于Chase算法的三维TPC软输入软输出（SISO）迭代译码算法,提出了三维TPC译码器硬件设计方案并在FPGA芯片上进行了仿真和验证。测试结果表明,该译码器具有较高的纠错能力,满足移动通信误码率的要求。     

多维映射BICM-ID系统的简化MD-LSD解映射算法

将二维映射下的软输入软输出解映射MAX-LOG-MAP算法扩展到多维映射比特交织编码调制及迭代译码(BICM-ID)系统,并首次结合多天线系统下的列表球形译码,提出一种简化MD-LSD(multi-dimensional list sphere decoding)算法.新算法大幅降低了多维解映射的计算复杂度.仿真结果表明,列表长度满足一定范围时,采用简化MD-LSD算法解映射算法的性能损失可以忽略.     

一种用于cdma2000年的低复杂度Turbo码译码器

由于Turbo码优异的纠错性能,使得其在第三代移动通信（3G)系统中倍受重视。无论是WCDMA还是cdma2000都将其作为侯选的信道编码方案,并且将其列为3G的核心技术之一。但是Turbo码存在译码复杂度大、译码延时长的缺点。在这里,我们提出一种用于cdma2000的低复杂度Turbo码译码器,即结合CRC校验来减少译码过程中的迭代次数。仿真结果证明使用该译码器可以在大信噪比时大大降低译码复杂度和译码延时。     

Modified min-sum SCAN decoding algorithm for polar codes

The state-of-the-art soft-output decoder of polar codes is the soft cancellation (SCAN) decoding algorithm, which performs well at the cost of plentiful computations. Based on the SCAN decoding algorithm, a modified method with revised iterative formula is proposed, marked modified min-sum SCAN (MMS-SCAN). The proposed algorithm simplifies the update formula of nodes and reduces the complexity of iterative decoding process by the piecewise approximation function. Meanwhile, the bit error rate (BER) of the proposed method can approach the performance of original SCAN decoding method without performance loss. The simulation reveals that the MMS-SCAN decoding algorithm can achieve the effect that the BER curve almost coincides with the original SCAN decoding curve.     

An improved AS-SCLF decoding algorithm of polar codes based on the assigned set

An improved successive cancellation list bit-flip based on assigned set (AS-SCLF) decoding algorithm is proposed to solve the problems that the successive decoding of the successive cancellation (SC) decoder has error propagation and the path extension of the successive cancellation list (SCL) decoder has the decision errors in the traditional cyclic redundancy check aided successive cancellation list (CA-SCL) decoding algorithm. The proposed algorithm constructs the AS firstly. The construction criterion is to use the Gaussian approximation principle to estimate the reliabilities of the polar subchannel and the error probabilities of the bits under SC decoding, and the normalized beliefs of the bits in actual decoding are obtained through the path metric under CA-SCL decoding, thus the error bits containing the SC state are identified and sorted in ascending order of the reliability. Then the SCLF decoding is performed. When the CA-SCL decoding fails for the first time, the decision results on the path of the SC state in the AS are exchanged. The simulation results show that compared with the CA-SCL decoding algorithm, the SCLF decoding algorithm based on the critical set and the decision post-processing decoding algorithm, the improved AS-SCLF decoding algorithm can improve the gain of about 0.29 dB, 0.22 dB and 0.1 dB respectively at the block error rate (BLER) of 10-4 and reduce the number of decoding at the low signal-to-noise ratio (SNR), thus the computational complexity is also reduced.     

Dual-CRC polar codes and dual-SCFlip decoding algorithm for cell search in 5G system

Polar codes become the coding scheme for control channels of enhanced mobile broadband (eMBB) scenarios in the fifth generation (5G) communication system due to their excellent decoding performance. For the cell search procedure in 5G system, some common information bits ( CIBs) are transmitted in consecutive synchronization signal blocks ( SSBs). In this paper, a dual-cyclic redundancy check ( dual-CRC) aided encoding scheme is proposed, and the corresponding dual-successive cancellation flip ( dual-SCFlip) algorithm is given to further improve the performance of polar codes in the low signal-to-noise ratio ( SNR) environment. In dual-CRC aided encoding structure, the information bits of polar codes in different transmission blocks add cyclic redundancy check (CRC) sequences respectively according to CIBs and different information bits (DIBs). The structure enlarges the size of CIBs to improve the block error ratio ( BLER) performance of the system. The dual-SCFlip decoder can perform bit flip immediately once CIBs is decoded completely, and then decode DIBs or terminate decoding in advance according to the CRC result, which reduces the delay of decoding and mitigates the error propagation effect. Simulation results show that the dual-CRC aided encoding scheme and dual-SCFlip decoder have significant performance improvement compared to other existing schemes with low SNR.     

Efficient SIC-MMSE MIMO detection with three iterative loops

In this paper, we propose an efficient joint iterative detection and decoding (JIDD) scheme with a soft interference cancellation minimum mean squared error (SIC-MMSE) based method for a turbo coded multiple-input multiple-output (MIMO) system. In the proposed method, we activate a loop inside the SIC-MMSE based MIMO detection process in addition to the iterative loop between the MIMO detector and turbo decoder, so that the iteration inside the SIC-MMSE detection can be performed in parallel to the iterations inside the turbo decoder. Subsequently, soft outputs from each loop is exchanged for next further iteration, and this makes three iterative loops in total. In comparison with the conventional JIDD schemes, employing additional loop inside the MIMO detection process largely contributes to enhance the performance. In addition, the additional loop speeds up the performance convergence and eventually requires smaller overall computational complexity at the same performance.     

SCMA场景下的极化码编解码方案改进研究

极化码是目前唯一一种被证明可达到信道容量的编码方式,稀疏码分多址接入(Sparse Code Division Multiple Access,SCMA)可以提高频谱资源的利用率和接入系统的用户接入数量。为了提升SCMA与极化码的联合系统的误码率性能和译码时延,使联合系统的应用越来越广泛,提出了2种降低译码复杂度的方式:简化的左信息更新方式和剪枝译码算法。简化的左信息更新方式对于N=256,N=1024的极化码分别能降低37.6%和44.6%的存储资源占用数;剪枝译码算法在码率为0.5时能降低50%左右的计算复杂度。基于简化的SCAN算法改进了联合检测译码算法,在接收机采用外循环迭代的结构,引入了阻尼机制,选取最优的阻尼方式和最优阻尼值。仿真分析了所提联合检测译码算法与原有联合检测译码算法的误码率性能差异,外迭代接收机性能与内外双循环迭代的接收机性能相同,采用阻尼机制联合接收机的性能比无阻尼接收机的性能高0.8 dB左右,SJIDD的误帧率性能比保留宽度为32的SCLJDD的性能低0.7 dB左右,但能使接收机处理时延降至原来的1/4~1/8。     

动态扰动辅助的串行抵消双比特翻转Polar译码算法

针对串行抵消翻转译码算法（Successive Cancellation Flip,SCF）受限于单比特翻转而性能提升有限问题,提出了一种双比特翻转译码算法（Successive Cancellation Flip with 2 Bits,SCF2）。针对SCP算法扰动方差初始值固定的问题,设计了一种扰动方差可随码长和码率变化的改进SCP算法。在此基础上,结合翻转和扰动机制,提出了一种动态扰动辅助的串行抵消双比特翻转（Dynamic Perturbation-Aided SCF2,DPA-SCF2）译码算法,并对其译码复杂度和性能进行了分析。仿真结果显示,相比于列表长度为4的循环冗余校验辅助串行抵消列表（Cyclic Redundancy Check Aided Successive Cancellation List,CA-SCL）译码算法,所提算法最大可获得约0.5 dB的性能增益。     

基于分布式奇偶校验码的低复杂度极化码SCLF译码算法

针对极化码串行抵消列表比特翻转(Successive Cancellation List Bit-Flip, SCLF)译码算法复杂度较高的问题,提出一种基于分布式奇偶校验码的低复杂度极化码SCLF译码(SCLF Decoding Algorithm for Low-Complexity Polar Codes Based on Distributed Parity Check Codes, DPC-SCLF)算法。与仅采用循环冗余校验(Cyclic Redundancy Check, CRC)码校验的SCLF译码算法不同,该算法首先利用极化信道偏序关系构造关键集,然后采用分布式奇偶校验(Parity Check, PC)码与CRC码结合的方式对错误比特进行检验、识别和翻转,提高了翻转精度,减少了重译码次数。此外,在译码时利用路径剪枝操作,提高了正确路径的竞争力,改善了误码性能,且利用提前终止译码进程操作,减少了译码比特数。仿真结果表明,与D-Post-SCLF译码算法和RCS-SCLF译码算法相比,所提出算法具有更低的译码复杂度且在中高信噪比下具有更好的误码性能。     

Complexity Reduction in SISO Decoding of Block Codes

SISO decoding for block codes can be carried out based on a trellis representation of the code. However, the complexity entailed by such decoding is most often prohibitive and thus prevents practical implementation. This paper examines a new decoding scheme based on the soft-output Viterbi algorithm (SOVA) applied to a sectionalized trellis for linear block codes. The computational complexities of the new SOVA decoder and of the conventional SOVA decoder, based on a bit-level trellis, are theoretically analyzed and derived for different linear block codes. These results are used to obtain optimum sectionalizations of a trellis for SOVA. For comparisons, the optimum sectionalizations for Maximum A Posteriori (MAP) and Maximum Logarithm MAP (Max-Log-MAP) algorithms, and their corresponding computational complexities are included. The results confirm that the new SOVA decoder is the most computationally efficient SISO decoder, in comparisons to MAP and Max-Log-MAP algorithms. The simulation results of the bit error rate (BER) performance, assuming binary phase -- shift keying (BPSK) and additive white Gaussian noise (AWGN) channel, demonstrate that the performance of the new decoding scheme is not degraded. The BER performance of iterative SOVA decoding of serially concatenated block codes shows no difference in the quality of the soft outputs of the new decoding scheme and of the conventional SOVA.