基于多项式遍历和码字相关的Turbo码盲识别

针对1/n码率Turbo码的盲识别问题,提出了一种基于多项式遍历和码字相关的检测识别方法.该方法首先对码字序列进行分组,利用分组验证的方法对数据中的卷积码进行快速检测,进而识别出Turbo码的码率;然后,利用欧几里得算法对Turbo码的分量编码器a的参数进行识别,进而通过对编码器b的遍历,恢复出伪随机交织序列;最后,通过与信息序列的码字相关,验证编码器b的参数是否正确,同时利用相关谱峰值所在位置识别交织器参数,实现了Turbo码的全部参数估计.仿真实验验证了该算法的有效性.对算法的误码适应能力进行的仿真分析表明,该方法能够在较高误码率条件下实现Turbo码的检测与识别.     

(n,1,m)RSC码的盲识别

(n,1,m)递归系统卷积码(RSC)是Turbo码分量编码采用最多的一种编码方式。针对RSC提出了基于改进欧几里德算法的识别方法,为Turbo码的识别奠定了基础。该方法首先将(2,1,m)卷积码的识别模型应用推广至(n,1,m)卷积码,即求解n个多项式的最高公因式,进而利用改进的欧几里德算法识别生成多项式。最后,实例仿真验证了该方法的有效性。     

Turbo码中的关键比特及保护

本文讨论了Turbo码中低码重码字中的非零比特对干扰的敏感度,指出码字的重量越低,对干扰的敏感度越大.然后,通过对这些高敏感度的比特—关键比特—进行保护,使码的抗干扰特性得以提高.理论分析表明,对关键比特的保护,相当于提高了码的最小重量.计算机仿真显示,无论是不删截的1/3码率,还是删截的1/2码率,误码率都有了明显改进.     

直升机卫星通信系统中Turbo码外交织器设计与仿真

在直升机卫星通信系统(HSCS)中,如何克服由于旋翼遮挡导致的系统性能恶化是一个亟需解决的关键问题。旋翼遮挡相当于对码字信息的成片删除,通过分析删余Turbo码中删余矩阵的设计准则,首先对Turbo码的编码结构进行改进,并提出了一种适用于直升机旋翼遮挡环境下的交织器。它满足以下特性:将删除均匀分散在整个码字序列中,变突发错误为随机错误;码字中每个信息位与其对应的2比特校验位中最多只删1位;与被删比特组相邻的两个比特组保留;删除部分中以信息位-校验位1-校验位2的模式循环,这些特性保证了删除信息的可靠恢复。最后对不同遮挡比例下新型交织器与传统交织器进行仿真比较,结果表明采用新型交织器改善了数据传输的误码率(BER)性能,提高了HSCS系统的可靠性。     

一种基于递归系统卷积码校验重量下限的匹配交织器设计方法

针对短帧Turbo码中交织器优化设计问题,提出了一种基于递归系统卷积码(RSC)校验重量下限的匹配交织器设计方法.文中重新分析了Turbo码中"局部坏点"具体形式,然后提出并证明了一种估计RSC分量码校验序列重量下限的方法,并将其应用于交织器映射方式优选时局部坏点对应Turbo码字重量下限估计,只有能够保证所有局部坏点对应码字重量的交织方法才被认为合法.仿真表明,与几种现有交织器设计方法相比,本文提出的匹配交织器设计方法性能更加优良,可以有效改善Turbo码的误比特性能.     

Turbo码的删截周期研究

考虑Turbo码的删截周期对汉明重量在删截位置上的分布的影响,得出删截方案的优选对性能的改善程度取决于删截周期的结论,最后通过计算机仿真进行了验证。这一结论对高码率Turbo码的删截方案的优选有重要的指导意义。     

Turbo乘积码构造方法的研究

Turbo乘积码因其具有接近香农限的译码性能和适合高速译码的并行结构,已成为纠错编码领域的研究热点。Turbo乘积码的分量码一般由扩展汉明码构造而成,所以该类码字编码和译码的硬件实现比较简单。当Turbo乘积码采用扩展汉明码作为子码时,随着信噪比的提高,码字的最小码重对误帧率的影响会逐步增大。文中改进了Turbo乘积码编码结构,在只增加较小的编译码复杂度和时延的情况下,提高了码字的最小码重,并减少了最小码重码字在码字空间所占的比例。通过仿真和分析,比较了这种码和TPC码在误帧率性能、码字的最小码重分布以及最小码间距估计上的差异。     

一种基于矩阵分析的Turbo码长识别算法

针对信息截获领域中Turbo码识别问题,提出了一种基于矩阵分析的Turbo码长识别算法。简述了Turbo码编码和归零的基本原理,深入分析了Turbo码第1路、第2路、第3路和整体的生成矩阵,得出其本质上是一种线性分组码。将线性分组码的码长识别方法引入到Turbo码识别当中,并对算法进行了改进。仿真实验表明,此方法在较高的误码率基础上有着良好的识别效果。     

删余Turbo乘积码的编译码算法分析

基于现有的Turbo乘积码的编译码方法,提出一种附加删余的Turbo乘积码编译码算法,介绍其编码器的构造方法,阐述了译码算法及实现框图,分析了删余信息对传输帧长的影响,仿真了其误码性能,并与未删余的Turbo乘积码做比较。分析和仿真结果表明,附加删余的Turbo乘积码可满足特定系统传输速率及帧长的需要,在相同的信噪比下,删余Turbo乘积码的误码性能优于未加删余的误码性能。     

分组Turbo码及其在802.16宽带无线接入中的应用

传统Turbo码采用的是以递归系统卷积码(RSC)为子码,在编码效率很高的情况下,性能会下降.以分组码为子码的Turbo码,在码率较高的情况下,编码增益较大.因而,在无线通信中分组Turbo码的使用广泛.简要探讨了分组Turbo码及其在802.16宽带无线接入城域网技术中的应用.最后,对802.16的发展作了展望.     

Turbo codes-based image transmission for channels with multiple types of distortion

Product codes are generally used for progressive image transmission when random errors and packet loss (or burst errors) co-exist. However, the optimal rate allocation considering both component codes gives rise to high-optimization complexity. In addition, the decoding performance may be degraded quickly when the channel varies beyond the design point. In this paper, we propose a new unequal error protection (UEP) scheme for progressive image transmission by using rate-compatible punctured Turbo codes (RCPT) and cyclic redundancy check (CRC) codes only. By sophisticatedly interleaving each coded frame, the packet loss can be converted into randomly punctured bits in a Turbo code. Therefore, error control in noisy channels with different types of errors is equivalent to dealing with random bit errors only, with reduced turbo code rates. A genetic algorithm-based method is presented to further reduce the optimization complexity. This proposed method not only gives a better performance than product codes in given channel conditions but is also more robust to the channel variation. Finally, to break down the error floor of turbo decoding, we further extend the above RCPT/CRC protection to a product code scheme by adding a Reed-Solomon (RS) code across the frames. The associated rate allocation is discussed and further improvement is demonstrated.     

Time-varying turbo codes

Turbo codes typically utilize time-invariant component codes whose total encoder memory is no greater than 4. In this letter, turbo codes with time-varying component codes are studied via EXIT analysis, distance spectrum analysis and simulation. Turbo codes with time-varying component codes and memory 6 are shown to have similar performance in the waterfall region and superior performance in the error floor region when compared to both the original memory 4 Berrou turbo code and the memory 8 big numerator-little denominator turbo codes.     

Evaluation of transfer functions for punctured turbo codes

A modified algorithm for evaluating transfer functions of turbo codes with punctured systematic bits is presented. The obtained transfer function leads to a more accurate estimation of the weight distribution of the code. Consequently, a tighter upper bound on the bit error rate performance of the code is obtained     

比特交织Turbo编码调制的8PSK符号映射

基于对Turbo编码器输出的系统比特和校验比特的不等错误保护(UEP),提出了一种新的比特交织Turbo编码调制(BITCM)的8PSK符号映射方案,即对于码率为1/3的Turbo码,校验比特映射到8PSK星座点中具有较好传输性能的比特位置上,而系统比特映射到较差传输性能的比特位置上。实现新映射方案的关键是比特交织器的设计。仿真结果表明,新的映射方案在AWGN信道下,误码率为10-3时,可获得大于0.2dB的信噪比增益,而这一增益的获得并没有牺牲频谱效率和增加系统的复杂性。     

极低码率Turbo码及其应用研究

针对极低信噪比条件下的传输,研究了极低码率Turbo码的编译码器结构,仿真分析了其性能。提出了极低码率Turbo码在高带宽容量、复杂信道环境,例如：短波通信、流星余迹通信等系统中的使用方法。比较了极低码率Turbo码与高码率Turbo码加扩频的性能。研究表明,极低码率Turbo码较传统高码率Turbo码有更好的性能,能将自适应调制编码技术向低信噪比环境扩展。     

Turbo-coded optical direct-detection CDMA system with PPMmodulation

The performance of an optical code division multiple access (CDMA) system with turbo coding is analyzed and simulated. Turbo codes are parallel concatenated convolutional codes (PCCCs) in which the information bits are first encoded by a recursive systematic convolutional code, and then, after passing through an interleaver, are encoded by a second systematic convolutional encoder. Turbo coding is superimposed on an intensity-modulated optical channel with pulse-position modulation (PPM) and direct detection of the received optical signal, and the performance is evaluated in terms of an upper bound on bit error probability. From the simulation results, it is seen that turbo coding offers considerable coding gain over other methods, with reasonable encoding/decoding complexity. Also, it is demonstrated that, for a fixed code rate, the performance of the optical CDMA system can be substantially improved by increasing the interleaver length and the number of iterations. Serially concatenated convolutional codes (SCCCs) are also considered, and are shown to perform comparably to PCCC in general and better than PCCCs for the case of large signal photocounts. The results in this paper can be applied, for example, to indoor optical wireless LANs     

Scalable image and video transmission using irregular repeat-accumulate codes with fast algorithm for optimal unequal error protection

This paper considers designing and applying punctured irregular repeat-accumulate (IRA) codes for scalable image and video transmission over binary symmetric channels. IRA codes of different rates are obtained by puncturing the parity bits of a mother IRA code, which uses a systematic encoder. One of the main ideas presented here is the design of the mother code such that the entire set of higher rate codes obtained by puncturing are good. To find a good unequal error protection for embedded bit streams, we employ the fast joint source-channel coding algorithm in Hamzaoui et al. to minimize the expected end-to-end distortion. We test with two scalable image coders (SPIHT and JPEG-2000) and two scalable video coders (3-D SPIHT and H.26L-based PFGS). Simulations show better results with IRA codes than those reported in Banister et al. with JPEG-2000 and turbo codes. The IRA codes proposed here also have lower decoding complexity than the turbo codes used by Banister et al.     

The Augmented State Diagram and its Application to Convolutional and Turbo Codes

Convolutional block codes, which are commonly used as constituent codes in turbo code configurations, accept a block of information bits as input rather than a continuous stream of bits. In this paper, we propose a technique for the calculation of the transfer function of convolutional block codes, both punctured and nonpunctured. The novelty of our approach lies in the augmentation of the conventional state diagram, which allows the enumeration of all codeword sequences of a convolutional block code. In the case of a turbo code, we can readily calculate an upper bound to its bit error rate performance if the transfer function of each constituent convolutional block code has been obtained. The bound gives an accurate estimate of the error floor of the turbo code and, consequently, our method provides a useful analytical tool for determining constituent codes or identifying puncturing patterns that improve the bit error rate performance of a turbo code, at high signal-to-noise ratios.     

AMR的信道编码设计及其DSP实现

对于超短波移动通信系统中AMR语音业务的传输，提出了基于码率兼容的删余卷积码和码率兼容的删余Turbo码这2种可变的不等差错保护信道编码方案。通过设计最优的删余方案和合适的速率匹配方法，这2种不等差错保护方案都可达到类内不等保护的目的，将对具有不同重要性的信源比特的作更精确不等保护。并基于DSP芯片TMS320C6416实时实现了这2种方案对AMR语音的不等差错保护。实验结果表明，这种方法具有合理的系统复杂度和很短的处理延时，适合于语音业务的应用。     

Energy-efficient node position identification through payoff matrix and variability analysis

This paper investigates the use of punctured recursive systematic convolutional codes for turbo coding in a 2-user binary adder channel (2-BAC) in the presence of additive white Gaussian noise, aiming to achieve a higher transmission sum rate with reduced decoding complexity. The encoders for the 2-BAC are assumed to be block synchronized and to employ identical puncturing patterns. Iterative decoding combining the Bahl Cocke Jelinek Raviv algorithm and a two-user punctured trellis is employed. For each user and for a fixed puncturing pattern, random interleavers of length 256 bits or 1024 bits, respectively, are simulated and corresponding curves relating bit error rate versus signal to noise ratio are presented for performance comparison purposes. Computer simulation indicates that the loss in performance of a punctured turbo code can be negligible when longer interleavers are used for both users, similarly to the single user case.