在卫星移动信道中不同条件下Turbo码的纠错性能研究

研究了采用Turbo码技术的抗衰落性能,首先分析了Turbo码在卫星移动遮蔽Rician衰落信道下的误差纠错性能限,然后通过计算机仿真模拟了三种不同的卫星移动衰落信道下Turbo码的性能,研究了不同衰落信道特性对Turbo码性能的影响情况,同时还讨论了在衰落信道下Turbo码的子码约束长度和交织器长度两个主要参数对性能的影响情况。     

基于混沌交织的Turbo码及其性能仿真

基于非线性混沌映射提出了一种S随机混沌交织算法。在不同遮蔽程度的卫星移动衰落信道模型中,使用不同的解码算法,通过仿真比较了不同伪随机交织算法的Turbo码性能、不同的交织长度对系统性能的影响。仿真结果表明,在信噪比较低的卫星衰落信道中采用MAP、SOVA译码算法时,使用S随机混沌交织器的Turbo码性能均较使用伪随机交织器的Tur-bo码的性能有明显改进。     

Turbo码随机性交织器设计

深空测控中为获得较高的编码增益需要用到信道编译码技术。Turbo码是一种逼近香农限的高性能的信道编译码,其中,交织器的设计是影响Turbo码性能的关键因素之一。论述了交织器设计的基本准则,并详细介绍了3种常见的随机性交织器:伪随机交织器、S随机交织器和S改进型交织器的交织原理,对比分析了3种交织器的优缺点并给出了仿真结果。结果表明,交织器生成方式的不同将带来不同的Turbo码译码性能。     

一种3GPP交织器在低信噪比条件下的改进方案

国际电信联合会在3GPP标准中推荐采用3GPP交织器,它在Turbo码中有优异的性能。本文在介绍3GPP交织器的基础上,对Turbo码的距离谱进行了分析,提出了一种3GPP交织器在低信噪比条件下的改进方案。通过仿真表明,在基本不改变原交织器的设计步骤情况下,改进方案精简了交织器的结构,并通过对短帧进行填充的方式,达到较长的交织长度,改善了短帧在低信噪比条件下传输的误码性能。      

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.     

短帧长CCPM信号优化设计及简化译码

针对突发通信和卫星测控通信中对于短帧长、高性能和低复杂度的需求,提出一种短帧长C2PM(codedcontinuous phase modulation)系统的优化设计方案,包括编码GMSK系统的优化设计及简化译码。对于编码GMSK系统,采用简化解调器、优化卷积码生成多项式和匹配交织器的方式,可实现系统参数优化。加性高斯白噪声(AWGN)信道下的仿真结果表明,系统性能优于常用卷积码性能,特别是在10-5误比特率时,略优于同帧长的Turbo码和LDPC码性能,且无误码平底出现。对编码GMSK系统复杂度的分析结果表明,该系统实现复杂度低于常用卷积码、同帧长Turbo码和LDPC码。     

采用Ⅲ型H-ARQ的BICM-ID系统研究

本文提出了采用Ⅲ型H-ARQ的BICM-ID系统实现方案.给出了传输协议及组合译码算法,从理论上分析了系统通过率.在Awgn信道和Bayleigh衰落信道下,对分别采用Ⅰ型,Ⅱ型,Ⅲ型H-ARQ的BICM-ID系统通过率进行了仿真比较.结果表明,与采用其他两种类型H-ARQ的BICM-ID系统相比,采用Ⅲ型H-ARQ的BICM-ID系统性能最优.而且,在低信噪比和Rayleigh信道下的优势更加突出.     

基于Henon混沌模型的随机交织器设计

本文对Turbo码中的关键组成部分-交织器作了分析，阐明了交织器在Turbo码中的重要作用；提出了一种基于Henon混沌模型的随机交织器设计方法，通过仿真实验，本文设计的交织器整体性能优于CDMA2000标准中Turbo码交织器性能，在高斯信道下，纠错性能平均改善0.15dB。     

采用预判决信息的LDPC码编码调制方案性能研究

低密度奇偶校验(LDPC)码是Turbo码以外另一种性能接近香农限的好码.本文将LDPC码与比特交织编码调制(BICM)相结合,首先给出了在不使用传统解调器与译码器之间迭代的情况下8PSK调制方案在AWGN信道和Rayleigh衰落信道中的性能(简称为无迭代方案).然后提出了一种新的接收端解决方案:首先对接收符号进行预判决,判决信息被用来调整解调器,从而在一定程度上弥补了不使用解调器与译码器之间迭代所造成的性能损失,并且相对于无迭代方案接收端复杂度几乎没有变化,但性能却有所提高.这说明原有比特度量产生方法并不是最佳的,该文使用预判决信息的方案给出了一个改善的思路.通过仿真结果可以得到结论:使用本文所提出的方案在AWGN信道和Rayleigh衰落信道中都可以在不增加复杂度的情况下提高性能.     

一种应用于实时语音传输的LDPC码的设计

文中设计了一种适于对声码器的输出码流进行前向纠错编码的低密度奇偶校验码(LDPC码).该低密度奇偶校验码具有半规则化的结构,编码简单,存储量少,调整码率方便,易于硬件实现.文中同时对汉明码,卷积码、Turbo码、低密度奇偶校验码分别在AWGN、Rayleigh信道下的传输性能进行了仿真比较.仿真结果表明,长度适合的LDPC码误码性能远超过汉明码、卷积码,综合性能与Turbo码接近.     

FEC scheme for a TDM-OFDM based satellite radio broadcasting system

There are two licenses, 12.5 MHz each, in the S-band for digital satellite-to-vehicle radio broadcasting in the United States. The potential advantages of such a system is that a motorist can enjoy commercial-free music, digital-quality sound and seamless coast-to-coast coverage. One proposal for the broadcast system is to have two satellites covering the continental USA at any given time. There will also be terrestrial repeaters in cities where the receivers on the vehicles cannot see the two satellites. The channels of these systems are affected by Rician, Rayleigh and flat fading caused by shadowing. This paper proposes a forward error correction (FEC) scheme that is not only robust against fading but also enables a low-delay tuning channel so that minimum tuning delay will occur when a user is switching and selecting programs. The scheme uses multiple source coded bit streams employing different interleaver depths. Large interleavers are used to ensure good decoded signal quality while small interleavers are used to minimize tuning delay. The proposed scheme also ensures that a program will not be interrupted by momentary shadowing frequently experienced by a motorist when, for example, a vehicle goes under a highway overpass. The impact of interleaver design on the real-time end-to-end delay and fading due to shadowing is analyzed. Finally, the channel code performance in Rician and Rayleigh fading channels are also presented     

Multistage recursive interleaver for turbo codes in DS-CDMA mobileradio

A multistage recursive block interleaver (MIL) is proposed for the turbo code internal interleaver. Unlike conventional block interleavers, the MIL repeats permutations of rows and columns in a recursive manner until reaching the final interleaving length. The bit error rate (BER) and frame error rate (FER) performance with turbo coding and MIL under frequency-selective Rayleigh fading are evaluated by computer simulation for direct-sequence code-division multiple-access mobile radio. The performance of rate-1/3 turbo codes with MIL is compared with pseudorandom and S-random interleavers assuming a spreading chip rate of 4.096 Mcps and an information bit rate of 32 kbps. When the interleaving length is 3068 bits, turbo coding with MIL outperforms the pseudorandom interleaver by 0.4 dB at an average BER of 10^-6 on a fading channel using the ITU-R defined Vehicular-B power-delay profile with the maximum Doppler frequency of f_D = 80 Hz. The results also show that turbo coding with MIL provides superior performance to convolutional and Reed-Solomon concatenated coding; the gain over concatenated coding is as much as 0.6 dB     

Turbo编码中的交织技术

Turbo码是近年来提出的一种高性能的信道编码.Turbo码交织器的设计是Turbo编解码器设计中的关键.文中介绍了交织器的基本原理,详细地介绍了3种常见的交织器的交织原理.最后给出了交织器的设计准则.     

基于短帧交织的Turbo码编码器研究

本文分析了Turbo码编码器及其输出码字的组成原理,基于使输出码字最小汉明重量最大化和使最小汉明重量输出码字出现的概率最小化的原则,结合结构化交织器和随机交织器的优点,提出了一种伪随机的结构化反块交织器,并进一步提出了采用双伪随机反块交织器的Turbo码编码器方案.该方案有效的增大了Turbo码输出码字的最小汉明距离,同时避免了Turbo码边缘效应且具有伪随机性,因此,可有效的提高系统的纠错性能.仿真实验结果显示,该方案在短帧传输的条件下有着最佳的综合性能.特别是在信噪比高时,采用该方案与采用其它交织器的Turbo码方案相比,在提高系统的可靠性上具有明显的优势.     

编织卷积码交织器的设计

编织卷积码(WovenConvolutionalCodes)是近年来所出现的一种新型高效纠错码,其中交织器的设计对分散突发错误、改善其纠错性能起着决定性的作用。传统的编织卷积码采用了行进列出的简单的交织方式,本文针对编织卷积码的结构特性设计了两种不同的交织器并通过系统仿真比较了它们的性能,仿真结果显示行式交织器极大地改善了系统性能,是目前为止最优的编织卷积码的交织器。     

Permutation Polynomial Interleavers: An Algebraic-Geometric Perspective

An interleaver is a critical component for the channel coding performance of turbo codes. Algebraic constructions are important because they admit analytical designs and simple, practical hardware implementation. The spread factor of an interleaver is a common measure for turbo coding applications. Maximum-spread interleavers are interleavers whose spread factors achieve the upper bound. An infinite sequence of quadratic PPs over integer rings that generate maximum-spread interleavers is presented. New properties of PP interleavers are investigated from an algebraic-geometric perspective resulting in a new non- linearity metric for interleavers. A new interleaver metric that is a function of both the nonlinearity metric and the spread factor is proposed. It is numerically demonstrated that the spread factor has a diminishing importance with the block length. A table of good interleavers for a variety of interleaver lengths according to the new metric is listed. Extensive computer simulation results with impressive frame error rates confirm the efficacy of the new metric. Further, when tail-biting constituent codes are used, the resulting turbo codes are quasi-cyclic.     

Adaptive interleaver based on rate-compatible punctured convolutional codes

This letter focuses on the design of an adaptive Bit- Interleaved Coded Modulation (BICM) scheme for frequency selective slow fading channels where the transmitter has certain knowledge of the channel response. In particular, we consider the design of the interleaver stage for a specific convolutional code operating with OFDM modulation. The adaptive interleaver uses the puncturing tables of the Rate-Compatible Punctured Convolutional Codes (RCPC codes) to rearrange the bits as a function of the fading values and the specific constellation. The performance of different interleavers are compared, revealing that the adaptive RCPC-based interleaver produces larger Euclidean distances between the received codewords and reduces the packet error rate (PER), specially when the number of deep-faded subcarriers increases. Numerical results also evidence the importance of the interleaver choice when comparing the performance of different power allocation strategies.     

Improved method for searching interleavers from a certain set using Garello’s method with applications for the LTE standard

In this paper, we propose a method for searching interleavers within a certain class, with the aim of designing turbo codes with good distance spectrum. The method is based on a modified version of Garello’s algorithm and consists in the calculation of frame error rate truncated upper bound. Here, it is applied to quadratic permutation polynomial (QPP) interleavers able to outperform those chosen for the long-term evolution (LTE) standard, for lengths up to 1,504 bits. Three classes of interleavers have been analyzed: (1) the set of QPP interleavers with the largest spread, (2) the set of QPP interleavers with a spread parameter equal to that of LTE interleaver and the highest refined nonlinearity degree, and (3) the complete set of all QPP interleavers for lengths up to 1,008. The distance spectrum optimization is made for all classes. Compared to previous methods for finding QPP-based interleavers, the search complexity is reduced, with improved performances in terms of search time, allowing interleavers of higher length. For lengths up to approximately 450, the best interleavers were found in the first class. For longer lengths, the second class contained the best ones.     

A Combined Interleaving Technique for Trellis Coded MPSK Systems in Rayleigh Fading Channels

Freedom of mobility is the latesttrend in the evolution of digital communicationsystems. In these systems bandwidth and powerconstraints limit the mobility of the users. TCM(trellis coded modulation) is a combined coding andmodulation scheme which increases the productivity ofa digital communication system without increasing thetransmitted power or the required bandwidth. A mobilecommunication channel is affected from noise andfading because of the multipath propagation. On aRayleigh fading channel, coding should be used withtechniques which uncorrelate the received energy ofeach consecutive coded symbol. Interleaving is one ofthese techniques and used to make burst errors intorandom errors which can be corrected by errorcorrecting codes. In this paper, the trellis codingsystem which combines a regular convolutional encoder,bit interleaver, coordinate interleaver, and anappropriate decoder is considered. The analytical biterror probability upper bounds are derived for the8-PSK TCM system whose diversity is increased by usinga regular 2/3 rate convolutional code followed bythree bit interleavers and a 8-PSK signal mapperfollowed by two coordinate interleavers. Theanalytical and simulation results show that toincrease the diversity of the trellis coded M-PSKsystems in Rayleigh fading channels is the primary keyfor reliable transmission of high quality voice anddigital data.     

Design of cyclic shift interleavers for Turbo Codes

In this paper we consider cyclic shift interleavers for turbo coding. The properties of cyclic shift interleavers are discussed and compared with S-random interleavers. It is shown that the cyclic shift interleavers are equivalent or better than the S-random interleavers in the ability to break low weight input patterns. We estimated the performance of turbo codes with cyclic shift interleavers and compared it with the performance of S-random interleavers for varions interleaver sizes. The simulation results show that a turbo code with a cyclic shift interleaver can achieve a better performance than an S-random interleaver if the parameters of the cyclic shift interleaver are chosen properly. In addition, the cyclic interleavers have the advantages of lower design complexity and memory requirements.