一种差分高阶调制联合LDPC编码方案及其FPGA实现

针对复杂环境中通信系统误码率高和硬件实现复杂度高的问题,提出基于正交频分复用( Orthogonal Frequency Division Multiplexing, OFDM)时域差分和 16 进制幅度差分相移键控( 16 Multilevel Differential Amplitude and Phase Shi...     

DIFFERENTIAL AMPLITUDE PHASE SHIFT KEYING：A NEW MODULATION METHOD FOR TURBO CODE IN DIGITAL RADIO BROADCASTING

The multilevel modulation techniques of M-Differential Amplitude Phase Shift Keying(DAPSK)have been proposed in combination with Turbo code scheme for digital radio broad-casting bands below 30 MHz radio channel.Comparison of this modulation method with channel coding in an Additive White Gaussian Noise(AWGN)and mulit-path fading channels has been presented.The analysis provides an iterative decoding of the Turbo code.     

基于多级码编码正交频分复用的差分幅度相位调制

数字调幅广播(DAMB)需要高速的数据传输率,为此本文提出一种具有高带宽效率的编码调制方案。采用16差分幅度相位(16DAPSK)加正交频分复用(OFDM)调制,采用多级码(MLC)作为纠错编码,其分量码为标准卷积码及其删除型卷积码,系统具有高的带宽利用率,抗多径传输,接收端可以并行解码,以减小通常逐层解码所带来的大的时延和误差传播,并且由于差分调制的引入,接收端可以采用非相关检测,且毋须均衡器,简化了接收机的设计,本文还比较了短波信道中,采用时域差分和频域差分的效果,并得出了相应的结论。     

Multi-resolution 64-DAPSK modulation in a hierarchical COFDMtransmission system

Two alternative modulation schemes of 64-QAM (quadrature amplitude modulation) and 64-DAPSK (differential amplitude and phase shift keying) with a coherent and incoherent demodulation have been proposed for digital terrestrial video broadcasting (DTVB) in combination with the coded orthogonal frequency division multiplexing (COFDM) technique (Schafer 1995, and Engels and Rohling 1995). Additionally, a hierarchical transmission system based on a multi-resolution (MR) 64-QAM is described in Engels and Rohling which extends the service area of a TV programme in decoding a stepwise reduced data rate with increasing transmitter distance (graceful degradation). This procedure corresponds to a decreasing picture quality. In this paper MR concepts for the 64-DAPSK are developed. A performance comparison between the hierarchical transmission systems (MR-64-QAM/OFDM and MR-64-DAPSK/OFDM) is described for the uncoded and coded case     

64DAPSK-OFDM与64QAM-OFDM系统性能比较

针对OFDM系统中的MQAM和MDAPSK两种子载波高阶调制技术,介绍了64QAM和64DAPSK信号的比特软输出解调方法,比较了64DAPSK-OFDM和64QAM-OFDM系统的误码性能。仿真结果表明,在频率选择性和时间选择性衰落信道下,若信道相邻子载波或相邻OFDM符号的相关性能得到保证,采用64DAPSK调制可以用较少的信噪比损失换取OFDM系统复杂度的大大降低。     

Soft decision metric generation for QAM with channel estimation error

The channel code bit log likelihood ratio (LLR) for soft decision decoding is derived for quadrature amplitude modulated signals (QAM). The effect of imperfect channel knowledge on soft decision decoding performance is studied. Our results indicate this effect increases with channel estimation error and/or QAM modulation level. A metric based on generalized log likelihood ratio (GLLR) is derived for soft decision channel decoding with imperfect channel knowledge. Numerical results show that the GLLR-based metric outperforms the conventional minimum distance decoding metric that does not take into account channel estimation error.     

结合6-QAM和双层LDPC码的编码调制研究

针对阶数为3×2p的非标准调制与纠错编码难以匹配的问题,提出了一种面向6阶正交幅度调制（QAM）的双层编码调制传输方案。在发送端,采用有限域GF(2)低密度奇偶校验（LDPC）码与GF(3) LDPC码进行分层编码,并将两种编码码字映射为6进制码字后进行6-QAM调制;在接收端,根据GF(2) LDPC码和GF(3) LDPC码的译码顺序,设计了两种双层迭代译码方法。仿真结果表明,在加性高斯白噪声（AWGN）信道下,执行一次整体迭代译码时,先执行GF(3) LDPC码译码的6-QAM分层编码调制方案比先执行GF(2) LDPC码译码的方案获得了更优的误符号率（SER）性能;随着迭代次数增加,纠错性能可获得进一步改善。比较6-QAM与6阶相移键控（6-PSK）调制,若先执行GF(3) LDPC码译码,当SER为10-5时,6-QAM结合双层LDPC码的传输方案在AWGN信道下可获得约1.3dB的增益。      

Joint Source and Channel Coding using Punctured Ring Convolutional Coded CPM

In this paper, a novel trellis source encoding scheme based on punctured ring convolutional codes is presented. Joint source and channel coding (JSCC) using trellis coded continuous phase modulation (CPM) with punctured convolutional codes over rings is investigated. The channels considered are the additive white gaussian noise (AWGN) channel and the Rayleigh fading channel. Optimal soft decoding for the proposed JSCC scheme is studied. The soft decoder is based on the a posteriori probability (APP) algorithm for trellis coded CPM with punctured ring convolutional codes. It is shown that these systems with soft decoding outperform the same systems with hard decoding especially when the systems operate at low to medium signal-to-noise ratio (SNR). Furthermore, adaptive JSCC approaches based on the proposed source coding scheme are investigated. Compared with JSCC schemes with fixed source coding rates, the proposed adaptive approaches can achieve much better performance in the high SNR region. The novelties of this work are the development of a trellis source encoding method based on punctured ring convolutional codes, the use of a soft decoder, the APP algorithm for the combined systems and the adaptive approaches to the JSCC problem.     

编码16DAPSK信号解调译码新方法

基于子载波采用16阶差分幅度相移键控(16DAPSK)的正交频分复用(OFDM)系统,提出并分析了编码16DAPSK信号的一种新的简单易行的比特软输出解调译码方法。仿真结果表明,在高斯信道、平坦Rayleigh衰落信道和多径Rayleigh衰落信道下,采用编码速率为3/4的punctured卷积码与16DAPSK信号的硬输出解调译码方法相比,系统的误码性能可改善约1.2dB。新方法应用在日本CRL开发的100Mbps毫米波16DAPSK-OFDM宽带移动接入实验系统,将进一步提高系统误码性能。     

QAM调制下基于卷积码与累加编码调制级联的纠错码性能研究

基于卷积码与累加编码的PPM调制级联码(SCPPM)在泊松信道光PPM调制下具有极优异的性能。文章将这种累加编码结构引入到QAM调制中,分析其性能。将卷积码+累加编码+QAM调制串行级联(SCAQAM)纠错方案与常规基于卷积码、并行级联卷积码(Turbo)以及低密度奇偶校验码(LDPC)的比特交织编码调制迭代译码(BICM-ID)系统进行比较,并进一步比较了SCAQAM系统的自然、格雷、反格雷星座映射方式。结果表明,在高阶QAM调制下,这种纠错结构具有极优异的误码性能。对于16QAM及64QAM调制,SCAQAM相对于另外几种纠错码结构的BICM-ID系统分别有约0.3和0.5 dB的性能提升,只有卷积码与累加码结合才更具性能优势。并且SCAQAM将累加后的比特流以反格雷方式映射具有更优异的性能。     

Soft decision decoding of linear block codes based on orderedstatistics for the Rayleigh fading channel with coherent detection

The soft decision decoding algorithm based on the ordered statistics proposed by Fossorier and Lin (see IEEE Trans. Inform. Theory, vol.41, no.9, p.1379-96, 1995) is applied to the Rayleigh fading channel with coherent detection. For an (N, K) block code, it is shown that order-1 reprocessing, or equivalently considering K+1 codeword candidates, provides most of the coding gain over uncoded binary phase shift keying (BPSK). In addition to its contribution to coding for the Rayleigh fading channel, the article also provides a general framework for evaluating the error performance of an algorithm based on a total or partial ordering of a random variable (RV) depending on one or many other RVs and illustrates how the reprocessing method of Fossorier et al. relates to the reliability measures defining the ordering     

级联纠错编码DS/BPSK系统性能分析与仿真

为了研究级联编码对DS/BPSK系统性能的影响,设计了一种基于RS与卷积码级联编码的DS/BPSK系统,分析了该级联编码直扩系统的性能,仿真了在纠错编码参数发生改变时的系统性能。仿真结果表明,级联编码的DS/BPSK系统性能比单码编码的DS/BPSK系统性能要好。在RS码参数保持不变时,降低卷积码的码率,采用软判决方式译码以及多比特软判决,能有效提升系统性能;同时,交织在一定程度上能改善系统的性能。     

适用于体全息存储系统的调制-阵列码的研究

提出了一种适用于体全息存储系统读写数据处理的新的编码结构 :调制 阵列码 ,同时提出了与其相适应的软判决度量方法。在此基础之上综合调制码探测、软判决、阵列码纠错和Turbo码译码原理 ,形成了一种新的迭代译码算法。实验结果表明 ,在信道的信噪比较低且有起伏 ,信道噪声参数不易统计的情况下 ,它能充分利用输入信号所包含的信息 ,只要原始误码率 (定义为采用全局最佳阈值量化后的误码率 )低于 4× 1 0 -2 ,8× 1 0调制 阵列码的使用效果就可与 1∶2调制码 (二者码率相当 )的使用效果相当 ;当原始误码率低于 1× 1 0 -2 后 ,其使用效果显著优于 1∶2调制码。将这种新的编译码技术用于包含音频和视频的多媒体数据的全息存储 ,重构数据基本能成功回放     

迭代译码的级联Reed-Solomon乘积码与卷积码

该文提出用Reed Solomon(RS)乘积码作为外码,卷积码作为内码的级联码方案并且内外码间用Congruential向量生成的交织图案对RS码符号进行重排列。对此级联码采用的迭代译码基于成员码的软译码算法。当迭代次数达到最大后,通过计算RS码的校正子,提出一种纠正残余错误的方法,进一步提高了系统的误比特性能。仿真结果表明,在AWGN信道中与迭代译码的级联RS/卷积码相比,当误比特率为1e-5时,新系统的编码增益大约有0.4 dB。     

Bit-interleaved coded modulation with iterative decoding

A simple iterative decoding technique using hard-decision feedback is presented for bit-interleaved coded modulation (BICM). With an 8-state, rate-2/3 convolutional code, and 8-PSK modulation, the improvement over the conventional BICM scheme exceeds 1 dB for a fully-interleaved Rayleigh flat-fading channel and exceeds 1.5 dB for a channel with additive white Gaussian noise. This robust performance makes BICM with iterative decoding suitable for both types of channels     

Correction of extrinsic information for iterative decoding in a serially concatenated multiuser DS-CDMA system

The system under study is a coded asynchronous DS-CDMA system with orthogonal modulation in time-varying Rayleigh fading multipath channels. Information bits are convolutionally encoded, block interleaved, and mapped to M-ary orthogonal Walsh codes, where the last step is essentially a process of block coding. This paper aims at tackling the problem of joint iterative decoding of this serially concatenated inner block code and outer convolutional code and estimating frequency-selective fading channels in multiuser environments. The (logarithm) maximum a posteriori probability, (Log)-MAP criterion is used to derive the iterative decoding schemes. In our system, the soft output from inner block decoder is used as a priori information for the outer decoder. The soft output from outer convolutional decoder is used for two purposes. First, it may be fed back to the inner decoder as extrinsic information for the systematic bits of the Walsh codeword. Secondly, it is utilized for channel estimation and multiuser detection (MUD). We also show that the inner decoding can be accomplished without extrinsic information, and in some cases, e.g., when the system is heavily loaded, yields better performance than the decoding with unprocessed extrinsic information. This implies the need for correcting the extrinsic information obtained from outer decoder. Different schemes are examined and compared numerically, and it is shown that iterative decoding with properly corrected extrinsic information or with non-extrinsic/extrinsic adaptation enables the system to operate reliably in the presence of severe multiuser interference, especially when the inner decoding is assisted by decision directed channel estimation and interference cancellation techniques.     

On turbo decoding of nonbinary codes

Symbol-by-symbol maximum a posteriori (MAP) decoding algorithms for nonbinary block and convolutional codes over an extension field GF(p ^a) are presented. Equivalent MAP decoding rules employing the dual code are given which are computationally more efficient for high-rate codes. It is shown that these algorithms meet all requirements needed for iterative decoding as the output of the decoder can be split into three independent estimates: soft channel value, a priori term and extrinsic value. The discussed algorithms are then applied to a parallel concatenated coding scheme with nonbinary component codes in conjunction with orthogonal signaling     

Error correcting RLL codes using high rate RSC or turbo code

A construction method of error correcting run-length limited (EC-RLL) codes using a high rate recursive systematic code (RSC) or turbo code for storage systems is proposed. The EC-RLL codes can be constructed by a concatenating conventional modulation code and RSC or turbo code with puncturing. The benefit of the scheme is the utilisation of soft decision and iterative detection algorithms for decoding     

衰落信道下卷积码的软判决译码

本文将交织、信道输出软信息、信道特征软信息相结合,研究Rayleigh衰落信道下卷积码的Viterbi软判决译码,在利用和不利用信道状态信息(CSI)两种情况下给出软判决的支路度量计算公式和性能仿真结果,计算了卷积码的性能上界;研究了解调器输出量化门限(量化级数目、量化间距)对译码性能的影响.结果与硬判决译码及AWGN信道的相关结论进行了比较.     

Performance evaluation of COFDM for digital audio broadcasting. I.Parametric study

This paper describes the performance of COFDM (coded orthogonal frequency division multiplexing) for digital audio broadcasting (DAB) over various multipath mobile radio channels. COFDM is a channel coding and modulation scheme which mitigates the adverse effects of fading by using wideband multicarrier modulation combined with time interleaving and a convolutional error correcting code. A guard interval is inserted at the transition between successive symbols to absorb the intersymbol interference created by the time domain spread of the mobile radio channel. The decoding process is performed using differential demodulation in conjunction with a soft decision Viterbi decoder. The COFDM evaluation is done by means of computer simulations. A parametric study of the proposed COFDM system is done in this first of a series of papers to determine the optimal system parameter values for operation at a radio frequency of 1.5 GHz. The results show that the parameter values proposed in the standard are indeed well suited for operation at 1.5 GHz. Using the set of optimal parameter values found, the COFDM performance is then evaluated in mobile radio channels typical of different geographical environments. Simulation results confirm the benefit that the system gains from frequency diversity found in the urban and hilly terrain areas