短波信道下的Turbo码性能研究

基于Watterson短波信道模型,构建了Turbo码在短波信道下的设计和仿真方法。在高信噪比区域中,推导出了不同信道条件下Turbo码的性能界公式;在低信噪比区域中,用Matlab仿真了短波信道下不同的信道条件及Turbo码的主要设计参数对其性能的影响,并给出了Turbo码在短波信道下的设计参数,为实际工程中的应用提供参考。     

低莱斯因子衰落信道下的Turbo码性能研究

基于Turbo码编译码技术,在Rician衰落信道模型下,详细研究了Turbo码Log-MAP译码算法和SOVA译码算法在低Rician因子衰落信道下的性能,并结合调制技术对整个编译码系统进行Matlab仿真。仿真结果表明,在低Rician因子信道下,Log-MAP译码算法的性能优于SOVA译码算法。     

紫外光通信系统Turbo码译码性能研究

针对紫外光通信信道的特殊性,采用当前优异的信道编码技术Turbo码进行编码,利用Matlab软件,在瑞利衰落信道务件下,仿真分析不同Turbo码译码算法对译码性能的影响,发现在相同条件下,Log-MAP算法性能好于SOVA算法.这为Turbo码在紫外光通信系统中的应用提供了一定的理论基础.     

Turbo码编码原理及仿真方法研究

文中进一步剖析了Turbo码的编码机理和编译码器结构,并研究了系统仿真的方法;给出了利用Matlab对Turbo码的部分功能进行仿真的流程图和程序;利用Jakes仿真器仿真在乎坦衰落信道中Turbo码误码性能曲线.     

宽带移动通信中Turbo乘积码的仿真研究

推出了一种新型的纠错码——Turbo乘积码(TPC),描述了Turbo乘积码的编译码基本思想,详细地分析了TPC的Turbo软迭代译码的核心思想,并对AWGN信道和瑞利衰落信道下的TPC的译码性能做了仿真分析,从仿真结果可以看出,在高编码效率时,TPC不仅具有更高的码率,而且可以获得很好的误码率性能,所以乘积码的软迭代译码方案有很好的应用性,在未来的宽带移动通信中具有广阔的应用前景。     

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。     

Turbo乘积码在无人机测控技术中的应用分析

Turbo乘积码是一种易于硬件实现的分组码,具有延时短和纠错性能好等优越性。通过对Turbo乘积码Chase软输出改进算法的分析和仿真,得出了不同码率和测试序列个数等参数对Turbo乘积码译码性能的影响。结合无人机常用的BPSK测控信号进行了仿真实验,对仿真结果进行了性能分析,验证了Turbo乘积码在无人机测控系统中应用的可行性,并给出了Turbo乘积码在无人机测控领域应用的建议参数。     

相关衰落信道Turbo乘积编码MDPSK的分集接收

由于无线衰落信道中差分检测Turbo乘积编码调制具有良好的性能,文中研究了相关平坦Rayleigh衰落信道中差分检测Turbo乘积编码MDPSK信号的等增益分集,这种等增益分集接收无需任何信道状态信息.研究结果表明,等增益合并可以改善快衰落信道中TPC-MDPSK的错误平底效应,等增益分集合并的Turbo乘积编码的MDPSK信号在相关系数为0.5的平坦Rayleigh衰落信道中的性能和独立衰落信道中的系统性能相差仅1 dB.     

基于衰落信道的Turbo码的设计与实现

Turbo码作为一种新颖的信道编码,可以获得接近香农理论极限的性能,IMT-2000已经将Turbo码作为第三代移动通信系统(3G)传输高速业务数据的信道编码标准之一.文中提出了一种在衰落信道下Turbo码的实现模型,并探讨了Turbo编、译码器的设计及其算法,最后用MATLAB语言完成了算法的仿真实现.仿真结果表明,在低信噪比的无线衰落信道中,Turbo码不仅可以获得更大的编码增益,有效地改善系统的性能,而且具有很强的抗衰落、抗干扰能力,在移动通信系统中有着很大的应用潜力.     

Turbo-TCM系统中几种交织器的性能研究

研究了Turbo码与网格编码调制(TCM)相结合的Turbo-TCM技术,将Turbo码中三类奇偶交织器的设计分别应用到Turbo-TCM中,并在Awgn信道和Rayleigh衰落信道下,对采用三种不同交织方式、不同帧长Turbo-TCM的性能进行了仿真。仿真结果表明,短帧条件下,Awgn信道中采用确定性奇偶交织器的Turbo-TCM性能最优,而Rayleigh衰落信道中三种交织方式的Turbo-TCM性能相近。长帧条件下,Awgn信道和Rayleigh衰落信道中,基于随机奇偶交织器的Tur-bo-TCM性能最优。     

Combined MMSE interference suppression and turbo coding for acoherent DS-CDMA system

The performance of a turbo-coded code division multiaccess system with a minimum mean-square error (MMSE) receiver for interference suppression is analyzed on a Rayleigh fading channel. In order to accurately estimate the performance of the turbo coding, two improvements are proposed on the conventional union bounds: the information of the minimum distance of a particular turbo interleaver is used to modify the average weight spectra, and the tangential bound is extended to the Rayleigh fading channel. Theoretical results are derived based on the optimum tap weights of the MMSE receiver and maximum-likelihood decoding. Simulation results incorporating iterative decoding, RLS adaptation, and the effects of finite interleaving are also presented. The results show that in the majority of the scenarios that we are concerned with, the MMSE receiver with a rate-1/2 turbo code will outperform a rate-1/4 turbo code. They also show that, for a bit error rate lower than 10^-3, the capacity of the system is increased by using turbo codes over convolutional codes, even with small block sizes     

On the Performance and Implementation Issues of Interleaved Single Parity Check Turbo Product Codes

In this paper, both performance and complexity aspects of two-dimensional single parity check turbo product codes (I-SPC-TPC) are investigated. Based on the proposed I-SPC-TPC coding scheme, a parallel decoding structure is developed to increase the decoding throughput with minor performance degradation compared with the serial structure. For both decoding architectures, a new helical interleaver is constructed to further improve the coding gain. In terms of decoding algorithm, the extremely simple Sign-Min decoding is alternatively derived with only three additions needed to compute each bit's extrinsic information. For performance evaluation, (16, 14, 2)² single parity check turbo product code with code rate 0.766 over AWGN channel using QPSK modulation is considered. The simulation results using Sign-Min decoding show that it can achieve bit-error-rate of 10^?5 at signal-to-noise ratio of 3.8 dB with 8 iterations. Compared to the same rate and codeword length turbo product code composed of extended Hamming codes, the considered scheme can achieve similar performance with much less complexity. Important implementation issues such as the finite precision analysis, efficient sorting circuit design and interleaver memory management are also presented.     

Joint iterative channel estimation and decoding in flat correlatedRayleigh fading

This paper addresses the design and performance evaluation with respect to capacity of M-PSK turbo-coded systems operating in frequency-flat time-selective Rayleigh fading. The receiver jointly performs channel estimation and turbo decoding, allowing the two processes to benefit from each other. To this end, we introduce a suitable Markov model with a finite number of states, designed to approximate both the values and the statistical properties of the correlated flat fading channel phase, which poses a more severe challenge to PSK transmission than amplitude hiding. Then, the forward-backward algorithm determines both the maximum a posteriori probability (MAP) value for each symbol in the data sequence and the MAP channel phase in each iteration. Simulations show good performance in standard correlated Rayleigh fading channels. A sequence of progressively tighter upper bounds to the capacity of a simplified Markov-phase channel is derived, and performance of a turbo code with joint iterative channel estimation and decoding is demonstrated to approach these capacity bounds     

Performance evaluation of superorthogonal turbo codes in AWGN andflat Rayleigh fading channels

Turbo codes are parallel concatenated codes whose performance in the additive white Gaussian noise (AWGN) channel has been shown to be near the theoretical limit. In this paper, we describe a low-rate superorthogonal turbo code that combines the principles of low-rate convolutional coding and that of parallel concatenation. Due to the bandwidth expansion, this code outperforms the ordinary turbo code both in AWGN and especially in fading channels. Thus, superorthogonal turbo codes are suited mainly for spread-spectrum applications. For the purposes of iterative decoding, we concisely describe the connection between the optimal maximum a posteriori symbol estimation and suboptimal soft-output decoding based on sequence estimation. The suboptimal decoder produces outputs that can directly be used as additive metrics at successive decoding iterations, without the need for estimating channel noise variance. Simulation results in AWGN and flat Rayleigh fading channels are also presented, along with analytical upper bounds of bit- and frame-error probabilities     

Performance of DPSK with Convolutional Encoding on Time-Varying Fading Channels

The bit error probability performance of a differentiallycoherent phase-shift keyed (DPSK) modem with convolutional encoding and Viterbi decoding on time-varying fading channels is examined. We consider both the Rician and the lognormal channels. Bit error probability upper bounds on fully-interleaved (zero-memory) fading channels are derived and substantiated by computer simulation. It is shown that the resulting coded system performance is a relatively insensitive function of the choice of channel model provided that the channel parameters are related according to the correspondence developed as part of this paper. Finally, a comparison of DPSK with a number of other modulation strategies is provided.     

On the design and selection of convolutional codes for anuninterleaved, bursty Rician channel

This article focuses on code design and code selection rules under power and decoding delay constraints for an antipodal (BPSK) modulated and convolutionally encoded communication system. The system operates over a slowly fading AWGN channel, described by the block-fading model. We emphasize perfect coherent detection with maximum likelihood decoding assuming ideal channel information (the instantaneous fading values). The dominant design criterion in this scenario is the code diversity level in terms of blocks while the standard Hamming distance plays a secondary role. A code design procedure, based on maximum distance separable (MDS) cyclic block codes is presented along with a code-search algorithm. The performance results of selected codes are assessed via simulation and compared to those achieved by Reed-Solomon codes with erasure and error decoding     

Adaptive Channel Estimation Aided Log-Map Turbo Decoder Implementation for DS-CDMA Based Mobile Systems

Practical implementation of convolutional turbo codec is impeded by the difficulty of real-time execution in high transmission rate communication systems due to high computational complexity, iterative block decoding structure, as well as the requirement of accurate on-line channel reliability estimation for maximum-likelihood decoding. Relying on innovative channel estimation techniques involving DS-CDMA specific noise/interference variance estimation and fading channel variation tracking, this paper provides a low-complexity all-digital design of an iterative SISO log-MAP turbo decoder for DS-CDMA based mobile communication systems. The issues of quantization and data flow in both pre-decoder processing module and iterative trellis decoding module are prudently addressed to ensure highly efficient hardware implementation. The efficient design strategies applied confine the decoding complexity while leading to an excellent performance within 0.2 dB of the software decoder.     

Recent Advances in Turbo Code Design and Theory

The discovery of turbo codes and the subsequent rediscovery of low-density parity-check (LDPC) codes represent major milestones in the field of channel coding. Recent advances in the design and theory of turbo codes and their relationship to LDPC codes are discussed. Several new interleaver designs for turbo codes are presented which illustrate the important role that the interleaver plays in these codes. The relationship between turbo codes and LDPC codes is explored via an explicit formulation of the parity-check matrix of a turbo code, and simulation results are given for sum product decoding of a turbo code.     

Performance analysis of turbo-equalized partial response channels

The performance of maximum-likelihood decoding of a serial concatenation comprising a high-rate block code, convolutional code, or a turbo code, a uniform interleaver, and a partial response channel with additive white Gaussian noise is addressed. The effect of a channel precoder on the system performance is also considered. Bit- and word-error rate estimates based upon properties of the average Euclidean distance spectrum of the coded partial response channel are derived. The estimates are compared to computer simulation results, and implications for system design are discussed