Turbo码解码过程中的加权算法

本文通过调整迭代解码过程中系统位接收值的加权系数,提出了一种Turbo码加权迭代解码算法。该算法改变了迭代运算后Turbo码解码器输出软值中系统位接收值信息和它的外部估计信息的比重,使Turbo码无论在低信噪比或是在高信噪比时均具有优良的纠错性能。仿真结果显示,采用Turbo码加权迭代解码算法,不仅能提高Turbo码的收敛速度,而且能进一步降低Turbo码解码时的地板值,使Turbo码的比特误码率在高、低信噪比时都能够得到进一步改善。     

改进的Summer算法及其在Turbo译码中的应用

由于Summer信噪比算法采用的信道模型为AWGN信道,他对衰落信道并不适用。通过在接收信号中增加了衰落因子,提出了一种能够应用于Nakagami衰落信道的改进Summer信噪比估计算法。仿真表明,运用改进的算法获得的信道信噪比信息非常接近实际的信噪比信息,同时,改进的Summer在线估计器使得Turbo译码性能得到明显的改善,而且不影响Turbo译码过程的总复杂度。     

T-TCM系统中的SNR失配分析

该文基于AWGN信道研究了SNR失配对T-TCM系统性能的影响。蒙特卡洛仿真结果表明,SNR欠估计偏差不大于4dB时,T-TCM系统性能基本不受影响,更大的SNR估计偏差则会导致系统性能迅速下降;而SNR过估计始终不会造成系统性能折损。该文结合雅可比对数式及迭代译码算法的特点从理论上给出了解释,进一步提出无需SNR估计的T-TCM译码方案,在保证性能没有损失的前提下降低了T-TCM的应用要求与实现复杂度。     

Outage Probability Analysis of Three-User Reed–Solomon Coded Cooperation Scheme for Wireless Slow Fading Channel

In a coded cooperation scheme, the relay must decode and re-encode data. This process needs to be completed rapidly. Therefore, a simple channel coding/decoding scheme that requires low computational loads is needed. Reed–Solomon (RS) codes are simple, forward error-correction codes with low decoding computational loads. This paper introduces a three-user RS coded cooperation scheme that aims to have simple encoding/decoding complexity as well as to increase diversity order. It also presents the mathematical derivations of outage probability and investigates the outage performance of the three-user RS coded cooperation scheme. The derived outage probability expressions prove that the three-user RS coded cooperation scheme can achieve full diversity. Numerical bit error rate comparisons show that the three-user RS coded cooperation scheme performs better than a two-user scheme under various inter-user and uplink channel conditions. Outage probability performance improves at approximately 5 dB for regions with low signal-to-noise ratio (SNR) and 10 dB for regions with high SNR under a slow-fading channel. The paper also presents the complete calculated numerical tables for outage probability terms (integral terms) that do not have closed-form solutions.     

分组相关快衰落信道下自适应Turbo码译码算法研究

分析了分组相关快衰落信道的特性，推导出该信道下Turbo码译码算法；研究了迭代次数对Turbo编码系统的影响，在小信噪比弥散度条件下，提出基于平均信噪比的最佳迭代译码次数自适应选择方案，可以兼顾译码性能和译码速度，得到较低的平均误比特率和较高的平均译码速度。仿真结果说明，本文提出的Turbo码译码算法，降低了对信道估计精度要求的同时，得到精确信道估计时的性能；对于目标误比特率为10^-4时，采用自适应Turbo译码算法，与固定迭代4次相比，平均误比特率降低了40％，提高了系统性能；而与固定迭代8次相比，迭代次数降低了约1／4，提高了译码速度。     

Forced sequence sequential decoding: a concatenated coding systemwith iterated sequential inner decoding

We describe a new concatenated decoding scheme based on iterations between an inner sequentially decoded convolutional code of rate R=1/4 and memory M=23, and block interleaved outer Reed-Solomon (RS) codes with nonuniform profile. With this scheme decoding with good performance is possible as low as E_b/N₀=0.6 dB, which is about 1.25 dB below the signal-to-noise ratio (SNR) that marks the cutoff rate for the full system. Accounting for about 0.45 dB due to the outer codes, sequential decoding takes place at about 1.7 dB below the SNR cutoff rate for the convolutional code. This is possible since the iteration process provides the sequential decoders with side information that allows a smaller average load and minimizes the probability of computational overflow. Analytical results for the probability that the first RS word is decoded after C computations are presented. These results are supported by simulation results that are also extended to other parameters     

基于正交空时分组码的酉空时码设计

提出了一种基于正交空时分组码构造酉空时码的方案,证明了所设计的酉空时码可以获得满分集.同原有方案相比,所提方案的优点是其码率较高,缺点是解码复杂度较原方案高.针对该缺点,提出了一种次优解码算法,该算法的复杂度同原方案几乎相同.Monte-Carlo仿真实验表明,在相同的频谱效率下,对同一误码率本文方案所需信噪比比原方案低5dB;同时,对同一误码率本文的次优解码算法同最优解码算法相比信噪比损失约1dB.     

软判决多步法相关攻击在PN码快速捕获中的应用

针对非协作接收的扩频通信系统,低信噪比情况下长周期且生成多项式抽头数较多的扩频码的快速捕获问题一直是研究的重点和难点。本文借鉴密码学中密钥攻击基本思想,提出一种基于软判决多步法快速相关攻击的长周期扩频码快速捕获新算法。通过将PN序列看成线性分组码,将序列相位捕获看成线性分组码的解码,采用软判决方法进行分步串行译码,充分利用序列本身的软信息,实现低信噪比情况下长周期扩频序列的快速捕获。理论分析和仿真结果表明本文算法与多项式抽头个数无关,具有较好的捕获性能,能够在低信噪比下稳定工作;与硬判决相关攻击方法相比,本文算法大约有3.5dB以上的性能提升。      

SNR estimation in Nakagami-m fading with diversity combining and its application to turbo decoding

We propose an online signal-to-noise ratio (SNR) estimation scheme for Nakagami-m (1960) fading channels with L branch equal gain combining (EGC) diversity. We derive the SNR estimate based on the statistical ratio of certain observables over a block of data, and use the SNR estimates in the iterative decoding of turbo codes on Nakagami-m fading channels with L branch EGC diversity. We evaluate the turbo decoder performance using the SNR estimate under various fading and diversity scenarios (m = 0.5, 1, 5 and L = 1, 2, 3) and compare it with the performance using perfect knowledge of the SNR and the fade amplitudes.     

Bit error probability of distributed Turbo coded relay systems over quasi-static Rayleigh fading channels

As is known, distributed Turbo coding (DTC) performs close to the theoretic outage probability bound of a relay channel when correct decoding is assumed at the relay. However, decoding error is inevitable in practical fading channels due to the error-prone feature of radio channels, and the decoding error propagation in DTC scheme will severely degrade the error performance of the relay system. As a result, it is necessary to evaluate the error performance of the DTC scheme in multi-hop relaying wireless systems in practical fading channels. Moreover, the theoretical method of analysis provides an effective tool for obtaining the error performance besides lengthy simulations. In this article, the concept of equivalent signal-to-noise ratio (SNR) of the two-hop relay channel and the method of computing equivalent SNR are developed, and then the upper bound on the bit error probability (BEP) of DTC relay systems is analyzed by use of Turbo code's distance spectrum, the concept of uniform interleaver, the limit-before-averaging technique, and the union bound method. Both theoretical analysis and numerical simulation are implemented for relay systems with DTC scheme over quasi-static Rayleigh fading channels. The results show that the upper bound approaches the simulation results in the medium to high SNR region.     

TBCC译码辅助的短数据块盲帧同步技术

咬尾卷积码（Tail-biting Convolutional Codes， TBCC）消除传统归零卷积码带来的码率损失，在短数据块编码时具有较明显的性能优势。本文结合TBCC译码，从降低同步开销，提高短数据块传输效率角度，提出一种适用于TBCC译码辅助盲帧同步方案。该方案利用TBCC校验矩阵约束构造节点矩阵，然后累加每个比特的真实度量作为同步度量准则，并在识别出正确同步位置的同时完成译码。仿真结果表明，对于短数据块盲同步，基于软判决的计算真实度量方案相比硬判决有明显的性能优势，在高信噪比下接近理想同步的性能。      

Rate optimization for IDMA systems with iterative joint multi-user decoding

In this letter, we develop a rate allocation scheme for interleave-division multiple-access (IDMA) systems with iterative decoding. We use a fully-analytical approach to predict the performance of the scheme. Then, we propose a modified linear programming method to find the best rate profile for the scheme. Numerical results show that with just repetition coding and optimal rate allocation, the performance of the scheme is only about 5 dB away from the capacity for a wide range of SNR, provided that the number of users is sufficiently large. Compared with power allocation schemes for IDMA, the proposed rate allocation scheme achieves a similar performance at a moderate spectral efficiency and the requirement of sophisticated power amplifiers can be relaxed.     

A New Data Rotation Based CP Synchronization Scheme for OFDM Systems

In this paper, a new data rotation scheme for improving the symbol timing and carrier frequency offset (CFO) estimation of orthogonal frequency-division multiplexing (OFDM) systems is proposed. The new data rotation scheme intentionally introduces a cyclic shift after the inverse fast Fourier transform (IFFT) in the transmitter so that a higher energy cyclic prefix (CP) is obtained. This cyclic shift will not impair the orthogonality among the subcarriers and will only results in phase shift in the demodulated signal at the receiver. To recover the cyclic shift and for data detection, the scheme makes use of double differential encoding and decoding at the transmitter and the receiver. We analyze the performance of the new data rotation scheme by using order statistics theory. Our results show that the new scheme can provide a 1.6 dB gain in the performance of the CFO estimator and a 6 dB gain for the timing estimator at 15 dB SNR over AWGN channel, as well as a 6 dB gain in lock-in probability and a 4 dB gain in CFO performance at 5 dB SNR over frequency selective fading channel.     

一种改进的准正交空时分组码设计方案

基于MIMO天线系统的空时编码技术是改善无线通信性能、提高带限系统数据速率的一种理想选择。但是由于正交空时分组码不能保证数据全速率传输,为此提出一种改进的准正交空时分组码设计方案。该编码方法利用准正交准则,能够保证数据以全速率传输。并在此基础上具体讨论和分析了编码的编、译码算法和误码性能。该编码方法既不降低分集增益也不增加译码复杂度,并且可以获得一定的编码增益。仿真结果表明,这种方法的误比特率无论在低信噪比还是在高信噪比条件下都要优于已有的准正交空时分组码——Jafarkhani码。     

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.     

一种低码率的LDPC码在LTE-A中的性能研究

本文通过分析LTE-Advanced系统中准循环LDPC码校验矩阵的构造方法,在不改变母码矩阵的基础上,采用一种灵活的扩展方法,构造了一种低码率的LDPC码。采用一种很实用的编码算法和差分译码算法,在MATLAB仿真平台下,比较了这种LDPC码和Turbo码的性能。结果表明：在短码情况下,这种LDPC码在低信噪比下性能略低于Turbo码,但随着信噪比的增加,LDPC码性能优于Turbo码;在长码情况下,LDPC码的性能明显优于Turbo码。为LTE-Advanced系统的信道编解码器的硬件设计提供了一套有效的编译码算法方案,具有较好的实用价值。     

一种全速率准正交空时分组码

空时分组码是发射分集中的一项新技术。通常的空时分组码采用正交设计，虽可以提供全分集增益，却不能保证全速率传输，造成发射端数据的积压。改进的空时分组码采用准正交设计，能够保证数据以全速率传输，但是其性能在低信噪比时优于正交空时分组码，在高信噪比时反而不如前者。提出一种改进的基于准正交设计的空时分组码。通过仿真表明，在不增加译码复杂度的情况下，其性能不论在低信噪比还是高信噪比时都优于正交设计的空时分组码，从而改善了系统性能。     

BICM-ID光通信系统中一种新颖星座映射方案的优化分析

针对传统Gray映射在中高信噪比区域内对迭代译码的比特交织编码调制(BICM-ID)光通信系统改善信道容量性能有限的问题,基于互信息准则和比特的不等保护度提出了一种新颖的16QAM星座映射方案.仿真分析表明:在中高信噪比下,所提出的新映射方案比传统Gray映射方案的信道容量最大改善值可达1.18 bit/channel.结合低密度奇偶校验(LDPC)码并借助外部信息传递(EXIT)图,该方案在光通信系统中具有很好的性能优势与应用前景.     

MAP译码算法对信道估计偏差敏感度分析

作为MAP译码算法的必要参数,信噪比通常通过信道估计单元得到。相关研究表明,信噪比估计值偏差对Turbo译码器输出性能将造成较大的影响。通过对MAP算法的求解,从理论上解释了MAP译码性能下降的主要因素,并通过理论分析和仿真验证,论证了当估计值较真实值小时译码性能明显降低的原因,同时证明了长帧Turbo码对信噪比参数更为敏感。     

Achieving 1/2 log (1+SNR) on the AWGN channel with lattice encoding and decoding

We address an open question, regarding whether a lattice code with lattice decoding (as opposed to maximum-likelihood (ML) decoding) can achieve the additive white Gaussian noise (AWGN) channel capacity. We first demonstrate how minimum mean-square error (MMSE) scaling along with dithering (lattice randomization) techniques can transform the power-constrained AWGN channel into a modulo-lattice additive noise channel, whose effective noise is reduced by a factor of /spl radic/(1+SNR/SNR). For the resulting channel, a uniform input maximizes mutual information, which in the limit of large lattice dimension becomes 1/2 log (1+SNR), i.e., the full capacity of the original power constrained AWGN channel. We then show that capacity may also be achieved using nested lattice codes, the coarse lattice serving for shaping via the modulo-lattice transformation, the fine lattice for channel coding. We show that such pairs exist for any desired nesting ratio, i.e., for any signal-to-noise ratio (SNR). Furthermore, for the modulo-lattice additive noise channel lattice decoding is optimal. Finally, we show that the error exponent of the proposed scheme is lower bounded by the Poltyrev exponent.