采用Turbo码的type Ⅲ HARQ性能分析

从理论研究和仿真分析两方面对type Ⅲ HARQ在无线信道环境下的性能进行了深入研究，并与其它两种HARQ方案的性能进行了分析对比。应用更新理论，得出了type IHARQ和type Ⅱ HARQ方案分别在AWGN和Rayleigh衰落信道下吞吐量的闭式解，对于type Ⅲ HARQ虽无闭式的解，但给出了积分形式的解。此外，采用Turbo码为前向纠错码，对三种HARQ分别在AWGN和Rayleigh衰落信道条件下的吞吐量和残余FER等性能做了仿真。结果显示，对于任意的BF信道，包括AWGN信道，type Ⅲ HARQ的性能总是比type Ⅱ HARQ好，而type Ⅱ HARQ总比type I HARQ好。而且，type Ⅲ HARQ的优越性在Rayleigh衰落信道下更加突出。     

基于IRA码的HARQ的性能分析

混合自动重传请求(Hybrid Automatic Repeat Request,HARQ)技术是保障数据可靠传输最有效的差错控制技术。在本文中,采用不规则重复码(Irregular Repeat Accumulate,IRA)码作为前向纠错码,得出了在AWGN信道下的吞吐率。仿真结果表明,IRA码在HARQ系统中的吞吐率接近turbo码,但译码复杂度远远低于Turbo码。     

基于LDPC码的多中继HARQ系统研究

根据不同中继节点建立的通信信道衰落特性的不同,利用中继节点可增强无线信道空间分集,提高整个链路的传输性能。纠错码的使用可更有效地提高信道传输效率的特点。文中介绍了基于LDPC码的多中继HARQ系统模型,在不降低传输速率的条件下,可更高效地传输数据。利用Matlab仿真了不同中继个数对系统平均误码率、吞吐量以及平均时延产生的不同影响,仿真结果表明,采用该系统模型可降低系统的平均误码率和平均时延,提高了系统的吞吐量。同时在码长较长的情况下,采用LDPC码的多中继HARQ系统性能优于采用Turbo码的多中继HARQ系统性能。     

3GPP LTE中基于HARQ技术的吞吐量性能研究

简要介绍了LTE系统下行链路中的混合自动请求重传(HARQ)技术原理。为证明HARQ对LTE系统吞吐量性能的改善,分别在QPSK、16QAM和64QAM三种调制方式下,对系统不加HARQ、强制重传及加入HARQ时系统的吞吐量性能进行了分析研究。仿真结果表明,加入HARQ时系统吞吐量明显提高,且提高范围介于未加HARQ及强制重传之间,证明了HARQ技术可有效改善LTE系统吞吐量性能,提高LTE系统的传输质量。     

OFDM系统中HARQ方案与性能仿真

研究了正交频分复用(OFDM)系统中采用的混合自动重传请求(HARQ)技术,对其性能和实现方案进行了分析;在采用高阶调制时,为均衡同一映射符号内比特可靠性差异采用星座重排方案,并对星座重排技术进行了研究;在典型城区多径信道环境下,对不采用HARQ、采用Type I HARQ、采用Type Ⅲ chase合并的HARQ和采用带有星座重排的Chase合并的HARQ4种方案的误码率和吞吐量性能分别进行了仿真;仿真结果表明,星座重排技术结合Chase合并的HARQ机制是无线通信系统中提高传输质量和吞吐量的一种高效可行的方案.     

一种CQI辅助的HARQ改进方案

下一代移动通信系统在高速移动的条件下,需要更高的吞吐量和更大的带宽。这就需要采用更好的信道编码（turbo码等）、HARQ策略和信道均衡技术。但是,turbo译码是一个复杂的过程,在进行信号处理时会耗费用户大量的时间和功率。因此与turbo译码相关的HARQ策略会对系统性能产生很大影响。提出了一种CQI辅助的HARQ策略。这种策略主要利用了已经测量得到的CQI来跳过HARQ在首次传输和重传过程中不必要的解调和译码过程。通过采用HARQ策略,当误帧率高于门限时可以节省UE端大约55%的功率。     

关于非规则LDPC码的基于度分布HARQ性能研究

该文提出了一种非规则LDPC码字基于度分布HARQ技术的改进方案。该方案在选择重传信息的过程中,不仅考虑了节点度分布的影响,而且考虑了非规则LDPC码字自身的不均等错误保护特性。与原始的基于度分布的HARQ方案相比,该方案使系统的误比特率和吞吐量指标得到了明显改善。     

一种改进的不限重传次数的HARQ重传方案

为了保证数据在无线衰落信道条件下的可靠传输,产生了联合前向纠错编码(FEC)与自动请求重传(ARQ)的混合ARQ(HARQ)技术。HARQ有多种重传方案,本文针对HARQ的无限次重传方案进行了研究,提出了一种改进的基于RCPT码的HARQ重传方案,并分别与传统RCPT-HARQ方案在瑞利快衰落、慢衰落信道下进行仿真比较,仿真结果显示出改进方案在慢衰落信道条件下获得了更高的通过率。     

基于并行级联LDPC码的递增冗余HARQ方案及性能分析

并行级联LDPC码是由多个码率不同的子码,经并行级联后得到的码率可变的LDPC码.本文提出了基于并行级联:LDPC码的递增冗余HARQ方案,给出了这种方案的吞吐量性能封闭解.在AWGN信道和Rayleigh衰落信道下,通过仿真将新方案的性能和随机LDPC码的性能进行了比较.结果显示,并行级联LDPC码的递增冗余HARQ方案性能接近随机LDPC码,但编、译码更简单,参数选择范围更广.     

结构半随机LDPC码的递增冗余HARQ方案

提出了结构半随机LDPC码,分析了其在不同码率时,编、译码具有兼容性的特性。介绍了基于结构半随机LDPC码的递增冗余HARQ方案,给出了这种方案的吞吐量性能封闭解。在AWGN信道和Rayleigh衰落信道下,通过仿真将新方案的性能和随机LDPC码的性能进行了比较,结果显示,结构半随机LDPC码的递增冗余HARQ方案性能接近随机LDPC码,但编、译码更简单,参数选择范围更广。     

A Code Assignment Algorithm for Nonblocking OVSF Codes in WCDMA

OVSF codes are used as channelization codes in WCDMA. Due to code blocking property of OVSF codes, the bandwidth available in the system is severely limited. Code reassignments mitigate the impact of the blocking property at the expense of causing delays and decreasing the throughput of the system. Nonblocking OVSF (NOVSF) codes have been proposed to alleviate the adverse effect of code reassignments. This paper presents a code assignment algorithm for NOVSF codes, which does not require any code reassignments. Simulation results show that NOVSF codes achieve better throughput than OVSF codes, even though code reassignments are allowed in the assignments of OVSF codes.     

Performance evaluation of multicast relay network using LDPC and convolutional channel codes along-with XOR network coding

In this paper,we have compared the performance of joint network channel coding(JNCC) for multicast relay network using low density parity check(LDPC) codes and Convolutional codes as channel codes while exclusive or(XOR) network coding used at the intermediate relay nodes.Multicast relay transmission is a type of transmission scheme in which two fixed relay nodes contribute in the second hop of end-to-end transmission between base transceiver station(BTS) and a pair of mobile stations.We have considered one way and two way multicast scenarios to evaluate the bit error rate(BER) and throughput performance.It has been shown that when using XOR network coding at the intermediate relay nodes,the same transmission becomes possible in less time slots hence throughput performance can be improved.Moreover we have also discussed two possible scenarios in the proposed system model,in which both diversity and multiplexing gain has been considered.It is worth notifying that BER and throughput achieved for LDPC codes is better than Convolutional codes for all the schemes discussed.     

Generalized type II hybrid ARQ scheme using punctured convolutionalcoding

A method is presented to construct rate-compatible convolutional (RCC) codes from known high-rate punctured convolutional codes, obtained from best-rate 1/2 codes. The construction method is rather simple and straightforward, and still yields good codes. Moreover, low-rate codes can be obtained without any limit on the lowest achievable code rate. Based on the RCC codes, a generalized type-II hybrid ARQ scheme, which combines the benefits of the modified type-II hybrid ARQ strategy of J. Hagenauer (1988) with the code-combining ARQ strategy of D. Chase (1985), is proposed and analyzed. With the proposed generalized type-II hybrid ARQ strategy, the throughput increases as the starting coding rage increases, and as the channel degrades, it tends to merge with the throughput of rate 1/2 type-II hybrid ARQ schemes with code combining, thus allowing the system to be flexible and adaptive to channel conditions, even under wide noise variations and severe degradations     

Cross-layer design based on RC-LDPC codes in MIMO channels with estimation errors

In this paper, we propose a cross-layer design framework combining adaptive modulation and coding (AMC) with hybrid automatic repeat request (HARQ) based on rate-compatible low-density parity-check codes (RC-LDPC) in multiple-input multiple-output (MIMO) fading channels with estimation errors. First, we propose a new puncturing pattern for RC-LDPC codes and demonstrate that the new puncturing pattern performs similar to the random puncturing but is easier to apply. Then, we apply RC-LDPC codes with the new puncturing pattern to the cross-layer design combing AMC with ARQ over MIMO fading channels and derive the expressions for the throughput of the system. The effect of channel estimation errors on the system throughput is also investigated. Numerical results show that the joint design of AMC and ARQ based on RC-LDPC codes can achieve considerable spectral efficiency gain.     

RCPT码的性能分析及其在混合ARQ中的应用研究

该文研究基于速率兼容的删余Turbo(RCPT)码的混合ARQ系统性能分析问题,提出将删余卷积码的网格图看成时变的网格图,并利用紧致界分析RVPT码的误帧率性能,进而计算RCPT-ARQ系统通过效率下界。经比较,理论分析结果与仿真结果十分吻合。     

Optimum subpacket transmission for hybrid ARQ systems

Hybrid automatic-repeat-request (ARQ) is a flexible and efficient technique for data transmissions. In hybrid ARQ, subpacket schemes are more attractive for systems with burst errors than complete packet schemes. Although subpacket schemes were proposed in ARQ systems, optimum subpacket transmission is more effective to maximize throughput in a dynamic channel. Since convolutional codes have properties of burst errors in decoding, the optimum subpacket can be applied to convolutional codes. This paper investigates the performance of subpacket transmission for convolutionally coded systems. An efficient method is proposed to estimate the optimum number of subpackets, and adaptive subpacket schemes, i.e., schemes that enable a system to employ different optimum numbers of subpackets under various conditions, are suggested to achieve the maximum throughput of the system. Numerical and simulation results show that the adaptive subpacket scheme is very effective for the convolutionally coded hybrid ARQ system, and it can provide higher throughput, smaller delay,and lower dropping rate than complete packet schemes. Moreover, the adaptive subpacket scheme can be flexibly used with packet combining techniques to further improve the system throughput.     

On the performance of hybrid FEC/ARQ systems using rate compatiblepunctured turbo (RCPT) codes

This paper introduces a hybrid forward-error correction/automatic repeat-request (ARQ) system that employs rate compatible punctured turbo (RCPT) codes to achieve enhanced throughput performance over a nonstationary Gaussian channel. The proposed RCPT-ARQ system combines the performance of turbo codes with the frugal use of incremental redundancy inherent in the rate compatible punctured convolutional codes of Hagenauer (1988). Moreover, this paper introduces the notion of puncturing the systematic code symbols of a turbo code to maximize throughput at signal-to-noise ratios (SNRs) of interest. The resulting system provides both an efficient family of achievable code rates at middle to high SNR and powerful low-rate error correction capability at low SNR     

基于II型H-ARQ系统速率可变低密度校验码的设计与研究

构造了一类用于II型H-ARQ系统、具有Z字形结构校验矩阵、性能优良的速率可变低密度校验码(RC-LDPC)。将渐进边增长(progressiveedgegrowth)算法推广应用到RC-LDPC码的构造中,扩大了码率动态变化范围,提高了码的性能。仿真结果表明将此类RC-LDPC码应用于II型H-ARQ系统,可获得较高的吞吐量,且其校验矩阵的Z字形结构极大地降低了系统实现的复杂度。     

Optimal Overlapped Message Passing Decoding of Quasi-Cyclic LDPC Codes

Efficient hardware implementation of low-density parity-check (LDPC) codes is of great interest since LDPC codes are being considered for a wide range of applications. Recently, overlapped message passing (OMP) decoding has been proposed to improve the throughput and hardware utilization efficiency (HUE) of decoder architectures for LDPC codes. In this paper, we first study the scheduling for the OMP decoding of LDPC codes, and show that maximizing the throughput gain amounts to minimizing the intra- and inter-iteration waiting times. We then focus on the OMP decoding of quasi-cyclic (QC) LDPC codes. We propose a partly parallel OMP decoder architecture and implement it using FPGA. For any QC LDPC code, our OMP decoder achieves the maximum throughput gain and HUE due to overlapping, hence has higher throughput and HUE than previously proposed OMP decoders while maintaining the same hardware requirements. We also show that the maximum throughput gain and HUE achieved by our OMP decoder are ultimately determined by the given code. Thus, we propose a coset-based construction method, which results in QC LDPC codes that allow our optimal OMP decoder to achieve higher throughput and HUE.     

Throughput performance of an FHMA system with variable rate coding

We compare throughput bounds for a frequency-hopped multiple-access (FHMA) system employing variable rate as well as fixed rate coding (FRC). Nonfading as well as Rayleigh-fading channels are explored. The throughput bounds for the variable rate coding (VRC) schemes are based on the assumption that the number of active users in the system, m, is known at any time while the bounds for the FRC scheme assumes that the fixed code rate is optimized for the user population mean, λ, where the population is assumed to be Poisson distributed. We present bounds for theoretical “perfect” codes which achieve the capacity as well as bounds for Reed-Solomon (RS) codes of practical block lengths. Finally, we show the dependence of a VRC scheme upon the accuracy of the estimates of m and present a general comparison of the gains of using VRC versus a realistic FRC scheme