Design of Adaptive Modulation and Coding Scheme for Truncated Hybrid ARQ

It has been known that adaptive modulation and coding (AMC) at the physical layer can be combined with a truncated automatic repeat request (ARQ) at the data link layer so as to maximize the spectral efficiency under prescribed delay and error performance constraint. In this paper, we consider the same joint design approach when incremental redundancy-based hybrid ARQ (IR-HARQ) is associated with an AMC design at the physical layer. The extensive simulation studies for predicting the progressive combining gain with each retransmission enables to evaluate the bandwidth efficiency that can be achieved by selecting a more aggressive modulation and coding rate set (MCS) at the expense of packet error rate in earlier transmissions. It has been demonstrated that the aggressive AMC design approach in association with IR-based truncated HARQ can improve bandwidth efficiency by 5.8 and 3.3 dB, as compared to the conservative AMC design approach with truncated HARQ and aggressive AMC design approach with truncated ARQ (i.e., without taking the progressive combining gain in HARQ into account), respectively.     

POMDP-Based Coding Rate Adaptation for Type-I Hybrid ARQ Systems over Fading Channels with Memory

We address the issue of optimal coding rate scheduling for adaptive type-I hybrid automatic repeat request wireless systems. In this scheme, the coding rate is varied depending on channel, buffer and incoming traffic conditions. In general, we consider the hidden Markov model for both time-varying flat fading channel and bursty correlated incoming traffic. It is shown that the appropriate framework for computing the optimal coding rate allocation policies is partially observable Markov decision process (POMDP). In this framework, the optimal coding rate allocation policy maximizes the reward function, which is a weighted sum of throughput and buffer occupancy with appropriate sign. Since polynomial amount of space is needed to calculate the optimal policy even for a simple POMDP problem, we investigate maximum-likelihood, voting and Q-MDP policy heuristic approaches for the purpose of efficient and real-time solution. Our results show that three heuristics perform close to completely observable system state case if the fading and/or traffic state mixing rate is slow. On the other hand, when the channel fading is fast, Q-MDP heuristic is the most throughput-efficient among considered heuristics. Also, its performance is close to the optimal coding rate allocation policy of fully observable system state case. We also explore the performances of the proposed heuristics in the bursty correlated traffic case and show that maximum-likelihood and voting heuristics consistently outperform the non-adaptive case     

Performance of Hybrid ARQ Schemes for the Mobile LEO Satellite Channel

This paper investigates the performance of hybrid ARQ schemes for the mobile Low Earth Orbit (LEO) satellite channel. The proposed schemes adapt their characteristics to the time-varying behavior of the channel. To obtain an unbiased comparison of different ARQ schemes an approximated analytical method is adopted. More precisely, the sphere-packing bound is used to estimate the best possible performance of a hybrid ARQ scheme. To assess the accuracy of the bound, simulation results, based on the use of turbo codes, are also presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance of Hybrid ARQ Schemes with ML Code Combining over a Block-Fading Rayleigh Channel

This paper considers two well-known selective-repeat retransmission schemes, namely, hybrid type-I ARQ and hybrid type-II ARQ, using convolutional coding, in conjunction with maximum-likelihood code combining. Our theoretical analysis, based upon the concept of generalized weight distribution, shows that the use of code combining yields a significant throughput at very high channel error rates not only in constant AWGN channels but also in fading channels. To demonstrate this, we consider a widely-used block-fading Rayleigh channel model, in which the channel is assumed to be constant during each block of data and the fading is assumed to be independent from block to block. A key parameter in designing retransmission protocols for delay-limited applications in such channels is the minimum number of retransmissions, needed to achieve error-free decoding at almost all channel conditions (low outage probability). This number can be reduced significantly when code combining is employed.     

Hybrid Turbo FEC/ARQ Systems and Distributed Space-Time Coding for Cooperative Transmission

Cooperative transmission can be seen as a “virtual” MIMO system, where the multiple transmit antennas are in fact implemented distributed by the antennas both at the source and the relay terminal. Depending on the system design, diversity/multiplexing gains are achievable. This design involves the definition of the type of retransmission (incremental redundancy, repetition coding), the design of the distributed space-time codes, the error correcting scheme, the operation of the relay (decode & forward or amplify & forward) and the number of antennas at each terminal. Proposed schemes are evaluated in different conditions in combination with forward error correcting codes (FEC), both for linear and near-optimum (sphere decoder) receivers, for its possible implementation in downlink high speed packet services of cellular networks. Results show the benefits of coded cooperation over direct transmission in terms of increased throughput. It is shown that multiplexing gains are observed even if the mobile station features a single antenna, provided that cell wide reuse of the relay radio resource is possible.     

Coding performance of hybrid ARQ schemes

We develop a unified performance metric and detailed analysis for hybrid automatic repeat request (HARQ) schemes based on incremental redundancy (IR) and Chase combining (CC). The general result is applicable to both symbol-based and bit-interleaved coded modulations, to HARQ processes based on rateless and fixed-rate mother codes, and IR schemes with and without a self-decodability restriction. The analysis shows that IR over CC coding gains tend to increase with the initial coding rate, but decrease with the signal-to-noise (SNR) variation between retransmissions. The gains can also be diminished when a fixed-rate mother code is used or when the self-decodability criterion is imposed. The theoretical prediction is compared with observed gains at 10% codeword error rates based on turbo-coding simulations. For scenarios with moderately varying SNR between retransmissions, the analytical model tracks actual simulation results very well. However, when the SNR varies widely and the systematic part of the turbo codeword is effectively erased, the CC scheme could, in fact, outperform some IR schemes. For these scenarios, which can be induced by fast time-varying fading or long retransmission delays, the self-decodable IR and the CC schemes prove to be more robust without much performance comprise. Finally, we discuss adaptive improvement to the conventional IR schemes based on the analytical result.     

Hybrid ARQ with selective combining for fading channels

We propose and analyze a hybrid automatic repeat request (ARQ) with a selective combining scheme using rate-compatible punctured convolutional (RCPC) codes for fading channels. A finite-state Markov channel model is used to represent the Rayleigh fading channels. We show that the hybrid ARQ with selective combining yields better performance than the generalized type-II ARQ scheme for fading channels. Furthermore, simulation results of real-time video time division multiple access (TDMA) transmission system are given. Better video quality can be obtained by our proposed scheme, with a bounded delay. Analytical results of throughput and packet error rate (PER) are compared to the simulated results. Our analysis based on a finite-state Markov channel model, is shown to give good agreement with simulations     

训练序列长度可变的混合ARQ方案

为了进一步提高系统的吞吐效率,本文提出了一种均衡器训练序列长度可变的混合ARQ方案.通过对该方案和现有方案吞吐效率的理论推导和计算复杂度分析得出:该方案可以在不增加计算复杂度的情况下,提高系统吞吐效率.数值仿真的结果进一步证实了该方案的有效性.     

An Adaptive Hybrid ARQ Scheme

A hybrid ARQ in which the transmitter adaptively selects an FEC code according to the channel condition is presented and analyzed. The code is selected according to the past transmissions and acknowledgements by an algorithm which is a generalization of that in [1]. The throughput is obtained as a function of the frame error rate for a general system employing the adaptive hybrid ARQ with acknowledgements that arrive instantly on an error-free return channel. The throughput is obtained as a function of the signal-to-noise ratio for an example quad rate system employing convolutional codes with non-coherent frequency shift keying over the uncorrelated Rayleigh fading channel. This allows the best choice for the parameters of the algorithm to be made. In the case that the channel bit errors are independent, the generalization offers performance improvement of less than 10% over that in [1]. But when the channel errors are bursty, as in the case of Rayleigh fading with finite bit interleaving, the generalization offers throughput improvement as high as 24%. We go on to consider incorporating code combining with the adaptive scheme to form an adaptive memory hybrid ARQ. Simulation of a system using complementary punctured convolutional codes with 4 code rates shows that 2-level code combining can extend the adaptive scheme's useful throughput into the low SNR region by approximately 4 dB.     

A Hybrid Coding Scheme for the Gilbert–Elliott Channel

In this paper, we study the performance of different graph-based error-correcting codes over Gilbert–Elliot channels. We propose a hybrid coding scheme in which each code bit is checked by both a parity check and a Hamming code. A hybrid code can be represented by a code-to-code graph, which can be used to optimize the code. Asymptotic minimum distance properties of the hybrid code are derived, and it is shown that the expected minimum distance of the hybrid code increases linearly with respect to the code length. Simulation results show that for a typical Gilbert–Elliott channel, hybrid codes can outperform regular low-density parity-check codes by more than an order of magnitude, in terms of bit-error rate.     

联合自适应调制编码与ARQ的跨层设计

为了提高无线系统数据速率,目前广泛地采用物理层自适应调制编码(AMC)和链路层自动重发请求(ARQ)协议相结合的跨层设计,这种设计方法能大大提高系统频谱利用率。本文在瑞利衰落信道模型下,在给定包时延和丢包率的情况下,推导出了联合AMC和ARQ的跨层设计频谱利用率的公式。同时也与纯AMC和纯ARQ的情况作了比较。     

无线数据传输中的混合ARQ

本文针对无线数据传输中的混合ARQ,介绍了混合ARQ的基本概念和技术,重点分析评述了用于混合ARQ系统中的各种包合并方案和相关的纠错编码技术,并对混合ARQ的相关研究工作进行了展望.     

结合视频压缩编码的动态图像水印方案

本文提出了一种新的、结合视频压缩编码的动态图像水印方案。在嵌入水印时，充分考虑动态图像压缩编码的特性，对帧内编码帧(I帧)，将水印信息嵌入到DCT低额系数中；面对帧间编码帧(P、B帧)，结合动态补偿/离散余弦变换(MC/DCT)混合编码，把水印信息嵌入到运动补偿后的残差图象的直流成分中。同时，在水印嵌入时，采用扩频技术与多维水印相结合的方法，并通过相关检测的方法判断水印的存在。由于水印的检测是对视频码流直接实施的，不需要对压缩数据进行完全解码，从而大大降低了计算量，提高了视频数据水印的适用性。     

几种信道编码方式的编码增益比较分析

简要介绍了几种编码方式的基本原理，包括线性分组码、卷积码、级联码、Turbo码和LDPC码，给出了误码率的计算公式和常用的好码，仿真绘制了不同编码方式下的系统允许传输误码率曲线，并以编码增益为参量对几种编码方式的性能进行了分析．     

联合信道网络编码研究综述

网络编码技术可以提高网络吞吐量和传输性能,均衡网络负载。在无线传感器网络中,应用网络编码和信道编码联合编码技术可以降低节点数据处理复杂度,大幅提升系统整体性能。基于传统网络编码模型,在节点中加入数据调制功能,可以实现网络编码和信道编码的联合编码,信道编码则采用各方面性能较好的Turbo码和LDPC码。结果表明,在10-4误码率下,联合编码方案的信噪比相比于传统编码方案有1.5 dB的节省。     

A Model for the Performance Evaluation of Packet Transmissions Using Type-II Hybrid ARQ over a Correlated Error Channel

Type-II Hybrid-ARQ (Type-II HARQ) has been shown, under certain circumstances, to increase the efficiency and reduce loss of data transmissions over a wireless channel. However, it is difficult to predict how it will perform when transmission symbol errors are correlated. We present a computationally efficient approach to the performance evaluation of packet transmissions over a wireless link employing Type-II HARQ error mitigation when the physical channel is subject to correlated transmission symbol errors. This provides a tool for static or online optimization of system parameters. We present numerical results for a wide range of channel statistics, illustrating the effect of bit error correlation, bit error rate, and block size on packet latency and loss rate.     

Hybrid ARQ scheme employing TCM and packet combining

A new hybrid automatic repeat request scheme employing packet combining based on the Viterbi decoder is presented. It is shown that the proposed form of combining, together with a rearrangement of the signal constellation, can outperform similar forms of packet combining such as average diversity combining     

Hybrid ARQ schemes employing coded modulation and sequencecombining

In this paper, we propose and analyze two hybrid automatic-repeat-request (ARQ) schemes employing bandwidth efficient coded modulation and coded sequence combining. In the first scheme, a trellis-coded modulation (TCM) is used to control channel noise; while in the second scheme a concatenated coded modulation is employed. The concatenated coded modulation is formed by cascading a Reed-Solomon (RS) outer code and a block coded modulation (BCM) inner code. In both schemes, the coded modulation decoder, by performing sequence combining and soft-decision maximum likelihood decoding, makes full use of the information available in all received sequences corresponding to a given information message. It is shown, by means of analysis as well as computer simulations, that both schemes are capable of providing high throughput efficiencies over a wide range of signal-to-noise ratios. The schemes are suitable for large file transfers over satellite communication links where high throughput and high reliability are required     

卫星网络中基于网络编码的ARQ机制

随着航空航天技术的发展,越来越多的应用任务需要利用卫星通信进行信息传输。在卫星网络中,已有的研究成果大都采用了ARQ机制来降低卫星信道的数据丢失率。然而由于卫星信道具有长时延的特点,因此ARQ所采用的反馈重传机制会大幅增加卫星信道的传输时延。因此,针对卫星网络,提出了一种基于网络编码的ARQ(SatNC-ARQ)机制来减少卫星信道的丢包数,并通过减少重传次数来降低卫星信道的传输时延。在Sat-NC-ARQ中,卫星终端除了发送几个真实业务终端的数据包外,还会创建一个虚拟业务终端发送网络编码数据包,从而在接收方,只要接收到足够多的数据包,就能对所有的数据包进行解码,于是可以大幅降低卫星信道的传输时延以及丢包数。还对Sat-NC-ARQ所具有的一些性质进行了理论分析。仿真结果显示,相对于选择性重传ARQ机制,Sat-NC-ARQ机制能够降低大约11%的传输时延和86%的丢包数。