Sequential decoding with ARQ and code combining: a robust hybridFEC/ARQ system

Sequential decoding with ARQ (automatic-repeat-request) and code combining under the timeout condition is considered. That is, whenever the decoding time of a given packet exceeds some predetermined duration, decoding is stopped and retransmission of the packet is requested. However, the unsuccessful packets are not discarded, but are combined with their retransmitted copies. It is shown that the use of code combining allows sequential decoding to operate efficiently even when the coding rate R exceeds the computational cutoff rate R _comp. Furthermore, an analysis of the selective-repeat ARQ scheme shows that the use of code combining yields a significant throughput even at very high channel error rates, thus making the system very robust under severe degradations of the channel     

Sequential decoding with an efficient incremental redundancy ARQscheme

Sequential decoding is analyzed in conjunction with an efficient incremental redundancy automatic repeat request (ARQ) scheme using punctured convolutional coding. With the incremental redundancy ARQ scheme, whenever the decoding time of a given data packet exceeds some predetermined value T_max, decoding of that data packet is stopped and incremental redundancy bits are provided by the transmitter, a few bits at a time, as needed. It is shown that the incremental redundancy ARQ scheme provides throughput improvement over the partial retransmission code combining ARQ scheme. The advantage of the incremental redundancy ARQ scheme is that the throughput increases as the starting coding rate increases over all ranges of signal-to-noise ratios     

A diversity combining DS/CDMA system with convolutional encodingand Viterbi decoding

Averaged diversity combining is applied to an asynchronous DS/CDMA system using convolutional encoding and Viterbi decoding. A cyclic redundancy check (CRC) code is included in the scheme to trigger retransmission requests. Multiple received packets are combined on a bit by bit basis to form a single, more reliable packet. The error correcting decoder operates on the combined packet, as opposed to the most recently received individual packet (e.g., as in a type-I hybrid ARQ protocol), substantially increasing the probability of acceptance with each additional transmission. We show that the proposed technique allows a significant increase in the CDMA system capacity, throughput, and reliability     

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.     

The throughput of hybrid-ARQ protocols for the Gaussian collisionchannel

In next-generation wireless communication systems, packet-oriented data transmission will be implemented in addition to standard mobile telephony. We take an information-theoretic view of some simple protocols for reliable packet communication based on “hybrid-ARQ,” over a slotted multiple-access Gaussian channel with fading and study their throughput (total bit per second per hertz) and average delay under idealized but fairly general assumptions. As an application of the renewal-reward theorem, we obtain closed-form throughput formulas. Then, we consider asymptotic behaviors with respect to various system parameters. The throughput of automatic retransmission request (ARQ) protocols is compared to that of code division multiple access (CDMA) with conventional decoding. Interestingly, the ARQ systems are not interference-limited even if no multiuser detection or joint decoding is used, as opposed to conventional CDMA     

Performance of ARQ with Sequential Decoding Over One-Hop and Two-Hop Radio Links

The stop-and-wait ARQ protocol with convolutional code and sequential decoding is considered. The channel throughput and optimum time-out before retransmission are obtained and the effects of the link parameters discussed. The results are extended to a twohop radio link, where a repeater receives the source's data and forwards them on the same radio channel to the destination. The ARQ protocols for the source and the repeater are discussed and a method presented for choosing the optimum time-out intervals for both.     

A comparison of trellis coded and Reed-Solomon coded hybrid-ARQ protocols over slowly fading Rayleigh channels

The performance of trellis coded and Reed-Solomon coded ARQ error control systems over slowly fading Rayleigh channels are compared and contrasted in this paper. First, a two-code CRC-TCM type-I hybrid-ARQ scheme based on separate error correction and error detection codes is compared to a one-code Reed-Solomon protocol in which retransmission requests are generated within the decoding process. The performance of the associated packet combining protocols is also compared. It is shown that for similar levels of complexity, a onecode Reed-Solomon approach offers both better throughput and reliability performance than the TCM schemes in almost all cases.     

Efficient stop-and-wait type II hybrid ARQ scheme

An efficient stop-and-wait ARQ protocol proposed by Sastry (1975) is modified to include a parity retransmission type II hybrid ARQ scheme. Unlike the Sastry scheme in which simple repeats of a data packet are transmitted, with the type II hybrid ARQ scheme, the data packet to be transmitted is encoded with a rate 1/2 code, and repetitions alternate between the two sequences obtained at the output of the encoder. It is found that the throughput can be substantially increased.<>     

RTX_PW：一种基于路径权值的CMT重传策略

针对多路径并行传输(CMT)情况下当路径质量存在较大差异时,部分路径传输优于全部路径的问题,建立了路径的平均吞吐量与丢包率和延迟的拟合关系,提出了一种基于路径权值的CMT重传策略-RTX_PW,该策略可有效减缓接收缓存阻塞,提高多路径并行传输的吞吐量.最后,仿真结果表明RTX_PW的性能优于传统重传策略RTX_CWND和RTX_SSTHRESH.     

Methods for packet combining in HARQ systems over bursty channels

The performance of ARQ systems can be improved by combining current and prior transmissions at the receiver. Two techniques for combining outputs in a packet-based communication system are presented. In both techniques the fundamental unit of retransmission is a packet, and the fundamental unit of combining is a codeword. The techniques are analyzed for a bursty channel and a system that employs Reed–Solomon coding and bounded-distance errors-and-erasures decoding. Performance results show that the packet-combining schemes provide significant gains in throughput and reductions in error probability when compared with a system that does not employ combining. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Comparison of Block and Convolutional Codes in ARQ Error Control Schemes

ARQ methods of error control can considerably improve the reliablity of data transmission in such areas as satellite communications, computer networks, etc. A number of ARQ schemes using both block and convolutional codes have appeared in the literature. In this paper, the following problem is addressed. Given two different implementations of an ARQ scheme, one using a block code and the other using a convolutional code, such that the bit error probability of both implementations does not exceed some specific value, which implementation has the higher throughput and under what conditions will it be attained? The comparison is made for three basic retransmission schemes using both hybrid and pure ARQ: stop-and-wait, go-back-N, and selective repeat. Numerical estimates of the throughput were obtained using approximate theoretical expressions for BCH codes and simulation results for sequential decoding of rate 1/2 convolutional codes. Parameters optimizing the performance of both block and convolutional codes for different channel conditions and round trip delays were found and were used to obtain these numerical estimates. Comparison of the quantitative results indicates a trend toward preferring convolutional codes as delay and/or block length increases. A binary symmetric channel with noiseless feedback was assumed. Possible implications for the Gaussian channel are also discussed.     

A Modified Selective-Repeat Type-II Hybrid ARQ System and Its Performance Analysis

The hybrid ARQ scheme with parity retransmission for error control, recently proposed by Lin and Yu [1], [2], is quite robust. This scheme provides both high system throughput and high system reliability. In this paper, a modified Lin-Yu hybrid ARQ scheme is presented. The modified scheme provides a slightly better throughput performance than the original Lin-Yu scheme; however, it is more flexible in utilizing the error-correction power of a code. The modified scheme can be incorporated with a rate 1/2 convolutional code using Viterbi decoding. Furthermore, the pure selectiverepeat ARQ is a degenerated case of the modified scheme in selective mode. Lin and Yu analyzed their scheme only for a receiver buffer of sizeNwhereNis the number of data blocks that can be transmitted in a round-trip delay interval. No analysis for other buffer sizes was given. In this paper, the throughput performance of the modified Lin-Yu scheme is analyzed for any size of receiver buffer. Consequently, the throughput efficiency of the pure selective-repeat ARQ for any receiver buffer size can be obtained. We also show that the modified scheme achieves the same order of reliability as a pure ARQ scheme.     

Cross-layered retransmission schemes for TCP-based services

Various retransmission schemes for wireless communication systems have been used to improve performance such as reliability and throughput. Each retransmission scheme is designed to improve the performance according to characteristics of each layer of protocol stacks, such as delay components and error control. Especially, a cross-layered retransmission scheme has been proposed to maximize the spectral efficiency by combining a retransmission scheme and adaptive modulation and coding (AMC). However, the cross-layered retransmission scheme is designed for performance improvement at the wireless access networks. The end-to-end performance is not taken into account for modeling of the cross-layered retransmission schemes. It is difficult to design retransmission schemes for the end-to-end performance improvement. In this paper, we analyze the delay and the throughput at the transport layer for the end-to-end performance when a system uses a cross-layered retransmission scheme and the transmission control protocol as the reliable transmission protocols. We also propose a cross-layered retransmission strategy, AMC combined with automatic repeat request (ARQ) and hybrid ARQ (HARQ), to improve end-to-end throughput. From the evaluation results, it is shown that the proposed cross-layered retransmission strategy is suitable for delay insensitive services that require high throughput.     

Adaptive Modulation and Coding with Selective Retransmission under OFDM signaling

In this paper, we present bandwidth efficient selective retransmission method in conjunction with adaptive modulation and coding (AMC) scheme for OFDM waveform. In the proposed method, when a packet failure occurs, receiver requests retransmission of information symbols prone to error corresponding to the low signal-to-noise ratio (SNR) sub-carriers of OFDM modulation. The selective retransmission avoids unnecessary retransmission and AMC chooses a proper modulation and coding scheme with an objective to maximize the throughput. Our method achieves higher throughput as compared to conventional retransmission methods such as Chase combining hybrid automatic repeat reQuest (CC-HARQ) and incremental redundancy hybrid automatic repeat reQuest (IR-HARQ). We also provide the throughput and delay analysis of the proposed method for non-truncated ARQ. The simulation results demonstrate throughput gain without significant impact on delay as compared to the conventional retransmission approaches.     

Throughput maximization of ad-hoc wireless networks using adaptive cooperative diversity and truncated ARQ

We propose a cross-layer design which combines truncated ARQ at the link layer and cooperative diversity at the physical layer. In this scheme, both the source node and the relay nodes utilize an orthogonal space-time block code for packet retransmission. In contrast to previous cooperative diversity protocols, here cooperative diversity is invoked only if the destination node receives an erroneous packet from the source node. In addition, the relay nodes are not fixed and are selected according to the channel conditions using CRC. It will be shown that this combination of adaptive cooperative diversity and truncated ARQ can greatly improve the system throughput compared to the conventional truncated ARQ scheme and fixed cooperative diversity protocols. We further maximize the throughput by optimizing the packet length and modulation level and will show that substantial gains can be achieved by this joint optimization. Since both the packet length and modulation level are usually discrete in practice, a computationally efficient algorithm is further proposed to obtain the discrete optimal packet length and modulation level.     

基于非均匀星座的改进ARQ方案及其性能分析

本文针对调制阶数大于4的MPSK和MQAM调制，在重传中采用非均匀星座图和符号比特重新排序，提出了一种改进的ARQ方案。通过对AWGN信道下ARQ方案进行理论分析和数值仿真，表明基于非均匀星座的新方案在信道条件较差时能有效地提高重要比特的可靠性，若重传中结合符号比特重排和分组合并，则可使接收端解调合并后的比特可靠性趋于均匀且总体得到提高，从而有效地减少重传次数，提高系统的吞吐率。由于本文所提方案并不改变调制解调规则和数据分组长度，故容易实现和控制。     

Reliability-based incremental redundancy with convolutional codes

Incremental redundancy, or Hybrid type-II ARQ (HARQ), algorithms use a combination of forward error correction and retransmissions to guarantee reliable packet data communications. In this work, we propose a HARQ algorithm that exploits received packet reliability to improve system performance. Specifically, the receiver uses the average magnitude of the log-likelihood ratios of the information bits as the packet reliability metric, which is then used to determine the sizes of subsequent retransmissions. The proposed retransmission strategy attempts to maximize user throughput while satisfying a maximum packet delay constraint. The performance of our reliability-based HARQ algorithm is evaluated in static and time-varying channels through simulations. Furthermore, analytical results on the relationship between the reliability metric, the code rate and the block error rate are presented.     

Maximum-likelihood decoding and code combining for DS/SSMA slottedALOHA

This paper considers the combination of multiple copies of a packet to improve the performance of a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) ALOHA packet radio system with coherent binary phase-shift keying (BPSK) modulation. Both slotted DS/SSMA ALOHA with and without forward error correction (FEC) are considered. For the case with FEC, maximum-likelihood decoding with code combining is used. Code combining allows for the combination of multiple copies of the same packet (which are typically discarded), to obtain a lower code rate for that specific packet, and therefore an improved probability of successful decoding. In both cases, combining multiple copies of the same packet results in a throughput which is an increasing function over a broad range of offered load, so that the system is more reliable from the point of view of stability. In addition, combining provides a higher throughput and a smaller time delay for packet transmission. This is illustrated by means of analytical and simulation results     

基于校正子的第一类混合ARQ及其性能分析

基于校正子的计算提出了一种第一类混合ARQ (HARQ) 方案,该HARQ采用Reed-Solomon (RS)码作为纠错子系统,将检错功能巧妙融于译码过程中。对系统误比特率和吞吐量的分析与仿真表明,短码宜采用前向校正子结构,长码宜采用后向校正子结构,而系统的吞吐量与可靠性之间的最佳折衷,可以通过选择恰当的最大重传次数实现。     

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