MIMO ARQ系统非理想信道估计条件下序贯线性预编码设计

针对MIMO ARQ系统中使用的重发机制,采用跨层设计思想,提出非理想信道估计条件下基于系统容量准则的次最优序贯线性预编码器的设计方案。首先推导出MIMO ARQ系统中存在信道估计误差时系统容量的上界和下界。理论分析和仿真结果表明,MIMO ARQ系统的容量在高信噪比时取决于信道估计误差。为简化处理,利用系统容量的下界并根据序贯预编码的思想,设计出ARQ重发时的次最优预编码器。仿真结果表明该次最优序贯预编码器可以获得良好的系统性能。     

Performance of H.263 video transmission over wireless channelsusing hybrid ARQ

This paper proposes a hybrid ARQ error control scheme based on the concatenation of a Reed-Solomon (RS) code and a rate compatible punctured convolutional (RCPC) code for low-bit-rate video transmission over wireless channels. The concatenated hybrid ARQ scheme we propose combines the advantages of both type-I and type-II hybrid ARQ schemes. Certain error correction capability is provided in each (re)transmitted packet, and the information can be recovered from each transmission or retransmission alone if the errors are within the error correction capability (similar to type-I hybrid ARQ). The retransmitted packet contains redundancy bits which, when combined with the previous transmission, result in a more powerful RS/convolutional concatenated code to recover information if error correction fails for the individual transmissions (similar to type-II hybrid ARQ). Bit-error rate (BER) or signal-to-noise ratio (SNR) of a radio channel changes over time due to mobile movement and fading. The channel quality at any instant depends on the previous channel conditions. For the accurate analysis of the performance of the hybrid ARQ scheme, we use a multistate Markov chain (MSMC) to model the radio channel at the data packet level. We propose a method to partition the range of the received SNR into a set of states for constructing the model so that the difference between the error rate of the real radio channel and that of the MSMC model is minimized. Based on the model, we analyze the performance of the concatenated hybrid ARQ scheme. The results give valuable insight into the effects of the error protection capability in each packet, the mobile speed, and the number of retransmissions. Finally, the transmission of H.263 coded video over a wireless channel with error protection provided by the concatenated hybrid ARQ scheme is studied by means of simulations     

Analysis of an Adaptive Selective-Reject Scheme in Time-Varying Channel with Non-Negligible Round-Trip Delay and Erroneous Feedback

In this article, an adaptive SR ARQ scheme is analyzed and optimized in a time-varying channel environment with unreliable feedback. To have an operational scheme, we choose the smaller packet size to be half of the bigger one. Thus, there is only one independent design parameter related to packet size. The other two parameters are associated with channel sensing. The performance of the adaptive scheme is measured by its average throughput, which is upper-bounded by the throughput of the so-called ideal adaptive scheme. This upper bound is very useful in the optimization of the packet size and other design parameters.     

无线视频的一种码率控制方法

无线信道的高误码率对视频图像质量有很大的影响,前向纠错(FEC)和自动重发请求(ARQ)对于降低无线信道的误码率,提高图像质量有很好的效果。通过对FEC和ARQ方法的有效性分析,在TMN8的基础上提出一种简单的混合FEC/ARQ自适应模式选择码率控制方法。该方法首先预测报文丢失数量和纠错报文传输时延,从而选择合适的纠错编码模式,并为纠错编码分配比特数。实验结果表明该方法有效降低无线信道下报文丢失率,显著提高了图像质量。     

A reliability output Viterbi algorithm with applications to hybridARQ

We present an algorithm that permits a receiver to calculate the probability of packet error in parallel with the Viterbi decoding process. This packet reliability value may be used to request retransmissions in a type-I hybrid ARQ scheme. It is shown that this scheme can be used to guarantee any required bound on the packet error probability. In addition, this scheme can be used in conjunction with packet combining. The performance of this scheme is compared with that of the Yamamoto-Itoh algorithm and is shown to provide a significant improvement in throughput     

Optimization of Hybrid ARQ for IP Packet Transmission

This paper presents, optimizes, and analyzes the performance of a novel hybridSelective Repeat/Multi Copy(SR/MC) Automatic Repeat Request (ARQ) scheme for transmitting fragmentedInternetProtocol (IP) packets. The ARQ scheme works in the SR mode until the last IPpacket fragment istransmitted. If a fragment is negatively acknowledged after the last fragmentis transmitted, then the system goes into theMC mode. In the MC mode, multiple copies of the erroneous fragment aretransmitted. After the IPfragments are received without error, the system returns to the SR mode.The optimization of the ARQ is done in terms of two parameters: fragment sizeand the optimum number of packetsto be transmitted in the MC mode, M. Optimum values for both parameters arecalculated for Bit ErrorRate (BER), throughput, IP packet size, and delay. The fragment size is alsocalculated for actual datathroughput for a given IP packet size, both with and without Forward ErrorCorrection (FEC). Then,the performance of the proposed scheme is evaluated in terms of BER andIP packet size with theoptimum M and fragment size. Performance results are obtained with and withoutBose ChaudhuriHocquenghem (BCH) error correction codes under Additive White Gaussian Noise(AWGN) as wellas Flat Rayleigh Fading channels. The ARQ scheme gives optimum performance forM equal to 10fragments and fragment size of 75 bytes. Under the AWGN channel, a throughputof 0.9 is achieved for any IPpacket size and at higher BER conditions compared to the Selective Repeat +Stutter Scheme 2 (SR + ST 2).An 8 dB improvement is achieved under the flat Rayleigh fading channel usingBCH(63, 51, 2) for a throughputof 0.9.     

An adaptive ARQ scheme with packet combining for time varyingchannels

The dependence of the efficiency of hybrid type-II ARQ schemes on the packet size in the context of a simple packet combining scheme is discussed. A simple algorithm for adopting the optimum packet size according to the channel bit error rate (BER) is presented. Also, a very simple method of estimating the channel BER is provided     

Performance Analysis of a Memory ARQ Scheme with Soft Decision Detectors

An automatic repeat-request (ARQ) scheme with memory and soft error detectors has been recently proposed by Benelli. Its performance was studied mainly through computer simulation. In this paper, a generalized version of this ARQ scheme is examined. The selection of certain thresholds and weights to minimize the bit error rate in systems using a fixed number of packet repeats is considered. Finally, the evaluation of the average number of transmissions per packet in systems in which negatively acknowledged packets are retransmitted until successfully received is described.     

Analysis and Optimization of an Adaptive Selective-Repeat Scheme for Time-Varying Channels with Feedback Errors

In this article, an adaptive SR ARQ scheme is analyzed and optimized in a time-varying channel environment with unreliable feedback. Two-state Markov models are assumed for both the forward and the returnchannel.This enables the time behaviour of the entire system to be modelledby a Markov chain. To have an easy-to-implement scheme, we choose the smaller packet size to be half of the bigger one. Thus, there is only oneindependent design parameter related to packet size. The other two parametersare associated with channel sensing. The performance of the adaptive schemeis measured by its average throughput, which is upper-bounded by the throughput of the so-called ideal adaptive scheme. This upper bound is very useful in the optimization of the packet size and other design parameters. From the results, it can be concluded that the selection of the packet size is at least as critical as the optimization of the other parameters. The feedback errors degrade the throughput of the scheme, but their effect on the parameter optimization turns out to be almost negligible.     

Retransmission Error Control with Memory

Automatic-repeat-request (ARQ) is one of the most commonly used error control techniques today. In this paper, an error control technique that is a basic improvement over ARQ is presented. The technique uses the simple idea of utilizing erroneously received blocks in an ARQ system for error control, retaining most of the other aspects of ARQ. The technique is termed ARQ-with-memory (MRQ). The general MRQ system is described, and simple upper and lower bounds are derived on the throughput achievable by MRQ. The performance of MRQ with respect to throughput, message delay and probability of error is compared to that of ARQ by simulating both systems using error data from a VHF satellite channel being operated in the ALOHA packet broadcasting mode [9].     

Modeling TCP SACK performance over wireless channels with semi-reliable ARQ/FEC

Providing reliable data communications over wireless channels is a challenging task because time-varying wireless channel characteristics often lead to bit errors. These errors result in loss of IP packets and, consequently, TCP segments encapsulated into these packets. Since TCP cannot distinguish packet losses due to bit corruption from those due to network congestion, any packet loss caused by wireless channel impairments leads to unnecessary execution of the TCP congestion control algorithms and, hence, sub-optimal performance. Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) try to improve communication reliability and reduce packet losses by detecting and recovering corrupted bits. Most analytical models that studied the effect of ARQ and FEC on TCP performance assumed that the ARQ scheme is perfectly persistent (i.e., completely reliable), thus a frame is always successfully transmitted irrespective of the number of transmission attempts it takes. In this paper, we develop an analytical cross-layer model for a TCP connection running over a wireless channel with a semi-reliable ARQ scheme, where the amount of transmission attempts is limited by some number. The model allows to evaluate the joint effect of stochastic properties of the wireless channel characteristics and various implementation-specific parameters on TCP performance, which makes it suitable for performance optimization studies. The input parameters include the bit error rate, the value of the normalized autocorrelation function of bit error observations at lag 1, the strength of the FEC code, the persistency of ARQ, the size of protocol data units at different layers, the raw data rate of the wireless channel, and the bottleneck link buffer size.     

Performance evaluation of the generalized type-II hybrid ARQ schemewith noisy feedback on Markov channels

The generalized type-II hybrid automatic repeat request (ARQ) scheme on Markov channels is examined in order to study the effect of feedback channel errors on the performance of ARQ systems. It is shown that it is possible to derive expressions for certain critical performance parameters, such as the throughput efficiency, the probabilities of packet loss, undetected error, and correct delivery. To provide a means of comparison, a parallel set of expressions is provided under the usual assumption of an error-free feedback channel. By use of simulations, the ARQ system performance is examined under noiseless feedback and noisy feedback. It is found that feedback channel noise can result in the loss of packets, an increase in the number of undetected errors, and the occurrence of unnecessary transmissions. To enhance the performance of the GH-II ARQ scheme, a predictor is used and found to lower the probability of undetected error, reduce the number of unnecessary transmissions, and increase the throughput efficiency     

SR ARQ for adaptive modulation systems combined with selection transmit diversity

Adaptive automatic repeat request (ARQ) schemes are quite effective for throughput enhancement in time-varying mobile channel environments. In this paper, both throughput and packet error rate are analyzed for a selective-repeat ARQ scheme based on a constant-power variable-rate adaptive M-QAM system combined with selection transmit diversity over multiple-input multiple-output Markovian-Nakagami channels. In this analysis, the impact of using outdated and/or imperfect channel state information on the performance of the system is considered.     

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     

Efficient ARQ schemes with multiple copy decoding

Several modifications of an efficient automatic repeat request (ARQ) scheme proposed by Weldon (see IEEE Trans. Commun., vol.COM-30, p.480, 1982) are studied. Unlike Weldon's scheme, in which all erroneous data packets are discarded, the present schemes make use of copies of the data packet which may contain errors. A number of channel models are considered, namely, a binary symmetric channel, a nonfading, and a Rayleigh fading channel with additive white Gaussian noise. In most cases, it is found that the throughput can be substantially increased. Under poor channel conditions, the use of forward error correction can lead to further improvement. A type-II ARQ scheme which does not suffer the throughput degradation under good channel conditions due to overhead parity bits associated with conventional forward error correction is also analyzed     

Performance of a type-II hybrid ARQ protocol in slotted DS-SSMApacket radio systems

The application of a type-II hybrid ARQ protocol in a slotted direct-sequence spread-spectrum multiple-access (DS-SSMA) packet radio system is investigated. Both the static performance and the dynamic performance of such a system are analyzed. In the physical layer, packet error and packet success probabilities are computed using the improved Gaussian approximation technique, which accounts for the bit-to-bit error dependence within a packet. In the data-link layer, two-dimensional Markov chains are employed to model the system dynamics. Based on this model, the performance of the type-II hybrid ARQ protocol is upper and lower bounded by considering, respectively, a superior scheme and an inferior scheme. Steady state throughput and delay performances of the two bounding schemes are obtained. Moreover, it is shown that for each fixed input load, there is an optimal retransmission probability under the finite user population assumption. Bounds on this optimal retransmission probability are also given     

Performance of hybrid ARQ for IP packet transmission on fadingchannel

This paper proposes and analyzes the performance of a hybrid selective repeat (SR)/multicopy (MC) automatic repeat request (ARQ) scheme to transmit fragmented Internet protocol (IP) packets. The ARQ scheme works in the SR mode until the last IP packet fragment is transmitted. If a fragment is negatively acknowledged after the last fragment is transmitted, then the system goes in the MC mode. In the MC mode, multiple copies of the erroneous fragment are transmitted. After all IP fragments are received without error, the system goes back to the SR mode. The performance of the proposed scheme is evaluated in terms of the bit error rate (BER), IP packet size, and fragmentation size with and without Bose Chaudhuri Hocquenghem (BCH) error correction codes. Both the results are obtained under additive white Gaussian noise (AWGN) as well as flat Rayleigh fading channels. The proposed scheme gives a throughput of 0.9, even at high BER conditions, for any IP packet size under an AWGN channel while, an 8-dB improvement is achieved, when using BCH(63, 51, 2) for throughput of 0.9, over selective repeat+stutter scheme 2 (SR+ST 2) under a flat Rayleigh fading channel     

Performance evaluation of a finite buffer generalized selectiverepeat ARQ scheme for satellite communications

This article presents a new generalized selective repeat automatic repeat request (ARQ) scheme for error control in broadcast and point-to-point satellite communication systems. In the proposed scheme, each bit in a packet is repeated m times consecutively to increase the transmission reliability. Finite capacity buffers have been assumed at the earth stations. The throughput, theoretically derived for the proposed scheme, is optimized with respect to the number of copies transmitted per bit. A suitable algorithm to adaptively choose this number in relation to the transmission channel propagation conditions can also be used. In comparison with classical and modified versions of the selective repeat ARQ scheme as described in the literature, the proposed scheme provides enhanced throughput, especially with poor channel conditions and a high number of receiving earth stations     

Complementary punctured convolutional (CPC) codes and theirapplications

Presents a new class of punctured convolutional codes that are complementary (CPC codes). A set of punctured convolutional codes derived from the same original low rate code are said to be complementary if they are equivalent (in terms of their distance properties) and if when combined yield at least the original low rate code. Based on these CPC codes the author proposes and analyzes a variation of the type II hybrid ARQ scheme which is called a type III hybrid ARQ scheme. With the type III hybrid ARQ scheme, the starting code rate can be chosen to match the channel noise requirements, and as with the type II scheme, packets that are detected in error are not discarded, but are combined with complementary transmissions provided by the transmitter to help recover the transmitted message. The main advantage is that any complementary sequence sent for a packet that is detected with errors is self decodable. That is the decoder does not have to rely on previously received sequences for the same data packet for decoding, as is generally the case with incremental redundancy ARQ schemes. This feature is desirable especially in situations where a transmitted packet can be lost or severely damaged as a result of interference. CPC codes can find applications in diversity transmission systems. A novel complementary diversity scheme which makes use of CPC codes is briefly discussed     

PEEC: a channel-adaptive feedback-based error

Reliable transmission is a challenging task over wireless LANs since wireless links are known to be susceptible to errors. Although the current IEEE802.11 standard ARQ error control protocol performs relatively well over channels with very low bit error rates (BERs), this performance deteriorates rapidly as the BER increases. This paper investigates the problem of reliable transmission in a contention free wireless LAN and introduces a packet embedded error control (PEEC) protocol, which employs packet-embedded parity symbols instead of ARQ-based retransmission for error recovery. Specifically, depending on receiver feedback, PEEC adaptively estimates channel conditions and administers the transmission of (data and parity) symbols within a packet. This enables successful recovery of both new data and old unrecovered data from prior transmissions. In addition to theoretically analyzing PEEC, the performance of the proposed scheme is extensively analyzed over real channel traces collected on 802.11b WLANs. We compare PEEC performance with the performance of the IEEE802.il standard ARQ protocol as well as contemporary protocols such as enhanced ARQ and the hybrid ARQ/FEC. Our analysis and experimental simulations show that PEEC outperforms all three competing protocols over a wide range of actual 802.11b WLAN collected traces. Finally, the design and implementation of PEEC using an adaptive low-density-parity-check (A-LDPC) decoder is presented.