分组无线网差错控制技术

分析分组无线网的信道特性,介绍在该网络信道下应用FEC（前向纠错）、ARQ（检错重传）和HFC（混合纠错）三种差错控制方式的特点和适合在该信道下的编码。     

分组无线网差错控制技术

分析分组无线网的信道特性，介绍在该网络信道下应用FEC（前向纠错），ARQ（检错重传）和HFC（混合纠错）三种差错控制方式的特点和适合在该信道下的编码。     

短波自适应数据传输中编码纠错性能的改善

根据传统的前向纠错方式(FEC)方式的GOLAY码纠错方法进行改进,提出了在无线短波数据传输中提高传输性能、降低误码率的方法。该方法经过北京-九江1000多km无线短波自适应数据传输系统多次试验,并通过软件实现方法使(23,12:7)达到了(23,12:8)的性能。给出了实验数据,并论述了自适应短波数据传输中的编码和纠错方法的前景。     

TD-LTE系统HARQ重传机制研究及性能分析

针对无线移动信道时变和多径衰落对信号传输的负面影响,TD-LTE系统采用前向纠错（FEC）和自动重传请求（ARQ）相结合的方法降低误码率;根据3GPP协议中对于冗余版本的规定以及LTurbo速率匹配的特点,研究不同的冗余版本号对应的重传数据分组对系统译码增益的提高空间,仿真分析不同重传机制对系统性能的影响,最后提出一个最佳的重传机制实施例使系统性能最优。     

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。     

移动通信系统HARQ技术的研究

数据通信最初是在有线网上发展起来的,通常要求较大的带宽和较高的传输质量.对于有线连接,数据传输的可靠性是通过重传来实现的.当前一次尝试传输失败时,就要求重传数据分组,这样的传输机制就称之为ARQ(自动请求重传).在无线传输环境下,信道噪声和由于移动性带来的衰落以及其他用户带来的干扰使得信道传输质量很差,所以应该对数据分组加以保护来抑制各种干扰.这种保护主要是采用前向纠错编码(FEC),在分组中传输额外的比特.然而,过多的前向纠错编码会使传输效率变低.因此,一种混合方案HARQ,即ARQ和FEC相结合的方案被提出了.本文对移动通信系统HARQ技术做了详细的研究.     

基于无线传输业务类型的HDLC差错控制技术研究

结合用于信息传输、战地指挥的跳频军用无线分组通信网络的研究课题．首先分析了有线领域传输的HDLC链路协议技术在传输中差错控制方面存在的问题;然后在此基础上提出了基于无线传输业务类型的改进HDLC链路差错控制方案,针对不同类型的业务采用前向纠错FEC或FEC与自动反馈重传ARQ相结合的技术。在该差错控制方案中,设计了信道级FEC和信息级FEC来保证实时型业务所需的误比特率,同时采用信道级FEC和信息级ARQ相结合的方式来保证非实时型数据业务所需的服务质量。最后通过分析和计算机仿真,验证该差错控制方案的有效性和可行性。     

突发信道下无线ATM的前向差错控制方案

在无线ATM网络中，无线信道的高误码率和突发特性要求对无线ATM信元进行较强的误码保护。本文提出了一种有效的前向差错控制（FEC）方案，对信元头采用较强的FEC，对信息域采用较弱的FEC，并针对信道特性和采用的前向差错控制编码的特点进行元头信元内交织，文中对无线ATM信元在突发信道下的信元丢失率和信元信息错误率进行了分析，仿真结果表明该方案在降低信元信息错误率的同时有效地降低了信元丢失率。     

SIP协议在NGN中的应用

结合用于信息传输、战地指挥的跳频军用无线分组通信网络的研究课题,首先分析了有线领域传输的HDLC链路协议技术在传输中差错控制方面存在的问题;然后在此基础上提出了基于无线传输业务类型的改进HDLC链路差错控制方案,针对不同类型的业务采用前向纠错FEC或FEC与自动反馈重传ARQ相结合的技术。在该差错控制方案中,设计了信道级FEC和信息级FEC来保证实时型业务所需。     

无线ATM系统前向纠错方案的改进

前向纠错（FEC）主要用于提高信道的传输性能,在ATM信元头中有CRC纠错方案HEC,但是主要是针对光纤等优良信道,对于干扰严重的无线信道,应有更有力的纠错方案。本文是在信道编码方案确定的条件下,提出进一步提高纠错能力、降低信无丢失率的方法。     

Adaptive source rate control for real‐time wireless video transmission

Hybrid ARQ schemes can yield much better throughput and reliability than static FEC schemes for the transmission of data over time-varying wireless channels. However these schemes result in extra delay. They adapt to the varying channel conditions by retransmitting erroneous packets, this causes variable effective data rates for current PCS networks because the channel bandwidth is constant. Hybrid ARQ schemes are currently being proposed as the error control schemes for real-time video transmission. An important issue is how to ensure low delay while taking advantage of the high throughput and reliability that these schemes provide for. In this paper we propose an adaptive source rate control (ASRC) scheme which can work together with the hybrid ARQ error control schemes to achieve efficient transmission of real-time video with low delay and high reliability. The ASRC scheme adjusts the source rate based on the channel conditions, the transport buffer occupancy and the delay constraints. It achieves good video quality by dynamically changing both the number of the forced update (intracoded) macroblocks and the quantization scale used in a frame. The number of the forced update macroblocks used in a frame is first adjusted according to the allocated source rate. This reduces the fluctuation of the quantization scale with the change in the channel conditions during encoding so that the uniformity of the video quality is improved. The simulation results show that the proposed ASRC scheme performs very well for both slow fading and fast fading channels. This revised version was published online in July 2006 with corrections to the Cover Date.     

H.26L视频在WLAN上的实时编码与传输研究

该文讨论了视频在WLAN上的实时编码和传输问题。首先针对视频编码的特点,提出了一种改进的混合ARQ/FEC算法,可有效地改进传输的实时性和可靠性。然后提出了一种依据接收端的反馈信息进行参考帧选择和帧内更新算法,可有效地解决因时间预测编码造成的差错一直向后传播问题,同时可保证编码的高效率。     

A combined multiple-candidate likelihood decoding and error concealment scheme for compressed video transmission over noisy channels

This paper presents a joint forward error correction (FEC) and error concealment (EC) scheme to enhance the quality of a compressed video signal transmitted over a noisy channel. A multiple candidate likelihood (MCL) channel decoding strategy is used in conjunction with redundancy in the compressed video (syntax validity and spatial discontinuity) to select the best-detected signal.

Simulation results on both objective and subjective performance measures indicate a significant improvement provided by the proposed scheme.     

A novel adaptive hybrid ARQ scheme for wireless ATM networks

This paper describes the design and performance of a novel adaptive hybrid ARQ scheme using concatenated FEC codes for error control over wireless ATM networks. The wireless links are characterized by higher, time‐varying error rates and burstier error patterns in comparison with the fiber‐based links for which ATM was designed. The purpose of the hybrid ARQ scheme is to provide a capability to dynamically support reliable ATM‐based transport over wireless channels by using a combination of our ARQ scheme (called SDLP) and the concatenated FEC scheme. The key ideas in the proposed hybrid ARQ scheme are to adapt the code rate to the channel conditions using incremental redundancy and to increase the starting code rate as much as possible with the concatenated FEC, maximizing the throughput efficiency. The numerical results show that our proposed scheme outperforms other ARQ schemes for all SNR values. This revised version was published online in July 2006 with corrections to the Cover Date.     

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     

Efficiency of error-control schemes for real-time wireless applications on the Gilbert channel

The design of a bandwidth-efficient physical layer for wireless access has always been a challenging task, due to the harsh environment, characterized by impairing phenomena such as radio interference, fading, and shadowing. With circuit switching, a bit-error rate suitable for real-time applications such as voice and video is guaranteed by adopting robust forward error correction (FEC) codes and proper power-budget margins to face fading problems. With this approach, automatic repeat request (ARQ) is used only for applications that require a much lower error rate and can tolerate high delays. The introduction of the packet technique allows the use of ARQ even for real-time traffic. We compare the efficiency of three error-recovering techniques in the presence of traffic with delay constraints, when the memory property of the wireless segment is represented by the Gilbert-Elliot channel. The techniques compared are FEC with interleaving, real-time ARQ, and erasure coding (EC). The comparisons are performed by using both analytical and simulation tools. Two new analytical models are introduced to evaluate the performance of FEC and EC. Simulation is used to validate the analytical results and to derive the performance of real-time ARQ. The numerical results show that when the channel memory increases well beyond the packet-transmission time, the performance of FEC impairs due to the limited interleaving depth, while ARQ and EC remain effective.     

Small‐block interleaving for low‐delay cross‐packet forward error correction over burst‐loss channels

By adding the redundant packets into source packet block, cross‐packet forward error correction (FEC) scheme performs error correction across packets and can recover both congestion packet loss and wireless bit errors accordingly. Because cross‐packet FEC typically trades the additional latency to combat burst losses in the wireless channel, this paper presents a FEC enhancement scheme using the small‐block interleaving technique to enhance cross‐packet FEC with the decreased delay and improved good‐put. Specifically, adopting short block size is effective in reducing FEC processing delay, whereas the corresponding effect of lower burst‐error correction capacity can be compensated by deliberately controlling the interleaving degree. The main features include (i) the proposed scheme that operates in the post‐processing manner to be compatible with the existing FEC control schemes and (ii) to maximize the data good‐put in lossy networks; an analytical FEC model is built on the interleaved Gilbert‐Elliott channel to determine the optimal FEC parameters. The simulation results show that the small‐block interleaved FEC scheme significantly improves the video streaming quality in lossy channels for delay‐sensitive video. Copyright © 2013 John Wiley & Sons, Ltd.     

QoS‐based adaptive error control for wireless networks

Wireless channels are highly affected by unpredictable factors such as cochannel interference, adjacent channel interference, propagation path loss, shadowing, and multipath fading. The unreliability of media seriously degrades the transmission quality. Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) schemes are frequently used in wireless environments to reduce the high bit error rate of the channel. In this paper, we propose an adaptive error‐control scheme for wireless networks on the basis of dynamic variation of error‐control strategy as a function of the channel bit error rate, desired QoS, and number of receivers. Reed–Solomon codes are used throughout this study because of their appropriate characteristics in terms of powerful coding and implementation simplicity. Simulation results show that our adaptive error‐control protocol decreases the waste of bandwidth due to retransmissions or extra coding overheads while satisfying the QoS requirements of the receivers. Copyright © 2002 John Wiley & Sons, Ltd.     

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     

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.