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。     

ARQ差错控制方式的分析设计及突发误码的影响

着重对无线ATM网中采用ARQ差错控制方式后的信元丢失进行了分析和设计,并得到了性能结果。同时还对无线信道的突发误码引起的连续信元丢失进行了理论分析和计算,得到了不同长度信元丢失的概率分布图。     

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。     

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中的ARQ机制

由于无线信道的多径、衰落等特性,无线ATM通信需要有效的、适合于多媒体业务在无线信道传输的差错控制方案.本文介绍了基本的差错控制机制--自动反馈重传,对其三种工作方式进行了分析;而后对应用于无线ATM网络的自适应HARQ系统进行了研究,并分析了与自适应速率传输或FEC冗余量相结合的系统性能.仿真结果显示结合自适应速率传输的系统性能总是好于传统HARQ,而带优先级冗余的自适应HARQ系统,与固定冗余系统相比,也可以提供较好的性能.     

SDH信号中的ATM信元实时检测算法

HEC段信息同整个ATM信头有关,利用8位循环冗余编码方式(CRC校验码)产生,用于单比特纠错和多比特查错.针对国内外广泛使用的SDH网络,利用HEC段功能进行SDH帧数据中ATM信元的识别,为SDH网络中ATM信元协议分析和重组的奠定基础.由于信元识别是基于信元本身的差错控制字段,所以能有效地提高识别性能,降低最大信元丢失率.     

ATM中突发业务的缓存性能分析

主要讨论突发业务情况下的ATM缓存的排队性能.首先采用状态转移概率进行模型分析,然后再给出信元丢失率和信元延时的分布.     

无线ATM系统的混合纠错方案及其在突发信道上的性能分析

本文提出了一种适用于无线ATM系统的混合纠错方案:用RS码保护话音信号,用截短RS/混合Ⅱ型ARQ保护图像和数据。文中分析和仿真了这一混合纠错方案在突发信道上的性能。结果表明,利用RS码强的纠错能力,通过有限次的重传就可获得低的信元丢失率和传输时延。     

具有业务量平滑功能的ATM交换机的性能分析

ATM网络支持大量的突发业务源。突发业务量可用间断Bernoulli过程描述。本文采用一种循环算法,分析了ATM交换机在既有连续比特流业务量又行突发业务量环境下的信元丢失率和平均延迟。数值分析结果和计算机仿真结果一致表明,具有业务量平滑功能的ATM交换机的性能有较大改进。     

无线ATM传输技术研究

从分析ATM业务传输的需求和技术指标出发,提出了适合E12、E22接口映射、传输的统一宏信元编码,并采用了抗衰落帧同步设计技术,该编码对纠正突发误码非常有效,纠错门限为2×10-3,适合具有衰落性能的微波、散射等无线信道传输。该设计拓宽了ATM无线传输组网的应用范围,适用于ATM技术无线机动组网。     

Cell discard and TDMA synchronization using FEC in wireless ATMsystems

The asynchronous transfer mode (ATM) employs header-error control (HEC) to protect the ATM cell header from bit error and/or avoid the misforwarding of ATM cells. However, wireless ATM systems require a more powerful forward-error correction (FEC) scheme to offer acceptable bit-error rate (BER) performance. This paper proposes the utilization of FEC, which makes it possible to discard ATM cells more reliably. Time-division multiple-access (TDMA) is very suitable for wireless ATM systems. In the TDMA scheme, synchronization is very important. This paper also proposes to combine FEC with unique word (UW) detection for improving TDMA synchronization characteristics     

Error correction and error detection techniques for wireless ATM systems

Error correction and error detection techniques are often used in wireless transmission systems. The Asynchronous Transfer Mode (ATM) employs Header Error Control (HEC). Since ATM specifications have been developed for high‐quality optical fiber transmission systems, HEC has single‐bit error correction and multiple‐bit error detection capabilities. When HEC detects multiple‐bit error, the cell is discarded. However, wireless ATM requires a more powerful Forward Error Correction (FEC) scheme to improve the Bit Error Rate (BER) performance resulting in a reduction in the transmission power and antenna size. This concatenation of wireless FEC and HEC of the ATM may effect cell loss performance. This paper proposes error correction and error detection techniques suitable for wireless ATM and analyzes the performance of the proposed schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

An integrated FEC coding scheme for ATM transmission over regenerative satellite networks

The application of asynchronous transfer mode (ATM) on both wireless and satellite networks requires system adaptation. This adaptation has to improve the overall system's performance, and achieve high quality‐of‐service classes approaching that for fibre‐optic communications. In this paper, a new integrated forward‐error‐correction (FEC) coding scheme is introduced for ATM transmission over regenerative satellite networks. The proposed FEC scheme is a concatenation of two Reed–Solomon codes tailored for the header and payload parts of the ATM cell. This integrated coding scheme is shown to significantly improve the cell loss ratio as compared to the standard CRC code used in the ATM cell header. We obtain both upper and lower performance bounds for the concatenated code and check their accuracy when compared to exact system's performance. Both analytical and simulation results show that a cell loss ratio and bit‐error rate (BER) of 10^?25 and 10^?7 can be, respectively, achieved with minimum delay requirements on the SATCOM link. Finally, an approximation for the system's throughout is obtained. It is shown that using a hybrid selective‐repeat automatic‐repeat‐request (SR‐ARQ) with the RS code, a large throughput of approximately 0.843 can be achieved at BERs lower than 10^?7 for data services. Copyright © 2005 John Wiley & Sons, Ltd.     

A New Transport Protocol for Broadcasting/Multicasting MPEG-2 Video Over Wireless ATM Access Networks

Because of the telecommunications de-regulation act and progress in wireless technologies, we will see the co-existence of heterogeneous broadband access infrastructures in the broadband video service industry in the near future. In this paper, we addressed the error control issue when transmitting MPEG-2 video streams over wireless access networks for broadband video broadcast or multicast services. An end-to-end transport protocol based on ATM and wireless ATM technologies is proposed. For video services, the underlying transport network should be transparent and quality should be maintained uniformly over all the segments whether wireline or wireless links. For network resources to be used efficiently, error control should be applied locally on the wireless segments so as to avoid the excessive overhead over the reliable wireline portions. Because a broadband video broadcast or multicast service is a one-to-multiple point service, FEC is the most prevalent error control mechanism. Due to the important role of MPEG-2 control information in the decoding process, priority MPEG-2 control information has to be differentiated from MPEG-2 data information, and excess error protection has to be allocated to it in order to achieve satisfactory QoS. Therefore, a header redundancy FEC (HRFEC) scheme for error control is applied at the local distribution centers before the MPEG-2 encoded video streams are transmitted over the wireless channels. HRFEC is an FEC-based selective protection scheme, which allocates extra error protection to important control information. Simulation results show that the quality of the reconstructed video sequence is vastly improved by using HRFEC, when the channel condition is poor.     

Forward error control for MPEG-2 video transport in a wireless ATM LAN

The possibility of providing multimedia services to mobile users has led to interest in designing broadband wireless networks that can guarantee quality of service for traffic flows. However, a fundamental problem in these networks is that severe losses may occur due to the random fading characteristics of the wireless channel. Error control algorithms which compensate for these losses are required in order to achieve reasonable loss rates. In this paper, the performance of error control based on forward error correction (FEC) for MPEG-2 video transmission in an indoor wireless ATM LAN is studied. A random bit error model and a multipath fading model are used to investigate the effect of errors on video transport. Combined source and channel coding techniques that employ single-layer and scalable MPEG-2 coding to combat channel errors are compared. Simulation results indicate that FEC-based error control in combination with 2-layer video coding techniques can lead to acceptable quality for indoor wireless ATM video.Work performed while the author was at AT&T Bell Laboratories on a D.O.E. fellowship program.     

Broadcast/multicast MPEG-2 video over broadband fixed wirelessaccess networks

With the emergence of broadband fixed wireless access networks, there is an increasing interest in providing broadband video services over outdoor wireless networks. We investigate some fundamental issues related to the broadcasting or multicasting of CBR MPEG-2 videos over fixed wireless channels in B-FWANs using FEC strategies. In B-FWANs, high-frequency wireless channels are used and a direct or indirect LOS propagation path is usually required between a transmitter and a receiver. The wireless channel is modeled by a K factor Rician fading model instead of a Rayleigh fading model. The unique characteristics of the physical channel require special consideration at the system design level. In order to evaluate the overall system performance properly, a set of parameters for objective video quality assessment is introduced and used in our simulation studies, including a definition of the objective grade point value, the number of reconstructed frames, and the conventional peak signal-to-noise ratio value. The feasibility of cell interleaving is also addressed. MPEG-2 control information (i.e., the control blocks) plays a critical role in the decoding process and can influence the reconstructed video quality dramatically; special consideration and excess protection should be given to this information. The concept of a new FEC strategy, header redundancy FEC, is introduced to address this issue. In HRFEC, selected important (high-priority) MPEG-2 control blocks (such as sequence header, sequence extensions, and picture header and corresponding extensions) are replicated before transmission, and duplicate copies are transmitted over the wireless link. Our results indicate that HRFEC is a simple, flexible, and effective error control strategy for broadcasting or multicasting MPEG-2 videos over error-prone and time-varying wireless channels     

Optimization and Adaptation of Error Control Algorithms for Wireless ATM

A common problem of all wireless digital datatransmission systems is the bit error rates of the radiosubsystem, which can be several orders of magnitudehigher than for a wire- or fiber-based technology. Forward error correction (FEC), automaticrepeat request (ARQ), and interleaving are used as meansto improve throughput and bandwidth efficiency. Thispaper presents some considerations on the optimization and adaptation of these algorithms with focuson recent wireless ATM developments. The optimization,with respect to the target bit error rate and themapping of the wireless connection quality to the ATM quality of service (QoS) concept, is discussedin detail. In addition to the theoretical evaluation,which is verified by extensive simulations, we presentcomprehensive architecture and implementation considerations on the design of an adaptiveerror control system for a wireless ATMnetwork.     

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.     

A recommended error control architecture for ATM networks withwireless links

This paper provides performance results through analysis and simulation for key error control problems encountered in using wireless links to transport asynchronous transfer mode (ATM) cells. Problems considered include the forward-error correction (FEC) and interleaving at the physical layer, the impact of wireless links on the ATM cell header-error control (HEC) sand cell delineation (CD) functions, the application of data link automatic repeat-request (ARQ) for traffic requiring reliable transport, and the impact of the choice of end-to-end ARQ protocol for reliable service. We conclude that it is very important to make the physical layer as SONET-like as possible through the use of powerful FEC, interleaving, and ARQ. These additional error control measures are especially necessary for disturbed channels because of the degrading effects of the channel on higher-layer functions. A recommended error control architecture is given with tradeoffs     

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.