一种适用于陆地移动通信的ARQ/FEC编码方式

本文介绍采用新I/Ⅱ型ARQ方式的实验室测试设备的开发工作.这种新的Ⅰ/Ⅱ型ARQ方式适用于陆地移动前向卫星线路.信道特性的研究表明虽然使用卷积码可以消除前向卫星通信线路中的随机差错,但还需使用ARQ方式来克服由于信号阻塞所引起的衰落. 为了实现V iterb i解码和数据包同步,硬件使用了市售的68000控制的VEM插件板及一些专用插件板. 由于受时间限制,给出的是硬件在高斯噪声条件下工作的结果,未用卫星衰减模拟.为了确保高度的数据完整性,数据包使用了差错检验技术,使残余差错率小于10~(-11),由于受时间限制这一点未被证实,然而长期测试确实表明差错率低于10~(-8).     

移动通信中基于Turbo码的混合ARQ方案

在移动环境中，由于信道的时变特性，单纯的FEC或ARQ机制往往无法提供所希望的系统性能。为了提高数据及图像的传输可靠性，需采用ARQ与FEC相结合的混合ARQ差错控制方案。首先介绍了几种常见的以Turbo码作为纠错码的混合ARQ方案，然后研究了基于Turbo码组合译码的有限次重传混合ARQ方案，给出了传输方案及组合译码算法。仿真结果表明，低Eb/No时，该方案对通过率有明显改善。     

引入FEC＆ARQ技术保障IPTV视频传输质量

在提升IPTV视频质量中必须要考虑网络丢包、时变的有效带宽和可变时延等特性对实时视频传输的影响。文章简要介绍了FEC、ARQ技术的原理,分析了在IPTV业务中引入FEC＆ARQ技术的必要性和可行性。深入探讨了FEC、ARQ技术引入到IPTV中提升视频传输质量的关键方案和具体的应用场景。     

基于LDPC码的可变冗余混合ARQ研究

在数字通信系统中,可变冗余混合ARQ方案既能提供通信的吞吐率,又能提高通信的可靠性。根据可变冗余混合ARQ方案的特性,本文设计了一种适合于可变冗余混合ARQ方案的LDPC码。仿真结果证明了基于LDPC码的可变冗余混合ARQ方案的良好性能。     

基于星上自适应FEC的卫星数据分发

为了解决卫星数据分发系统中雨衰对下行链路的异构性影响,建立了基于再生转发器和多波束技术的卫星数据分发系统简化模型,提出了采用星上自适应分组级FEC(Forward Error Control)的下行链路差错控制方法,针对下行链路的降雨等级自适应选择纠错码率,在不占用上行共享链路的情况下,实现对下行链路差错控制的动态调整,给出了采用RSE码的星上自适应FEC的算法公式,通过MATLAB软件和端到端的FEC技术进行了仿真比较分析,结果表明,当下行链路降雨率小于50%时,网络吞吐率可提高12%~25%。该策略可以为多波束宽带卫星数据分发系统的设计提供参考。     

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.     

一种有效的水声通信网络中用于半双工信道的ARQ协议

自动重传请求(ARQ)在保证通信网络可靠传输中起着关键的作用。但是，在水声通信网络中，由于水声信道的半双工以及信道的长传播时延特性，使得水声通信网络的吞叶性能受到极大的制约。本文针对水声信道长传播时延这一特点，利用扩频通信技术，将单个信道分成两个子信道；一个用于前向信道(从发送方到接收方)，另一个用于反向信道(从接收方到发送方)，从而使得对每个分组数据的响应时间大大缩短，提出了一种有效的适合于半双工特性的ARQ协议。理论分析和仿真结果表明，相对于传统的SW ARQ协议而言，该协议在水声信道下具有更优的吞吐性能。     

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

In this paper, we propose an analytical cross‐layer model for a Transmission Control Protocol (TCP) connection running over a covariance‐stationary wireless channel with a completely reliable Automatic Repeat reQuest scheme combined with Forward Error Correction (FEC) coding. Since backbone networks today are highly overprovisioned, we assume that the wireless channel is the only one bottleneck in the system which causes packets to be buffered at the wired/wireless interface and dropped as a result of buffer overflow. We develop the model in two steps. At the first step, we consider the service process of the wireless channel and derive the probability distribution of the time required to successfully transmit an IP packet over the wireless channel. This distribution is used at the next step of the modeling, where we derive expressions for the TCP long‐term steady‐state throughput, the mean round‐trip time, and the spurious timeout probability. The developed model allows to quantify the joint effect of many implementation‐specific parameters on the TCP performance over both correlated and non‐correlated wireless channels. We also demonstrate that TCP spurious timeouts, reported in some empirical studies, do not occur when wireless channel conditions are covariance‐stationary and their presence in those measurements should be attributed to non‐stationary behavior of the wireless channel characteristics. Copyright © 2011 John Wiley & Sons, Ltd.     

An ARQ/FEC coding scheme for land mobile communication

This paper describes the development of a laboratory test unit that implements a new Type I/II ARQ scheme for use on a land mobile forward satellite link. Investigation of channel characteristics showed that it was possible to use convolutional coding to combat random errors, but it was also necessary to employ an ARQ scheme in order to overcome fades due to signal blockage. The hardware development used commercial 68000-based VME cards as well as special-purpose cards to perform the functions of Viterbi decoding and packet synchronization. Results are presented for the hardware operating with Gaussian noise as time limitations excluded the use of satellite fading simulation. In order to ensure a high degree of data integrity error detection was applied to the data packets such that a residual error rate of less than 10^?11 should result. This was not able to be verified due to the limited time. However, long term tests did indicate that an error rate less than 10^?8 was achieved.     

Energy Efficient Hybrid ARQ Scheme under Error Constraints

Due to the volatile characteristics of wireless channel and limited battery resource in the handheld devices, high throughput and energy efficiency are important criteria for the design of mobile communication protocols. This paper proposes an energy efficient error control scheme, which has on-demand quality of services for wireless data networks. This scheme can be utilized to accomplish the dual goals of reducing energy consumption and preserving quality of service over wireless links. It combines a simple power control scheme with a hybrid automatic repeat request strategy using rate-compatible punctured convolutional codes. In order to increase the system utility, the power and the coding rate for the data transmission are adjusted to match the channel variation. In case of frame error rate being constrained, such as 10^–6, thethroughput and utility are analysed and it is found that the proposed scheme outperforms the existing schemes that use only error control.     

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.     

卫星数据分发系统中的分组级FEC技术性能分析

本文根据所给出的信道差错模型和里德所罗门删除码(RSE)编码技术,研究了在卫星数据分发系统中采用分组级前向纠错(FEC)技术的文件成功分发概率和吞吐量效率与文件长度、分组长度、接收站点数及RSE码纠错能力之间的关系,所得到的结论对于卫星数据分发系统中的参数选择及性能优化具有指导意义。     

自适应调制混合ARQ系统中低时延冗余递增策略的研究

冗余递增混合ARQ能提供较高的数据通过率,但也带来了较大的传输时延。该文提出一种具备低时延冗余递增策略的混合ARQ系统并与自适应调制系统相结合,不但根据不同的接收信噪比,选取不同的调制方式,而且还选择不同的冗余递增策略。仿真和计算结果表明,与采用固定冗余递增策略的自适应调制混合ARQ系统相比,该系统在保证较高的数据通过率的前提下,大大降低了系统传输时延。     

基于中继择优选择的协同ARQ吞吐量分析

本文分为两个部分:基于中继择优选择,分析选择多个中继情况下系统的中断概率;考虑系统延时,仅仅对双中继协同系统、单中继协同ARQ系统和双中继协同ARQ系统的吞吐量进行比较。理论分析和仿真结果说明,协同系统最优中继选择个数越多,系统中断概率就越小;选择单个中继和两个中继的协同ARQ系统的吞吐量,无论高信噪比还是低信噪比情况下,都明显优于非ARQ协同系统。     

Super FEC技术

结合现有的SuperFEC产品介绍了SuperFEC技术，就其发展现状指出了SuperFEC存在的非标准性和非透明性的缺陷，并提出了SuperFEC规范化的方法。