动态错误恢复机制和错误控制算法

在无线通信系统中,最重要的问题是在噪声和多路衰减的情况下保证数据能够正确地到达接收方。蓝牙提供了两种技术用来处理链路层的传输错误、自动请求重发和前向纠错方案。本文系统地介绍把两种技术混合使用的一种动态错误恢复机制以及利用开环和闭环错误控制算法提高系统的性能。     

自适应前向纠错增强TCP在无线链路上性能研究

针对无线链路引发的TCP性能缺陷,提出一种适用于TCP端对端前向纠错的自适应算法,并在此基础上利用Reed Solomon码实现一种新的TCP ARS。TCP ARS利用包一级的前向纠错在传输层恢复丢失的分组,并能自适应地根据网络丢包率、往返时延等参数调整前向纠错的冗余信息度,较好地解决了TCP在无线环境中的性能缺陷问题。     

TCP协议在无线网络中的一种改进方法

近年来,无线网络飞速发展,但由于其物理特性的影响,使其不如有线网络那么可靠,无线网络上的丢包率大大高于有线网络.当无线网络中出现丢包后,传统TCP协议会启动其拥塞控制机制,从而造成TCP性能的极大下降.对此提出了一种在传输层上改进wired-cum-wireless网络上TCP协议的方法--WirelessACK响应机制,力图在不改变有线网络的基础上提高TCP的性能.     

TCP Performance and Behaviors with Local Retransmissions

TCP has been the dominant transport protocol over the global Internet, and its performance over a hybrid wireless/wireline network has attracted much attention in recent years. This paper investigates the end-to-end TCP performance, in terms of normalized throughput, effective goodput, and packet delay, over wireless lossy links with local retransmissions. The results reveal that local retransmissions can increase the normalized TCP throughput in different wireless bandwidth, delay, and error settings, at the cost of a decrease in effective goodput and an increased packet delay. The performance observation is explained by the explored TCP endpoint behaviors, including the spurious timeout and duplicated acknowledgment. Analysis shows that spurious timeouts with local retransmissions are rare due to the conservative TCP timeout algorithm. However, spurious duplicated acknowledgments have negative impact and a further improvement with the D-SACK proposal is evaluated.     

基于集成FEC的可靠多目广播及性能评价

对点对点通信，数据的传输常使用自动重复求技术，而前向纠错多用于半可靠实时传输。然而，ＡＲＱ用于多目广播的性能不佳。     

Adaptive hybrid error correction model for video streaming over wireless networks

The Hybrid ARQ (HARQ) mechanism is the well-known error packet recovery solution composed of the Automation Repeat reQuest (ARQ) mechanism and the Forward Error Correction (FEC) mechanism. However, the HARQ mechanism neither retransmits the packet to the receiver in time when the packet cannot be recovered by the FEC scheme nor dynamically adjusts the number of FEC redundant packets according to network conditions. In this paper, the Adaptive Hybrid Error Correction Model (AHECM) is proposed to improve the HARQ mechanism. The AHECM can limit the packet retransmission delay to the most tolerable end-to-end delay. Besides, the AHECM can find the appropriate FEC parameter to avoid network congestion and reduce the number of FEC redundant packets by predicting the effective packet loss rate. Meanwhile, when the end-to-end delay requirement can be met, the AHECM will only retransmit the necessary number of redundant FEC packets to receiver in comparison with legacy HARQ mechanisms. Furthermore, the AHECM can use an Unequal Error Protection to protect important multimedia frames against channel errors of wireless networks. Besides, the AHECM uses the Markov model to estimate the burst bit error condition over wireless networks. The AHECM is evaluated by several metrics such as the effective packet loss rate, the error recovery efficiency, the decodable frame rate, and the peak signal to noise ratio to verify the efficiency in delivering video streaming over wireless networks.     

一种基于带宽估计的无线网拥塞控制机制

针对无线网提出了一种基于带宽估计的拥塞控制机制。该机制利用TCP确认帧携带的数据包到达时间来估算包到达速率，从而得到带宽的估计值。在此基础上用带宽的估计值更新拥塞窗口，避免在发生链路错误时启动拥塞控制机制，由此提高了TCP在无线网上的性能。实验结果表明，算法能减少链路差错对TCP性能带来的影响，提高了TcP在无线网上的吞吐率。     

TCP Yuelu:一种基于有线/无线混合网络端到端的拥塞控制机制

无线链路传输数据的比特率出错导致TCP协议在有线／无线混合网络环境下性能低下,在改进算法TCPReno的基础上,文章提出了一种适用于有线／无线混合网络的拥塞控制机制,该机制包括一种分阶段平滑慢启动机制,改善了突发流量对网络性能的损害,引入网络测量技术获得了往返时间（RTT）、网络带宽、瓶颈链路队列长度等网络状态参数,区分网络拥塞和无线链路比特差错,避免了终端节点对网络状态不了解产生的盲目行为,有效改进了TCP的加性增加乘性减少（AIMD）窗口调节机制,提高了网络性能．同时,在仿真软件NS2中实现了该算法,进行了大量的仿真实验,实验结果表明TCP Yuelu有效降低了网络抖动,提高了网络传输性能,并保持了良好的公平性和对其它TCP流的友好性．     

Header Detection to Improve Multimedia Quality Over Wireless Networks

Wireless multimedia studies have revealed that forward error correction (FEC) on corrupted packets yields better bandwidth utilization and lower delay than retransmissions. To facilitate FEC-based recovery, corrupted packets should not be dropped so that maximum number of packets is relayed to a wireless receiver's FEC decoder. Previous studies proposed to mitigate wireless packet drops by a partial checksum that ignored payload errors. Such schemes require modifications to both transmitters and receivers, and incur packet-losses due to header errors. In this paper, we introduce a receiver-based scheme which uses the history of active multimedia sessions to detect transmitted values of corrupted packet headers, thereby improving wireless multimedia throughput. Header detection is posed as the decision-theoretic problem of multihypothesis detection of known parameters in noise. Performance of the proposed scheme is evaluated using trace-driven video simulations on an 802.11b local area network. We show that header detection with application layer FEC provides significant throughput and video quality improvements over the conventional UDP/IP/802.11 protocol stack     

一种适用于有线-无线混合网络的性能增强代理

为了改善传输控制协议(TCP)在无线网络中的传输性能,提高链路带宽利用率,提出一种适用于有线-无线混合网络环境的性能增强代理( PEP),并在此代理中采用新的流量控制算法.实验结果表明:与标准TCP协议相比,使用此PEP能够显著增加无线链路的带宽利用率,提高TCP在长时延环境下的传输性能.     

MPSSF:一种低失序的缓存转发移动切换方案

全IP无线移动网络的微移动协议在无线接入网采用快速切换技术降低移动切换时延，同时采用了数据包缓存转发技术来解决切换过程中的丢包。多流转发方案存在较多的失序，使上层的TCP协议不适当地启动拥塞控制机制而降低吞吐量。单流转发方案虽然没有失序，但是会占用较多的网络资源并增加数据包的时延。提出一种多径单流转发方案MPSSF，较好地解决了移动切换过程中数据包的丢失与失序问题，同时网络资源消耗以及数据包时延也比单流转发方案显著减小。网络模拟实验表明，MPSSF在移动切换时避免了数据包失序，保持了TCP的拥塞窗口，对TCP性能的改善效果优于多流转发方案及单流转发方案。     

无线传感器网络跳数和通信距离自适应差错控制策略

无线传感器网络(WSNS)的动态信道特性、网络带宽和节点能量受限等特点,使得在无线环境下为数据传输提供可靠性保证面临更大的挑战.本文提出一种适用于WSNS的自适应链路层差错控制策略(AEC-Hops/RSSI),以便改善WSNS的通信性能.首先建立数学模型,分析数据帧被转发所经历的跳数与能效的变化规律,然后分析前向纠错...     

一个具有链路层支持的快速Mobile IP切换算法

由于目前流行的Mobile IP切换都假定了IP层无法得到链路层信息,所以,只能通过周期性地广播代理广告来实现位置移动检测,因而浪费了无线带宽,延长了切换时间,降低了TCP性能.一方面随着无线网络带宽的不断增高(当前的带宽已达到2Mbps),无线链路上的信息传输延迟将越来越小;另一方面,在移动计算环境中,如果IP层能够及时获得一些无线链路层的信息,那么上述的缺点就能被有效地克服.本文提出了一种具有链路层支持的快速Mobile IP切换算法,分析了快速Mobile IP切换算法和三个已知切换算法的切换时间,并在我们已完成的宽带无线IP网络中对上述切换算法进行了对比实验.理论分析和对比实验均表明快速Mobile IP切换算法的延迟降低了一个数量级且极大地改善了TCP性能.     

Joint loss pattern characterization and unequal interleaved FEC protection for robust H.264 video distribution over wireless LAN

The recently adopted H.264 standard achieves efficient video encoding and bandwidth savings. Thus, designing communication protocols and QoS control mechanisms for H.264 video distribution over wireless IP networks is a topic of intense research interest. Delivering video streams to terminals via a wireless last hop is indeed a challenging task due to the varying nature of the wireless link. While a common approach suggests exploiting the variations of the wireless channel, an alternative is to exploit characteristics of the video stream to improve the transmission. In this paper, we combine both approaches through an efficient wireless loss characterization and a low-delay unequal interleaved FEC protection. Besides deriving new QoS metrics for FEC block allocation, the wireless loss characterization is as well used to adjust the interleaving level depending on the loss correlation exhibited by the wireless channel. This novel unequal interleaved FEC (UI-FEC) protocol allows graceful video quality degradation over error-prone wireless links while minimizing the overall bandwidth consumption and the end-to-end latency.     

Real-time video streaming over multipath in multi-hop wireless networks

Given the limited wireless link throughput, high loss rate, and varying end-to-end delay, supporting video applications in multi-hop wireless networks becomes a challenging task. Path diversity exploits multiple routes for each session simultaneously, which achieves higher aggregated bandwidth and potentially decreases delay and packet loss. Unfortunately, for TCP-based video streaming, naive load splitting often results in inaccurate estimation of round trip time (RTT) and packet reordering. As a result, it can suffer from significant instability or even throughput reduction, which is also validated by our analysis and simulation in multi-hop wireless networks. To make real-time TCP-based streaming viable over multi-hop wireless networks, we propose a novel cross-layer design with a smart traffic split scheme, namely, multiple path retransmission (MPR). MPR differentiates the original data packets and the retransmitted packets and works with a novel QoS-aware multi-path routing protocol, QAOMDV, to distribute them separately. MPR does not suffer from the RTT underestimation and extra packet reordering, which ensures stable throughput improvement over single-path routing. Through extensive simulations, we further demonstrate that, as compared with state-of-the-art multi-path protocols, our MPR with QAOMDV noticeably enhances the TCP streaming throughput and reduces bandwidth fluctuation, with no obvious impact to fairness.     

基于无线TCP的簇生丢失重传协议

为提高TCP在无线网络中的传输性能,提出一种局部数据链路层重传协议,簇生丢失重传协议CLRP(Clustered-Loss Retransmission Protoc01)．针对无线链路上突发丢失性强、分组丢失率高的特点,CLRP协议与移动主机端TCP相结合,一方面为重发提供明确的分组丢失种类和高效的无线多分组丢失信息;另一方面提出了更为完善的无线丢失重发控制机制．此外,本协议无需对固定主机端TCP做任何改动．     

Relay-assisted hierarchical adaptation scheme for multi-user scalable video delivery to heterogeneous mobile devices

In multi-user video (MUV) delivery scenarios,the available resources of receiver devices,such as processing capability,link packet error rate (PER),and bandwidth,are usually different.We propose a relay-assisted hierarchical adaptation (RHA) scheme to maximize the total perceptual quality of all users when transmitting video streams coded via scalable video coding (SVC).First,MUV bitstreams are adaptively extracted under the constraints of network bandwidth and individual decoding capacity.Next,the relay links are introduced as substitutes of possible bad direct links for packets retransmissions.Approximately equal opportunity of transmission is allocated to each stream while the packets inside a stream are scheduled according to their priorities.The priorities are determined by the links states and packets loss distortions.Simulation results show that our RHA scheme has significant performance improvements compared with other schemes.     

The impact of error control schemes on lifetime of energy harvesting wireless sensor networks in industrial environments

Due to the harsh channel conditions of the industrial environments, the data transmission over the wireless channel suffers from erroneous packets. The energy consumption of error control schemes is of great importance for battery-limited Wireless Sensor Networks (WSNs) in industrial environments. In this paper, the lifetime analysis of error control schemes, i.e., Automatic Repeat Request (ARQ), Forward Error Correction (FEC) and Hybrid ARQ (HARQ), is presented under different industrial environment channel conditions. Furthermore, the impact of energy harvesting methods on the network lifetime is investigated. A novel Mixed Integer Programming (MIP) framework is developed to maximize the network lifetime while meeting application reliability. Performance results show that utilizing HARQ-II error control scheme for Mica2 and BCH(31,21,5) for Telos improves the network lifetime while meeting the desired application reliability rate.     

信源-信道联合编码的FGS增强层视频传输研究

研究了基于IP无线网络中精细粒度可伸缩性（FGS）视频的侍输。基于包交换的IP无线网络通常由两段链路组成：有线链路和无线链路。为了处理这种混合网络中不同类型数据包的丢失情况，对FGS视频增强层数据运用了一个具有比特平面间不平等差错保护（BPUEP）的多乘积码前向纠错（MPFEC）方案进行信道编码。对FGS增强层每一个比特平面（BP），在传输层，采用里德——索罗蒙码（RS）提供比特平面间的保护；而在链路层，则运用循环冗余校验码（CRC）串联率兼容穿孔卷积码（RCPC）提供数据包内保护。还提出了一个率失真优化的信源——信道联合编码的码率配置方案，仿真结果显示出该方案在提高接收端视频质量方面的优势。     

基于IP无线网络FGS视频传输的多乘积码方案

研究基于IP无线网络中精细粒度可伸缩性(FGS)视频的传输。基于包交换的IP无线网络通常由两段链路组成:有线链路和无线链路。为了处理这种混合网络中不同类型数据包的丢失情况,对FGS视频增强层数据运用了一个具有比特平面间不平等差错保护(BPUEP)的多乘积码前向纠错(MPFEC)方案进行信道编码。对FGS增强层每一个比特平面(BP),在传输层,采用里德—索罗蒙码(RS)提供比特平面间的保护;而在链路层,则运用循环冗余校验码(CRC)串联率兼容穿孔卷积码(RCPC)提供数据包内保护。还提出了一个率失真优化的信源—信道联合编码的码率配置方案,仿真结果显示出该方案在提高接收端视频质量方面的优势。