一种新的基于虚拟队列的无线多播网络编码调度策略

网络编码由于其传输效率高的特性,近年来在无线多播网络中得到广泛的应用。针对无线多播网络中丢包自动重传效率低的问题,该文提出一种新的基于虚拟队列中数据包到达时间的编码调度策略(CSAT)。在CSAT策略中,为了提高编码效率,采用虚拟队列来存放初始以及未被所有接收者接收到的数据包。考虑到队列的稳定性,CSAT策略按照一定的比率从主次队列选择发送;在次队列发送数据包时,结合了编码和非编码两种方式,根据数据包到达队列的先后,选取能够使较多数据包参与编码的方式发送。仿真结果表明,该文所提的CSAT编码调度策略在有效提高了数据包传输效率的同时,提高了网络的吞吐量并降低了平均等待时延。     

中继协作无线网络中不完美反馈下基于网络编码的重传方案

无线广播网络传输过程中,目的节点反馈信息丢失或部分丢失导致发送节点不能了解目的节点的真实接收状态.为提高不完美反馈下无线网络的重传效率,本文提出中继协作无线网络中不完美反馈下基于网络编码的重传方案.本方案基于部分可观察马尔科夫决策过程对不完美反馈下的重传过程进行建模.发送节点根据系统观测状态和最大置信度更新系统估计状态,根据数据包发送顺序,优先选择最早丢失且能够恢复最多丢包的编码包重传.目的节点缓存不可解编码包以提升编解码机会.重传过程中源节点关注目的节点请求包需求,相同情况优先选择传输可靠性较高的中继节点,以提升传输有效性.仿真结果表明,在不完美反馈下相对于传统方案,本方案可有效提高重传效率.     

基于机会式网络编码的低时延广播传输算法

为了提高无线网络中数据包广播传输的效率,本文提出了一种基于机会式网络编码的广播传输算法.该算法在发送端按一定顺序选择不同终端的丢包,并采用异或运算编码重传包,在终端采用从重传包中解码数据包的方法恢复丢包.该算法优先恢复时间重要性较高的丢包,并使多个终端同时从单个重传包恢复其丢包,因此有效地提高了广播传输效率并降低了传输...     

一种基于机会式网络编码的高效广播重传方法

为了提高无线广播网络中数据传输的效率,该文提出了一种新颖的基于机会式网络编码的重传方法。将机会式网络编码技术应用于丢包的重传,并采用高效的丢包组合策略生成重传包。根据网络终端的丢包情况,首先创建丢包的哈希表,再根据哈希表快速选择满足一定编码条件的丢包以生成重传数据包,从而在提高重传性能的同时,有效地降低了重传方法的复杂度。仿真结果表明该方法相比已有算法能有效地减少重传次数,并提高重传包发送和接收的效率。     

A reliable overlay video transport protocol for multicast agents in wireless mesh networks

A new video transport protocol for multicast agents in wireless mesh networks (WMNs) is proposed in this paper. The proposed protocol enables a significant reduction in the transmission overhead, while providing reliable communication for its use in multicast applications. This proposed reliable protocol provides a practical approach for an overlay peer‐to‐peer multicast facility supported within the application layer. This obviates the need to give upgraded routers capable of handling multicast broadcasting or modify the existing protocol stack. The protocol tolerates partial losses in multimedia transmissions, while supporting control of the delay sensitivity of such transmissions in WMNs. The key issue in this protocol is the ability to detect packet loss, anticipate retransmission requests, and use the anticipated retransmission requests to transmit the lost packets prior to requests from other receiving agents. The proposed protocol allows for the receiver to determine if retransmission of lost packets is required, ensuring the greatest flexibility needed for a reliable multicast protocol. Copyright © 2009 John Wiley & Sons, Ltd.     

Erasure coding for reliable adaptive retransmission in wireless broadcast/multicast systems

In this paper, we present new adaptive automatic repeat request (ARQ) schemes for wireless broadcast/multicast combining erasure coding (EC) and packet retransmission. Traditional approaches rely on retransmitting the lost packets in a point-to-point or point-to-multipoint mode. The main idea behind the presented protocols is to retransmit adaptive combinations of the lost packets using EC, which can help several receivers to recover the lost information with fewer retransmission attempts. We propose two versions of EC-based ARQ protocols, and investigate theoretically the corresponding transmission bandwidths in different contexts. We show through simulation results the efficiency of the proposed protocols with respect to conventional ARQ strategies and new published ARQ works for broadcast/multicast. Finally, a new sliding window NACK feedback policy is presented for the case of a high number of receivers to avoid the feedback implosion problem.     

D2D网络中基于立即可解网络编码的时延最小化重传方案

该文针对D2D无线网络中多终端并发协作重传冲突避免问题,提出一种基于立即可解网络编码的时延最小化重传方案。在重传阶段,充分利用D2D无线网络终端协作传输数据的优势,结合各终端数据包接收状态,综合考虑时延的影响因素,选取单次重传时延增量较小的数据包生成编码包,最小化重传时延。同时,构建终端冲突图,在图中搜索极大独立集,根据各终端的编码包权重值,选择最大加权独立集中的终端作为并发协作重传终端,从而降低重传次数。仿真结果表明,所提方案能够进一步改善D2D无线网络的重传效率。     

中继协作多播网络中基于最小集合覆盖的编码重传方案

为提高单中继协作多播传输效率,本文提出一种基于最小集合覆盖的分类网络编码重传方案.该方案充分利用中继节点协作传输的优势,将接收端的丢包按中继节点的接收状态分为两类,并按类先后进行编码重传.在各类丢包内部,根据对应的状态反馈矩阵寻找编码机会生成编码包,并将编码包的选择过程抽象为集合覆盖问题,通过求最小集合覆盖使重传次数逼近最小值.此外,在不增加所得前类编码包数的前提下,利用两类丢包之间的编码机会进一步生成新编码包,以减少重传编码包数,从而提高重传效率.分析与仿真结果表明了该方案的有效性.     

Weight Pick: an efficient packet selection algorithm for network coding based multicast retransmission in mobile communication networks

This paper proposes an efficient packet selection algorithm, called Weight Pick, for improving the efficiency of a network coding based multicast retransmission protocol in mobile communication networks. Unlike existing packet selection algorithms, Weight Pick introduces the concept of a dynamic combination number in performing network coding. Based on this concept, a base station dynamically determines the number of packets combined or encoded in a retransmission packet based on the current packet receiving status of users and the combination number for each retransmission packet can be different. In packet selection, Weight Pick attempts to find an encoding combination whose weight is not less than (C ? 1) for every user, where C is the combination number of that retransmission packet. Simulation results show that Weight Pick can significantly improve the retransmission performance as compared with existing packet selection algorithms in terms of both packet loss ratio and packet transmission delay.     

Efficient wireless multicast retransmission using network coding

In wireless multicast,network coding has recently attracted attentions as a substantial improvement to packet retransmission schemes.However,the problem of finding the optimal network code which minimizes the retransmissions is hard to solve or approximate.This paper presents two schemes to reduce the number of retransmissions for reliable multicast efficiently.One is retransmission using network coding based on improved Vandermonde matrix(VRNC),the other is retransmission using network coding based on adaptive improved Vandermonde matrix(AVRNC).Using VRNC scheme the sender selects the packets all receivers have lost and encodes them with improved Vandermonde matrix;when receivers receive enough encoded retransmission packets,all the lost packets can be recovered.With AVRNC scheme,the sender can obtain the recovery information from all the receivers after sending out per retransmission packet,and then the improved Vandermonde matrix can be updated,thus reducing the complexity of encoding and decoding.Our proposed schemes can achieve the theoretical lower bound assuming retransmission packets lossless,and approach the theoretical lower bound considering retransmission packets loss.Simulation results show that the proposed algorithms can efficiently reduce the number of retransmissions,thus improving transmission efficiency.     

Rate-Adaptive MAC Protocol for Wireless Multicast Over OFDMA-Based MANETs

Unlike in unicast transmissions, a feedback channel has not been implemented for multicast transmission over Mobile ad hoc networks (MANET), due to the increase in the overhead with increasing group member size. As a result, rate-adaptation for wireless multicast has not been considered either. In this paper, a novel rate-adaptive Medium Access Control protocol is proposed to allow dynamic rate-adaptation for wireless multicast transmission over MANETs by utilizing the orthogonality of the subcarriers in an Orthogonal Frequency-Division Multiplexing system. In the proposed rate-adaptation method, each member station is assigned a unique subcarrier and by using this subcarrier, its preferred data rate in the current channel condition is reported to the multicast source. Due to their orthogonality, the feedbacked packets simultaneously transmitted by the group members can be distinguished at the source. Therefore, the source chooses the most appropriate data rate for all member stations. By using this method, the data rate for wireless multicast is able to be adaptively changed, so that the overall network performance is improved.     

Reliable Multicast in Multi-Access Wireless LANs

Multicast is an efficient paradigm for transmitting data from a sender to a group of receivers. In this paper, we focus on multicast in single channel multi-access wireless local area networks (LANs) comprising several small cells. In such a system, a receiver cannot correctly receive a packet if two or more packets are sent to it at the same time, because the packets collide. Therefore, one has to ensure that only one node sends at a time. We look at two important issues. First, we consider the problem of the sender acquiring the multi-access channel for multicast transmission. Second, for reliable multicast in each cell of the wireless LAN, we examine ARQ-based approaches. The second issue is important because the wireless link error rates can be very high.We present a new approach to overcome the problem of feedback collision in single channel multi-access wireless LANs, both for the purpose of acquiring the channel and for reliability. Our approach involves the election of one of the multicast group members (receivers) as a leader or representative for the purpose of sending feedback to the sender. For reliable multicast, on erroneous reception of a packet, the leader does not send an acknowledgment, prompting a retransmission. On erroneous reception of the packet at receivers other than the leader, our protocol allows negative acknowledgments from these receivers to collide with the acknowledgment from the leader, thus destroying the acknowledgment and prompting the sender to retransmit the packet.Using analytical models, we demonstrate that the leader-based protocol exhibits higher throughput in comparison to two other protocols which use traditional delayed feedback-based probabilistic methods. Last, we present a simple scheme for leader election.     

Error recovery for ATM transmission over wireless channels

The authors present a technique for efficient recovery from transmission errors to be used when transmitting ATM-like data packets in a wireless channel affected by bursty errors (jamming). Issues related to packet format error protection code structure and retransmission protocol are discussed and simulation results are shown that prove the effectiveness of the proposed approach     

Network Coding in Multicast Routing for Wireless Link Breakage Problem

Link breakage is one of the critical problems that limit the performance of multicast routing in wireless networks. To ease the problem, we apply network coding to the routing operation. In our proposal, data packets are encoded by a random coding scheme. By performing a re-encoding process, the coding scheme is able to keep conveying the data in the network even though link breakage occurs (without the need of waiting for retransmission). To route encoded packets in the network, a disjoint-path tree is used, which is the routing structure constructed by combining a number of multicast trees without the overlapping links among them. Simulation results show that our proposal can effectively ease the impact of link breakage, achieving better packet delivery ratio and higher multicast capacity under different scenarios.     

支持WiMAX节点灵活休眠的两阶段可靠多播策略

节能是无线网络的一个重要课题.针对IEEE 802.16e标准第2类节能模型中监听窗口长度固定会导致一些空闲移动站因得不到及时休眠而浪费能量这一不足,该文提出"两阶段可靠多播策略",让基站在第1阶段多播数据包,在第2阶段对第1阶段丢失的数据包进行网络编码并重播.该策略让移动站一旦空闲就进入休眠,实现了时延约束下数据包的可靠传递.仿真试验表明,该策略可以降低能耗,且移动站的占空比、能耗、吞吐率、丢包率等指标均优于传统的重传与确认方案.     

最小化重传次数的无线网络编码广播重传算法

提出了一种最小化重传次数的无线网络编码广播重传算法。针对无线广播网络,本文首先引入了缓存网络编码（C-IDNC）的概念,在接收端,正确接收但不能解码的网络编码数据包将被缓存起来等待将来的解码机会而不是简单的丢弃该编码包。其次,通过对基于IDNC重传策略的问题描述,分析了不同因素对重传次数的影响,并把这些影响因子量化为可度量的数值。随后,构造了IDNC图 ,用于表征所有可行编码和编码增益,并把最小化重传次数问题转化为最大权重搜寻问题,给出了寻找最优解的编码方法。同时,为降低算法复杂度和计算量,提出一种启发式的最大权重搜寻算法（CI-MWSA）。仿真结果表明,与传统方案相比,提出的策略和算法能有效提高重传效率、减少重传次数。      

基于机会式网络编码的高效广播传输算法

为了提高无线网络广播传输的效率,针对单跳无线网络提出了采用编码方法的广播传输算法。在传统的无线广播传输模型的基础上,分别实现了基于机会式网络编码的单组合分组广播传输算法和多组合分组广播传输算法。它们采用不同的策略选择多个丢失分组编码组合成重传分组,并通过从编码组合数据分组中恢复丢失分组的方式来提高广播传输的吞吐量。仿真结果表明,新算法在不同无线信道传输模型下相比已有的算法有效地降低了广播传输所需的传输带宽。     

An Adaptive Delayed Acknowledgment Strategy to Improve TCP Performance in Multi-hop Wireless Networks

In multi-hop wireless networks, transmission control protocol (TCP) suffers from performance deterioration due to poor wireless channel characteristics. Earlier studies have shown that the small TCP acknowledgments consume as much wireless resources as the long TCP data packets. Moreover, generating an acknowledgment (ACK) for each incoming data packet reduces the performance of TCP. The main factor affecting TCP performance in multi-hop wireless networks is the contention and collision between ACK and data packets that share the same path. Thus, lowering the number of ACKs using the delayed acknowledgment option defined in IETF RFC 1122 will improve TCP performance. However, large cumulative ACKs will induce packet loss due to retransmission time-out at the sender side of TCP. Motivated by this understanding, we propose a new TCP receiver with an adaptive delayed ACK strategy to improve TCP performance in multi-hop wireless networks. Extensive simulations have been done to prove and evaluate our strategy over different topologies. The simulation results demonstrate that our strategy can improve TCP performance significantly.     

WiNoC中EF-ACK容错无线接口设计

无线片上网络中的无线信道面临着严重的可靠性挑战,无线路由器的容错设计对整个片上网络的传输效率有着较大的影响.本文提出一种EF-ACK容错无线接口设计,将多条确认信息配置在一个数据包内,通过无线信道传递确认信息数据包;在无线接口处设立重传数据缓冲区,以更高效的方式确认数据以及控制错误数据包的重传;另外,提出了基于网络状态的编解码控制,在网络情况较差时用BCH编码的方式提高数据的鲁棒性.实验表明,本文方案使用了较小的额外面积和功耗开销,高效地完成了对于数据的无线确认反馈,且在错误率较高时,可以保证网络中较低的网络延迟和较高的饱和吞吐量,大大提高了网络的性能.     

An adaptive opportunistic retransmission control scheme environment-aware-based for wireless multimedia Mesh networks

In this paper, we propose an aware-based adaptive opportunistic retransmission control scheme for wireless multimedia Mesh networks. The proposed scheme provides maximum retransmission count optimization based on environment-aware to improve packet relay probability. The scheme discriminates the types of packet loss in wireless link by means of environment information and selects the retransmission count by taking the IEEE 802.11 wireless channel characteristics into consideration. Furthermore, the maximum retransmission count of MAC is adjusted adaptively. Extensive simulations demonstrate that the proposed scheme significantly reduces packet collision probability and packet loss rate, and thus improves network throughput.