无线自组织网络中基于网络编码的可靠中继多播方案

无线自组织网络由于节点能量受限、无线链路可靠性较差等特性使得在设计数据可靠传输方案时必须考虑上述问题.提出了一个无线自组织中基于网络编码的可靠中继多播方案,本方案让一部分接收节点担当信源节点的发送任务,以中继的形式完成链路失效率较高的节点的传输.理论分析和数值分析结果表明,所提出的方案是可行的,在一定程度上提高了无线自...     

X信道中一种改进的空时编码传输方案

为提高空时编码传输效率,提出一种在X信道中为每个用户配置2根天线的改进空时编码传输方案。每个用户采用全速率全分集空时分组码,将每个码字的部分元素旋转适当的角度,并且对每个码字进行两层预编码。通过一层预编码使得每个接收端的非期望接收码字对齐,在每个码字中引入零向量以及接收端的线性运算,消除每个接收端的非期望接收码字。通过另一层预编码使得每个接收端的期望接收码字正交传输,从而消除多用户干扰。仿真结果显示,与相同场景中已有空时编码传输方案相比,该方案能有效提高传输效率,且可靠性较优。     

一种基于TCP控制报文的MAC层自适应算法

由于无线信道的特殊性,在WLAN应用中,TCP的传输性能会下降。提出依据TCP报文控制段采用不同的MAC传输参数的调整方案。该方案考虑到了802.11MAC参数的可调整性和TCP控制报文在传输流程的重要性,可有效提高控制报文在无线信道上传输能力,避免了由于信道访问冲突和拥塞而造成TCP性能下降的问题,从而提高TCP的传输效率。通过仿真验证了该方案的可行性。     

一种因特网上视频数据的分层编码和传输方法

分层的视频编码和传输在因特网广播／多播系统中起着非常重要的作用。它能够生成多个互补的压缩编码层次,其中每个层次可以分别利用因特网的一个多播通道传送。用户在其中可以做出一定的选择,接收其中的一个、几个,或全部的子流。这些编码层次能够组合成为具有不同时间分辨率和空间分辨率的视频,以满足不同接收端的处理能力限制、带宽限制或其它的用户要求,并同时保持网络的传输效率。该文改进了现在MBone上的PVH算法,利用3D－DCT来构造时间频率层次,以在保持实时处理的同时,提高PVH算法的帧间压缩能力,并使编码所产生的视频层次组合具有时间和空间双重可调整性。     

协同MIMO移动Ad Hoc网络中的一种新型Alamouti编码

针对协同MIMO(Multi-Input Multi-Output)移动ad hoc网络无线带宽相对有限、无线信道噪声干扰强烈而导致的信号传输质量不佳等问题,提出一种基于反相对称调制法的Alamouti空时编码方案。通过在编码过程中加入噪声相消运算环节而大大减小接收端接收到的噪声干扰强度;重点分析此种方案的编译码过程,并通过理论分析和系统仿真表明,相较于传统的Alamouti空时编码,此方案可使传输系统获得更优越的抗噪声性能和更小的传输误码率,大大提高了系统传输可靠性。     

基于干扰感知的无线自组网多播机制

在采用网络编码的无线自组网多播场景中,为了有效地克服节点密度较大时干扰对多播整体性能的影响,提出了一种衡量路径干扰情况的路由度量标准。基于该度量标准,对网络编码机会和节点间干扰避免进行了均衡处理,构建出一种基于部分网络编码的无线自组网干扰感知多播路由机制。仿真结果表明,该机制在能耗、延时和吞吐量等性能方面均优于基于传统网络编码的多播方案,因此特别适用于节点密度较大的场合。     

RSNs中一种基于货币的数据转发算法

在综合RFID和无线传感器网络的RSNs中,无线移动设备存在冗余,因此可以为数据报文的转发提供帮助.提出一种基于货币的信使转发(MCR)启发式算法.该算法在每个报文传输前使用了门槛价格,并通过RSN网络架构中的移动信使将数据从源节点转发到访问点时集成了价格协商机制,或将报文转发给信使,是否将报文直接传输给访问点,取决于重要度函数以及与报文门槛价格相关的信使要价.仿真实验结果表明,与其他主流移动传输方案相比较,本文算法在能耗、成本和送达率方面的性能更优.     

异构无线网络中基于非正交多址的可伸缩视频多播机制

文中提出了异构无线网络下基于非正交多址的可伸缩视频多播的资源管理框架.该框架综合考虑了不同基站间的频谱切分、切片内多播组之间的频谱分配和多播组内的发射功率分配,目的是最大化多播组所有用户设备的整体视频质量.考虑到每个多播组请求视频的不同、不同的用户设备位置和小基站间的干扰,将联合资源管理问题转化为一个整数线性规划问题,并将该优化问题解耦为多播组内发射功率划分问题和基站间频谱切分与基站内多组频谱资源分配问题.前者通过多重循环求得了叠加编码每一层所需的最优发射功率,后者通过背包算法得到了最优的解.仿真结果表明,所提方案在频谱利用率和用户设备平均视频质量方面优于现有方案.     

视频传感网中鲁棒多视角分布式视频编码

针对传统无线视频传感器网络中存在的信息丢失和传感器之间需要建立通信等问题,提出一种鲁棒多视角分布式视频编码系统。通过采用改进的PRISM编码结构,在利用视角间冗余信息提高编码增益的同时将冗余用于增加编码在有损信道中传输的鲁棒性。实验结果表明,该系统在利用信息冗余获得视频压缩的基础上,对无线信道固有的数据包丢失也具有较好的鲁棒性。     

一种基于NOMA的多播无线隐蔽信道

随着移动互联网技术的飞速发展,大量的无线通信场景已经成为无线隐蔽信道的重要载体.当无线隐蔽信道需要在有限的时频资源与多个接收方实现通信时,多播无线隐蔽信道较现有的单播方法具有明显优势.提出一种基于非正交多址接入技术(NOMA)的多播无线隐蔽信道.信道中,发送方将多方秘密信息调制成人工噪声并叠加在正常信号上传输.各接收方通过差分解调去除其它人工噪声的干扰,得到对应的秘密信息.实验结果表明,所提多播无线隐蔽信道,相较传统单播无线隐蔽信道,在保持相同的抗检测性的同时,有效地提高了可靠性.     

基于集成FEC和层次传输的可靠组播的流控技术

端系统能力和网络带宽的异构性给大规模组播的流控带来很大困难。本文将前向纠错（ＦＥＣ）技术与层次传输相结合,较好地解决了异构环境下可靠组播的流控问题。我们给出了传输调度和信道速率分配的算法,讨论了差错控制问题。性能分析和模拟表明,该方法对大规模、异构组播组可显著减少平均传输时间并且有效地利用网络带宽。只需较少数目的组播组就能得到性能的很大提高。软件ＦＥＣ编码器的速度能够匹配当前的网络条件,算法易于实     

Symbol-level reliable broadcasting of sensitive data in error-prone wireless networks

Reliable packet transmission over error-prone wireless networks has received a lot of attention from the research community. In this paper, instead of using simple packet retransmissions to provide reliability, we consider a novel retransmission approach, which is based on the importance of bits (symbols). We study the problem of maximizing the total gain in the case of partial data delivery in error-prone wireless networks, in which each set of bits (called symbols) has a different weight. We first address the case of one-hop single packet transmission, and prove that the optimal solution that maximizes the total gain has a round-robin symbol transmission pattern. Then, we extend our solution to the case of multiple packets. We also enhance the expected gain using random linear network coding. Our simulation results show that our proposed multiple packets transmission mechanism can increase the gain up to 60%, compared to that of a simple retransmission. Moreover, our network coding scheme enhances the expected total gain up to 15%, compared to our non-coding mechanism.     

面向MIMO多跳无线网络的多用户视频传输优化方法

MIMO(multi-input multi-output)作为一种有效提高无线信道可靠性和带宽的新兴技术,已在无线网络中得到广泛应用.但是,如何利用MIMO在多跳无线网络中为多用户提供高质量视频服务,尚未得到广泛关注.多跳无线链路之间的共信道干扰是需要解决的关键问题.提出一种面向多跳无线网络的多用户视频传输方法,利用链路选择、MIMO的空间复用和空间分集等特点,减少链路间的共信道干扰,最大化多用户的平均视频传输质量.通过对链路选择和天线分组进行建模,将上述传输策略抽象成一个最优化问题,该问题是一个NP-hard问题.为了降低求解复杂度,引入遗传算法来求解链路选择问题.该算法采用基因遗传“优胜劣汰”的特性,在保证性能的同时,大幅度降低了求解复杂度.另外,由于遗传算法中每条“染色体”的“优劣”与天线分组策略有关,因此结合可伸缩视频的失真模型,将天线分组问题转化为一个标准的0/1背包问题,并在搜索时采用深度优先和分支限界技术,进一步降低算法复杂度.实验结果表明,所提出的链路选择算法和天线分组算法均能显著提高用户接收视频的质量.     

基于网络编码的多射频Mesh网组播时延建模与分析

网络编码在提高多射频无线Mesh网组播吞吐量的同时也增加了组播传输时延.针对该问题,在建模分析基于网络编码的多射频无线Mesh网组播传输时延特征的基础上,设计了平均组播传输时延(AMTD)的计算方法并给出时延整体优化方案.首先提出1个由双排队系统串联构成的多射频组播模型.其次,运用该模型对组播传输时延特征进行分析,通过计算每个排队系统平均等待时间之和给出AMTD计算公式,得到时延与各网络参数之间的量化关系.最后通过理论分析和仿真实验指明如何调整多个网络参数以优化平均组播传输时延.结果表明,网络状态确定时,同样的射频比例在不同网络编码体积下未必总是最优,应用提出的AMTD公式恰当调整射频用于收?发的比值,可以最优化平均组播传输时延.     

A network coding based hybrid ARQ algorithm for wireless video broadcast

This paper proposes a network coding (NC) based hybrid ARQ (HARQ) algorithm for video broad- cast over wireless networks. The sender applies NC technique to combine the lost packets of different terminals, so that multiple terminals can recover their lost packets via per transmission from the sender. The proposed algorithm combines the advantage of FEC scheme and NC based ARQ scheme so as to maximize not only wireless throughput but also video quality for broadcast communication. Simulation results show tha...     

无线传感网使用网络编码的新型数据传输方法

网络编码能提高无线传感器网络数据传输可靠性,针对现有基于网络编码的数据传输策略随机选取编码向量和使用固定路径所带来的缺陷,设计了一个新的编码矩阵构造方法,并提出了一种新型的基于网络编码的可靠数据传输方法。该编码方案能保证任意k个编码向量线性无关,且不用传输编码向量。数据转发使用"区域推进"机制,自动选取最佳转发节点,将数据包可靠地向sin"k推进",并实现了最少冗余传输和网络均衡能耗。分析与仿真表明,新的数据传输策略能消除现有方法的缺陷,提高数据传输可靠性,降低能耗。     

Multicast-Unicast Data Delivery Method in Wireless IPv6 Networks

Multicast IPv6 is an efficient way of transmitting data simultaneously to a group of IPv6 users. It has the advantage of reducing the required bandwidth of IPv6 data delivery compared to unicast transmission. The data rate of multicast transmission over WLAN is confined by the user with the lowest rate in the multicast group, which is called the fixed base rate problem. This paper proposes a delivery method that incorporates both multicast and unicast transmissions to solve the fixed base rate problem. The proposed method divides the IPv6 network into two levels: multicast mode for the upper level of the network [IPv6 server to Access Point (AP)], and unicast mode for the lower level (AP to mobile nodes). To maintain the end-to-end multicast transmission, the AP is responsible for converting multicast packets to unicast packets. Such a combination enables the proposed method to inherit the advantages of both multicast and unicast transmissions. The performance of our proposed method is evaluated in a test-bed environment that considers the transmission of real-time video application. The proposed multicast-unicast is able to improve the throughput and video quality experienced by the end user, with low packet loss and transmission delay.     

基于网络编码的无线传感器网络数据可靠性分析*

分析了网络编码在提高无线传感器网络数据传输可靠性的途径,并在不同的数据传输路径方式下应用网络编码进行数据传输。在使用网络编码的多路径传输中,提出一种新的传输机制,通过选择源节点的编码数据包数,在对可靠性影响较小的情况下,降低冗余数据包的数量。通过理论分析和计算机模拟给出了网络编码在不同的传输路径下对数据可靠性的效益,得出在数据传输率较高或适中时,在单路径传输下使用网络编码的可靠性优于不使用网络编码的可靠性。     

Wireless multimedia delivery over 802.11e with cross-layer optimization techniques

The use of wireless networks has spread further than simple data transfer to delay sensitive and loss tolerant multimedia applications. Over the past few years, wireless multimedia transmission across Wireless Local area Networks (WLANs) has gained a lot of attention because of the introduction of technologies such as Bluetooth, IEEE 802.11, 3G, and WiMAX. The IEEE 802.11 WLAN has become a dominating technology due to its low cost and ease of implementation. But, transmitting video over WLANs in real time remains a challenge because it imposes strong demands on video codec, the underlying network, and the Media Access Control (MAC) layer. This paper presents a cross-layer mapping algorithm to improve the quality of transmission of H.264 (a recently-developed video coding standard of the ITU-T Video Coding Experts Group) video stream over IEEE 802.11e-based wireless networks. The major goals of H.264 standard were on improving the rate distortion and the enhanced compression performance. Our proposed cross-layer design involves the mapping of H.264 video slices (packets) to appropriate access categories of IEEE 802.11e according to their information significance. We evaluate the performance of our proposed cross-layer design and the results obtained demonstrate its effectiveness in exploiting characteristics of the MAC and application layers to improve the video transmission quality.     

Network coding for unicast in a WiFi hotspot: Promises,challenges, and testbed implementation

In offices and residential buildings, WiFi networks have become a primary means for providing Internet access to wireless devices whose dominant traffic pattern is unicast. In the meantime, the emergence of network coding has brought about great promises for multicast in communication networks where intermediate nodes are allowed to process independent incoming information flows. Little is known about network coding for unicast, however. The objective of this paper is thus to depart from multicast scenarios and shed light on several possible unicast scenarios to which network coding may be applied in a WiFi hotspot in order to obtain communication benefits such as throughput gain, fairness, and reduced protocol complexity. We identify five representative scenarios in which network coding may be used to benefit unicasting in a WiFi hotspot. Several open research issues and practical challenges related to each scenario are discussed individually. To illustrate the benefits of network coding for unicast in a WiFi hotspot, we propose and implement iCORE: The interface COoperation Repeater-aided network coding Engine. iCORE is a practical system in which multi-channel multi-radio repeaters are used to relay unicast traffic for those terminals sitting far away from an access point and suffering from weak signals at a WiFi hotspot. It is based on our last scenario which illustrates the synergy among network coding, opportunistic routing, and interface management. Utilizing idle wireless interfaces and listening to traffic opportunistically, iCORE allows packets to move across the interfaces and to be coded across flows whenever it sees more transmission opportunities. We evaluate iCORE on a four-node chain-like topology testbed implemented using IEEE 802.11b/g radios and compare it to MORE – the state-of-art intra-flow network coding implementation based on opportunistic routing. Our experimental results reveal promising gains in terms of throughput over MORE.