无线视频传输的跨层动态映射算法

在IEEE 802.11e EDCA机制和基于场景的马尔可夫链模型基础上,提出跨层动态映射算法来改善无线视频传输的服务质量（QoS）。根据视频帧的重要性和网络的负荷情况,将来自应用层的视频帧信息动态地映射到MAC层中合适的队列中去,并且采用网络仿真工具NS2进行仿真,来比较IEEE 802.11e EDCA机制以及跨层动态映射算法。仿真结果表明跨层动态映射算法能明显提高传输后的视频质量。     

基于IEEE 802.11a/g的视频传输系统

介绍了一种基于IEEE 802.11a/g无线传输DVD视频信号的系统.介绍了IEEE 802.11a/g协议的特点及其一些重要的技术机制,阐述了基于该协议实现视频传输的优势和应用前景,以DVD无线视频传输为例,介绍了基于IEEE 802.11a/g和嵌入式系统的无线视频传输的实现方案,概述了它的系统结构、工作流程和软件部分所要完成的工作,分析了实现过程中的若干关键技术.     

基于自适应竞争窗口的车联网视频传输

针对车联网IEEE 802.11p协议的视频传输展开研究工作。首先分析无线802.11p传输机制,说明吞吐量很大程度上受节点MAC层竞争窗口值影响;其次提出针对视频节点的竞争窗口自适应算法;最后通过NS仿真实验对比,结果表明CWSA算法在画面质量与传输延迟上优于IEEE 802.11p默认竞争窗口算法。     

车用自组网媒体访问控制机制改进

为提升车用自组网传输音频、视频的服务质量,对基于IEEE802.11p的车用无线接入技术MAC机制进行改进,提出竞争窗口自适应EDCA机制。仿真实验表明,竞争窗口自适应EDCA机制有效地降低了车用自组网中音频、视频流的传输时延、时延抖动和丢包率,保证了车用自组网传输VoIP、视频会议、音视频流媒体等多媒体业务的服务质量。     

面向802.11网络实时视频传输的调度算法研究

视频传输是802.11网络通信所承载的重要业务类型。如何在网络资源受限的条件下高质量的传输视频数据是一个亟待解决的问题,也是当前网络技术研究的热点。本文结合压缩视频数据的特点,针对802.11网络,系统而深入地研究了视频传输中质量驱动的包调度算法,并通仿真实验验证了其性能。     

基于WLAN网络的视频流组播传输机制研究

本文针对基于IEEE802.11的无线局域网上组播视频流时终端异构问题,提出一种对客户端分组要：组播传输机制。该机制中,AP根据不同终端的接收能力和实时视频流的码率,将组播组内的站点进行分组,对划分的子组采用不同速率进行组播,以此来提高IEEE802.11无线局域网的传输性能,降低差站点对好站点视频接收效果的限制。NS-2仿真实验结果表明,分组组播机制有效地提高了无线局域网和好站点的性能。     

一种车载网络的簇间碰撞避免MAC协议

车载网络采用IEEE802.11p作为底层协议来保证通信的可靠性,IEEE1609.4标准是IEEE802.11p的拓展。然而,这种基于IEEE1609.4标准的信道访问机制存在一些不足。本论文提出一种保证安全信息的可靠传输,提高服务信道的吞吐量的基于簇的碰撞避免的MAC协议。     

延迟容忍网络自适应差错控制方法

根据延迟容忍网络的时延较大、误码率较高等特点,在现有的传输控制层和MAC层差错控制的基础上改进,结合IEEE 802.11 DCF机制的特点,提出一种基于MAC层丢包率的自适应差错控制方案.该方案能有效改善延迟容忍网络的传输时延,满足对时延要求比较敏感的业务的要求.     

60GHz毫米波无线通信技术标准综述

60 GHz无线通信技术可以提供数吉比特速率传输支持高清视频传输、快速同步、无线USB和高速无线局域网.毫米波标准包括了IEEE 802.15.3c、ECMA 387、IEEE 802.11ad、IEEE 802.11aj和中国CWPAN标准.主要介绍了我国毫米波标准、IEEE 802.11ad和IEEE 802.11aj标准及未来60 GHz无线技术.     

IEEE 802.11n标准的提高吞吐量技术

IEEE802.11系列是目前业界普遍认可的主流无线局域网协议。但高速增长的业务和不断增加的应用种类对无线局域网的性能和服务质量扩展性提出了更高要求。文章介绍了IEEE802.11n协议的LongNAV、MTBA、PSMP等MAC层新技术,它们从设定传输时间、简化帧结构和改进应答传输方式等方面优化帧结构和提高网络吞吐量,整体提高无线局域网数据速率,从而达到性能优化的目的。     

Retry Limit Based ULP for Scalable Video Transmission over IEEE 802.11e WLANs

We investigate the packet loss behavior in the IEEE 802.11e wireless local area networks (WLANs) under various retry limit settings. Considering scalable video traffic delivery over the IEEE 802.11e WLANs, our study shows the importance of adaptiveness in retry limit settings for the unequal loss protection (ULP) design. Based on the study, we present a simple yet effective retry limit based ULP which adaptively adjusts the retry limit setting of the IEEE 802.11e medium access control protocol to maintain a strong loss protection for critical video traffic transmission. The simulation results illustrate significant advantages in the delivered video quality for our proposed design.     

On the capabilities of IEEE 802.11e for multimedia communications over heterogeneous 802.11/802.11e WLANs

Multimedia communications over WLAN is widely acknowledged as one of the key, emerging applications for wireless LANs. As with any multi-service network, there is the need to provision the WLANs with the QoS mechanisms capable of guaranteeing the requirements of various services. The upcoming IEEE 802.11e (EDCA) standard is a proposal defining the mechanisms for wireless LANs aiming to provide QoS support to time-sensitive applications such as voice and video communications. Due to the fact that the IEEE 802.11e interface cards will take over the WLAN market, replacing the use of legacy IEEE 802.11 interface cards in most WLAN applications, an important number of networking scenarios will consist of a hybrid configuration comprising legacy IEEE 802.11-based stations and IEEE 802.11e-based stations. For this reason, in this paper we carry out a performance analysis on the effectiveness of the IEEE 802.11e (EDCA) upcoming standard when supporting different services, such as, voice, video, best-effort, background and in the presence of traffic generated by legacy 802.11 (DCF) based stations.     

Supporting multimedia streaming and best‐effort data transmission over IEEE 802.11e EDCA

As demand for broadband multimedia wireless services increases, improving quality of service (QoS) of the widely deployed IEEE 802.11 wireless LAN (WLAN) has become crucial. To support the QoS required by a wide range of applications, the IEEE 802.11 working group has defined a new standard: IEEE 802.11e. In this paper, we propose a measurement‐based dynamic media time allocation (MBDMTA) scheme combined with a concatenating window scheme to support real‐time variable bit rate (rt‐VBR) video and best‐effort (BE) data transmission using IEEE 802.11e enhanced distributed channel access (EDCA). To provide the QoS guarantee for rt‐VBR video, the proposed MBDMTA scheme dynamically assigns channel time to the rt‐VBR video based on the estimate of the required network resources. On the other hand, the concatenating window scheme controls the contention window (CW) ranges of different priority flows such that real‐time services always have higher channel access probability, thus achieving the capability of preemptive priorities. In addition, the concatenating window scheme preserves fairness among flows of the same class and attains high channel utilization under different network conditions. Simulation results demonstrate that the throughput and delay performance improve significantly for the transmission of rt‐VBR video and BE traffic as compared to those for the 802.11e EDCA specification. It is also revealed that combining the two proposed schemes provides seamless integration and reliable transmission of digital video and data service within the 802.11e EDCA framework. Copyright © 2007 John Wiley & Sons, Ltd.     

下一代WLAN技术标准802.11ac/ad

基于IEEE802.11n标准的WLAN能够支持高达600 Mbit/s的传输速率,但在支持无线高清视频传输等高吞吐量无线数据业务时仍然会遇到瓶颈。面对这一挑战I,EEE已启动下一代WLAN技术标准802.11ac和802.11ad的制定工作,数据吞吐量将达到几个Gbit/s,能够更好地满足快速增长的市场需求。     

A traffic control system for IEEE 802.11 networks based on available bandwidth estimation

To support Quality of service (QoS)‐sensitive applications like real‐time video streaming in IEEE 802.11 networks, a MAC layer extension for QoS, IEEE 802.11e, has been recently ratified as a standard. This MAC layer solution, however, addresses only the issue of prioritized access to the wireless medium and leaves such issues as QoS guarantee and admission control to the traffic control systems at the higher layers. This paper presents an IP‐layer traffic control system for IEEE 802.11 networks based on available bandwidth estimation. We build an analytical model for estimating the available bandwidth by extending an existing throughput computation model, and implement a traffic control system that provides QoS guarantees and admission control by utilizing the estimated available bandwidth information. We have conducted extensive performance evaluation of the proposed scheme via both simulations and measurements in the real test‐bed. The experiment results show that our estimation model and traffic control system work accurately and effectively in various network load conditions without IEEE 802.11e. The presence of IEEE 802.11e will allow even more efficient QoS provision, as the proposed scheme and the MAC layer QoS support will complement each other. Copyright © 2006 John Wiley & Sons, Ltd.     

A Throughput Model of IEEE 802.11aa Intra-Access Category Prioritization

In this paper the first saturation throughput model of an IEEE 802.11 network is presented, which includes the intra-access category prioritization introduced in the recently approved IEEE 802.11aa standard. This new feature was proposed to support finer grained prioritization of audio video streams in comparison to the existing Enhanced Distributed Channel Access (EDCA) function. The presented model implements different transmission probabilities for the primary and alternate voice and video queues. Additionally, it includes such features as virtual collision handling, backoff differentiation, and Arbitration Inter-Frame Space differentiation. The presented results show the difference in the operation of IEEE 802.11aa intra-access category prioritization and EDCA inter-access category prioritization. They also allow to derive several novel conclusions.     

Assessing the IEEE 802.11e QoS effectiveness in multi-hop indoor scenarios

The IEEE 802.11e technology is receiving much interest due to the enhancements offered to wireless local area networks in terms of QoS. Other application fields for this technology are wireless ad hoc networks, wireless mesh networks, and vehicular ad hoc networks. In the literature, most of the research works available focusing on the IEEE 802.11e technology offer simulation results alone, being hard to find empirical results of implementations that prove its effectiveness in realistic scenarios. Additionally, we consider that studies of IEEE 802.11e based on simulation platforms have not been thoroughly validated using real-life results. In this work we analyze the performance of the IEEE 802.11e technology in real multi-hop ad hoc networks. With this purpose we first we devise a set of experiments where we compare the results obtained on a small testbed to those from the ns-2 simulation platform. A significant consistency in terms of overall trends is found, although remarkable differences can be appreciated in terms of both delay and throughput results. Afterward we proceed with a full deployment of IEEE 802.11e enabled stations throughout the floor of an university building, performing several experiments using both static and dynamic routing. Experimental results show that QoS can be reasonably sustained for both voice and video traffic in multi-hop ad hoc networks, although dynamic routing protocols can hinder performance by provoking frequent on-off connectivity problems.     

Per-packet rate adaptation for wireless video

Streaming video over error-prone wireless channels is a challenge as the dynamic network conditions and slow adaptation to channel degradations may affect the quality of the streamed video. Unequal error protection (UEP) can potentially address this issue by considering the importance of each video packet and its impact on the quality of reconstructed video. This paper proposes a cross-layer UEP solution for wireless video streaming over IEEE 802.11 networks. Video packets are prioritized based on the relative importance of the video packet. UEP is achieved by adapting the link layer parameters on a per-packet basis, using inherent forward error correction and adaptive modulation capabilities of the 802.11n network. Experimental results revealed that the proposed solution achieves comparable performance to the state-of-the-art methods at a lower complexity.