无线Ad Hoc网络QoS路由协议研究的进展与展望

无线ad hoc网络是一种无固定通信设备支持、节点可自由移动的多跳全分布式无线网络。无线ad hoc网络的应用环境以及与Internet的互连要求它必须提供一定的服务质量(QoS)保证，而QoS路由协议是无线ad hoc网络支持QoS的一个关键理论和技术，也是目前的一个研究热点。本文回顾了近年来国内外在无线ad hoc网络QoS路由协议研究方面取得的研究成果，对已有的无线ad hoc网络的QoS路由协议进行了分类．并对它们作了较全面的概括。总结和深入的比较分析，系统阐述了在无线ad hoc网络中实现QoS路由协议时需要考虑的因素，指出了亟待解决的问题和今后的研究方向。     

基于IEEE802.11e EDCA的接纳控制方案

随着无线局域网的快速发展,人们对服务质量提出了迫切的要求,IEEE 802．11e协议应运而生,为QoS的实施提供了参考标准。EDCA是802．11e中实现QoS的分布式机制,本文基于EDCA,提出了一整套接纳控制方案和EDCA参数调节机制。本方案QoS参数考虑全面,实现简单,而且能够运用在全分布的ad hoc网络中。     

手机家族新成员——WLAN手机

Above Cable公司最近宣布推出了基于802．11标准的终端PVA(Personal Video／Voice Assistant)设备，工作在2．4GHz-2．497GHz频段，支持802．11b和802．11g无线标准，这就是手机家族的新成员——WLAN手机。它与现有的PDA、Smart Phone、GSM、CDMA手机家族的所有成员以及小灵通不同，这种第一代PVA是借助无线局域网和Internet实现语音传输的智能通信终端设备。     

一种面向无线Ad Hoc网络的新型分布式哈希表

为了在无线ad hoc网络上构建各种应用系统，有必要提供一种高效的数据共享机制，使得网络中各节点之间能够方便地进行协同和交互。该文将分布式哈希表(DHT)的基本思想与无线ad hoc网络中的基于地理位置的路由技术结合起来，提出了一种新型的面向无线ad hoc网络的数据共享方案——基于位置的DHT(LDHT)。与传统的DHT方案相比，LDHT不是通过逻辑上的覆盖网络来实现，而是直接基于网络的物理拓扑结构来构建，有效地消除了传统DHT方案的拓扑结构不匹配问题，提高了在无线ad hoc网络中进行数据共享的效率。     

带宽：WLAN的温饱

从802．11b、802．11b+、802．11a到802．11g，从迅驰、SmartDisplay判无线投影机，在几乎所有使用WLAN的设备的测试中，习惯了有线网络的《微电脑世界》的评测工程师总是会对WLAN的传输速率蹙眉，与有线网络的小康水平相比，WLAN在带宽方面还处于刚刚温饱的状态。     

无线Ad Hoc网络支持QoS的研究进展与展望

无线ad hoc网络的应用环境以及与Internet的互连要求它必须提供一定的服务质量(QoS)保证,然而,无线信道固有的特点及节点移动造成网络拓扑的频繁变化,使得在无线ad hoc网络中支持QoS面临许多新的挑战.从无线ad hoc网络的QoS体系结构、QoS路由、QoS信令、支持业务区分和资源预留的介质访问控制协议这4个方面出发,对近年来国内外在该方向取得的研究成果作了全面的概括总结和比较分析,系统阐述了在无线ad hoc网络中支持QoS的问题,指出了亟待解决的问题和今后的研究方向.     

无线Ad Hoc网络及其安全研究

无线ad hoc网络是一种新型的无线移动网络。介绍了ad hoc网络的体系结构和主要特点,归纳了ad hoc网络的安全目标,提出了解决其安全问题的安全策略。最后,展望了无线ad hoc网络的研究方向。     

蓝牙网络封装协议的应用及其测试

蓝牙SIG定义了蓝牙网络封装协议BNEP，该协议对上层口协议提供了类似于以太网的接口。对于IEEE802．3／Ethemet封装支持的网络协议，蓝牙网络封装均支持。BNEP协议把这些网络协议包封装起来，直接通过蓝牙I2CAP协议进行无线传输。蓝牙网络封装主要应用在蓝牙个人无线局域网(PAN)中，PAN应用是指由两个或者更多的设备形成一个特定网络，而且这些设备能通过一个网络接入点来访问远程网络。由于蓝牙SIG只是用自然语言定义了协议规范，不同的实现者由于理解的差异可能会导致不同的结果，这可能会影响到产品的互通性，因此对协议的测试是至关重要的。BNEP协议的测试是蓝牙一致性测试，这种测试是完全自动化的。     

风起无线电子商务

目前流行的无线局域网解决方案主要基于IEEE 802.11b和IEEE802.11a。新的IEEE 802.11g标准备受瞩目。它在速度和安全等各方面都比以前的标准有所提高．例如．无线局域网用户的连接速度高达54Mbps，连接距离长达100m．几乎相当于现行802．11b无线产品的5倍。802．11g可以保证和802.11b的兼容性，同时对障碍物的穿透能力也较强。由于802.11g产品和前期产品相兼容，因此其客户机都能够配置在相同的网络内。这样既保护了用户的网络投资．又允许用户根据预算和时间来升级或扩展网络。     

移动自组织网QoS路由协议研究

该文首先分析了无线ad hoc网络的QoS体系结构、QoS信令,接着对常见的QoS路由作了简单的概括。最后对ad hoc网络的AODV协议和基于AODV的、支持Qos的Q_AODV协议做了分析和比较,仿真实验表明Q_AODV在某些性能上优于AODV。     

A scalable multimedia QoS architecture for ad hoc networks

Communication demands have grown from separate data and voice to integrated multimedia, paving the way to converging fixed, mobile and IP networks. Supporting Multimedia is a challenging task for wireless ad hoc network designers. Multimedia forms high data rate traffic with stringent Quality of Service (QoS) requirements. Wireless ad hoc networks are characterized by frequent topology changes, unreliable wireless channel, network congestion and resource contention. Providing scalable QoS is the most important challenge for multimedia delivery over ad hoc networks. We introduce here a provisioning and routing architecture for ad hoc networks which scales well while provisioning QoS. The proposed architecture is analysed using a mix of HTTP, voice and video streaming applications over 54 Mbps 802.11 g-based ad hoc networks. The architecture is simulated and compared to well-known routing protocols using the OPNET Modeller. The results show that our architecture scales well with increase in the network size, and outperforms well-known routing protocols.     

基于移动Ad hoc网络的混合式视频传输方案

混合式视频传输方案结合了基于C／S结构的流模式和基于P2P结构的下载模式,并以接收端驱动的协调控制算法来协调上述两种模式的运行及转换。将该方案应用于移动Ad hoc网络,形成了一种基于移动Ad hoc网络的混合式视频传输方案,从而提高了无线网络上的视频传输效率和质量。     

Transmission of layered video streaming via multi-path on ad hoc networks

Mobile ad hoc networks without centralized infrastructure change their topology rapidly because of node mobility, making multimedia applications difficult to run across wireless networks. Moreover, video transmission over ad hoc networks causes frequent transmission loss of video packets owing to end-to-end transmission with a number of wireless links, and requires essential bandwidth and restricted delay to provide quality-guaranteed display. This paper presents an architecture supporting transmission of multiple video streams in ad hoc networks by establishing multiple routing paths to provide extra video coding and transport schemes. This study also proposes an on-demand multicast routing protocol to transport layered video streams. The multicast routing protocol transmits layered video streaming based on a weight criterion, which is derived according to the number of receivers, delay and expiration time of a route. A simulation is performed herein to indicate the viability and performance of the proposed approach. The simulation results demonstrate that the proposed transport scheme is more effective than other video transport schemes with single or multiple paths.

IEEE 802.11e中基于失真度度量的视频包传输方法

为改善H. 264编码的视频流在802. 11e中的传输性能, 提出了一种结合H. 264/AVC中不同类型的数据分割对视频重建质量的重要性因子和队列状态的视频包映射方法。首先定量分析H. 264/AVC中A、B、C三种分割的丢失对视频重建质量的影响, 得到其重要因子; 然后依据重要因子和队列长度将视频数据包映射到802. 11e的不同EDCA队列中。算法改进了EDCA机制中数据包的静态映射机制, 根据视频分割数据的不等重要性, 提供差异性服务。仿真结果表明, 与目前的视频包静态映射机制相比, 该算法提高了视频重建质量, 最好可提高1 dB以上。     

A fuzzy control scheme for video transmission in Bluetooth wireless

This paper is concerned with transmission of Moving Picture Expert Group (MPEG) video over a Bluetooth wireless network using a fuzzy approach. MPEG Variable Bit Rate (VBR) video sources suffer from long delay and excessive loss due to the sudden bursts in bit rate. Constant Bit Rate (CBR) encoding scheme may work well for a network with a guaranteed bandwidth. However, a Bluetooth channel is subject to wireless interference and can never guarantee a constant bandwidth. Subsequently, it is impossible to transmit a CBR video over Bluetooth wireless without data loss or image quality degradation. To resolve this problem, a fuzzy control system is introduced at the Host Controller Interface (HCI). The system consists of a traffic-shaping buffer whose role is to prevent excessive back-to-back cells being generated during the peak transmissions of MPEG video sources. The output bit rate of the traffic-shaping buffer is controlled by a fuzzy controller to ensure that the video stream from the host conforms to the traffic condition of the Bluetooth channel. Another fuzzy controller regulates the average arrival bit rate to the traffic-shaper to guarantee that the buffer is neither full nor empty. Computer simulation results demonstrate that the use of the fuzzy controllers reduces excessive data loss at the HCI as compared with an open loop VBR/CBR video transmission in Bluetooth.     

Enhancing wireless video streaming using lightweight approximate authentication

In this paper, we propose a novel lightweight approximate authentication algorithm that provides efficient protection for wireless video streaming where attacks on the stream are possible, but classical integrity protection algorithms are impractical because bit errors occur naturally. The benefits of the proposed algorithm over other algorithms are fast execution and small message authentication code size. Moreover, the approximate authentication supports error resilient video decoding by dropping seriously damaged packets, thus improving the perceived quality of the video stream. The performance of the algorithm is demonstrated via numerical analysis, simulations and measurements over modeled and real wireless channels.     

CStream: neighborhood bandwidth aggregation for better video streaming

Despite the popularity of watching videos online, challenges still remain in video streaming in many scenarios. Limited home broadband and mobile phone 3G bandwidths mean many users stream videos at compromised quality. To provide additional bandwidth for streaming, we propose CStream, a system that aggregates bandwidth from multiple cooperating users in a neighborhood environment for better video streaming. CStream exploits the fact that wireless devices have multiple network interfaces and connects cooperating users with a wireless ad-hoc network to aggregate their unused downlink Internet bandwidth. CStream dynamically generates a streaming plan to stream a single video using multiple connections, continuously adapting to changes in the neighborhood and variations in the available bandwidth. CStream is developed and evaluated on a test bed of computers, allowing for a detailed, controlled evaluation of performance. Analysis of the results shows a linear increase in throughput over single-connection streaming and improved video quality as the number of cooperating users in a neighborhood increase.     

An adaptive control for video transmission over bluetooth

This paper is concerned with transmission of a moving picture expert group (MPEG) video stream over a Bluetooth channel, using an adaptive neuro-fuzzy technique. MPEG variable bit rate (VBR) video sources over a network generally experience long delay and unacceptable data loss, due to high variations in bit rate. Furthermore, transmission rate could be unpredictable in a Bluetooth network due to interferences by other wireless devices or general Bluetooth channel noises. Subsequently, it is almost impossible to transmit VBR data sources over Bluetooth without excessive delay or data loss. In this work, an adaptive scheme is introduced so that the controller may adjust itself to the current state of the system under control. This paper utilizes a traffic-shaping buffer to prevent excessive back-to-back transmissions of MPEG VBR data sources. A novel adaptive neuro-fuzzy scheme regulates the output rate of the buffer to ensure that the video stream from the host conforms to the traffic conditions of the Bluetooth channel during the transmission period. The computer simulation results show that the use of the neuro-fuzzy controller reduces excessive delay and data loss at the host-controller-interface, as compared with a conventional VBR video transmission and a rule-based fuzzy controller (RBF1) in Bluetooth.     

Wireless video sensor networks for sparse, resource-constrained, multi-robot teams

Small-size robots provide access and maneuverability in the tight confines of highly rubbled and uncertain environments such as those encountered in Urban Search and Rescue (USAR). Small size also provides easy portability and deployability and the potential for redundancy through multi-robot teaming. Unfortunately, small size does not diminish the data demands of these applications, such as high-resolution imagery and other forms of high bandwidth data. Furthermore, achieving redundancy in tight environments requires wireless operation to avoid the entanglement of tethers, but wireless communication links have proven unreliable in such environments. The net effect of this is a set of robust networking requirements that include high bandwidth, low latency, and low power with multi-hop routing in a sparse and highly volatile network configuration, which has been collectively difficult to achieve. Our metric for benchmarking these requirements is a stream of uncompressed 320 ×  240, 24-bit color images updated at 1 frame per second (roughly 1.8 Mbps - image compression is not the focus of this research as it only serves to increase the possible resolution or frame rate). No existing ad hoc wireless sensor network approaches have been able to achieve these requirements. Wi-Fi requires high power and size and does not have the latency, while Zig-bee does not have the bandwidth. Instead, this work focuses on augmenting the Bluetooth protocol, which is master/slave based, with a hybrid, multi-hop routing protocol. Bluetooth has the desired low power and high bandwidth characteristics, but lacks multi-hop routing and rapid recovery. In this paper, a hybrid routing protocol for ad hoc multi-robot networking is described that features: (1) high-bandwidth, (2) low power, and (3) low latency of data traffic for sparse, highly volatile networks—exactly what is required for large teams of highly distributed, small-scale robots. Furthermore, this paper compares simulations and robot implementations of different routing protocols over Bluetooth sensor networks and demonstrates the viability of our protocol as a wireless network solution for multi-robot teams characterized by high mobility in difficult RF environments. To the best of our knowledge, the work presented in this paper is the first attempt at comparison of different routing protocols for real robots with physical experiments over Bluetooth sensor networks.