In this paper, a novel cross-layer optimization scheme for video streaming in wireless relay networks is proposed. It takes into account of delay constraints at the application (APP) layer, relay node selection at the MAC layer and dynamic fading of wireless channels at the physical (PHY) layer in an integrated mode to improve the quality of video transmission. At the PHY layer, a finite state Markov channels (FSMC) model is used to estimate the channel states and a modified RTS/CTS scheme is proposed to facilitate the path selection at the MAC layer. The impacts of delay constraints and other factors at the APP layer are investigated. At the MAC layer, the source node can choose the proper path to transmit video data while considering video delay requirements and wireless channel states simultaneously. A typical three-node uploading scenario in video surveillance applications is considered as an example for performance evaluation. The experimental results show that the proposed scheme could improve video transmission quality and achieve a near-optimal performance.

This paper introduces the design of telemedicine ECG monitoring system based on GPRS.This system combined holter monitoring technology and advanced wireless public communication network, which realizes user outside the hospital can be achieved by heart disease remote real-time monitoring function.This paper firstly introduced the structure design of this system, and then the electrocardio monitoring terminal, the communication circuit as well as the software and hardware of monitoring centers respectively. Clinical experiments showed that this system can realize remote real-time monitoring, and has important clinical significance.

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The COMPASS/Beidou Satellite Navigation System is no-blind zone for China and limited transmission capacity. It is critical for increasing the performance of disaster warning distribution by the COMPASS/Beidou system. By further analyzing the characteristics of transmission of COMPASS/Beidou, we find the method of solving that problem and also introduce some optimizations into the algorithm. The algorithm is based on application layer FEC to achieve the warning transmission probabilities. Simulation results show that the new scheme can efficiently be used disaster warning distribution system.

in this paper, we study the power control strategy in wireless ad hoc networks. First the paper analyses the energy saving principles of basic power control and PCM protocol. Then it further explains the implementation in GloMoSim. Finally, simulation results are provided to evaluate the performance of these power control strategies. The simulation results show that, to some extent, these power control mechanisms can achieve energy savings, however, these power control protocols can not consider the influence of the cumulative noise interference on nodes transmission successful probability in multi-hop wireless ad hoc networks, so that the effect of energy saving will be greatly affected when the nodes incurs the serious cumulative concurrent transmission interference. 【摘要】本文针对多跳无线 ad hoc 网络环境下的功率控制策略展开研究。首先分析了基本功率控制机制和 PCM 协议的 节能原理，然后详细说明了上述功率控制策略在 GloMoSim 仿真环境中的实现方法，最后结合仿真实验，对上述功率控 制策略的性能进行分析。仿真结果表明，基本功率控制机制和 PCM 协议能在一定程度上实现能量节省，但这两种功率控 制策略都没有考虑多跳无线 ad hoc 网络环境下累积噪声干扰对节点传输成功概率的影响，因而在累积并发噪声干扰较为 严重的情况下，上述功率控制策略的能量节省效果会受到很大的影响。 【关键词】Ad Hoc 网络；功率控制；实现；仿真分析； 1 引言 无线 ad hoc 网络(wireless ad hoc networks)是一种新 型的无线网络。 它由一系列地位完全平等的移动节点组成， 无需任何固定或预设的网络设施。网络中的每个节点既是 终端又是路由器，它们在信道访问控制(Medium Access Control，MAC)协议的控制下，以多跳共享的方式接入无 线信道。由于 ad hoc 网络中的移动节点一般依赖寿命非常 有限的电池供电，能量是非常宝贵的资源，因而在 MAC 协议的设计中应该考虑尽量节省节点的能耗，从而延长节 点的工作时间和网络的生存时间。 目前已有的 MAC 协议能量节省机制大致可以分为节 点休眠控制机制 [1], [2] 和节点功率控制机制 [3-5] 两大类。其 中，节点休眠控制机制允许节点在适当的时候切换到低功 耗的休眠状态，从而降低节点的能耗；而节点功率控制机 制要求在保证信号发送成功的前提下，尽可能的节省节点 的发射功耗。由于网络的频率空间复用度与节点的发送功 率大小直接相关，因而合理的功率控制机制不仅能有效的 节省节点的能耗，还能提高网络的频率空间复用度，从而 提高网络的平均吞吐量。本文研究的即为 MAC 协议中的 节点功率控制机制。 IEEE 802.11 DCF(Distributed Coordination Function) [6] 是无线局域网中的标准协议， 目前已被广泛应用于 ad hoc 网络的各种仿真和测试床，成为了事实上的 ad hoc 网络 MAC 协议规范。 该协议通过物理载波检测机制和虚拟载波 检测机制避免发送节点之间的冲突， 并采用 RTS-CTS 控制 帧握手机制部分的解决了隐终端问题 [7] 。但是，该协议却 没有引入节点功率控制机制来进一步提高网络的性能。目 前， 研究人员已经在 DCF 协议的框架内提出了几种功率控 制机制。 文 献 [3] 和 文 献 [4] 提 出 的 一 种 基 本 功 率 控 制 机 制 BASIC。该机制为以最大的发送功率发送 RTS 和 CTS 帧，