【作者】 朱晓亮；

【导师】 杨宗凯；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2006， 博士

【摘要】 目前,诸多无线接入技术,特别是无线网状网(Wireless Mesh Network,WMN)的进展为无线流媒体业务的推广奠定了基础。WMN具有可靠性高、网络扩展性好等优势,但其通信环境以及多媒体应用的特点给流媒体传输速率控制带来了巨大的挑战。首先,流媒体传输速率控制必须适应链路带宽的高误码和时变等特征;其次,必须提供抗节点间干扰的能力;再者,必须改善现有机制应用于WMN面临的TCP友好性的降低和吞吐量的下降。本文针对上述问题,研究适于WMN的流媒体传输速率控制机制。本文的研究从四个方面展开:(1)基于流媒体传输需求的链路层速率控制的研究;(2)流媒体帧传输时延最小化速率控制模型的研究;(3)基于区分的TCP友好流媒体接入速率控制方程的研究;(4)多描述符编码(Multiple Descriptions Coding, MDC)流媒体多径传输速率控制模型的研究。这些工作得到国家自然科学基金项目“基于媒体传输特性的无线多媒体技术的研究”(No.60202005)和“基于Internet的交互式流媒体分发技术研究”(No.60302004)以及湖北省自然科学基金“基于质量时间二维属性的流媒体网络缓存研究”(No.2005ABA264)等项目的支持和资助。本文取得的研究成果包括如下几个方面:(1)基于干扰距离约束的链路层速率控制:引入干扰距离和发送速率的关系模型,提出基于干扰级别的抑制远程节点干扰的链路层优化速率选择算法和跨层的帧错误率保障方案以实现链路帧错误率和传输速率间的较好平衡。仿真试验证明该机制可有效降低WMN链路丢包率、速率调整也更平滑,大大改善了流媒体传输的性能。(2)基于帧时延最小化的可变包长速率控制:针对WMN链路层重传机制的不足,研究基于广义误码率和包重传概率的时延约束方程理论,给出满足帧传输时延最小化传输层包长调整理论模型与相关计算,提出基于时延约束的速率控制协议。仿真试验的结果验证了该方法可有效改善流媒体传输延时及抖动。(3)基于区分比例的TCP友好速率控制:综合WMN链路错误丢包以及拥塞丢包事件的统计特征,根据TCP流量调整规律,提出基于区分比例的TCP友好速率控制方程并建立实用的速率控制机制。仿真结果验证了该机制能够获得比现有机制更高的吞吐量和较平缓的发送速率,并具备较好的TCP友好特征。(4)基于MDC的协作式速率控制:考虑WMN的路径多样性特征,基于H.264的多描述编码技术,满足多描述符多径传输时延和用户缓冲区等约束,提出多描述符速率分配和补偿算法。仿真试验验证了该机制可有效降低传输丢包率,改善多描述符编码多径传输的服务质量。更多还原

【Abstract】 In recent years, the developments of wireless accessing techniques, especially those of Wireless Mesh Network (WMN), have paved the way to popularize wireless streaming media services. WMN owns some advantages, such as high reliability and good scalability. However, it also brings new challenges and pressures in rate contol scheme due to the features of WMN communication environment and streaming applications in the following issues: One of the key problems for rate control streaming over WMN is how to adapt to features of links including high transmission Bit Error Rate (BER) and timely variation. Another is to provide capability to resist interference among the nodes. In addition, it should improve TCP fairness and throughput performance when transmitting streaming over WMN.To solve the above problems, this thesis addresses on rate control for streaming media transmission over WMN. The content of this thesis includes four issues: (1) researching on rate control in link layer to satisfy streaming media transmission; (2) researching and modeling on rate control to minimize transmission delay for streaming media; (3) rate control equation TCP-friendly streaming media access based on packet differentiation; (4) modeling on multipath rate control for streaming media based on Multiple Descriptions Coding (MDC).The work in this thesis has been supported by the National Science Foundation of China“Investigation of Wireless Multimedia Techniques based on Multimedia Transmission Property”(No.60202005) and the National Science Foundation of China“Research on Interactive streaming delivery based on Internet”(No. 60302004), and also supported by the National Science Foundation of Hubei province“Research on network cache for streaming based on quality-time 2D attributes”(No. 2005ABA264). The contributions of this thesis include:(1) Research on link layer rate control base on interference range constraint: This thesis proposes a model to describe the relation between interference range and transmission rate. Based on this model, a rate control algorithm to resist interference from distance nodes based on adjusting interference level is presented with a cross layer policy to guarantee FER, which build a tradeoff between FER and transmission rate and provide best effort PER-guaranteeing service for streaming transport. Simulation results demonstrate that lower PLR, smoother sending rate and better performance can be achieved by our proposed mechanism when transmitting streaming in WMN.(2) Variable-Packet-size Rate control based on transmission delay minimum: In order to getting rid of the shortages of ARQ in link layer, this thesis proposes a delay-constrain theory based rate control scheme for streaming media transmission in WMN by researching on the policy of transport layer packet size adjustment according to delay-constrain equation by considering wireless Packet Retransmission Rate (PPR). The theoretical model and relevant detailed deduction are also presented. Simulation results demonstrate our proposed mechanism can effectively improve transmission delay and jitter performance of streaming media transmission over WMN.(3) TCP-friendly Rate control scheme base on ratio of loss differentiation: Considering statistic features of packet loss due to error and congestion events in WMN,this thesis proposes a TCP-friendly rate control equation for streaming media delivery based on ratio of loss differentiation. Besides, a practical rate control mechanism is constructed. Simulation results demonstrate that higher throughput, better fairness and smoother sending rate can be achieved by our proposed mechanism.(4) Research on cooperative rate control for MDC transmission over WMN: Considering feature of path diversity in WMN, this thesis proposes a MD rate allocation algorithm based on MDC adopting H.264 technique to satisfy MDC transmission delay constrains and prevent buffer overflow. Simulation results demonstrate that this mechanism can depress PLR and improve QoS performance of MDC transmission with MPT.更多还原