无线多媒体网络中端到端自适应QoS保证

Guaranteeing End-to-End Adaptive QoS in Wireless Multimedia Networks

无线网络中较高的信道误码率和不稳定的可用带宽等因素给多媒体传输服务质量 (QoS)保证带来了新的挑战 .该文提出了一种基于二级反馈的两层自适应QoS保证方法 ,即应用层QoS和传输层QoS ,提出了将应用层的最小流速率λmin和最大帧错误率Emax两个QoS参数映射到传输层的最大端到端帧延迟Dmax的计算公式 .在应用层提出了自适应节的系统资源的分配公式、自适应QoS调节算法A和算法B .在传输层提出了保证端到端帧延迟Dmax的包长计算公式 ,给出了自适应包长调节算法 .

In a wireless environment, due to characteristics of media (interference in radio signals) the bandwidth of a link is unpredictable and possibly very low, and the error rates are variable and extremely high. The guarantee of QoS in such an environment is a very challenging problem. In this paper we propose an adaptive QoS framework which is based on two layers of feedback, application QoS and transmission QoS. The working process of QoS guarantee is discussed after formats of adaptive packet and feedback packet. A formula is presented for mapping the minimum rate of stream λmin and the maximum rate of error frames Emax in application layer to the maximum end-to-end frame delay Dmax. In application layer we also address the adaptive session, system resource allocation, and adaptive algorithm A and B. In transmission layer we discuss the best size of packet for minimum end-to-end frame delay and present adaptive algorithm for the size of packet. Finally, simulation experiments show that the sending rate drops rapidly by means of adaptive adjustment with algorithm A when the BER of channel grows gradually, but playing quality is improving jitterlessly, and the playing jitter is smooth by means of adaptive adjustment with algorithm B when the BER of channel changes suddenly.