Research On Cross-layer QoS Scheme For Realtime Services In Wireless Multihop Networks

Wireless multihop networks are good networking modes to improve the coverage of wireless network,and wireless sensor networks and wireless Ad hoc networks are two main types of wireless multihop networks.As multimedia nodes have shown up,supporting real-time and non-real-time services simultaneously has become the mainstream of operation mode of wireless multihop networks,and how to satisfy QoS requirements of a variety of services has become an important research subject.Cross-layer optimization method adopts cooperation and information sharing among different layers to adapt to the dynamic wireless environment,as well as regards the network as a whole to achieve the optimal network performance.This dissertation focuses on the design of cross-layer QoS schemes under wireless multimedia sensor networks and wireless Ad hoc networks using cross-layer optimization methods.Under wireless multimedia sensors networks,the problems of how to set scheduling priorities for different services and set weight values of optimization objects in each node are in research and a cross-layer QoS scheme is proposed.Considering the structure characteristics and application requirements of wireless multimedia sensor networks,the proposed scheme adjusts the weight values of performance optimization and energy control in the optimization to obtain a good tradeoff of QoS performances and network lifetime.In the proposed scheme,according to the characteristic of wireless sensor networks that network lifetime is determined by the maximum lifetime of nodes in the surrounding area of the sink node,two kinds of distance coefficients and normalization are applied to control the weight values of queues in the Lyapunov function.In addition,differentiated queueing services(DQS)and delay coefficients are used to endow different services with adaptive scheduling priorities in the scheme.The optimization problem is transformed into a joint flow control,routing,scheduling and power control problem.Two distributed algorithms of solving the power control problem that is a convex optimization problem are designed,as well as a distributed medium access control scheme is proposed to reduce the computational complexity.Simulation results show that,compared with existing schemes,the proposed QoS scheme can reach a good tradeoff of QoS performances and network lifetime.For the problem that existing QoS schemes with deterministic bound of end-toend delay in nodes suffer from unreasonable packet drop decision,a QoS scheme is proposed.With providing deterministic bound of waiting delay in nodes,this scheme can adjust transmission rates and drop packets according to the status of the average end-to-end delay of sessions.To improve the reasonability of transmission rate control and packet drop decision,and to reduce the amount of packets dropped unreasonably,a novel virtual queue that is updated according to the status of the average end-to-end delay of sessions is designed.Theoretical proof indicates that using this novel queue the proposed scheme can guarantee bounded worst case waiting delay of packets in nodes.Another virtual queue is also designed to strengthen constrains on the average end-to-end delay of sessions.Analysis indicates that the overhead caused by the virtual queue does not affect the normal operation of the scheme.In addition,a distributed joint routing and scheduling scheme with low computational complexity is designed.The characteristics of this scheme that the worst case queue backlogs are bounded and the throughput utility optimality characteristic of the scheme are also proved.Simulation results show that,compared with existing schemes,this QoS scheme can improve the QoS performances on throughput and the average end-to-end delay,and the theoretical proof results are verified by simulation results.Co-optimization of routing,scheduling and playout buffer in video transmission QoS scheme under wireless Ad hoc networks is studied and a cross-layer QoS scheme supporting H.264 protocol is proposed.The proposed scheme introduces the virtual queue of video frame buffer whose update method is designed according to H.264 decoding protocol.This scheme also schedules video frames at destination nodes according to the status of frame playout buffers to reduce video frame buffer underflows and increase video playout continuity.In addition,the proposed scheme schedules packets according to waiting delays of the head-of-line packets to provide deterministic end-to-end delay bound.As packet generation rates of I frame,P frame and B frame encoded using H.264 protocol are diverse,this scheme assigns different types of video frames with diverse priorities according to their data arrival rates to provide different kinds of video frames with different QoS guarantees.To balance the transmission capacities of all links of video sessions,a power control algorithm that can maintain all the SINR(signal to interference plus noise ratio)at receiving nodes of each link identical is proposed.Simulation results show that,compared with existing schemes,the proposed cross-layer scheme can improve QoS performances,playout continuity and playout qualities of videos in multihop networks.The main works and contributions of this dissertation include:(1)a cross-layer QoS scheme that can dynamically set scheduling priorities for different services and weight values of optimization objects is proposed for wireless multimedia sensor networks,and under this scheme a good tradeoff of QoS performances and network lifetime can be obtained.(2)A cross-layer QoS scheme with deterministic bound of waiting delay in nodes whose packet drop mechanism is improved is proposed for wireless Ad hoc networks.This new scheme can increase the QoS performances.(3)A cross-layer QoS scheme is proposed for H.264 video transmission in wireless Ad hoc networks.This joint routing,scheduling and playout buffer optimization scheme can improve playout qualities of videos at destination nodes.