Research On Key Technologies Of Cross-layer Optimization For QoS Support In Wireless Multimedia Mesh Networks

In recent years, with the development of Wireless Multimedia Mesh Networks (WMMNs), the requirement for the Quality of Service (QoS) in WMMNs is high. Hence, exploring the cross-layer design techniques (across Physical, MAC, and Network layers) to enhance the wireless resource utilization, as well as satisfy the QoS requirement of multimedia services becomes imperative. As a result, the significance of the research of the QoS guarantee techniques is not only in the fundamental theories, but also in the future applications.With such a background, this dissertation has studied key cross-layer design and rate control technologies for the QoS in WMMNs. The main contents of this dissertation are organized as follows.(1) We introduce the developments, characteristics and application scenarios of WMMNs. Furthermore, we systematically classify the QoS guarantee techniques in the three layers (i.e. physical layer, MAC layer and routing layer), and the cross-layer design techniques. Additionally, we review their research developments in detail, and analyze their research difficulties as well as future research directions.(2) A model-based channel capacity prediction scheme is proposed to provide statistical quality-of-service (QoS) guarantees under a high traffic load for wireless multimedia networks. The proposed scheme perceives the state of wireless link through the retransmission of MAC layer, and calculates the statistical channel capacity especially the capacity with the saturated traffic load.(3) We further design a QoS resource reservation and cross-layer routing optimization using the capacity-aware model. Based on the cross-layer design approach, the scheme allocates network resource and forwards data packet under the consideration of the interference among flows and the link state. The simulation results show that the proposed scheme achieves more accurate capacity prediction and higher resource utilization than previous QoS routing schemes, and improves the network performance.(4) We investigate the retransmission control issues in WMNs and propose an aware-based adaptive optimization retransmission control scheme to improve the packet relay probability. The proposed scheme discriminates the types of packet loss in wireless link by means of the environment information and selects the optimal retransmission count with the IEEE 802.11 wireless channel characteristics. Furthermore, the maximum retransmission count in the MAC layer is adjusted adaptively. Extensive simulations demonstrate that the proposed scheme significantly reduces the packet collision probability, the packet loss rate, and improves the network throughput.(5) In the network layer, based on an adaptive retransmission strategy of the MAC layer and statistics of path state, a heuristic environment-aware QoS dynamic routing optimization algorithm HEAOR (Heuristic Environment-Aware Optimal Routing) for IEEE 802.11 wireless Mesh networks is proposed. Using a gray correlation analysis method and the dynamic information from the bottom layers links, the proposed heuristic scheme can adaptively select an optimal path to improve the routing efficiency and reduce the probability of packet loss without increasing the routing computational complexity. NS2 simulation results show that the proposed optimal routing selection scheme can reduce the rerouting frequency and the link failure probability. It is also effective in improving throughput and reducing end-to-end delay. The proposed scheme enables us to find an optimal MAC layer retransmission scheme, and select an optimal path over error-prone wireless links.(6) A packet loss discrimination based wireless multimedia transmission control (WMTCPLD) method over wireless-wired networks is proposed. Utilizing the wireless channel model and a special packet sending scheme with different packet sizes, theoretical analysis and detailed implementation of WMTCPLD shows that this method can detect the network status and differentiate packet loss types (wireless or congestion losses). Further, based on adaption to the network status and discrimination of packet loss types, this method achieves the wireless stream media transmission control. Simulation results illustrate that the proposed method outperforms previous algorithms in the aspects of increasing packet delivery ratio and congestion packet loss control.