Research On The Mechanisms Of Quality Of Service In Wireless Access Networks

With the rapid development of wireless access network in recent years, wireless access technology has become a hot research topic in the field of communications. Wireless access network is free from the traditional shackles of wiring and has advantages of the flexibility of network configuration, easy deployment and maintenance, allowing the access of mobile users, etc. It can currently provide bandwidth of up to100Mbps and furnish end users plenty of multimedia applications. Wireless access network technology has become a powerful tool for the information exchange. However, wireless access network has its shortcomings. Compared to wired channel, wireless channel still has less bandwidth and more bandwidth variations. Applications of high-bandwidth, high-quality services are restricted by network capacity. In the distributed access network, the Quality of Service (QoS) can not be guaranteed due to characteristics of distributed access mechanism. How to offer the services with QoS guarantees, especially for real-time services, is an important issue for the further deployment of wireless access network. Therefore, it is particularly necessary to study the QoS mechanisms and look for the optimization mechanisms and algorithms for real-time services.IEEE802.16/WiMAX network with centralized scheduling and802.11Mesh network with distributed scheduling have drawn more attention in recent years. This paper studies on the QoS guarantee mechanisms and algorithms of the two networks. The major works of this paper are as follows:1. We proposed a QoS enhancement mechanism for the IEEE802.16/WiMAX system based on the Cognitive Radio (CR) technology. On the one hand, the system capacity is increased through CR technology. On the other hand, the damages to the real-time services Jone by the appearance of the primary users have been reduced as much as possible by the resource reservation, fast switching, etc. In order to balance the forced temination probability of real-time services and network capacity, non-integer bandwidth reservation mechanism proposed takes adaptive adjustment to bandwidth reseveration according to the appearance probability of the primary users, arriving rates of service connections, etc. In addition, the system has the advantages of few modifications and low-cost deployment and is especially fit for the scenarios with burst traffic. The simulation results validate the theory models and show that proposed non-integer reservation mechanism has the highest utilization rate of bandwidth and optimal value of cost-function compared with Guard Channel (GC) and interger reservation mechanism.2. We proposed an analytical model of QoS performance for IEEE802.11Mesh network with Internet applications. Internet applications are expected to be one of the main applications for end users in wireless access network. Aimed at this application, the proposed model evaluates the throughput and end-to-end delay of the network based on the Hybrid Wireless Mesh Protocol (HWMP) defined in the latest draft IEEE802.11s standard. According to the different characteristics of inter-mesh services and intra-mesh services, the effects of the tree routing and on-demand routing on network performance are analyses respectively. Then we show the impact of HWMP on the performance of whole network. The analysis results of the model provides a useful reference for the researches of QoS-guarantee mechanisms, design and deployment of the802.11mesh network.3. We proposed a novel congestion control mechanism for802.11Mesh network based on HWMP. HWMP treats the nodes with different locations equally in the process of path selection, and the inter-mesh traffic is disturbed by intra-mesh traffic. Compared to intra-mesh delivery, the inter-mesh delivery usually has more hops and requires more guarantees about QoS. In order to improve the QoS performance of inter-mesh services, proposed mechanism makes an improvement on HWMP protocol. The new measurement of congestion is added in the process of routing, and nodes in the vicinity of the root node are avoided as much as possible to appear in the path of intra-mesh delivery according to the degree of the congestion. Consequently, the mechanism relieves the congestion of area near the root to a great extent and improves the QoS performance of inter-mesh service. Compared to original HWMP, the simulation results show that the throughput and delay of inter-mesh service have achieved notable improvement when congestion appears in the network, and the total network throughput is also increased.