Study On Call Admission Control Technology In Broadband Wireless Metropolitan Area Network

With the development of technology and society, as well as the popularity of Internet, requirements of sounds,video and data are increasing. Wireless communication satisfy people's desires of accessing network wherever and whenever. As a competive technology of Broadband Wireless Metropolitan Area Network, IEEE802.16 provides a uniform worldwide standard for Broadband Wireless Access. IEEE802.16 MAC layer protocol defines comprehensive QoS guaranteeing mechanism, including complete signaling system, scheduling service types and bandwidth request/allocation, and so on.The research on wireless resource management algorithms for IEEE802.16 is of great significance.Call admission control is very important for QoS guaranteeing. Its main task is to determine whether allow a new service flow or not according certain policy. The entry of new one may decrease current online services'QoS performance. However, network has to absorb businesses as many as possible. Call admission control can be used to find the trade-off to ensure the Qos of existent services, meanwhile maintain the bandwidth utilization at a high level.Based on the introduction of IEEE802.16 system and call admission control technology, this thesis is specially about call admission control of Qos realization. The main contents are as follows:1. The QoS mechanism of MAC layer was analyed in detail. A proposal was posed in order to perfect the QoS realization architecture. The main functional modules of this architecture were defined. The operations of SS and BS were described when signaling or data were exchanging between them.2. Call admission control algorithm based on a threshold strategy was studied. In order to maintain conversation in handoff process and ensure higher QoS requests for real time services, this algorithm defined priorities among services. Five thresholds were set according to above-mentioned priorities. Different priority services were admitted under different bandwidth usage circumstances, which was controlled by these thresholds. A bandwidth borrowing mechanism was adopted by taking advantage of the adaptive bandwidth traits of ERTPS,RTPS and NRTPS in order to maximize the number of connections and bandwidth utilization.The simulation results showed that the method of setting thresholds guaranteed high-priority services better access ratio at the cost of low-priority services'access ratio.3. Considering the various rates of services in IEEE802.16 network, this thesis improved a weight-based dynamic call admission control algorithm. The product of average arrival rate and transfer rate in measurement unit time were used as weight to distribute bandwidth for different services. The simulation results showed that, comparing with the old method which used average arrival rate as weight to allocate bandwidth only, the improved method could reflect the bandwidth requirement of each service more exactly. In this way, it improved the blocking probability, dropping probability and bandwidth utilization of system.