| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 93 === It is expected that various kinds of services, e.g., voice, video, multimedia data, etc., will be provided in the next generation of mobile/wireless communication systems. For multimedia traffic to be supported successfully over wireless links, it is necessary to provide quality of service (QoS) guarantees between the end-systems in wireless networks. We propose a call admission control with restriction and degradation (CAC-RD) for wireless networks which uses adaptive bandwidth allocation to provide users multi-level QoS. We derive the associated analytical model and the expressions for new call blocking probability, handoff failure probability, and average bandwidth. Due to mathematical complexity, degradation ratio and upgrade/degrade frequency are found via computer simulation. The simulation program is written in C language not only to verify the accuracy the analytical results but also to understand and control the details of various CAC schemes. It is shown that the analytical results are in reasonable agreement with simulation results, especially when the offered load is light. For comparison purposes, the model for CAC with restriction but no degradation (CAC-R) is also shown. It is shown that, with service degradation (CAC-RD), the new call blocking probability and handoff failure probability are smaller than those without service degradation (CAC-R). The effects of restriction threshold, traffic mix and call holding time on performance measures are also studied. It is concluded that CAC for wireless networks should take into account the offered load, traffic mix, and the call holding time in order to satisfy all required QoS requirements.
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