| Summary: | 碩士 === 國立中央大學 === 資訊工程研究所 === 89 === GPRS (General Packet Radio Service) based on packet-switched transmission over the air interface can provide a ubiquitous data access service to mobile users and offer more efficient resource utilization. For further multimedia services, the proper Quality of Service functions must be implemented and well addressed. Specifically, for supporting real-time applications over GPRS system, the scheme to fit in with end-to-end delay, loss rate and bandwidth requirement plays an important role. Besides, in order to support typical data service, reducing data access delay is another key issue.
In this thesis, we devote to decreasing the transmission delay time and real-time loss rate on air interface for supporting real-time and data applications simultaneously. Also, for supplying enough bandwidth to real-time service, real-time application will be given higher priority for channel resources. Since current backbone bandwidth ability is much more powerful than air interface in the deployed cellular system and the delay time on air interface is the main reason of the End-to-End delay, so we assume the backbone delay as a constant value and research on air interface delay. We design a new scheduling method AI-EDF (Air Interface Earliest Deadline First) aimed at GPRS access requests on Base station subsystem (BSS) to decrease delay cost and to increase system capacity owing to supporting higher system load under the same delay requirement.
Since GPRS MAC access control mechanism is slotted-aloha, a real-time access request may collide with other access requests. In order to reduce collision and avoid packet loss, we adopt a real-time buffer control mechanism (RTBC) to avoid collision. Further, an optimal interval time to send out a real-time access request on air interface is analyzed.
In order to verify our algorithm performance, we adopt OPNET as our simulation tool. In our simulation environment, four kinds of real traffic type and their combinations including email, fleet management, WWW, and VoIP application are studied. Results show that our improvement can offer more capacity and reduce end-to-end delay compared to the other alternatives.
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