Wednesday, June 24, 2009

Wireless cellular network, packet scheduling, multi-user diversity effect, opportunity scheduling

It has been several decades since the existence of wireless cellular network, which has brought tremendous conveniences to the world society with the developments on top. At present, the traditional telecommunications market is gradually merging its business with data together. As a result, the next-generation wireless cellular networks are heading towards the direction of all-IP packet networks. In addition, the proportion that data division business holds within all business of cellular network will become more importantly, which then makes the packet scheduling mechanisms become more important. With an increasing demand for the end-to-end quality of service, and the contradictions of significant increase in data traffic with the limited resources of the wireless resources, such as video, file transfer, and other data services, all of which are challenging the scheduling mechanisms in the network environment. Furthermore, how to improve the wireless cellular network system throughput to meet the requirements of the user's Quality of Service (QoS), how to provide a fair service to all users, have become the major issues which need to be addressed in the packet scheduling mechanisms for wireless cellular network.

The packet scheduling mechanism for the wireless cellular network is based on cross-layer design concept, which will consider all layers to make scheduling decisions. For example, the physical layer, will have a multi-user diversity effect due to varying characteristics(无线衰落信道具有时变特性). Using (exploit) multi-user diversity effect (多用户分集效应) can effectively enhance the data throughput of the wireless cellular system. Scheduling such as the opportunity scheduling, is commonly used in the packet scheduling mechanism for the wireless cellular networks. This thesis mainly focus on the theoretical model of opportunity scheduling and its specific algorithms.

With Regards to the theoretical model of opportunity scheduling, the author has classified and summarized the various existing theoretical models, including the division-level model and flow-level models. In terms of opportunity scheduling performance indicators and the typical opportunity scheduling algorithm in the division-level model and flow-level model of performance evaluation, experiment has also been conducted to analyse the existing methods and results. Finally, the author gives an predicting analysis of the theoretical tools that can be used in future in this area.

Regarding the specific algorithms used in opportunity scheduling, existing algorithms were summarized and compared, including the scheduling algorithm which uses OFDM technology in the wireless cellular network. The author discovered that the traditional method usually pay more attention to improve system throughput, however fails to provide a fair and user-satisfactory QoS. A new algorithm, without the sacrificing of system throughput ,was presented, to ensure the relatively fairness between all users and each user's QoS demand are met.

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