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Förslaget inkom 2003-03-19

A Dynamic Rate Adaptation Scheme for Packet Data in WCDMA Systems with Adaptive Antennas

In third generation mobile communication systems e.g. WCDMA, adaptive antenna arrays at the base station is one of the techniques which can be used to help improve both uplink and downlink capacity (or coverage). Due to the expected growth in the number of subscribers using different services in the coming years, capacity limitations may appear in certain deployment scenario (e.g. in dense urban environments). Furthermore, macro cells in rural areas will benefit from the increased coverage of adaptive antenna systems.
The interaction of Radio Network Algorithms (e.g. admission control, congestion control, rate adaptation, etc.) with adaptive antenna (AA) is essential to guarantee an acceptable Quality of Service (QoS). In order to ensure that all users maintain their required performance, admission control is used to decide whether a new link should be setup or not. A conservative admission control may guarantee the desired quality but at the expense of capacity loss. On the other hand a lenient admission policy may lead to system degradation when channel conditions deteriorate over time. Congestion control is used to compensate any variation in traffic and radio conditions. In order to have an effective control on the system performance, it is advantageous to have an adaptive scheme which could combine both admission control and congestion control. Our aim is to have an adaptive scheme which could periodically update the user rate according to the radio conditions and traffic requirements.
Problem Definition
Adaptive antennas optimize the power utilization in the angular dimension (i.e. spatial separation). But it does not provide gain with respect to the sectorized case in the rectilinear dimension for example when a user moves in a straight line away from the base station. On the other hand rate adaptation (RA) based on power fairness can optimize the power usage in the latter dimension. The
combination of AA with RA is expected to fully exploit the radio resources.
The aim of the thesis is to study the impact of the rate adaptation scheme on system performance for adaptive antennas using fixed multi beams. The objective is to optimize the system capacity and at the same time fulfill the user minimum QoS requirement by benefiting from the angular and rectilinear dimensions. Performance evaluation of the proposed thesis will be carried out using system level simulations.


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