Research On Power Allocation Strategies For The Downlink In A WCDMA System And Its Performance Analysis

This paper intends to give a detailed analysis of an optimal power allocationstrategy on the downlink of a WCDMA mobile communication system, and with theaim of assessing the network capacity. It is known that the downlink capacity for abase station is limited by the maximum transmit power, which is a common resourceto be shared by all users; if one user requires a large fraction of the allowed transmitpower, the overall capacity could be decreased. In the work herein we analyze theimpact on the capacity of a power allocation strategy which limits the maximumfraction of transmit power per link and give the universal calculating formulation forassessing the network capacity.A simple semi-analytical model for UMTS system has been presented,considering a classical propagation model and taking soft and softer handover and amulti-service that means voice and LCD data services scenario into account. Thefinal simulating results show the cell capacity as a function of some significantparameters, such as the cell radius and the maximum number of users that can beserved. Depending on the analysis the equation expression which shows the relationof the cell radius and the maximum number of users can be obtained and the optimalnumber of base stations that should be connected to the users in handover zone hasbeen roughly evaluated. Finally, the impact on the system performances of a powerlimitation on each single link has been studied and a comparison between theomni-directional and the sectorised case. All this work would lead to a betterunderstanding of the downlink performance and the capacity of the cell in theWCDMA system.Meanwhile the power control which is both one of the key strategy of the radioresource management and the key technology of the CDMA system is roughlyintroduced, taking both the algorithm of distributed power control on uplink and thedesigning procedure of the closed-loop power control on down link as examples.