Impact of orthogonality factor on UMTS capacity simulation

Radio network planning for the Universal Mobile Telecommunication System (UMTS) is generally based on simulations, because it is convenient to represent various combinations of input parameters graphically. The accuracy and reliability of the simulated results, however, depend on the accuracy of the inputs (eg. the traffic conditions, the terrain details etc.) and on the modelling assumptions. Sometimes due to lack of information on input conditions or in order to avoid complexity of incorporating too much details, simplified assumptions have to be made during system level simulations. A common practice during radio network planning using planning tools is to assume an average and constant Orthogonality Factor (OF) over the entire network area, even though in a real world scenario mobile users will have different OFs depending on their location, speed and the channel conditions. This modelling assumption produces network capacity estimate which is not accurate. In this paper we have analysed network capacity using clutter dependent OF distribution in a Wideband Code Division Multiple Access (WCDMA) system. The differences in the capacity results indicate the sensitivity of UMTS system performance on the downlink OFs.