Analysis and results for the orthogonality factor in WCDMA downlinks

The presence of multipath leads to a loss of orthogonality between the signals transmitted simultaneously on a WCDMA downlink. We derive general analytical expressions for the orthogonality factor (OF), which quantifies this loss of orthogonality. We show that the orthogonality factor exhibits a significant temporal variation for the three channel profiles suggested in the WCDMA standard, namely, typical urban, rural area, and hilly terrain, which span a wide range of realistic cases. Moreover, its temporal variations and statistics vary significantly from one channel profile to another. Also, while the pulse shape and the number of RAKE fingers has only a marginal impact on the OF´s statistics, the granularity in setting the finger positions has a considerable impact. The results of the work can be directly used for evaluation of the system performance of WCDMA cellular systems.