Performance of site selection diversity transmission in WCDMA

Soft handoff is considered to be essential in direct sequence-code division multiple access (DS-CDMA) based mobile communication systems. However the interference resulting from the transmissions from multiple base sites in the forward link during the soft handoff constrains the multiple access capacity. Site selection diversity transmission (SSDT) technique is able to mitigate the interference caused by transmissions from the multiple base sites. The 3^rd Generation Partnership Project (3GPP) has specified this technique for the W-CDMA FDD component of UMTS. This paper describes the SSDT technique and presents capacity simulation results. It is shown that the capacity gain is dependent on the Doppler speed of mobile terminals and correlation of shadow fading between adjacent cells.