Diversity effects on the soft handover gain in UMTS networks

In cellular wideband code division multiple access (WCDMA) networks, interference on the uplink is the limiting factor for the number of users that can be served in a single cell. Thus, interference reduction mechanisms are of significant importance. Soft handover, which is primarily a mechanism for seamless handovers (make before break), also reduces the interference within the cells by exploiting multiple simultaneous connections to lower the transmit power of the mobile stations. We present an analytical model for soft handover where multiple connections between a mobile station and the base stations within reach are taken into account. An approximation of the frame error rate based on the received signal strength in the uplink is provided for 12.2 kbps service. In addition the approach taken to calculate the soft handover gain is described and results are presented.