Evaluatfon of soft handover algorithms for UMTS

Soft handover (HO) is becoming quite important because of its suitability for CDMA based systems. Soft handover promises better performance than hard handover. The two most well-known benefits are fade margin improvement and higher uplink capacity, while the disadvantages include lower downlink capacity and more complex implementation. Proper design of handover is one of the main challenges in mobile communications, since it has a great impact on the system performance and capacity. Whereas in hard handover a definite decision is made on whether to handover or not, in soft handover a conditional decision is made based on the variety of parameters involving several base stations. This makes the soft handover design and parameter optimisation even more complex. Several initiation algorithms have been used and proposed in IS-95 and CDMA2000 respectively and their performances have been evaluated in literature. However, their performance have not been compared under similar conditions in terms of propagation, environment and mobility behaviour. In our study, four different soft handover algorithms have been considered, their performance have been evaluated in the same operating environments and conditions and the corresponding results are reported.