Downlink soft handover performance for different cell selection schemes in WCDMA system

Soft handover is used in WCDMA system because it could provides smoother transitions and enhanced the communication quality. The handover procedure is actually a kind of cell selection process. In this paper, downlink soft handover performance for different cell selection schemes namely, distance based, E_c/I₀ based and combination of both parameters (distance and E_c/I₀) are evaluated. The link level study begins with the downlink interference analysis and power allocations for each downlink dedicated channels. Downlink soft handover gain is used in the system level simulation as a main parameter to evaluate the effects of cell selection schemes on the downlink soft handover performance. Simulation result has shown that the 2-way soft handover is able to reduce the required dedicated transmission power up to 3 dB. Besides that, the cell selection scheme based on distance and E_c/I₀ value gives better SHO gain (1.3 dB) to the system with SHO overhead equals to 30%. Simulation also has shown that the system can benefit from the soft handover process at 20% to 30% of the SHO overhead.