Performance analysis of link proportional power allocation for downlink soft handoff in CDMA systems

This paper investigates the performance of current downlink power allocation mechanisms for soft handoff in CDMA systems, including the equal power allocation (EPA), quality balancing power allocation (QBPA), site selection diversity transmission (SSDT), and link proportional power allocation (LPPA). We evaluate the outage performance of these power allocation schemes from the perspectives of base station transmission power limit and power control error. Traditionally, the SSDT scheme has been viewed as the optimal solution for downlink handoff from the standpoint of power efficiency. The SSDT scheme selects the best base station from the active set to transmit downlink signals to the user. However, we find that SSDT is very sensitive to power control error as the user is at the cell boundary. Thus, with consideration of both base station power shortage and transmission control errors, LPPA exhibits the lowest outage probability when the system load is not heavy, while SSDT is the best choice only in the case of heavy traffic load.