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

Abstract

The growing demands of downlink traffic volume in mobile environments have posed a new challenge on wireless data networks. This paper investigates the performance of current downlink power allocation mechanisms for soft handoff in the code division multiple access (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 site selection diversity transmission (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 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.