Outage probability analysis of downlink power allocation mechanisms in CDMA systems during soft handoff

Abstract

This paper presents an analytical approach to evaluate the downlink outage probability for a handoff user in code division multiple access (CDMA) systems under the log-normally shadowed and Rician fading channel subject to co-channel interference. Since soft handoff performance is related to the power allocation algorithms, we consider various downlink power allocation schemes, including the site selection diversity transmission (SSDT), the link proportional power allocation (LPPA), the equal power allocation (EPA), and the quality balancing power allocation (QBPA). From our analytical model, it is shown that SSDT is most sensitive to fast fading and co-channel interference. By contrast, LPPA can achieve better outage in the presence of fast fading at the cost of slightly sacrificing power efficiency. The proposed analytical framework can be applied to evaluate the effects of handoff thresholds, orthogonality factors of channelization codes, and Rician factors on the outage performance of soft handoff users subject to co-channel interference from other cells.