Analysis of handoff algorithms in CDMA cellular system

Abstract

The code-division multiple-access (CDMA) scheme has been considered as one possible choice of the future standards for cellular networks because of its various advantages. Since there can be only one carrier frequency being used in CDMA systems, a handoff scheme with diversity, a so-called handoff, was proposed for higher communication quality and capacity. Unlike the reverse link, soft handoff on the forward link requires additional resources such as CDMA codes and transmit power and also causes additional interference. If handoff requests can be processed and completed instantaneously, transmission from the base station with the best link to the user would achieve a significant fraction of the macrodiversity gain without utilizing additional resources. However, in practical systems, there is a nonzero handoff completion delay and soft handoff provides the required robustness to delays. We present a model for analyzing the performance of handoff algorithms based on signal strength measurements made by mobile stations in a lognormal fading environment. This model enables us to evaluate the effect of averaging and hysteresis on the handoff process and to study their sensitivity to the delay in the execution of the handoff. Outage probability and the total average power required are used as performance metrics.