Delay sensitivity analysis of CDMA downlink handoff algorithms

We analyze the performance of different handoff algorithms for the forward link or downlink of a CDMA cellular system. 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 instantaneously, transmission from the base station with the best link to the user would achieve significant fraction of the macro-diversity gain without utilizing additional resources. However, in practical systems there is a non zero execution delay and soft-handoff provides the required robustness to delays although it comes at the expense of additional network resources. There is thus a tradeoff between the extent of soft handoff required and the handoff execution delay. We compare the performance of the hard and soft handoff schemes and study their sensitivity to the delay in actual execution. Onstage probability and the total average power required are used as performance metrics. We present an analytical framework to study this tradeoff. We also provide simulation results with field-data. The results provide insight on when soft handoff is required and help select the appropriate handoff thresholds.