Analysis of soft handoff algorithms with dynamic spreading WCDMA system

The undergoing 3G wireless network needs to support integration of voice and multimedia data services with varying QoS requirements. It is critical that the least BER for voice traffic, WWW traffic, and streaming video traffic be guaranteed at all time. With the capability of dynamically changing spreading factor, CDMA system could provide a range of QoS fitting the needs for different traffic type. In this paper, we extend our dynamic spreading admission control scheme to a multi-cell situation, by proposing a dynamic spreading enable soft handoff framework. The static system behavior is analyzed through the studying of the updating probability for both handoff mobile and target cell. Our analysis shows that the updating probability varies according the traffic of interest. A general expression of the joint updating probability is given assuming an equal distribution of traffic type. The processing time of the handoff request is analyzed. We found that the update process caused by handoff is the major component of delay. Further investigation shows that the update associated with handoff might consume too much access channel time, and increase the delay of handoff, especially when handoff traffic is heavy. We therefore adopt a batch mechanism such that multiple handoff requests could be processed simultaneously. The average delay is reduced from 1.12 seconds to 800 ms in heavy handoff rate.