Handoff schemes in CDMA cellular systems

Abstract

This paper presents a soft handoff technique, which is based upon previous handoff schemes on adaptive traffic load shedding and a scheme on channel assignment strategies using soft handoff area sizing. We refer to the algorithm as adaptive load shedding with soft handoff sizing (ALS-SHS). It takes advantage of the soft handoff and soft capacity features of CDMA to dynamically adjust the soft handoff area of the base station so as to maintain a specified signal-to-interference ratio in the cell. This scheme is particularly useful in cases where hot-spot cells develop: these are heavily loaded cells surrounded by lightly loaded cells. Hot-spot cells occur in situations such as traffic accidents on a highway. The active mobiles in the cell may outnumber the capacity and an excessive increase in CDMA noise may, in the worst case, block all calls in the cell. Dynamic adjustment of the soft handoff area allows the reduction of traffic in the cell by altering the cell's soft handoff area so that users are accommodated based upon the SIR value within the cell.