We are concerned with a CDMA cellular system with unbalanced traffic environment such that a cell with high traffic should be assigned a frequency additional to the common one shared with its neighboring cells. To remove quality-dropping inter-cell hard handoffs, the cell with high traffic was first partitioned into three regions. Then, the common frequency is assigned in the outermost region, and the additional frequency is operated in the innermost region, whereas both the common frequency and the additional frequency are operated in the middle region. This frequency assignment strategy is shown not only to remove inter-cell hard handoffs without requiring extra hardware, but also to reduce intra-cell hard handoffs.

For a CDMA system with a single carrier, we consider a call control policy at each cell, which gives priority to handoff calls over new calls while meeting the overall call quality. New calls are first under the call control of the threshold type, and then receive services together with the handoff calls but under the outage restriction guaranteeing a pre-specified call quality. An optimization model with such quality-guaranteeing constraints is formulated, which is to determine the threshold value for each cell, minimizing the new call blocking probability. We propose a solution heuristic, with which a number of simulations are conducted under a variety of traffic environments. The computational experiments evaluate the usefulness of our call control scheme in that handoff calls are given an appropriate level of priority while the system capacity is effectively utilized.