Prioritized handoff strategies using channel borrowing-based dynamic channel assignment

Since call termination as a result of handoff failure is considerably less desirable from the user's viewpoint than the blocking of a new call, a prioritized handoff scheme is essential. Especially for microcellular systems where the mobile cell boundary crossing rate is high. Therefore an efficient DCA should give priority to handoff calls. Two DCA strategies for prioritized handoff are proposed based on a DCA called BDCL (borrowing with directional channel locking): (i) FCA with BDCL for handoff calls, and (ii) BDCL with channel reservation. FCA with BDCL for handoff calls allows a handoff call to borrow a channel using BDCL strategy if no free nominal channel in the call arrival cell is available. In BDCL with channel reservation, both the new call and handoff call can use a borrowed channel. But a fixed number of nominal channels in a cell are reserved for exclusive use of handoff calls. To study the performance of the two proposed strategies, a widely accepted mobility model is adopted. Based on this model, we derive the handoff call arrival rates and channel holding time from the given mean mobile speed. The performance of the two proposed algorithms is studied by simulations and we found that they are very effective in reducing the handoff call blocking probability while not affecting the new call performance.