Hybrid-dynamic-system-based modeling and controlling of CDMA soft handoff

Soft handoff is one of the unique and key technologies in 3G CDMA mobile communications systems. It plays an important role in controlling and optimizing of radio resources in CDMA systems. Control of CDMA soft handoff process can be viewed as control of a hybrid dynamic system. The CDMA soft handoff process is modeled using hybrid switching optimal control system (HSOCS) in three layers, i.e., the continuous controlled plant layer, the discrete event system layer, and the interface layer. The CDMA soft handoff decision is formulated as controlling of the switching within the discrete-event systems to optimize the object functions of three performance criteria, i.e., the number of soft handoffs, the size of the active set, and the number of link degradations. Optimal decisions on the soft handoff process can be obtained through dynamic programming. To achieve tradeoff between efficiency and performance for handoff decisions, a suboptimal soft handoff algorithm is proposed. This algorithm considers the traffic loads in candidate cells, treats handoff bang-bang, and is easy to be implemented in practice. Simulations are conducted to evaluate performance of the suboptimal algorithm. The simulation results show the effectiveness of this algorithm.