Performance modeling of multitier PCS system

The emergence of multitier wireless access is being driven by the different compromises in technology required to provide wireless service in different environments. Three major tiers of wireless access are likely to emerge to providepersonal communications services (PCS): high-tier, low-tier, and unlicensed. Because of the service costs of the three tiers, the unlicensed system is given the highest priority to deliver the calls, and the high-tier system has the lowest priority to deliver the calls. To maintain this delivery priority, two multitier mobility management strategies have been proposed: the single registration strategy (SR) and the modified multiregistration strategy (MR). This paper proposes a new strategy called the lazy deregistration strategy (LDR) and compares the performance of the three strategies. We show that in most cases, LDR outperforms both SR and MR. The registration cost of SR is always no less than the cost of MR. The advantage of MR over SR is more significant if (i) when the user moves into the low-tier system, it is more likely that the currently visited low-tier VLR (visitor location register) is the same as the previously visited VLR, and (ii) the mobile station (MS) is more likely to move between the low-tier system and the high-tier system. The call delivery cost of MR is always no less than the cost of SR. The advantage of SR over MR is more significant if (i) the call arrival rate is large, (ii) the cost of delivering a call to the low-tier system is large, and (iii) the MS is likely to stay in the high-tier system.