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The development of reconfigurable and multimode terminals enable service providers to use the excess bandwidth to support services from other networks, at the expense of terminals performing vertical handover when a call is served by another network. The improvement in the performance of such an overlay heterogeneous network is expressed in terms of the increase in capacity while fulfilling each networkspsila grade-of-service (GoS). Our results show that if there is no proper control in the admission of handover requests from other networks and only a simple first-come-first-serve (FCFS) policy is adopted, although each network can achieve better spectrum usage, the overall service capacity is still limited by the network which first violates its GoS requirement. We propose and analyze the performance of two admission control schemes for efficient resource sharing, namely, the reservation and the random early discard (RED) schemes. In the reservation scheme, the performance limiting network reserves some resources for exclusive access by its users. For the RED scheme, selective admission is used to limit the requests from the other networks. Using a four-dimensional Markov model, the call blocking probabilities and the vertical handoff probabilities for the case where there are two overlay networks are computed. Our results show that the two proposed schemes achieve higher service capacity and hence better spectrum usage when compared with the FCFS scheme. In addition, the RED scheme is more effective in balancing the two service loads over the reservation scheme. Analytical results derived from the Markov chain model show good agreement with the simulated results.
Date of Conference: 15-18 Sept. 2008