User-Network Association in an 802.11 WLAN & 3G UMTS Hybrid Cell: Individual Optimality

More and more users subscribing to wireless broadband services are seeking to have access to both WLAN and UMTS networks. We study individually optimal user-network association in an integrated WLAN and UMTS hybrid cell. The association problem is formulated within a non-cooperative game framework. In the formulation, mobile arrivals are assumed to follow the Poisson process and each mobile considers its average service time in each network as the decision criteria to connect to either of the WLAN or UMTS networks. We seek to compute the optimal association or decision policy that achieves the Nash equilibrium. For this we develop a generic system of linear equations for estimating the average service time of a mobile. This system is then solved assuming a particular model for the WLAN and UMTS networks and we explicitly compute the optimal association policy that is observed to possess a descending staircase curve structure.