  We study optimal user-network association in an integrated 802.11 WLAN and
3G-UMTS hybrid cell. Assuming saturated resource allocation on the downlink of
WLAN and UMTS networks and a single QoS class of mobiles arriving at an average
location in the hybrid cell, we formulate the problem with two different
approaches: Global and Individual optimality. The Globally optimal association
is formulated as an SMDP (Semi Markov Decision Process) connection routing
decision problem where rewards comprise a financial gain component and an
aggregate network throughput component. The corresponding Dynamic Programming
equations are solved using Value Iteration method and a stationary optimal
policy with neither convex nor concave type switching curve structure is
obtained. Threshold type and symmetric switching curves are observed for the
analogous homogenous network cases. The Individual optimality is studied under
a non-cooperative dynamic game framework with expected service time of a mobile
as the decision cost criteria. It is shown that individual optimality in a
WLAN-UMTS hybrid cell, results in a threshold policy curve of descending
staircase form with increasing Poisson arrival rate of mobiles.
