Network architecture. (a) Cellular: scalable and highly dependable architecture used in existing systems; the mobiles communicate with the base stations (BSs), which are under control of the mobile switching center. (b) Ad hoc
: flexible, self-organizing architecture.
(c) Heterogeneous: a fusion of cellular and ad hoc
architectures, showing the licence-free OW/RF hotspots, which hence inherits the advantages of both the cellular and ad hoc