  Focusing on a femtocell communications market, we study the entrant network
service provider's (NSP's) long-term decision: whether to enter the market and
which spectrum sharing technology to select to maximize its profit. This
long-term decision is closely related to the entrant's pricing strategy and the
users' aggregate demand, which we model as medium-term and short-term
decisions, respectively. We consider two markets, one with no incumbent and the
other with one incumbent. For both markets, we show the existence and
uniqueness of an equilibrium point in the user subscription dynamics, and
provide a sufficient condition for the convergence of the dynamics. For the
market with no incumbent, we derive upper and lower bounds on the optimal price
and market share that maximize the entrant's revenue, based on which the
entrant selects an available technology to maximize its long-term profit. For
the market with one incumbent, we model competition between the two NSPs as a
non-cooperative game, in which the incumbent and the entrant choose their
market shares independently, and provide a sufficient condition that guarantees
the existence of at least one pure Nash equilibrium. Finally, we formalize the
problem of entry and spectrum sharing scheme selection for the entrant and
provide numerical results to complement our analysis.
