  This paper studies dynamic spectrum leasing in a cognitive radio network.
There are two spectrum sellers, who are two primary networks, each with an
amount of licensed spectrum bandwidth. When a seller has some unused spectrum,
it would like to lease the unused spectrum to secondary users. A coordinator
helps to perform the spectrum leasing stage-by-stage. As the two sellers may
have different leasing period, there are three epochs, in which seller 1 has
spectrum to lease in Epochs II and III, while seller 2 has spectrum to lease in
Epochs I and II. Each seller needs to decide how much spectrum it should lease
to secondary users in each stage of its leasing period, with a target at
revenue maximization. It is shown that, when the two sellers both have spectrum
to lease (i.e., in Epoch II), the spectrum leasing can be formulated as a
non-cooperative game. Nash equilibria of the game are found in closed form.
Solutions of the two users in the three epochs are derived.
