  In this work, we study the problem of band allocation of $M_s$ buffered
secondary users (SUs) to $M_p$ primary bands licensed to (owned by) $M_p$
buffered primary users (PUs). The bands are assigned to SUs in an orthogonal
(one-to-one) fashion such that neither band sharing nor multi-band allocations
are permitted. In order to study the stability region of the secondary network,
the optimization problem used to obtain the stability region's envelope
(closure) is established and is shown to be a linear program which can be
solved efficiently and reliably. We compare our orthogonal allocation system
with two typical low-complexity and intuitive band allocation systems. In one
system, each cognitive user chooses a band randomly in each time slot with some
assignment probability designed such that the system maintained stable, while
in the other system fixed (deterministic) band assignment is adopted throughout
the lifetime of the network. We derive the stability regions of these two
systems. We prove mathematically, as well as through numerical results, the
advantages of our proposed orthogonal system over the other two systems.
