  A significant portion of the radio frequency spectrum remains underutilized
due to exclusive and static allocation of spectrum. Provisioning secondary
access to the underutilized spectrum could be beneficial to the incumbents if
they could gain significant value out of the fallow spectrum while ensuring
protection of their primary services. From an incumbent perspective, the
spectrum sharing approach needs to be non-harmful as well as efficient. In
order to make spectrum sharing efficient, it is necessary to maximize the
spectrum available for secondary access as well as maximize its exploitation.
We examine the impact of the conservative assumptions that lead to lesser
availability of spectrum for secondary access. The problem of joint scheduling
and spectrum-access footprint allocation is at the heart of maximizing the
exploitation. This problem is NP-hard and we present a suboptimal approach
based on the minimal spectrum consumption cost of a spectrum-access request. In
order to improve the spectrum sharing potential, we investigate the impact of
the various design choices for a spectrum access mechanism. The experiments
demonstrate the significance of the active role of the incumbents, the benefits
of fine granular spectrum access, and the need for transceiver standards for
accomplishing efficient usage of the spectrum.
