Estimation of maximum interference-free power level for opportunistic spectrum access

We consider a scenario in which frequency agile radios opportunistically share a fixed spectrum resource with a set of primary nodes. We develop a collaborative scheme for a group of frequency agile radios to estimate the maximum power at which they can transmit on a given frequency channel, without causing harmful interference to the primary receivers. The proposed scheme relies on signal strength measurements taken by a group of frequency agile radios, which are then used by a target node to characterize the spatial size of its perceived spectrum hole in terms of the maximum permissible transmit power. We derive an approximation to the maximum interference-free transmit power using the Cramer-Rao bound on localization accuracy. We present numerical results to demonstrate the effectiveness of the proposed scheme under a variety of scenarios.