Fast wideband spectrum scanning for multi-channel cognitive radio systems

This paper considers how to scan a wideband spectrum for a multi-channel cognitive radio system with small delay and small error probabilities. Two scenarios are particularly investigated. In the first scenario, the spectrum scanning needs to be complete within a certain period of time, which we call the finite-horizon case. In the second scenario, the spectrum scanning continues until the completion of the detection process, which we call the infinite-horizon case. In both scenarios, spectrum scanning algorithms are developed to minimize a cost function, which strikes a desirable tradeoff between detection error probabilities and the detection delay. In the finite-horizon case, the optimal algorithm requires large look-up tables and frequent update of posterior probabilities, thus incurring a prohibitively high implementation complexity. In the infinite-horizon case, the optimal algorithm is nothing but a concatenated sequential probability ratio test (C-SPRT). The truncated C-SPRT is proposed as a reduced complexity scanning algorithm for the finite-horizon case. Several truncation methods are proposed and investigated. Simulation examples are provided to illustrate the effectiveness of the proposed algorithms.