Spectrum reuse at the border of a primary user cell

Most algorithms for secondary spectrum usage are solely based on signal detection. The frequencies where the primary signal is detected with level comparable to the noise are considered occupied. As a result vast areas in the proximity of primary cells become illegal for spectrum reuse. In this paper we propose an algorithm that enhances spatial spectrum reuse by allowing secondary users to communicate in the presence of primary signal. We study how much the spectrum utilization is increased by using the proposed algorithm. The algorithm has multiple decision stages and it is based both on signal detection and generated interference estimation. It allows to minimize the decision errors and control the generated interference to primary user receivers. The algorithm is modeled by using Bayesian hypothesis testing approach. The required prior probabilities are related to the geographical interpretation of the studied system. The constructed model allows to find the optimal decision levels through the Lagrangian optimization. The algorithm performance is evaluated as a function of the number of measured power samples. Comparison to a simple detection based scheme indicates recognizable improvement especially for a low number of samples.