Cooperative Spectrum Sensing for Dynamic Spectrum Access

In cognitive networks, cooperative spectrum sensing is employed to detect the presence of primary user quickly. In this paper, we study the sensing performance of a cognitive user U₁ by allowing another cognitive user U₂ to act as its relay. We vary the scaling factors (used by the relay U₂ to amplify its received signal) of the unconstrained scheme (there is not power constrain for relay), and develop the formulas of detection and false alarm probability for cooperative scheme based on cooperative relay. We then pay much attention to studying how to find a proper relay U₂ for U₁ so that the detection capability of U₁ can be improved. We find that, the normalized received power of U₂ should be larger than a certain value which is called gain point if U₁ can benefit from the cooperation. We present the relationship of gain points between the constrained scheme and unconstrained scheme. Results are well interpreted and supported by exhausted numerical computations.