Collaborative Spectrum Sensing under Spatially Correlated Shadowing Fading

Cognitive Radio is an innovative technology that allows unlicensed (secondary users) users to opportunistically access channels licensed to other users (primary users). A key procedure in the context of opportunistic access is the spectrum sensing, performed by secondary user to determine whether the channel is idle or busy. However, decisions regarding the channel state can be corrupted by fading conditions, leading to wrong decisions regarding the channel state. Collaborative spectrum sensing schemes have been proposed in the literature as a possible way to mitigate the effects of fading. In these schemes, local decisions or observations about the channel state are combined to reach a global decision. Even though collaborative spectrum sensing in general leads to a higher performance, correlated shadowing may reduce the benefits of collaboration. In this paper we investigate the performance of different combining rules in collaborative spectrum sensing in correlated shadowing environment. Our results show that the incremental performance gain achieved by adding more users in the collaboration scheme tends to reduce when the number of users in the collaboration grows, indication that there is a limit in the performance of collaborative spectrum sensing.