Opportunistic Spectrum Access in Fading Channels Through Collaborative Sensing

Spectrum scarcity is becoming a major issue for service providers interested in either deploying new services or enhancing the capacity for existing applications. On the other hand, recent measurements suggest that many portions of the licensed (primary) spectrum remain unused for significant periods of time. This has led the regulatory bodies to consider opening up under-utilized licensed frequency bands for opportunistic access by unlicensed (secondary) users. Among different options, sensing-based access incurs a very low infrastructure cost and is backwardcompatible with the legacy primary systems. In this paper, we investigate the effect of user collaboration on the performance of sensing-based secondary access in fading channels. In particular, we demonstrate that under independent fading or shadowing, a low-overhead collaboration scheme with a very simple detector as its building block, 1) improves the spectrum utilization significantly, 2) enables the individual users to employ less sensitive detectors, thereby allowing a wider range of devices to access the primary bands, 3) increases the robustness toward noise uncertainty, 4) reduces the time and bandwidth resources required for satisfactory sensing which translates into higher agility and efficiency of the secondary access.