Exploiting Interference Diversity for Event-Based Spectrum Sensing

Spectrum sensing is a core problem in cognitive radio. Detecting the presence/absence of very weak primary users with a single antenna can be very difficult. Environmental uncertainties result in SNR walls that detectors cannot overcome. Multiple-antenna approaches show some potential gains, but we show here that single-user multiple-antenna detection still must suffer from an SNR wall. The reason is that the real-world uncertainty in noise is dominated by the potential presence of an unknown number of low-power and time-varying interference sources in the external environment. Traditional collaborative spectrum sensing attempts to use the shadowing/multipath diversity across different users to boost the reliability of detection. We show that there is another kind of diversity that is also available: interference diversity. This captures the fact that low-powered interference sources are local to individual users whereas the primary user has a global footprint. To exploit this diversity, we must shift our perspective from existence- based detection (whether the primary is present or not) to event-based detection (whether the primary has turned off or on).