Subspace-based spectrum guarding

Cognitive radio is regarded as the most promising technology for driving the future development of next-generation wireless networks, increasing spectrum efficiency by dynamic spectrum access. Allowing white spaces to be used in a deregulated manner exposes the radio spectrum to anomalous usage, which in turn may intentionally or unintentionally cause interference to primary users (PUs) as well as secondary users (SUs). In this paper we propose a subspace-based spectrum guarding detector (SSGD) to address the security of unauthorized spectrum usage. In particular, we consider the scenario where ongoing authorized transmissions by PUs have to be preserved from concurrent unauthorized emissions in the same frequency bands. The detector operates in two phases: a training phase where SSGD collects samples of the authorized transmissions, and a detection (on-line) phase where the spectrum is guarded against anomalous emissions. The performance of SSGD is analyzed in terms of detection and false alarm probabilities highlighting the effects of the propagation scenario, the PU characteristics, the signal-to-noise ratio (SNR) and the duration of both training and on-line phases. Numerical results show that in practical scenarios SSGD provides a remarkable SNR improvement of several dB over the conventional energy detector (ED).