Exploring the Use of Two Antennas for Crosscorrelation Spectrum Sensing

Spectrum sensing is one of the key characteristics of a cognitive radio. Energy detection provides maximum flexibility by not relying on any prior knowledge, but suffers from an SNR-wall due to noise uncertainty. Crosscorrelation of the outputs of two receiver paths is a technique to reduce the noise level of the total receiver, and hence improves the SNR. The reduction of the noise is limited by correlated noise originating from shared components near the antenna. In this paper we explore the use of a separate antenna for each receiver for crosscorrelation spectrum sensing. One immediate advantage is that due to the removal of the splitter, which was necessary to interface the single antenna to two receivers, the SNR improves, significantly reducing the required measurement time. A lot of the noise correlation can be removed, leading to a lower residual noise floor. The noise at each antenna will still be partially correlated due to mutual coupling, spatial noise correlation and man-made noise. We show that some signal power can be lost in the sensing process due to partial decorrelation of the signal at the two antennas. Fortunately, this seems to be a problem only in highly mobile environments, which makes the use of two-antenna crosscorrelation spectrum sensing an interesting solution towards more reliable energy detection.