Interference Rejection Combining for Black-Space Cognitive Radio Communications

This paper focuses on multi-antenna interference rejection combing (IRC) based black-space cognitive radio (BS-CR) operation. The idea of BS-CR is to transmit secondary user (SU) signal in the same frequency band with the primary user (PU) such that SU’s power spectral density is clearly below that of the PU, and no significant interference is inflicted on the PU receivers. We develop a novel blind IRC technique which allows such operation mode for effective reuse of the PU spectrum for relatively short-distance CR communication. We assume that both the PU system and the BS-CR use orthogonal frequency division multiplexing (OFDM) waveforms with common frame structure. In this case the PU interference on the BS-CR signal is strictly flat-fading at subcarrier level. Sample covariance matrix based IRC adaptation is applied during silent gaps in CR operation. During CR transmission, the target signal detection and channel estimation utilize multiple outputs from the IRC process obtained with linearly independent steering vectors. The performance of the proposed IRC scheme is tested considering terrestrial digital TV broadcasting (DVB-T) as the primary service. The resulting interference suppression capability is evaluated with different PU interference power levels, silent gap durations, and CR device mobilities.