Opportunistic interference avoidance scheduling for underlay cognitive radio networks

An opportunistic scheduling scheme that avoids the interference that a primary multi-antenna Base Station (BS) generates in the secondary single-antenna links of an underlay cognitive radio network is proposed. In this scenario, the primary BS applies a pseudo-random sequence of transmit beamforming vectors to serve its users, which is known beforehand at the secondary Receivers (RXs). Combining this information with the estimated values of slow-varying channel gains, the secondary RXs are able to identify the time instants where the signals from the different transmit antennas of primary BS sum up destructively in reception. Taking advantage of this information, the secondary transmitters are able to delay their transmissions until the interference coming from the primary BS is far from its peak. Closed form expressions for the mean data rate of the secondary link are derived for different SNR regimes. As expected, the interference mitigation capability of the proposed opportunistic scheduling scheme grows as both the SIR and the activity period of secondary links decrease.