Enhancing the performance of OFDMA underlay cognitive radio networks via secondary pattern nulling and primary beam steering

Cognitive radio networks are receiving a lot of research attention lately. Most user equipment in state-of-the-art wireless communication systems are equipped with two antennas. In this paper, we take advantage of the two transmit antennas in an underlay cognitive radio network scenario. Secondary users use the two transmit antennas in order to insert a null in the direction of the primary base station, thus protecting primary users from interference on their uplink transmissions. Primary users benefit from the antennas in order to perform beam steering in direction of the primary BS, thus enhancing their uplink SINR without being concerned of the presence of the secondary users. This has the additional possible benefit of directing most primary radiation away from the secondary BS, thus reducing the interference on uplink secondary transmissions.