Spectrum sharing for bi-directional communication in cognitive radio networks

In this paper, we propose a spectrum sharing protocol where a pair of secondary users and a pair of primary users bidirectionally communicate. A secondary relay equipped with two antennas is deployed to ensure two-way relaying for primary users and thus they give the chance for secondary users to access the spectrum. To transmit its data, the secondary transmitter does not take into account the interference caused to primary receiver. It adjusts its transmit power so that the secondary required data rate is attained. In return, the relay uses zero forcing precoding to make two way relaying for primary users with no interference. We analytically derive the average outage probability and bit error probability of secondary transmissions. Analytical results are verified through simulations. Our proposed spectrum sharing scheme is proved to significantly outperform the conventional underlay scheme while respecting the performances requirement of the primary users.