Spectrum sharing for bidirectional communication exploiting zero-forcing and singular value decomposition beamforming

In this paper, we propose a dynamic spectrum sharing protocol where a pair of secondary users and a pair of primary users bidirectionally communicate. A secondary relay equipped with multiple antennas is deployed to assist the secondary transmissions and improve the secondary access to the spectrum. We employ a new time division access so that no interference may exist between primary and secondary users. The proposed scheme is then compared to the axiomatic and simple scheme where the secondary users communicate with each other with the assistance of the relay in underlay mode. We study and compare the performances of the two schemes in terms of outage probability. An upper bound for the secondary outage probability of the proposed scheme is derived. Our simulation results prove that the proposed scheme significantly outperforms the underlay spectrum sharing while in both schemes, the primary outage probability is kept identical to the case where secondary users are absent.