Amplify-and-forward secondary spectrum access in multicarrier cognitive radio systems

Innovative spectrum sharing policies, possibly leveraged by cognitive radio (CR) technologies, are expected to play a significant role in forthcoming 5G systems, employing multicarrier techniques for modulation and multiple-access. In this paper, we propose an opportunistic amplify-and-forward relaying scheme for a multicarrier CR network, where a secondary user (SU) is allowed to share communication resources with a primary user (PU) transmitting with orthogonal frequency-division multiplexing (OFDM) technology. Instead of minimizing the interference to the PU, the SU transmitter relays the received PU signal on the different OFDM subcarriers by using a precoding matrix depending on the symbols that must be delivered to the SU receiver. The information-theoretic capacity of the proposed protocol is assessed, showing that, under mild conditions, the SU can gain a significant data-rate performance, while not degrading (but even improving) the PU performance.