Investigation on cooperative SC-FDE relaying for spectrum sharing

In this paper, an amplify-and-forward cooperative single carrier-frequency domain equalizer system for spectrum sharing is proposed to improve the performance of the primary user (PU) and allow the secondary user (SU) to transmit its information simultaneously. To achieve this purpose, a modified data-dependent superimposed training (DDST) scheme is employed. In the original DDST scheme, a part of the frequency bins of the information signal is discarded to insert pilots. In the proposed approach, after receiving PU´s data SU firstly serves as a relay and amplifies PU´s data. Following, the modified DDST scheme is utilized to discard a part of the subcarriers to insert SU´s data. The overall signals are transmitted to the destination. At the destination, the signals from PU and SU are combined for detection by maximizing the signal-to-noise ratio in the frequency domain. Furthermore, the signal-to-interference plus noise ratio of the primary system is analyzed. If the BER of the primary system is given, the number of subcarriers shared to the SU can be determined. The simulation results reveal that the proposed approach is more suitable for spectrum sharing compared with cooperative orthogonal frequency division multiplexing system.