Noncoherent amplify-and-forward cooperative OFDM in block fading channels

In this paper, we investigate noncoherent detection methods for amplify-and-forward cooperative OFDM systems in frequency-selective block fading channels. In particular, by exploiting the time-frequency relationship of OFDM, a noncoherent detector is proposed for phase-shift keying modulated signals. The proposed noncoherent detector uses only one OFDM block signal for data detection, and therefore is suitable for relatively fast time-varying environments. We show that the noncoherent detection can be cast as a quadratic maximization problem, which can be efficiently solved by the convex approximation technique, namely, semidefinite relaxation. Simulation results demonstrate that the noncoherent detector exhibits near-coherent performance and outperforms channel-estimation-aided detection methods.