A fourth-order algorithm for blind characterization of OFDM signals

In the framework of cognitive radio, electro-magnetic environment sensing is a crucial task. In order to distinguish various systems relying on OFDM modulations from each others (such as WiMAX, WiFi, DVB-T), we need to be able to estimate precisely the inter-carrier spacing used in the transmitted signal. When the ratio between cyclic prefix and OFDM symbol duration is small or when the multipath propagation channel is almost as large as the cyclic prefix, standard approaches based on detection of cyclic prefix via an autocorrelation fall down. Therefore we propose a new algorithm to estimate the parameters of an OFDM modulated signal (especially the inter-carrier spacing) relying on the fourth order statistics of the received signal. We theoretically prove its robustness to multipath channels, time offset and frequency offset. Then its performance is analysed through numerical simulations and compared to standard approach which confirms the accuracy of the new algorithm.