New algorithms for blind recognition of OFDM based systems

In the context of cognitive radio or military applications, it is a crucial task to distinguish blindly various OFDM based systems (e.g., Wifi, Wimax, 3GPP/LTE, DVB-T) from each others. Existing OFDM based systems differ from their subcarrier spacing used in OFDM modulation. One can thus carry out recognition algorithms based on the value of the subcarrier spacing. Standard approaches developed in the literature rely on the detection of the cyclic prefix which enables to exhibit the value of the used subcarrier spacing. Nevertheless these approaches fail when either the cyclic prefix duration is small or the channel impulse response is almost as large as the cyclic prefix. Therefore we propose four new algorithms to estimate the parameters of OFDM modulated signal (especially the subcarrier spacing) relying on (i) the normalized kurtosis, (ii) the maximum-likelihood principle, (iii) the matched filter, and (iv) the second-order cyclostationary property. We show the strong robustness of proposed algorithms to short cyclic prefix, multipath channel, time offset, and frequency offset. Comparisons between proposed algorithms and the state of art techniques are done by means of computer simulations. (C) 2009 Elsevier B.V. All rights reserved.