On Blind Symbol-Timing Estimation for FBMC Systems: The Case of FBMC-PAM

This paper deals with the problem of blind symbol timing estimation for filter bank multicarrier systems with pulse amplitude modulation (FBMe-PAM). In FBMe-PAM a sequence of real-valued symbols can be transmitted over 2 $M$ spectrally separated subcarriers operating at the same symbol rate as OFDM. This recently proposed system exhibits many advantages in comparison with the OFDM system; in particular, it does not require a cyclic prefix and, in the multi-user context, it provides a high level of spectral separation among users. In this paper is derived the maximum likelihood (ML) blind symbol timing estimator for AWGN channel under the assumption of low SNR conditions. Since the FBMe-PAM signal is a noncircular random process (i.e., its conjugate correlation function or relation function is different from zero), the obtained ML estimator exploits both the conjugate and the unconjugate correlation. In addition, a closed-form low-complexity blind estimator exploiting only the unconjugate correlation, is proposed. The performance of the derived estimators, assessed via computer simulation, is compared with that of the two estimators obtained by separately maximizing the contribution to the ML cost function exploiting the unconjugate correlation or the conjugate correlation.