Improved interference approximation method for preamble-based channel estimation in FBMC/OQAM

Filter bank-based multicarrier modulation (FBMC) using offset quadrature amplitude modulation (OQAM), known as FBMC/OQAM (or OFDM/OQAM), provides an attractive alternative to the conventional cyclic prefix-based orthogonal frequency division multiplexing (CP-OFDM), especially in terms of increased robustness to frequency offset and Doppler spread, and high bandwidth efficiency. It suffers, however, from an inherent (intrinsic) imaginary intercarrier/inter-symbol interference that complicates signal processing tasks such as channel estimation (CE). Recently, the so-called interference approximation method (IAM) was proposed for preamble-based CE. It relies on the knowledge of the pilot´s neighborhood to approximate this interference and constructively exploit it in simplifying CE and improving its performance. The IAM preamble with nulls at the neighboring time instants that results in optimum CE performance was recently reported. This paper investigates an extended version of it, which can provide significant improvement through an appropriate exploitation of the interfering symbols from neighboring time instants as well. Simulation results are presented that compare the methods, with each other and with CP-OFDM, in both mildly and highly frequencyselective channels.