Preamble-based channel estimation in MIMO-OFDM/OQAM systems

Filter bank-based multicarrier modulation (FBMC) using offset quadrature amplitude modulation (OQAM), known as OFDM/OQAM (or FBMC/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 inter-carrier/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 in single-input single-output (SISO) systems. 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. A number of IAM preambles have been proposed, with varying CE performance. This paper is concerned with the application of the IAM idea in multi-input multi-output (MIMO) systems. The most prominent IAM variants are considered and their MIMO extensions with their relative advantages and practical issues are investigated. The IAM preambles are compared, with each other and with CP-OFDM, via simulations in both mildly and highly frequency-selective channels.