Orthogonal frequency division multiplexing (OFDM) is the most popular scheme for broadband communications. However, it has been shown that OFDM has disadvantages in time-varying channels. Filter bank multicarrier (FBMC) is an alternative multicarrier modulation method that can be designed for robust performance in doubly (time and frequency) dispersive channels. The emphasis of this paper is on a class of FBMC systems that are called filtered multitone (FMT). We note that although unlike the more popular FBMC systems that use offset quadrature amplitude modulation (OQAM) or cosine modulated techniques to achieve full bandwidth efficiency, FMT does not have full bandwidth efficiency, its possible use in multiple-input multiple-output (MIMO) channels still makes it an attractive method. In a recent work, we have noted that the FBMC systems that are based on OQAM/cosine modulated techniques are very restrictive in MIMO channels and introduced a class of FMT systems with robust performance in doubly dispersive channels. This paper extends our previous results and shows that further improvement can be obtained by organizing the data symbols in a hexagonal lattice structure, as compared to the more popular rectangular structure. In addition, results that compare our proposed FMT systems with the conventional FMT and OFDM are presented and we show that a substantial gain in performance is achieved.
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