Standard OFDM systems are associated with a rectangular grid in the time-frequency plane. However such a setup is in general not optimal for pulse shaping OFDM systems for doubly dispersive channels. We introduce lattice-OFDM systems (LOFDM), which are OFDM systems constructed with respect to general lattices in the time-frequency plane. We show how to design optimal pulse shapes for LOFDM system. Furthermore we demonstrate by theoretical considerations and numerical simulations that LOFDM systems using hexagonal-type lattices outperform ordinary OFDM systems with regard to robustness against ISI/ICI.

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