On the time-frequency symbol density of FBMC/QAM systems

Filter bank multicarrier (FBMC) systems suffer from an inherent interference, which needs to be eliminated at the detection process. Orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) is a well-known FBMC system, which transmits real-valued symbols. In OFDM/OQAM, the time and frequency spacing between adjacent transmitted symbols are organized such that the inherent interference becomes pure imaginary and can be removed by a real-taking operation. Although OFDM/OQAM provides the maximal bandwidth efficiency, it falls short in handling the spatial multiplexing techniques in multi-input multi-output channels. In this regard, those modified FBMC systems, which transmit complex QAM symbols (FBMC/QAM) are used to support the spatial multiplexing techniques. In this article, we present a novel matrix formulation for the FBMC/QAM transmission procedure. On the basis of this presentation, we show that the maximal achievable time-frequency symbol density of FBMC/QAM, with the ability of perfectly removing the interference, is equal to that of the primer OFDM/OQAM.