Performance comparison between FBMC and OFDM in MIMO systems under channel uncertainty

In this paper we present a performance comparison between two different multi-carrier transmission techniques: OFDM, based on the FFT and cyclic prefix (CP) addition; and FBMC (FilterBank MultiCarrier), which, as indicated by its name, is based on a filterbank architecture. For both schemes, we propose a joint beamforming design to be applied in multi-input-multi-output (MIMO) systems, which requires channel state information (CSI) at both communication ends. If perfect CSI is assumed, FBMC presents a higher energy-efficiency since it does not require a CP, differently to OFDM. However, in the imperfect CSI case, the opposite occurs: while in OFDM the presence of errors in the CSI does not cause intersymbol interference (ISI) and inter-carrier interference (ICI), in the FBMC case we show, both analytically and through simulation results, that imperfections in the CSI imply both ISI and ICI, which leads to an energy-efficiency loss. To mitigate this loss, we propose a novel robust receive beamforming strategy. In the simulations section, the performance of FBMC with robust beamforming is shown to outperform OFDM even in imperfect CSI conditions. The characterization of the tradeoff between energy-efficiency and robustness against channel uncertainty, both with robust and non-robust strategies, is, therefore, the objective of the present paper and also the motivation for future robust designs for FBMC multiantenna systems.