Optimal MISO pre-equalization for filter bank based multicarrier systems

One of the phenomena that degrades the performance of multicarrier modulation (MCM) systems is the spectral nulls that multipath channel may have. As a result, the affected subcarrier signals may be severely degraded resulting in a loss of symbols. In this paper we have studied how to overcome this problem by taking advantage of spatial diversity along with the knowledge of channel state information at both ends of the link. To that end we devise broadband beamformers that work on a per-subcarrier basis for filter bank based multicarrier (FBMC) systems. In particular we have focused on the orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) scheme. The criterion that has been followed to design the transmit filters consists of minimizing the transmitted power while the quality of service (QoS) constraints are satisfied. Simulation-based results demonstrate the efficacy of the proposed optimal and suboptimal designs to reduce the transmitted power when compared to the Alamouti scheme at the same BER targets. Although the optimal design is more demanding in terms of complexity it yields 1dB of savings in the transmitted power in comparison to the sub-optimal alternative.