Precoder Design to Improve Performance of Multi-User OQAM DCO-FBMC Underwater Visible Light Communication

Due to the three undesirable factors of absorption, dispersion and turbulence induced fading, performance of underwater visible light communications (UVLC) is severely reduced. In this paper, performance of a multi-input single-output (MISO) ULVC broadcasting with DC-biased optical filter-bank multi-carrier (DCO-FBMC) modulation using offset-QAM (OQAM) has been studied. The OQAM DCO-FMBC has higher spectrum efficiency than DCO-OFDM modulation since it does not need cyclic prefix; however, due to inherent inter-symbol interference (ISI) and intercarrier interference (ICI), bit-error rate (BER) of OQAM-DCO-FMBC system is saturated in high data rates under adverse conditions of ULVC channel, especially turbulence induced fading. In order to deal with undesirable factors of underwater channel, as well as minimizing the inherent interference of OQAM DCO-FBMC modulation, employing multi-tap precoders in the transmitter is recommended; therefor, performance of a downlink system for transferring data from a MISO base station with space diversity to multiple mobile users in the ULVC channel has been investigated. Computation of precoder coefficients are done by minimizing the mean square error (MMSE) according to the channel state information (CSI). simulation results show that the proposed method can significantly improve the system performance in UVLC channels with weak turbulence as well as reducing absorption and dispersion.