Polarized digital pulse interval modulation for underwater wireless optical communications

In practical underwater wireless optical communications (UWOC), pulse modulation technique has been widely used due to the high optical power efficiency and relatively low system complexity. Compared with the simplest on-off keying (OOK) scheme, digital pulse interval modulation (DPIM) improves both power efficiency and error performance and requires no symbol synchronization. Polarization shift keying (PolSK) is an another appropriate modulation scheme which can effectively restrain background noise. In this paper, we have proposed a polarized DPIM (P-DPIM) scheme by combining DPIM and PolSK to further improve the performance, and derived its bit-error-rate (BER) expression in additive white Gaussian noise (AWGN) channel. Numerical results by Monte Carlo simulation in UWOC channel suggest that P-DPIM scheme can improve both the power efficiency and error performance as well as communication distance compared with traditional PPM and DPIM schemes. Therefore P-DPIM is more suitable for relatively low signal-to-noise ratio (SNR) scenarios.