Effect of receiver aperture diameter on the performance of a 20 Gbps 4-QAM-OFDM underwater optical wireless communication system under varying water turbidity

Abstract

The current paper is a performance analysis of an underwater optical wireless communication (UOWC) system based on 4-QAM-OFDM and working at 20 Gbps. The receiver aperture diameter effect on link performance is explored under five conditions of water channel in the sea which include, pure sea, clear ocean, coastal ocean, Harbor I, and Harbor II. Log (BER) and received optical power (ROP) are also considered as the performance parameters of the three aperture diameters of 16 cm, 18 cm, and 20 cm, and FEC threshold of log (BER) = −2.42 is taken as a parameter of the acceptable link quality. Findings indicate that the aperture of 20 cm is the most effective in terms of performance with all types of water. At 43 m using the 20 cm aperture a log (BER) of −3.67 and ROP of −17.29 dBm are obtained whereas the 16 cm aperture results in a log (BER) of −1.29 and −21.16 dBm at the same range. The 20 cm aperture in Harbor II gives a log (BER) of −3.91, and ROP of −17.13 dBm at 4.8 m, relative to −1.34 and −21.01 dBm at the 16 cm aperture. The power difference continually favors the larger aperture of about 3.87 dBm in comparison to the 16 cm one, and is indicative of receiver aperture sizing as an essential design factor in the UOWC system. The signal quality trends in BER curves are further validated by signal quality constellation diagrams at the chosen ranges of each water type.