Optical module of a bimodal system for underwater wireless communication

Abstract

This article presents the results of the development of the receiving and transmitting module of the underwater wireless optical communication (UWOC) system. This module can be used as part of a wireless optical bridge for various telecommunication applications. A comparative analysis of publications devoted to the development of wireless underwater optical communication systems has been carried out. The developed optical receiving and transmitting module (ORTM) is an integral part of a bimodal modem for organizing underwater communications. The ORTM communicates with the modem via the RS-232 protocol. The ORTM consists of three boards — a digital signal processing board, a receiver board and a transmitter board. Software has been developed for FPGAs that provides the formation of a pulse train with pulse position modulation (PPM) from a digital sequence coming from the modem, as well as the reverse conversion of the pulse train coming to the FPGA from the receiver unit. According to the RS-232 protocol, a data transfer rate of 115200 bits per second is implemented with a distance between optical modules of up to 5 m. A sealed design of the ORTM prototype has been developed. The dimensions of the cylindrical ORTM prototype were 70×77×77 mm. The supply voltage line, downlink and uplink channels are organized between the ORTM and the modem via a cable through a deep-sea connectors. The ORTM tests were carried out as part of a bimodal modem, one channel of which involves transmitting data via an acoustic channel, the second channel via an optical channel, that is, using the developed ORTM. In the future, it is planned to develop the ORTM software in the direction of using noise-resistant coding and deeper integration of digital signal processing in the ORTM receiving path.