Short-range optical OFDM

This paper presents a proof-of-concept for a short range underwater optical wireless communication system. It investigates of the use of Optical Orthogonal Frequency Division Multiplexing (OOFDM) as a modulation scheme and presents the characteristics of the underwater propagation channel for amplitude modulated optical waves. Although system under investigation utilizes a data rate of 1 Mbpsm, it is evident that higher data rates are possible with minor changes in the optical front-end hardware and the signal processing chain. To evaluate the system performance, tests were conducted in clear water for distances up to three meters and in three simulated scenarios of dirty water (deep, medium and shallow) for a distance of half a meter. All test were performed in a controlled laboratory environment using a water tank. The performance of the system has been evaluated using offline processing of the received OOFDM symbols. The Bit-Error Rate (BER) performance of the system is investigated as function of bandwidth, distance of transmission, and Signal-to-Noise Ratio (SNR). Additionally, the transfer function of the optical underwater channel characteristics are presented along with measured statistics of delay spread of the channel to show the presence or absence of multi-path effects. It should be noted that the intended application of this system is docking of remotely operated and autonomous underwater vehicles, where high speed data transfers are essential. Another possible application is data collection from deployed sensors gathering data over a long periods of time.