Research and Implementation on a Real-Time OSDM MODEM for Underwater Acoustic Communications

With the increasing demand for marine-sensing information, more and more research has been investigated on underwater wireless sensor networks (UWSNs). Underwater acoustic communication (UWAC) modulators & demodulators (MODEMs) that are used to exchange marine-sensing data have attracted wide attention because they are the most important part of UWSNs. Orthogonal signal-division multiplexing (OSDM) is a compromise between single-carrier communication and multiple-carrier communication. The OSDM communication system is less sensitive to multipath and Doppler shift and has lower peak-to-average power ratio (PAPR). The OSDM UWAC recently has been investigated in theoretical analysis, but as far as we know, there is extremely limited research on real-time OSDM UWAC MODEM design. Aiming at addressing this gap, in this article, a real-time OSDM MODEM is researched and implemented for UWAC, including hardware and software. Specifically, the preamplifier, the bandpass filter, the power amplifier, and the signal processor are introduced. Moreover, detailed procedures for modulation and demodulation are also presented. In addition, to accommodate the different underwater acoustic channels and to get the balance between bit error rate (BER) and data rate, the parameters such as the number of zero vectors and pilot vectors are investigated. Our OSDM MODEM achieves error-free with the data rate of 4.35 kb/s by using the minimum-mean-square-error (MMSE) equalizer and polar decoding under slow time-varying channels, and the communication range reaches larger than 5 km.