Design Method of an Ocean Induction Coupling Chain Communication System that Resists the Multipath Effect of a Seawater Channel

In this study, a mathematical model of multipath channels is established, and the delay parameters of 10-path models are calculated at 300 m. A multipath-channel hardware simulator based on a field programmable gate array (FPGA) is designed and verified at 100 kHz, 200 kHz, 500 kHz, 1 MHz, and 24 MHz transmission frequencies. According to the characteristics of the ocean induction coupling chain channel, the orthogonal frequency-division multiplexing (OFDM) algorithm parameters are designed by referring to the wireless communication protocol. The appropriate length cyclic prefix (CP) is added in the OFDM symbol to resist the multipath effect of the seawater channel, and the FPGA hardware transceiver based on the OFDM algorithm is realized. The hardware platform of the ocean induction coupling chain communication system is developed to resist the multipath effect of the seawater channel and tested at 24 MHz. The experimental results show that 800 ns is the best CP length for the developed system, which can effectively resist the multipath effect, with a signal-to-noise ratio above 24 dB and a bit error rate below 1%. This study provides a hardware simulation test platform and an effective method to resist the multipath effect of a seawater channel and improve the transmission performance of the seawater channel.