Design and Verification of Underwater Electric Field Communication System Based Spread Spectrum Techniques

Due to being easily affected by the environment, underwater acoustic communication and underwater optical communication are not suitable for small underwater robots communication. According to the principle of underwater electric field communication, a miniaturized underwater electric field communication system with low power consumption, low bit error rate and adaptive position change is designed. The system adopts the spread spectrum techniques with strong anti-interference ability and the binary phase shift keying (2PSK) modulation method. The system includes two units of transmitting and receiving. In the transmitting unit, signal spread spectrum and carrier modulation are realized through field programmable gate array (FPGA). The signal realizes digital-to-analog conversion and power amplification through the analog circuit, and then is transmitted through the transmitting electrodes. In the receiving unit, the signal is received through the receiving electrodes. The signal is amplified and converted into a digital signal. The Costas loop is used for down-conversion and despreading in the FPGA. Finally, the demodulated signal is transmitted to the Raspberry Pi for processing. The communication experiment is carried out in fresh water to verify the performance of the communication system. The experiment shows that the underwater electric field communication system based on spread spectrum communication can realize error-free communication with a data transmission rate of 1.2 Kbps within 8 m. Compared with the previous systems with 2.4 m communication distance based on 2ASK and 3.8 m communication distance based on 2FSK, the new system has the advantages of lower communication bit error rate and longer communication distance.