Orthogonal Frequency Division Multiplexing Adaptive Technology for Multinode Users of Seawater Channel Based on Inductively Coupled Mooring Chain

As an important part of buoy-type ocean monitoring systems, the inductively coupled mooring chain solves the problem of data cotransmission through the multinode sensors that it carries, which is significant for the rapid acquisition of fish, hydrology, and other information. This paper is based on a seawater channel transmission model with a depth of 300 m and a bandwidth of 2 MHz. An orthogonal frequency division multiplexing (OFDM) technology is used to overcome the multipath effect of signal transmission on a seawater medium. The adaptive technology is integrated into the OFDM, and an improved joint subcarrier and bit power allocation algorithm is proposed. This algorithm solves the problem of dynamic subcarrier allocation during the cotransmission of underwater multinode user data in seawater channels. The results show that the algorithm complexity can be reduced by 0.18126×10 −2 s during one complete OFDM system data transmission by the improved greedy algorithm, and a total of 216 bits are transmitted by the OFDM. The normalized channel capacity can be improved by 0.012 bit s −1 Hz −1 . At the bit error ratio (BER) of 10 −3 , the BER performance can be improved by approximately 6 dB. When the numbers of users are 4 and 8, the improved algorithm increases the channel capacity, and the higher the number of users, the more evident the channel capacity improvement effect is. The results of this paper have an important reference value for enhancing the transmission performance of inductively coupled mooring chain underwater multinode data.