## 2 Related Work  
### Underwater Magnetic Induction MIMO Communication  
The study of underwater magnetic induction communication has attracted considerable attention from academia and industry worldwide. [PERSON] et al. [20] extended the range of underwater communication using a spherical magnetic induction antenna. [PERSON] et al. [21] constructed an MI-based multi-hop network to study the distance of underwater MI communication while ensuring the bit error ratio (BER) by extending the communication range through relay nodes. [PERSON] et al. [22] used MIMO in magnetic induction communication to analyze the signal transmission loss and channel capacity of the 2 \(\times\) 2 and N \(\times\) N antenna array and designed MI-MIMO antennas using metamaterials. In addition, [PERSON] et al. [23] used three-way coils for MI-MIMO communication and achieved low power consumption and high information throughput for underwater autonomous robots by selecting appropriate coils. To build an underwater communication system, [PERSON] et al. [24] reduced antenna crosstalk by partially overlapping antenna coils in a 3 \(\times\) 3 or 4 \(\times\) 4 MI-MIMO system. [PERSON] et al. [25] designed a heterogeneous antenna array that enabled MI-MIMO channel capacity to eliminate inter-coil crosstalk, providing a new antenna combination for underwater MI-MIMO communication. [PERSON] et al. [26] introduced magnetically induced MIMO system models and revealed that using more receivers for better downlink communication is desirable to increase communication capacity.  
In addition, [PERSON] et al. [27] constructed an MI-MIMO system on an FPGA board using different frequencies and transmission rates. In contrast, [PERSON] et al. [28] used orthogonal frequency division multiplexing (OFDM) technology for underwater magnetic induction communication to increase signal capacity and improve signal immunity. [PERSON] [29] integrated OFDM with MI-MIMO to thoroughly analyze dual-coil, tri-coil, quad-coil, and N \(\times\) N-array magnetic induction systems. [PERSON] et al. [30] built an OFDM-based magnetic induction communication model to create a multi-input-single-output (MISO) system that fully utilizes each frequency to achieve high-speed data transmission. In this model, multiple transmit antennas are configured at the transmitter side and a single antenna at the receiver side. [PERSON] et al. [31] designed a heterogeneous MIMO communication network for acoustic and magnetic induction communication to achieve high-speed data transmission in water. [PERSON] et al. [32] investigated the influence of MI communication on the channel capacity after using MIMO technology. They derived the capacity and loss formula of the MI-MIMO system without signal crosstalk. [PERSON] et al. [33] discussed the transmit-side channel estimation without receiver channel information feedback when using MI communication. [PERSON] et al. [34] presented an underwater magnetic induction (MI)-assisted acoustic cooperative MIMO system. They proposed an optimization algorithm based on cooperative MIMO, for which the expected transmission distance and power constraints were considered. [PERSON] et al. [35] proposed a mathematical model to analyze the connectivity of the underwater MI-assisted acoustic cooperative MIMO systems. The lower and upper bounds of the connectivity probability were derived, providing guidelines for the network design and deployment.