## 3 Simulation of Underwater Electric Field Communication
### CSMA/CA Channel Backoff Algorithm Design and Simulation Analysis
#### 4.2.4 Channel Detection
The experimental results of AUV point-to-point underwater dynamic electric field communication are shown in Figure 15.

During the experiment, the distance between two AUV nodes for communication was increased by 0.5 m at each interval, while keeping the two AUVs in a relatively low-speed dynamic state, to observe the bit error rate of the speed dynamic state, and observe the bit error rate of the receiving node. When the bit error rate changed from 0 to 1, it indicated that effective data transmission was not possible at the current point, thus determining the maximum communication distance. The experimental results show that the minimum communication distance Pmin was 3.5 m, indicating the farthest communication distance. The results demonstrate that the underwater electric field communication system based on 2 FSK modulation and demodu

Figure 14: Underwater electric field point-to-point dynamic communication experiment. Figure 15: AUV point-to-point underwater dynamic electric field communication. lation can achieve mobile underwater electric field communication with a bit error rate of 0-0.628% within the communication distance range of 0 to 3.5 m. This is because, during the process of AUV movement, the communication distance changed, and the PGA amplification factor was able to achieve error-free communication within a certain communication distance range. However, when the PGA amplification factor needed to be adjusted, some bit errors may have occurred due to the slow convergence speed of adaptive feedback control of the PGA amplification factor. This experiment also validated the feasibility of the designed mobile underwater electric field communication system. 3.2 Experimental Verification of Underwater Electric Field Multi-Node Networking Communication Based on AUV

To address the issue of channel conflict during the communication process of underwater electric field AUV multi-node, where multiple nodes simultaneously emit signals, resulting in the distortion of the underwater electric field, distribution, and increased bit error rate, a design and implementation of a multi-node communication system for underwater electric fields was conducted. The CSMA/CA channel backoff algorithm was proposed to solve the channel conflict problem. Dynamic backoff experiments based on CSMA/CA were conducted to verify the feasibility of this algorithm. The experimental scenario is shown in Figure 16a, where the red AUV serves as the receiving node, and the blue AUVs serve as the transmitting nodes. Four transmitting nodes surround the receiving node and perform parallel advancement to conduct multi-node backoff experiments. This experiment was conducted in a pool environment, as shown in Figure 16b. During the experiment, as each AUV emitted its unique identification code (ID), it was still possible to check which one emitted the electric field communication signal in the experimental results. This article sets the IDs of five AUV Nodes 1, 2, 3, 4, and 5 as 0 \(\times\) 01, 0 \(\times\) 02, 0 \(\times\) 03, 0 \(\times\) 04, and 0 \(\times\) 05, respectively. AUV2, AUV3, AUV4, and AUV5 cyclically sent electric field communication information with their IDs to AUV1. During this process, four AUVs competed for the CSMA/CA channel simultaneously, waited, and sent the

Figure 16: Illustration and experimental diagram of multi-node backoff based on CSMA/CA. (**a**) Schematic diagram of multi-node communication and backoff based on CSMA/CA. (**b**) Experimental diagram of multi-node communication and backoff based on CSMA/CA. information according to the proposed mechanism. All transmitted data were monitored by the receiving electrode of AUV1 and sent to the computer through an external receiving and transmitting unit connected to the receiving electrode. By identifying the ID, the specific AUV transmitting the communication data was determined, completing the real-time dynamic backoff process of the entire AUV multi-node.