## 3 Simulation of Underwater Electric Field Communication
### CSMA/CA Channel Backoff Algorithm Design and Simulation Analysis
#### 4.2.4 Channel Detection
It can be seen that the AUV can accurately receive the electric field communication information with other AUV identity information. Due to the Raspberry Pi's adoption of dual-thread synchronous operation of the CSMA/CA backoff algorithm and channel detection algorithm, AUV Node 1 detected that the channel was occupied during communication, entered the backoff process, which is consistent with the simulation and analysis of the underwater electric field communication channel backoff protocol, verifying the accuracy of the integration of the CSMA/CA backoff algorithm and channel detection algorithm in the underwater multi-node communication system designed in this article. The experimental results based on CSMA/CA dynamic backoff are shown in Figure 17, where the \(x\)-axis represents the number of data received by the receiving AUV, and the \(y\)-axis represents the transmitting AUV nodes. Different transmitting nodes emitted signals at different times, and the same receiving node received signals from different transmitting nodes and decoded them to obtain the corresponding coordinates. From the experimental results, it can be seen that the AUV running the CSMA/CA-based electric field communication protocol can communicate well without communication collisions or conflicts, which still proves the effectiveness of the protocol. This article measured the performance of the underwater electric field multi-node communication system designed in this article based on the bit error rate of 50 other nodes' underwater electric field communication packets received by AUV1. Through analysis and calculation, it can be concluded that this system can achieve underwater electric field dynamic multi-node communication with a bit error rate ranging from 0% to 0.96%, indicating a low bit error rate. This was mainly caused by the changing communication distances between robots in the multi-node AUV. During the experiment, when the AUV cluster moved forward parallel to each other, the transmitting and receiving electrodes remained parallel, resulting in a bit error rate of 0. However, when the AUV moves at a certain direction angle, the angle between the transmitting and receiving electrode plates constantly changed, leading to a change in bit error rate. Subsequently, the stability of the AUV itself can be increased to reduce the bit error rate. However, based on the experimental results, it can be observed that there was no channel collision and large-scale garbled code generation between nodes during underwater communication, thus verifying the effectiveness of the CSMA/CA backoff protocol designed in this article. Figure 12.0 Experimental results of dynamic backoff based on CSMA/CA. ## 5 Conclusions

This article mainly researches the AUV multi-node networking communication based on underwater electric field CSMA/CA channel. In the NS-3.31 simulation process, the propagation physical layer of electric field communication in seawater medium was theoretically calculated, and the program parameters of nodes, channels, network devices, and topology structure were set. The results showed that effective communication could be achieved within a range of 14.86 m between two nodes. The transmission characteristics of five nodes under different protocols were analyzed, and the results showed that the OLSR protocol had a smaller routing reception packet delay time and higher reliability than the AODV protocol in a 60 m\(\times\) 60 m area. Then, in response to the signal distortion caused by underwater attenuation, a 2 FSK underwater electric field communication system was established, and dynamic communication experiments were conducted between two AUV nodes. The experimental results show that the system can achieve underwater dynamic electric field communication within the range of 0 to 3.5 m, with an error rate of 0 to 0.628%. Finally, to avoid channel blockage in underwater AUV multi-node communication, this article proposes a dynamic backoff method for AUV multi-node communication based on CSMA/CA.