# On Reliability of Underwater Magnetic Induction Communications with Tri-Axis Coils

## TL;DR

This paper analyzes the reliability and multiplexing capabilities of underwater magnetic induction communications using tri-axis coils, demonstrating that reliable communication is achievable without mutual inductance information and providing insights into power-efficient design.

## Contribution

It introduces coil selection strategies for UWMICs with tri-axis coils, analyzing performance without mutual inductance information and multiple users, which is novel.

## Key findings

- Reliability can be achieved without using all coils or mutual inductance information.
- Multiplexing gain is 5dB lower than terrestrial fading channels.
- Power-efficient coil selection enhances underwater communication performance.

## Abstract

Underwater magnetic induction communications (UWMICs) provide a low-power and high-throughput solution for autonomous underwater vehicles (AUVs), which are envisioned to explore and monitor the underwater environment. UWMIC with tri-axis coils increases the reliability of the wireless channel by exploring the coil orientation diversity. However, the UWMIC channel is different from typical fading channels and the mutual inductance information (MII) is not always available. It is not clear the performance of the tri-axis coil MIMO without MII. Also, its performances with multiple users have not been investigated. In this paper, we analyze the reliability and multiplexing gain of UWMICs with tri-axis coils by using coil selection. We optimally select the transmit and receive coils to reduce the computation complexity and power consumption and explore the diversity for multiple users. We find that without using all the coils and MII, we can still achieve reliability. Also, the multiplexing gain of UWMIC without MII is 5dB smaller than typical terrestrial fading channels. The results of this paper provide a more power-efficient way to use UWMICs with tri-axis coils.