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

Underwater magnetic induction communication (UWMIC) provides a low-power and high-throughput solution for autonomous underwater vehicles (AUVs). UWMIC with tri-axis coils increases the reliability of 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 UWMIC 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 5 dB smaller than typical terrestrial fading channels. The results of this paper provide a more power-efficient way to use UWMIC with tri-axis coils.