Interference cancellation in multiuser acoustic underwater networks using probabilistic SDMA

Combating interference is an important yet challenging issue for multiuser communications especially in the harsh underwater acoustic environment. In this paper, a novel Angle-Of-Departure (AOD)-based technique is proposed, which accounts for the inherent position uncertainty of underwater propeller-driven Autonomous Underwater Vehicles (AUVs) or buoyancy-driven gliders. A new probabilistic Space Division Multiple Access (SDMA) technique is studied using confidence interval estimation, and an effective approach to manage interference statistically is discussed. Also, an optimization problem is proposed to mitigate multiuser interference while keeping the transmitter antennae beam width at a desirable value so to find a trade off among (i) spreading the beam towards the receiver to combat position uncertainty, (ii) focusing such beam to minimize dispersion, and (iii) minimizing interference to other vehicles in the surrounding. Solutions and algorithms are proposed to overcome the multiuser interference via a hybrid SDMA-Time Division Multiple Access (TDMA) method. Simulation results show that the solution mitigates statistical interference, lessens packet retransmission rate, and obtains Signal-to-Interference-plus-Noise Ratio (SINR) gain and rate efficiency over conventional TDMA and SDMA methods.