Overlaying multiple users in acoustic communications using MIMO spatial diversity equalization

The available bandwidth of ocean acoustic channels is inherently narrow which impedes high transmission rate and makes it difficult for multiple users to communicate simultaneously. To alleviate this problem, spatial diversity antennas are used in an ocean environment to increase the data rate. We apply spatial diversity equalizers (SDE) to ocean acoustic channels and show that multi-user communication is possible despite the narrow channel bandwidth. In addition, we show that the advantage of SDE is not because of the use of more taps, but because of the data carried through various ocean paths. By applying the saddle point integration method to multi-input multi-output (MIMO) channels, we compute the probability of error (PE) to show that a factor of 3-4 of channel reuse is possible.