Angular MIMO for Underwater Wireless Optical Communications: Channel Modelling and Capacity

An alternative architecture for imaging multiple-input/multiple-output (MIMO) underwater wireless optical communications (UWOCs) is proposed which relies on the transmission in angle rather than directly in space. The angular MIMO (A-MIMO) system has advantages over conventional underwater MIMO systems (C-MIMO) in that the image magnification is invariant to link range, and angular transmission greatly relaxes the alignment requirements of such links. These features are especially important for underwater wireless sensor networks (UWSNs), where the maintaining alignment between underwater vehicles and floating sensors nodes may be difficult in such dynamic environments. In this paper, we describe the architecture of A-MIMO for underwater channels and numerically characterize it in clear and coastal seawater conditions. For comparison a C-MIMO underwater system with similar parameters is also characterized and the channel capacities for A-MIMO and a C-MIMO are contrasted against link distances and misalignment errors. The numerical results show that A-MIMO maintains the link capacity against the misalignment conditions far better than C-MIMO while using a smaller size transceiver.