On the Capacity of MIMO Optical Wireless Channels

This paper investigates the capacity of the multiple- input multiple-output free-space optical intensity channel under a per-input-antenna peak-power constraint and a total average-power constraint over all input antennas. Our work considers the setup with more transmit than receive antennas, and characterizes capacity as an alternative optimization problem over the distribution of the input vector times the channel matrix. This alternative capacity expression is then used to obtain upper and lower bounds on the capacity, which match asymptotically in the high signal-to-noise ratio regime.