BER performance of MIMO diffuse free-space optical systems

In this paper, Multiple-Input Multiple-Output (MIMO) technology is applied to difiuse free-space optical (DFSO) links. We compare the theoretical BER performance of simulated MIMO and Single-Input Single-output (SISO) optical links in an indoor office environment. An iterative site-based simulation tool is used to determine the impulse response of wireless infrared (IR) channels for specified locations within a room. For our purposes, we use a MIMO 4 × 4 orthogonal space-time block code. Using this scheme a BER calculation is done based on received signal power and the corresponding channel gains. By setting a BER threshold within which the system can operate, we are able to see the coverage area provided by MIMO and SISO DFSO system architecture. We simulate a stationary transmitter while the receiver is moved through 735 difierent locations in the room, resulting in a BER contour plot of the system for a specified room. Simulation results show that by using 4-element arrays at both ends of the link, along with space-time block coding techniques, allows the effiective coverage area to be increased by approximately 4 times. Also, when operating with a BER threshold of 10-3, the MIMO architecture requires up to 15dB less signal power than the SISO architecture to remain below the threshold. An optical testbed is used to begin hardware validation of our theory, both with and without optical orthogonal frequency division multiplexing (OFDM) techniques. We provide initial measurement results for the proposed optical system.