Shadowing and blockage in indoor optical wireless communications

In this paper, we investigate vulnerability of a so called "cellular" and that of a multi-spot diffusing (MSD) multi-input-multi-output (MIMO) architecture to shadowing and its effect on communications cell size and the required transmit power. Because signal path obstruction by furniture is easier to predict and avoid, we are mainly concerned with shadowing and blockage caused by people either sitting or standing. To avoid blockage of communication link by a user of portable units, maximum radiation angle at the transmitter in both configurations must not exceed 45°. This restricts communication cell size. We show the probability of blockage of a cellular link depends almost linearly on the distance of the portable unit from the communication cell center. Unlike cellular links, MSD-MIMO links can be designed to be robust against blockage, though still vulnerable to shadowing. In a typical office having a height of 3 m, probability of shadowing is less than 2% and in majority of cases shadowing causes less than 50% reduction in the received signal power. Power penalty due to shadowing is insignificant (less than 0.1 dB) with a 1% outage.