Hybrid OCS/MDRZ wavelength division multiplexing millimeter wave radio over free space system

Free space optics has been a subject of interest since few decades ago due to its huge unlicensed spectrum, huge data carrying capacity and immunity to electromagnetic interference among other reasons. In this paper a novel technique for conveying 40 GHz frequency doubled Optical Carrier Suppressed (OCS) millimeter wave radio signals over free space has been proposed and simulated. After suppression of the carrier frequency the baseband data was modulated using Modified Duobinary Return to Zero in the electrical domain onto the lower sideband. A coupler was then used to combine the sidebands and such wavelengths from 8 transmitters were multiplexed and launched in free space through diversity technique. The maximum distance in the downstream (towards receiver) was 4.609 km in clear weather. The proposed architecture was very effective for upstream data transmission. It greatly improves the upstream bit error rate as compared to an architecture were all the sidebands were carrying data in the downstream.