Free space optical communication based outdoor wireless sensor node data acquisition using 532 nm laser

Free-Space Optical Communication (FSOC) system uses light as a medium to transfer information wirelessly along free-space. FSOC system that uses visible lasers typically uses the commonly available Red lasers. This paper implements a laser based FSOC system for outdoor use, particularly under sunlight condition, to transfer sample temperature data within a distance of 10 meters. A transmitter modulates the laser using On-Off keying and the receiver uses two phototransistor — one for receiving laser signal and the other as a reference on the ambient light present within the receiver cover. Testing is done using Red and Green laser one at a time for both day time and night time conditions to obtain the Bit-Error-Rate (BER) of the system. The Two-tailed T-test of the experiment results shows a T-value within the critical values which indicates the acceptance of the null hypothesis that Green laser has no observable advantage and disadvantage over Red laser on both night time and day time within a 10 meter gap. Testing also shows that the system performs practically the same under day time and night time condition which suggest the resilience of the system to ambient light inside the receiver cover caused by sunlight.