An optical data link for line of sight communications

Abstract

Reliable long distance communications is crucial for Unmanned Aerial Vehicles (UAVs), especially in military applications. Free Space Optics (FSO), using focused, line-of-sight laser communications, can provide the required reliable bi-directional communications channel at high data rates. This dissertation analyses the practical limitations of FSO, in order to enable prediction of the operational range and the bit error rate at specific atmospheric conditions, thus obtaining a measure of reliability. Several circuit topologies were considered, in order to enable transmitting and receiving voltage signals which are directly derived from twisted-pair cables within an Ethernet based connection, without including any additional digital components in order to obtain a cost-effective solution. Test equipment, consisting of hardware and software solutions was specifically designed in order to facilitate fault finding and to enable obtaining a set of results. The system which was designed within this project operated successfully at a data rate of 10Mbit/s with a negligible data rate, due to excellent Signal to Noise Ratio (SNR) levels. When compared to other commercially available systems, operation was achieved at superior operational ranges and at a fraction of the cost. Complete operation at 100Mbit/s could not be obtained, as an initiated connection is not being properly maintained by the connected Network Interface Card (NIC), and as a result further testing and fine-tuning is required in order to obtain full functionality.