Measurement Approaches and Implementation of a Fading Characterization Tester for Evaluating Optical Turbulent Channels

Optical wireless communication (OWC) systems can exhibit high percentage availability, yet suffering from frequent intensity fades caused by turbulence effects and pointing errors. The intuitive method to character the link is using commercial bit error rate testers (BERT) by measuring the output sequence of the receiver, which provides limited information. Thus we propose the algorithms for measuring the outage and synchronization performance, bit error rate (BER), throughput, and fading statistics. The inputs consist of decoded data sequence and received optical power. Both the bit level and packet level measurements are presented. Then a fading characterization tester (FCT) having these functions is implemented based on a field programmable gate array (FPGA). Our indoor experiment reveals the measurement accuracy of the FCT by comparing the measured results with the derived theoretical ones. Another 1.9 km OWC experiment is also carried out. These measured results by FCT are presented, which can not only measure the OWC link, but also help the researchers to improve the system performance, such as the design of error correction approaches like forward error correction, the design of packet based network protocols.