Raptor-coded free-space optical communications experiment

While free-space optical (FSO) links have many inherent advantages, such as high data rates and license-free operation, they are sensitive to atmospheric conditions. A promising solution to improve the reliability of such communication links is to combine FSO and radio frequency (RF) channels using Raptor codes. This paper presents a first in-field demonstration of real-time Raptor-coded FSO communication over a 1.87 km urban link. This work serves as an important initial step toward field-programmable gate array (FPGA)-based implementation of Raptor-coded hybrid FSO/RF links. The hardware architecture of a Raptor 10 decoder based on a novel resource- and time-efficient matrix inversion algorithm is presented and implemented in an FPGA platform. The receiver is implemented in a pipelined architecture to maximize link utilization. The throughput of the Raptor-coded FSO link is measured both experimentally and numerically under real-life weather conditions for a continuous period of 8 h. Experimental results demonstrate that Raptor-coded FSO links are capable of tracking changes in the channel state to maximize link utilization.