Demonstration of Reliable High-Rate Optical Communication over an Atmospheric Link using ARQ

Optical communication systems for satellites in low-Earth orbit are capable of offloading large quantities of sensor data, on the order of terabytes per pass, to a ground terminal or network of ground terminals. NASA plans to demonstrate this capability with the Terabyte Infrared Delivery (TBIRD) program, which leverages fiber-telecom transceivers to burst data down to ground at 200 Gbps during short passes. The cornerstone of the TBIRD architecture is the use of commercial off-the-shelf transceivers, which perform well in fiber channels but do not guarantee reliable communication in space-to-ground atmospheric channels. To address this deficiency, we have built an Automatic Repeat reQuest (ARQ) system on top of the transceivers that enables high-rate error-free communication over fading channels of interest. The ARQ system implements the digital logic required to process custom data frames and uses a low-rate feedback link for frame retransmission requests. To validate the system, we have operated over a several-kilometer atmospheric link. We have successfully demonstrated error-free communication at data rates close to 100 Gbps in a variety of atmospheric fading conditions.