GPU receivers for deep space optical communications

The NASA/JPL Deep Space Optical Communication (DSOC) project has demonstrated high-bandwidth data downlink from over 3 AU using the High Photon Efficiency (HPE) modulation scheme. The DSOC flight terminal transmits its laser signal to the 5m Palomar Hale Telescope, where it is detected with a superconducting nanowire single photon detector (SNSPD) and digitized with a time-to-digital converter (TDC). Once digital, we process the signal with a new Graphics Processing Unit (GPU)-based decoder in lieu of a standard FPGA-based decoder. The GPU-based decoder includes synchronization and the Bahl-Cocke-Jelinek-Raviv (BCJR) error correction algorithm. The GPU-based system successfully decoded a 75 Megabits per second (Mbps) signal in real time from DSOC at a distance of 1.5 AU, establishing a new record for data rate from this distance. In this paper, we describe the algorithms, implementation, and performance of the GPU-based decoder system.