Specialized mixed-signal (radio frequency and digital) hardware and processing techniques are employed to enable processing of the multi-GHz signal bandwidth, along with the instruction of an inter-symbol guard time (ISGT) to facilitate synchronization to the received pulse-position modulation (PPM) signal.
The receiver performs signal detection, synchronization, and channel estimation of an optical PPM with ISGT modulated signal incident on a photoncounting detector. The receiver takes as input the electrical output of a photon-counting detector, and outputs, via a XAUI 10-Gb/s quad optical fiber interface, a time series of 4-bit Poisson log-like-lihood ratio for each PPM slot. Slot rates between 125 MHz and 2 GHz are supported corresponding to data rates of 30 to 470 Mb/s. The receiver supports interconnection with Deep Space Network (DSN) timing and frequency standards, and is controlled through a 1-Gb/s Ethernet UDP/IP (User Datagram Protocol/ Internet Protocol) interface.
A deep-space optical communication link has not yet been demonstrated. This ground station receiver was developed to demonstrate this capability, and is unique in its ability to process such a signal.