Title of Presentation: A Receiver Architecture for a Photon Counting Optical PPM Communications System

Primary (Corresponding) Author: Jonathan W. Gin

Organization of Primary Author: NASA Jet Propulsion Laboratory

Co-Authors: Danh H. Nguyen, and Kevin J. Quirk

Abstract: In a deep space optical communications link the limited transmit power and distances will require the receiver to operate in a photon starved regime. Under these conditions large effective receiver apertures, achieved through the use of an optical receiver array, photon counting detectors, and powerful error-correcting codes are used to enable high data rate communications. In order to utilize the array and coding gains the receiver must frst be synchronized to the received signal without the benefits of an array architecture or error correction-code. The design of a signaling format that effciently trades off allocating a portion of the transmit energy and or throughput for synchronization becomes paramount; the complexity of realizing the signaling format and its associated synchronization techniques in a parallelized hardware architecture necessitated by high data rates must also be considered.

Areas to be presented are an optical pulse position modulation (PPM) signaling scheme using an intersymbol guard time, a technique that inserts a fixed delay between symbol transmissions, for timing and synchronization, a realizable receiver architecture able to support high data rates for an optical array, and an architecture for a scalable distributed decoder. A hardware prototype implementation of a 150 Mbps, 16 PPM receiver developed at the Jet Propulsion Laboratory and integrated within an optical communications test bed is described. This prototype takes as input the electrical output from a photon counting detector and synchronizes and demodulates the PPM modulation producing estimates which are passed to the decoder. Finally, results demonstrating the receiver operation in an end-to-end test bed are discussed.