Design and Analysis of a First-Generation Optical Pulse-Position Modulation Receiver

In this article, the requirements and design of a prototype pulse-position modulation (PPM) receiver are considered. This article focuses on a prototype optical receiver concept that will be used to demonstrate and validate optical reception under conditions representative of deep-space communications, where Earth and spacecraft dynamics must be taken into account. The system will rely on PPM, which is a viable high-data-rate format that enables the use of high-peak-power lasers for interplanetary communications. The design incorporates an amplifler front end that provides the required dynamic range, along with a capability to evaluate various detectors, including photo-multiplier tubes and avalanche photodiode detectors. The digital section is designed to achieve and maintain PPM slot and frame synchronization, detect PPM symbols, estimate range, and eventually interface with decoding equipment. These receiver functions will be implemented using fleld-programmable gate arrays. This prototype receiver will provide a test bed for validating optical communications concepts in the laboratory, over mountain-to-mountain terrestrial links, and eventually with retrore∞ected signals from Earth-orbiting satellites.