title: A simple delay-line 4-PPM demodulator with near-optimum performance.
abstract: We describe a simple 4-PPM demodulator that uses analog delay lines and simple 1-bit comparators to determine the least-significant bit and most-significant bit of the 4-PPM encoded data without additional digital signal processing. We show that with good optical filtering the comparator-based demodulator can theoretically operate with sensitivity only 0.23 dB from the optimum 4-ary receiver. We describe as an example of this approach the demodulator built for the Lunar Laser Communication Demonstration and show measured performance within 1.1 dB of the expected sensitivity. The technique is extendable to higher-order, and higher-symbol-rate orthogonal modulation formats.
authors.affiliation: MIT Lincoln Laboratory 244 Wood Street, Lexington, Massachusetts 02420, USA. stevens@ll.mit.edu
authors.forename: M L
authors.initials: ML
authors.lastname: Stevens
authors.forename: D M
authors.initials: DM
authors.lastname: Boroson
mesh_terms: D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007834:Lasers; D055096:Optical Devices; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D013685:Telecommunications / Q000295:instrumentation*