The  proliferation  of  small  satellites  offers  new  opportunities  for  space  communications.  Current  satellite  constellations  use  radio  frequency  (RF)  links  to  communicate  with  ground  stations  and  user  terminals.  However, free-space optical communications technologies can achieve higher data rates while using lower SWaP (Size, Weight, and Power) hardware than their RF counterparts.This  project  proposes  to  investigate  future  high-capacity  free-space  optical  satellite  networks,  initially  focusing on near-earth links that are anticipated to have the largest bandwidth demands, eventually extending the  investigation  to  include  longer-distance  links  that  are  relevant  to  NASA’s  deep-space  exploration  missions.  Of  particular  interest  is  the  study  of  enhancements  to  NASA’s  Laser  Communication  Relay Demonstration (LCRD), scheduled for launch in the 2020 timeframe.   LCRD uses multi-rate, burst-mode, Differential  Phase  Shift  Keying  (DPSK)  optical  transmitters  and  optically-preamplifed,  direct-detection receivers,  based  on  passive  delay-line  interferometers.    Since  these  transceivers  are  becoming  a  NASA  standard  for  high-rate  laser  communications,  any  improvements  to  their  performance  will  directly  benefit  NASA’s space program. 


In this project, we will examine three different approaches for performance improvement: 

  • Increasing data rates using higher-order DPSK constellations (e.g., 4- and 8-DPSK).
  • Improving DPSK receiver sensitivity using multi-symbol differential detection schemes.
  • Using alternative modulation formats with direct-detection and coherent optical receivers


We  will  assess,  both  theoretically  and  experimentally,  the  advantages  and  disadvantages  of  these  approaches in terms of complexity, power-requirements, and outage probability in the context of disruption-tolerant, free-space optical satellite networks.

Contact Info

Mail John Roudas
Electrical and Computer Science
Montana State University
Bozeman, MT 59717
E-mail: John Roudas
Phone: (406) 994-5960
Website: John Roudas