The following information obtained from UNAVCO's online DOI system:
(https://www.unavco.org/data/doi/search/search.html)

GGN GPS Network - USN7-U.S. Naval Observatory Time Service P.S.
Start: 10-Dec-2014
End: 14-Nov-2022
Powers, Edward, Stowers, David A., 2014, GGN GPS Network - USN7-U.S. Naval Observatory Time Service P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5S75DNR