Free download at IGS (1.3 MB)
http://acc.igs.org/understanding-GPS_Ch03.pdf
"GPS System Segments" by A.J. Dorsey, W.A. Marquis, P.M. Fyfe, E.D.
Kaplan, & L.F. Widerholt (in Understanding GPS -- Principles and
Applications, E.D. Kaplan & C.J. Hegarty, eds., Artech House, Chapter
3, pp. 67-112, 2006)