Spread Spectrum Modulation - Digital Communication: Principles and System Modelling - page 157

Bits

10 01 10 10 01 00 00 11

0

Time

PN Code 100 101 001 101

Fig. 7.15 Frequency variation over a complete period of the PN sequence

It is transmitted at a rate of 50 bps and repeated cyclically. The message contains
information about the positions of the satellites, data to correct errors in propaga-
tion time, satellite clock bias, etc. a method of producing L1 signal is depicted in
the Fig. 7.17 .
The control segment consists of 5 monitor stations (Hawaii, Colorado Springs,
Ascension Islang, Diego Gracia and Kwajalan Island), four ground stations and
operational control centre. All the monitor stations except Hawaii contain ground
antenna upload stations. The clocks of the satellites are synchronized by a ground
station of California. It also supplies the positions of the satellites obtained from