User`s guide

Chapter 2 - NAVSTAR GPS Overview

Figure 2.1 NAVSTAR GPS Segments

The GPS navigation message is the data supplied to the user from a satellite. Signals are

transmitted at two L-band frequencies, L1 and L2, to permit corrections to be made for

ionospheric delays in signal propagation time in dual frequency receivers. The L1 carrier is

modulated with a 10.23 MHz precise (P-code) ranging signal and a 1.023 MHz coarse acquisition

(C/A code) ranging signal.

NOTE: The P-Code is intended for military use

and is only available to authorized users

using special receivers.

The P and C/A codes are pseudo-random-noise (PRN) codes in phase quadrature. The L2 signal

is modulated with the P-code only. Both the L1 and L2 signals are also continuously modulated

with a data stream at 50 bits per second. The P-code is a PRN sequence with a period of 38(+)

weeks. The C/A code is a shorter PRN sequence of 1023 bits having a period of one millisecond.

Motorola GPS Products - M12+ User's Guide Revision 6.X 09FEB05