GPS Signal
The signal
leaves from GPS satellite antenna with a combination of the three components:
- Carrier wave
- Ranging codes
- Navigation Message
GPS Satellites transmit
frequencies L1=1575.42 MHz and L2=1227.6 MHz modulated with two types of code,
P-code and C/A code and with navigation message. Fundamental frequency is 10.23
MHz and can be modify to different frequency. This P-Code and C/A code come
with two carrier frequency L1 and L2.
Modernization of GPS Signal
GPS codes and carrier phase
P(Precise) Code
P-code PRN
code is 6.1871 × 1012 bits long
The C/A code
is a repeating 1 MHz Pseudo Random Noise (PRN) Code
Each
satellite repeats its portion of the P code every 7 days
P code is
unique for each satellite
P-code was
modulated with the W-code to generate the Y-code
Users can’t access the P Code and Y code on both L1 and L2 without an
encryption key.
P-Code modulates both the L1 and L2 carrier phases
C/A Code
The C/A Code (Coarse Acquisition) modulates the L1 carrier phase.
The C/A code repeats every 1023 bits (one millisecond)
Navigation Message
Navigation Message modulates the L1-C/A code signal
The Navigation Message is a 50 Hz signal consisting of data bits that
describe the GPS satellite orbits.
The Navigation Message corrects Clock corrections, and other system
parameters.
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