GPS satellites transmit two types of carrier signals, namely L1 carrier with a frequency of 1575.42MHz and L2 carrier with a frequency of 1227.60Mhz. Their frequencies are 154 times and 120 times that of the basic frequency 10.23MHz, respectively, and their wavelengths are 19.03cm. And 24.42cm. A variety of signals are separately modulated on L1 and L2. These signals mainly include:
C/A code
The C/A code is also called a coarse acquisition code. It is modulated on the L1 carrier and is a 1MHz pseudorandom noise code (PRN code) with a code length of 1023 bits (period of 1ms). Because the C/A code of each satellite is different, we often use their PRN numbers to distinguish them. The C/A code is a main signal used by ordinary users to determine the distance between the station and the satellite.
P code
The P code is also known as the fine code. It is modulated on the L1 and L2 carriers and is a 10MHz pseudo-random noise code with a period of seven days. In the implementation of AS, P code and W code are added modulo two to generate a secret Y code. At this time, general users cannot use P code for navigation and positioning.
Y code
See P code.
