The pseudo random code (prc) is a fundamental part of gps. Physically it’s just a very complicated digital code, or in other words, a complicated sequence of “on” and “off” pulses.the signal is so complicated that it almost looks like random electrical noise. Hence the name “pseudo-random”
There are two types of pseudo-random code.
The first pseudo-random code is called the c/a (coarse acquisition) code. It modulates the l1 carrier. It repeats every 1023 bits and modulates at a 1 mhz rate. Each satellite has a unique pseudo-random code. The c/a code is the basis for civilian gps use.
The second pseudo-random code is called the p (precise) code. It repeats on a seven day cycle and modulates both the l1 and l2 carriers at a 10 mhz rate. This code is intended for military users and can be encrypted. When it’s encrypted it’s called “y” code.
Since p code is more complicated than c/a it’s more difficult for receivers to acquire. That’s why many military receivers start by acquiring the c/a code first and then move on to p code.