The PRN signal code used by GPS is repeated every how many milliseconds?

The PRN signal code used by GPS is repeated every how many milliseconds?

• A. 1 millisecond
• B. 1 microsecond
• C. 1 second
• D. 1 nanosecond

Answer: (A)

The GPS PRN code uses a C/A code that is 1.023 Mbps and consists of 1023 chips per epoch. At that chip rate, transmitting 1023 chips takes 1023 / 1.023e6 seconds, which is about 0.999 milliseconds—essentially 1 millisecond. So the entire PRN sequence repeats every about 1 ms. This millisecond repeat interval is why the correct choice is 1 millisecond: it defines the code epoch used for measuring code phase and determining pseudorange to the satellite. The other intervals (microseconds, seconds, or nanoseconds) don’t match the code epoch determined by the 1023-chip sequence at the 1.023 Mbps rate.

The GPS PRN code uses a C/A code that is 1.023 Mbps and consists of 1023 chips per epoch. At that chip rate, transmitting 1023 chips takes 1023 / 1.023e6 seconds, which is about 0.999 milliseconds—essentially 1 millisecond. So the entire PRN sequence repeats every about 1 ms. This millisecond repeat interval is why the correct choice is 1 millisecond: it defines the code epoch used for measuring code phase and determining pseudorange to the satellite. The other intervals (microseconds, seconds, or nanoseconds) don’t match the code epoch determined by the 1023-chip sequence at the 1.023 Mbps rate.