The PRN codes repeat themselves over specific intervals. What are the periods of those cycles, and what is their significance?

• A. The P code repeats every 2 weeks; the C/A code repeats every second.
• B. The P code repeats every 38 weeks with each week assigned to a different satellite; the C/A code repeats every millisecond (1023 codes per second) with a different code per satellite.
• C. The P code repeats every year; the C/A code repeats every 10 seconds.
• D. Both codes repeat every 38 weeks with identical patterns across satellites.

Answer: (A)

PRN codes are spread-spectrum sequences that GPS satellites use to let receivers identify and distinguish signals from different satellites while measuring precise ranges. The C/A code, the one most often discussed for civilian receivers, is a short 1023-chip sequence that repeats every 1 millisecond. That rapid repetition makes acquisition fast and allows continuous tracking with a well-defined code phase that repeats each millisecond. Each satellite has its own C/A code sequence, so the code seen on the air is distinct per satellite.

The P code is a much longer sequence that repeats on a weekly cycle within the GPS week. It provides higher precision for pseudorange measurements and is encrypted for authorized users as the P(Y) code. Because the P code runs over a longer cycle, receivers can rely on a more stable and robust ranging signal, which is important for high-accuracy applications.

The key significance is that the short, rapidly repeating C/A code enables quick acquisition and broad accessibility, while the long, weekly-repeating P code supports higher-precision timing and positioning. The other proposed time scales don’t match how GPS PRN codes operate.