Which statement best describes the initial computation of pseudorange measurements by a GPS receiver?

• A. It computes pseudorange measurements by correlating the receiver's locally generated code with the satellite's code.
• B. It computes range using Doppler shifts alone.
• C. It uses carrier phase to measure distance.
• D. It does not require any satellite signals.

Answer: (A)

The initial distance estimate comes from code correlation. The receiver generates a replica of the satellite’s C/A code and correlates it with the incoming signal. The peak of this correlation reveals the code phase offset, which is the time difference between when the satellite sent the code and when it was received. This time difference, multiplied by the speed of light, yields the pseudorange value. That pseudorange includes the receiver’s unknown clock bias, which is what makes it a pseudorange rather than a true geometric range. Doppler and carrier-phase measurements are used later for velocity and higher precision, but the first distance estimate is obtained from correlating the locally generated code with the satellite’s code.