The GNSS measured distance is called a pseudo-range because it has a constant bias error due to the clock error of the ______.

• A. Receiver
• B. Computer
• C. Observer
• D. Satellite

Answer: (A)

The measured distance from GNSS satellites is called a pseudo-range because the receiver’s internal clock is not synchronized to GNSS time. This creates a constant time error in the time-of-flight measurement, which translates into a bias in distance equal to the speed of light times the receiver clock error. Since the true geometric distance would require perfect timing, this extra bias makes the measurement a pseudo-range rather than a true range.

In practice, this receiver clock bias is treated as an unknown to be solved for along with the receiver’s position (and sometimes atmospheric parameters). Satellite clock errors exist as well, but those are addressed through the navigation messages and corrections; the remaining uncalibrated part that appears in the measurement and must be estimated is the receiver clock bias. That’s why the correct understanding is that the constant bias comes from the receiver’s clock error.