In GNSS, a pseudo-range measurement is biased by clock error of which component?

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

Answer: (B)

In GNSS, a pseudorange is built from the time of flight of the signal, converted to a distance by multiplying by the speed of light. The timing reference comes from the receiver’s local clock, which is not synchronized to GPS time. This means any offset of the receiver’s clock from true GPS time directly adds a bias to the measured pseudorange, proportional to c times that offset. The satellite clock errors do exist, but they are accounted for in the system corrections and the navigation solution, whereas the unmodeled bias that shows up directly in the measurement is the receiver’s clock error. So the receiver’s clock offset is what biases the pseudorange measurement. For example, a 1 microsecond error in the receiver clock would skew the pseudorange by about 300 meters.