Global Positioning System Reference
In-Depth Information
Figure 6.4
Positioning errors due to noise.
The second approach to temporal measurement is to use the phase of the
carrier. A pure unmodulated signal is a sine wave with its phase varying between
0 and 360 degrees over each cycle. If such as signal is compared with time
reference, a phase measurement can be taken. Thus two similar signals can be
compared and the time shift expressed as a phase difference, as shown in Figure
6.5.
Figure 6.5
Phase shift between signals.
If a reference carrier is produced locally in the receiver and compared with
the incoming signal, there will be a fixed offset between the actual cycles. For
example, carriers would normally be pure sine waves that have regular zero-
