GPS Receiver-Related Subjects - Fundamentals of Global Positioning System Receivers: A Software Approach - page 309

narrowed from 500 Hz. In order to keep a more accurate

Doppler frequency, YUMA data close to the specific date should be used.
The satellite constellation for the given time and user position is shown in
Figure 12.1. In these figures the constellations are obtained from YUMA data
139, 138, 140, and 127. It shows that the constellations are quite similar, even
though YUMA 127 is more than 10 weeks away from the other three YUMA
data sets.
If there are errors in the given desired time and user location, it is important to
know the variation of Doppler frequency, which is used in acquisition. Again, for
the time and user location selected earlier, but with errors deliberately introduced,

± 5 kHz to about ±

TABLE 12.2 Doppler Frequencies Calculated Using Different Time and Location

Reference: Time: 2002 April 25, 8 o'clock AM 04 min 00 sec

Location: Latitude: 39.7772 Longitude: − 84.0821 Altitude: 179.2

1 2 3 4 5 6 7 8 9 10

Time off
(min) 0 1 − 1 1 − 1

Latitudinal
distance
off (Km)

0 100 100 − 100 − 100

Longitudinal
distance
off (Km) 0 100 100 − 100 − 100

Frequency
Off

Frequency
Off

Frequency
Off

Frequency
Off Satellite Doppler Doppler Doppler Doppler Doppler

Hz Hz Hz Hz Hz Hz Hz Hz Hz

4 3928 3935 − 7 3938 − 10 3914 14 3920 8

7 1525 1588 − 63 1620 − 95 1427 98 1460 65

8 − 2647 − 2729 82 − 2669 22 − 2624 − 23 − 2563 − 84

11 − 1507 − 1474 − 33 − 1406 − 101 − 1604 97 − 1539 32

20 2698 2752 − 54 2763 − 65 2630 68 2642 56

26 − 1528 − 1625 97 − 1575 47 − 1481 − 47 − 1430 − 98

27 − 3686 − 3712 26 − 3692 6 − 3680 − 6 − 3657 − 29

28 803 784 19 829 − 26 776 27 818 − 15

31 − 3274 − 3286 12 − 3290 16 − 3257 − 17 − 3263 − 11