GPS Receiver-Related Subjects - Fundamentals of Global Positioning System Receivers: A Software Approach - page 308

find discrepancies in the results. As discussed in Sections 5.12 and 9.5, the week
number has 10 bits. It started on January 5/6, 1980, and rolled over on August
21/22, 1999. The week numbers listed here are the values after the roll over.
Each sidereal day is 23 hours 56 minutes and 4.0954 seconds. It is 3 minutes
and 55.9046 seconds shorter than a solar day. When a different set of YUMA
data is used, this time difference must be taken into consideration. Since the
YUMA data are separated by 1 week, the time should be corrected for 7 days.
Some example results are shown in Table 12.1. In this table the satellite number
is listed in column1. Columns 2, 3, 5, and 7 are the Doppler frequency values
obtained from YUMA data 139, 138, 140, and 127, respectively. Columns 4, 6,
and 8 list difference frequencies using the frequencies in column 2 as reference.
The maximum difference frequency in columns 4 and 6 is less than 50 Hz, but
one extra satellite (29) is obtained from data 140. When the YUMA data 127,
which is 12 weeks away from YUMA data 139, is used, the Doppler frequency
calculated can be off by over 500 Hz, as shown in column 8 for satellite number
26. Even with this frequency difference, the carrier frequency search can be

SATELLITE SKYPLOT
NORTH

SATELLITE SKYPLOT
NORTH

31 31

26 26

11 11

28 28

WEST 7 EAST WEST EAST

7

20 8

8 20

27

27

4

4

SOUTH SOUTH

(a) From YUMA 139 (b) From YUMA 138

SATELLITE SKYPLOT
NORTH

SATELLITE SKYPLOT
NORTH

29

26 31

31

26

11 28

28

11

WEST 7 EAST WEST EAST

7

2

8

20

8

20

27

27

4

4

SOUTH SOUTH

(c) From YUMA 140 (d) From YUMA 127
FIGURE 12.1 Satellite constellations from different YUMA data.