Global Positioning System Reference
In-Depth Information
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[77
Lin
—
0.3
——
No
*PgE
Figure 3.8
Digital modulation methods.
One of the tasks to be accomplished is reading the navigation message at the
receiver. We need this information to compute the positions of the satellites. To
accomplish this, the data streams (a) and (b) in Figure 3.9 are modulo-2 added
before transmission at the satellite. Modulo-2 addition follows the well-known rules:
0
[77
0. The result is labeled (c). The figure also
shows the phase history of the transmitted carrier. Whenever a binary 1 occurs in the
+
0
=
0, 1
+
0
=
1, 0
+
1
=
1, and 1
+
1
=
Figure 3.9
Modulo-2 addition of binary data streams.
