Global Positioning System Reference
In-Depth Information
sequence for the first 10 chips of PRN 5 C/A code is 1001011011 and for the first 12
chips of PRN 5 P code is 100011111111. Note that the first 12 P code chips of PRN
10 through PRN 37 are identical. This number of chips is insignificant for P code, so
the differences in the sequence do not become apparent until later in the sequence.
4.3.2 Power Levels
Table 4.5 summarizes the minimum received power levels for the three GPS signals.
The levels are specified in terms of decibels with respect to 1W (dBW). The specified
received GPS signal power levels [10] are based on a user antenna that is linearly
polarized with 3-dB gain. Since the GPS SVs transmit RHCP signals, the table is
adjusted for a typical RHCP antenna with unity gain and also accounts for the
polarization mismatch adjustment that is included in the SV link budget for their
RHCP antenna array (see Table 4.6). The RHCP antenna unity gain can be
expressed as: 0 dBic
0 dB with respect to an isotropic circularly polarized antenna.
The resulting RHCP antenna received signal levels are slightly stronger than the
minimum specified received signal, since the linear polarization mismatch is not
double counted in the receiver RHCP antenna. However, this should be considered
as receiver design margin and the specified minimum received power levels used for
worst-case analysis.
Figure 4.12 illustrates that the minimum received power is met when the SV is at
two elevation angles: 5º from the user's horizon and at the user's zenith. In between
=
Table 4.5
Minimum Received GPS Signal Power
L2 P(Y) Code
or C/A Code
L1 C/A Code L1 P(Y) Code
User minimum received power at 3-dB
gain linearly polarized antenna (dBW)
158.5
161.5
164.5
Adjustment for unity gain antenna (dB)
3.0
3.0
3.0
Adjustment for typical RHCP antenna
versus linearly polarized antenna (dB)
3.4
3.4
4.4
User minimum received power at unity
gain RHCP antenna (dBW)
158.1
161.1
163.1
Table 4.6
L1 and L2 Navigation Satellite Signal Power Budget
L1 C/A Code
L1 P Code
L2
User minimum received power
158.5 dBW
161.5 dBW
164.5 dBW
Users linear antenna gain
3.0 dB
3.0 dB
3.0 dB
Free space propagation loss
184.4 dB
184.4 dB
182.3 dB
Total atmospheric loss
0.5 dB
0.5 dB
0.5 dB
Polarization mismatch loss
3.4 dB
3.4 dB
4.4 dB
Required satellite EIRP
26.8 dBW
23.8 dBW
19.7 dBW
Satellite antenna gain at 14.3º
worst-case BLK II off-axis angle (dB)
13.4 dB
13.4 dB
11.5 dB
13.4 dBW
21.9W
10.4 dBW
11.1W
8.2 dBW
6.6W
Required minimum satellite
antenna input power
 
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