Global Positioning System Reference
In-Depth Information
4. Within Chapter 4, the thermal noise power was computed for a 2 MHz band-
width (approximate null-null bandwidth of the GPS C/A code signal) at 290 K
(typically considered to be ambient temperature).
(a) What would the noise power be for a temperature of 100 K?
(b) What would the noise power be if the two primary lobes of the Galileo L1
BOC (1,1) signal were utilized to define the bandwidth while maintaining
the 290 K temperature?
Comment on the dependence of the resulting noise power from changes in tem-
perature and bandwidth.
5. What is the noise figure of the system depicted in Figure 4.2? What would
it be if a passive antenna were utilized (move the filter and amplifier within the
antenna to after the RF cable)?
6.
160 dBW,
how many satellites must be a collected data set where the front end has a 2 dB
noise figure and the C/A code sinc spectrum appears 2 dB above the filter shape
in the collected data? Now redo the computation assuming the same 2 dB above
the filter shape but now all the power results from a single satellite?
Assuming the received GPS signal power from each satellite is
7. Assume it is possible to implement an ideal bandpass filter. Further assume
that the transmitted signal has infinite bandwidth.
(a) What filter bandwidth is required to capture 98% of the GPS C/A code
power? 98% of the Galileo L1 BOC(1,1) power?
(b) If the filter was designed to capture the first main spectrum lobe [lobes for
the Galileo BOC(1,1) signal] what percent of the total power would that
provide for the GPS C/A code signal? the Galileo L1 BOC(1,1)?
8. The collected data from the front end are represented as 8-bit samples (signed
char format). Develop an M -file to convert this to
(a) 1 bit (
±
1) values,
(b) 2 bit (
±
1
, ±
3).
9. The M -file codegen generates any of the 32 PRN codes used in GPS. Com-
pute the autocorrelation function for PRN 1 and notice the maximum and mini-
mum values. Plot the resulting correlation function.
Hint: The correlation function between two sequences can be computed as
1022
R xy (
n
) =
x
(
l
)
y
(
l
+
n
),
l
=
0
or you may use the M -function xcorr .
Search WWH ::




Custom Search