design of gps software receiver
TRANSCRIPT
GLOBAL NAVIGATION SATELLITE SYSTEMS
(FINAL PROJECT REPORT)
A GPS software receiver has been designed in this project for acquisition and tracking of the
GPS signals code, carrier phase and carrier frequency.
The main design processes for the design of the software receiver are:
Coarse Acquisition: The main motive of coarse acquisition is for detection of the GPS
satellite signal and a rough estimation of the carrier Doppler frequency and the CA code
phase. The course acquisition is computed in the frequency domain (FFT method).
Fine Acquisition: After a rough estimate of Doppler frequency is done, fine acquisition
is performed. The known coarse Doppler frequency and the code phase is wiped off and
fine frequency acquisition is acquired by Carrier phase method (Considering conditions
for Navigation data bit transition).
Tracking: Tracking can be regarded just as a more refined acquisition process. The only
difference is that acquisition aim to achieve rough estimations while tracking seeks
precise estimations. Tracking mainly consists of four main modules:
Correlators – It performs various correlation calculations between the input signal
and a reference signal. The sole purpose of the correlators is to find the best match
between a reference signal and the input signal.
Discriminators – It is a function that allows us to gain a direct measure of one
signal parameter whilst on the other hand, it suppresses any variations caused by
other signal parameters.
Filters – As per the name, they filter the noise in the discriminator output. In order
to reduce the impact of noise on the accuracy of the discriminator outputs,
appropriate filtering is essential. Typically, LPFs are used that will allow the
features associated with the signal parameters to pass and smooth out the noise
effects.
Reference Generation – After all this, a reference signal is generated using the
fresh parameters like carrier phase, code phase, and carrier Doppler and this
signal is again fed back to the correlator for processing of the next block. This
process repeats itself continuously as long as the receiver is in operation.
This basically, is the concept of tracking.
Following are the detailed plots for GPS signal acquisition and tracking from the files
class_1.25_5.sc4 (PRN: 11 & 14) & g072602f.dat (PRN: 18 & 23)
1. PRN 11 =>
2. PRN 14 =>
3. PRN 18 =>
4. PRN 23 =>