design of gps software receiver

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 =>