GNSS Signal Simulation - A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach - page 146

GNSS Signal Simulation

B.1 GPS Signal Simulation

When implementing the signal processing parts of the GPS receiver, it is neces-
sary to have some data available for testing their functionality. The final goal is to
have a GPS receiver working in real time on data obtained from a GPS antenna
through an RF front end and an ADC. In the phase of developing the signal pro-
cessing algorithms, however, it is not optimal to use real sampled data. The main
reason for this is that it is impossible to control the properties of the received and
sampled GPS signals. It is not only impossible to control the received signals, it
is also impossible to know all the properties of the received signals.
The solution to this problem is to use simulated data. In lack of a suitable GPS
signal simulator, it may be necessary to implement one.
A useful L1 GPS signal simulator should include the following global parame-
ters associated with the downconversion and sampling of the signal:

Intermediate Frequency It should be possible to input the value of the IF. The
IF will then be the reference frequency to which the Doppler shift of the
satellite signals should be compared.

Sampling Frequency It should be possible to input the value of the sampling fre-
quency used to sample the GPS signals.

With the possibility of setting these parameters, it would be possible to test the
algorithms with simulated data with the same properties as the data sampled from
a GPS antenna through an RF front end.