MATLAB Code - A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach - page 141

tracking.m return

yes

predefine arrays,
seek in file to
acquisition result,
and set PRN to
processed

all channels
processed?

no

yes

read in one
millisecond of
data to process

all data
processed?

no

generate sine
and cosine local
oscillator
signals and mix
to baseband

compute loop
discriminators,
apply filters, and
update code/carrier
frequencies

correlator PRN
code replicas with
downconverted
data to obtain: I E ,
I P , I L , Q E , Q P , Q L

generate early,
prompt, and
late code
period replicas

FIGURE A.3. GNSS tracking flow diagram.

acq_searchBand Specifies the frequency band in which to search for satellite sig-
nals, kHz integer. It is centered around the IF. While searching for available
signals the acquisition function uses steps of 0.5 kHz.
acq_threshold Determines the threshold of the signal detector.

The output is an array structure acqResults containing search results for all
satellites specified in acq_satelliteList . If a satellite signal is detected, the field
signalDetected is set to 1 for that particular satellite.

A.4 Tracking Function

This function tracks the GPS signals allocated to each channel; see Figure A.3.
The function takes the following parameters: a block of the recorded signal
from the front end, structure channel , sine, cosine, and C/A code tables. The