MATLAB Code - A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach - page 142

function processes the block of the samples and returns two structures: tracking
results trackResults and an updated structure channel .
Structure channel is used to pass initial information for each channel and is
also used to store information on the current channel. The second purpose of
this structure is to make the tracking continuous. In this way, processing of two
or more signal blocks can be made continuous. The structure contains current
(from last processed ms) information on the carrier frequency, code phase, PRN
number of the track satellite, temporal values for the loop filters, and local signal
generators.
The parameters for carrier tracking are contained in the settings structure
PLL_dampingRatio Damping ratio.
PLL_noiseBandwidth Noise bandwidth of the PLL.
The list below is the code tracking specific variables contained in the settings
structure:
DLL_CACorrelatorSpacing Spacing between the early and late correlators, unit
of chip.
DLL_dampingRatio Damping ratio for the delay lock loop.
DLL_noiseBandwidth Noise bandwidth of the delay lock loop.
The structure trackResults is the main output from tracking function. It con-
tains results for all channels and for each ms of the processed block: information
about signal properties (carrier frequency and code phase) and outputs from all
six correlators and the loop discriminator.
The output from the tracking code is used as input for the postNavigation func-
tion. Additional information is used to plot tracking results and to analyze per-
formance of the receiver. Execute command plotTracking to plot results for any
individual channel.

A.5 Function postNavigation

The function starts by finding bit transitions and preamble locations. Then the bit
values are obtained. The ephemerides are decoded. This involves only information
from subframes 1, 2, and 3. Also decoding of subframes 4 and 5 may be included;
see Figure A.4.
Next the function calls the pseudorange measurement function and computes
position coordinates. Pseudorange and position computations are done covering a
specified period described in the receiver settings .
The input for the function is the tracking results and settings structure and the
output is pseudoranges and receiver coordinates.
The function postNavigation reads the following variables:
navSolPeriod Tells the software how often pseudoranges and position should be
computed.