GNSS Signal Simulation - A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach - page 153

AW GN

B-FFT
Spectrum
Scope

Zero-Order
Hold2

>= 0
Sine wave to
square wave 1

AW GN
Channel

Sin for
BOC(1,1)

Bernoulli
Binary
L1 OS, data
nav data

Continuous-Time
VCO

Doppler rate

cosine

XOR Unipolar to

Bipolar
Converter
Binary to
Bipolar 1

Gold Sequence
Generator

XOR

-K-

Data

L1 OS, data

Unipolar to
Bipolar
Converter
Binary to
Bipolar 2

Gold Sequence
Generator
L1 OS, pilot

XOR

-K-

XOR

Pilot

1
L1 signal

0 0 0, 0 0 1, 0 1 0, 1 1

L1 OS, pilot
Secondary code

Continuous-Time
VCO
sine

Bernoulli
Binary
L1 PRS
nav data

XOR Unipolar to

Bipolar
Converter
Binary to
Bipolar 3

L1P

XOR

2/3

Gold Sequence
Generator
L1 PRS

1/3

>= 0
Sine wave to
square wave 2

Re
Im
Real-Imag to
Complex

Cos for
BOC(15, 2.5)

Zero-Order
Hold1 Discrete-Time

Scatter Plot
Scope

FIGURE B.5. The Simulink model that generates the L1 signal. The gray blocks generate
the Galileo signal, and the white blocks are used to visualize the signal.

generator directly implements the BOC, CASM, and other steps described earlier
in this chapter. It is easy to see CASM constants and math operations in the model
that correspond to (3.2)-(3.4).
The model can be divided into three parts from left to right (excluding the white
blocks). The first part consists of the generators of PRN, BOC signal, and random
bits of navigation messages. This is the left part of the model. It makes all three
navigation signals at the baseband (from the top to the bottom): data channel, pilot
channel, and restricted access channel.
The center part of the diagram converts binary signals of the left side to bipolar

± 1 signals. Simulink PRN generators are generating binary data and the bipolar

signals are required for the CASM algorithm.
The CASM part is implemented on the right side of the model. The output of
the model is Galileo L1 signal at the L1 frequency. The zero-order hold blocks are
used to sample continuous signal. The sampling frequency is 110.5 MHz, and the
result of sampling the IF is about 28 MHz. The signal spectrum after sampling is
shown in Figure B.6. It clearly shows the two main lobes of BOC(1,1) at the center
of the spectrum. The two OS signals are sharing this part of the spectrum. The two