gpsWaveformGenerator

Generate GPS waveform (legacy L1 and L2, modernized L1C, L2C, and L5)

Since R2025a

Description

The gpsWaveformGenerator System object™ creates a Global Positioning System (GPS) waveform generator that supports generation of these GPS waveforms.

• Legacy L1 and L2 — Applies when you set the SignalType property to "legacy".

• Modernized L1C — Applies when you set the SignalType property to "l1c".

• Modernized L2C — Applies when you set the SignalType property to "l2c".

• L5 — Applies when you set the SignalType property to "l5".

To understand the algorithms associated with each waveform generated using gpsWaveformGenerator, see Algorithms.

To create a GPS waveform generator:

1. Create the gpsWaveformGenerator object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Syntax

gpsWaveObj = gpsWaveformGenerator

gpsWaveObj = gpsWaveformGenerator(Name=Value)

Description

gpsWaveObj = gpsWaveformGenerator creates a default GPS waveform generator System object.

gpsWaveObj = gpsWaveformGenerator(Name=Value) sets properties using one or more name-value arguments. For example, gpsWaveformGenerator(PRNID=10) specifies a pseudo-random noise (PRN) ID of 10.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

SignalType — Type of baseband signal to generate

"legacy" (default) | "l1c" | "l2c" | "l5"

Type of baseband signal to generate, specified as one of these options

• "legacy" — Use this option to generate a legacy L1 or L2 signal.

• "l1c" — Use this option to generate a modernized L1 signal.

• "l2c" — Use this option to generate a modernized L2 signal.

• "l5" — Use this option to generate a modernized L5 signal.

PRNID — Satellite PRN index

1 (default) | integer in the range [1, 210] | vector of integers in the range [1, 210]

Satellite PRN index, specified as one of these options.

• Integer in the range [1, 210] — Use this option to input a PRN index for a single satellite.

• Vector of integers in the range [1, 210] — Use this option to input PRN indices for multiple satellites.

Note

When you set the SignalType property to "l2c", PRN indices must be in the range [1, 63] or [159, 210].

Data Types: double | uint8

IsL2CInPhaseQuadrature — Option to enable phase-quadrature for L2C and L2P

true or 1 (default) | false or 0

Option to enable phase-quadrature for L2C and L2P, specified as a numeric or logical 1 (true) or 0 (false).

• true — Use this option to set the precision code (P-code) on the in-phase branch (I-branch), and the civil-moderate (CM) code and the civil-long length (CL) code on the quadrature-branch (Q-branch).

• false — Use this option to set all codes on the I-branch.

Dependencies

To enable this property, set the SignalType property to "l2c".

EnablePCode — P-code indicator

false or 0 (default) | true or 1

P-code indicator, specified as a numeric or logical 1 (true) or 0 (false).

In cases where you do not need the P-code, set this property to false to improve the execution speed. When set to false, the P-code on the I-branch is set to 0.

Dependencies

To enable this property, set the SignalType property to "legacy" or "l2c".

HasDataWithPCode — Option to enable data with P-code

true or 1 (default) | false or 0

Option to enable data with P-code, specified as a numeric or logical 1 (true) or 0 (false). When set to true, data is transmitted along with the P-code.

Dependencies

To enable this property, you must satisfy these conditions.

• Set the SignalType property to "legacy" or "l2c".

• Set the EnablePCode property to true.

HasDataWithCACode — Option to enable data with C/A-code

true or 1 (default) | false or 0

Option to enable data with coarse acquisition code (C/A-code), specified as a numeric or logical 1 (true) or 0 (false). When set to true, data is transmitted along with the C/A-code.

Dependencies

To enable this property, set the SignalType property to "legacy".

InitialTime — Initial time within one week

0 (default) | real scalar in range [0, 604800]

Initial time within one week in seconds, specified as a real scalar in the range [0, 604800].

This property is not visible when the SignalType property to "legacy" and the EnablePCode property to false.

Data Types: double

SampleRate — Sample rate for signal

10.23e6 (default) | numeric scalar greater than 1e6

Sample rate for the signal, in hertz, specified as a numeric scalar greater than 1e6. This property specifies the sample rate of the signal output by the step object function.

Data Types: double

BitDuration — Duration of input bits

Read-only: "0.01 | "0.02"

This property is read-only.

Duration of input bits, represented as one of these values.

• "0.01" — Applies when the SignalType property is set to "l1c" or "l5".

• "0.02" — Applies when the SignalType property is set to "legacy" or "l2c".

ChipRate — Chip rate of slowest code in waveform

Read-only: "1.023e6 | "511.5e3" | "10.23e6"

This property is read-only.

Chip rate of the slowest code in the waveform, represented as one of these values.

• "1.023e6" — Applies when you set the SignalType property is set to "legacy" or "l1c".

• "511.5e3" — Applies when you set the SignalType property is set to "l2c".

• "10.23e6" — Applies when you set the SignalType property is set to "l5".

Usage

Syntax

waveform = gpsWaveObj(navdata)

Description

waveform = gpsWaveObj(navdata) generates the time-domain GPS waveform.

Input Arguments

navdata — Navigation data

binary matrix | cell array

Navigation data, specified as one of these options.

• Binary matrix — The number of columns must be equal to the length of the PRNID property, as each column corresponds to a PRNID. The number of rows represents the number of navigation data bits.

• Cell array — Must contain either one or two elements.

  • Cell array with one element — The cell must contain a binary matrix with the same characteristics for when you specify navdata as a binary matrix.

    For example, consider these cases:

    • Case A — navdata = randi([0 1],100,numsat] creates a binary matrix of size 100-by-numsat.

    • Case B — navdata = {randi([0 1],100,numsat]} creates a cell array of a single element, which is a binary matrix of size 100-by-numsat.

    When navdata is specified as a cell array with a single element (Case B), then the element must contain a binary matrix with the same characteristics as described in Case A.

  • Cell array with two elements — Use this option when you set the SignalType property to "l2c". The gpsWaveObj treats the first element as legacy navigation (LNAV) message bits and the second element as civil navigation (CNAV) message bits. The sizes of the cell elements must be same.

    For all other SignalType property values, gpsWaveObj ignores the second element.

Note

When you set the SignalType property to "l2c" and specify navdata as a binary matrix or a cell array with one element, then gpsWaveObj assigns the same value to both LNAV and CNAV.

Data Types: double | int8 | logical

Output Arguments

waveform — Generated GPS waveform

matrix

Generated GPS waveform, returned as a matrix. Each column is the waveform of the corresponding PRNID property value.

The number of rows is equal to the product of BitDuration × SampleRate × numBits, where numBits is the number of input bits and is equal to size(navdata,1).

The sample rate of the waveform matches the value specified in the SampleRate property.

Data Types: double
Complex Number Support: Yes

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Specific to gpsWaveformGenerator

info	Characteristic information about object

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
clone	Create duplicate System object
isLocked	Determine if System object is in use
reset	Reset internal states of System object

Examples

Generate Legacy GPS Waveform

Generate random bits of navigation data.

navdata = randi([0 1],2,1);      

Create a GPS waveform generation System object™, and set its properties.

gpswaveobj = gpsWaveformGenerator;
gpswaveobj.EnablePCode = true;
gpswaveobj.SampleRate = 4*10.23e6;

Generate a legacy GPS waveform.

waveform = gpswaveobj(navdata);

Visualize the spectrum of the waveform.

txscope = spectrumAnalyzer(SampleRate=gpswaveobj.SampleRate, ...
    SpectrumType="power-density",SpectrumUnits="dBW/Hz");
txscope(waveform)

Generate GPS L1C Waveform

Set the PRN indices, and generate random bits of navigation data.

prn = [4 70];
numsat = length(prn);
numbits = 100;
msg = randi([0 1],numbits,numsat);

Create a GPS waveform generation System object™, and set its properties.

fs = 25e6;
gpswaveobj = gpsWaveformGenerator(SignalType="l1c", ...
                     PRNID=prn,SampleRate=fs);

Generate a GPS L1C waveform.

waveform = gpswaveobj(msg);

Visualize the spectrum of the waveform.

txscope = spectrumAnalyzer(SampleRate=fs, ...
   SpectrumType="power-density",SpectrumUnits="dBW/Hz");
txscope(waveform)

Generate GPS L2C Waveform

Generate a GPS L2C waveform with random LNAV and CNAV data for four GPS satellites.

Set the PRN indices and generate random LNAV and CNAV data.

prn = [7 11 20 28];
numsat = length(prn);
numbits = 10;
lnavdata = randi([0 1],numbits,numsat);
cnavdata = randi([0 1],numbits,numsat);

Create a GPS waveform generation System object™, and set its properties.

gpswaveobj = gpsWaveformGenerator;
gpswaveobj.SignalType = "l2c";
gpswaveobj.PRNID = prn;
gpswaveobj.SampleRate = 15e6;
gpswaveobj.EnablePCode = true;

Get the characteristic information about the GPS waveform generator.

info(gpswaveobj)

ans = struct with fields:
         CurrentTime: 0
      SecondsElapsed: 0
    NumBitsProcessed: 0

Generate a GPS L2C waveform.

waveform = gpswaveobj({lnavdata cnavdata});
size(waveform)

ans = 1×2

     3000000           4

Generate GPS L5 Waveform

Generate a GPS L5 waveform, add impairments, and visualize the resultant waveform.

Generate L5 Waveform

Set the PRN indices, and generate random navigation data.

prn = [185, 189];
numsat = length(prn);
numbits = 40;
msg = randi([0,1],numbits,numsat);

Create a GPS waveform generation System object™, and set its properties.

fs = 25e6;
gpswaveobj = gpsWaveformGenerator(SignalType="l5",PRNID=prn, ...
    InitialTime=42123, SampleRate=fs);

Generate a GPS L5 waveform.

waveform = gpswaveobj(msg);
% Generated waveform has 2 columns, corresponding to the two satellites
size(waveform)         

ans = 1×2

    10000000           2

Introduce Impairments

Initialize objects that model the impairments.

fqyoffsetobj = comm.PhaseFrequencyOffset(FrequencyOffsetSource="Input port", ...
    SampleRate=fs);
delayval = 5.23e-4;
delobj = dsp.Delay(round(delayval*fs));

Add impairments to the waveform to get the resultant waveform.

fwave = fqyoffsetobj(waveform,[3e3 -4.6e3]); % Add frequency offset
dwave = delobj(fwave);                        % Add delay
bbwave = sum(dwave,2);                        % Add all signals to get final signal
size(bbwave)                                  % Resultant baseband waveform is a complex column vector

ans = 1×2

    10000000           1

Visualize Waveform

Visualize the resultant waveform.

txscope = spectrumAnalyzer(SampleRate=fs, ...
    SpectrumType="power-density",SpectrumUnits="dBW/Hz");
txscope(bbwave)

Algorithms

The sections detail the algorithm used to generate GPS waveforms using gpsWaveformGenerator.

Generate Legacy Waveforms

This section details the algorithm used to generate legacy waveforms using gpsWaveformGenerator.

You can generate legacy GPS waveforms by following these steps.

1. Generate C/A-code using gnssCACode.

2. XOR the incoming legacy navigation (LNAV) data with the C/A-code. Ensure that the sample rates of LNAV data and C/A-code match.

3. Map bit 0 to +1 and bit 1 to –1 and then place this waveform on the Q-branch.

4. Generate P-code using gpsPCode.

5. XOR the incoming LNAV data with the P-code. Ensure that the sample rates of LNAV data and P-code match.

6. Map bit 0 to +1/sqrt(2) and bit 1 to –1/sqrt(2) and then place this waveform on the I-branch.

   The resultant IQ waveform is the legacy waveform, with the P-code waveform on the I-branch and the C/A-waveform on the Q-branch.

Generate L1C Waveform

This section details the algorithm used to generate GPS L1C waveform using gpsWaveformGenerator.

You can generate an L1C waveform by following these steps.

1. Generate the data at 100 bits per second and each bit is of 10 millisecond duration, as defined in IS-GPS-800.

2. L1C uses two types of ranging codes: a ranging code for the data (L1CD code) and a ranging code for the pilot (L1CP code). The chip rate of both the L1CD and L1CP codes is 1.023 mega chips per second with 10 milliseconds in length. Therefore, the number of chips before repeating is 10,230.

   Because one 10 millisecond data bit exactly matches the ranging code block size, one data bit is spread with one block of ranging code.

3. Spread the L1CD code with the user data bits to obtain the data component. The rate of the user data bits is 100 bits per second.

4. Spread the L1CP code with the overlay code (L1CO code) to obtain the pilot component. The rate of the L1CO code is 100 bits per second.

5. Modulate the data component by using BOC (1,1).

6. Modulate the pilot component by using the time-multiplexed BOC (TMBOC) modulation technique.

   The final IQ waveform formed is the GPS L1C waveform. For more information on TMBOC modulation, see GPS L1C Waveform Generation.

Generate L2C Waveform

This section details the algorithm used to generate GPS L2C waveform using gpsWaveformGenerator.

You can generate an L2C waveform by following these steps.

1. Generate an L2-CM and an L2-CL code.

2. XOR the civil navigation (CNAV) data with only the L2-CM code.

3. Multiplex the XORed CNAV and L2-CM data bit-by-bit with L2-CL code.

4. Because L2-CM and L2-CL each consists of 511.5 kilo chips per seconds, the multiplexed stream of bits consists of 1.023e6 chips per second

5. For the multiplexed stream generated in point 4, map bit 0 to +1 and bit 1 to –1. Place this waveform on the Q-branch.

6. Generate P-code using gpsPCode.

7. XOR the incoming legacy navigation (LNAV) data with the P-code. Ensure that the sample rates of LNAV data and P-code match.

8. For the XORed LNAV and P-code data, map bit 0 to +1/sqrt(2) and bit 1 to –1/sqrt(2) and then place this waveform on the I-branch.

   The resultant IQ waveform is the baseband GPS L2C waveform.

Generate L5 Waveform

This section details the algorithm used to generate GPS L5 waveform using gpsWaveformGenerator.

You can generate the L5 waveform by following these steps.

1. Generate GPS L5 CNAV data, as defined in IS-GPS-705 standard.

2. Generate the ranging code for in-phase (I5-code) and quadrature-phase (Q5-code) components separately, as described in the standard.

   Both I5 and Q5-code are at 10.23MHz chip rate and repeat after every 10230 chips. Hence, each code block is of 1 millisecond duration.

3. The GPS L5 data is at 100 bits per second. XOR each data bit with 10 Newman Huffman code bits for I-branch. This makes the output after this XOR operation to be at 1 kilo baud, meaning every bit will be of 1 millisecond duration, which is equal to one code block of spreading code.

4. XOR the 1 millisecond bit from the output of step 3 with I5-code block. Map bit 0 to +1/sqrt(2) and bit 1 to -1/sqrt(2) to get the in-phase branch signal component of the final waveform.

5. Generate 20 bits of Newman Huffman code for Q-branch which is at 1 kilo baud.

6. XOR each Q5-code block with the Newman Huffman code. Map bit 0 to +1/sqrt(2) and bit 1 to -1/sqrt(2) to get the quadrature-phase branch signal component of the final waveform.

7. The final IQ waveform formed is the baseband GPS L5 waveform.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2025a