vlc-rm 0.1.dev196

The package implements a recursive model to simulate a VLC system inside of rectangular empty room.

What is VLC-RM ?

VLC-RM is a package designed to simulate Visible Light Communication (VLC) systems based on Color Shift Keying modulation within indoor environments. The package calculates the propagation of light for multiple wavelengths in a rectangular empty room. Building upon a modified version of the Recursive Model (RM) presented in [1], this package provides the DC gain at each central wavelength. In order to compute this propagation, VLC-RM takes into account the spectral power distribution of multiple LEDs, the spectral response of the multiple color detectors, and the reflectance of the room’s walls at central wavelengths. The spectral power distribution emitted by the LED-based transmitter is assumed to have a Gaussian shape, and the spatial intensity distribution is assumed to be a Lambertian radiator. A grid of points is used to discretize the room’s walls into smaller square areas.

The package executes a recursive algorithm to obtain the DC gain at each central wavelength and the minimum distance of the constellation. Based on the computation of the DC gain, the interchannel interference of the CSK-VLC system is estimated, along with the lighting parameters. The recursive algorithm assumes that the room’s walls are perfect diffuse reflectors and that the transmitter is a point light source. The package simulates the transmission of CSK symbols through an Additive White Gaussian Noise (AWGN) channel. The received symbols are computed in the photodetected current space using the interchannel interference matrix and adding a gaussian noise.

• Free software: BSD 3-Clause License

Installation

pip install vlc-rm

You can also install the in-development version with:

pip install https://github.com/jufgutierrezgo/python-vlc-rm/archive/main.zip

An example of a VLC simulation

This example describes the usage of the VLC-RM package for characterizing a VLC system based on IEEE 16-CSK modulation within an empty rectangular space. The modulation is defined in [2].

Defining the VLC transmitter

The VLC system is composed of three elements: the LED-based transmitter, the photodetector, and the indoor environment (empty rectangular room). To define the transmitter of the VLC system is used the transmitter-module. The module must be imported, and then a transmitter-type object is created as follows:

# Import Transmitter
from vlc_rm.transmitter import Transmitter

# Create a transmitter-type object
transmitter = Transmitter(
        "Led1",
        position=[2.5, 2.5, 3],
        normal=[0, 0, -1],
        mlambert=1,
        wavelengths=[620, 530, 475],
        fwhm=[20, 30, 20],
        modulation='ieee16',
        luminous_flux=5000
                )

‘transmitter’ object is defined from seven parameters. The position and normal parameters are defined by the 3D-cartesian coordinates. It means that the transmitter will be located in [x=2.5, y=2.5, z=3]. Through the wavelengths parameter, three central wavelengths (in nanometers) are fixed as [620, 530, 475], which means that the transmitter uses three color red (620 nm), green (530 nm), and blue (475 nm). The fwhm parameter set the full width at half maximum (in nanometers) for each color LED as [20, 30, 20]. The modulation parameter defines the type of CSK modulation that can be simulated. modulation parameter is ‘ieee16’ as default. The luminous_flux (in Lumens) defines the average luminous flux emitted by the transmitter. After defining the ‘transmitter’ module, the string representation of the object can be realized as follows:

# Print the 'transmitter' object
print(transmitter)

which produces an output similar to:

List of parameters for LED transmitter:
Name: Led1
Position [x y z]: [2.5000e+00 2.5000e+00 3.0000e+00]
Normal Vector [x y z]: [[0.0000e+00 0.0000e+00 -1.0000e+00]]
Lambert Number: 1.0
Central Wavelengths [nm]: [6.2000e+02 5.3000e+02 4.7500e+02]
FWHM [nm]: [2.0000e+01 3.0000e+01 2.0000e+01]
Luminous Flux [lm]: 5000.0
ILER [W/lm]:
[[3.8001e-03 0.0000e+00 0.0000e+00]
[0.0000e+00 1.8197e-03 0.0000e+00]
[0.0000e+00 0.0000e+00 1.1960e-02]]
Average Power per Channel Color:
[6.3336e+00 3.0328e+00 1.9934e+01]
Total Power emitted by the Transmitter [W]:
29.30032767693627

The spectral power distribution of the LED transmitter according to the central wavelengths, the FWDM, and the luminous flux can be plotted with:

# Plot the normalized spectral power distribution
transmitter.plot_spd_normalized()

The output image is:

Defining the VLC photodetector

To define the photodetector is used the photodetector-module. The module must be imported and creating a photodetector-type object as follows:

pd = Photodetector(
    "PD1",
    position=[1.5, 1.5, 0.85],
    normal=[0, 0, 1],
    area=(1e-6)/3,
    #area=1e-4,
    fov=85,
    sensor='S10917-35GT',
    idark=1e-12
            )

‘photodetector’ object is defined from six parameters. The position parameter is defined as a three-dimensional array that represents the 3D-cartesian coordinate. The position is equal to [x=0.5, y=1.0, z=0.85]. The normal vector to the LED’s area is configured through the normal parameter, which is equal to [0, 0, 1]. The area parameter is configured equal to (1e-6)/3 (square meters), and it represents the active area of the photodetector. The field-of-view parameter defines the solid angle through which a detector is sensitive, and for this example, it is 85. The sensor parameter represents the detector reference which defines the spectral responsivity of the optical-to-electrical conversion. Getting the available sensor list by using the next command:

pd.list_sensors()

The idark parameter defines the dark current of the photodetector and it is set as 1e-12. After defining the ‘transmitter’ module, the string representation of the object can be realized as follows:

After defining the ‘photodetetor’ module, the string representation of the object can be realized as follows:

# Print the 'transmitter' object
print(pd)

which produces an output similar to:

List of parameters for photodetector PD1:
Name: PD1
Position [x y z]: [1.5000e+00 1.5000e+00 8.5000e-01]
Normal Vector [x y z]: [[0.0000e+00 0.0000e+00 1.0000e+00]]
Active Area[m2]: 3.3333333249174757e-07
FOV: 85.0
Sensor: S10917-35GT

The spectral responsivity of the photodetector can be plotted as:

# Plot the normalized spectral power distribution
pd.plot_responsivity()

The output image is:

Defining the VLC Indoor Environment

The indoor space for VLC is defined by using the ‘IndoorEnv’ module. The size parameter (in meters) specifies the length, width, and height of the rectangular room. This parameter is defined as the three-dimensional array [5, 5, 3]. The no_reflections parameter specifies the order of reflection to compute the lighting parameters and the interchannel interference. The package support from 0-order to 10-order of reflection. The reflectance at the central wavelengths of each wall can be defined. The resolution parameter (in meters) determines the length of the smaller square areas. The accuracy of the model depends on the resolution.

room = Indoorenv(
    "Room",
    size=[5, 5, 3],
    no_reflections=10,
    resolution=1/8,
    ceiling=[0.82, 0.71, 0.64],
    west=[0.82, 0.71, 0.64],
    north=[0.82, 0.71, 0.64],
    east=[0.82, 0.71, 0.64],
    south=[0.82, 0.71, 0.64],
    floor=[0.635, 0.61, 0.58]
        )

The ‘create_environment()’ method is used to create a grid of points and two pairwise parameters of the indoor environment [Article Reference].

room.create_environment()

if this method computes the grid and pairwise parameters correctly, it produces an output similar to

Creating parameters of indoor environment ...
Parameters created!

Simulate the indoor VLC system

The simulation of the indoor CSK-based VLC is carried out by the ‘RecursiveModel’ module, which is defined as follows.

channel_model = Recursivemodel(
    name="ChannelModelA",
    led=transmitter,
    photodetector=photodetector,
    room=indoor_env
    )

the ‘channel_model’ is an object that is defined from the transmitter, pd, and room objects. The channel simulation is executed through the ‘simulate_channel()’ method.

# Simulate indoor channel
channel_model.simulate_channel()

if this method simulates successfully, it produces an output similar to

Creating parameters of indoor environment ...
Parameters created!

To Get the simulation results can be used the print function:

# Print results of the simulation
print(channel_model)

obtaining an output similar to:

|=============== Simulation results ================|
Name: ChannelModelA
DC-Gain with respect to 1-W [W]:
[2.0109e-08 1.7362e-08 1.6087e-08]
Crosstalk Matrix at 5000.0-lm:
[[2.0059e-08 3.6404e-12 1.0877e-12]
[3.0197e-10 1.0295e-08 4.6459e-09]
[1.0395e-10 1.6943e-09 6.0081e-08]]
Lighting Parameters at 5000.0-lm
Illuminance [lx]: [[2.6779e+02]]
CIExyz: [[2.5761e-01 2.0534e-01 5.3705e-01]]
CRI: [[1.4296e+01]]
Min-Distance: 6.914522683100047e-09

The VLC-RM package reports the radiometric power received at the photodetector when each LED radiates 1 W. The Crosstalk matrix at the luminous flux is reported. This matrix related the transmitted symbols represented in the luminous flux space, and the received symbols represented in the current space. The minimum distance is reported according to the Crosstalk matrix, and the constellation at the transmitter. The illuminance, the CIE color coordinates, and the color rendering index are reported. The VLR-RM uses the Luxpy Python package (https://pypi.org/project/luxpy/) to compute photometric and colorimetric indexes.

Documentation

https://python-vlc-rm.readthedocs.io/

Development

To run all the tests run:

tox

Note, to combine the coverage data from all the tox environments run:

Windows	set PYTEST_ADDOPTS=--cov-append tox
Other	PYTEST_ADDOPTS=--cov-append tox

References

[1] Barry, J. R., Kahn, J. M., Krause, W. J., Lee, E. A., & Messerschmitt, D. G. (1993). Simulation of multipath impulse response for indoor wireless optical channels. IEEE journal on selected areas in communications, 11(3), 367-379.

[2] IEEE Standards Association. (2019). IEEE Standard for Local and metropolitan area networks—Part 15.7: Short-Range Optical Wireless Communications (IEEE Std 802.15.7-2018, Revision of IEEE Std 802.15.7-2011) (pp. 1-407). https://ieeexplore.ieee.org/document/8697198

Changelog

0.0.0 (2022-10-28)

• First release on PyPI.