p681LMSChannel

Filter input signal through ITU-R P.681-11 LMS frequency-flat fading channel

Since R2022a

Description

The p681LMSChannel System object™ filters a real or complex input signal through a frequency-flat fading land mobile-satellite (LMS) communication channel, as defined in the ITU-R Recommendation P.681-11 Section 6.2 [1].

To filter an input signal through a P.681-11 LMS time-varying channel:

1. Create the p681LMSChannel 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

chan = p681LMSChannel

chan = p681LMSChannel(Name=Value)

Description

chan = p681LMSChannel creates an ITU-R P.681-11 LMS frequency-flat fading channel System object.

The default System object has the environment set to an urban scenario, with carrier frequency of 2.2 GHz and an elevation angle of 45 degrees. This object models a single geostationary satellite.

chan = p681LMSChannel(Name=Value) sets properties using one or more name-value arguments. For example, SampleRate=20e3 sets the input signal sample rate to 20e3.

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.

SampleRate — Input signal sample rate

7.68e6 (default) | positive scalar

Input signal sample rate in hertz, specified as a positive scalar.

Data Types: double

InitialState — Initial state of channel

"Good" (default) | "Bad"

Initial state of the channel, specified as "Good" or "Bad".

Data Types: char | string

CarrierFrequency — Carrier frequency

2.2e9 (default) | nonnegative scalar

Carrier frequency in hertz, specified as a nonnegative scalar.

Data Types: double

ElevationAngle — Path elevation angle to geostationary satellite

45 (default) | scalar

Path elevation angle to a geostationary satellite in degrees, specified as a scalar. The nominal value is in the range [0, 90].

Data Types: double

MobileSpeed — Speed of mobile terminal

0.8333 (default) | nonnegative scalar

Speed of mobile terminal in m/s, specified as a nonnegative scalar. The default value of 0.8333 m/s translates to 3 km/h.

This property affects the Doppler spread applied to the multipath component and also the Doppler shift applied to the direct path component.

Setting this property to 0, results in a static channel. In this case, the Doppler spread is not applicable for the multipath component and the Doppler shift is also not applied in direct path component of the channel.

Data Types: double

AzimuthOrientation — Azimuth orientation

0 (default) | scalar

Azimuth orientation in degrees, specified as a scalar. This value specifies the direction of movement of the ground or mobile terminal. The nominal value is in the range [0, 360].

When you set this property to odd multiples of 90, the Doppler shift caused by the mobile movement in the direct path component is nonexistent.

Data Types: double

Environment — Type of propagation environment

"Urban" (default) | "Suburban" | "RuralWooded" | "Village" | "Residential" | "Highway" | "Rural" | "Train" | "Custom"

Type of propagation environment, specified as one of these values.

• "Urban"

• "Suburban"

• "RuralWooded"

• "Village"

• "Residential"

• "Highway" — Applicable only when you set the value of CarrierFrequency property in the range [10, 20] GHz

• "Rural" — Applicable only when you set the value of CarrierFrequency property in the range [10, 20] GHz

• "Train" — Applicable only when you set the value of CarrierFrequency property in the range [10, 20] GHz

• "Custom"

When you set this property to "Custom", configure the propagation environment using these properties.

• StateDistribution

• MinStateDuration

• DirectPathDistribution

• MultipathPowerCoefficients

• StandardDeviationCoefficients

• DirectPathCorrelationDistance

• TransitionLengthCoefficients

• StateProbabilityRange

Data Types: char | string

StateDistribution — Parameters of state duration distribution

[3.0639 2.9108; 1.6980 1.2602] (default) | 2-by-2 matrix

Parameters of state duration distribution in dB, specified as a 2-by-2 matrix. For example, if you specify the input as [muG, muB; sigmaG, sigmaB], then:

• muG and sigmaG represent the mean and standard deviation of good state duration, respectively.

• muB and sigmaB represent the mean and standard deviation of bad state duration, respectively.

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

MinStateDuration — Minimum duration of each state

[10 6] (default) | two-element row vector

Minimum duration of each state in meters, specified as a two-element row vector. The first element corresponds to good state and the second element corresponds to bad state.

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

DirectPathDistribution — Parameters of direct path amplitude distribution

[-1.8225 -15.4844; 1.1317 3.3245] (default) | 2-by-2 matrix

Parameters of direct path amplitude distribution in dB, specified as a 2-by-2 matrix. For example, if you specify the input as [muMaG, muMaB; sigmaMaG, sigmaMaB], then:

• muMaG and sigmaMaG represent the mean of the direct path amplitude (Ma) and the standard deviation of Ma in good state, respectively.

• muMaB and sigmaMaB represent the mean and standard deviation of Ma in bad state, respectively.

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

MultipathPowerCoefficients — Coefficients to compute multipath power

[-0.0481 0.9434; -14.7450 -1.7555] (default) | 2-by-2 matrix

Coefficients to compute the multipath power, specified as a 2-by-2 matrix. For example, if you specify the input as [h1G, h1B; h2G, h2B], then:

• h1G and h2G represent the coefficients in good state.

• h1B and h2B represent the coefficients in bad state.

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

StandardDeviationCoefficients — Coefficients to compute standard deviation of direct path amplitude

[-0.4643 -0.0798; 0.3334 2.8101] (default) | 2-by-2 matrix

Coefficients to compute standard deviation of direct path amplitude in all states, specified as a 2-by-2 matrix. For example, if you specify the input as [g1G, g1B; g2G, g2B], then:

• g1G and g2G represent the coefficients in good state.

• g1B and g2B represent the coefficients in bad state.

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

DirectPathCorrelationDistance — Direct path amplitude correlation distance

[1.7910 1.7910] (default) | two-element row vector

Direct path amplitude correlation distance (Lcorr) in meters, specified as a two-element row vector. The first element corresponds to good state and the second element corresponds to bad state.

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

TransitionLengthCoefficients — Coefficients to compute transition length

[0.0744; 2.1423] (default) | two-element column vector

Coefficients to compute the transition length (f1;f2), specified as a two-element column vector.

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

StateProbabilityRange — Minimum and maximum probability of each state

[0.05 0.1; 0.95 0.9] (default) | 2-by-2 matrix

Minimum and maximum probability of each state, specified as a 2-by-2 matrix. For example, if you specify the input as [pminG, pminB; pmaxG, pmaxB], then:

• pminG and pmaxG represent the minimum and maximum values of state probability in good state.

• pminB and pmaxB represent the minimum and maximum values of state probability in bad state.

The minimum probability must be less than the maximum probability in a state. The value of each element must be in range [0, 1].

Dependencies

To enable this property, set the Environment property to "Custom".

Data Types: double

ChannelFiltering — Channel filtering

true or 1 (default) | false or 0

Channel filtering, specified as one of these logical values.

• 1 (true) — The object accepts an input signal and produces a filtered output signal, in addition to the channel path gains, sample times, and state series.

• 0 (false) — The object does not accept an input signal, produces no filtered output signal, and outputs only channel path gains, sample times, and state series. You must specify the duration of the fading process by using the NumSamples property, and the sampling rate by using the SampleRate property.

Data Types: logical

NumSamples — Number of time samples

7680 (default) | nonnegative integer

Number of time samples used to set the duration of the fading process realization, specified as a nonnegative integer.

Tunable: Yes

Dependencies

To enable this property, set ChannelFiltering property to false.

Data Types: double

OutputDataType — Data type of outputs

"double" (default) | "single"

Data type of outputs, specified as one of these values.

• "double"

• "single"

Dependencies

To enable this property, set ChannelFiltering property to false.

Data Types: char | string

FadingTechnique — Channel model fading technique

"Filtered Gaussian noise" (default) | "Sum of sinusoids"

Channel model fading technique, specified as "Filtered Gaussian noise" or "Sum of sinusoids".

Data Types: char | string

NumSinusoids — Number of sinusoids used

48 (default) | positive integer

Number of sinusoids used to generate the Doppler fading samples, specified as a positive integer.

Dependencies

To enable this property, set the FadingTechnique property to "Sum of sinusoids".

Data Types: double | uint16

RandomStream — Source of random number stream

"Global stream" (default) | "mt19937ar with seed"

Source of the random number stream, specified as "Global stream" or "mt19937ar with seed".

• When you specify "Global stream", the object uses the current global random number stream for uniformly and normally distributed random number generation. In this case, the reset object function resets only the filters.

• When you specify "mt19937ar with seed", the object uses the mt19937ar algorithm for uniformly and normally distributed random number generation. In this case, the reset object function resets the filters and reinitializes the random number stream to the value of the Seed property.

Data Types: char | string

Seed — Initial seed

73 (default) | nonnegative integer

Initial seed of the mt19937ar random number stream generator algorithm, specified as a nonnegative integer. When you call the reset object function, it reinitializes the mt19937ar random number stream to the Seed value.

Dependencies

To enable this property, set the RandomStream property to "mt19937ar with seed".

Data Types: double | uint32

Visualization — Channel visualization

"Off" (default) | "Impulse response" | "Frequency response" | "Impulse and frequency responses" | "Doppler spectrum"

Channel visualization, specified as one of these options.

• "Off"

• "Impulse response"

• "Frequency response"

• "Impulse and frequency responses"

• "Doppler spectrum"

When you set this property to enable the visualization, selected channel characteristics are animated in separate figures, with each System object call.

For more information, see the Channel Visualization section.

Data Types: char | string

Usage

Syntax

[pathgains,sampletimes,stateseries] = chan()

[y,pathgains,sampletimes,stateseries] = chan(x)

Description

[pathgains,sampletimes,stateseries] = chan() produces path gains, pathgains, sample times, sampletimes, and state series, stateseries for an ITU-R P.681-11 LMS flat fading channel.

In this case, the System object acts as a source of path gains, sample times, and state series.

Specify the duration of the fading process by using the NumSamples property. Specify the datatype of outputs using the OutputDataType property.

Note

This syntax is applicable when you set the ChannelFiltering property to false.

[y,pathgains,sampletimes,stateseries] = chan(x) filters the input signal, x, through an ITU-R P.681-11 LMS flat fading channel, and returns the output channel-impaired signal in y, in addition to the outputs in the previous syntax.

Note

This syntax is applicable when you set the ChannelFiltering property to true.

Input Arguments

x — Input signal

N_S-by-1 vector

Input signal, specified as an N_S-by-1 vector, where N_S is the number of input samples.

Data Types: single | double
Complex Number Support: Yes

Output Arguments

y — Output signal

N_S-by-1 vector

Output signal, returned as an N_S-by-1 vector of complex values with the same data precision and length as the input signal x. N_S is the number of input samples.

Data Types: single | double
Complex Number Support: Yes

pathgains — Channel path gains of fading process

N_S-by-1 vector

Channel path gains of fading process, returned as an N_S-by-1 vector of complex values.

• When you set the ChannelFiltering property to true, pathgains is of the same data precision as the input signal x, and N_S is the number of input samples.

• When you set the ChannelFiltering property to false, pathgains is of the same data precision as the OutputDataType property and N_S is equal to the NumSamples property.

Data Types: single | double
Complex Number Support: Yes

sampletimes — Sample times of channel snapshots

N_S-by-1 vector

Sample times of channel snapshots, returned as an N_S-by-1 vector.

• When you set the ChannelFiltering property to true, sampletimes is of the same data precision as the input signal x, and N_S is the number of input samples.

• When you set the ChannelFiltering property to false, sampletimes is of the same data precision as the OutputDataType property and N_S is equal to the NumSamples property.

Data Types: single | double

stateseries — State series of channel

N_S-by-1 vector

State series of the channel, returned as an N_S-by-1 vector. Each value of this vector describes the state in which channel is present for that channel snapshot. A value of 0 represents bad state. A value of 1 represents good state. A value between 0 and 1 represents a state transition.

• When you set the ChannelFiltering property to true, stateseries is of the same data precision as the input signal x, and N_S is the number of input samples.

• When you set the ChannelFiltering property to false, stateseries is of the same data precision as the OutputDataType property and N_S is equal to the NumSamples property.

Data Types: single | double

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 p681LMSChannel

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

Transmit Signal Through P.681-11 LMS Channel

Create and Configure the Channel

Create an ITU-R P.681-11 LMS channel and configure it for a suburban scenario with a carrier frequency of 20 GHz and an elevation angle of 50 degrees. Set the sample rate to 6000 kHz.

Specify the mobile terminal speed to 50 m/s, with an azimuth orientation of 20 degrees.

chan = p681LMSChannel;
chan.SampleRate = 6e6;           % Hz
chan.CarrierFrequency = 20e9;    % Hz
chan.ElevationAngle = 50;        % degrees
chan.Environment = "Suburban";
chan.MobileSpeed = 50;           % m/s
chan.AzimuthOrientation = 20;    % degrees

Display the channel characteristics.

disp(chan)

  p681LMSChannel with properties:

            SampleRate: 6000000
          InitialState: "Good"
      CarrierFrequency: 2.0000e+10
        ElevationAngle: 50
           MobileSpeed: 50
    AzimuthOrientation: 20
           Environment: "Suburban"
      ChannelFiltering: true

  Use get to show all properties

Transmit Input Signal Through Channel

Set the random number generation seed as default.

rng("default")

Generate a random QPSK-modulated input signal.

numSamples = 6e6;              
txWaveform = pskmod(randi([0 3],numSamples,1),4); % Modulation order = 4

Filter the signal through the channel.

[rxWaveform,pathGains,sampleTimes,stateSeries] = chan(txWaveform);

Visualize Space Series and State Series

Plot the space series as a function of time.

figure                                      % Create figure window
subplot(2,1,1)
plot(sampleTimes,20*log10(abs(pathGains)))
title('Space Series')
xlabel('Time (in s)')
ylabel('Path Gain (in dB)')
grid on

Plot the state series as a function of time.

subplot(2,1,2)
plot(sampleTimes,stateSeries)
title('State Series')
xlabel('Time (in s)')
ylabel('State')
grid on

Plot Doppler Spectrum for P.681-11 LMS Channel

Define the channel configuration using a p681LMSChannel System object and specify its properties.

Set the visualization as Doppler spectrum and disable the channel filtering.

chan = p681LMSChannel;
chan.SampleRate = 450000;                % Hz
chan.CarrierFrequency = 11e9;            % Hz
chan.ElevationAngle = 50;                % degrees
chan.MobileSpeed = 20;                   % m/s
chan.Visualization = "Doppler spectrum";
chan.ChannelFiltering = false;
chan.NumSamples = 4e7;

Display the channel characteristics.

disp(chan)

  p681LMSChannel with properties:

            SampleRate: 450000
          InitialState: "Good"
      CarrierFrequency: 1.1000e+10
        ElevationAngle: 50
           MobileSpeed: 20
    AzimuthOrientation: 0
           Environment: "Urban"
      ChannelFiltering: false
            NumSamples: 40000000
        OutputDataType: "double"

  Use get to show all properties

Get the path gains, sample times, and state series of the channel. Also, observe the Doppler spectrum.

[pathGains,sampleTimes,stateSeries] = chan();

Get P.681-11 LMS Channel Information

Get channel information from a p681LMSChannel System object by using the info object function.

Create an ITU-R P.681-11 LMS channel System object and specify its properties.

chan = p681LMSChannel;
chan.SampleRate = 10e3;             % Hz
chan.MobileSpeed = 2;               % m/s
chan.Environment = "RuralWooded";
disp(chan)

  p681LMSChannel with properties:

            SampleRate: 10000
          InitialState: "Good"
      CarrierFrequency: 2.2000e+09
        ElevationAngle: 45
           MobileSpeed: 2
    AzimuthOrientation: 0
           Environment: "RuralWooded"
      ChannelFiltering: true

  Use get to show all properties

QPSK-modulate a random input signal, and then pass it through the channel.

numSamples = 2e4;
txWaveform = pskmod(randi([0 3],numSamples,1),4);
[rxWaveform,pathGains,sampleTimes,stateSeries] = chan(txWaveform);

Get the characteristic information about the P.681-11 LMS channel.

info(chan)

ans = struct with fields:
                   PathDelays: 0
           ChannelFilterDelay: 0
    ChannelFilterCoefficients: 1
          NumSamplesProcessed: 20000

Transmit another QPSK-modulated random input signal through the channel

numSamples2 = 3e4;
txWaveform2 = pskmod(randi([0 3],numSamples2,1),4);
[rxWaveform2,pathGains2,sampleTimes2,stateSeries2] = chan(txWaveform2);

Observe the change in number of samples processed.

info(chan)

ans = struct with fields:
                   PathDelays: 0
           ChannelFilterDelay: 0
    ChannelFilterCoefficients: 1
          NumSamplesProcessed: 50000

Algorithms

Doppler Phenomena

To calculate the Doppler spread and Doppler shift due to the movement of the mobile on Earth, refer to these formulas.

• The maximum Doppler spread due to mobile movement is given by the following formula:

  F_{mob_max_spread} = (v_mob*f_c) / c

  where:

  • v_mob is the speed of the mobile terminal on Earth in m/s, specified as the MobileSpeed property.

  • f_c is the carrier frequency in Hz, specified by the CarrierFrequency property.

  • c is the speed of light in free space in m/s, specified as physconst('lightspeed').

• The Doppler shift due to mobile movement is given by the following formula:

  fd_mob = F_{mob_max_spread} * cosd(θ) * cosd(φ)

  where:

  • F_{mob_max_spread} is the maximum Doppler spread due to mobile movement.

  • θ is the path elevation angle to the satellite in degrees, specified by the ElevationAngle property.

  • φ is the azimuth orientation in degrees, specified by the AzimuthOrientation property.

The maximum Doppler shift caused by the movement of the mobile must be less than one-tenth of SampleRate property.

Channel Visualization

The p681LMSChannel System object enables visualization of the channel impulse response, frequency response, and Doppler spectrum.

• The Doppler spectrum plot displays the empirically determined spectrum from the path gains of the channel. The Doppler spectrum values are in dB.

  When there is no mobile movement, the channel is static channel. The empirical data is displayed as a line for the case of nonstatic channels and as a point for static channels. Before the empirical plot is updated, the internal buffer must be completely filled with the required number of channel samples. The empirical plot is the running mean of the spectrum that is calculated from each full buffer. For nonstatic channels, the number of input samples that is needed before the next update is displayed in the status bar located at the bottom of plot. The number of samples that is needed is a function of the sample rate and the maximum Doppler shift depending on mobile movement. For static channels, the text "Reset fading channel for next update" is displayed.

  Nonstatic Channel

  

  Static Channel

  

• For channel impulse and frequency visualizations, see Channel Visualization.

References

[1] ITU-R Recommendation P.681-11 (08/2019). “Propagation data required for the design systems in the land mobile-satellite service.” P Series; Radiowave propagation.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• Code generation is available only when the Visualization property is "Off".

• See System Objects in MATLAB Code Generation (MATLAB Coder).

Version History

Introduced in R2022a