wlanTGnChannel

Filter signal through 802.11n multipath fading channel

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Description

The wlanTGnChannel System object™ filters an input signal through an 802.11n™ (TGn) multipath fading channel.

The fading processing assumes the same parameters for all NT-by-NR links of the TGn channel. NT is the number of transmit antennas and NR is the number of receive antennas. Each link comprises all multipaths for that link.

To filter an input signal using a TGn multipath fading channel:

  1. Create the wlanTGnChannel 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

tgn = wlanTGnChannel
tgn = wlanTGnChannel(Name,Value)

Description

tgn = wlanTGnChannel creates a TGn fading channel System object, tgn. This object filters a real or complex input signal through the TGn channel to obtain the channel-impaired signal.

example

tgn = wlanTGnChannel(Name,Value) creates a TGn channel object, tgn, and sets properties using one or more name-value pairs. Enclose each property name in quotes. For example, wlanTGnChannel('NumReceiveAntennas',2,'SampleRate',10e6) creates a TGn channel with two receive antennas and a 10 MHz sample rate.

Properties

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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.

Sample rate of the input signal in Hz, specified as a positive scalar.

Dependencies

When you specify DelayProfile as 'None', this property does not apply.

Data Types: double

Delay profile model, specified as 'Model-A', 'Model-B', 'Model-C', 'Model-D', 'Model-E', 'Model-F', or 'None'. When you choose 'None', the System object does not apply fading. In this case, the channel matrix is a discrete Fourier transform (DFT) matrix.

The table summarizes the properties of the models.

PropertyModel
ABCDEF
Breakpoint distance (m)555102030
RMS delay spread (ns)0153050100150
Maximum delay (ns)0802003907301050
Rician K-factor (dB)000366
Number of taps1914181818
Number of clusters122346
Propagation scenarioFlat fadingIndoor residentialIndoor residential or small officeOfficeLarge office/warehouseLarge space indoor (pseudo-outdoor)

Data Types: char | string

RF carrier frequency in Hz, specified as a positive scalar.

Dependencies

When you specify DelayProfile as 'None', this property does not apply.

Data Types: double

Speed of the scatterers in km/h, specified as a positive scalar.

Dependencies

When you specify DelayProfile as 'None', this property does not apply.

Data Types: double

Distance between the transmitter and receiver in meters, specified as a positive scalar.

TransmitReceiveDistance is used to compute the path loss, and to determine whether the channel has a line of sight (LOS) or non line of sight (NLOS) condition. The path loss and standard deviation of shadow fading loss depend on the separation between the transmitter and the receiver.

Dependencies

When you specify DelayProfile as 'None', this property does not apply.

Data Types: double

Normalize path gains, specified as a numeric or logical 1 (true) or 0 (false). To normalize the fading processes such that the total power of the path gains, averaged over time, is 0 dB, set this property to 1 (true). Otherwise, set this property to 0 (false).

Dependencies

When you specify DelayProfile as 'None', this property does not apply because the path gains are always normalized when the channel matrix is a DFT matrix.

Data Types: logical

Number of transmit antennas, specified as a positive integer.

Data Types: double

Distance between transmit antenna elements, specified as a positive scalar expressed in wavelengths.

TransmitAntennaSpacing supports uniform linear arrays only.

Dependencies

  • To enable this property, set the NumTransmitAntennas property to a value greater than 1.

  • When you specify DelayProfile as 'None', this property does not apply.

Data Types: double

Number of receive antennas, specified as a positive integer.

Data Types: double

Distance between receive antenna elements, specified as a positive scalar expressed in wavelengths.

ReceiveAntennaSpacing supports uniform linear arrays only.

Dependencies

  • To enable this property, set the NumReceiveAntennas property to a value greater than 1.

  • When you specify DelayProfile as 'None', this property does not apply.

Data Types: double

Large-scale fading effects applied in the channel, specified as 'None', 'Pathloss', 'Shadowing', or 'Pathloss and shadowing'.

Dependencies

When you specify DelayProfile as 'None', the value of this property must be 'None'.

Data Types: char | string

Fluorescent effect, specified as a numeric or logical 1 (true) or 0 (false). To include Doppler effects from fluorescent lighting, set this property to 1 (true).

Dependencies

To enable this property, set the DelayProfile property to 'Model-D' or 'Model-E'.

Data Types: logical

Power line frequency in Hz, specified as '50Hz' or '60Hz'.

The power line frequency is 60 Hz in the United States and 50 Hz in Europe.

Dependencies

To enable this property, set the FluorescentEffect property to 1 (true) and the DelayProfile property to 'Model-D' or 'Model-E'.

Data Types: char | string

Normalize channel outputs by the number of receive antennas, specified as a numeric or logical 1 (true) or 0 (false).

Data Types: logical

Enable channel filtering, specified as a numeric or logical 1 (true) or 0 (false). To enable channel filtering, set this property to 1 (true). To disable channel filtering, set this property to 0 (false)..

Note

If you set this property to 0 (false), the step object function does not accept an input signal. In this case, the NumSamples and SampleRate properties determine the duration of the fading process realization. The object acts as a source of path gains without filtering an input signal.

Data Types: logical

Number of time-domain samples used to get path gain samples, specified as a positive integer.

Dependencies

To enable this property, set the ChannelFiltering property to false.

Data Types: double

Data type of impaired signal, specified as one of these values:

  • 'double' – Return the pathGains output as a double-precision matrix

  • 'single' – Return the pathGains output as a single-precision matrix

Dependencies

To enable this property, set the ChannelFiltering property to 0 (false).

Data Types: char | string

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

If you set this property to 'Global stream', the System object uses the current global random number stream to generate random numbers. In this case, the reset function resets the filters and creates a new channel realization.

If you set this property to 'mt19937ar with seed', the mt19937ar algorithm generates random numbers. In this case, the reset function not only resets the filters, but also reinitializes the random number stream to the value of the Seed property. This results in the same channel realization.

Note

The random numbers of the channel components are distributed as follows:

  • The random phase of the Doppler component due to fluorescent lights is uniformly distributed. See equation 27 of TGn Channel Models for more information.

  • In multi-user scenarios using the TGac, TGah, or TGax channel models, the per-user angle-of-arrival (AoA) and angle-of-departure (AoD) rotations discussed in the MIMO Enhancements section are uniformly distributed.

  • The fading samples are generated by a normally-distributed complex uncorrelated Gaussian process with zero mean and unit variance in discrete time.

Dependencies

When you specify DelayProfile as 'None', this property does not apply.

Data Types: char | string

Initial seed of an mt19937ar random number stream, specified as a nonnegative integer. The Seed property reinitializes the mt19937ar random number stream in the reset function.

Dependencies

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

  • When you specify DelayProfile as 'None', this property does not apply.

Data Types: double

Enable path gain output computation, specified as a numeric or logical 1 (true) or 0 (false).

Data Types: logical

Usage

Syntax

y = tgn(x)
[y,pathGains] = tgn(x)
pathGains = tgac(x)

Description

y = tgn(x) filters input signal x through the TGn fading channel defined by the wlanTGnChannel System object, tgn, and returns the result in y.

example

[y,pathGains] = tgn(x) also returns in pathGains the TGn channel path gains of the underlying fading process.

This syntax applies when you set the PathGainsOutputPort property to 1 (true).

pathGains = tgac(x) returns the path gains. The NumSamples property determines the duration of the fading process.

This syntax applies when you set the ChannelFiltering property to 0 (false).

Input Arguments

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Input signal, specified as a real or complex NS-by-NT matrix, where:

  • NS is the number of samples.

  • NT is the number of transmit antennas and must be equal to the NumTransmitAntennas property value.

Data Types: single | double
Complex Number Support: Yes

Output Arguments

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Output signal, returned as an NS-by-NR complex matrix, where:

  • NS is the number of samples.

  • NR is the number of receive antennas and is equal to the NumReceiveAntennas property value.

Data Types: single | double

Path gains of the fading process, returned as an NS-by-NP-by-NT-by-NR complex array, where:

  • NS is the number of samples.

  • NP is the number of resolvable paths, that is, the number of paths defined for the case specified by the DelayProfile property.

  • NT is the number of transmit antennas and is equal to the NumTransmitAntennas property value.

  • NR is the number of receive antennas and is equal to the NumReceiveAntennas property value.

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)

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infoCharacteristic information about multipath fading channels
stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Note

reset: If the RandomStream property of the System object is set to 'Global stream', the reset function resets the filters only. If you set RandomStream to 'mt19937ar with seed', the reset function not only resets the filters, but also reinitializes the random number stream to the value of the Seed property. This results in the same channel realization.

Examples

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Open Live Script

Generate an HT waveform and pass it through a TGn SISO channel. Display the spectrum of the resultant signal.

Set the channel bandwidth and the corresponding sample rate.

bw = 'CBW40';
fs = 40e6;

Generate an HT waveform for a 40 MHz channel.

cfg = wlanHTConfig('ChannelBandwidth',bw);
txSig = wlanWaveformGenerator(randi([0 1],1000,1),cfg);

Create a TGn SISO channel with path loss and shadowing enabled.

tgnChan = wlanTGnChannel('SampleRate',fs, ...
    'LargeScaleFadingEffect','Pathloss and shadowing');

Pass the HT waveform through the channel. 

rxSig = tgnChan(txSig);

Plot the spectrum of the received waveform. 

saScope = spectrumAnalyzer(SampleRate=fs,YLimits=[-120 -40]);
saScope(rxSig)

Because path loss and shadowing are enabled, the mean received power across the spectrum is approximately -60 dBm.

Open Live Script

Create an HT waveform having four transmit antennas and two space-time streams.

cfg = wlanHTConfig('NumTransmitAntennas',4,'NumSpaceTimeStreams',2, ...
    'SpatialMapping','Fourier');
txSig = wlanWaveformGenerator([1;0;0;1],cfg);

Create a 4x2 MIMO TGn channel and disable large-scale fading effects.

tgnChan = wlanTGnChannel('SampleRate',20e6, ...
    'NumTransmitAntennas',4, ...
    'NumReceiveAntennas',2, ...
    'LargeScaleFadingEffect','None');

Pass the transmit waveform through the channel.

rxSig = tgnChan(txSig);

Display the spectrum of the two received space-time streams.

saScope = spectrumAnalyzer(SampleRate=20e6, ...
    ShowLegend=true, ...
    ChannelNames={'Stream 1','Stream 2'});
saScope(rxSig)

Open Live Script

Transmit an HT-LTF and an HT data field through a noisy 2x2 MIMO channel. Demodulate the received HT-LTF to estimate the channel coefficients. Recover the HT data and determine the number of bit errors.

Set the channel bandwidth and corresponding sample rate.

bw = 'CBW40';
fs = 40e6;

Create HT-LTF and HT data fields having two transmit antennas and two space-time streams.

cfg = wlanHTConfig('ChannelBandwidth',bw, ...
    'NumTransmitAntennas',2,'NumSpaceTimeStreams',2);
txPSDU = randi([0 1],8*cfg.PSDULength,1);
txLTF = wlanHTLTF(cfg);
txDataSig = wlanHTData(txPSDU,cfg);

Create a 2x2 MIMO TGn channel with path loss and shadowing enabled.

tgnChan = wlanTGnChannel('SampleRate',fs, ...
    'NumTransmitAntennas',2,'NumReceiveAntennas',2, ...
    'LargeScaleFadingEffect','None');

Create AWGN channel noise, setting SNR = 15 dB.

chNoise = comm.AWGNChannel('NoiseMethod','Signal to noise ratio (SNR)',...
    'SNR',15);

Pass the signals through the TGn channel and noise models.

rxLTF = chNoise(tgnChan(txLTF));
rxDataSig = chNoise(tgnChan(txDataSig));

Create an AWGN channel for a 40 MHz channel with a 9 dB noise figure. The noise variance, nVar, is equal to kTBF, where k is Boltzmann's constant, T is the ambient temperature of 290 K, B is the bandwidth (sample rate), and F is the receiver noise figure.

nVar = 10^((-228.6 + 10*log10(290) + 10*log10(fs) + 9)/10);
awgnChan = comm.AWGNChannel('NoiseMethod','Variance','Variance',nVar);

Pass the signals through the channel.

rxLTF = awgnChan(rxLTF);
rxDataSig = awgnChan(rxDataSig);

Demodulate the HT-LTF. Use the demodulated signal to estimate the channel coefficients.

dLTF = wlanHTLTFDemodulate(rxLTF,cfg);
chEst = wlanHTLTFChannelEstimate(dLTF,cfg);

Recover the data and determine the number of bit errors.

rxPSDU = wlanHTDataRecover(rxDataSig,chEst,nVar,cfg);
numErr = biterr(txPSDU,rxPSDU)
numErr = 
0
Open Live Script

Create a non-HT configuration object with default parameters. Generate a waveform for the configuration.

cfg = wlanNonHTConfig;
tx = wlanWaveformGenerator([1;0;0;1],cfg);

Create a TGn channel System object with default parameters. Display the value of the RandomStream property.

tgnChan = wlanTGnChannel;
disp(tgnChan.RandomStream)
Global stream

Pass the waveform through the channel twice, resetting the System object between the two iterations.

for i = 1:2
    rx(:,i) = tgnChan(tx);
    reset(tgnChan);
end

Compare the two received waveforms. They are different because the reset object function resets the filters and the channel object takes new random numbers from the global stream. This causes it to generate a different channel realization.

isequal(rx(:,1),rx(:,2))
ans = logical
   0

Now release the System object and set the RandomStream property to "mt19937ar with seed".

release(tgnChan);
tgnChan.RandomStream = "mt19937ar with seed";

Pass the waveform through the channel twice, resetting the System object between the two iterations.

for i = 1:2
    rx(:,i) = tgnChan(tx);
    reset(tgnChan);
end

Compare the two received waveforms. They are equal because the channel realization is the same for both iterations. This happens because the reset function reinitializes the random number stream to the value of the Seed property, so the channel object uses the same random numbers for both channel realizations.

isequal(rx(:,1),rx(:,2))
ans = logical
   1

Algorithms

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The 802.11n channel object uses a filtered Gaussian noise model in which the path delays, powers, angular spread, angles of arrival, and angles of departure are determined empirically. The specific modeling approach is described in [1].

References

[1] Erceg, V., L. Schumacher, P. Kyritsi, et al. TGn Channel Models. Version 4. IEEE 802.11-03/940r4, May 2004.

[2] Kermoal, J. P., L. Schumacher, K. I. Pedersen, P. E. Mogensen, and F. Frederiksen, “A Stochastic MIMO Radio Channel Model with Experimental Validation”. IEEE Journal on Selected Areas in Communications., Vol. 20, No. 6, August 2002, pp. 1211–1226.

Extended Capabilities

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Version History

Introduced in R2015b

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See Also

Objects