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wlanTGnChannel

Filter signal through 802.11n multipath fading channel

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? (MATLAB).

Creation

Syntax

tgn = wlanTGnChannel
tgn = wlanTGnChannel(Name,Value)

Description

example

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.

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 (MATLAB).

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

Data Types: double

Delay profile model, specified as 'Model-A', 'Model-B', 'Model-C', 'Model-D', 'Model-E', or 'Model-F'.

The table summarizes the models properties before the bandwidth reduction factor.

ParameterModel
ABCDEF
Breakpoint distance (m)555102030
RMS delay spread (ns)0153050100150
Maximum delay (ns)0802003907301050
Rician K-factor (dB)000366
Number of clusters122346
Number of taps1914181818

Data Types: char | string

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

Data Types: double

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

Data Types: double

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

Data Types: double

Normalize path gains, specified as true or 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 true (default). When you set this property to false, the path gains are not normalized.

Data Types: logical

Number of transmit antennas, specified as a positive integer from 1 to 4.

Data Types: double

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

TransmitAntennaSpacing supports uniform linear arrays only.

Dependencies

This property applies only when NumTransmitAntennas is greater than 1.

Data Types: double

Number of receive antennas, specified as a positive integer from 1 to 4.

Data Types: double

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

ReceiveAntennaSpacing supports uniform linear arrays only.

Dependencies

This property applies only when NumReceiveAntennas is greater than 1.

Data Types: double

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

Data Types: char | string

Fluorescent effect, specified as true or false. To include Doppler effects from fluorescent lighting set this property to true.

Dependencies

The FluorescentEffect property applies only when DelayProfile is '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

This property applies only when you set FluorescentEffect to true and DelayProfile to 'Model-D' or 'Model-E'.

Data Types: char | string

Normalize channel outputs by the number of receive antennas, specified as a true or false.

Data Types: logical

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

If you set RandomStream to 'Global stream', the current global random number stream generates normally distributed random numbers. In this case, the reset function resets the filters only.

If you set RandomStream to 'mt19937ar with seed', the mt19937ar algorithm generates normally distributed random numbers. In this case, the reset function also reinitializes the random number stream to the value of the Seed property.

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

This property applies only when you set the RandomStream property to 'mt19937ar with seed'.

Data Types: double

Enable path gain output computation, specified as true or false.

Data Types: logical

Usage

Syntax

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

Description

example

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.

[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 true.

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: 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: 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: 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 TGn, TGah, TGac, and TGax 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 also reinitializes the random number stream to the value of the Seed property.

Examples

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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 = dsp.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.

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

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

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

Introduced in R2015b