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wlanTGnChannel System object

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. Define and set up your TGn channel object. See Construction.

  2. Call step to filter the input signal through a TGn multipath fading channel according to the properties of wlanTGnChannel.

Note

Alternatively, instead of using the step method to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

Construction

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, with the specified property Name set to the specified Value. You can specify additional name-value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Properties

SampleRate

Input signal sample rate (Hz)

Sample rate of the input signal in Hz, specified as a real positive scalar. The default is 20e6.

DelayProfile

Delay profile model

Delay profile model, specified as 'Model-A', 'Model-B', 'Model-C', 'Model-D', 'Model-E', or 'Model-F'. The default is 'Model-B'. To enable the FluorescentEffect property, select either 'Model-D' or 'Model-E' .

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

CarrierFrequency

RF carrier frequency (Hz)

Carrier frequency of the channel in Hz, specified as a real positive scalar. The default is 5.25e9.

NormalizePathGains

Normalize path gains

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.

NumTransmitAntennas

Number of transmit antennas

Number of transmit antennas, specified as a positive integer scalar from 1 to 4. The default is 1.

TransmitAntennaSpacing

Distance between transmit antenna elements

Distance between transmit antenna elements, specified as a real positive scalar expressed in wavelengths. The default is 0.5. This property is available when NumTransmitAntennas is greater than 1.

NumReceiveAntennas

Number of receive antennas

Number of receive antennas, specified as a positive integer scalar from 1 to 4. The default is 1.

ReceiveAntennaSpacing

Distance between receive antenna elements

Distance between receive antenna elements, specified as a real positive scalar expressed in wavelengths. The default is 0.5. This property is available when NumReceiveAntennas is greater than 1.

LargeScaleFadingEffect

Large scale fading effects

Type of large-scale fading effects, specified as 'None', 'Pathloss', 'Shadowing', or 'Pathloss and shadowing'. The default is 'None'.

TransmitReceiveDistance

Distance between the transmitter and receiver (m)

Distance in meters between the transmitter and receiver, specified as a real positive scalar. The default is 3.

FluorescentEffect

Enable fluorescent effect

To include Doppler effects due to fluorescent lighting, set this property to true (default). This property is available when DelayProfile is 'Model-D' or 'Model-E'.

PowerLineFrequency

Frequency of the power line (Hz)

Frequency of the power line in Hz, specified as either '50Hz' or '60Hz'. The default is '60Hz'. This property is available when FluorescentEffect is true and DelayProfile is 'Model-D' or 'Model-E'.

NormalizeChannelOutputs

Normalize channel outputs

To normalize the channel outputs by the number of receive antennas, set this property to true (default).

RandomStream

Source of random number stream

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

If you set RandomStream to 'Global stream', the current global random number stream is used for normally distributed random number generation. In this case, the reset method resets the filters only.

If you set RandomStream to 'mt19937ar with seed', the mt19937ar algorithm is used for normally distributed random number generation. In this case, the reset method not only resets the filters but also reinitializes the random number stream to the value of the Seed property.

Seed

Initial seed of mt19937ar random number stream

Initial seed of an mt19937ar random number generator algorithm, specified as a real, nonnegative integer scalar. The default is 73. This property applies when you set the RandomStream property to 'mt19937ar with seed'. The Seed property reinitializes the mt19937ar random number stream in the reset method.

PathGainsOutputPort

Enable path gain output

To enable computation of path gain output, set this property to true. The default value of this property is false.

Methods

infoCharacteristic information about TGn Channel
resetReset states of the wlanTGnChannel object
stepFilter signal through 802.11n multipath fading channel
Common to All System Objects
clone

Create System object with same property values

getNumInputs

Expected number of inputs to a System object

getNumOutputs

Expected number of outputs of a System object

isLocked

Check locked states of a System object (logical)

release

Allow System object property value changes

Examples

expand all

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

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].

Multipath Parameters

The channel is modeled as several clusters each of which represents an independent propagation path between the transmitter and the receiver. A cluster is composed of subpaths or taps which share angular spreads, angles of arrival, and angles of departure. Delay and power level vary from tap to tap. Within the TGn model, clusters comprise 1–7 taps. The cluster parameters for cluster 1 of Model B are shown in the table.

ParameterTap
12345
Delay (ns)010203040
Power (dB)0–5.4–10.8–16.2–21.7
Angle of arrival (°)4.34.34.34.34.3
Receiver angular spread (°)14.414.414.414.414.4
Angle of departure (°)225.1225.1225.1225.1225.1
Transmitter angular spread (°)14.414.414.414.414.4

For each model, the first tap has a line-of-sight (LOS) between the transmitter and receiver, whereas all other taps are non-line-of-sight (NLOS). As a result, the first tap exhibits Rician behavior, while the others exhibit Rayleigh behavior. The Rician K-factor is the ratio between the power in the first tap and the power in the other taps. A large K-factor indicates a strong, LOS component.

The angles of arrival and departure for each cluster are randomly selected from a uniform distribution over [0, 2π]. These angles are independent of each other and are fixed for all channel realizations. By fixing the values, the transmit and receive correlation matrices are computed only once. Angular spread values were indirectly determined from empirical data and fall within the 20° to 40° range.

Path Loss and Shadowing

The path loss exponent and the standard deviation of the shadow fading loss characterize each model. The two parameters are depend on the presence of a line-of-sight between the transmitter and receiver. For paths with a transmitter-to-receiver distance, d, less that the breakpoint distance, dBP, the LOS parameters apply. For d >dBP, the NLOS parameters apply. The table summarizes the path loss and shadow fading parameters.

ParameterModel
ABCDEF
Breakpoint distance, dBP (m)555102030
Path loss exponent for ddBP222222
Path loss exponent for d >dBP3.53.53.53.53.53.5
Shadow fading σ (dB) for ddBP333333
Shadow fading σ (dB) for d >dBP445566

Doppler Effects

In indoor environments, the transmitter and receiver are stationary, and Doppler effects arise from people moving between them. The TGn model employs a bell-shaped Doppler spectrum in which the environmental speed, ν0, is 1.2 km/hr. The Doppler spread, fd, is calculated as fd = ν0/λ, where λ is the carrier wavelength.

In addition to basic Doppler effects resulting from environmental motion, fluorescent lights introduce signal fading at twice the power line frequency. The effects show up as frequency-selective amplitude modulation. The effect is included in models D and E. To disable this effect, set the FluorescentEffects property to false.

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

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