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wlanTGahChannel System object

Filter signal through 802.11ah multipath fading channel

Description

The wlanTGahChannel System object™ filters an input signal through an 802.11ah™ (TGah) indoor MIMO channel as specified in [1], following the MIMO modeling approach in [4].

The fading processing assumes the same parameters for all NT-by-NR links of the TGah channel, where 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 TGah multipath fading channel:

  1. Define and set up your TGah channel object. See Construction.

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

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

tgah = wlanTGahChannel creates a TGah fading channel System object, tgah. This object filters a real or complex input signal through the TGah channel to obtain the channel-impaired signal.

tgah = wlanTGahChannel(Name,Value) creates a TGah channel object, tgah, 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

Sample rate of the input signal in Hz, specified as a real positive scalar. The default is 2e6.

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'.

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 taps1914181818
Number of clusters122346

The number of clusters represents the number of independently modeled propagation paths.

ChannelBandwidth

Channel bandwidth

Channel bandwidth, specified as 'CBW1', 'CBW2', 'CBW4', 'CBW8', or 'CBW16'. The default is 'CBW2', which corresponds to a 2 MHz channel bandwidth.

As specified in TGac Channel Model Addendum [3], a reduction factor is applied to the multipath spacing of the power delay profile for channel bandwidths greater than 4 MHz. The reduction factor applied to the multipath spacing is 2ceil(log2(BW/4)), where BW is the channel bandwidth in MHz.

CarrierFrequency

RF carrier frequency

RF carrier frequency in Hz, specified as a real positive scalar. The default is 915e6 Hz.

TransmitReceiveDistance

Distance between transmitter and receiver

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

TransmitReceiveDistance is used to compute the path loss, and to determine whether the channel has a line-of-sight (LOS) or no-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.

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.

UserIndex

User index for single or multi-user scenario

User index, specified as a nonnegative integer scalar. UserIndex specifies the single user or a particular user in a multiuser scenario. The default is 0.

A pseudorandom per-user angle-of-arrival (AoA) and angle-of-departure (AoD) rotation is applied to support a multi-user scenario. A value of 0 indicates a simulation scenario that does not require per-user angle diversity and assumes the TGn defined cluster AoAs and AoDs.

TransmissionDirection

Transmission direction

Transmission direction of the active link, specified as either 'Uplink' or 'Downlink'. The default is 'Downlink'.

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.

TransmitAntennaSpacing supports uniform linear array only. This property applies only 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.

ReceiveAntennaSpacing supports uniform linear array only. This property applies only 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'.

FloorSeparation

Floor separation

Floor separation, specified as a real scalar, indicating the number of building floors between the transmitter and the receiver in order to account for the floor attenuation loss in the calculation of path loss in a multiple floor scenario. The default is 0, which represents a communication link between a transmitter and a receiver located on the same floor.

The FloorSeparation property applies only when DelayProfile is 'Model-A' or 'Model-B'.

FluorescentEffect

Enable fluorescent effect

To include Doppler effects due to fluorescent lighting, set this property to true (default).

The FluorescentEffect property applies only when DelayProfile is 'Model-D' or 'Model-E'.

PowerLineFrequency

Frequency of the power line (Hz)

Frequency of the power line in Hz, specified as '50Hz' or '60Hz'. The default is '60Hz'.

The power line frequency is 60 Hz in USA and 50 Hz in Europe. This property applies only when you set FluorescentEffect to true and DelayProfile to '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 stream, specified as a real, nonnegative integer scalar. The default is 73.

This property applies only 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 is false.

Methods

infoDisplay information about TGah Channel object
resetReset states of the wlanTGahChannel object
stepFilter signal through 802.11ah 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

Filter an 802.11ah waveform through a TGah channel. Specify a seed value to produce a repeatable channel output.

Create an S1G configuration object and waveform.

cfgS1G = wlanS1GConfig;
txWaveform = wlanWaveformGenerator([1;0;0;1],cfgS1G);

Create a TGah channel object and adjust some default properties. Pass the S1G waveform through the channel by supplying it as an input to the TGah channel object.

tgah = wlanTGahChannel;
tgah.LargeScaleFadingEffect = 'PathLoss and shadowing';
tgah.FloorSeparation = 2;
tgah.RandomStream = 'mt19937ar with seed';
tgah.Seed = 10;

channelOutput = tgah(txWaveform);

Confirm the channel bandwidth and set the corresponding sample rate.

cfgS1G.ChannelBandwidth
fs = 2e6;
ans =

    'CBW2'

Plot the spectrum of the channel output waveform.

saScope = dsp.SpectrumAnalyzer('SampleRate',fs,'YLimits',[-110 -30]);
saScope(channelOutput)

Across the spectrum, the mean power of the channel output waveform is approximately -50 dBm.

Plot the delay profile for an impulse waveform passed through a TGah channel.

Create an impulse waveform.

txWaveform = zeros(100,1);
% The impulse is delayed by 10 samples. This is equivalent to 10nsec in
% time.
txWaveform(11) = 1;

Create a TGah channel object. Here we specify the seed so that results can be replicated.

tgah = wlanTGahChannel;
tgah.RandomStream = 'mt19937ar with seed';
tgah.Seed = 10;

Set the sample rate so that sampling of the channel multipaths are integer multiples of integer sampling delay.

tgah.SampleRate = 1e9;

chOut = tgah(txWaveform);
plot((0:length(chOut)-1)*1/tgah.SampleRate,abs(chOut));
xlabel('Time[sec]'); ylabel('abs(chOut)');
title('Channel power delay profile: Model-B')

Create a S1G waveform generated using four transmit antennas and two spatial streams.

cfg = wlanS1GConfig('NumTransmitAntennas',4,'NumSpaceTimeStreams',2, ...
    'SpatialMapping','Fourier');
txSig = wlanWaveformGenerator([1;0;0;1],cfg);

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

tgahChan = wlanTGahChannel('SampleRate',1e6,'ChannelBandwidth','CBW1', ...
    'NumTransmitAntennas',4,'NumReceiveAntennas',2, ...
    'LargeScaleFadingEffect','None');

Pass the transmit waveform through the channel.

rxSig = tgahChan(txSig);

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

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

Algorithms

The algorithms used to model the TGah channel are based on those used for the TGn channel (as described in wlanTGnChannel and TGn Channel Models [2]) and the TGac channel (as described in wlanTGacChannel and TGac Channel Model Addendum [3]). Complete information on the changes required to support TGah channels can be found in TGah Channel Model [1]. The changes to support the TGah channel include lower bandwidths, floor separation attenuation, MIMO enhancements, and path loss and shadowing.

Lower Bandwidths

The TGah channel model supports channel bandwidths down to 1 MHz.

Floor Separation Attenuation

The TGah channel model includes floor separation attenuation effects. In the TGah channel, the path loss model used in the spatial correlation computation is updated to include floor separation attenuation effects. The FloorSeparation property applies only when DelayProfile is 'Model-A' or 'Model-B', and LargeScaleFadingEffect is 'Pathloss', 'Shadowing', or 'Pathloss and shadowing'. For more information, see TGah Channel Model [1].

MIMO Enhancements

The TGah channel model supports no more than 4x4 MIMO.

The TGah model also includes support for multiple users as simultaneous communication takes place between access points and user stations. Accordingly, the TGah model extends the concept of cluster angles of arrival and departure to account for point-to-multipoint transmission. For more information, see Stochastic MIMO Radio Channel Model with Experimental Validation [4].

Path Loss and Shadowing

TGah Channel Model [1], Table 2 defines path loss parameters that are slightly modified from those defined for TGn. Specifically, the shadow fading values corresponding to breakpoint distance are 1 dB less for all TGah channel models.

The path loss exponent and the standard deviation of the shadow fading loss characterize each model. The two parameters 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 d ≤ dBP222222
Path loss exponent for d > dBP3.53.53.53.53.53.5
Shadow fading σ (dB) for d ≤ dBP222222
Shadow fading σ (dB) for d > dBP334455

References

[1] Porat R., S.K.. Yong, and K. Doppler. TGah Channel Model. IEEE 802.11-11/0968r4, March 2015.

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

[3] Breit, G., H. Sampath, S. Vermani, et al. TGac Channel Model Addendum. Version 12. IEEE 802.11-09/0308r12, March 2010.

[4] 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 R2017a

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