wlanTGaxChannel
Filter signal through 802.11ax multipath fading channel
Description
The wlanTGaxChannel
System object™ filters an input signal through an 802.11ax™ (TGax) indoor MIMO channel as specified in [1], following the MIMO modeling approach described in [4].
The fading processing assumes the same parameters for all NT-by-NR links of the TGax 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 TGax multipath fading channel:
Create the
wlanTGaxChannelobject and set its properties.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
Description
tgax = wlanTGaxChanneltgax. This object filters a real or complex
input signal through the TGax channel to obtain the channel-impaired
signal.
tgax = wlanTGaxChannel(Name=Value)tgax, and sets properties
using one or more name-value arguments. For example,
wlanTGaxChannel(NumReceiveAntennas=2,SampleRate=10e6)
creates a TGax channel with two receive antennas and a 10 MHz sample
rate.
Properties
Usage
Description
[
also returns in y,pathGains] = tgax(x)pathGains the TGax channel path gains of
the underlying fading process.
This syntax applies when you set the PathGainsOutputPort property of tgax to
1 (true).
Input Arguments
Output Arguments
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)
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
Obtain a channel impulse response by filtering an impulse through a TGax channel.
Create an impulse.
input = zeros(100,1); input(10) = 1;
Create the TGax channel System Object with path loss and shadowing, two penetrated floors, and a sampling rate of 1 GHz.
tgax = wlanTGaxChannel; tgax.LargeScaleFadingEffect = 'Pathloss and shadowing'; tgax.NumPenetratedFloors = 2; tgax.RandomStream = 'mt19937ar with seed'; tgax.Seed = 10; tgax.SampleRate = 1e9;
Plot the output impulse response of the channel.
figure time = (1/tgax.SampleRate)*(0:length(input)-1); stem(time,abs(tgax(input))) xlabel('Time (s)') ylabel('Amplitude') title('Channel Impulse Response')
Plot the delay profile and path gains of a TGax channel.
Create an impulse.
input = zeros(100,4); input(10) = 1;
Create the TGax channel System Object. Enable path gains at the output, and specify path loss, 20 MHz of channel bandwidth, a 4x2 MIMO channel, four penetrated floors, and a sampling rate of 1 GHz.
tgax = wlanTGaxChannel; tgax.LargeScaleFadingEffect = 'Pathloss'; tgax.ChannelBandwidth = 'CBW20'; tgax.NumTransmitAntennas = 4; tgax.NumReceiveAntennas = 2; tgax.NumPenetratedFloors = 4; tgax.RandomStream = 'mt19937ar with seed'; tgax.Seed = 10; tgax.SampleRate = 1e9; tgax.PathGainsOutputPort = true;
Filter the input impulse. Use the TGax channel object to generate the output response and the path gains.
[out,pathgains]= tgax(input);
Plot the output impulse response of the channel. The channel has two delay profiles, one per each receive antenna.
figure time = (1/tgax.SampleRate)*(0:length(input)-1); stem(time,abs(out)) xlabel('Time (s)') ylabel('Amplitude') title('Delay Profile')
The path gains of the channel are contained in a four dimensional array since the channel has nine resolvable paths, four transmit antennas and two receive antennas.
size(pathgains)
ans = 1×4
100 9 4 2
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
References
[1] Jianhan, L., Ron, P. et al. TGax Channel Model. IEEE 802.11-14/0882r4, September 2014.
[2] Erceg, V., Schumacher, L., Kyritsi, P. et al. TGn Channel Models. Version 4. IEEE 802.11-03/940r4, May 2004.
[3] Breit, G., Sampath, H., Vermani, S. 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.
