wlanTGacChannel

Filter signal through 802.11ac multipath fading channel

Description

The wlanTGacChannel System object™ filters an input signal through an 802.11ac™ (TGac) multipath fading channel.

The fading processing assumes the same parameters for all N_T-by-N_R links of the TGac channel, where N_T is the number of transmit antennas and N_R is the number of receive antennas. Each link comprises all multipaths for that link.

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

Create the wlanTGacChannel object 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

Syntax

tgac = wlanTGacChannel

tgac = wlanTGacChannel(Name,Value)

Description

example

tgac = wlanTGacChannel creates a TGac fading channel System object, tgac. This object filters a real or complex input signal through the TGac channel to obtain the channel-impaired signal.

tgac = wlanTGacChannel(Name,Value) creates a TGac channel object, tgac, and sets properties using one or more name-value pairs. Enclose each property name in quotes. For example, wlanTGacChannel('NumReceiveAntennas',2,'SampleRate',10e6) creates a TGac 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.

`SampleRate` — Sample rate of the input signal
`80e6` (default) | positive scalar

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

Data Types: double

`DelayProfile` — Delay profile model
`'Model-B'` (default) | `'Model-A'` | `'Model-C'` | `'Model-D'` | `'Model-E'` | `'Model-F'`

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

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

Parameter	Model
Parameter	A	B	C	D	E	F
Breakpoint distance (m)	5	5	5	10	20	30
RMS delay spread (ns)	0	15	30	50	100	150
Maximum delay (ns)	0	80	200	390	730	1050
Rician K-factor (dB)	0	0	0	3	6	6
Number of taps	1	9	14	18	18	18
Number of clusters	1	2	2	3	4	6

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

Data Types: char | string

`ChannelBandwidth` — Channel bandwidth
`'CBW80'` (default) | `'CBW20'` | `'CBW40'` | `'CBW160'`

Channel bandwidth, specified as 'CBW20', 'CBW40', 'CBW80', or 'CBW160'. The default is 'CBW80', which corresponds to an 80 MHz channel bandwidth.

Data Types: char | string

`CarrierFrequency` — RF carrier frequency
`5.25e9` (default) | positive scalar

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

Data Types: double

`EnvironmentalSpeed` — Speed of the scatterers
`0.089` (default) | positive scalar

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

Data Types: double

`TransmitReceiveDistance` — Distance between transmitter and receiver
`3` (default) | positive scalar

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.

Data Types: double

`NormalizePathGains` — Normalize path gains
`true` or `1` (default) | `false` or `0`

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).

Data Types: logical

`UserIndex` — User index for single or multi-user scenario
`0` (default) | nonnegative integer

User index, specified as a nonnegative integer. This property specifies the single user or a particular user in a multiuser scenario.

Data Types: double

`TransmissionDirection` — Transmission direction
`'Downlink'` (default) | `'Uplink'`

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

Data Types: char | string

`NumTransmitAntennas` — Number of transmit antennas
`1` (default) | positive integer

Number of transmit antennas, specified as a positive integer.

Data Types: double

`TransmitAntennaSpacing` — Distance between transmit antenna elements
`0.5` (default) | positive scalar

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.

Data Types: double

`NumReceiveAntennas` — Number of receive antennas
`1` (default) | positive integer

Number of receive antennas, specified as a positive integer.

Data Types: double

`ReceiveAntennaSpacing` — Distance between receive antenna elements
`0.5` (default) | positive scalar

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.

Data Types: double

`LargeScaleFadingEffect` — Large-scale fading effects
`'None'` (default) | `'Pathloss'` | `'Shadowing'` | `'Pathloss and shadowing'`

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

Data Types: char | string

`FluorescentEffect` — Fluorescent effect
`true` or `1` (default) | `false` or `0`

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

`PowerLineFrequency` — Power line frequency
`'60Hz'` (default) | `'50Hz'`

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

`NormalizeChannelOutputs` — Normalize channel outputs
`true` or `1` (default) | `false` or `0`

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

Data Types: logical

`ChannelFiltering` — Enable channel filtering
`true` or `1` (default) | `false` or `0`

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.

Data Types: logical

`NumSamples` — Number of time-domain samples
`320` (default) | positive integer

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 0 (false).

Data Types: double

`OutputDataType` — Data type of impaired signal
`'double'` (default) | `'single'`

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

`RandomStream` — Source of random number stream
`'Global stream'` (default) | `'mt19937ar with seed'`

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

If you set this property to 'Global stream', the current global random number stream generates normally-distributed 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 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

`Seed` — Initial seed of mt19937ar random number stream
`73` (default) | nonnegative integer

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'.

Data Types: double

`PathGainsOutputPort` — Enable path gain output
`false` or `0` (default) | `true` or `1`

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

Data Types: logical

Usage

Syntax

y = tgac(x)

[y,pathGains] = tgac(x)

pathGains = tgac(x)

Description

example

y = tgac(x) filters input signal x through the TGac fading channel defined by the wlanTGacChannel System object, tgac, and returns the result in y.

[y,pathGains] = tgac(x) also returns in pathGains the TGac 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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`x` — Input signal
complex matrix

Input signal, specified as a real or complex N_S-by-N_T matrix, where:

N_S is the number of samples.
N_T 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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`y` — Output signal
complex matrix

Output signal, returned as an N_S-by-N_R complex matrix, where:

N_S is the number of samples.
N_R is the number of receive antennas and is equal to the NumReceiveAntennas property value.

Data Types: single | double

`pathGains` — Path gains of the fading process
complex array

Path gains of the fading process, returned as an N_S-by-N_P-by-N_T-by-N_R complex array, where:

N_S is the number of samples.
N_P is the number of resolvable paths, that is, the number of paths defined for the case specified by the DelayProfile property.
N_T is the number of transmit antennas and is equal to the NumTransmitAntennas property value.
N_R 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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Specific to wlanTGacChannel

info Characteristic information about TGn, TGah, TGac, and TGax multipath fading channels

Common to All System Objects

`step`	Run System object algorithm
`release`	Release resources and allow changes to System object property values and input characteristics
`reset`	Reset 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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Transmit VHT Waveform Through TGac Channel

Open Script

Generate a VHT waveform and pass it through a TGac SISO channel. Display the spectrum of the resultant signal.

Set the channel bandwidth and the corresponding sample rate.

bw = 'CBW80';
fs = 80e6;

Generate a VHT waveform.

cfg = wlanVHTConfig;
txSig = wlanWaveformGenerator(randi([0 1],1000,1),cfg);

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

tgacChan = wlanTGacChannel('SampleRate',fs,'ChannelBandwidth',bw, ...
    'LargeScaleFadingEffect','Pathloss and shadowing');

Pass the VHT waveform through the channel.

rxSig = tgacChan(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.

Transmit VHT Waveform Through 4x2 MIMO Channel

Open Script

Create a VHT waveform having four transmit antennas and two space-time streams.

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

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

tgacChan = wlanTGacChannel('SampleRate',80e6,'ChannelBandwidth','CBW80', ...
    'NumTransmitAntennas',4,'NumReceiveAntennas',2, ...
    'LargeScaleFadingEffect','None');

Pass the transmit waveform through the channel.

rxSig = tgacChan(txSig);

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

saScope = dsp.SpectrumAnalyzer('SampleRate',80e6, ...
    'ShowLegend',true, ...
    'ChannelNames',{'Stream 1','Stream 2'});
saScope(rxSig)

Recover VHT Data from 2x2 MIMO Channel

Open Live Script

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

Set the channel bandwidth and corresponding sample rate.

bw = 'CBW160';
fs = 160e6;

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

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

Create a 2x2 MIMO TGac channel.

tgacChan = wlanTGacChannel('SampleRate',fs,'ChannelBandwidth',bw, ...
    'NumTransmitAntennas',2,'NumReceiveAntennas',2);

Create an AWGN channel noise, setting SNR = 15 dB.

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

Pass the signals through the TGac channel and noise models.

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

Create an AWGN channel for a 160 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);
rxNoise = comm.AWGNChannel('NoiseMethod','Variance','Variance',nVar);

Pass the signals through the receiver noise model.

rxLTF = rxNoise(rxLTF);
rxDataSig = rxNoise(rxDataSig);

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

dLTF = wlanVHTLTFDemodulate(rxLTF,cfg);
chEst = wlanVHTLTFChannelEstimate(dLTF,cfg);

Recover the data and determine the number of bit errors.

rxPSDU = wlanVHTDataRecover(rxDataSig,chEst,nVar,cfg);
numErr = biterr(txPSDU,rxPSDU)

numErr = 0

Algorithms

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The algorithms used to model the TGac channel are based on those used for the TGn channel and are described in wlanTGnChannel and [1]. The changes to support the TGac channel include:

increased bandwidth
higher-order MIMO
multi-user MIMO
reduced Doppler

Complete information on the changes required to support TGac channels can be found in [2].

Increased Bandwidth

TGac channels support bandwidths of up to 1.28 GHz, whereas TGn channels have a maximum bandwidth of 40 MHz. By increasing the sampling rate and decreasing the tap spacing of the power delay profile (PDP), the TGn model is used as the basis for TGac. The channel sampling rate is increased by a factor of $2^{⌈ \log_{2} (W / 40) ⌉}$ , where W is the bandwidth. The PDP tap spacing is reduced by the same factor.

Bandwidth, W	Sampling Rate Expansion Factor	PDP Tap Spacing (ns)
W ≤ 40 MHz	1	10
40 MHz < W ≤ 80 MHz	2	5
80 MHz < W ≤ 160 MHz	4	2.5
160 MHz < W ≤ 320 MHz	8	1.25
320 MHz < W ≤ 640 MHz	16	0.625
640 MHz < W ≤ 1280 MHz	32	0.3125

MIMO Enhancements

The TGn channel model supports no more than 4x4 MIMO, while the TGac model supports 8x8 MIMO.

The TGac model also includes support for multiple users while simultaneous communication takes place between access points and user stations. Accordingly, the TGac model extends the concept of cluster angles of arrival and departure to account for point-to-multipoint transmission. For more details, see [3].

Reduced Doppler

Indoor channel measurements indicate that the magnitude of Doppler assumed in the TGn channel model is too high for stationary users. As such, the TGac channel model uses a reduced environment velocity of 0.089 km/hr. This model assumes a coherence time of 800 ms or, equivalently, an RMS Doppler spread of 0.4 Hz for a 5 GHz carrier frequency.

References

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

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

[3] 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.

Documentation

wlanTGacChannel

Description

Creation

Syntax

Description

Properties

SampleRate — Sample rate of the input signal 80e6 (default) | positive scalar

DelayProfile — Delay profile model 'Model-B' (default) | 'Model-A' | 'Model-C' | 'Model-D' | 'Model-E' | 'Model-F'

ChannelBandwidth — Channel bandwidth 'CBW80' (default) | 'CBW20' | 'CBW40' | 'CBW160'

CarrierFrequency — RF carrier frequency 5.25e9 (default) | positive scalar

EnvironmentalSpeed — Speed of the scatterers 0.089 (default) | positive scalar

TransmitReceiveDistance — Distance between transmitter and receiver 3 (default) | positive scalar

NormalizePathGains — Normalize path gains true or 1 (default) | false or 0

UserIndex — User index for single or multi-user scenario 0 (default) | nonnegative integer

TransmissionDirection — Transmission direction 'Downlink' (default) | 'Uplink'

NumTransmitAntennas — Number of transmit antennas 1 (default) | positive integer

TransmitAntennaSpacing — Distance between transmit antenna elements 0.5 (default) | positive scalar

Dependencies

NumReceiveAntennas — Number of receive antennas 1 (default) | positive integer

ReceiveAntennaSpacing — Distance between receive antenna elements 0.5 (default) | positive scalar

Dependencies

LargeScaleFadingEffect — Large-scale fading effects 'None' (default) | 'Pathloss' | 'Shadowing' | 'Pathloss and shadowing'

FluorescentEffect — Fluorescent effect true or 1 (default) | false or 0

Dependencies

PowerLineFrequency — Power line frequency '60Hz' (default) | '50Hz'

Dependencies

NormalizeChannelOutputs — Normalize channel outputs true or 1 (default) | false or 0

ChannelFiltering — Enable channel filtering true or 1 (default) | false or 0

NumSamples — Number of time-domain samples 320 (default) | positive integer

Dependencies

OutputDataType — Data type of impaired signal 'double' (default) | 'single'

Dependencies

RandomStream — Source of random number stream 'Global stream' (default) | 'mt19937ar with seed'

Seed — Initial seed of mt19937ar random number stream 73 (default) | nonnegative integer

Dependencies

PathGainsOutputPort — Enable path gain output false or 0 (default) | true or 1

Usage

Syntax

Description

Input Arguments

x — Input signal complex matrix

Output Arguments

y — Output signal complex matrix

pathGains — Path gains of the fading process complex array

Object Functions

Specific to wlanTGacChannel

Common to All System Objects

Examples

Transmit VHT Waveform Through TGac Channel

Transmit VHT Waveform Through 4x2 MIMO Channel

Recover VHT Data from 2x2 MIMO Channel

Algorithms

Increased Bandwidth

MIMO Enhancements

Reduced Doppler

References

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™.

See Also

Objects

WLAN Toolbox Documentation

Support

`SampleRate` — Sample rate of the input signal
`80e6` (default) | positive scalar

`DelayProfile` — Delay profile model
`'Model-B'` (default) | `'Model-A'` | `'Model-C'` | `'Model-D'` | `'Model-E'` | `'Model-F'`

`ChannelBandwidth` — Channel bandwidth
`'CBW80'` (default) | `'CBW20'` | `'CBW40'` | `'CBW160'`

`CarrierFrequency` — RF carrier frequency
`5.25e9` (default) | positive scalar

`EnvironmentalSpeed` — Speed of the scatterers
`0.089` (default) | positive scalar

`TransmitReceiveDistance` — Distance between transmitter and receiver
`3` (default) | positive scalar

`NormalizePathGains` — Normalize path gains
`true` or `1` (default) | `false` or `0`

`UserIndex` — User index for single or multi-user scenario
`0` (default) | nonnegative integer

`TransmissionDirection` — Transmission direction
`'Downlink'` (default) | `'Uplink'`

`NumTransmitAntennas` — Number of transmit antennas
`1` (default) | positive integer

`TransmitAntennaSpacing` — Distance between transmit antenna elements
`0.5` (default) | positive scalar

`NumReceiveAntennas` — Number of receive antennas
`1` (default) | positive integer

`ReceiveAntennaSpacing` — Distance between receive antenna elements
`0.5` (default) | positive scalar

`LargeScaleFadingEffect` — Large-scale fading effects
`'None'` (default) | `'Pathloss'` | `'Shadowing'` | `'Pathloss and shadowing'`

`FluorescentEffect` — Fluorescent effect
`true` or `1` (default) | `false` or `0`

`PowerLineFrequency` — Power line frequency
`'60Hz'` (default) | `'50Hz'`

`NormalizeChannelOutputs` — Normalize channel outputs
`true` or `1` (default) | `false` or `0`

`ChannelFiltering` — Enable channel filtering
`true` or `1` (default) | `false` or `0`

`NumSamples` — Number of time-domain samples
`320` (default) | positive integer

`OutputDataType` — Data type of impaired signal
`'double'` (default) | `'single'`

`RandomStream` — Source of random number stream
`'Global stream'` (default) | `'mt19937ar with seed'`

`Seed` — Initial seed of mt19937ar random number stream
`73` (default) | nonnegative integer

`PathGainsOutputPort` — Enable path gain output
`false` or `0` (default) | `true` or `1`

`x` — Input signal
complex matrix

`y` — Output signal
complex matrix

`pathGains` — Path gains of the fading process
complex array

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.