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wlanHTLTFDemodulate

Demodulate HT-LTF waveform

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Syntax

sym = wlanHTLTFDemodulate(rx,cfg)
sym = wlanHTLTFDemodulate(rx,cfg,symOffset)

Description

example

sym= wlanHTLTFDemodulate(rx,cfg)returns the demodulatedHT-LTF1by demodulating received time-domain HT-LTF signalrx. The input signal is a component of theHT-mixedformatPPDU. The function demodulates the signal by using the transmission parameterscfg.

example

sym= wlanHTLTFDemodulate(rx,cfg,symOffset)specifies the OFDM symbol sampling offset as a fraction of the cyclic prefix length.

Examples

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Open Live Script

Create an HT configuration object.

cfg = wlanHTConfig;

Generate an HT-LTF signal based on the object.

x = wlanHTLTF(cfg);

Pass the HT-LTF signal through an AWGN channel.

y = awgn(x,20);

Demodulate the received signal.

z = wlanHTLTFDemodulate(y,cfg);

Display the scatter plot of the demodulated signal.

scatterplot(z)

图散点图包含an axes object. The axes object with title Scatter plot contains an object of type line. This object represents Channel 1.

Open Live Script

Create an HT configuration object having two transmit antennas and two space-time streams.

cfg = wlanHTConfig('NumTransmitAntennas',2,'NumSpaceTimeStreams',2,...'MCS',8);

Generate the HT-LTF based on the configuration object.

x = wlanHTLTF(cfg);

Pass the HT-LTF signal through an AWGN channel.

y = awgn(x,10);

Demodulate the received signal. Set the OFDM symbol offset to0.5, which corresponds to 1/2 of the cyclic prefix length.

z = wlanHTLTFDemodulate(y,cfg,0.5);

Input Arguments

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Received time-domain signal, specified as a complex-valued matrix of sizeNs-by-Nr.

  • Nsis the number of time-domain samples. IfNsis not an integer multiple of the OFDM symbol length,Ls, for the specified field,then the function ignores the remainingmod(Ns,Ls)symbols.

  • Nris the number of receive antennas.

Data Types:double
Complex Number Support:Yes

HT format configuration, specified as awlanHTConfigobject.

OFDM symbol sampling offset, as a fraction of the cyclic prefix length, specified as a scalar in the interval [0, 1].

The value that you specify indicates the start location for OFDM demodulation relative to the beginning of the cyclic prefix.

Example:0.45

Data Types:double

Output Arguments

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Demodulated frequency-domain signal, returned as a complex-valued array of sizeNsc-by-Nsym-by-Nr.

  • Nscis the number of active occupied subcarriers in the demodulated field.

  • Nsymis the number of OFDM symbols.

  • Nris the number of receive antennas.

Data Types:double
Complex Number Support:Yes

More About

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HT-LTF

The high throughput long training field (HT-LTF) is located between the HT-STF and data field of an HT-mixed packet.

As described in Section 19.3.9.4.6 of IEEE®Std 802.11™-2016, the receiver can use the HT-LTF to estimate the MIMO channel between the set of QAM mapper outputs (or, if STBC is applied, the STBC encoder outputs) and the receive chains. The HT-LTF portion has one or two parts. The first part consists of one, two, or four HT-LTFs that are necessary for demodulation of the HT-Data portion of the PPDU. These HT-LTFs are referred to as HT-DLTFs. The optional second part consists of zero, one, two, or four HT-LTFs that can be used to sound extra spatial dimensions of the MIMO channel not utilized by the HT-Data portion of the PPDU. These HT-LTFs are referred to as HT-ELTFs. Each HT long training symbol is 4 μs. The number of space-time streams and the number of extension streams determines the number of HT-LTF symbols transmitted.

Tables 19-12, 19-13 and 90-14 from IEEE Std 802.11-2012 are reproduced here.

NSTSDetermination NHTDLTFDetermination NHTELTFDetermination

Table 19-12 defines the number of space-time streams (NSTS) based on the number of spatial streams (NSS) from the MCS and the STBC field.

Table 19-13 defines the number of HT-DLTFs required for theNSTS.

Table 19-14 defines the number of HT-ELTFs required for the number of extension spatial streams (NESS).NESSis defined in HT-SIG2.

NSSfrom MCS STBC field NSTS
1 0 1
1 1 2
2 0 2
2 1 3
2 2 4
3 0 3
3 1 4
4 0 4

NSTS NHTDLTF
1 1
2 2
3 4
4 4

NESS NHTELTF
0 0
1 1
2 2
3 4

Additional constraints include:

  • NHTLTF=NHTDLTF+NHTELTF≤ 5.

  • NSTS+NESS≤ 4.

    • WhenNSTS= 3,NESScannot exceed one.

    • IfNESS= 1whenNSTS= 3thenNHTLTF= 5.

HT-mixed

High throughput mixed (HT-mixed) format devices support a mixed mode in which the PLCP header is compatible with HT and non-HT modes.

PPDU

The physical layer convergence procedure (PLCP) protocol data unit (PPDU) is the complete PLCP frame, including PLCP headers, MAC headers, the MAC data field, and the MAC and PLCP trailers.

References

[1] IEEE Std 802.11™-2012 IEEE Standard for Information technology — Telecommunications and information exchange between systems — Local and metropolitan area networks — Specific requirements — Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.

Extended Capabilities

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Version History

Introduced in R2015b

See Also

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1IEEE Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.