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Demodulate HT-LTF waveform


y = wlanHTLTFDemodulate(x,cfg)
y = wlanHTLTFDemodulate(x,cfg,OFDMSymbolOffset)



y = wlanHTLTFDemodulate(x,cfg) returns the demodulated HT-LTF[1] , y, given received HT-LTF x. The input signal is a component of the HT-mixed format PPDU. The function demodulates the signal using the information in the wlanHTConfig object, cfg.


y = wlanHTLTFDemodulate(x,cfg,OFDMSymbolOffset) specifies the OFDM symbol sampling offset.


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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.


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

cfg = wlanHTConfig('NumTransmitAntennas',2,'NumSpaceTimeStreams',2, ...

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 to 0.5, which corresponds to 1/2 of the cyclic prefix length.

z = wlanHTLTFDemodulate(y,cfg,0.5);

Input Arguments

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Input signal comprising an HT-LTF, specified as an NS-by-NR matrix. NS is the number of samples and NR is the number of receive antennas. You can generate the signal by using the wlanHTLTF function.

Data Types: double
Complex Number Support: Yes

HT format configuration, specified as a wlanHTConfig object. The function uses the following wlanHTConfig object properties:

Channel bandwidth in MHz, specified as 'CBW20' or 'CBW40'.

Data Types: char | string

Number of space-time streams in the transmission, specified as 1, 2, 3, or 4.

Data Types: double

Number of extension spatial streams in the transmission, specified as 0, 1, 2, or 3. When NumExtensionStreams is greater than 0, SpatialMapping must be 'Custom'.

Data Types: double

OFDM symbol sampling offset represented as a fraction of the cyclic prefix (CP) length, specified as a scalar value from 0 to 1. This value indicates the start location for OFDM demodulation, relative to the beginning of the cyclic prefix. OFDMSymbolOffset = 0 represents the start of the cyclic prefix and OFDMSymbolOffset = 1 represents the end of the cyclic prefix.

Data Types: double

Output Arguments

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Demodulated HT-LTF signal for an HT-Mixed PPDU, returned as an NST-by-NSYM-by-NR matrix or array. NST is the number of data and pilot subcarriers. NSYM is the number of OFDM symbols in the HT-LTF. NR is the number of receive antennas.

Data Types: double
Complex Number Support: Yes

More About

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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 IEEE® Std 802.11™-2012, Section, 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 20-12, 20-13 and 20-14 from IEEE Std 802.11-2012 are reproduced here.

NSTS DeterminationNHTDLTF DeterminationNHTELTF Determination

Table 20-12 defines the number of space-time streams (NSTS) based on the number of spatial streams (NSS) from the MCS and the STBC field.

Table 20-13 defines the number of HT-DLTFs required for the NSTS.

Table 20-14 defines the number of HT-ELTFs required for the number of extension spatial streams (NESS). NESS is defined in HT-SIG2.




Additional constraints include:


  • NSTS + NESS ≤ 4.

    • When NSTS = 3, NESS cannot exceed one.

    • If NESS = 1 when NSTS = 3 then NHTLTF = 5.


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


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.


[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

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

Introduced in R2015b

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