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Demodulate HT-LTF waveform



sym = wlanHTLTFDemodulate(rx,cfg) returns the demodulated HT-LTF1 by demodulating received time-domain HT-LTF signal rx. The input signal is a component of the HT-mixed format PPDU. The function demodulates the signal by using the transmission parameters cfg.


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


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

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

  • Nr is the number of receive antennas.

Data Types: single | double
Complex Number Support: Yes

HT format configuration, specified as a wlanHTConfig object.

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.

Different values of OFDM symbol sampling offset

Example: 0.45

Data Types: single | double

Output Arguments

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

  • Nsc is the number of active occupied subcarriers in the demodulated field.

  • Nsym is the number of OFDM symbols.

  • Nr is the number of receive antennas.

Data Types: single | 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.

The HT-LTF in an HT-mixed packet

As described in Section 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.

NSTS DeterminationNHTDLTF DeterminationNHTELTF Determination

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 the NSTS.

Table 19-14 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™.

Version History

Introduced in R2015b

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