Demodulate L-LTF waveform
Demodulate L-LTF for Non-HT Format Transmission
Demodulate the L-LTF used in a non-HT OFDM transmission, after passing the L-LTF through an AWGN channel.
Create a non-HT configuration object and use it to generate an L-LTF signal.
cfg = wlanNonHTConfig; txSig = wlanLLTF(cfg);
Pass the L-LTF signal through an AWGN channel. Demodulate the received signal.
rxSig = awgn(txSig,15,'measured'); y = wlanLLTFDemodulate(rxSig,'CBW20');
Demodulate L-LTF for VHT Format Transmission
Demodulate the L-LTF used in a VHT transmission, after passing the L-LTF through an AWGN channel.
Create a VHT configuration object and use it to generate an L-LTF signal.
cfg = wlanVHTConfig; txSig = wlanLLTF(cfg);
Pass the L-LTF signal through an AWGN channel.
rxSig = awgn(txSig,5);
Demodulate the received L-LTF using the information from the
y = wlanLLTFDemodulate(rxSig,cfg);
Demodulate L-LTF with OFDM Symbol Offset
Demodulate the L-LTF for the HT-mixed transmission format, given a custom OFDM symbol offset.
Set the channel bandwidth to 40 MHz and the OFDM symbol offset to 1. That way, the FFT takes place after the guard interval.
cbw = 'CBW40'; ofdmSymOffset = 1;
Create an HT configuration object and use it to generate an L-LTF signal.
cfg = wlanHTConfig('ChannelBandwidth',cbw); txSig = wlanLLTF(cfg);
Pass the L-LTF signal through an AWGN channel.
rxSig = awgn(txSig,10);
Demodulate the received L-LTF using a custom OFDM symbol offset.
y = wlanLLTFDemodulate(rxSig,'CBW40',ofdmSymOffset);
x — Time-domain input signal
vector | matrix
Time-domain input signal corresponding to the L-LTF of the PPDU, specified as an NS-by-NR vector or matrix. NS is the number of samples and NR is the number of receive antennas.
NS is proportional to the channel bandwidth. The time-domain waveform consists of two symbols.
Complex Number Support: Yes
cbw — Channel bandwidth
Channel bandwidth, specified as one of these values.
'CBW5'– Channel bandwidth of 5 MHz
'CBW10'– Channel bandwidth of 10 MHz
'CBW20'– Channel bandwidth of 20 MHz
'CBW40'– Channel bandwidth of 40 MHz
'CBW80'– Channel bandwidth of 80 MHz
'CBW160'– Channel bandwidth of 160 MHz
'CBW320'– Channel bandwidth of 320 MHz
cfg — Format information
Format information, specified as a WLAN
configuration object. To create these objects, see
symOffset — OFDM symbol sampling offset
0.75 (default) | scalar in the interval [0, 1]
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.
y — Demodulated L-LTF signal
3-D OFDM symbol array
Demodulated L-LTF signal, returned as an NST-by-NSYM-by-NR array. NST is the number of occupied subcarriers, NSYM is the number of OFDM symbols, and NR is the number of receive antennas. For the L-LTF, NSYM is always 2.
NST varies with channel bandwidth.
|Number of Occupied Subcarriers (NST)|
The L-LTF is the second field in the 802.11™ OFDM PLCP legacy preamble. The L-LTF is a component of EHT, HE, VHT, HT, and non-HT PPDUs.
Channel estimation, fine frequency offset estimation, and fine symbol timing offset estimation rely on the L-LTF.
The L-LTF is composed of a cyclic prefix (CP) followed by two identical long training symbols (C1 and C2). The CP consists of the second half of the long training symbol.
The L-LTF duration varies with channel bandwidth.
|Channel Bandwidth (MHz)||Subcarrier Frequency Spacing ΔF (kHz)||Fast Fourier Transform (FFT) Period (TFFT = 1 / ΔF)||Cyclic Prefix or Training Symbol Guard Interval (GI2) Duration (TGI2 = TFFT / 2)||L-LTF Duration (TLONG = TGI2 + 2 × TFFT)|
|20, 40, 80, 160, and 320||312.5||3.2 μs||1.6 μs||8 μs|
|10||156.25||6.4 μs||3.2 μs||16 μs|
|5||78.125||12.8 μs||6.4 μs||32 μs|
The physical layer convergence procedure (PLCP) is the upper component of the physical layer in 802.11 networks. Each physical layer has its own PLCP, which provides auxiliary framing to the MAC .
 IEEE Std 802.11™-2016 (Revision of IEEE Std 802.11-2012). “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.” IEEE Standard for Information technology — Telecommunications and information exchange between systems — Local and metropolitan area networks — Specific requirements.
 Gast, Matthew S. 802.11n: A Survival Guide. Sebastopol, CA: O’Reilly Media Inc., 2012, p. 120.
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Version HistoryIntroduced in R2015b
R2022b: Single precision support
You can specify the function's numeric inputs as single precision values.
1 IEEE® Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.