Generate L-SIG waveform
Create a non-HT configuration object. The default modulation and coding scheme (MCS) is
cfg = wlanNonHTConfig;
Generate the L-SIG waveform and information bits. Extract the rate from the returned bits.
[~,bits] = wlanLSIG(cfg);
Display the first four bits, which contain the rate information. As defined in Table 18-6 of IEEE Std 802.11™-2012, a value of
[1 1 0 1] corresponds to a rate of 6 Mbps for 20 MHz channel spacing.
1 1 0 1
MCS to 7 then generate the corresponding L-SIG waveform and information bits. Extract the rate from the returned bits and analyze. The rate information is contained in the first four bits.
cfg.MCS = 7; [y,bits] = wlanLSIG(cfg);
Display the first four bits. As defined in IEEE Std 802.11-2012, Table 18-6, a value of
[0 0 1 1] corresponds to a rate of 54 Mbps for 20 MHz channel spacing.
0 0 1 1
Configure an 80 MHz VHT transmission.
cfgVHT = wlanVHTConfig(ChannelBandwidth="CBW80");
Specify an oversampling rate and generate the L-SIG waveform.
osf = 2; [y,bits] = wlanLSIG(cfgVHT,OversamplingFactor=osf); size(y)
ans = 1×2 640 1
osf— Oversampling factor
1(default) | scalar greater than or equal to 1
Oversampling factor, specified as a scalar greater than or equal to 1. The oversampled cyclic prefix length must be an integer number of samples.
y— L-SIG time-domain waveform
L-SIG time-domain waveform, returned as an NS-by-NT matrix. NS is the number of time-domain samples, and NT is the number of transmit antennas.
NS is proportional to the channel bandwidth.
Complex Number Support: Yes
bits— Signaling bits
Signaling bits from the legacy signal field, returned as a 24-by-1 bit column vector. See L-SIG for the bit field description.
The legacy signal (L-SIG) field is the third field of the 802.11™ OFDM PLCP legacy preamble. It consists of 24 bits that contain rate, length, and parity information. The L-SIG is a component of HE, VHT, HT, and non-HT PPDUs. It is transmitted using BPSK modulation with rate 1/2 binary convolutional coding (BCC).
The L-SIG is one OFDM symbol with a duration that varies with channel bandwidth.
|Channel Bandwidth (MHz)||Subcarrier frequency spacing, ΔF (kHz)||Fast Fourier Transform (FFT) period (TFFT = 1 / ΔF)||Guard Interval (GI) Duration (TGI = TFFT / 4)||L-SIG duration (TSIGNAL = TGI + TFFT)|
|20, 40, 80, and 160||312.5||3.2 μs||0.8 μs||4 μs|
|10||156.25||6.4 μs||1.6 μs||8 μs|
|5||78.125||12.8 μs||3.2 μs||16 μs|
The L-SIG contains packet information for the received configuration,
Bits 0 through 3 specify the data rate (modulation and coding rate) for the non-HT format.
|Rate (bits 0–3)||Modulation|
Coding rate (R)
|Data Rate (Mb/s)|
|20 MHz channel bandwidth||10 MHz channel bandwidth||5 MHz channel bandwidth|
For HT and VHT formats, the
L-SIG rate bits are set to
'1 1 0 1'. Data rate
information for HT and VHT formats is signaled in format-specific
Bit 4 is reserved for future use.
Bits 5 through 16:
For non-HT, specify the data length (amount of data transmitted in octets) as described in Table 17-1 and section 10.26.4 IEEE® Std 802.11-2016.
For HT-mixed, specify the transmission time as described in sections 18.104.22.168.5 and 10.26.4 of IEEE Std 802.11-2016.
For VHT, specify the transmission time as described in section 22.214.171.124.4 of IEEE Std 802.11-2016.
Bit 17 has the even parity of bits 0 through 16.
Bits 18 through 23 contain all zeros for the signal tail bits.
For the HT-mixed format, section 126.96.36.199.3 of IEEE Std 802.11-2016 describes HT-SIG bit settings.
For the VHT format, sections 188.8.131.52.3 and 184.108.40.206.6 of IEEE Std 802.11-2016 describe bit settings for the VHT-SIG-A and VHT-SIG-B fields, respectively.
The L-SIG follows the L-STF and L-LTF of the preamble in the packet structure.
For L-SIG transmission processing algorithm details, see:
An oversampled signal is a signal sampled at a frequency that is higher than the Nyquist rate. WLAN signals maximize occupied bandwidth by using small guardbands, which can pose problems for anti-imaging and anti-aliasing filters. Oversampling increases guardband width relative to the total signal bandwidth, thereby increasing the number of samples in the signal.
This function performs oversampling by using a larger IFFT and zero pad when generating an OFDM waveform. This diagram shows the oversampling process for an OFDM waveform with NFFT subcarriers comprising Ng guardband subcarriers on either side of Nst occupied bandwidth subcarriers.
 IEEE Std 802.11ac™-2013 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 — Amendment 4: Enhancements for Very High Throughput for Operation in Bands below 6 GHz.
 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.
 IEEE Std 802.11-2012 Adapted and reprinted with permission from IEEE. Copyright IEEE 2012. All rights reserved.