Generate L-SIG waveform
[y, bits] = wlanLSIG(cfgFormat)
Generate the L-SIG waveform for an 80 MHz VHT transmission format packet.
cfgVHT = wlanVHTConfig; cfgVHT.ChannelBandwidth = 'CBW80'; lsigOut = wlanLSIG(cfgVHT); size(lsigOut)
ans = 1×2 320 1
The L-SIG waveform returned contains one symbol with 320 complex samples for an 80 MHz channel bandwidth.
Create a non-HT configuration object. The default
MCS is 0.
cfg = wlanNonHTConfig
cfg = wlanNonHTConfig with properties: Modulation: 'OFDM' ChannelBandwidth: 'CBW20' MCS: 0 PSDULength: 1000 NumTransmitAntennas: 1
Generate the L-SIG waveform and information bits. Extract the rate from the returned bits. The rate information is contained in the first four bits.
[y,bits] = wlanLSIG(cfg); rateBits = bits(1:4)
rateBits = 4x1 int8 column vector 1 1 0 1
As defined in IEEE Std 802.11™-2012, Table 18-6, a value of
[1 1 0 1] corresponds to a rate of 6 Mbps for 20 MHz channel spacing.
MCS to 7 then regenerate the 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
cfg = wlanNonHTConfig with properties: Modulation: 'OFDM' ChannelBandwidth: 'CBW20' MCS: 7 PSDULength: 1000 NumTransmitAntennas: 1
[y,bits] = wlanLSIG(cfg); rateBits = bits(1:4)
rateBits = 4x1 int8 column vector 0 0 1 1
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.
cfgFormat— Format configuration
|Transmission Format||Configuration Object||Applicable Object Properties|
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 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 IEEE® Std 802.11-2012, Table 18-1 and Section 9.23.4.
For HT-mixed, specify the transmission time as described in IEEE Std 802.11-2012, Section 184.108.40.206.5 and Section 9.23.4.
For VHT, specify the transmission time as described in IEEE Std 802.11ac™-2013, Section 220.127.116.11.4.
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, IEEE Std 802.11-2012, Section 18.104.22.168.3 describes HT-SIG bit settings.
For the VHT format, IEEE Std 802.11ac-2013, Section 22.214.171.124.3 and Section 126.96.36.199.6 describe bit settings for VHT-SIG-A and VHT-SIG-B, 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:
 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.