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wlanLSIG

Generate L-SIG waveform

Syntax

[y, bits] = wlanLSIG(cfgFormat)

Description

example

[y, bits] = wlanLSIG(cfgFormat) generates an L-SIG[1] time-domain waveform using the specified configuration object.

Examples

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Generate the L-SIG waveform for an 80 MHz VHT transmission format packet.

cfgVHT = wlanVHTConfig;
cfgVHT.ChannelBandwidth = 'CBW80';
lsigOut = wlanLSIG(cfgVHT);
size(lsigOut)
ans =

   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.

Change 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
[y,bits] = wlanLSIG(cfg);

rateBits = bits(1:4)
cfg = 

  wlanNonHTConfig with properties:

             Modulation: 'OFDM'
       ChannelBandwidth: 'CBW20'
                    MCS: 7
             PSDULength: 1000
    NumTransmitAntennas: 1


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.

Input Arguments

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Format configuration, specified as a wlanVHTConfig, wlanHTConfig, or wlanNonHTConfig object. For a specified format, the wlanLSIG function uses only the object properties indicated.

Transmission FormatConfiguration ObjectApplicable Object Properties

VHT

wlanVHTConfig

ChannelBandwidth, NumUsers, NumTransmitAntennas, NumSpaceTimeStreams, STBC, MCS, ChannelCoding, APEPLength, GuardInterval

HT

wlanHTConfig

ChannelBandwidth, NumTransmitAntennas, NumSpaceTimeStreams, MCS, GuardInterval, ChannelCoding, PSDULength

non-HT

See note 1 and 2

wlanNonHTConfig

ChannelBandwidth, Modulation, MCS, PSDULength, NumTransmitAntennas

Note:
  1. Only OFDM modulation is supported for a wlanNonHTConfig object input.

  2. For non-HT format, when channel bandwidth is 5 MHz or 10 MHz, NumTransmitAntennas is not applicable because only one transmit antenna is permitted.

Example: wlanVHTConfig

Output Arguments

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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.

ChannelBandwidthNS
'CBW5', 'CBW10', 'CBW20'80
'CBW40'160
'CBW80'320
'CBW160'640

Data Types: double
Complex Number Support: Yes

Signaling bits from the legacy signal field, returned as a 24-by-1 bit column vector. See L-SIG for the bit field description.

Data Types: int8

More About

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L-SIG

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 160312.53.2 μs0.8 μs4 μs
10156.256.4 μs1.6 μs8 μs
578.12512.8 μs3.2 μs16 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 bandwidth10 MHz channel bandwidth5 MHz channel bandwidth
    1101BPSK1/2631.5
    1111BPSK3/494.52.25
    0101QPSK1/21263
    0111QPSK3/41894.5
    100116-QAM1/224126
    101116-QAM3/436189
    000164-QAM2/3482412
    001164-QAM3/4542713.5

    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 signaling fields.

  • 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 20.3.9.3.5 and Section 9.23.4.

    • For VHT, specify the transmission time as described in IEEE Std 802.11ac™-2013, Section 22.3.8.2.4.

  • Bit 17 has the even parity of bits 0 through 16.

  • Bits 18 through 23 contain all zeros for the signal tail bits.

Note

Signaling fields added for HT (wlanHTSIG) and VHT (wlanVHTSIGA, wlanVHTSIGB) formats provide data rate and configuration information for those formats.

  • For the HT-mixed format, IEEE Std 802.11-2012, Section 20.3.9.4.3 describes HT-SIG bit settings.

  • For the VHT format, IEEE Std 802.11ac-2013, Section 22.3.8.3.3 and Section 22.3.8.3.6 describe bit settings for VHT-SIG-A and VHT-SIG-B, respectively.

Algorithms

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:

  • VHT format – refer to IEEE Std 802.11ac-2013 [1], Section 22.3.8.2.4

  • HT format – refer to IEEE Std 802.11-2012 [2], Sections 20.3.9.3.5

  • non-HT format – refer to IEEE Std 802.11-2012 [2], Sections 18.3.4

The wlanLSIG function performs transmitter processing on the L-SIG field and outputs the time-domain waveform.

References

[1] 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.

[2] 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

Introduced in R2015b


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

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