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WLAN Packet Structure

Physical Layer Conformance Procedure Protocol Data Unit

IEEE® 802.11™[1] [2] is a packet-based protocol. Each physical layer conformance procedure (PLCP) protocol data unit (PPDU) contains preamble and data fields. The preamble field contains the transmission vector format information. The data field contains the user payload and higher layer headers, such as MAC fields and CRC. The transmission vector format and the PPDU packet structure vary depending on the 802.11 version being configured for transmission. The transmission vector (TXVECTOR) format parameter is classified as:

  • DMG to specify a directional multi-gigabit PHY implementation.

    • DMG refers to preamble fields formatted for association with 802.11ad™ data. IEEE Std 802.11ad-2012 [4] Section 21.3-21.6 defines and describes the DMG PHY layer and PPDU.

    • For DMG, the TXVECTOR parameters, as defined in IEEE Std 802.11ad-2012 [4] Table 21-1, determines the structure of PPDUs transmitted by a DMG STA. For a DMG STA, the MCS parameter determines the overall structure of the DMG PPDU.

  • S1G to specify a sub 1 GHz PHY implementation.

    • S1G refers to preamble fields formatted for association with 802.11ah™ data. The draft standard IEEE P802.11ah/D5.0, defines and describes the S1G PHY layer and PPDU.

    • For S1G, the TXVECTOR parameters, as defined in IEEE P802.11ah/D5.0, Table 24-1, determines the structure of PPDUs transmitted by an S1G STA. For an S1G STA, the FORMAT parameter determines the overall structure of the S1G PPDU.

  • VHT to specify a very high throughput PHY implementation.

    • VHT refers to preamble fields formatted for association with 802.11ac™ data. IEEE IEEE Std 802.11ac-2013 [3], Section 22 defines and describes the VHT PHY layer and PPDU.

    • For VHT, the TXVECTOR parameters, as defined in IEEE Std 802.11ac-2013 [3], Table 22-1, determine the structure of PPDUs transmitted by a VHT STA. For a VHT STA, the FORMAT parameter determines the overall structure of the PPDU and enables:

      • Non-HT format (NON_HT), based on Section 18 and including non-HT duplicate format.

      • HT-mixed format (HT_MF), as specified in Section 20.

      • HT-greenfield format (HT_GF), as specified in Section 20. WLAN System Toolbox™ does not support HT_GF format.

      • VHT format (VHT), as specified in Section 22. The VHT format PPDUs contain a preamble compatible with Section 18 and Section 20 STAs. The non-VHT portions of the VHT format preamble (the parts of VHT preamble preceding the VHT-SIG-A field) are defined to enable decoding of the PPDU by VHT STAs.

  • HT to specify a high throughput PHY implementation.

    • HT refers to preamble fields formatted for association with 802.11n™ data. IEEE Std 802.11-2012 [2], Section 20 defines and describes the HT PHY layer and PPDU. The standard defines two HT formats:

      • HT_MF indicates the HT-mixed format and contains a preamble compatible with HT and non-HT receivers. Support for HT-mixed format is mandatory.

        • HT_GF indicates the HT-greenfield format and does not contain a non-HT compatible part. WLAN System Toolbox does not support HT_GF format.

  • non-HT to specify a PHY implementation that is not HT and is not VHT.

    • Non-HT refers to preamble fields formatted for association with pre-802.11n data. IEEE Std 802.11-2012 [2], Section 18 defines and describes the OFDM PHY layer and PPDU for non-HT transmission. In addition to supporting non-HT synchronization, the non-HT preamble fields are used in support of HT and VHT synchronization.

The table shows 802.11 versions that the toolbox supports, along with the supported TXVECTOR options and associated modulation formats.

802.11 version

Transmission Vector Format

Modulation format

Bandwidths (MHz)

802.11b

non-HT

DSSS/CCK

11

802.11a

non-HT

OFDM only

5, 10, 20

802.11j

non-HT

OFDM only

10

802.11p

non-HT

OFDM only

5, 10

802.11g

non-HT

OFDM

20

non-HT

DSSS/CCK

11

802.11n

HT_MF, Non-HT

OFDM only

20, 40

802.11ac

VHT, HT_MF, Non-HT

OFDM only

20, 40, 80, 160

802.11ah

S1G

OFDM only

1, 2, 4, 8, 16

802.11ad

DMG

Single Carrier and OFDM

2640

WLAN System Toolbox configuration objects define the properties that enable creation of PPDUs and waveforms for the specified 802.11 transmission format. See wlanDMGConfig Properties, wlanS1GConfig Properties, wlanVHTConfig Properties, wlanHTConfig Properties, wlanNonHTConfig Properties, and wlanGeneratorConfig Properties.

DMG Format PPDU Field Structure

In DMG, there are three physical layer (PHY) modulation schemes supported: control, single carrier, and OFDM.

The single-carrier chip timing, TC = 1/FC = 0.57 ns. For more information, see Waveform Sampling Rate on the wlanWaveformGenerator function reference page.

The supported DMG format PPDU field structures each contain these fields:

  • The preamble contains a short training field (STF) and channel estimation field (CEF). The preamble is used for packet detection, AGC, frequency offset estimation, synchronization, indication of modulation type (Control, SC, or OFDM), and channel estimation. The format of the preamble is common to the Control, SC, and OFDM PHY packets.

    • The STF is composed of Golay Ga sequences as specified in 802.11ad-2012 [4], Section 21.3.6.2.

    • The CEF is composed of Golay Gu and Gv sequences as specified in 802.11ad-2012 [4], Section 21.3.6.3.

      • When the header and data fields of the packet are modulated using a single carrier (control PHY and SC PHY), the Golay sequencing for the CEF waveform is shown in 802.11ad-2012 [4], Figure 21-5.

      • When the header and data fields of the packet are modulated using OFDM (OFDM PHY), the Golay sequencing for the CEF waveform is shown in 802.11ad-2012 [4], Figure 21-6.

  • The header field is decoded by the receiver to determine transmission parameters.

  • The data field is variable in length. It carries the user data payload.

  • The training fields (AGC and TRN-R/T subfields) are optional. They can be included to refine beamforming.

IEEE 802.11ad-2012 [4] specifies the common aspects of the DMG PPDU packet structure in Section 21.3. The PHY modulation-specific aspects of the packet structure are specified in these sections:

  • The DMG control PHY packet structure is specified in Section 21.4.

  • The DMG OFDM PHY packet structure is specified in Section 21.5.

  • The DMG SC PHY packet structure is specified in Section 21.6.

S1G Format PPDU Field Structure

In S1G, there are three transmission modes:

  • ≥2-MHz long preamble mode

  • ≥2-MHz short preamble mode

  • 1-MHz mode

Each transmission mode has a specific PPDU preamble structure:

  • An S1G ≥2-MHz long preamble mode PPDU supports single-user and multi-user transmissions. The long preamble PPDU consists of two portions; the omni-directional portion and the beam-changeable portion.

    • The omni-directional portion is transmitted to all users without beamforming. It consists of three fields:

      • The short training field (STF) is used for coarse synchronization.

      • The long training field (LTF1) is used for fine synchronization and initial channel estimation.

      • The signal A field (SIG-A) is decoded by the receiver to determine transmission parameters relevant to all users.

    • The data portion can be beamformed to each user. It consists of four fields:

      • The beamformed short training field (D-STF) is used by the receiver for automatic gain control.

      • The beamformed long training fields (D-LTF-N) are used for MIMO channel estimation.

      • The signal B field (SIG-B) in a multi-user transmission, signals the MCS for each user. In a single-user transmission, the MCS is signaled in the SIG-A field of the omni-directional portion of the preamble. Therefore, in a single-user transmission the SIG-B symbol transmitted is an exact repetition of the first D-LTF. This repetition allows for improved channel estimation.

      • The data field is variable in length. It carries the user data payload.

  • An S1G ≥2-MHz short preamble mode PPDU supports single-user transmissions. All fields in the PPDU can be beamformed.

    The PPDU consists of these five fields:

    • The short training field (STF) is used for coarse synchronization.

    • The first long training field (LTF1) is used for fine synchronization and initial channel estimation.

    • The signaling field (SIG) is decoded by the receiver to determine transmission parameters.

    • The subsequent long training fields (LTF2-N) are used for MIMO channel estimation. NSYMBOLS = 1 per subsequent LTF

    • The data field is variable in length. It carries the user data payload.

  • An S1G 1-MHz mode PPDU supports single-user transmissions. It is composed of the same five fields as the S1G ≥2-MHz short preamble mode PPDU and all fields can be beamformed. An S1G 1-MHz mode PPDU has longer STF, LTF1, and SIG fields so this narrower bandwidth mode can achieve sensitivity that is similar to the S1G ≥2-MHz short preamble mode transmissions.

VHT, HT-Mixed, and Non-HT Format PPDU Field Structures

The field structure for VHT, HT, and non-HT PPDUs consist of preamble and data portions. The legacy preamble fields (L-STF, L-LTF, and L-SIG) are common to VHT, HT, and non-HT format preambles. VHT and HT format preamble fields include additional format-specific training and signaling fields. Each format defines a data field for transmission of user payload data.

PPDU Field Abbreviation

Description

L-STF

Non-HT Short Training field

L-LTF

Non-HT Long Training field

L-SIG

Non-HT SIGNAL field

HT-SIG

HT SIGNAL field

HT-STF

HT Short Training field

HT-LTF

HT Long Training field, multiple HT-LTFs are transmitted as indicated by the MCS

VHT-SIG-A

VHT Signal A field

VHT-STF

VHT Short Training field

VHT-LTF

VHT Long Training field

VHT-SIG-B

VHT Signal B field

Data

VHT, HT, and non-HT Data fields include the service bits, PSDU, tail bits, and pad bits

See IEEE 802.11-2012 [2], Section 20.3.2 for more information.

Non-HT (Legacy) Short Training Field

The legacy short training field (L-STF) is the first field of the 802.11 OFDM PLCP legacy preamble. The L-STF is a component of VHT, HT, and non-HT PPDUs.

The L-STF duration varies with channel bandwidth.

Channel Bandwidth (MHz)Subcarrier Frequency Spacing, ΔF (kHz)Fast Fourier Transform (FFT) Period (TFFT = 1 / ΔF)L-STF Duration (TSHORT = 10 × TFFT / 4)
20, 40, 80, and 160312.53.2 μs8 μs
10156.256.4 μs16 μs
578.12512.8 μs32 μs

Because the sequence has good correlation properties, it is used for start-of-packet detection, for coarse frequency correction, and for setting the AGC. The sequence uses 12 of the 52 subcarriers that are available per 20 MHz channel bandwidth segment. For 5 MHz, 10 MHz, and 20 MHz bandwidths, the number of channel bandwidths segments is 1.

Non-HT (Legacy) Long Training Field

The legacy long training field (L-LTF) is the second field in the 802.11 OFDM PLCP legacy preamble. The L-LTF is a component of 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, and 160312.53.2 μs1.6 μs8 μs
10156.256.4 μs3.2 μs16 μs
578.12512.8 μs6.4 μs32 μs

Non-HT (Legacy) Signal Field

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.

Non-HT Data Field

The non-high throughput data (non-HT data) field is used to transmit MAC frames and is composed of a service field, a PSDU, tail bits, and pad bits.

  • Service field — Contains 16 zeros to initialize the data scrambler.

  • PSDU — Variable-length field containing the PLCP service data unit (PSDU).

  • Tail — Tail bits required to terminate a convolutional code. The field uses six zeros for the single encoding stream.

  • Pad Bits — Variable-length field required to ensure that the non-HT data field contains an integer number of symbols.

Processing of an 802.11a™ data field is defined in IEEE 802.11-2012 [2], Section 18.3.5.

The six tail bits are set to zero after a 127-bit scrambling sequence has been applied to the full data field. The receiver uses the first seven bits of the service field to determine the initial state of the scrambler. Rate 1/2 BCC encoding is performed on the scrambled data. The zeroed tail bits cause the BCC encoder to return to a zero state. Puncturing is applied as needed for the selected rate.

The coded data is grouped into several bits per symbol, and two permutations of block interleaving are applied to each group of data. The groups of bits are then modulated to the selected rate (BPSK, QPSK, 16-QAM, or 64-QAM) and the complex symbols are then mapped onto corresponding subcarriers. For each symbol, the pilot subcarriers are inserted. An IFFT is used to transform each symbol group to the time domain and the cyclic prefix is prepended.

The final processing preceding DAC up-conversion to RF and the power amplifier is to apply a pulse shaping filter on the data to smooth transitions between symbols. The standard provides an example pulse shaping function but does not specifically require one.

High Throughput Signal Field

The high throughput signal (HT-SIG) field is located between the L-SIG field and HT-STF and is part of the HT-mixed format preamble. It is composed of two symbols, HT-SIG1 and HT-SIG2.

HT-SIG carries information used to decode the HT packet, including the MCS, packet length, FEC coding type, guard interval, number of extension spatial streams, and whether there is payload aggregation. The HT-SIG symbols are also used for auto-detection between HT-mixed format and legacy OFDM packets.

Refer to IEEE Std 802.11-2012, Section 20.3.9.4.3 for a detailed description of the HT-SIG field.

High Throughput Short Training Field

The high throughput short training field (HT-STF) is located between the HT-SIG and HT-LTF fields of an HT-mixed packet. The HT-STF is 4 μs in length and is used to improve automatic gain control estimation for a MIMO system. For a 20 MHz transmission, the frequency sequence used to construct the HT-STF is identical to that of the L-STF. For a 40 MHz transmission, the upper subcarriers of the HT-STF are constructed from a frequency-shifted and phase-rotated version of the L-STF.

High Throughput Long Training Fields

The high throughput long training field (HT-LTF) is located between the HT-STF and data field of an HT-mixed packet.

As described in IEEE Std 802.11-2012, Section 20.3.9.4.6, 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 20-12, 20-13 and 20-14 from IEEE Std 802.11-2012 are reproduced here.

NSTS DeterminationNHTDLTF DeterminationNHTELTF Determination

Table 20-12 defines the number of space-time streams (NSTS) based on the number of spatial streams (NSS) from the MCS and the STBC field.

Table 20-13 defines the number of HT-DLTFs required for the NSTS.

Table 20-14 defines the number of HT-ELTFs required for the number of extension spatial streams (NESS). NESS is defined in HT-SIG2.

NSS from MCSSTBC fieldNSTS
101
112
202
213
224
303
314
404

NSTSNHTDLTF
11
22
34
44

NESSNHTELTF
00
11
22
34

Additional constraints include:

  • NHTLTF = NHTDLTF + NHTELTF ≤ 5.

  • NSTS + NESS ≤ 4.

    • When NSTS = 3, NESS cannot exceed one.

    • If NESS = 1 when NSTS = 3 then NHTLTF = 5.

HT Data Field

The high throughput data field (HT-Data) follows the last HT-LTF of an HT-mixed packet.

The high throughput data field is used to transmit one or more frames from the MAC layer and consists of four subfields.

  • Service field — Contains 16 zeros to initialize the data scrambler.

  • PSDU — Variable-length field containing the PLCP service data unit (PSDU). In 802.11, the PSDU can consist of an aggregate of several MAC service data units.

  • Tail — Tail bits required to terminate a convolutional code. The field uses six zeros for each encoding stream.

  • Pad Bits — Variable-length field required to ensure that the HT-Data field consists of an integer number of symbols.

Very High Throughput SIG-A Field

The very high throughput signal A (VHT-SIG-A) field contains information required to interpret VHT format packets. Similar to the non-HT signal (L-SIG) field for the non-HT OFDM format, this field stores the actual rate value, channel coding, guard interval, MIMO scheme, and other configuration details for the VHT format packet. Unlike the HT-SIG field, this field does not store the packet length information. Packet length information is derived from L-SIG and is captured in the VHT-SIG-B field for the VHT format.

The VHT-SIG-A field consists of two symbols: VHT-SIG-A1 and VHT-SIG-A2. These symbols are located between the L-SIG and the VHT-STF portion of the VHT format PPDU.

The VHT-SIG-A field is defined in IEEE Std 802.11ac-2013, Section 22.3.8.3.3.

The VHT-SIG-A field includes these components. The bit field structures for VHT-SIG-A1 and VHT-SIG-A2 vary for single user or multi-user transmissions.

  • BW — A two-bit field that indicates 0 for 20 MHz, 1 for 40 MHz, 2 for 80 MHz, or 3 for 160 MHz.

  • STBC — A bit that indicates the presence of space-time block coding.

  • Group ID — A six-bit field that indicates the group and user position assigned to a STA.

  • NSTS — A three-bit field for a single user or 4 three-bit fields for a multi-user scenario, that indicates the number of space-time streams per user.

  • Partial AID — An identifier that combines the association ID and the BSSID.

  • TXOP_PS_NOT_ALLOWED — An indicator bit that shows if client devices are allowed to enter dose state. This bit is set to false when the VHT-SIG-A structure is populated, indicating that the client device is allowed to enter dose state.

  • Short GI — A bit that indicates use of the 400 ns guard interval.

  • Short GI NSYM Disambiguation — A bit that indicates if an extra symbol is required when the short GI is used.

  • SU/MU[0] Coding — A bit field that indicates if convolutional or LDPC coding is used for a single user or for user MU[0] in a multi-user scenario.

  • LDPC Extra OFDM Symbol — A bit that indicates if an extra OFDM symbol is required to transmit the data field.

  • MCS — A four-bit field.

    • For a single user scenario, it indicates the modulation and coding scheme used.

    • For a multi-user scenario, it indicates use of convolutional or LDPC coding and the MCS setting is conveyed in the VHT-SIG-B field.

  • Beamformed — An indicator bit set to 1 when a beamforming matrix is applied to the transmission.

  • CRC — An eight-bit field used to detect errors in the VHT-SIG-A transmission.

  • Tail — A six-bit field used to terminate the convolutional code.

Very High Throughput Short Training Field

The very high throughput short training field (VHT-STF) is a single OFDM symbol (4 μs in length) that is used to improve automatic gain control estimation in a MIMO transmission. It is located between the VHT-SIG-A and VHT-LTF portions of the VHT packet.

The frequency domain sequence used to construct the VHT-STF for a 20 MHz transmission is identical to the L-STF sequence. Duplicate L-STF sequences are frequency shifted and phase rotated to support VHT transmissions for the 40 MHz, 80 MHz, and 160 MHz channel bandwidths. As such, the L-STF and HT-STF are subsets of the VHT-STF.

The VHT-STF is defined in IEEE Std 802.11ac-2013, Section 22.3.8.3.4.

Very High Throughput Long Training Fields

The very high throughput long training field (VHT-LTF) is located between the VHT-STF and VHT-SIG-B portion of the VHT packet.

It is used for MIMO channel estimation and pilot subcarrier tracking. The VHT-LTF includes one VHT long training symbol for each spatial stream indicated by the selected MCS. Each symbol is 4 μs long. A maximum of eight symbols are permitted in the VHT-LTF.

The VHT-LTF is defined in IEEE Std 802.11ac-2013, Section 22.3.8.3.5.

Very High Throughput SIG-B Field

The very high throughput signal B field (VHT-SIG-B) is used for multi-user scenario to set up the data rate and to fine-tune MIMO reception. It is modulated using MCS 0 and is transmitted in a single OFDM symbol.

The VHT-SIG-B field consists of a single OFDM symbol located between the VHT-LTF and the data portion of the VHT format PPDU.

The very high throughput signal B (VHT-SIG-B) field contains the actual rate and A-MPDU length value per user. The VHT-SIG-B is defined in IEEE Std 802.11ac-2013, Section 22.3.8.3.6, and Table 22–14. The number of bits in the VHT-SIG-B field varies with the channel bandwidth and the assignment depends on whether single user or multi-user scenario in allocated. For single user configurations, the same information is available in the L-SIG field but the VHT-SIG-B field is included for continuity purposes.

Field

VHT MU PPDU Allocation (bits)

VHT SU PPDU Allocation (bits)

Description

 

20 MHz

40 MHz

80 MHz, 160 MHz

20 MHz

40 MHz

80 MHz, 160 MHz

 

VHT-SIG-B

B0-15 (16)

B0-16 (17)

B0-18 (19)

B0-16 (17)

B0-18 (19)

B0-20 (21)

A variable-length field that indicates the size of the data payload in four-byte units. The length of the field depends on the channel bandwidth.

VHT-MCS

B16-19 (4)

B17-20 (4)

B19-22 (4)

N/A

N/A

N/A

A four-bit field that is included for multi-user scenarios only.

Reserved

N/A

N/A

N/A

B17–19 (3)

B19-20 (2)

B21-22 (2)

All ones

Tail

B20-25 (6)

B21-26 (6)

B23-28 (6)

B20-25 (6)

B21-26 (6)

B23-28 (6)

Six zero-bits used to terminate the convolutional code.

Total # bits

26

27

29

26

27

29

 

Bit field repetition

1

2

4

For 160 MHz, the 80 MHz channel is repeated twice.

1

2

4

For 160 MHz, the 80 MHz channel is repeated twice.
 

For a null data packet (NDP), the VHT-SIG-B bits are set according to IEEE Std 802.11ac-2013, Table 22-15.

VHT Data Field

The very high throughput data (VHT data) field is used to transmit one or more frames from the MAC layer. It follows the VHT-SIG-B field in the packet structure for the VHT format PPDUs.

The VHT data field is defined in IEEE Std 802.11ac-2013, Section 22.3.10. It is composed of four subfields.

  • Service field — Contains a seven-bit scrambler initialization state, one bit reserved for future considerations, and eight bits for the VHT-SIG-B CRC field.

  • PSDU — Variable-length field containing the PLCP service data unit. In 802.11, the PSDU can consist of an aggregate of several MAC service data units.

  • PHY Pad — Variable number of bits passed to the transmitter to create a complete OFDM symbol.

  • Tail — Bits used to terminate a convolutional code. Tail bits are not needed when LDPC is used.

References

[1] IEEE 802.11™: Wireless LANs. http://standards.ieee.org/about/get/802/802.11.html

[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.

[3] 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.

[4] IEEE Std 802.11ad™-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 — Amendment 3: Enhancements for Very High Throughput in the 60 GHz Band.

[5] Perahia, E., and R. Stacey. Next Generation Wireless LANs: 802.11n and 802.11ac. 2nd Edition. United Kingdom: Cambridge University Press, 2013.

See Also

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

[2] IEEE Std 802.11ac-2013 Adapted and reprinted with permission from IEEE. Copyright IEEE 2013. All rights reserved.

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