EHT PPDU Structure

WLAN Toolbox™ enables you to model various 802.11™ versions. Each version of the standard uses a different format for data transmission.

Packet Definition

IEEE® 802.11is a packet-based protocol, which means that it transmits data in discrete units. The units are called packets or physical layer protocol data units (PPDUs). Each PPDU contains preamble and data fields. The preamble fields contain the transmission vector format information. The data field contains the user payload and higher layer headers, such as medium access control (MAC) fields and cyclic redundancy check (CRC). The transmission vector format and the PPDU structure vary between 802.11 versions. The transmission vector (TXVECTOR) format parameter is classified as:

  • EHT to specify an extremely high-throughput (EHT) physical layer (PHY) implementation.

    • EHT refers to fields formatted for association with 802.11be™(Wi-Fi 7) data. Reference [1] defines and describes the EHT PHY layer and PPDU.

    • For EHT, the TXVECTOR parameters, as defined in Table 36-1 of [1], determine the structure of PPDUs transmitted by an EHT station (STA).

Supported 802.11 Versions

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

802.11 Version

Transmission Vector Format

Modulation Format

Bandwidth/MHz
802.11bn™ (Wi-Fi 8)UHROFDMA

20, 40, 80, 160, 320

802.11be (Wi-Fi 7)

EHT

OFDMA

20, 40, 80, 160, 320

802.11ba™WURMC-OOK20, 40, 80

802.11ax™ (Wi-Fi 6)

HE

OFDMA

20, 40, 80, 160

802.11ad™

DMG

Single carrier and OFDM

2640

802.11ah™

S1G

OFDM only

1, 2, 4, 8, 16

802.11ac™ (Wi-Fi 5)

VHT

OFDM only

20, 40, 80, 160

802.11n™ (Wi-Fi 4)

HT

OFDM only

20, 40

802.11g™

Non-HT

OFDM

20

Non-HT

DSSS/CCK

11

802.11p™

Non-HT

OFDM only

5, 10

802.11j™

Non-HT

OFDM only

10

802.11a™

Non-HT

OFDM only

5, 10, 20

802.11b™

Non-HT

DSSS/CCK

11

Field Structure

EHT has two transmission modes: EHT multi-user (EHT MU) and EHT trigger-based (EHT TB). The wlanEHTMUConfig and wlanEHTTBConfig configuration objects enable you to create PPDUs and waveforms for both of them.

The field structure for EHT PPDUs consists of preamble and data portions. The legacy preamble fields (L-STF, L-LTF, and L-SIG) are present in EHT, WUR, HE, VHT, and non-HT PPDUs. The RL-SIG and PE fields are common to EHT and HE PPDUs. This table summarizes the structure of an EHT MU PPDU.

PPDU Field Abbreviation

Description

Duration (µs)

L-STF

Non-HT Short Training field

8

L-LTF

Non-HT Long Training field

8

L-SIG

Non-HT Signal field

4

RL-SIG

Repeated Non-HT Signal field

4

U-SIG

Universal Signal field

8 (4 µs per OFDM symbol)

EHT-SIG

EHT Signal field

Variable (4 µs per OFDM symbol)

EHT-STF

EHT Short Training field

4

EHT-LTF

EHT Long Training field

Variable (depends on the guard interval and EHT-LTF compression mode)

EHT-Data

Data field carrying the PSDUs

Variable (depends on the PSDU lengths)

PE

Packet Extension field

0, 4, 8, 12, 16, or 20

The structure of an EHT TB PPDU is the same, except that the EHT-SIG field is not present and the EHT-STF has double the duration. For more information, see Section 36.3.4 of [1].

EHT Preamble Fields

In EHT PPDUs, the universal signaling field (U-SIG) is located after the RL-SIG field. It consists of two OFDM symbols, U-SIG-1 and U-SIG-2. Each OFDM symbol contains 26 data bits that contain packet information for the received configuration. The U-SIG field uses BPSK modulation with rate 1/2 binary convolutional coding (BCC). Bits labeled Validate or Disregard are reserved for future use.

In an EHT MU packet, the U-SIG field contains these components:

  • PHY Version Identifier — A three-bit field that indicates the PHY version. Its value is 0 for EHT. Values 1–7 are Validate.

  • Channel Bandwidth — A three-bit field that indicates the channel bandwidth. Its value is as follows:

    • 0 — 20 MHz

    • 1 — 40 MHz

    • 2 — 80 MHz

    • 3 — 160 MHz

    • 4 — 320 MHz-1

    • 5 — 320 MHz-2

    320 MHz-1 and 320 MHz-2 denote the two different 320 MHz channelizations of the 6 GHz band. For more information on channelization, see Valid Channel Number and Bandwidth Combinations. Values 6 and 7 are Validate.

  • UL/DL — A bit that indicates the transmission direction. This bit is 1 for uplink and 0 for downlink.

  • BSS Color — A six-bit field that identifies the basic service set (BSS).

  • TXOP — A seven-bit field that carries information about the TXOP duration.

  • PPDU Type and Compression Mode — A two-bit field that indicates the PPDU type and compression mode. Its meaning depends on the UL/DL bit.

    UL/DL ValuePPDU Type and Compression Mode Field ValueIndicated PPDU Type
    00Downlink OFDMA
    1EHT single user or EHT sounding NDP
    2Downlink non-OFDMA MU-MIMO
    3Validate
    10EHT TB
    1EHT single user or EHT sounding NDP
    2Validate
    3

  • Punctured Channel Information —A five-bit field that carries information about punctured channels.

  • EHT-SIG MCS — A two-bit field that indicates the modulation and coding scheme of the EHT-SIG field. Its value is as follows:

    • 0 — EHT-SIG MCS 0

    • 1 — EHT-SIG MCS 1

    • 2 — EHT-SIG MCS 3

    • 3 — EHT-SIG MCS 13

  • Number of EHT-SIG Symbols — A five-bit field that indicates the number of EHT-SIG symbols. Its value is the number of EHT-SIG symbols minus one.

  • CRC — A four-bit field that detects errors in the transmission.

  • Tail — A six-bit field that terminates the convolutional code. All six bits are 0.

In an EHT TB packet, the U-SIG field contains these components:

  • Except for Spatial Reuse 1 and 2, all field names have the same definitions as above.

  • These fields do not exist in the U-SIG field of an EHT TB packet:

    • Punctured Channel Information

    • EHT-SIG MCS

    • Number of EHT-SIG Symbols

  • Spatial Reuse 1 and Spatial Reuse 2 — Two four-bit fields that indicate whether spatial reuse is allowed for different portions of the channel bandwidth. The Spatial Reuse 1 field applies to the lower half of the channel bandwidth, and the Spatial Reuse 2 field applies to the upper half. The four bits of each field correspond to 20 MHz subchannels.

For a detailed description of the U-SIG field, see Section 36.3.12.7 of IEEE P802.11be.

References

[1] IEEE P802.11be/D7.0. “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 8: Enhancements for Extremely High Throughput (EHT).” Draft Standard for Information Technology — Telecommunications and Information Exchange between Systems — Local and Metropolitan Area Networks — Specific Requirements, https://ieeexplore.ieee.org/document/10622056.

See Also

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