Main Content

S1G PPDU Structure

IEEE® 802.11™1 is a packet-based protocol. Each packet, also called a physical layer protocol data unit (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:

  • S1G to specify a sub-1-GHz (S1G) PHY implementation.

    • S1G refers to preamble fields formatted for association with 802.11ah™ data. Section 23 of [1] defines and describes the S1G PHY layer and PPDU.

    • For S1G, the TXVECTOR parameters, as defined in Table 23-1 of [1], determine the structure of PPDUs transmitted by an S1G station (STA). For an S1G STA, the FORMAT parameter determines the overall structure of the S1G PPDU.

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

802.11b™

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™ (Wi-Fi 4)

HT_MF, Non-HT

OFDM only

20, 40

802.11ac™ (Wi-Fi 5)

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

802.11ax™ (Wi-Fi 6)

HE

OFDMA

20, 40, 80, 160

802.11ba™WURMC-OOK20, 40, 80
802.11be™ (Wi-Fi 7)

EHT

OFDMA

20, 40, 80, 160, 320

In S1G, there are three transmission modes:

  • ≥2 MHz long preamble mode

  • ≥2 MHz short preamble mode

  • 1 MHz mode

The wlanS1GConfig object enables you to create PPDUs and waveforms for all of them. 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 structure of an S1G ≥2 MHz long preamble mode PPDU

    • The transmitter sends the omni-directional portion to all users without beamforming. It consists of three fields:

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

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

      • The signal A field (SIG-A) determines 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 for automatic gain control.

      • The beamformed long training fields (D-LTF-N) are 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 is an exact repetition of the first D-LTF. This repetition enables better 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 structure of an S1G ≥2 MHz short preamble mode PPDU

    The PPDU consists of five fields:

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

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

    • The signaling field (SIG) determines transmission parameters.

    • The subsequent long training fields (LTF2-N) are 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. All of the fields can be beamformed. An S1G 1 MHz mode PPDU has longer STF, LTF1, and SIG fields, so this mode can achieve sensitivity that is similar to the S1G ≥2 MHz short-preamble mode transmissions.

    The structure of an S1G 1 MHz mode PPDU

References

[1] IEEE Std 802.11-2020 (Revision of IEEE Std 802.11-2016). “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.

1 IEEE Std 802.11-2016 Adapted and reprinted with permission from IEEE. Copyright IEEE 2016. All rights reserved.