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Understanding WiFi 7 PPDU Formats and their fields as per IEEE 802.11be WLAN Standard

wifi 7 PPDU Format ieee 802.11be PPDU fields WLAN

WLAN 802.11be is referred as Wi-Fi 7 which defines two PPDU formats viz. multiuser (MU) and trigger based (TB). Both of these Physical (PHY) layer formats follow structure defined in previous WLAN standard i.e. 802.11ax (WiFi 6) and respective HE MU and TB PPDU formats.

THe EHT TB format is mainly used for up link transmissions approved by AP where as EHT MU format is used for everything including both up link/down link single user transmissions.

WiFi 7 PPDU Formats

WiFi 7 PPDU formats and fields as per IEEE 802.11be

WiFi 7 PHY receiver must perform PHY format detection on each received PPDU in order to support previous generations of WiFi. Following table mentions all the fields used in the PPDU formats shown in the figure.

U-SIG (Universal Signal) field is introduced in WiFi 7 which is different from SIG design of WiFi 6 and previous versions. This U-SIG field simplifies PPDU format identification process at the receiver.

PPDU FieldsFunction
L-STF (Legacy Short Training Field)It is inserted at the start of PPDU. It is used for PPDU detection, AGC and coarse carrier recovery.
L-LTF (Legacy Long Training Field)It is used for fine carrier recovery, timing recovery and channel estimation and equalization.
L-SIG and RL-SIGUsed together to identify that a PPDU is an EHT PPDU. it helps to identify format of PPDU whether MU or TB. It also reports length of PPDU in units of 4 us.
U-SIGCarry details of third party STAs and common information for rest of PPDU. It is similar to HT SIG-A, VHT SIG-A and HE SIG fields defined in WiFi 4, 5 and 6 respectively. Some of the bits are used for 802.11be and rest are reserved for future.
EHT SIGUsed in MU PPDUs.
EHT-STFUsed for AGC refinement and still finer carrier recovery and timing estimation.
EHT-LTFUsed for channel estimation and equalization of data field. The number of EHT-LTF is indicated in common field of EHT-SIG field. There are at least as many of EHT LTFs as spatial streams per RU.
Data FieldCarries payload designated as PSDU(s).
Packet Extension (PE)Keeps the medium appearing as busy to allow processing of PPDU due to this extra time delay.