Terminology » UHR MU PPDU vs. UHR TB PPDU: Wi-Fi 8 Frame Formats

UHR MU PPDU vs. UHR TB PPDU: Wi-Fi 8 Frame Formats

wifi 8 mu ppdu tb ppdu wi-fi 8 wlan

Introduction : In the architecture of Wi-Fi 8 (IEEE 802.11bn), the way data is packaged and sent over the air is defined by the UHR (Ultra High Reliability) PPDU formats. These “packets” at the physical layer ensure that the new reliability features like DRU and Multi-AP coordination; can actually be communicated between devices. The two primary formats introduced in this generation are the UHR MU PPDU and the UHR TB PPDU. Let us explore their differences in how they function and when they are applied.

UHR MU PPDU (Multi User)

It is the standard “broadcast” format of Wi-Fi 8. It is primarily used by an Access Point (AP) to send data to one or more devices simultaneously.

Think of the MU PPDU as a delivery truck with a detailed manifest. The most important part of this frame is the UHR-SIG (Signal) field. This field contains the “map” for the transmission which tells every client device on the network exactly which Resource Units (RUs) belong to them and how to decode the data. Because it carries its own instructions, it can be sent independently by an AP to manage the downlink (router to device) traffic efficiently.

Wi-Fi 8 UHR MU PPDU Frame Format Image Courtesy : Rohde & Schwarz

UHR TB PPDU (Trigger Based)

The UHR TB PPDU is the “coordinated response” format. It is used in modern Wi-Fi, especially for uplink (device to router) traffic. The TB PPDU is not sent independently; it is a mandatory response to a “Trigger Frame” sent by the AP. When the AP wants several devices to talk at the same time without crashing into each other, it sends a trigger. The devices then reply using the UHR TB PPDU.

Because the AP already gave the instructions in the Trigger Frame, the TB PPDU is “leaner”. It does not need a UHR SIG field. Instead, it focuses heavily on the UHR-STF and UHR-LTF fields, which help the AP synchronize the incoming signals from multiple devices so they arrive at the router perfectly aligned in time and frequency.

Wi-Fi 8 UHR TB PPDU Frame Format Image Courtesy : Rohde & Schwarz

Comparison: UHR MU vs. UHR TB PPDU

FeatureUHR MU PPDU (Multi-User)UHR TB PPDU (Trigger-Based)
Primary roleGeneral data delivery and broadcasting.Coordinated, simultaneous responses.
DirectionMostly Downlink (AP to Devices).Mostly Uplink (Devices to AP).
Key fieldUHR-SIG: Contains the resource map.No UHR-SIG: Instructions are pre-sent.
Trigger Req.Can be sent independently.Required: Must follow a Trigger Frame.
Design focusInforming users of resource allocation.Precise timing and frequency alignment.
AnalogyA TV Broadcast with a program guide.An Orchestra following a conductor.
Backward Comp.Includes U-SIG for Wi-Fi 7/8 awareness.Optimized for extreme synchronization.

Summary

The MU PPDU allows the router to tell the world how the airwaves are being divided, while the TB PPDU allows devices to speak in a perfectly timed harmony. Together, these two formats provide the structural foundation for features like OFDMA and Multi-AP coordination, ensuring that Wi-Fi 8 can handle the high density, low latency demands of the future networks.