IEEE 802.11az: WiFi for Micro-Location Positioning

This page covers the features of the IEEE WiFi 802.11az standard. It outlines the benefits or advantages of using 802.11az WiFi for micro-location positioning.

IEEE 802.11az WiFi Explained

Bluetooth 5.1, UWB (Ultra Wide Band), and 802.11az technologies are all used for micro-location positioning, which has various uses. These applications include locating items in homes and warehouses, detecting cars and their components, enabling auto-following drones, and preventing accidents.

The IEEE 802.11az WiFi standard defines a ToA (Time of Arrival) based position estimation algorithm for WiFi clients (i.e., STATIONS) in a multi-path environment. This standard helps a Station (STA) identify its position in a WiFi network relative to multiple APs (Access Points) or Routers. This 802.11az amendment defines modifications to both the PHY layer and the MAC layer.

Compared to the previous IEEE standard, 802.11-2016, 11az enables both absolute and relative position estimation with high accuracy. It’s known as the Next Generation Positioning (NGP) standard, which was planned to be finalized by 2022. Unlike RSSI-based positioning, this NGP standard uses the Fine Timing Measurement (FTM) method to determine the position of a WiFi STA.

The figure depicts ToF (Time of Flight) measurement and range calculation.

• ToF = [ (t4-t1) - (t3-t2)]/2
• Range = Speed of light x ToF

Key Features of 802.11az Micro-Location Technology

Here are the defining characteristics of the 802.11az micro-location technology:

• Defines two PPDU formats: HE ranging NDP & HE trigger-based ranging NDP (Null Data Packet).
• Uses multiple repetitions of HE-LTF symbols in both single-user and multi-user waveforms.
• Employs FTM, which uses RTT (Round Trip Time) information to estimate the distance between Wi-Fi-enabled STAs (i.e., clients or stations) and WiFi APs (access points). RTT uses ToD (Time of Departure) and ToA (Time of Arrival) timestamps.
• Utilizes wide bandwidth channels (up to 160 MHz in WiFi 6 and up to 320 MHz in WiFi 7) for improved positioning accuracy.
• Leverages multi-user capabilities as defined in the WiFi 6 standard.
• APs use OFDMA in the uplink and downlink, and trigger-based ranging to obtain ranging information from multiple STAs in a single transmit opportunity.

Benefits or Advantages of 802.11az

The following are the advantages of 802.11az technology:

• Improved Location and Positioning: Enhances the location and positioning accuracy for WiFi users, enabling WiFi routers to quickly and accurately track the precise location of WiFi clients.
• Increased Energy Efficiency: Improves the energy efficiency of the WiFi network.
• Reduced Wireless Medium Utilization: Reduces the overall utilization of the wireless medium.
• Scalability in Dense Environments: Scales effectively in densely deployed environments.
• Security Features: Incorporates enhanced security features.
• Higher Resolution: Offers higher resolution due to the use of wider bandwidth channels.
• MIMO Resilience: Uses MIMO (Multiple-Input Multiple-Output) to provide better resilience to multi-path effects.
• Reduced Overhead: Trigger-based ranging significantly reduces overhead and improves scalability to support more STAs (i.e., stations).

Accuracy Comparison

Out of the three technologies (UWB, Bluetooth 5.1, and 802.11az), UWB provides the highest accuracy, achieving centimeter-level positioning. Bluetooth 5.1 offers sub-meter level accuracy, while 802.11az based WiFi provides decimeter-level accuracy.