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Introduction
Qualcomm's IPQ Platform now supports IEEE 802.11mc with the SPF.11 release of the SDK (Software Development Kit). IEEE 802.11mc measures the distance between a Wi-Fi access point and a client using Wi-Fi radio waves, and can be used as an indoor positioning method where GPS cannot reach. If three or more 802.11mc-enabled access points with known locations are accessible, it is possible to determine the client's location by measuring the distance to them.
Mechanism of distance measurement
There are the following methods for distance measurement using WLAN Round Trip Time.
・1-Sided Round Trip Time
The access point only sends an ACK for NULL frames.
・2-Sided Round Trip Time
The access point uses the protocol defined by 802.11mc to communicate using time stamps.
1-Sided Round Trip Time
Distance is calculated by the time between a packet sent and its ACK. The 1-Sided Round Trip Time measurement is not suitable for estimating absolute distances because the time required for response is not constant.
2-Sided Round Trip Time
The protocol utilizes the IEEE 802.11mc standard. Both initiators (stations such as smartphones) and responders (access points) must support 802.11mc. A more accurate distance measurement is possible because the response time of the responder does not have to be considered.
Using IEEE 802.11mc
To use IEEE 802.11mc functions, both responder and initiator must support IEEE 802.11mc.
Corresponding responder
Qualcomm's Networking Pro series evaluation board with SPF.11 or later is available. This time, we will use the evaluation board (AP.HK01) equipped with the IPQ8074A. To enable IEEE 802.11mc, refer to the configuration documentation for the LOWI (LOcation Wireless Interface) command in the Command Reference and the Programmer's Guide to enable the LOWI feature.
AP.HK01
Compatible initiator
The Qualcom Networking Pro series evaluation board also works as an initiator. However, it is inconvenient to move around and measure distances with an evaluation board that gets power from an outlet. Since Android 9 (API level 28) or later supports IEEE 802.11mc, it is convenient to use an Android terminal that can use IEEE 802.11mc.
Also, for testing purposes, an app called WifiRttScan is provided by Google, so you can easily check the operation of any Android device that can use IEEE 802.11mc.
A list of Android devices that support IEEE 802.11mc can be found on the Android developer site page shown below.
in action
In the diagram introduced in 2-Sided Round Trip Time,
① FTM request
③ FTM1
⑤ FTM2
The packet of is as follows, and you can confirm that it is working.
① FTM request
③ FTM1
⑤ FTM2
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