Wireless data transmission indoor positioning technology for IoT: AOA and AOD
In order to solve the problem that satellite positioning cannot be used in indoor environments, there are many different indoor positioning technologies on the market.
Common indoor wireless positioning technologies include: WiFi communication module , Bluetooth module , infrared remote control switch , ultra-wideband wireless communication technology , RFID radio frequency technology , ZigBee module, cat.1 positioning module, GPS positioning and navigation module , etc.
As a short-distance, low-power wireless transmission technology, the Bluetooth wireless communication module installs an appropriate Bluetooth LAN access point indoors, configures the network into a multi-user basic network connection mode, and ensures that the Bluetooth LAN access point is always the main device of this micro network. In this way, the user's location information can be obtained by detecting the signal strength.
AOA and AOD ranging principles
Two new and more accurate positioning methods are proposed in the 5.1 protocol of the Bluetooth wireless communication module. One is the angle of arrival (AOA) and the other is the angle of departure (AOD).
AOA positioning : The Bluetooth module receiver has multiple antennas. The distance between the transmitting antenna and each receiving antenna is different. Therefore, the transmitted signal has a reception time difference at each receiving antenna, and the phase difference can be calculated.
AOD positioning : The positioning beacon of the Bluetooth module sends a signal through the antenna array, and the receiving device receives the signal through a single antenna and calculates the direction of the signal by decoding the received signal.
Through this triangulated distance measurement, high-precision real-time indoor positioning can be achieved.
It is worth mentioning that whether AOA or AOD positioning, it is necessary to ensure that the environment between the transmitter and the receiver is open and unobstructed. When there are obvious obstacles between the two, the Bluetooth signal strength will decrease, which will inevitably lead to a very obvious decrease in positioning accuracy.
This direction-finding function uses in-phase and quadrature sampling to measure the antenna's receiving phase.
For example, in the angle of arrival measurement method, the signal process is to send test data through all antennas in the array in sequence according to a pre-designed antenna sequence.
The data is transmitted to the Bluetooth protocol stack inside the device through the host's controller interface, and the algorithm in the protocol stack is used to determine the direction of one device relative to another device. Then, through multiple antenna orientations, the device's position on the other device is confirmed.
Throughout the application, the real-time positioning system device used to track the device will call several Bluetooth receivers installed in fixed locations throughout the scene. This device is generally called a locator. The locator will be connected to the data center of the entire system, that is, concentrated on the server. Place the Bluetooth transmitter on the object whose position needs to be tracked. The transmitter will send positioning signals to the surroundings at a certain period. The positioning system will roughly calculate the location of each transmitter through each signal. Users can query specific Bluetooth positioning beacons by accessing applications on mobile phones and other application terminals. The application can infer the real-time location of the queried beacon through the quality of the signal received in real time and display it.
Compared with other indoor positioning technologies, AOA and AOD positioning have more precise positioning accuracy, and use Bluetooth wireless communication module technology, which can be directly adapted to the user's mobile phone. It is more flexible and convenient to use and is suitable for applications such as indoor navigation.
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