In response to 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: Wi-Fi, Bluetooth, infrared, ultra-wideband, RFID, ZigBee, etc. Bluetooth is a short-range and low-power wireless transmission technology. After installing an appropriate Bluetooth LAN access point indoors, the network is configured into a multi-user basic network connection mode, and the micro-network is always around the Bluetooth LAN access point. The main device of the network, so that the user’s location information can be obtained by detecting signal strength.
What is AOA&AOD positioning?
Two new more accurate positioning methods are proposed in the Bluetooth 5.1 protocol. One is the arrival point of view (AOA), and the other is the departure point of view (AOD).
AOA positioning: The Bluetooth receiver has multiple antennas, and the distance between the transmitting antenna and each receiving antenna is different. Therefore, the emitted signal has a reception time difference at each receiving antenna, and the phase difference can be calculated.
AOD positioning: The positioning beacon of Bluetooth sends a signal through the antenna array, and the receiving device receives the signal through a single antenna, and calculates the sending direction of the signal by decoding the received signal.
Through this triangular distance measurement, real-time indoor positioning with higher accuracy can be easily achieved. It is worth mentioning that regardless of AOA or AOD positioning, the environment between the transmitter and the receiver needs to be clear and unobstructed. When there are obvious obstacles between the two, the Bluetooth signal strength will decrease. The decrease will inevitably lead to a significant decrease in positioning accuracy.
This direction-finding function uses in-phase and quadrature sampling to measure the received phase of the antenna. For example, in the measurement method of reaching the viewpoint, the signal process is through all the antennas in the array, and the test data is sent in sequence according to the pre-designed antenna sequence. The selection data is transferred to the Bluetooth protocol stack inside the device through the controller interface of the host. The algorithm operation in the protocol stack is used to determine the direction of one device to another device. Through multiple antenna orientations, it is confirmed that the device is in Which position on another device.
Throughout the application, the real-time positioning system device used to track the device will call a plurality of fixed-position Bluetooth receivers installed in the entire scene. This device is generally called a locator. The locator will be connected to the data center of the entire system, that is, the centralized server. Place the Bluetooth transmitter on the object that needs to be tracked, and the transmitter will send positioning data to the surroundings at a certain period. The positioning system will roughly calculate the position of each transmitter through each signal. Users can query specific Bluetooth positioning beacons by accessing applications on mobile phones and other terminals. The application can ultimately calculate the real-time location of the queried beacon based on the signal quality received in real time and display it.
Compared with other indoor positioning technologies, the positioning accuracy of AOA and AOD positioning is more accurate, and using Bluetooth technology, it can be directly adapted to the user’s mobile phone, making it more flexible and convenient to use, and is suitable for indoor navigation and other applications. Keywords: cost-effective 4G RTU