블루투스 5.1 AoA 위치 서비스 구현 이론
The Arrived of Angle(AoA) technology has been introduced to BLE since Bluetooth 5.1 Core Specification for Bluetooth Direction's purpose. Now, Bluetooth 5.1 AoA has been widely used in two fields: indoor positioning, and keyless entry. Now, we will explain how AoA works and how it applies into indoor positioning with Bluetooth 5.1 AoA technology. 1. Indoor Positioning Technology Overview There are four solutions for indoor positioning: UWB, Wi-Fi, BLE beacon / BLE AoA. For the accuracy range, UWB is 0.1 m ~ 1 m; Wi-Fi and BLE beacon is 5 m ~ 20 m with a larger error range. As the first commercial BLE AoA positioning service company, Quuppa can control the accuracy range within 0.1 m ~ 1 m (with the TI CC254x and Nordic nRF5281x chips). The following is the test data of Quuppa. 2. Analysis of Indoor Positioning Theory No matter what kind of positioning method, the indoor positioning system needs to draw the architectural modeling of the actual scene, deploy the receiver router in the indoor area, and mark the corresponding location on the modeling map. The mobile phone or the beacon module broadcast wireless signals. The receiver router deployed in a fixed position can confirm the location area range of the beacon after received the wireless signals. The arrival angle of the beacon signal can be measured by multiple antennas after confirmed the location area range. Combined with triangulation positioning, the accurate position of beacon equipment can be calculated. Triangulation Triangulation is to measure the position of the beacon device through two sets of AoA data. As shown in the figure below, two sets of antennas can measure one AoA data, and two AoA data can measure the position of device A. Both d and D are known parameters, how we can get θ1 and θ2. 3. AoA Measurement Theory Frequency: Bluetooth operates in the ISM (Industrial Scientific and Medical) band from 2.40 GHz to 2.41 GHz with a bandwidth of 2 MHz. Bluetooth is divided into three broadcast channels 37, 38, and 39. In the Bluetooth v5.x core specification, the extended broadcast of the Bluetooth LE can be broadcasted in any channel from 0 to 39, that is, the Bluetooth v5.1 beacon can work on any Bluetooth channel. (The frequency of Bluetooth is inconsistent when it is working, which will affect the Bluetooth wavelength λ.) Phase: The wireless signal is continuous in the air. The RX receiver receives and demodulates the signal of the entire wave cycle of 0 ~ 2 π under the frequency range. AoA calculation: Supposing that there is a fixed-frequency Bluetooth beacon signal broadcasting in an open area (ignoring obstacles and other 2.4 GHz signal interference in the air). If the two receivers are on the same radius and at the same TX end, at a certain time t, the phase difference received by the RX receiver should be 0. But if the receiver is in a position with an inconsistent radius, at a certain time t, there is a difference in the phase of the RX receiver. If the above diagram...
