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Against the backdrop of the rapid development of the Internet of Things (IoT) and smart cities, indoor positioning technology has become the core link between physical space and digital services. Bluetooth AOA (Angle of Arrival) positioning technology has become a popular solution in the fields of industry, medical care, retail, etc. with its centimeter-level accuracy, low power consumption and high compatibility. This article will systematically analyze the implementation logic and value advantages of Bluetooth AOA positioning technology from four dimensions: technical principles, system composition, core features and application scenarios.
Technical principle: Direction finding positioning based on phase difference
The core of Bluetooth AOA positioning technology is to measure the direction of the signal source through antenna array phase difference analysis. Its mathematical model is:
θ=arcsin(λΔΦ/2πd)
Where θ is the signal incident angle, λ is the signal wavelength, ΔΦ is the phase difference, and d is the antenna spacing.
Signal transmission and reception
Transmitter: The Bluetooth tag (such as a positioning card) sends a dedicated data packet containing CTE (Constant Tone Extension). CTE is an unmodulated pure carrier signal lasting 16-160 microseconds for direction finding.
Receiving end: Linear/rectangular/circular array antennas are deployed on the base station side, and the antenna spacing is usually half the wavelength of the signal (such as about 6cm for 2.4GHz signals) to ensure the uniqueness of the phase difference calculation.
Phase difference solution and spatial positioning
Phase difference measurement: By comparing the phase difference of the CTE signal received by different antennas, the signal incident angle (azimuth/elevation angle) is calculated in combination with the antenna spacing and wavelength.
Single base station positioning: According to the known tag height (such as 1-1.5 meters when worn by a person), the two-dimensional coordinates are calculated in combination with the incident angle. The coverage range of single base station positioning is a cone area centered on the base station. The farther away from the base station, the greater the impact of angle error on the accuracy.
Multi-base station collaboration: The angle measurement values of multiple base stations are intersected by triangulation to improve the three-dimensional spatial positioning accuracy. For example, in a warehouse of 1,200 square meters and a floor height of 3 meters, deploying 4 base stations can achieve sub-meter coverage of the entire area.
Comparison technology: The difference between AOA and AOD
AOA (angle of arrival): The transmitting end is a single antenna, and the receiving end is an antenna array. The signal direction is calculated by phase difference.
AOD (angle of departure): The transmitting end is an antenna array, and the receiving end is a single antenna. Direction finding is achieved by switching the transmitting antenna.
AOA has become the mainstream solution due to its flexible deployment at the base station end and lower cost.
System composition: hardware, algorithm and deployment strategy
Hardware design
Antenna array:
Linear array: One-dimensional positioning, only obtaining azimuth, suitable for linear scenes such as corridors and channels.
Rectangular array/circular array: Two-dimensional positioning, obtaining azimuth and elevation angles at the same time, suitable for complex indoor environments.
Receiver: Integrated digital signal processing (DSP) function, supports signal capture, demodulation and phase difference calculation.
Tag device: Compatible with Bluetooth 5.1 protocol, supports CTE signal transmission, and battery life exceeds 5 years after power consumption optimization.
Signal processing algorithm
Multipath suppression: Use algorithms such as MUSIC and ESPRIT to reduce the phase error caused by metal/glass reflection. For example, in a medical environment, the error caused by multipath interference can be reduced from 1 meter to 0.3 meters through algorithm optimization.
Angle estimation: Improve the angle measurement accuracy through maximum likelihood estimation or compressed sensing algorithm.
Deployment strategy
Base station coverage: The coverage radius of a single base station is 1.2-1.5 times the deployment height (e.g., 6-7.5 meters for a 5-meter floor height).
Power supply mode: Supports PoE (Power over Ethernet) to simplify the installation process.
Positioning frequency: Up to 10Hz (10 times per second), meeting dynamic tracking needs.
Core features: Balance between accuracy, cost and deployment
High-precision positioning
Technical parameters: Positioning accuracy of 10-30 cm, strong anti-multipath interference capability.
Application value: Meet the needs of scenarios such as industrial asset tracking and medical equipment management. For example, in automobile factories, AOA technology can achieve centimeter-level positioning of AGV cars to avoid collision risks.
Single base station coverage
Technical parameters: Single base station achieves two-dimensional positioning, and multiple base stations expand to three-dimensional space.
Application value: Reduce hardware costs (reduced by more than 50% compared with UWB solutions) and adapt to complex environments (such as nursing homes and hospitals). For example, in a nursing home, a single base station can cover one floor, reducing deployment costs.
Low power consumption and long battery life
Technical parameters: The power consumption of tag devices is optimized, and the battery life exceeds 5 years.
Application value: Reduce maintenance costs and support large-scale deployment. For example, in retail scenarios, thousands of positioning tags can be deployed without frequent battery replacement.
Low-cost ecology
Technical parameters: The unit price of tags is as low as tens of yuan, relying on the global ecosystem of billions of Bluetooth devices.
Application value: No additional hardware is required to adapt to smartphones, lowering the user threshold. For example, consumers can directly enjoy high-precision positioning services through mobile phones that support Bluetooth 5.1.
Flexible deployment
Technical parameters: Supports ceiling/wall/desktop installation, and the base station is powered by PoE.
Application value: The coverage radius of a single base station is 1.2-1.5 times the deployment height, which quickly expands the coverage range. For example, in shopping malls, the coverage radius can be optimized by adjusting the base station height.
Bluetooth AOA positioning technology has achieved breakthroughs in centimeter-level accuracy, single base station deployment, low power consumption and low cost through phase difference direction finding and triangulation algorithms, becoming one of the mainstream solutions for high-precision indoor positioning. Despite facing challenges such as multipath interference, its compatibility and cost advantages have enabled it to be quickly implemented in industries such as industry, medical care, and retail, pushing the Internet of Things from "connection" to "perception".
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