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Bluetooth Direction Finding: Knowing AoA/AoD Direction Finding

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In addition to finding keys, the application space of Bluetooth 5.1 direction finding is much larger than you think. As a major wireless communication technology, Bluetooth has spread all over our life and has been widely used in audio transmission, low-power data transmission, positioning and device network. The four major services are also called the four innovative applications in Bluetooth history.

At the same time, driven by the Bluetooth Technology Alliance (SIG), Bluetooth technology continues to innovate to meet increasingly complex communication needs, improve various services, and make innovative applications possible. On the basis of Bluetooth 5.0, Bluetooth 5.1 has added direction finding , and Bluetooth positioning accuracy has been improved to the centimeter level, meeting the market’s demand for more accurate positioning service capabilities. Of course, Bluetooth 5.1 ‘s direction finding function and centimeter-level positioning service are far more than that.

Technical principle

Location-based Bluetooth service solutions are usually divided into two categories: proximity-based solutions and positioning systems. At present, whether it is real-time positioning, Indoor Location/Indoor Scene Recognition or item tracking, the principle of Bluetooth-based positioning services is: a (Received Signal Strength Indication Received Signal Strength) mechanism is added to the transmission data packet, the signal is transmitted by the Beacon, and the Bluetooth device receives the signal and feeds it back. When the device enters the range, the distance between the Bluetooth devices in the system is estimated. Through this technology, the positioning system can determine the location of a specific device with precision up to the meter level.

With the direction finding function added in Bluetooth 5.1, the system can determine the location of the device through signal strength and direction at the same time, and its accuracy can be improved to centimeter level. The direction finding mainly uses two positioning technologies, one is the measurement technology of angle of arrival (Angle-of-Arrival:AOA), and the other is the measurement of angle of departure (AoD, Angle of Departure).

Angle-of-Arrival measurement (AOA)

The angle of arrival (AOA) measurement is that the transmitter sends a special data packet through a single antenna, and the receiver receives it through multiple antennas. Due to the different distances from each antenna to the transmitter, a phase difference will be generated. Calculate the angular relationship between each other through the phase difference and the distance between the antennas, and use the trilateration method to find the direction.

Departure angle (Angle of Departure: AOD)

The departure angle (AOD) is opposite to the arrival angle. The receiver is a single antenna. Multiple antennas of the transmitter transmit special data packets. The receiver calculates the relative direction and distance according to the generated phase difference and antenna distance.

Generally speaking, the angle of arrival (AOA) measurement is mainly used in RTLS (real-time positioning system), item tracking and landmark information, and the angle of departure (AOD) is mainly used in logistics, warehousing and other industries.

Application Based on Bluetooth Direction Finding Function

The direction finding function of Bluetooth 5.1 can not only find the direction where the target tracking item is located, but also improve the positioning accuracy to centimeter level, greatly improving the user experience and work efficiency. The application directions include but are not limited to the following points.

Item tracking (loss prevention)

When smartphone suppliers integrate Bluetooth, which supports angle-of-arrival orientation, into the phone, they can detect the distance and direction of objects. For example, the most common key finding and remote control finding.

Landmark Information Solutions (Museum)

The Landmark (POI) information solution is also based on the smartphone’s angle of arrival direction finding function. Typical applications such as museums have Beacons installed at the location of each exhibit. The Landmark information application on the smartphone can provide users with location information for exhibits in the exhibition hall. In addition, when the phone is pointed at the exhibit, the user can also obtain detailed information about the exhibit.

Bluetooth real-time location system (RTLS) solution (asset tracking, security management)

Bluetooth’s real-time location system (RTLS) solution can track important assets, such as identifying important equipment assets in warehouses and hospitals. A battery-powered low-energy Bluetooth transmitter (tag) is installed on the asset to send the current location and received signal strength of the asset to a fixed Bluetooth receiver for accurate positioning.

On the one hand, it can accurately track the location or process of the article; on the other hand, the centimeter-level positioning can give an alarm and remind workers in time when entering dangerous areas.

Indoor Location/Indoor Scene Recognition System (IPS) Solution: Improving the Navigation Experience

The Indoor Location/Indoor Scene Recognition System (IPS) solution works in the opposite way to the RTLS solution and corresponds to the measurement method of the AOA arrival angle. Install the Beacon (Bluetooth transmitter) at a fixed location in the facility, locate the Beacon and the received signal strength from each known location through the mobile phone application, and calculate its current position through trilateral measurement. Typical applications lie in airports, supermarkets, gymnasiums and other places, which can not only provide accurate navigation and shelf instructions, but also collect the popularity of products in this area. At present, many large venues such as Mall of America, Target, a well-known retailer in the United States, and Gateway Airport have used Bluetooth IPS solutions to provide navigation services for visitors. In addition, Indoor Location/Indoor Scene Recognition can help users quickly find exits at subway transportation hubs with many exits.In addition to the above four solutions, Ren Kai also pointed out that Bluetooth direction finding has great room for innovative applications, such as access control systems for automobiles and houses, and tire pressure detection for automobiles. Car, house access control.A locator is installed in the car, and the mobile phone of the eligible user is detected through the direction finding function, so as to judge the distance and angle between the user’s position (at the front door and the back door) and the car door, and automatically open the car door when approaching the car door, and the same is true for the entrance guard of the house. Since each car is fixed with only one car key, this keyless entry method is expected to allow car owners to issue car keys to other family members by authorizing them to open the car door with their mobile phones. In addition, the Bluetooth direction finding function will also be able to be applied in tire pressure detection, parking (pile AOA measurement) and other aspects, bringing practical experience improvement to users.

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