Overview
The emergence of Bluetooth AOA positioning technology makes up for the defect of low positioning accuracy of Bluetooth RSSI value. In theory, it can replace the current Bluetooth RSSI positioning scheme to a certain extent. Of course, in the field of high-precision positioning applications, UWB positioning has been maturely commercialized in batches. Bluetooth AOA also has high positioning accuracy, so in the field of centimeter-level high-precision positioning, can Bluetooth AOA positioning compete with UWB positioning technology? This article analyzes the advantages and disadvantages of the three positioning schemes from a technical level.
What is Bluetooth RSSI?
Bluetooth RSSI positioning determines the position based on the relationship between signal strength and distance. Because the relationship between signal strength and distance is nonlinear and the signal strength is affected by various factors (such as occlusion, different directions, different broadcast channels, etc.), the positioning accuracy is low.
Bluetooth RSSI positioning is divided into two methods: regional positioning and triangulation positioning. The Bluetooth beacon + Bluetooth gateway method can achieve regional placement, and the Bluetooth beacon + Bluetooth positioning card + Bluetooth gateway technology can achieve triangulation. The positioning card collects the location information of the beacon, which is sent to the Bluetooth gateway, which then sends the data to the server for location calculation.
Bluetooth RSSI positioning is based on Trilateration
The fluctuating RSSI is smoothed by averaging (or signal processing) RSSI readings at different times. Unknown directions can be solved using trilateration, which involves using three gates to calculate the distance to three directions, thereby calculating the 2D position.
There are two types of RSSI positioning. The first case involves the gateway being in a known position when the beacon moves. The second is when the beacon remains stationary when the detector moves. In either case, the gateway receives the beacon ID and the receiving electronic device provides the signal strength. The RSSI value can be used to calculate the distance between the detector and the beacon.
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How to improve Bluetooth RSSI positioning accuracy
The above physical factors that affect RSSI can be reduced by accurately measuring RSSI at a specific location and properly calibrating the device. The closer the beacon is to the detector, the greater the fluctuation of RSSI with distance. It is difficult to determine whether the RSSI change at the edge of the beacon signal is the result of distance change or radio noise because the fluctuation of RSSI with distance is small. So for a system that leverages signal processing, trilateration, and calibration, accuracy can typically be around 1.5 meters in a small space at shorter distances, and around 5 meters at longer distances.
Main Challenges with RSSI
The fundamental problem with RSSI is that it fluctuates too much over time to be used for accurate distance measurement. When there is only one beacon and one detector, the direction is similarly unknown. Even when nothing is moving, RSSI can vary because Bluetooth radio signals are reflected, deflected by physical obstacles, and interfered with by other devices using the same radio frequency
Rooms, beacons that transmit unevenly across 360 degrees, walls, other objects, and even people can all have an effect on received signal strength. The way a user holds the detection phone changes the efficacy of the antenna, which changes the signal strength.
What is UWB positioning?
UWB is a communication medium that distributes information over a wide frequency band. This allows UWB positioning transmitters to send large amounts of data with minimal transmit energy. The distance between a reference point and a target is calculated using the time difference of arrival (TDOA) or RF signal in UWB positioning
UWB positioning systems rely on extremely short pulses and methods that allow radio energy to propagate with very low power spectral density (over a wide frequency range). Its high data throughput allows for fast communications. Because the frequency of UWB pulses is so low, they can effectively pass through common items such as furniture and other small objects.
UWB works over very close distances and wide bandwidths by design. UWB uses the 802.16.5 protocol to connect with peer devices. UWB uses pulsed radio to broadcast broadband in short cycles while requiring minimal power. By broadcasting more pulses per second, UWB uses high pulse repetition rates to increase positioning accuracy and data speeds.
Major Challenges of UWB
Although UWB positioning systems offer many advantages, they also have certain disadvantages. For example, misconfiguration may interfere with neighboring devices operating in the ultra-wide spectrum, causing severe interference to certain communication systems and services. In addition, simultaneous ranging between many UWB tags may lead to problems with channel access management, resulting in frequent degradation of UWB positioning accuracy. Although there are several advantages to using very short pulses in UWB, UWB receivers require signal acquisition, synchronization, and tracking. Timing accuracy is relatively good relative to pulse rate. These stages take a long time.
What is BLE·AOA?
Tags or smartphones or almost anything with a Bluetooth transmitter can be tracked based on their location using a network-centric AoA approach. Devices transmit direction-finding-enabled packets through a single antenna to provide their location to location service applications. The locator receives the radio signal and estimates the angle. Finally, the data is transmitted to the positioning engine, which calculates the location information and transmits the specific location of the device
Advantages of BLE·AOA
- The Bluetooth ecosystem is large and mature, with billions of Bluetooth devices shipped each year, which lays a good foundation for the expansion of the Bluetooth AoA positioning market.
- Bluetooth RSSI value positioning has been popularized as a positioning technology seven or eight years ago. It has not only formed a relatively complete industrial chain, but also has certain accumulation and attempts in many applications. Bluetooth AoA positioning with higher positioning accuracy can replace previous technologies to a certain extent.
- Bluetooth tags have low cost, especially mobile phones have Bluetooth. In some solutions, there is no need to use additional tags, and mobile phones can play the role of Bluetooth tags, with a slightly higher overall cost performance.
- The characteristic of Bluetooth AOA positioning solution is that the smaller the distance, the higher the accuracy. Therefore, in indoor scenes with many obstructions and dense walls, it is necessary to lay dense base stations, and Bluetooth AOA is very suitable.
Main challenges of BLE AOA
The positioning range of BLE AOA solution is limited, and multiple IoT gateways are required when the scene is relatively large. In addition, AOA gateways can only be installed on the ceiling. Most indoor buildings are very close, so many AOA base stations need to be deployed, which limits its application scenarios. BLE AOA is generally used in museums, exhibition halls, logistics warehouses and other scenes with high distances and many positioning objects.
In addition, Bluetooth technology uses the 2.4G global free frequency band, and there are many interference signals in this frequency band.
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