With the continuous development of Bluetooth Low Energy (BLE) technology, there are more and more ranging algorithms for Bluetooth positioning, such as RSSI (Received Signal Strength Indication), AoA (Angle of Arrival), AoD (Angle of Departure), and ToA (Angle of Arrival). time), TDoA (time difference of arrival), ToF (time of flight), etc. Different ranging algorithms have different implementation difficulty, power consumption and accuracy. You can choose the corresponding ranging algorithm according to your own budget and accuracy requirements. Among many ranging algorithms, RSSI is the most cost-effective, with the advantages of low power consumption, low cost, and simple use.
RSSI is the abbreviation of Received Signal Strength Indication. It is a received signal strength indication and an optional part of the wireless transmission layer. It is used to determine the connection quality and whether to increase the broadcast transmission strength. A positioning technology that measures the distance between the signal point and the receiving point based on the strength of the received signal, and then performs positioning calculations based on the corresponding data. Bluetooth RSSI positioning refers to a positioning method based on Bluetooth 4.0 or above protocols that uses the correlation between Bluetooth RSSI signal attenuation and distance to calculate the location of a Bluetooth terminal. In practical applications, the transmitter is usually a Bluetooth beacon, and the receiver is usually a smartphone.
When a Bluetooth device is broadcasting, the farther the signal receiving end is from the transmitting end, the weaker the received RSSI field strength value; the closer the signal receiving end is to the transmitting end, the stronger the received RSSI field strength value. The dBm of the wireless signal received by the receiving end is generally a negative value. The larger the signal value, the stronger the signal. The RSSI signal range is between 0 and -100. 0 is an ideal situation and does not exist in practical applications.
According to different application requirements, Bluetooth positioning can generally be divided into presence detection positioning and triangulation precise positioning. Presence positioning is usually used in patrol attendance. One transmitter and one receiver can complete the application, which can prove that it exists in a certain area. The application principle is simple; next, we will focus on the RSSI triangulation positioning principle.
Triangulation positioning principle: The position of the transmitter is fixed. For example, there are three transmitters in an area, that is, three Bluetooth beacons are laid, BS1 (x1, y1), BS2 (x2, y2) and BS3 (x3, y3) .
As shown in the figure: Point E receives signals from BS1, BS2, and BS3, and obtains the RSSI of different points. The triangulation positioning algorithm deduces the coordinates of point E through the three known coordinates.
The coordinates of the three transmitting ends (BS1, BS2, BS3) are fixed. The position of the receiving end can be approximately calculated using the three-point positioning principle. That is, the transmitting end signal spreads out 360 degrees to form a spherical intersection, and then the calculation Get the location of E(x,y);
In practical applications, the algorithm is not only that simple, but also takes into account different attenuation factors in different environments, and uses filtering algorithms to filter signal interference to make the positioning point more stable. In some positioning algorithms, inertial navigation algorithms are also added. Even so, the position calculated using Bluetooth RSSI field strength is still an approximate position.
