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How to Measure Distance Through Bluetooth RSSI

Release date:2022-4-26 0:04:08

RSSI stands for received signal strength. The strength depends on distance and broadcast power. In addition to RSSI, there is also dBm, which is related to signal strength. RSSI is a relative index, and dBm is an absolute data. The power value is expressed in mW. Because there are many factors that affect the Bluetooth signal strength, such as the RF design of the transceiver device itself, transmit power, absorption, interference, obstacle diffraction, etc., RSSI is usually an unstable value.

There are many challenges in the currently used RSSI method, resulting in reduced accuracy and stability. One of the biggest challenges is that the signal strength measurement is sensitive to the environment, and radio signal propagation is affected by reflection, absorption, degradation, etc.

Following as a comparison of the actual measured value of RSSI with the curve of the ideal expected exponential signal:

If you want to calculate the Bluetooth transmission distance, it needs to be a point-to-point fixed device in an open and unobstructed environment, and it needs to be calibrated and calibrated.

For RSSI reading, BLE has corresponding RSSI registers, which can be read directly:

RSSI is the basic principle of the bluetooth beacon indoor positioning solution. It is realized through the broadcast mode of low-power bluetooth. Only low-power bluetooth modules have broadcast mode, and the bluetooth power consumption is very low, supporting frequent on-off and fast connection. The low-power bluetooth module realizes ranging RSSI, which is the BLE bluetooth module in the broadcast mode, and another bluetooth device, such as a smart phone, is connected to the bluetooth module. According to the strength of the signal, based on a set of indoor positioning algorithms, it is calculated through mathematical relationships. The distance between the two Bluetooth devices can be calculated, so as to realize the measurement of converting the signal strength into distance.

If you need to follow automatically, A device follows B device, you can know the distance change, but you can't judge the direction. Most of the small wireless area positioning uses the 3-point positioning principle, as shown below:

The position is calculated by collecting the RSSI intensity between the three base stations and the target.

The main applications of BLE in location judgment are proximity detection, anti-lost, search, etc.

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