The management of staff and assets has always been an issue that cannot be avoided in an office setting. Look at the many fingerprint punching machines on the market to know how strong this demand is.
Regardless of whether employees are happy or not, managers always have a strong desire to know where they are during working hours. The traditional way of punching or fingerprinting relies on the active behavior of employees. The amount of data collected is small, and only the time of commuting can be detected, and the analysis value is low. In addition, because the behavior data is small, the data is easy to fake. There is a need for a comprehensive approach that is simple, reliable, and informative. It can even analyze data based on location and time data to assess the employee's day-to-day work.
The need to monitor asset locations in certain environments is equally strong! For example, in some wards or laboratories, it is often the case that a certain piece of Equipment is found. In fact, it is very similar to the previous scene. If you abstract it, the core is actually the mode of electronic tag + sensor + cloud positioning. The electronic tag is worn on the monitored object, and the sensor senses the tag and reports the specific data to the cloud through the Internet, and the cloud completes the positioning and subsequent business logic.
Basic process of positioning
In general, according to the wireless technology to complete the ranging, the position of the point E of the test point can be obtained according to the coordinates of the known points BS1, BS2, and BS3 and the values of r1, r2, and r3 determined after the ranging is completed. This process is called trigonometry.
The triangulation process of RSSI (Received Signal Strength IndicaTIon) and TOA (TIme of Arrival) is the same, and is based on the formula of plane analytic geometry:
The difference is the technical principle of ranging:
The RSSI method literally refers to the positioning method based on the field strength of the test signal, and the TOA method refers to the positioning method for calculating the distance according to the transmission delay.
1) Since the wireless signal transmission conforms to the attenuation formula:
Therefore, it is known that the signal strength P0 received by the sensor and the signal strength Pd transmitted by the Bluetooth tag can be calculated according to the company. Can visually see the picture below
2) The TOA method literally means time arrival, that is to say, the method of calculating the distance according to the transmission delay, the formula is as follows:
Ri=(TI-t0)c According to the time signal delay of the E to 3 base stations being tested, multiply by the speed of light to get the distance r.
It is well known that due to transmission or device reasons, the higher the signal frequency, the more unstable the signal strength in transmission. The measurement result of RSSI value often changes without change, which can be interpreted as noise, which affects the accuracy of ranging. Therefore, the TOA method avoids the stability problem of the RF signal relative to the measured RSSI and does not change due to occlusion. For example, wearing a earmuff, the volume of the sound you hear will decrease, but as long as it is within a range, the content of the speech can be decoded correctly. Therefore, the UWB technology using the TOA method has high positioning accuracy, and the delay (the time from label movement to system positioning completion) is small. Under the current technical conditions, the positioning delay Bluetooth mode can be achieved within 500ms, and UWB can be implemented for several ms.
