In the context of the Internet of Everything, the acquisition and application of location information is becoming increasingly important in project implementation. Compared to outdoor positioning, indoor positioning has a more complex and sophisticated working environment, and its technology is more diverse.
In general, we can divide the indoor positioning technology into the following according to the technical principles and the different signal sources:
Divided by positioning principle: ID positioning, interval positioning, trilateral positioning, signal arrival angle positioning, fingerprint positioning, inertial estimation, etc .;
According to the signal source used for positioning: WiFi positioning, ZigBee positioning, Bluetooth positioning, UWB positioning, RFID positioning, satellite positioning, low-frequency trigger positioning, base station positioning, acoustic positioning, optical positioning, geomagnetic positioning, etc.
In the future, indoor positioning technology will sweep all aspects of our production and life, such as: smart factory personnel and cargo management and scheduling, production safety management, underground car parking navigation, smart building personnel / visitor positioning management, exhibition location navigation, etc.
Now let ’s explore three types of indoor positioning technologies based on wireless local area networks that are more common in current industry applications.
WiFi positioning began to be applied in the field of personnel monitoring based on positioning tags around 2010. In 2013, applications such as mobile phone-based WiFi detection also emerged.
At present, WiFi positioning is a relatively popular indoor positioning technology. The positioning method is based on the signal strength propagation model method and fingerprint identification method.
The signal strength propagation model method refers to using a certain channel fading model assumed in the current environment to estimate the distance between the terminal and a known location AP according to its mathematical relationship. If the user hears multiple AP signals, it can pass three sides The positioning algorithm is used to obtain the user's location information. The fingerprint identification method is based on the propagation characteristics of the WiFi signal, combining the detection data of multiple APs into fingerprint information, and comparing the reference data to estimate the possible location of the moving object.
In some scenarios where the positioning accuracy is meter level, WiFi can be used for coverage. This technology is suitable for the positioning and navigation of people / cars, medical institutions, shopping malls, theme parks and other scenarios.
Around 2014, Bluetooth-based positioning technology began to be applied in the field of monitoring and positioning.
In July 2017, Bluetooth mesh was officially launched. In one and a half years, more than 105 products with Bluetooth mesh network functions have been certified, including chip, protocol stack, module and terminal product suppliers.
In order to meet the growing demand of the location service market, the new Bluetooth 5.1 standard adds a seek function, which can help the device to clarify the direction of the Bluetooth signal, and then help developers interpret the Bluetooth proximity solution of the device direction to achieve a centimeter-level location Precision Bluetooth positioning system.
Location-based Bluetooth service solutions are generally divided into two categories: proximity solutions and positioning systems. Whether it is real-time positioning or indoor positioning, the principle is similar, that is, the RSSI (received signal strength) mechanism is added to the data packet transmission, and the approximate range of the product is virtualized through RSSI, and then the trilateral measurement method is used to achieve mutual intersection. Measurement algorithm to complete indoor positioning.
Bluetooth positioning, as long as the Bluetooth function of the device is turned on, it can be positioned. Bluetooth transmission is not affected by line-of-sight, but for complex space environments, the stability of the Bluetooth system is slightly worse, it is greatly affected by noise signals, and Bluetooth devices and equipment are more expensive.
According to the "2019 Bluetooth Market Update", location services have become the fastest growing Bluetooth solution, and its compound annual growth rate is expected to reach 43% in the next five years.
Bluetooth positioning is mainly used for small-scale positioning of people, such as single-story halls or stores, and has been used by some manufacturers for LBS promotion.
In recent years, with the maturity of UWB chip solutions and the decline in costs, domestic companies that have researched UWB positioning technology have continued to emerge. UWB is a wireless positioning technology with high transmission rate (up to 1000Mbps or higher), low transmission power, and strong penetration ability.
UWB positioning uses multiple sensors to analyze the tag position using TDOA (Time Difference of Arrival) and AOA positioning algorithms. It has the characteristics of multipath resolution, high accuracy, and centimeter-level positioning accuracy.
TDOA is a method that uses the time difference of arrival to perform positioning, also known as hyperbolic positioning. The tag card sends a UWB signal once, and all base stations within the tag's wireless coverage area will receive the radio signal. If two base stations with known coordinate points receive the signal and the distance between the tag and the two base stations is different, then the time points when the two base stations receive the signal are different.
Signal time-based positioning systems, such as UWB, need to be re-deployed if they encounter wall occlusion. For the same area, double the number of rooms, and the base station usage will also double. It is easier to deploy base stations in open scenes.
The industries currently using UWB positioning technology are tunnels, chemical plants, prisons, hospitals, nursing homes, mines and other industries.
Comparison of LAN positioning technologies
The above-mentioned wireless LAN-based positioning technologies. Among them, ultra-wideband positioning systems generally have centimeter-level positioning accuracy, but such positioning applications are relatively small, the network needs to be re-deployed, and users need to use dedicated signals. The measurement equipment has a higher implementation cost. Although the accuracy of other positioning methods is slightly worse, the cost is also lower. Generally, the signal strength is used as a reference.
These types of wireless local area networks are generally used in indoor scenarios. Due to the complex influence of the indoor environment, the strength of signal reception can easily fluctuate, and it is difficult to achieve accurate positioning using only the signal strength.
Therefore, depending on the measurement parameters, it is also possible to use the method based on the arrival time of the received signal and the method based on the arrival angle of the received signal to achieve positioning.
The three technologies of WiFi, Bluetooth and UWB, in terms of positioning accuracy, UWB can reach centimeter level positioning, Bluetooth is centimeter to meter level, and WiFi is only meter level accuracy; in terms of anti-multipath and anti-interference, UWB Obviously better than the other two; in terms of transmission distance, WiFi is the farthest, UWB is next, and Bluetooth transmission distance is the closest; In addition, in terms of construction costs, UWB costs are much higher than WiFi and Bluetooth.
WLAN positioning is mainly used for indoor positioning. Depending on the characteristics of the signal and the network architecture, its positioning accuracy can range from centimeters to meters. In different scenarios, when we choose a specific positioning technology, we must not only consider accuracy performance, but also consider cost and power consumption. Therefore, although UWB has the highest accuracy, other positioning technologies also have their own markets.
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