As we know, in the context of the Internet of Things, the acquisition and application of location information is becoming more and more important. Compared with outdoor positioning, the working environment of indoor positioning is more complex and delicate, and its technology is more diverse. For example, smart factory personnel and cargo management and scheduling, production safety management, underground parking car search navigation, smart building personnel / visitor positioning management, exhibition location navigation, etc.
In general, we can divide indoor positioning technologies into Wi-Fi 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. Let's discuss the three common indoor positioning technologies of WiFi, UWB and Bluetooth.
Wi-Fi positioning began to be applied in the field of personnel monitoring based on positioning tags around 2010. In 2013, applications such as Wi-Fi detection based on mobile phones also emerged.
At present, Wi-Fi positioning is a popular indoor positioning technology, and its positioning method is based on the signal strength propagation model method and fingerprint recognition 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 the known location AP according to its mathematical relationship. If the user hears multiple AP signals, it can pass through the three sides Positioning algorithm to obtain the user's location information; fingerprint identification method is based on the propagation characteristics of Wi-Fi signal, the detection data of multiple APs are combined into fingerprint information, and the possible position of the moving object is estimated by comparing with the reference data.
In some scenarios where the positioning accuracy is meter level, Wi-Fi 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 a year and a half, more than 105 products with Bluetooth mesh network functions have been certified, including chips, protocol stacks, modules, and terminal product suppliers.
In order to meet the growing demand of the location service market, the new Bluetooth 5.1 standard has added a directional function, which can help the device to clarify the direction of the Bluetooth signal, and then help the developer to 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. Measurement algorithm, and finally complete indoor positioning.
Bluetooth positioning, as long as the device's Bluetooth function is turned on, you can locate it. With the release of Bluetooth 5.x and so many more smartphones/pads/laptops integrating with Bluetooth, Bluetooth is expected to take much more share from the location-based service market. 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 used for both small-scale and large-scale positioning of people / assets, such as single-storey halls or shops, exhibition halls, stadiums, warehouses, factories.
In recent years, as UWB chip solutions have matured and costs have fallen, domestic companies studying UWB positioning technology have emerged. UWB is a wireless positioning technology with high transmission rate (up to 1000Mbps or more), low transmit power, and strong penetration capability.
UWB positioning is a multi-sensor using TDOA (Time Difference of Arrival, time of arrival difference) and AOA positioning algorithm to analyze the label position, with multi-path resolution, high accuracy, positioning accuracy can reach centimeter level and other characteristics.
TDOA is a method of positioning using time difference of arrival, also known as hyperbolic positioning. The tag card sends a UWB signal externally, and all base stations within the wireless coverage of the tag will receive the wireless 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 at which the two base stations receive the signal are different.
Signal time-based positioning systems, such as UWB, need to be redeployed once they encounter wall occlusion. For the same area, the number of rooms will double, and the base station usage will also double. It will be easier to deploy base stations in open spaces.
The industries currently using UWB positioning technology are tunnels, chemical plants, prisons, hospitals, nursing homes, mines and other industries.
Comparison of local area network positioning technology
The above-mentioned positioning technologies based on wireless local area network, among them, ultra-wideband positioning system, the positioning accuracy is generally up to centimeter level, but such positioning application range is small, the network needs to be redeployed, and users need to use dedicated signals, the measurement equipment has a relatively high 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 scenes. Due to the complex influence of the indoor environment, the signal reception strength will easily fluctuate. It is difficult to achieve accurate positioning using only the signal strength.
Therefore, depending on the measurement parameters, positioning can also be achieved using a method based on the time of arrival of the received signal and a method based on the angle of arrival of the received signal.
The three technologies of Wi-Fi, Bluetooth and UWB, in terms of positioning accuracy, UWB can reach centimeter-level positioning, Bluetooth is centimeter-to-meter level, and Wi-Fi is only meter-level accuracy; In terms of interference, UWB is significantly better than the other two; in terms of transmission distance, Wi-Fi is the farthest, UWB is second, and Bluetooth is the shortest; in addition; In terms of construction cost, UWB costs are much higher than Wi -Fi and Bluetooth, Wi-Fi and Bluetooth are better able to interact with today’s smartphones; In terms of power consumption, Bluetooth uses the least power, UWB is second, and Wi-Fi is the highest. If we consider all these factors, Bluetooth is likely to have a good chance to become a new fashion in the indoor-positioning market, and other technologies will have their own markets.