Three wireless LAN positioning technologies: Wi-Fi, Bluetooth and UWB

In the context of the Internet of Everything, the acquisition and application of location information is becoming increasingly important in project implementation. Compared with outdoor positioning, the working environment of indoor positioning is more complex and sophisticated, and its technologies are more diverse.

Generally speaking, we can classify indoor positioning technologies into the following types based on the technical principles and signal sources used:

• According to the positioning principle: ID positioning, interval positioning, three-side positioning, signal arrival angle positioning, fingerprint positioning, inertial dead reckoning, etc.
• According to the signal source used for positioning: Wi-Fi positioning, ZigBee positioning, Bluetooth positioning, UWB positioning, RFID positioning, satellite positioning, low-frequency trigger positioning, base station positioning, sound wave positioning, light positioning, geomagnetic positioning, etc.

In the future, indoor positioning technology will sweep all aspects of our production and life, such as: personnel and cargo management and scheduling in smart factories, production safety management, car navigation in underground parking lots, personnel/visitor positioning management in smart buildings, exhibition location navigation, etc.

Let’s discuss the three most common indoor positioning technologies based on wireless LAN in current industry applications.

Wi-Fi

Wi-Fi positioning began to be used in the personnel monitoring industry based on positioning tags around 2010. In 2013, applications such as mobile phone-based Wi-Fi detection also came to the fore.

At present, Wi-Fi positioning is a relatively popular indoor positioning technology, and its positioning method is based on the propagation model method and fingerprint recognition method of signal strength.

The signal strength propagation model method refers to the use of a certain channel fading model assumed in the current environment to estimate the distance between the terminal and the AP with a known location based on its mathematical relationship. If the user hears multiple AP signals, the user's location information can be obtained through the three-sided positioning algorithm; the fingerprint recognition method is based on the propagation characteristics of Wi-Fi signals. The detection data of multiple APs are combined into fingerprint information, and the possible location of the moving object is estimated by comparing it with the reference data.

In some scenarios where the positioning accuracy is at the meter level, Wi-Fi can be used for coverage. This technology is suitable for positioning and navigation of people/vehicles, medical institutions, shopping malls, theme parks and other scenarios.

Bluetooth

Around 2014, Bluetooth-based positioning technology began to be used in the field of monitoring and positioning.

Bluetooth mesh was officially launched in July 2017. In the past 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.

To meet the growing needs of the location services market, the new Bluetooth 5.1 standard has added a direction-finding function that helps devices determine the direction of Bluetooth signals, thereby helping developers interpret the Bluetooth proximity solution for device direction and achieve a Bluetooth positioning system with centimeter-level location accuracy.

Bluetooth location-based service solutions are usually divided into two categories: proximity solutions and positioning systems. Whether it is real-time positioning or indoor positioning, the principle is similar, that is, adding RSSI (received signal strength) mechanism to data packet transmission, using RSSI to virtualize the approximate range of the product, and then using trilateral measurement to achieve mutual intersection measurement algorithm, and finally complete indoor positioning.

Bluetooth positioning, as long as the Bluetooth function of the device is turned on, it can be located. Bluetooth transmission is not affected by line of sight, but for complex space environments, the stability of the Bluetooth system is slightly poor, it is greatly interfered by noise signals, and the price of Bluetooth components and equipment is relatively expensive.

According to the "2019 Bluetooth Market Latest Information", location services have become the fastest growing Bluetooth solution, and its annual compound 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 a single-story hall or a store, and is now being used by some manufacturers for LBS promotion.

UWB

In recent years, with the maturity of UWB chip solutions and the decline in costs, domestic companies researching UWB positioning technology have continued to emerge. UWB is a wireless positioning technology with high transmission rate (up to 1000Mbps), low transmission power and strong penetration ability.

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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 positioning accuracy up to centimeter level.

TDOA is a positioning method that uses the time difference of arrival, also known as hyperbolic positioning. The tag card sends a UWB signal to the outside, and all base stations within the wireless coverage range of the tag will receive the wireless signal. If two base stations with known coordinates 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.

Positioning systems based on signal time, such as UWB, need to be redeployed once they encounter wall obstruction. For the same area, if the number of rooms doubles, the number of base stations will also double, and base stations are easier to deploy in open areas.

The industries currently using UWB positioning technology include tunnels, chemical plants, prisons, hospitals, nursing homes, mines, etc.

Comparison of LAN Positioning Technologies

Among the above-mentioned wireless LAN-based positioning technologies, the ultra-wideband positioning system can generally achieve centimeter-level positioning accuracy, but the application scope of such positioning is small, the network needs to be redeployed, and users need to use dedicated signal measurement equipment, which has a high implementation cost; although the accuracy of other positioning methods is slightly worse, the cost is also lower, and signal strength is generally used as a reference.

These wireless LANs are generally used in indoor scenarios. Due to the complex influence of the indoor environment, the signal reception strength is prone to fluctuations, and it is difficult to achieve accurate positioning using only signal strength.

Therefore, depending on the measurement parameters, positioning can also be achieved using a method based on the received signal arrival time or a method based on the received signal arrival angle.

Among the three technologies of Wi-Fi, Bluetooth and UWB, in terms of positioning accuracy, UWB can achieve centimeter-level positioning, Bluetooth is centimeter to meter level, and Wi-Fi is only meter level accuracy; in terms of anti-multipath and anti-interference, UWB is significantly better than the other two; in terms of transmission distance, Wi-Fi is the farthest, followed by UWB, and Bluetooth has the shortest transmission distance; in addition, in terms of construction cost, the cost of UWB is much higher than Wi-Fi and Bluetooth.

Wireless LAN 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 choosing a specific positioning technology, we must not only consider the accuracy performance, but also the cost and power consumption. Therefore, although UWB has the highest accuracy, other positioning technologies also have their own markets.

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