Several indoor positioning technologies are introduced.

With the rapid growth of data and multimedia services, the demand for positioning and navigation is growing, especially in complex indoor environments, in environments such as airport halls, exhibition halls, warehouses, supermarkets, libraries, underground parking lots, and mines, it is often necessary to determine the location of mobile terminals or their owners, facilities and items in the room. However, due to the limitations of positioning time, positioning accuracy, and complex indoor environment, the well-developed positioning technology cannot be well utilized at present. Therefore, experts and scholars have proposed many indoor positioning technical solutions, such as A-GPS positioning technology, ultrasonic positioning technology, Bluetooth technology, infrared technology, RFID technology, ultra broadband technology, wireless local area network, optical tracking and positioning technology, as well as image analysis, beacon positioning, and computer vision positioning technology. In general, these indoor positioning technologies can be classified into several categories, namely, the GPS technology (such as pseudo satellites ), wireless Positioning Technology (wireless communication signals, RF wireless tags, ultrasound, optical tracking, wireless sensor positioning technology, etc.), other Positioning Technology (computer vision, aerial estimation, etc ), and gps and wireless positioning combined Positioning Technology (A-GPS or A-GNSS ).

　　Indoor GPS Positioning Technology

GPS is currently the most widely used positioning technology. When the GPS receiver works indoors, the signal is greatly reduced due to the influence of buildings, and the positioning accuracy is also very low, it is impossible to extract navigation data and time information from satellite broadcasting directly, just like outdoors. In order to obtain high signal sensitivity, it is necessary to prolong the stay time on each code delay, A-GPS technology provides the possibility to solve this problem. The indoor GPS technology uses a large number of related devices to concurrently search for possible latency codes, and also helps to achieve rapid positioning.

The advantage of GPS positioning is that the satellite has a large effective coverage and the positioning and navigation signals are free of charge. The disadvantage is that the positioning signal is weak when it reaches the ground and cannot penetrate the building, and the cost of the positioner terminal is high.

　　Indoor wireless positioning technology

With the development of wireless communication technology, emerging wireless network technologies, such as WiFi, ZigBee, Bluetooth, and ultra-broadband, have been widely used in offices, homes, and factories.

-- Infrared indoor positioning technology. The principle of the infrared indoor positioning technology is that the infrared IR marks the infrared rays that emit modulation and are located by receiving an optical sensor installed in the room. Although infrared rays have relatively high indoor positioning accuracy, infrared rays can only be transmitted over the line of sight because light cannot pass through obstacles. The two main disadvantages of linear line-of-sight (BLOS) and short transmission distance make the indoor positioning very poor. It cannot work normally when the logo is placed in a pocket or with walls or other obstruction. it is costly to install a Receiving Antenna in each room or corridor. Therefore, infrared rays are suitable for short-distance transmission and are easily disturbed by fluorescent lights or lights in the room. They have limitations in precise positioning.

-- Ultrasonic positioning technology. Ultrasonic Ranging mainly uses the reflection detection method, and uses triangle positioning and other algorithms to determine the object location, that is, transmitting an ultrasonic wave and receiving the echo generated by the tested object, the distance to be tested is calculated based on the time difference between the ECHO and the emission wave, and some adopt the unidirectional attention method. The ultrasonic positioning system can be composed of several Referer and one main referer. The main Referer is placed on the tested object, under the action of a microcomputer instruction signal, a fixed-position responder is sent to the same-frequency radio signal. After receiving the radio signal, the responder sends an ultrasonic signal to the main receiver at the same time, obtain the distance between the master receiver and each responder. When three or more of the Two-dimensional coordinates of the objects to be tested are responded to, the two-dimensional coordinate system of the objects to be tested can be determined based on relevant calculations.

The overall positioning accuracy of ultrasonic positioning is relatively high and the structure is simple. However, ultrasonic positioning is greatly affected by the multi-path effect and non-line-of-sight propagation. At the same time, a large amount of underlying hardware equipment investment is required, resulting in high costs.

-- Bluetooth technology. Bluetooth technology is used to determine the signal strength. This is a short-distance and low-power wireless transmission technology. An appropriate Bluetooth LAN access point is installed in the room, and the network is configured based on the basic network connection mode of multiple users, make sure that the Access Point of the Bluetooth LAN is always the master device of the picturenet to obtain the user's location information. Bluetooth technology is mainly used for small-scale positioning, such as single-level hall or warehouse.

The biggest advantage of the Bluetooth indoor positioning technology is that the devices are small and easy to integrate into PDAs, PCs, and mobile phones, so they are easy to popularize. In theory, the Bluetooth indoor location system can determine the location of a mobile device that has a bluetooth device integrated. When using this technology for indoor short-distance positioning, it is easy to find equipment and the signal transmission is not affected by the line of sight. The disadvantage is that Bluetooth devices and devices are expensive, and the stability of the Bluetooth system is slightly poor in complex spatial environments, resulting in high noise signal interference.

-- RFID technology. Radio Frequency Identification technology uses radio frequency for non-contact two-way communication and data exchange for identification and positioning. This technology has a short distance, generally up to dozens of meters. However, it can obtain information with centimeter-level positioning accuracy within several milliseconds, with a large transmission range and a low cost. In addition, because of its advantages such as non-contact and non-line-of-sight, it is expected to become the preferred indoor positioning technology. At present, the hotspot and difficulty of radio frequency identification research lies in the establishment of theoretical communication models, user security and privacy, and international standardization. The advantage is that the logo is small in size and the cost is relatively low, but the function is close, it does not have the communication capability, and it is not easy to integrate into other systems.

-- Ultra-broadband technology. Ultra-broadband is a new communication technology that is significantly different from traditional communication technologies. It does not need to use carriers in traditional communication systems. Instead, it transmits data by sending and receiving extremely narrow pulses with nanoseconds or below, so as to have GHz bandwidth. Ultra-Wideband can be used for precise indoor positioning, such as location discovery of battlefield soldiers and robot motion tracking.

Compared with traditional narrowband systems, the ultra-wideband system has the advantages of strong penetration, low power consumption, good multi-path resistance, high security, low system complexity, and accurate positioning accuracy. Therefore, the ultra-broadband technology can be applied to indoor static or mobile objects as well as positioning, tracking, and navigation of people, and can provide very accurate positioning accuracy.

-- Wi-Fi technology. Wireless LAN (WLAN) is a brand new information acquisition platform. It can implement complex large-scale locating, monitoring, and tracking tasks in a wide range of application fields, the positioning of network nodes is the basis and prerequisite for most applications. Currently, the most popular Wi-Fi Positioning Solution is one of the IEEE Wireless LAN standards. The system is easy to install by combining the empirical test and the signal transmission model. It requires few base stations and can adopt the same underlying wireless network structure. The total precision of the system is high.

Ekahau in Finland developed software that can use Wi-Fi for indoor positioning. The accuracy of Wi-Fi plotting ranges from 1 m to 20 m. In general, it is more accurate than the cellular network triangle measurement and positioning method. However, if the positioning measurement only depends on the nearest Wi-Fi access point, rather than the signal strength diagram, the floor positioning is prone to errors. Currently, it is applicable to small-scale indoor positioning, with a low cost. However, whether used for indoor or outdoor positioning, the Wi-Fi Transceiver can only cover areas with a radius of less than 90 meters and is vulnerable to interference from other signals, thus affecting its accuracy, the energy consumption of the positioner is also high.

-- ZigBee technology. ZigBee is a new short-distance and low-rate wireless network technology. It is between Radio Frequency Identification and Bluetooth and can also be used for indoor location. It has its own radio standards that coordinate communication between thousands of small sensors for positioning. These sensors only need a small amount of energy, and transmit data from one sensor to another through radio waves through relays, so their communication efficiency is very high. The most significant technical feature of ZigBee is its low power consumption and low cost.

In addition to the positioning technology mentioned above, it also includes computer vision, optical tracking and positioning, image analysis, magnetic field and beacon positioning. In addition, there are image analysis-based positioning technology, beacon positioning, triangle positioning, and so on. At present, many technologies are still in the research and experimental phase, such as magnetic field pressure sensing-based positioning technology.

GPS positioning technology, wireless sensor networks, and other positioning methods have limitations. In the future, the trend of indoor positioning technology is the combination of satellite navigation technology and wireless positioning technology, which combines GPS Positioning Technology with wireless positioning technology to give full play to their respective advantages, it not only provides better accuracy and response speed, but also covers a wide range to achieve seamless and accurate positioning. (Wu Yuhang Wu Cai Cong Chen xiuwan 2008.1.29)