"Arm For You" indoor wireless positioning technology (1)

Wireless technology is rapidly developing and diversified in various categories. It is suitable for different environments and different user requirements. The indoor wireless positioning technology developed from wireless technology is also full of development potential. From well-known infrared positioning systems to ultrasonic positioning, to today's bluetooth, wifi and other wireless technology positioning technologies, we can see that indoor wireless positioning technology is facing a new revolution.

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 wireless 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, that is, GPS technologies, such as pseudo satellites ), wireless Positioning Technology: wireless communication signals, RF wireless tags, ultrasonic waves, 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 wireless positioning technology. The principle of Wireless Positioning Technology in the infrared room is that infrared IR marks the infrared rays that emit modulation, and is 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 indoor wireless 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 Bluetooth indoor wireless location technology is that 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, due to its advantages such as non-contact and non-line-of-sight, it is expected to become the preferred indoor wireless 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.