Indoor positioning technology
Overview of indoor positioning technology
In the course of nearly 50 years of development, GNSS positioning technology has encountered many challenges and obstacles, but by continuously improving its usability and accuracy, and integrating with various mature or emerging technologies, GNSS positioning again and again Successfully break through obstacles and move to new heights. Nowadays, in the face of the new application field of indoor positioning, GNSS positioning is facing new technical challenges. Satellite positioning signals have inherent limitations that can only be transmitted within line of sight, making it difficult to receive them in an indoor environment. With strong demand from social networking and business location-aware applications, indoor positioning technology has become one of the most popular research areas. With the rapid spread of smart phones, indoor positioning applications have gradually entered the field of vision. The built-in inertial sensors and Wi-Fi communication modules of smart phones can not only improve the accuracy of satellite positioning, but also the basis of the latest satellite positioning results. Accurate indoor positioning. Twenty-two companies, including Nokia, Sony and Samsung, also jointly established the In-Location indoor positioning alliance, and promised to jointly carry out indoor positioning research, open interfaces and start indoor positioning standardization (Peng Yu et al., 2011).
Current status and trends of indoor positioning technology at home and abroad
The rapid development of social economy and science and technology has led to an increasing demand for positioning and navigation. Currently the most widely used is GNSS positioning technology. However, when the GNSS receiver is working indoors, the signal is greatly attenuated by the influence of the building, and the positioning accuracy is low, which cannot meet the demand for indoor positioning navigation (location-based service) with frequent activities. To this end, domestic and foreign experts and scholars have explored many technical methods to meet the needs of wireless indoor positioning, and proposed many indoor positioning technologies and indoor positioning systems. Commonly used indoor positioning technologies mainly include ultrasonic positioning technology, infrared-based positioning technology, ultra-wideband based positioning technology, and radio frequency identification positioning technology.
1 Ultrasonic based positioning technology
Most of the ultrasonic-based positioning currently uses the reflective ranging method. The system consists of a main range finder and several electronic tags. The main range finder can be placed on the mobile robot body, and each electronic tag is placed in a fixed position in the indoor space. The positioning process is as follows: first, the host computer sends the same frequency signal to each electronic tag, and the electronic tag is reflected and transmitted to the main range finder, so that the distance between each electronic tag and the main range finder can be determined, and Positioning coordinates. At present, there are two popular techniques for ultrasonic indoor positioning: one is to combine ultrasonic and radio frequency technology for positioning. Since the radio frequency signal transmission rate is close to the speed of light and much higher than the radio frequency rate, the radio frequency signal can be used to activate the electronic tag and then receive the ultrasonic signal, and the time difference is used to measure the distance. This technology is low in cost, low in power consumption, and high in precision. The other is multi-ultrasonic positioning. The technology adopts global positioning, and four ultrasonic sensors can be installed on the mobile robot body, and the space to be positioned is partitioned, and the coordinates are formed by the ultrasonic sensor. The technology has strong anti-interference and high precision, and can solve the problem of robot lost. Ultrasonic-based positioning technology can reach centimeter accuracy. The main drawback is that the ultrasonic wave attenuates significantly during transmission, thus affecting the effective range of its positioning.
2 infrared based positioning technology
Infrared is an electromagnetic wave between wavelengths of radio waves and visible waves. The typical infrared-based indoor positioning system Activebadges attaches an electronic identifier to the object to be tested, and the identifier transmits the unique ID number of the object to be tested periodically through the infrared transmitter to the infrared receiver fixedly placed indoors, and the receiver then transmits the cable through the wired network. The data is transmitted to the database, but this positioning technology consumes a lot of power and is often blocked by indoor walls or objects, and is less practical. If the infrared and ultrasonic technologies are combined, the positioning function can be conveniently realized, that is, the infrared ray is used to trigger the positioning signal to cause the ultrasonic transmitter of the reference point to transmit ultrasonic waves to the point to be measured, and the TOA basic algorithm is applied to locate the position by the timer. The technology reduces the power consumption on the one hand, and avoids the short transmission distance of the ultrasonic reflective positioning technology on the other hand, so that the infrared technology and the ultrasonic technology complement each other. The positioning accuracy based on infrared positioning technology is 5~10m. The main defect is that infrared light is easily blocked by objects or walls during transmission and the transmission distance is short. The positioning system is more complicated, and the effectiveness and practicability are still different from other technologies. .
3 Ultra-wideband based positioning technology
Ultra-wideband technology is a new wireless technology in recent years. At present, countries including the United States, Japan, and Canada are studying this technology, and have good prospects in the field of wireless indoor positioning. Ultra-wideband technology is a wireless technology with a high transmission rate (up to 1000 Mbps or higher), low transmission power, strong penetration capability and based on extremely narrow pulses. Ultra-wideband indoor positioning technology often adopts TDOA demonstration ranging positioning algorithm, which is based on the time difference of signal arrival, and locates the ultra-wideband system through hyperbolic intersection. During the positioning process, the UWB receiver receives the UWB signal transmitted by the tag, and filters the various noise interferences in the electromagnetic wave transmission process to obtain a signal containing valid information, and then performs calculation and analysis of the ranging by the central processing unit. A typical example of an indoor positioning system based on ultra-wideband technology is Ubisense. The positioning method is three-side positioning. The positioning accuracy based on ultra-wideband positioning technology is 6~10cm, and the main defect is high cost.
4 Radio frequency identification based positioning technology
The radio frequency identification based positioning technology is very convenient to implement, and the system is less affected by the environment, and the electronic tag information can be edited and rewritten, which is more flexible. Radio Frequency Identification (RFID) technology is a simple and easy-to-use technology for automatic control. It utilizes the transmission characteristics of inductance and electromagnetic coupling or radar reflection to realize automatic recognition of recognized objects. Radio frequency (RF) is an electromagnetic wave with a certain wavelength, and its frequency is described as kHz, MHz, GHz, ranging from low frequency to microwave. The system typically consists of an electronic tag, an RF reader, middleware, and a computer database. The radio frequency tag and the reader are exchanged data through a transmission channel of space electromagnetic waves erected by the antenna. In the positioning system application, the radio frequency reader is placed on the moving object to be tested, and the radio frequency electronic tag is embedded in the operating environment. The electronic tag stores information for location identification, and the reader/writer connects to the information database by wire or wireless. Common frequency bands for RFID include low frequency, high frequency, ultra high frequency, and microwave. In the RFID location technology, WLAN and ZigBee are the two main key technologies.
(1) WLAN technology
The wireless local area network technology based on the IEEE802.11b standard is applied to the indoor positioning system, and the access point or the wireless network card in the wireless local area network can easily measure the strength of the wireless signal, and the use of this method can be performed by matching the signal strength. Location fingerprinting is a commonly used wireless local area network positioning technology. The typical system is the RADAR prototype system, developed by Microsoft. The RADAR indoor positioning system based on RSSI technology runs in two processes. Firstly, the location information and signal strength are collected offline at several fixed points in the system coverage area, and transmitted to the data center through the wired network to form a location fingerprint database. The signal strength measured by the real-time object to be tested is matched by the nearest neighbor method. The positioning accuracy of this technology is 2~3m. The main defect is the large amount of data collected, and in order to achieve higher precision, the position measurement setting of fixed points is cumbersome (Gu Zonghai, 2011).
(2) ZigBee technology
It is applied to short-range wireless communication, mainly for wireless personal area network (PAN, Perso nal Area Network). The network system exhibits close-range, low-power, low-cost characteristics in applications, which can meet the requirements of indoor positioning system. Requirements and conditions. The indoor positioning system using ZigBee technology is to arrange the reference nodes in the sensor network, the mobile nodes constitute the system, and the reference nodes are static nodes, which send the position information and the RSSI value to the mobile node to be tested, and the node writes the data into the positioning module. , the analysis calculates its own position. The system often uses distributed node settings to reduce network data workload and communication latency. The positioning accuracy of this technology is less than 2m, with an average of 1m. The main drawback of the technology is that the network stability needs to be improved and is susceptible to environmental interference (Li Weifeng et al., 2010).
Application of indoor positioning technology in digital cities
Indoor positioning technology is very practical in digital cities. In complex digital urban environments, such as libraries, gymnasiums, underground garages, goods warehouses, etc., you can quickly locate people and items, guide in the venue, merchandise shopping guide, and personnel positioning. The application of logistics, transportation and other aspects has a large expansion space. At present, the smart handheld devices represented by Apple's iPhone and iPad not only greatly enhance the data processing capability, but also integrate MEMS sensors such as accelerometers and gyroscopes. At the same time, they also have strong software expansion capabilities and can be equipped with inertial indoors. The excellent carrier of the positioning system lays the foundation for the application of digital city interior modeling navigation.
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