Now is the era of big data where everything is connected, and many scenes, devices, and items can be connected to each other. Efficient management and positioning. With the vigorous development of the Internet of Things industry in the past two years, the demand for positioning technology in various Internet of Things application scenarios has also greatly increased. Here we will introduce several indoor and outdoor positioning technologies.
1. Bluetooth positioning technology
Bluetooth technology determines location by measuring signal strength. This is a short-distance, low-power wireless transmission technology. Install an appropriate Bluetooth LAN access point indoors, configure the network into a multi-user basic network connection mode, and ensure that the Bluetooth LAN access point is always the piconet. (piconet)’s main device can obtain the user’s location information.
Bluetooth technology is mainly used for small-scale positioning, such as single-story halls or warehouses. The biggest advantage of Bluetooth indoor positioning technology is that the device is small and easy to integrate into PDAs, PCs and mobile phones, so it is easy to popularize. Theoretically, for users who hold mobile terminal devices with integrated Bluetooth functions, as long as the Bluetooth function of the device is turned on, the Bluetooth indoor positioning system can determine their location. When using this technology for indoor short-distance positioning, the equipment is easy to find and the signal transmission is not affected by the line of sight. Depending on the technical means or algorithms used by different companies, the accuracy can be maintained at 3m~15m.
2. Wi-Fi indoor positioning technology
There are two types of Wi-Fi positioning technology. One is to use the wireless signal strength of mobile devices and three wireless network access points to more accurately triangulate positioning of people and vehicles through differential algorithms. The other is to record the signal strength of a large number of determined location points in advance, and determine the location by comparing the signal strength of the newly added device with a database containing a huge amount of data.
Wi-Fi positioning can achieve complex large-scale positioning, monitoring, and tracking tasks in a wide range of application fields. The total accuracy is relatively high. However, the accuracy for indoor positioning can only reach about 2 meters, and precise positioning cannot be achieved. Due to the popularity of Wi-Fi routers and mobile terminals, the positioning system can share the network with other customers, the hardware cost is very low, and the Wi-Fi positioning system can reduce the possibility of radio frequency (RF) interference.
Wi-Fi positioning is suitable for positioning and navigation of people or vehicles, and can be used in various situations that require positioning and navigation, such as medical institutions, theme parks, factories, shopping malls, etc.
3. Radio frequency identification indoor positioning technology
RFID indoor positioning technology uses radio frequency and a fixed antenna to tune the radio signal into an electromagnetic field. The tag attached to the object generates an induced current after passing through the magnetic field to transmit the data. Multiple pairs of two-way communication exchange data to achieve the purpose of identification and triangulation positioning.
Radio frequency identification indoor positioning technology has a very short range, but it can obtain information with centimeter-level positioning accuracy within a few milliseconds. Due to the advantages of electromagnetic fields such as non-line-of-sight, the transmission range is large, the size of the sign is relatively small, and the cost is relatively low. However, it has no communication capabilities, poor anti-interference ability, and is not easy to integrate into other systems. Moreover, user security and privacy protection and international standardization are not perfect enough.
Radio frequency identification indoor positioning has been widely used in warehouses, factories, and shopping malls to position goods and merchandise circulation.
4. ZigBee indoor positioning technology
This technology forms a network between several blind nodes to be positioned and a reference node with a known position and a gateway. Each tiny blind node coordinates communication with each other to achieve full positioning.
ZigBee is an emerging short-distance, low-rate wireless network technology. These sensors require very little energy to transmit data from one node to another via radio waves in a relay manner. As a low-power and low-cost Communication system, ZigBee works very efficiently. However, ZigBee signal transmission is greatly affected by multipath effects and movement, and positioning accuracy depends on the physical quality of the channel, signal source density, environment and algorithm accuracy, resulting in a high cost of positioning software, and there is still a lot of room for improvement. .
ZigBee indoor positioning has been adopted by many large factories and workshops as personnel on-the-job management systems.
5. Ultra-wideband (UWB) positioning technology
Ultra-wideband technology is a new wireless communication technology that has emerged in recent years and is very different from traditional communication technology. It does not require the use of carrier waves in the traditional communication system, but transmits data by sending and receiving extremely narrow pulses with a nanosecond or microsecond level, thus having a bandwidth of 3.1~10.6GHz. At present, countries including the United States, Japan, Canada, etc. are studying this technology, which has good prospects in the field of wireless indoor positioning.
UWB technology is a wireless technology with high transmission rate, low transmit power, strong penetration ability and is based on extremely narrow pulses without carrier. It is these advantages that enable it to achieve more accurate results in the field of indoor positioning.
Ultra-wideband indoor positioning technology often uses TDOA to demonstrate the ranging and positioning algorithm, which is based on the time difference of signal arrival and hyperbola intersection. Ultra-wideband systems include radio systems that generate, transmit, receive, and process extremely narrow pulse signals. The ultra-wideband indoor positioning system includes UWB receivers, UWB reference tags and active UWB tags. During the positioning process, the UWB receiver receives the UWB signal emitted by the tag, and by filtering various noise interference contained in the electromagnetic wave transmission process, a signal containing effective information is obtained, and then the central processing unit performs ranging and positioning calculation and analysis.
Ultra-wideband can be used for indoor precise positioning, such as location discovery of battlefield soldiers, robot motion tracking, etc. Compared with traditional narrowband systems, ultra-wideband systems have the advantages of strong penetration, low power consumption, good anti-interference effect, high security, low system complexity, and can provide precise positioning accuracy. Therefore, ultra-wideband technology can be applied to indoor positioning tracking and navigation of stationary or moving objects and people, and can provide very precise positioning accuracy. Depending on the technical means or algorithms used by different companies, the accuracy can be maintained at 0.1m~0.5m.
6. Infrared positioning technology
Infrared rays are electromagnetic waves with wavelengths between radio waves and visible light waves. The principle of infrared indoor positioning technology is that infrared signs emit modulated infrared rays, which are received by optical sensors installed indoors for positioning. Although infrared rays have relatively high indoor positioning accuracy, infrared rays can only propagate within line-of-sight because light cannot pass through obstacles. The two main shortcomings of short straight line of sight and short transmission distance make indoor positioning effect very poor. When the logo is placed in a pocket or is blocked by walls or other obstructions, it will not work properly. It is necessary to install receiving antennas in each room and corridor, which is expensive. Therefore, infrared rays are only suitable for short-distance propagation and are easily interfered by fluorescent lamps or room lights, which have limitations in precise positioning.
Typical infrared indoor positioning system Activebadges attaches an electronic tag to the object to be measured, which periodically sends the unique ID of the object to be measured to an infrared receiver fixedly placed indoors through an infrared transmitter, and the receiver then transmits the data to the infrared receiver through a wired network. database. This positioning technology consumes a lot of power and is often blocked by indoor walls or objects, making it less practical. If infrared and ultrasonic technology are combined, the positioning function can also be easily realized. Use infrared rays to trigger the positioning signal to make the ultrasonic transmitter at the reference point emit ultrasonic waves to the point to be measured, and apply the TOA basic algorithm to measure distance and position through the timer. On the one hand, it reduces power consumption, and on the other hand, it avoids the shortcomings of short transmission distance of ultrasonic reflection positioning technology. The advantages of infrared technology and ultrasonic technology complement each other.
7. Ultrasonic positioning technology
Ultrasonic positioning technology installs multiple ultrasonic speakers indoors to emit ultrasonic signals that can be detected by terminal microphones. Through the arrival time difference of different sound waves, the location of the terminal can be inferred.
Since the transmission speed of sound waves is much lower than that of electromagnetic waves, the difficulty of system implementation is very low. Wireless synchronization of the system can be achieved very simply, and then the ultrasonic transmitter is used to send, and the receiving end uses a microphone to receive, and the position can be calculated by oneself.
Since the speed of sound waves is relatively low, it takes a long time to transmit the same content. Only through methods similar to TDoA can larger system capacity be obtained.
8. Geomagnetic positioning technology
The Earth can be thought of as a magnetic dipole, with one pole located near the geographic North Pole and the other near the geographic South Pole. The geomagnetic field consists of two parts: the basic magnetic field and the changing magnetic field. The basic magnetic field is the main part of the geomagnetic field. It originates from the interior of the earth. It is relatively stable and belongs to the static magnetic field. The changing magnetic field includes various short-term changes in the geomagnetic field, which mainly originate from the interior of the earth and are relatively weak.
The reinforced concrete structures of modern buildings can disrupt the geomagnetic field on a local scale, and compasses may be affected as a result. In principle, a non-uniform magnetic field environment will produce different magnetic field observation results due to different paths. This positioning technology, called IndoorAtlas, uses changes in geomagnetism indoors for indoor navigation, and the navigation accuracy can reach 0.1 to 2 meters.
However, the process of using this technology to navigate is still a bit cumbersome. You need to first upload the indoor floor plan to the map cloud provided by IndoorAtlas, and then you need to use its mobile client to record the geomagnetic field in different directions of the target location. The recorded geomagnetic data will be uploaded to the cloud by the client, so that others can use the recorded geomagnetic data for accurate indoor navigation.
Baidu made a strategic investment in geomagnetic positioning technology developer IndoorAtlas in 2014, and announced in June 2015 that it would use its geomagnetic positioning technology in its own map application, using the technology in conjunction with Wi-Fi hotspot maps and inertial navigation technology. The accuracy is high, and in commercial applications, it can reach meter-level positioning standards. However, the magnetic signal is easily interfered by the changing electrical and magnetic signal sources in the environment. The positioning result is unstable and the accuracy will be affected.
9. Base station positioning technology
Base station positioning is generally used for mobile phone users. The mobile phone base station positioning service is also called mobile location service (LBS – Location Based Service). It obtains the location information (latitude and longitude coordinates) of mobile terminal users through the network of telecommunications mobile operators (such as GSM network). ), a value-added service that provides users with corresponding services with the support of the electronic map platform, such as the dynamic location query service currently provided by China Mobile M-Zone.
Since GPS positioning consumes more power, base station positioning is a common function of GPS equipment. However, the base station positioning accuracy is low, generally within an error of 100 meters to 2,000 meters.
10. Positioning technologies such as GPS and Beidou satellites
Beidou satellite positioning is independently developed by China and uses geosynchronous satellites to provide users with an all-weather, regional satellite positioning system. It can quickly determine the target or user’s geographical location and provide navigation information to users and authorities.
The Beidou satellite navigation system played an important role in the earthquake relief of the 2008 Wenchuan earthquake. When local communication facilities are severely damaged, communication between various points and departments can be achieved through the Beidou satellite system, and the locations of various disaster relief forces can be accurately determined so that new rescue missions can be issued in a timely manner according to the disaster situation.
At this stage, Beidou satellites are rarely used in civil affairs, and Beidou mobile phones and Beidou car navigation can also be seen on the market.
In addition to the above mentioned, there are currently dozens or even hundreds of types of positioning technologies, and each positioning technology has its own advantages, disadvantages and suitable application scenarios. Which technology will ultimately win is still unknown and needs to be tested over time by the entire industry.
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