Practical information! Analysis of the principles of the top ten indoor positioning technologies in the Internet of Things

Faxian, a monk in the Eastern Jin Dynasty, wrote on his return trip to the West in search of the Dharma: The sea is vast and boundless, and I cannot tell east from west. I can only look to the sun, moon, and stars to navigate. The general idea is that the sea is vast and boundless, and I cannot tell east from west, north from south, and I can only look to the stars and the moon to navigate.

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origin

In order to avoid getting lost in the vast nature, humans have invented tools such as compasses and needles. The advent of satellite positioning has solved the problem of "where am I". In today's highly urbanized world, indoor spaces are becoming increasingly large and complex. Humans have conquered nature, but have lost their way in the reinforced concrete they have built .

In hospitals, even with floor maps and guide signs, most of the time spent seeing a doctor is still wasted on finding the department. In parking lots, there are many people wandering around because they can't find a parking space.

Under the increasingly urgent demand, indoor positioning has attracted great attention in recent years.

Indoor positioning, as the name implies, is to achieve positioning in an indoor environment. Nokia made it very clear when it explained why they wanted to do indoor positioning many years ago.

Data source: Nokia

Satellites cannot locate indoors, and people spend most of their time indoors, yet related services are not yet popular. It can be said that indoor positioning hides huge business opportunities.

In commercial applications, indoor positioning technology is divided into consumer grade and industrial grade according to different application scenarios.

Applications in the consumer market include: shopping guides in shopping malls, reverse car search in parking lots, preventing family members from getting lost, etc. The positioning accuracy requirement is not high, and an accuracy of 1m can meet most applications, but it requires the system to be compatible with the popular mobile smart terminals.

Enterprise market applications include: crowd monitoring and analysis, intelligent manufacturing, emergency rescue and personnel asset management, etc. Industrial-grade technology requires higher positioning accuracy, and needs to distinguish between operating objects, individuals in the crowd, etc. It is used in conjunction with special tags and sensors, and generally does not consider compatibility with existing smart terminals.

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Technical School

Unlike outdoor satellite positioning, which dominates the market, various indoor positioning technologies are flourishing.

Indoor positioning is flourishing

The commercial value of indoor positioning is proportional to its accuracy. When the accuracy is 3-5 meters, it can determine whether you are standing in front of a 7-11 convenience store or a Jack Jones store. When the accuracy is 1 meter, it can determine whether you are standing in front of a Coca-Cola shelf or a Durex shelf.

At present, the commonly used positioning methods for indoor positioning are mainly divided into: proximity detection method, centroid method, pole method, multilateral positioning method, fingerprint method and dead reckoning method in principle.

Comparison of main indoor positioning methods

Each principle has its own advantages and disadvantages. Different principles can also be combined for different application scenarios and budget requirements. The mainstream technologies are as follows:

WiFi Positioning Technology

Currently, WiFi is a relatively mature and widely used technology. In recent years, many companies have invested in this field. There are two main types of WiFi indoor positioning technologies.

WiFi positioning Generally, the "nearest neighbor method" is used for judgment, that is, the closest hotspot or base station is considered to be in that location. If there are multiple signal sources nearby, cross positioning (three-sided positioning) can be used to improve positioning accuracy.

Since WiFi is already widespread, there is no need to lay special equipment for positioning. When users use their smartphones and turn on Wi-Fi or mobile cellular networks, they can become data sources. This technology has the advantages of easy expansion, automatic data update, and low cost, so it was the first to achieve scale.

However, WiFi hotspots are greatly affected by the surrounding environment and have low accuracy. In order to be more accurate, some companies have collected WiFi fingerprints , recording the signal strength of a large number of determined location points in advance, and determining the location by comparing the signal strength of the newly added device with a database with a huge amount of data.

Since the collection work requires a large number of personnel to carry out and regular maintenance, the technology is difficult to expand, and few companies can regularly update the fingerprint data of so many shopping malls in China.

WiFi positioning can achieve complex large-scale positioning, but the accuracy can only reach about 2 meters, which is not accurate. Therefore, it is suitable for positioning and navigation of people or cars, and can be used in medical institutions, theme parks, factories, shopping malls and other occasions where positioning and navigation are required.

Representative companies include: WIFISLAM, Sensewhere, and Tuju Intelligence

In addition, geomagnetic positioning technology uses the difference in geomagnetic fields at different locations indoors to determine indoor locations. It is similar to WiFi fingerprinting, so I will not introduce it here.

Inertial Navigation Technology

This is a purely client-side technology that mainly uses motion data collected by terminal inertial sensors, such as accelerometers and gyroscopes, to measure the speed, direction, acceleration and other information of an object. Based on the dead reckoning method, the location information of the object is obtained through various calculations.

As walking time increases, the error of inertial navigation positioning is also accumulating. It needs external data sources with higher precision to calibrate it. Therefore, inertial navigation is generally combined with WiFi fingerprints. The indoor position is requested through WiFi every once in a while to correct the error generated by MEMS. This technology is currently commercially mature and widely used in sweeping robots.

Bluetooth Beacon Technology

Bluetooth beacon technology Currently, it is widely deployed and is a relatively mature technology. The difference between Bluetooth and WiFi is not too big, and the accuracy is slightly higher than WiFi.

This technology was first initiated by Nokia, but it had little impact. In 2013, Apple released the iBeacon protocol based on Bluetooth 4.0 Low Energy (BLE), mainly for retail applications, which attracted widespread attention.

The normal operation of iBeacon Bluetooth beacon technology requires the collaborative work of Bluetooth beacon hardware, applications on smart terminals, and application backgrounds on the cloud.

The beacon broadcasts its ID to the surrounding area via Bluetooth. After obtaining the ID of the nearby beacon, the application on the terminal will take corresponding actions, such as pulling the location information and marketing information corresponding to this ID from the cloud background. The terminal can measure the received signal strength at its location to estimate the distance to the beacon. Therefore, as long as there are three or more beacons near the terminal, the terminal's location can be calculated using the three-sided positioning method.

Under the influence of Apple's strong appeal, a large number of startups have rushed into the development and promotion of iBeacon applications. The main problem at present is the replacement of beacon batteries. If a manufacturer deploys tens of thousands of beacon devices, the workload of replacing batteries after one year or when the batteries are exhausted is very heavy.

Representative companies: Estimote, Xunxi Electronics

In addition, ZigBee technology is similar to Bluetooth, so it will not be introduced here.

RFID Technology

The basic principle of RFID positioning is to read the characteristic information of the target RFID tag (such as identity ID, received signal strength, etc.) through a set of fixed readers. The location of the tag can also be determined by the nearest neighbor method, multilateral positioning method, received signal strength and other methods.

Radio frequency identification indoor positioning technology has a short range, but it can obtain centimeter-level positioning accuracy information within a few milliseconds. Due to the advantages of electromagnetic field non-line-of-sight, the transmission range is large, and the size of the tag is relatively small and the cost is relatively low. However, it does not have communication capabilities, has poor anti-interference capabilities, is not easy to integrate into other systems, and the user's security and privacy protection and international standardization are not perfect.

Currently, there are a large number of mature commercial positioning solutions based on RFID technology, which are widely used in emergency rescue, asset management, personnel tracking and other fields.

Infrared technology

There are two main specific implementation methods of infrared positioning. One is to attach an electronic tag that emits infrared rays to the positioning object, and use multiple infrared sensors placed indoors to measure the distance or angle of the signal source to calculate the location of the object.

This method can easily achieve high accuracy in an open room and can realize passive positioning of infrared radiation sources, but infrared can be easily blocked by obstacles and the transmission distance is not long, so a large number of sensors need to be deployed densely, resulting in high hardware and construction costs. In addition, infrared is easily interfered by heat sources, lights, etc., resulting in reduced positioning precision and accuracy.

This technology is currently mainly used in the military for the passive positioning of infrared radiation sources such as aircraft, tanks, and missiles. It is also used for the positioning of indoor self-propelled robots.

Another infrared positioning method is infrared weaving, which covers the space to be measured through an infrared network woven by multiple pairs of transmitters and receivers to directly locate the moving target.

The advantage of this method is that it does not require the positioning object to carry any terminal or tag, and it is highly concealed and is often used in the security field. The disadvantage is that to achieve high-precision positioning, a large number of infrared receivers and transmitters need to be deployed, which is very expensive, so only high-level security will adopt this technology.

Ultrasonic technology

Ultrasonic positioning mainly uses the reflection ranging method to determine the position of an object through methods such as multilateral positioning. The system consists of a main rangefinder and several receivers. The main rangefinder can be placed on the target to be measured, and the receiver is fixed in an indoor environment. During positioning, a signal of the same frequency is transmitted to the receiver, which is then reflected and transmitted to the main rangefinder after receiving it. The distance is calculated based on the time difference between the echo and the transmitted wave, thereby determining the position.

Ultrasonic positioning has high overall positioning accuracy and a simple structure, but ultrasonic waves are greatly affected by multipath effects and non-line-of-sight propagation, and the ultrasonic frequency is affected by the Doppler effect and temperature. It also requires a large amount of basic hardware facilities and is costly.

Representative company: Shopkick

Ultra-Wideband Technology

Ultra-wideband (UWB) positioning technology Use pre-deployed anchor nodes and bridge nodes with known locations to communicate with newly added blind nodes, and use triangulation or "fingerprint" positioning to determine the location.

From a technical point of view, whether analyzed from the perspectives of positioning accuracy, security, anti-interference, power consumption, etc., UWB is undoubtedly one of the most ideal industrial positioning technologies.

Comprehensive comparison of several other UWB technologies:

However, UWB also has prominent disadvantages. On the one hand, it is difficult to achieve large-scale indoor coverage, and on the other hand, the system construction cost is much higher than RFID, Bluetooth beacon and other technologies, which also limits the promotion and popularization of this technology.

Representative companies: Ubisense, Zhonghaida’s subsidiary Lianrui Electronics, and Tsinghua-affiliated company Tsinghua Research and Development Co., Ltd.

LED Visible Light Technology

Visible light is an emerging field. By encoding each LED light and modulating the ID on the light, the light will continuously emit its own ID, and these codes can be identified by using the front camera of the mobile phone. The corresponding location information is determined in the map database using the obtained identification information to complete the positioning.

Qualcomm further refines the positioning results based on the angle of light arrival, and achieves centimeter-level positioning accuracy. Since there is no need to deploy additional infrastructure, the expansion of the number of terminals has no impact on performance, and a very high accuracy can be achieved, this technology is favored by Qualcomm.

Currently, visible light technology has been deployed in many shopping malls in North America. After users download the app and go to a shelf in the mall, they can know their specific location by detecting the lights around the shelf. Merchants use this method to promote discounts and other information to consumers.

Representative company: Huace Optical Communications.

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Technology integration is the trend

Indoor positioning technology is in constant development and is a hot research field with good application prospects. However, there is still a lack of large-scale commercial cases. The industry The main difficulties are as follows:

1. Complex indoor environment

The layout of the indoor environment is complex and changeable, with many obstacles, including furniture, rooms, and pedestrians. At the same time, there are many interference sources in the indoor environment, such as lighting, temperature, and sound, which will have a certain impact on positioning.

Comprehensive comparison of various technologies

2. Lack of unified standards

There are many indoor positioning technologies, each with its own limitations, and to a certain extent, they compete with each other. The market is relatively chaotic, which has greatly affected the development of the indoor positioning industry. For example, satellite positioning has become the de facto standard for outdoor positioning, and currently no other technology can compete with satellite positioning.

3. It is difficult to strike a balance between accuracy and cost

The current high-precision indoor positioning technologies all require relatively expensive additional auxiliary equipment or a lot of manual processing in the early stage, which greatly restricts the promotion and popularization of the technology. Low-cost positioning technology needs to improve positioning accuracy. Reducing costs on the basis of providing high-precision positioning is also a direction for indoor positioning.

The general trend of the world is that after a long period of division, there will be unification, and after a long period of unification, there will be division. At present, there are too many indoor positioning technologies, which have seriously hindered the development of the industry. The future trend must be the integration and use of multiple technologies to achieve complementary advantages in order to face complex environments. Among them, the technology with lower cost, better compatibility and higher accuracy will be easier to popularize.

Exclusive compilation of Global Internet of Things Observation

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