Deep analysis of 10 kinds of indoor positioning technology principles

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In order to prevent themselves from being lost in the vast nature, human beings have invented tools such as compasses and compasses. The advent of satellite positioning has solved the problem of "where am I?" In today's highly urbanized, indoor spaces are becoming more and more complex. Humans have overcome nature, but they have lost their way in the reinforced concrete they built.

When the Eastern Jin Dynasty sorghum method appeared on the west, he wrote a boat trip back to China and wrote: The sea is full of boundlessness, not knowing things, and hopes to enter the day, the moon, and the stars. The general idea is that the sea is vast and infinite, and it is impossible to distinguish between east and west. It can only look at the stars and look forward to the moon to locate.

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origin

In order to prevent themselves from being lost in the vast nature, human beings have invented tools such as compasses and compasses. The advent of satellite positioning has solved the problem of "where am I?" In today's highly urbanized, indoor spaces are becoming more and more complex. Humans have overcome nature, but they have lost their way in the reinforced concrete they built.

In the hospital, even if there is a floor map and a guide sign, most of the time spent on medical treatment is still wasted in finding a department. In the parking lot, people who can't find parking spaces and turn around are everywhere.

In the increasingly urgent demand, indoor positioning has attracted a lot of attention in recent years.

Indoor positioning, as its name suggests, is positioning in an indoor environment. The significance of this, Nokia explained how they did indoor positioning many years ago, the problem is very clear.

Source: Nokia

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

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

Consumer market applications include: shopping mall shopping guides, reverse parking for car parks, and family anti-dislocation. The positioning accuracy is not high, and the accuracy of 1m can satisfy most applications, but it requires the system to be compatible with the popular mobile intelligent terminals.

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

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Technical martial art

Unlike the situation in which outdoor satellite positioning dominates the world, various technologies for indoor positioning present a scene of blooming.

Indoor positioning

The commercial value of indoor positioning is directly proportional to accuracy. When the accuracy is 3-5 meters, you can determine whether you are standing at the door of the 7-11 convenience store or at the entrance of Jack Jones. When the accuracy is 1 meter, you can determine whether you are standing in front of Coca-Cola's shelves or Durex's shelves.

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

Comparison of main indoor positioning methods

Various principles have their own advantages and disadvantages. Different principles can be combined in different application scenarios and different budget requirements. The mainstream technologies are as follows:

WiFi positioning technology

At present, 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 technology.

WiFi positioning is generally judged by the "near neighbor method", that is, which hotspot or base station is closest to it, that is, where it is considered to be located. If there are multiple sources nearby, cross positioning (trilateral positioning) can be used to improve positioning accuracy.

Since WiFi has become popular, there is no need to lay special equipment for positioning. When a user turns on Wi-Fi or a mobile cellular network while using a smartphone, it may become a data source. This technology has the advantage of being easy to expand, automatically updating data, and low cost, so it is the first to achieve scale.

However, WiFi hotspots are more affected by the surrounding environment and have lower precision. In order to do a good job, the company did a WiFi fingerprint collection, recorded a huge amount of signal strength at a certain location point in advance, and determined the location by comparing the database with the huge amount of data with the signal strength of the newly added device.

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

WiFi positioning can achieve complex large-scale positioning, but the accuracy can only reach about 2 meters, and it is impossible to achieve precise positioning. Therefore, it is suitable for positioning and navigation of people or vehicles, and can be used in various places where medical navigation, theme parks, factories, shopping malls, and the like need to be positioned and navigated.

Representative companies are: WIFISLAM, Sensewhere, map gathering intelligence

In addition, the geomagnetic positioning technology uses the difference of the geomagnetic field at different positions in the room to determine the indoor position. Similar to WiFi fingerprints, it will not be introduced.

Inertial navigation technology

This is a pure client-side technology, which mainly uses the motion data collected by the terminal inertial sensor, such as acceleration sensor, gyroscope, etc. to measure the speed, direction, acceleration and other information of the object. Based on the dead reckoning method, the object is obtained through various operations. location information.

As the walking time increases, the error of inertial navigation positioning is also accumulating. It requires a more accurate data source from the outside to calibrate it. Therefore, inertial navigation is generally combined with WiFi fingerprints, and the indoor position is requested by WiFi every time, so as to correct the error generated by the MEMS. The technology is currently commercially available and is widely used in sweeping robots.

Bluetooth beacon technology

Bluetooth beacon technology is currently deployed more and is relatively mature technology. The difference between Bluetooth and WiFi is not too big, and the accuracy will be slightly higher than WiFi.

The technology was first initiated by Nokia, but the impact was small. In 2013, Apple released the iBeacon protocol based on the Bluetooth 4.0 Low Power Protocol (BLE), which is mainly aimed at retail applications and has attracted widespread attention.

The normal operation of iBeacon Bluetooth beacon technology requires Bluetooth beacon hardware, applications on smart terminals, and applications on the cloud to work together in the background.

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

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

Representative company: Estimote, interest-seeking electronics

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

RFID technology

The basic principle of RFID positioning is to read the feature information of the target RFID tag (such as identity ID, received signal strength, etc.) through a fixed set of readers, and also determine the tag by neighboring method, multilateral positioning method, and received signal strength. location.

The radio frequency identification indoor positioning technology has a very close working distance, but it can obtain centimeter-level positioning accuracy information within a few milliseconds, and because of the advantages of electromagnetic field non-line of sight, the transmission range is large, and the volume of the logo is relatively small, and the cost is relatively low. However, it does not have the communication capability, the anti-interference ability is poor, it is not easy to integrate into other systems, and the user's security privacy protection and international standardization are not perfect.

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

Infrared technology

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

This method is easy to achieve high precision in an open room, and can achieve passive positioning of the infrared radiation source, but the infrared is easily blocked by obstacles and the transmission distance is not long, so a large number of densely deployed sensors are required, resulting in higher hardware. And construction costs. In addition, the infrared is easily disturbed by heat sources, lights, etc., resulting in a decrease in positioning accuracy and accuracy.

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

Another method of infrared positioning is an infrared woven mesh, that is, an infrared ray woven by a plurality of pairs of transmitters and receivers covers the space to be tested, and directly positions the moving target.

The advantage of this method is that it does not require any positioning object to carry any terminal or label, which is concealed and is often used in the security field. The disadvantage is that to achieve high precision positioning requires the deployment of a large number of infrared receivers and transmitters, the cost is very high, so only a high level of security will use this technology.

Ultrasonic technology

Ultrasonic positioning mainly uses the reflective ranging method to determine the position of the object by means of multilateral positioning. The system consists of a main range finder and several receivers. The main range finder can be placed on the target to be tested, and the receiver is fixed in the indoor environment. in. During positioning, the same frequency signal is transmitted to the receiver, and the receiver receives the reflection and transmits it to the main range finder, and calculates the distance according to the time difference between the echo and the transmitted wave, thereby determining the position.

The ultrasonic positioning has higher overall positioning accuracy and simple structure, but the ultrasonic wave is greatly affected by multipath effect and non-line-of-sight propagation, and the ultrasonic frequency is affected by the Doppler effect and temperature. At the same time, a large amount of basic hardware facilities are required, and the cost is high.

Representative company: Shopkick

Ultra-wideband technology

Ultra-wideband (UWB) positioning technology utilizes pre-arranged anchor nodes and bridge nodes of known locations to communicate with newly added blind nodes and utilizes triangulation or "fingerprint" positioning to determine position.

From a technical point of view, UWB is undoubtedly one of the most ideal industrial positioning technologies, from the perspective of positioning accuracy, safety, anti-interference, and power consumption.

A comprehensive comparison of several other UWB technologies:

However, the disadvantages of UWB are also very prominent. On the one hand, it is difficult to achieve large-scale indoor coverage. 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 the technology.

On behalf of the company: Ubisense, Zhonghaida subsidiary Lianrui Electronics, Tsinghua Department of the company.

LED visible light technology

Visible light is an emerging field. By encoding each LED light, the ID is modulated on the light, and the light constantly emits its own ID, which is identified by using the front camera of the mobile phone. The corresponding location information is determined in the map database by using the acquired identification information, and the positioning is completed.

According to the angle of arrival of the light to further refine the positioning results, Qualcomm has achieved 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 can achieve a very high precision, which is optimistic about Qualcomm.

Currently, there are many stores in North America where visible light technology is already deployed. After the user downloads the application, he arrives at a certain shelf in the shopping mall, and can detect the specific location by detecting the light around the shelf, and the merchant promotes the discount of the commodity to the consumer through such a method.

Representative enterprise: Huace Optical Communication

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Technology convergence is the trend

Indoor positioning technology is in constant development and is currently a hot research field with good application prospects. However, there is currently a lack of a particularly large-scale commercial case. The industry has the following difficulties:

1. The indoor environment is complicated

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

Comprehensive comparison of technologies

2. Lack of uniform specifications

There are many indoor positioning technologies, and various technologies have their own limitations, and they compete with each other to some extent. The market is relatively chaotic, which has greatly affected the development of the indoor positioning industry. If outdoor positioning satellite positioning becomes the de facto standard, there is currently no other technology that can compete with satellite positioning.

3. It is difficult to balance accuracy and cost

The current high-precision indoor positioning technology requires relatively expensive additional auxiliary equipment or a large amount of manual processing in the early stage, which greatly restricts the popularization of technology. Low-cost positioning technology needs to be improved in positioning accuracy. Reducing costs based on providing high-precision positioning is also a direction of indoor positioning.

The general trend of the world, the long-term must be combined, the long-term must be divided. 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 of multiple technologies to achieve complementary advantages to face complex environments. The lower the cost, the better the compatibility, and the higher the accuracy, the easier it is to spread.