Source: Internet

Organized and published by the IoT Think Tank

As early as the 15th century, when humans began exploring the oceans, positioning technology was born. The positioning methods at that time were very crude, using navigation charts and star maps to determine one’s position.

With the advancement of society and technology, positioning technology has made qualitative leaps in technical means, positioning accuracy, and availability, gradually penetrating various aspects of social life from high-end fields such as navigation, aerospace, aviation, surveying, military, and natural disaster prevention, becoming an indispensable important application in daily life—such as personnel search, location finding, traffic management, vehicle navigation, and route planning…

In general, positioning can be divided into two main categories based on different usage scenarios: indoor positioning and outdoor positioning. Because the scenarios are different, the needs are also different, so the positioning technologies used are also different.

Mature Outdoor Positioning Technologies

Currently, the mainstream technologies used for outdoor positioning are mainly satellite positioning and base station positioning.

1. Satellite Positioning

Satellite positioning is to determine the position by receiving latitude and longitude coordinate signals provided by satellites. The satellite positioning systems mainly include: the United States Global Positioning System (GPS), Russia’s GLONASS, Europe’s GALILEO system, and China’s BeiDou Navigation Satellite System, among which the GPS system is currently the most widely used and technically mature satellite positioning technology.

The GPS global satellite positioning system consists of three parts: the space segment, the ground control segment, and the user equipment segment.

• Space Segment consists of 24 working satellites evenly distributed across 6 orbital planes (4 satellites per plane), allowing the observation of more than 4 satellites anywhere in the world at any time, maintaining good positioning calculation accuracy;

• Control Segment is mainly composed of monitoring stations, master control stations, backup master control stations, and information injection stations, responsible for managing and controlling the GPS satellite constellation;

• User Equipment Segment mainly consists of GPS receivers, which receive signals transmitted by GPS satellites to obtain positioning information and observations, achieving positioning through data processing.

The principle of GPS positioning is simply to determine the location of the GPS receiver using four satellites with known positions.

To achieve this, the satellite’s position can be found in the satellite ephemeris based on the time recorded by the onboard clock. The distance from the user to the satellite is calculated by recording the time it takes for the satellite signal to reach the user, multiplied by the speed of light (due to interference from the atmosphere and ionosphere, this distance is not the true distance between the user and the satellite, but a pseudo-range).

When GPS satellites are functioning normally, they continuously transmit navigation messages composed of pseudo-random codes (shortened to pseudo-codes) made up of binary code 1s and 0s. The navigation message includes satellite ephemeris, operational status, clock corrections, ionospheric delay corrections, atmospheric refraction corrections, and other information. However, because the clock used by the user’s receiver cannot always be synchronized with the satellite’s onboard clock, in addition to the user’s three-dimensional coordinates x, y, and z, a variable t representing the time difference between the satellite and the receiver is introduced as an unknown. Then, four equations are used to solve these four unknowns. Therefore, to know the position of the receiver, at least four satellite signals must be received. As shown in the figure below:

Figure: GPS Positioning Principle

Although satellite positioning has high accuracy and wide coverage, it is expensive and has high power consumption, making it unsuitable for all users.

2. Base Station Positioning

Base station positioning is generally applied to mobile phone users. Mobile base station positioning services, also known as Location Based Services (LBS), obtain the location information of mobile terminal users through the network of telecom operators (such as GSM networks).

After inserting the SIM card and powering on, mobile devices such as mobile phones actively search for surrounding base station information and establish contact with the base stations. In areas where signals can be searched, the mobile phone can detect multiple base stations, but the distance and signal strength vary. When communicating, it will select the nearest and strongest signal base station as the communication base station. The other base stations are not useless; when your position changes, the signal strength of different base stations will change. If the signal from base station A is weaker than that from base station B, the phone will first communicate with base station B to prevent sudden disconnection, and after coordinating the communication method, it will switch from A to B. This is why your phone consumes more power on a train than at home; it continuously searches and connects to base stations.

The principle of base station positioning is also simple: we know that the farther away from the base station, the weaker the signal. By estimating the distance to the base station based on the signal strength received by the phone, when the phone simultaneously detects signals from at least three base stations (which is very easy with current network coverage), it can roughly estimate the distance from the base stations; base stations in the mobile network are uniquely determined, and their geographic locations are also unique, allowing the distances from the phone to three base stations (three points) to be obtained. According to the principle of three-point positioning, circles can be drawn multiple times with the base station as the center and the distance as the radius, and the intersection of these circles is the position of the phone.

Figure: Base Station “Three-Point Positioning” Principle

Since the signals in base station positioning are easily interfered with, it inherently determines its inaccuracy, with an accuracy of about 150 meters, making it basically unsuitable for driving navigation. The positioning condition is that the phone must be in an area with base station signals and in a SIM card registered state (it cannot work in flight mode with Wi-Fi on or with the SIM card removed), and it must receive signals from three base stations, regardless of whether indoors or outdoors. However, the positioning speed is extremely fast; once there is a signal, positioning can be done quickly. Its main use is to quickly understand your location when there is no GPS and no Wi-Fi.

Table: Comparison of Two Outdoor Positioning Technologies

Positioning Technology Moving from Outdoor to Indoor

GPS and base station positioning technologies basically meet users’ needs for location services in outdoor scenarios. However, people spend 80% of their lives indoors, and a large number of positioning needs occur indoors for personal users, service robots, and new IoT devices. Indoor scenes are obstructed by buildings, GNSS signals quickly attenuate, or are completely blocked, making it impossible to meet the navigation and positioning needs in indoor scenarios.

In recent years, location service-related technologies and industries have been developing from outdoor to indoor to provide ubiquitous location-based services, driven mainly by the enormous application and commercial potential of indoor location services. Many companies, including OS providers, service providers, and device and chip providers, are competing in this market.

1. Indoor Positioning Applications

Indoor positioning refers to the technology used to determine people’s real-time location or movement trajectory indoors. Based on this information, various applications can be realized.

• Merchants in large shopping malls can use indoor positioning technology to understand where foot traffic is highest, which routes customers usually take, etc., to more scientifically arrange counters or choose locations for promotional events.

• Customers can also use indoor positioning technology to find the placement area of the items they need more conveniently and obtain the best route to that location.

• Parents no longer need to worry about their children getting lost in the mall, as indoor positioning technology can provide real-time location tracking of the child.

• Company managers can use indoor positioning technology to know the status of personnel indoors in real time, optimizing the use of air conditioning to achieve energy saving and emission reduction, and also effectively improve security levels.

• By deploying indoor positioning technology, telecom operators can better identify indoor coverage “blind spots” and “hot spots” and provide better communication services to users indoors.

• ……

2. Challenges Facing Indoor Positioning

Compared to outdoor positioning, indoor positioning faces many unique challenges, such as the strong dynamism of indoor environments, which can vary widely; different buildings have different indoor layouts; the indoor environment is more complex, requiring higher precision to distinguish different features.

So what requirements must practical indoor positioning solutions meet? They mainly include the following aspects: accuracy, coverage, reliability, cost, power consumption, scalability, and response time.

Accuracy: The accuracy requirements vary greatly for different applications. For example, finding a specific product in a supermarket or warehouse may require an accuracy of 1 meter or even lower. If searching for a specific brand or restaurant in a shopping center, an accuracy of 5-10 meters is sufficient.

Coverage: Coverage mainly refers to how large an area a technology and solution can provide coverage with sufficient accuracy. Some technologies require corresponding or dedicated infrastructure support and need to be used in conjunction with corresponding positioning terminals, so their coverage is limited to the area where the relevant technology is deployed.

Reliability: As mentioned earlier, the indoor environment is highly dynamic and changes frequently, such as the settings and partitions in malls. On the other hand, the infrastructure that positioning relies on also changes frequently. For example, in large conferences, exhibitors may set up their own Wi-Fi hotspots, which can change location dynamically, sometimes being on, sometimes off. If the positioning technology is Wi-Fi-based, a reliable system should not be affected by these factors.

Cost and Complexity: Cost and complexity indicators cover two aspects. One is the cost of positioning terminals, whether existing hardware can be used without adding new hardware. The other aspect is the cost and complexity of layout and maintenance, including the facilities required for layout and maintenance and the collection of related databases.

Power Consumption: The power consumption generated by positioning is a very important indicator, especially for battery-operated mobile devices. If the power consumption is high, the device will run out of battery quickly, limiting user usage. Surveys show that excessive battery consumption is a major reason many users do not turn on the positioning function. Therefore, to achieve location awareness anytime and anywhere, the additional power consumption caused by positioning must be reduced.

Scalability: Scalability refers to the ability of a solution to extend to a larger coverage area and the ability to easily adapt to different environments and applications.

Response Time: The time required for the system to provide a location update is the response time. Different applications have different requirements; for example, mobile users and navigation applications require fast location updates.

Rapidly Developing Indoor Positioning Technologies

Indoor positioning technology has diverse branches. The following diagram compares various indoor positioning solutions:

The commonly used indoor positioning methods can be divided into seven categories based on their principles: proximity detection, centroid positioning, multilateration, triangulation, polar method, fingerprint positioning, and dead reckoning.

Different indoor positioning methods choose different observation quantities and extract the necessary information through different observation quantity extraction algorithms. The following table provides a brief introduction to the main observation quantities.

Based on the positioning principles and observation quantities introduced above, various indoor positioning technologies have emerged. Below is a brief introduction to the mainstream indoor positioning technologies.

1. Wi-Fi Positioning Technology

Currently, Wi-Fi is a relatively mature and widely used technology, with many companies investing in this field in recent years. Wi-Fi indoor positioning technology mainly has two types.

Wi-Fi positioning generally adopts the “nearest neighbor method,” which determines the position based on the nearest hotspot or base station. If there are multiple signal sources nearby, cross-positioning (triangulation) can be used to improve positioning accuracy.

Since Wi-Fi is widely used, there is no need to deploy dedicated equipment for positioning. Users can become data sources by enabling Wi-Fi and mobile cellular networks on their smartphones. This technology has advantages such as easy expansion, automatic data updates, and low cost, thus achieving large-scale implementation first.

However, Wi-Fi hotspots are greatly affected by the surrounding environment, resulting in lower accuracy. To improve accuracy, some companies have implemented Wi-Fi fingerprint collection, recording a massive amount of signal strength at known locations and comparing it with the signal strength of new devices against the extensive database to determine the position.

Since the collection work requires a large number of personnel and regular maintenance, the technology is difficult to scale, and few companies can regularly update fingerprint data in so many malls across the country.

Wi-Fi positioning can achieve complex large-scale positioning, but accuracy can only reach about 2 meters, making it unsuitable for precise positioning. Therefore, it is suitable for locating and navigating people or vehicles in various scenarios such as medical institutions, theme parks, factories, and shopping malls.

2. RFID Positioning

The basic principle of RFID positioning is to read the characteristic information (such as ID, received signal strength, etc.) of the target RFID tag through a group of fixed readers, and can also use proximity detection, multilateration, or received signal strength methods to determine the location of the tag.

This technology has a short effective range, generally up to several tens of meters. However, it can achieve centimeter-level positioning accuracy within a few milliseconds and has a large transmission range at a low cost. Additionally, due to its non-contact and non-line-of-sight features, it is expected to become a preferred indoor positioning technology.

Currently, the hot spots and challenges of RFID research include establishing theoretical propagation models, user security and privacy, and international standardization issues. Its advantages are small size and low cost, but it has a short effective range, lacks communication capabilities, and is difficult to integrate into other systems, making precise positioning challenging. The deployment of readers and antennas requires substantial engineering experience, which is difficult.

3. Infrared Technology

Infrared is an electromagnetic wave with a wavelength between radio waves and visible light. Infrared positioning mainly has two specific implementation methods: 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 object’s location.

This method can easily achieve high accuracy in open indoor spaces, allowing for passive positioning of infrared radiation sources. However, infrared signals are easily obstructed by obstacles, and the transmission distance is not long, thus requiring a dense deployment of sensors, resulting in high hardware and construction costs. Additionally, infrared is easily affected by heat sources, lighting, etc., leading to decreased positioning accuracy and reliability.

This technology is currently mainly used for passive positioning of infrared radiation sources such as aircraft, tanks, and missiles in military applications, and also for positioning of indoor autonomous robots.

The other method of infrared positioning is infrared networking, which covers the space to be measured with a network of multiple pairs of transmitters and receivers, directly positioning the moving target.

The advantage of this method is that it does not require the positioning object to carry any terminals or tags, providing strong concealment. The disadvantage is that achieving high-precision positioning requires a large number of infrared receivers and transmitters, leading to very high costs, and therefore only high-level security applications adopt this technology.

4. Ultrasonic Technology

Ultrasonic positioning currently mostly adopts reflective distance measurement methods. The system consists of a main distance meter and several electronic tags. The main distance meter can be placed on the mobile robot, while various electronic tags are fixed in indoor spaces.

The positioning process is as follows: first, the upper computer sends signals of the same frequency to each electronic tag, which then reflects the signals back to the main distance meter, allowing the distances between each electronic tag and the main distance meter to be determined, thus obtaining positioning coordinates.

Currently, there are two popular ultrasonic indoor positioning technologies: one combines ultrasonic and radio frequency technologies for positioning. Since radio frequency signals travel at nearly the speed of light, much faster than ultrasonic signals, the radio frequency signal can first activate the electronic tag, followed by receiving ultrasonic signals to measure distance based on the time difference. This technology is cost-effective, has low power consumption, and high accuracy. The other technology is multi-ultrasonic positioning. This method uses global positioning, installing four ultrasonic sensors on the mobile robot in four orientations, partitioning the space to be positioned, measuring distances using ultrasonic sensors to form coordinates, and overall grasping data, providing strong anti-interference capabilities and high accuracy while solving the problem of the robot getting lost.

Ultrasonic positioning can achieve centimeter-level accuracy, making it relatively high precision. However, the significant attenuation of ultrasonic signals during transmission affects its effective range.

5. Bluetooth Technology

Bluetooth positioning is based on the RSSI (Received Signal Strength Indication) positioning principle. Depending on the positioning end, Bluetooth positioning can be divided into network-side positioning and terminal-side positioning.

The network-side positioning system consists of terminals (such as smartphones with low-power Bluetooth), Bluetooth beacon nodes, Bluetooth gateways, wireless local area networks, and back-end data servers. The specific positioning process is:

1) First, deploy beacons and Bluetooth gateways in the area.

2) When the terminal enters the coverage of the beacon signal, it can sense the broadcast signal of the beacon, then calculate the RSSI value under a certain beacon. This information is transmitted to the back-end data server through the Bluetooth gateway via Wi-Fi, where the built-in positioning algorithm calculates the terminal’s specific location.

The terminal-side positioning system consists of terminal devices (such as smartphones embedded with SDK software packages) and beacons. The specific positioning principle is:

1) First, deploy Bluetooth beacons in the area.

2) Beacons continuously broadcast signals and data packets to the surrounding area.

3) When terminal devices enter the coverage of the beacon signal, they measure the RSSI values under different base stations and then calculate the specific location using the built-in positioning algorithm on the smartphone.

Terminal-side positioning is generally used for indoor positioning navigation, precise location marketing, etc.; while network-side positioning is mainly used for personnel tracking, asset positioning, and traffic analysis. The advantages of Bluetooth positioning include ease of implementation, positioning accuracy closely related to the density and transmission power of Bluetooth beacons, and significant power savings achieved through deep sleep, no connection, and simple protocols.

6. 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 object’s speed, direction, acceleration, etc., based on dead reckoning, and performs various calculations to obtain the object’s location.

As walking time increases, the errors in inertial navigation positioning also accumulate. Higher precision data sources from the outside are needed to calibrate it. Therefore, inertial navigation is generally combined with Wi-Fi fingerprints, requesting indoor positions via Wi-Fi at intervals to correct the errors generated by MEMS. This technology is currently quite mature in commercial use and is widely applied in vacuum cleaning robots.

7. Ultra-Wideband (UWB) Positioning Technology

Ultra-wideband technology is a new communication wireless technology that has emerged in recent years, significantly different from traditional communication technologies. It does not require carriers used in traditional communication systems but instead transmits data by sending and receiving extremely narrow pulses with nanosecond or microsecond levels, achieving a bandwidth of 3.1~10.6GHz. Currently, countries including the United States, Japan, and Canada are researching this technology, which has good prospects in the field of wireless indoor positioning.

UWB technology is a high transmission rate, low emission power, strong penetration capability, and carrier-free wireless technology. These advantages allow it to achieve relatively accurate results in indoor positioning.

Ultra-wideband (UWB) positioning technology uses pre-arranged known-position anchor nodes and bridge nodes to communicate with newly introduced blind nodes, employing triangulation or “fingerprint” positioning methods to determine the position.

UWB can be used for precise indoor positioning, such as discovering the positions of soldiers on the battlefield and tracking the movements of robots. Compared to traditional narrowband systems, UWB systems have strong penetration, low power consumption, good anti-interference effects, high security, low system complexity, and can provide highly precise positioning accuracy. Depending on the different technologies or algorithms used by different companies, accuracy can be maintained at 0.1m to 0.5m.

8. Visible Light Technology

Visible light is an emerging field where each LED light is encoded, and the ID is modulated onto the light. The lights continuously emit their IDs, and the mobile phone’s front camera is used to recognize these codes. Using the acquired recognition information, the corresponding location information can be determined in the map database, completing the positioning.

By further refining the positioning results based on the angle at which the light arrives, Qualcomm has achieved centimeter-level positioning accuracy. Since no additional infrastructure is required, increasing the number of terminals does not affect performance, and it can achieve very high accuracy, making this technology promising in Qualcomm’s view.

Currently, visible light technology is being deployed in many shopping malls in North America. After users download the app, they can determine their specific location by detecting the light around a certain shelf in the mall.

9. Geomagnetic Positioning Technology

The Earth can be viewed 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 varying magnetic field. The basic magnetic field is the main part of the geomagnetic field, originating from within the Earth, and is relatively stable, belonging to the static magnetic field. The varying magnetic field includes various short-term changes in the geomagnetic field, mainly originating from within the Earth, and is relatively weak.

The steel and concrete structures of modern buildings can disrupt the geomagnetic field locally, potentially affecting compasses. In principle, a non-uniform magnetic field environment will produce different magnetic field observation results due to different paths. This geomagnetic positioning technology, known as IndoorAtlas, utilizes the variations of geomagnetism indoors for navigation, achieving positioning accuracy between 0.1 meters to 2 meters.

However, the process of using this technology for navigation is somewhat cumbersome. You need to 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 at different orientations in the target location. The recorded geomagnetic data will be uploaded to the cloud, allowing others to use the recorded geomagnetic data for precise indoor navigation.

Baidu strategically invested in the geomagnetic positioning technology developer IndoorAtlas in 2014 and announced in June 2015 that it would use this geomagnetic positioning technology in its mapping application, combining it with Wi-Fi hotspot maps and inertial navigation technology. The accuracy is high, and in commercial applications, it can achieve meter-level positioning standards, but magnetic signals are easily affected by constantly changing electrical and magnetic signal sources in the environment, making positioning results unstable and accuracy affected.

10. Visual Positioning

Visual positioning systems can be divided into two categories: one type uses moving sensors (such as cameras) to capture images to determine the position of the sensor, while the other type uses fixed-position sensors to determine the position of the target in the image. Depending on the choice of reference points, they can also be divided into reference 3D building models, images, pre-deployed targets, projected targets, reference other sensors, and no reference.

Reference 3D building models and images compare against existing building structure databases and pre-calibrated images. To improve robustness, reference-pre-deployed targets use specific image markers (such as QR codes) as reference points; projected targets create reference points in the indoor environment based on reference-pre-deployed targets.

In addition to the aforementioned technologies, there are dozens or even hundreds of positioning technologies available, each with its own advantages and disadvantages, suitable for different application scenarios. Deploying solutions tailored to different needs is the best approach.~

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