WiFi indoor positioning technology and its evolution that has triggered the Internet of Things application

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WiFi indoor positioning technology and its evolution that has triggered the Internet of Things application [Copy link]

When people are in an unfamiliar environment, the thing they want to know most urgently is: "Where am I?" The process of getting the answer to this question is positioning. As early as in ancient times, people have learned to identify their position by the sun and stars; the invention of quadrants and sextants allowed those enthusiastic gold diggers in the Age of Exploration to know the longitude and latitude of their voyage in the vast ocean; and in the 21st century, people generally use map navigation on smartphones to determine their location and driving route.

With the rapid development of technology, people's demand for positioning applications has become more diversified, especially in today's booming Internet of Things business: in factories, managers want to accurately track valuable materials and production equipment; in fire scenes, firefighters need to implement effective rescue in thick smoke; in hospitals, valuable medical equipment worth millions needs to be managed; while driving, drivers want to get the most unobstructed route and the nearest vacant parking space; in shopping malls, consumers want to get accurate store and product positioning, and sellers also want to achieve accurate advertising push; the realization of smart homes is inseparable from the return of users with accurate positioning; the most urgent hope of parents is to know the whereabouts of their children running around in the crowd... Positioning applications are spread across industrial, industry and consumer fields. Almost wherever there is IoT, there is a need for positioning.

WiFi Advantages in Indoor Positioning Technology
In recent years, the research and development of positioning applications in the field of the Internet of Things has become increasingly intense. The current mainstream technologies in the field of positioning include cellular networks, satellites, ZigBee, Bluetooth, ultra-wideband and WiFi. The positioning accuracy of hundreds of meters on cellular networks cannot meet the requirements of small-scale positioning in the Internet of Things, and the fatal flaw of satellite positioning is that it is basically impossible to receive usable signals indoors. Although short-range wireless communication technologies such as ZigBee, Bluetooth and ultra-wideband are suitable for the positioning requirements of application scenarios, ultra-wideband technology is too expensive and difficult to promote. The positioning accuracy of ZigBee and Bluetooth is only about 5 to 10 meters, and its bandwidth limitation makes it difficult for the two to be greatly improved in the future.

而WiFi在定位方面有着得天独厚的带宽优势，其也在向更高带宽和多天线的方向演进，更高的带宽意味着更好的测时/测距分辨率，更多天线的支持意味着为测角引入更多维度，从而显著提高定位的精度。WiFi的另一个优势是其在现实中的商业成功会产生良性循环，对其它领域的应用形成正向驱动——WiFi芯片早已是智能手机的标配，而WiFi接入点已有大量部署，这些现成的基础设施将为定位应用的商业推广提供便利，WiFi的日益广泛应用还会进一步降低其成本。

Analysis of the pain points of key technologies for WiFi indoor positioning
However, WiFi indoor positioning has not yet been widely used in the field of the Internet of Things, mainly due to four aspects.

The solution is not universal.
Positioning applications in the field of IoT are mostly in indoor environments, such as shopping malls, exhibition halls and other public places with huge crowds. Positioning signals are easily interfered and attenuated during transmission, which affects the accuracy. In addition, the difference in the accuracy of equipment and components and the placement of objects in the venue will cause positioning deviations, especially in different indoor environments. This leads to the complexity and diversity of positioning solutions, and also brings additional cost expenses.

The later maintenance cost of the solution is too high
Positioning solutions are usually based on two types of technologies: ranging or fingerprinting. The ranging-based technology requires additional deployment of anchor points and recording of the anchor point locations, and often requires a large number of tests to perform channel modeling, resulting in excessive costs; while the fingerprint-based technology requires the collection of a large amount of field data in advance. Due to differences in positioning environments, the automation rate of fingerprint collection is low, and it is often extremely labor-intensive. At the same time, the granularity of fingerprint collection is related to positioning accuracy. The higher the positioning accuracy, the higher the data maintenance cost. What is even more troubling is that slight changes in the environment and changes in anchor points will affect the positioning environment and require the maintenance of the fingerprint library, thereby increasing maintenance costs.

The immature industrial chain leads to high costs
. The industrial chain of positioning applications involves multiple industrial links such as terminal positioning equipment manufacturers, map managers, overall positioning solution integrators, back-end positioning application developers and positioning service operators. However, they almost act independently, and the industrial chain ecosystem is still in its early stages and has not yet reached the mature low-cost stage of the industrial chain.

Positioning accuracy cannot meet the needs of the Internet of Things
The main reason is that WiFi was designed with only communication needs in mind, and positioning was only an additional function later. If the first three reasons are attributed to high costs, in the long run, the cost limit may gradually disappear with the improvement of technology development. Therefore, improving positioning accuracy will be an important issue that needs to be solved urgently.

Although WiFi
has a good prospect in positioning, its potential for precise positioning has not been fully explored. The rapid development of new applications, especially those related to the Internet of Things, has made the relatively backward positioning accuracy a shackle. Therefore, it is necessary to transform WiFi technology to release its potential in high-precision positioning. Let us turn our attention to new technologies that may improve WiFi positioning accuracy.

Millimeter wave frequency band technology
Millimeter wave refers to electromagnetic waves with a frequency of 30GHz to 300GHz. Due to its large attenuation and the fact that some frequency bands are easily absorbed by the atmosphere, it is considered unsuitable for long-distance wireless communication. However, due to its abundant spectrum resources and the fact that the dense deployment of microcells can reduce the communication range, the problem of short-distance communication is no longer an obstacle. Therefore, it is listed as one of the main development technologies of 5G communication. It is also included in the next-generation 60G communication standard by the IEEE 802.11 standard group, which makes the millimeter wave technology based on WiFi highly anticipated. The ultra-high bandwidth provided by the millimeter wave frequency band can ensure a higher timing resolution granularity. Moreover, the millimeter wave has a narrow beam and high angular resolution, making it more suitable for high-precision indoor positioning. Although the short transmission distance of millimeter waves, sensitivity to occlusion and movement, and interference introduced by the lack of networking management will affect the accuracy and stability of positioning, its integration with WiFi technology will likely overcome these defects.

Fine Timing Measurement (FTM)
Currently, TOA/TDOA timing/ranging technology is also one of the positioning technologies. In theory, it can achieve higher positioning accuracy, but it depends on higher signal bandwidth. In the newly released IEEE 802.11 standard revision, the FTM mechanism is defined to support precise time measurement, with a timing granularity of 0.1ns. This means that WiFi technology based on this protocol can achieve a ranging granularity of 3 cm through precise timing. In the evolution of the new standard, more precise time measurement mechanisms will be discussed.

CSI technology (Channel State Information)
CSI is an OFDM technology for the WiFi physical layer. It can provide information on the amplitude and phase changes of wireless signals after spatial propagation at the granularity of subcarriers. This means lower-level, more stable channel information and higher spatial resolution, which in turn corresponds to more stable and accurate positioning performance, and can overcome the defects of poor positioning performance caused by unstable signals in the currently widely used RSSI positioning. Of course, CSI technology also has technical difficulties - the ideal CSI value is an accurate reflection of the time/frequency response of the spatial channel experienced by the signal, but because the receiving end and the transmitting end cannot be perfectly synchronized in dimensions such as time, frequency and phase, the synchronization error will cause the CSI value to be "contaminated" and difficult to be used directly as a location feature. How to purify the obtained CSI has become a current research hotspot. At present, a research team has achieved a positioning accuracy of about 1 meter using CSI fingerprints in a laboratory environment, which means that CSI technology based on WiFi will become one of the breakthrough directions for high-precision WiFi positioning.

Millimeter wave and FTM technology make it possible for WiFi to support centimeter-level positioning accuracy, making WiFi not only applicable to the consumer field, but also increasingly favored by industrial control, security and other industries that have stringent requirements for positioning accuracy. For example, in the future, mining excavators can use WiFi to perform precise operations, and large warehouses can use WiFi to accurately locate small goods. CSI technology will further improve the accuracy of existing fingerprint-based positioning solutions and bring user experience to a new level. For example, supermarket shelf positioning, indoor navigation and security monitoring solutions that can achieve sub-meter accuracy will be just around the corner. These emerging technologies all require modifications to the underlying technology of WiFi to unleash the potential of WiFi in high-precision positioning. It is conceivable that WiFi, which integrates emerging technologies represented by millimeter waves, precise timing, and CSI, will become the first choice for universal positioning solutions in the near future, and will detonate thousands of applications in the Internet of Things with its excellent positioning performance.

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Wi-Fi positioning should be good