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At the recent press conference, Apple released the long-difficult airtag, which is not cheap, but it is used to solve a problem: the indoor positioning of items. According to Apple's official website, Airtag uses Bluetooth +uwb technology to achieve indoor positioning, Bluetooth technology for close-range induction search, and uwb technology for accurate search.
Apple airtag Bluetooth locator
Outdoor positioning technology has been very mature - the base station can be roughly positioned, civilian GPS/Beidou can be accurate to the meter level, plus the direction of the mobile phone gyroscope to assist in judging. Indoor positioning has always been a difficult problem, and people may not be found when they turn around in large shopping malls. Indoor GPS signals cannot be searched, and additional equipment is required to achieve meter-level positioning. At present, the mainstream application mode is uwb and Bluetooth, that is, two positioning methods on the airtag, in addition to these two, there are base stations, Wi-Fi, vslam and so on. This article will briefly describe these methods.
Key indicators of different positioning technologies [from China Mobile Research Institute]
<b>UWB (ultra-broadband) positioning</b>
UWB positioning cost is high, positioning accuracy is high, chip suppliers are few. This positioning method has been elaborated in the previous popular science article analysis of ultra-broadband technology and application [doc]link=00008670[/doc]. The principle is:
Through a narrow pulse signal, uwb technology can achieve a principle similar to achieving high-precision positioning, which is tof+gps. To put it simply, the mobile phone transmits the signal, the small base station used for monitoring receives the signal, and the unit time difference between the different monitoring points reached the signal through the signal is located for the wireless signal transmission source. As long as there are three base stations indoors, they can be positioned by means of arrival time differences.
The main problem with this positioning method is that <b>chip suppliers are few and relatively expensive, and the standby power is relatively high. </b>After all, the uwb chip still belongs to broadband communication, and its power is relatively high compared to the current mainstream low-power narrowband Bluetooth. At present, there are only three main UWB chips that can be mass-produced on a large scale: Apple, NXP, Decawave (now acquired by QORVO), including NXP and other UWB chip designers within Decawave, and the UWB chip process in the current design is also stuck in the 22-28nm flat process, while the mainstream products are still in the mature process of the 65-90nm process. After all, it is still not if the son has money. In order to reduce power consumption, the rich Apple frantically gave the U1 chip a 14nm finfet process, and could only realize the airtag most of the time using Bluetooth positioning, accurately finding the function of using uwb positioning.
As a result of these two problems, <b>uwb technology lacks consumer-grade hardware support</b>. UWB positioning technology is mature, but it is difficult to roll out large-scale applications in consumer markets, and is currently mainly used in prisons, hospitals, nursing care and other places where costs are relatively insensitive. Apple can only do itself, redesigning the chip. However, Apple's closedness has led to the fact that even if the downstream field hopes to add uwb positioning base stations indoors, it cannot choose the industrial-grade mature products of the existing nxp or decawave solutions, and can only wait for Apple to open up the license.
<b>Bluetooth positioning</b>
At present, Bluetooth positioning technology can be divided into two categories, based on Bluetooth 4.2 and bluetooth 5.1. The former has lower accuracy, mature schemes, and lower costs; the latter has only been applied since 2019, with higher accuracy and lower maturity of schemes, but also lower costs.
Bluetooth electronic fence applied to shared bicycle parking management
Compared with uwb positioning, Bluetooth positioning applications are much more extensive. Bluetooth chip suppliers, chips are cheap, and low power consumption, a battery can easily standby for a year or even longer, and all mobile phones are basically with Bluetooth function, no additional cost. For example, I am in Beijing, shared bicycles in some areas can only be parked in designated places, otherwise the car will not be locked, even if it is locked, it will charge additional scheduling fees, even if I turn off the mobile phone, I will still prompt the parking location is incorrect. This electronic fence technology is based on Bluetooth positioning technology.
Bluetooth positioning technology based on bluetooth 4.2 series has relatively low accuracy, usually with an accuracy of 1-3 meters.
Distance-based positioning principles
Positioning based on the Bluetooth 4.2 series can be understood as distance-based positioning, that is, the Bluetooth signal is transmitted through the positioning terminal, the Bluetooth signal strength is measured at several positioning nodes (beacons, beacons), and the terminal positioning is located according to the strength of the Bluetooth signal and the position of the positioning node, the professional term is called rssi.
This positioning principle is relatively simple and the cost is low. The main problem is in the positioning accuracy, when the beacon spacing is 6 meters, the positioning accuracy can only reach 2 meters, if the beacon spacing is twice as large to 12 meters, the positioning accuracy is only 5 meters, and its practical value will drop significantly. Airtag also uses this technology on a daily basis, that is, to achieve positioning through surrounding Apple devices.
This application can do some indoor positioning that requires relatively low accuracy, such as finding a car in an underground parking lot.
The AOA positioning technology based on Bluetooth 5.1 has relatively high accuracy and can reach the decimeter level.
AOA and aod positioning principles
AOA and AOD Positioning Principles (from https://www.silabs.com/wireless/bluetooth/bluetooth-5-1) In January 2019, Bluetooth Alliance wrote Bluetooth AOA/AOD technology to the latest Bluetooth 5.1 standard. At present, it is mainly used in positioning, which is the AOA technology with low demand for terminal antennas.
AOA's full name is angel of arrival, the reach angle. This positioning technology is the Bluetooth terminal transmits the signal, and the receiver receives through multiple antennas, because the distance from each antenna to the Bluetooth terminal is different, so the phase difference is formed, and the angle relationship between each other is calculated through the phase difference and antenna distance, and then the positioning is realized. This method can reach the highest centimeter level of positioning, which is close to the theoretical value of the uwb technology.
Compared with UWB technology, Bluetooth Aoa technology has more chip suppliers and more downstream terminals. However, due to the fact that the relevant technology was officially released in 2019, its current application is small, the main difficulty lies in the antenna design and distance algorithm, and there are not many manufacturers who can provide solutions at present, so it may take time to popularize. The top manufacturer overseas is called Quuppa – from Finland, the former Nokia team. There are also some start-up enterprises in China that have begun to get involved in this field. This technical index can be comparable to uwb technology, the cost is lower, so it has been applied in hospitals, prisons and other scenarios. Benefiting from the popularity of the device and the low power consumption of Bluetooth standby, this technology has also begun to enter the industrial and commercial scenes, for example, some industrial enterprises use this method to improve employee safety, and in business, Beijing skp and Guobo have successively adopted this technology to assist indoor positioning.
<b>Other targeting methods</b>
In addition to uwb and Bluetooth, indoor positioning also has 4/5G base station positioning, visual positioning, and Wi-Fi positioning. But these are not mainstream, just talk about it.
<b>Base station positioning</b>
In the 2020 frozen R16 standard, 5G NR base station positioning technology, multi-rtt positioning, was added. In the 3G and 4G years, the distribution of mobile phone base stations is relatively sparse, but after entering the 5G era, the number of base stations has increased significantly, and it is theoretically possible to achieve positioning through 5G base stations. Its positioning accuracy is about 1/4 to 1/3 station spacing. It can simply meet the traffic statistics of shopping malls and the basic positioning and navigation needs of individuals. However, this method requires the mobile phone to receive the precise beam of more than 3 base stations at the same time, because the number of 5G base stations is still not dense enough, it is difficult to achieve on a large scale at present.
<b>Visual positioning</b>
Visual positioning is called vslam (synchronous positioning and map construction), that is, based on the principle of geometric image, through the camera at different angles of shooting, forming a three-dimensional modeling of the scene. The most common application of this is the sweeping robot. If you choose to use lidar, the cost will remain high; if you choose a pure camera solution, its modeling and algorithm requirements will be very high, and the positioning efficiency is low, and it is mainly used for industrial scenarios, such as automatic cars (agv, also known as amr), sweeping robots, etc.
<b>Wi-fi positioning</b>
Wi-Fi positioning is implemented by dividing the room into n*m small cells, and then recording the Wi-Fi signal intensity issued by several routers in the small grid in turn, that is, the eigenvalue. After the mobile phone enters this place, the measured eigenvalue is compared with the value in the library, and the terminal position is obtained according to the matching algorithm. The early stage of the workload is huge, and a little change in the field in the later stage will lead to a change in the eigenvalue, which needs to be re-collected. Therefore, Wi-Fi positioning is not yet widespread.
Wi-Fi positioning principle illustration
<b>summary</b>
Airtag cleverly combines Bluetooth and uwb positioning technology for item loss prevention. But future positioning technology may be much more than that, at least for now, Bluetooth-based positioning technology is rapidly gaining popularity. Domestic operators and large manufacturers are also improving indoor positioning accuracy according to their own conditions. I hope that indoor positioning can be popularized as soon as possible, so that if you go to the mall to find a food, you don't have to look at the house number.