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Bringing the itinerary code home to quarantine? Migrant workers, don't panic! Find out about the positioning accuracy of the base station

Release on : Jan 19, 2022

Bringing the itinerary code home to quarantine? Migrant workers, don't panic! Find out about the positioning accuracy of the base station
Base station positioning
The Spring Festival is approaching, but perhaps what everyone is most worried about this year is not that they can't buy a ticket to go home, but that they will be quarantined after they go home. Indeed, starting in November last year, the mutated strain of the new coronavirus, Omicron, began to spread rapidly around the world, and all parts of the country began to re-strengthen epidemic prevention measures. Pass".

However, due to the specific anti-epidemic measures in different places, some public places will refuse entry of people with an asterisk in the itinerary code, or require a 48-hour nucleic acid test report, and even some areas will quarantine people who enter the outside world with an asterisk in the itinerary code. measure.

Because the recording rule of the itinerary code is that when the residence time in a city exceeds 4 hours, it will be recorded. For many people who drive home by themselves, it is very likely that after passing through the city where the high-risk area is located, there will be a star on the itinerary code. Therefore, many people worry that if the itinerary code has a star, will they be quarantined when they go home?

However, recently, the official subscription number of the "Communication Itinerary Card" (Itinerary Code) has provided authoritative answers to some questions about the use of the itinerary code. The main account of the "Communication Itinerary Card" is the China Academy of Information and Communications Technology (hereinafter referred to as the China Academy of Information and Communications Technology). The itinerary code query service is guided by the Ministry of Industry and Information Technology.

Regarding the question of whether the asterisks on the itinerary card will be isolated, the China Academy of Information and Communications Technology officially stated that it is not recommended to directly take isolation measures for the users of the itinerary card with asterisks.
Rules for determining itinerary
Why "it is not recommended to directly take isolation measures for users of itinerary cards with asterisks", the main reason here is that the asterisks in the itinerary code only represent that the user has visited cities in the past 14 days that contain medium and high risk areas, does not mean The user has actually traveled to one of the high-risk areas.

On the other hand, the itinerary card analyzes mobile phone signaling and bill data, which is obtained by the operator through the location of the base station where the mobile phone number used by the user is located. Due to technical reasons such as possible cross coverage of base station signals, limited accuracy of signaling data, and delayed data update, there may be some deviations in travel card service data.

For example, at the junction of two city administrative divisions, it may happen that the other city has not been visited, but the itinerary of the other city appears on the itinerary code. When operators deploy base stations, in order to ensure continuous signals and reduce coverage blind spots, base station signals may overlap at the junction of the two places, resulting in the possibility of recording travel records in neighboring cities in this city.

Therefore, at the end of the answer, the official said that the local government can use the itinerary card service as an auxiliary epidemic prevention and control management tool, but it is not recommended to use it as the only basis for judgment.
How high is the positioning accuracy of the base station?
As mentioned above, the location information of the travel code is obtained through the location of the base station where the mobile phone number provided by the operator is located. So how accurate is the current base station positioning?

As early as in the 2G era of the GSM standard, a method of positioning using a communication base station has already appeared. The infrastructure of the GSM network consists of a series of communication base stations arranged in a cellular arrangement, which is also the origin of the name of the cellular network.

In the GSM system of the 2G era, one of the base stations in the cellular network must be accessed during the communication process, so fuzzy positioning can be performed through a single base station at that time, that is, according to the cellular base station that the device is currently connected to, the location of the base station can be obtained. To determine the location, this method is called COO (Cell of Origin) positioning.

COO positioning is the cheapest and most convenient positioning method, but the disadvantage is also obvious, that is, the accuracy is very low, and the accuracy depends entirely on the density of base stations.

For example, in the city center, the division of cells (the area covered by a single base station in the cellular network) is generally relatively small, and the positioning accuracy of the base station can reach about 50 meters. In other areas, when the base stations are scattered, the cell radius will become Very large, then the accuracy can be as low as a few kilometers range.

Of course, there are more precise positioning methods. TOA (Time of Arrival, time of arrival), TDOA (Time Difference of Arrival, time difference of arrival) are two positioning methods based on the propagation time of electromagnetic waves. Both methods need to have three known positions at the same time during the positioning process. base station can do this.

TOA's calculation of distance is completely dependent on the accuracy of time, so the time synchronization between the entire device and the base station is very high, and slight errors will lead to large position deviations, so it is not practical. Compared with TOA, TDOA has a certain improvement. By detecting the absolute time difference between the arrival of the signal to the two base stations, the two arrival time differences can be obtained by using three different base stations at the same time. Precise positioning.

In addition, there is AOA (Angle of Arrival, angle of arrival) positioning, which is based on two base stations, positioning according to the signal incidence angle of the device. However, there are high requirements for the device antenna, and an antenna array with strong directivity is required.

With the increasing demand for mobile Internet based on location services, the iteration of mobile communication technology is also improving the accuracy of positioning based on communication base stations.


Source: User Localization in 5G Mobile Networks/Simone Zügner, Marton Kajo

In the 5G R16 standard frozen in 2020, a variety of new indoor positioning technologies are defined, including cell-based round trip time (RTT), time difference of arrival (TDOA), angle of arrival (AoA), departure Angle measurement method (AoD), etc., and the most accurate Multi-RTT technology can achieve indoor errors within 1 meter.

The R16 standard utilizes the characteristics of 5G's large bandwidth (high temporal resolution) and multi-beam angle information, and finally achieves the goal of outdoor positioning accuracy of less than 5 meters and indoor positioning accuracy of less than 3 meters under 5G NR.

In the future 5G R17 standard, it is expected that the accuracy will be improved to within 30cm, which is close to the 10cm-level accuracy of the current GNSS system.
write at the end
Although the accuracy of 5G base station positioning has reached a very high level, from the description of the China Academy of Information and Communications Technology, the itinerary code only uses the most basic information about the location of the base station, so it can only record the visited cities, but cannot Accurate to whether the high risk area is reached.

Of course, this is also easy to understand. After all, more precise positioning may involve the privacy of individual users. It is a good compromise to blur the positioning based on the location information of the base station. As the CAICT said, the itinerary card service is only used as an auxiliary epidemic prevention and control management tool, and should not be used as the only basis for judgment.