Global positioning system
發(fā)布日期：2017-01-09After April 6, the GPS, which is often used in people's daily life, will usher in a new cycle. At the RSA American Information Security Conference held in San Francisco recently, some experts predicted that the old GPS system would make a mistake similar to the computer millennium bug on April 6; More security experts said that they would never fly on the same day
Why does GPS "return to zero"? What impact will this have on us? Does China's Beidou system also have this problem? What do scientists think? What are the solutions? To this end, the reporter of Science and Technology Daily interviewed relevant experts of the Chinese Academy of Sciences.
What is "GPS Week Flip"?
According to the notice issued recently by the Civil GPS Service Interface Committee (CGSIC) of the United States, the whole week count of GPS will be changed from 1023 to 0 at 24:00 on April 6, 2019, which is called GPS week reversal. This means that GPS week counting will usher in a new cycle.
Why does this happen? "This should be explained by the interface design of the GPS system." Xu Ying, a scientist who has been engaged in the construction of the Beidou navigation system for a long time and a researcher and doctoral supervisor of the Academy of Astronautics and Astronautics of the Chinese Academy of Sciences, said that the GPS system, as a global navigation, positioning and time service system, has established its own time system at the beginning of its design, called GPS time, This starting point corresponds to 0:00 on January 6, 1980, UTC time. In order to achieve the purpose of time service, the GPS system continuously broadcasts the GPS time corresponding to the current time to the user through the navigation signal. The system designer jointly represents the time difference between the current time and the GPS initial time through the week count (WN) and the intra-week second (TOW), so as to obtain the current UTC time and complete the time service.
He Zhizhi, an engineer of the Aerospace Information Research Institute of the Chinese Academy of Sciences, said that due to various reasons, at the beginning of the design of GPS, the designers only used 10 bits to represent WN, resulting in WN only circulating between 0 and 1023. When WN changes from 1023 to 0, the GPS week number will flip, and the saying of welcoming the new week will appear. 1024 weeks corresponds to about 19.7 years in the first half of the year. From the beginning of the GPS system, the last GPS week rollover occurred on August 21, 1999. This time it happened to be April 6, 2019. The next GPS week rollover will occur on November 20, 2038.
"For example, because the child has not learned more than 100, he starts counting from 0 every time he counts to 100. According to the decimal counting rule, the number after 100 is 101200 and the number after 201... and so on, and the child will return to 0 every time he meets 100. This is similar to the GPS cycle reversal." He Zhizhi said.
What is the possible impact?
"The GPS receiver will return the output time of the receiver to about 19 years ago without the preprocessing of GPS cycle reversal. This may have an impact on any system and application that relies on GPS timing." He Zhizhi believes that in the field of civil aviation, timing is basically completed by satellite navigation system, and all automatic equipment is based on this time.
Therefore, the cycle reversal may cause confusion of ATC radar signal data, which may cause data interruption, and the target track is not related to the plan.
At the same time, the information exchange between meteorological equipment will also be unable to automatically complete the alignment of meteorological information due to time jump, resulting in difficulties in weather forecast, which may affect flight scheduling and bring unnecessary losses.
In addition, the use of receivers without GPS cycle reversal processing will also have an impact on some infrastructure areas of automatic operation, such as the BITS system used in the fields of power, communications and finance. If the BITS system only refers to the GPS time service signal, it will cause the time jump of the BITS system, which may cause the system paralysis and affect the public use. In the financial field, it may also lead to the inability to complete the settlement and bring economic losses to users.
How to eliminate hidden dangers?
He Zhizhi said that in order to deal with the problem of GPS week reversal, on the one hand, all industries should contact the GPS receiver supplier in advance to check whether there is a timing error caused by GPS week reversal. If so, the GPS receiver supplier should be required to update the firmware. On the other hand, users who use GPS for time service should make plans and simulation tests to eliminate hidden dangers.
How do I check whether the receiver will be affected by GPS cycle turnover? For ordinary users, you can contact your GPS receiver supplier to ask if there is a hidden danger, when it will occur, and update the firmware in time. For professional users, you can use the GPS signal simulator to set the time of signal transmission, set it to any time after April 6, 2019, and repeatedly test whether the GPS receiver will be affected by the week reversal.
Is there a bug in the Beidou system?
As one of the four global satellite navigation systems, which are as famous as GPS in the United States, China's independently developed Beidou navigation system has become a dazzling "national business card" of contemporary China. Is there any similar bug in the Beidou navigation system?
Xu Ying said that China's Beidou navigation system also has the problem of BD cycle turnover. However, in combination with the short cycle of GPS cycle turnover and the service life of the general GNSS receiver, the Beidou system designers in China have effectively avoided this problem by using the cycle count of 13 bits in design. The cycle turnover is 8192 weeks, which is generally 160 years. In fact, the problem of the number of weeks of the corresponding satellite navigation system is bound to occur. It is only the problem of the length of the rotation period. However, a reasonable algorithm can be designed in the user receiver to avoid this problem and become a bug-free perpetual calendar.
