(Global Position System, GPS for short) is a navigation, timing and positioning system developed by the United States. It consists of airborne satellites, ground-based tracking stations, terrestrial satellite data injection stations, terrestrial data processing centers, and data communication networks. Users only need to purchase a GPS receiver to enjoy free navigation, timing and location services.
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Global Positioning System technology is now widely used in agriculture, forestry, water conservancy, transportation, aviation, mapping, security, military, power, communications, urban management and other departments.
First, the introduction and connotation of GPS satellite modernization
The method of GPS modernization was published on January 25, 1999 by the US Vice President in the form of a notice. The report only proposed the improvement and development of several civilian GPS navigation technologies, but the essence of the entire GPS modernization is to strengthen the support of GPS in the modernization war of the US military and maintain the leading position in the global civil navigation field. Subsequently, the articles published by the US military and Boeing (the main manufacturer of GPS systems) clarified his connotation: First, protection, that is, GPS modernization is to better protect the use of the US and friendly parties, to develop military codes and strengthen The security performance of the military code enhances the anti-jamming capability; the second is to prevent: the use of the enemy's opponents, the application of interference, the application of SA, AS, etc.; the third is to maintain, that is, to keep the civilian users outside the threatened area more accurate Safer to use.
The 28 satellites currently in orbit are functioning normally. 26 of them belong to the GPS BLOCK IIA type and are expected to operate normally for another 2 years. By the beginning of 2002, the original 5-year life expectancy was extended to 10.6 years. Two of the BLOCK IIR models of GPS satellites are in orbit. Operation, one of which was launched on October 7, 1999.
The latest BLOCK IIF has entered the factory production line with six, and the first and second plans are launched this year.
Second, the military part of the GPS modernization plan
The basic purpose of the United States to propose GPS modernization is to meet and adapt to the needs of the 21st century US modernization of national defense, which is the first and fundamental in GPS modernization. Specifically, GPS modernization is to better support and guarantee military operations. To quote the words of a US military general: in military operations, or in dangerous or threatened environments, GPS is required to provide better support for the combat effectiveness of combat members and provide a safer guarantee for their lives. Can help all types of weapons to play a more effective role.
According to the survey in the United States, the demand for GPS by military users generally has the following four main aspects.
1. In the context of future "information warfare" and "electronic warfare", GPS must have better resistance to electronic interference;
2. To have a safe use of GPS, this includes two aspects, one is that GPS users can use it safely, and the other is to have different scopes of use for different types of GPS users, to be treated differently;
3. GPS users should have a shorter initial initialization time;
4. Match with other military navigation systems and various types of weapons and equipment.
In addition to the US military using the US GPS fine code P (Y), there are currently 27 military use in the countries and regions where the US military is authorized. Among them, the military of NATO countries is mainly used in the countries and regions authorized by the military in the Asia-Pacific region: South Korea, Taiwan, Japan, Singapore, Saudi Arabia, Kuwait, Thailand, etc.
In addition to its enormous role in the navigation and positioning of various types of vehicles, including manned and firearms, GPS plays a key role in supporting and assisting combatants and is therefore highly rated.
Based on the above-mentioned military user demand survey, the US military and intelligence agencies made the following four GPS modernization response technical measures in June 1999.
1. Increase the signal strength of GPS satellites to increase the ability to resist electronic interference.
2. On the GPS signal channel, add a new military code (M code), which should be separated from the civilian code. M code should have better anti-deciphering confidentiality and security performance.
3. Military users have better protection devices than civilians, especially anti-interference ability and fast initialization function.
4. Create new technologies to block and block enemy use of GPS.
Third, the civilian part of the GPS modernization plan
In order to better meet the needs of civil navigation, positioning, and atmospheric detection, the US believes that he has the following five main aspects.
1. Improve the accuracy of civil navigation and positioning;
2. Expand the coverage of services and improve the continuity of services;
3. Improve the security of navigation, such as enhancing signal power, increasing navigation signals and channels;
4. Maintain GPS's leading position in technology and sales in GPS;
5. Pay attention to the matching and compatibility with existing and future civil space navigation systems.
Based on the above requirements, the measures the US intends to take are:
1. Based on the annual assessment, decide whether to reduce the SA signal strength to zero. Stopping the playback of the SA will increase the accuracy of civilian real-time positioning and navigation by 3-5 times. This has been implemented at 0:00 on May 1 this year. Here to explain, the US military has mastered the technology of GPS application of SA, that is, GPS can increase the SA signal strength in a local area, so that the enemy can seriously reduce the positioning accuracy when using GPS, and cannot be used for military operations.
2. Add a second civil code, the CA code, on the L2 channel. This allows the user to have better redundant observations to improve positioning accuracy and facilitate correction of the ionosphere.
3. Increase the L5 civilian frequency, which is conducive to improving the accuracy of civil real-time positioning and navigation safety.
Fourth, the process of GPS modernization plan
1. The first stage of GPS modernization
Launched 12 improved GPS BLOCK IIR satellites with some new features. It can not only transmit the second civil code, that is, load the CA code on L2; while broadcasting the P(Y) code on L1 and L2, it also experimentally loads the new military code (M code) simultaneously on these two frequencies. The signal transmission power of the IIR type is greatly improved in both civil and military channels.
2. The second stage of GPS modernization
Launched 6 GPS BLOCK IIFs ("IIFLite"). In addition to the functions of the GPS BLOCK IIR satellite mentioned above, the GPS BLOCK IIF satellite further enhances the power of transmitting the M code and increases the transmission of the third civilian frequency, the L5 channel. The first launch of the GPS IIF satellite is no later than 2005. In 2008, there were at least 18 IIF satellites in the airborne GPS satellites to ensure global coverage of the M code. By 2016, GPS satellite systems should all be operated by IIF satellites, totaling 24+3.
3. The third stage of the GPS modernization plan
The launched GPS BLOCK III satellite completed the design of a fully modernized GPS design code-named GPS III by 2003. The future needs of GPS satellite navigation are being studied, and the structure of the GPS III satellite system, system security, reliability and various possible risks are discussed. The first experimental satellite of GPS III is planned to be launched in 2008. It is planned to complete the GPS III program in nearly 20 years, replacing the current GPS II.
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