That is to say, other satellite navigation systems only tell you when and where you are, while the Beidou satellite navigation system not only allows you to know when and where you are, but also sends out your location information, allowing others you want to inform to know more about you, solving the problem of who, what, and where. The Beidou short message has significant application value, and its extensive practice in the Wenchuan earthquake relief fully demonstrated its enormous role and significance.Recently, many friends have also reported that RDSS services and related descriptions cannot be found in a series of official documents of Beidou-3. Instead, Regional Short Message Service (RSMC) and Global Short Message Service (GSMC) have been used.At the relevant conference attended by the author, similar questions were raised, and many people were puzzled about the relationship between short message services and RDSS. Some also suggested that RDSS is a part of short message services! Perhaps based on the Beidou Satellite Navigation System Application Service System (version 1.0), the RDSS positioning accuracy is included in the regional short message service.oneThe Development History of Satellite Radio NavigationSatellite radio navigation was founded in the 1960s. In the 1960s, the United States built the Transit system and the Soviet Union began designing the Tsiklon system. Neither of the above two systems can provide users with accurate velocity and positioning information, and their stability is poor. Therefore, around 1973, the two countries proposed GPS and GLONASS schemes respectively, both of which use RNSS mode as the basic principle. By measuring the pseudorange and Doppler of signals from four or more satellites, the three-dimensional position, velocity vector, and positioning time of the user are determined. The Global Navigation Satellite System (GNSS) has gradually developed since then.In 1983, one of the founders of the Beidou system, Academician Chen Fangyun, proposed the idea of dual star positioning, which was the earliest positioning concept based on RDSS in China. At the same time, American scientists O'Neil and others proposed the construction of GEOSTAR, a geosynchronous orbit satellite navigation system based on RDSS, and conducted experimental work using two satellites. In 1991, GEOSTAR declared bankruptcy.The construction of China's Beidou Navigation System started in 1994, more than 30 years later than the Meridian and Cicada systems, and 20 years later than GPS and GLONASS. The time span is so large that both user needs and navigation technology have undergone epoch-making changes. However, at that time, the country's financial resources were very insufficient, and the funding for basic satellites could not be guaranteed. Therefore, the choice of Beidou system technology system needed to be very cautious, and it was not realistic to move towards a global constellation similar to GPS in one step.At the beginning of the Beidou system, there were two templates around me: the excellent student GPS was in full swing at the time, and GEOSTAR, who had not achieved his dream, had been captured dead on the beach; According to current statements, even the Beidou copying homework is not proficient. Amidst doubts, they raised the banner of RDSS without hesitation. In the current environment, Beidou emerged from the dead, and innovation became inevitable.After continuous experimentation and practice, in 1994, the country approved the establishment of the "Double Star Navigation and Positioning System" and named it "Beidou-1". At the cost of two satellites, a practical satellite wireless positioning system was built, marking the beginning of the construction of a satellite radio system with the goal of accurately measuring time and space. The engineering objectives clearly indicate that positioning reports and short message communication are the main services of Beidou-1. The theoretical challenges and technical difficulties faced are very prominent.The basic process of Beidou-1 RDSS service: Under the condition that the satellite position is known, the true geometric distance between the user machine and the two satellites can be calculated. In this way, two spheres are determined with two satellites as the centers and the distance from the user machine to the two satellites as the radius; The user is on the intersection of these two spheres; Given the known ground elevation, there are two intersections between the Earth's surface and the aforementioned intersection line, one in the southern hemisphere and the other in the northern hemisphere service area. For Chinese users, the latter refers to their location, which is the principle of three sphere intersection positioning.Principle of Beidou RDSS Three sphere Intersection PositioningIn 2000, China successfully launched two Beidou-1 satellites, truly practicing the RDSS concept, theory, and system architecture through the dual star positioning principle and positioning reporting business. The Beidou-1 system, officially completed in 2003, made China the third country in the world to have an independent satellite navigation system.Through breakthroughs and engineering implementation of a series of key technologies, Beidou-1 has achieved world-class innovative results and formed distinctive features:② Bidirectional timing accuracy of 10ns;④ Positioning and reporting are completed on the same channel, and users know "where I am" and "where we are";(1) The world's first system that integrates RNSS and RDSS technology systems. Solved the compatibility and coordination of numerous network frequencies for navigation services, satellite fixed services, and satellite mobile services. The Beidou dual-mode user device is favored by a large number of users and has become a popular equipment for satellite navigation and communication integrated applications.(2) The world's first three orbit hybrid navigation constellation, based on the idea of serving the Asia Pacific region first and expanding globally, has constructed a hybrid constellation of 5 GEO+5 IGSO+4 MEO satellites while building and using, highlighting key points.(3) The first navigation system with complete triple frequency service capability. The Beidou system had the complete three frequency service capabilities of B1, B2, and B3 in 2012, which is nearly 10 years ahead of the GPS implementation of the L1, L2, and L5 three frequency service plan.(4) Enriched and expanded the service capabilities and content of RDSS, utilizing 5 GEO satellites to expand the service capacity of RDSS; The precision and rapid positioning based on RDSS adopts ground center processing of three frequency observation data, and the positioning accuracy is better than 1.0m within a response time of 2min positioning report. Based on RDSS, user rapid tracking and distress rescue alarm have been implemented. The principle of RDSS positioning report system provides excellent performance for applications such as user tracking and life rescue. Through observation and processing by users and the central system, the accuracy of user positioning report is in the meter level, and the response time is less than 2s.The short message service capability of Beidou-3 has been greatly improved, with the receiver transmission power reduced to 1-3W, the single communication capability increased to 1000 Chinese characters, and the service capacity increased to over 10 million times per hour. (Beidou Satellite Navigation System Application Service System Version 1.0)Appendix: Main Performance Indicators of GSMC Services in Beidou SystemFull route position monitoringPort entry and exit dispatch managementRailway industry: remote monitoring and diagnostic system for locomotives, natural disaster warning and real-time monitoring along railway linesForest fire prevention, flood warning, geological monitoringShort communicationThe road of life must be winding, but I still need to establish my own aspirations.