GPS summary

GPS summary
    Namely global positioning system (Global Positioning System). To be simple, this is a satellite system made up of 24 satellites covering the whole world. This system can be guaranteed at wanton moment, wanton on the earth can spot 4 satellites at the same time at all, so as to ensure satellites can gather to the longitude and latitude and height of this observation station, in order to realize such functions as navigating, making a reservation, time service, etc. This technology can be used for guiding plane, shipping, vehicle and individual, reach the destination on time along the selected route safely, accurately.
    Global positioning system (GPS) Navigate the navigation system by U.S.A. of new generation space satellite that the army, the navy and the air forces develop jointly will it be the seventies the 20th century. Its main purpose is to offer the real-time, all-weather and global navigation service for land, sea, empty three major fields, used in the information is collected, the core produces and monitors and meets an urgent need such some military purposes as communication, etc., it is a important composition that U.S.A.  dominates the global strategy exclusively. Cost 30 billion dollars through the research experiment of more than 20 years, to March of 1994, global coverage rate up to 98% 24 satellite constellation own to lay finishing GPS.  
    GPS GPS is made up of three parts: Space part - -GPS constellation; Control some on the ground - -Ground monitoring system; Part of user's equipment - -GPS signal receiver.   GPS predecessor        A kind of meridian instrument global position system that GPS systematic predecessor develops for the American army (Transit), Developed in 1958, came into operation formally in 64. This system works with the star net that 5 to 6 satellites make up, move round the earth 13 times at most every day, and unable to provide high information, not fully up to expectations in orienting the precision. However, the meridian instrument system makes the research and development department orient and make preliminary experience to the satellite, prove the feasibility is it orientate to go on by the satellite system med, bury foreshadowing for the research of GPS system. Because the satellite makes a reservation demonstrates the enormous defect of the respect has existed and navigated to the submarine and naval vessel in enormous superiority and meridian instrument system in navigating. The army of Sea-Air-Land U.S.A. and civilian department all feel that need a kind of new satellite navigation systems urgently.
     For this reason, USN research laboratory) Have proposed being called orienting the network and planning the network to combine with the whole world where 12 to 18 satellites make up 10000km height of Imation, and each launched one and tested satellites in 67, 69 and 74, systematic when have tested the atom clock to count tentatively on these satellites, this is an accurate foundation that makes a reservation of GPS system. The American air force has proposed 621- the B one make up the plans of group of 3 to 4 stars with a group of 4 to 5 satellites of every star, adopt slope track of 24h that life cycle is of the rest of synchronous track except one in these satellites. This plan is with false at random yard (PRN) Based on propagate satellite find range signal, its strong function, can measure it out too when the density of signal is lower than 1 of the ambient noise. False success of yard is used is an important foundation that GPS system can achieve success at random. The plan of the navy is used for offering low 2 dynamic for naval vessel and linking the localization mainly, the plan of the air force for offering the high dynamic service, but the system is too complicated. Will cause enormous expenses and two plans here to both designed in order to offer the whole world to make a reservation because of developing two systems at the same time, the reason why American national defence inferior officer 2 person combined into a single unit in 1973, and the satellite taken the lead in from Ministry of National Defence navigated and made a reservation to jointly plan the office ( JPO) The leader, also set up the executive office and locate in air force spaceflight of Los Angeles. Organization this member numerous, including American ground force, navy, marine corps, Ministry of Communications, national defence make maps office, NATO, representative of Australia.

   GPS forming
1. Space part
   The space part of GPS is made up of 24 jobs satellite, it lies in from the sky of the earth's surface 20200km, is distributed evenly 6 tracks (4 each track)  ,The track inclination is 55 degrees. In addition, 4 back up satellites to operate actively in the rail. The distribution of the satellite makes in any place of the whole world, can spot more than 4 satellites any time, and can keep good and make a reservation to solve the geometry picture which can be regarded as the precision. This has offered ability of navigating in continuous the whole world on time. GPS satellite produces two groups of codes, one group is called C/A yard (Coarse/ Acquisition Code11023MHz); One group is called Pad yard (Precise Code 10123MHz) Frequency is relatively high, difficult to be interfered, it is high to orient the precision, controlled by the American military, there is a password, it is generally folk and unable to understand, serve American military mainly. C/ A yards of people for take measures and reduce after the precision sedulously, main to give among the people using while being open.  

2. The ground controlling part

   Controlling some by a master station on the earth's surface, 5 monitoring station and 3 pieces of region in the world control and stand and make up. The monitoring station is worthy of being equipped with the accurate cesium clock and can be measured to all acceptance machines which can see the satellite in succession. The monitoring station observes the satellite obtained the data, including ionosphere and meteorological data, after dealing with tentatively, convey to the master station. The master station is collected from every monitoring station the data of following, calculate out the track of the satellite and clock parameter, then send 3 ground the result to control and stand. Ground is it is it when each satellite operates to the sky, navigate these datum and master station order inject into the satellite to stand to control. These kinds pours into each one GPS satellite correctly once a day, and carry on last pouring into before the satellite leaves and pours into the sphere of action of the station. If one ground satellite station breaks down, the navigation information that is then presorted in the satellite can also take some time, but navigate the precision will be reduced gradually.

3. Part of user's equipment

    The part of user's equipment is GPS signal receiver. Main function its to can is it is it end what horn choose await measuring the satellite according to certain satellite to get to catch, follow the operation of these satellites. After the receiver is caught to the satellite signal followed, it can measure reception antenna to satellite is false distance and from rate of change, demodulation produces such data as the track parameter of satellites, etc.. According to these data, little treatment of receiver computer can according to is it is it regard as method is it is it calculate to orientate to go on to solve to make a reservation, such information as the longitude and latitude, height, speed, time to calculate out users' geographical position, etc.. The after treatment software package of the software and GPS data forms intact GPS user's equipment in the hardware of the receiver and machine. Two parts that the structure of GPS receiver is divided into a unit of an aerial and received the unit. And two kinds of direct current sources outside the machine in the adopting machine the same of receiver. The purpose of the power does not cut off observing in succession while lying in changing the other power in the setting up machine. The battery is being charged automatically in the opportunity of the power outside the machine. After shut-down, machine battery supply power for RAM memory, in order to prevent data from lose. Of different types at present to accept the organism and accumulate smaller and smaller, weight is lighter and lighter, observe and use in the convenient field.

GPS principle
    The basic principle of GPS navigation system is to measure the distance that the satellite in the known position gets between user's receiver, then the concrete position that can know the receiver in data which synthesize many satellites. Should achieve this purpose, the position of the satellite can be found in the star of the satellite goes through according to star year. Users go to the distance of the satellite to spread the time that users go through noting down the satellite signal, multiply by it velocity of light get (because of interference, atmosphere of ionosphere, this from user and true distance of satellite and then, but false distance (PR): When GPS satellite works normally, false at random yard that will be made up of one yard of Yuan for 1 and 0 binary scale constantly (abbreviate as false yard) Transmission navigation text. False yard used in GPS system is two kinds altogether, including civil C/A yard and military P (Y) Yard. One yard of frequency 1.023MHz of C/A, repeats one millisecond of cycles, one microsecond for one yard of intervals, equivalent to 300m; One yard of frequency 10.23MHz of P, repeats cycle for 266.4 days, 0.1 microseconds for one yard of intervals, equivalent to 30m. And Y yard takes shape on the basis of P yard, secret performance is better. Navigate text including satellite star go through, work state, clock not to correct, prolong revise, atmospheric refraction person who revise information when the ionosphere. It is that demodulation was made out, modulated and launched on carrier frequency with 50b/s from the signal of the satellite. Navigate and include every frame long 6s of 5 stature frames of the main frames of each one of text. Three the first frames are each 10 word yards; A repeated once every 30 seconds, upgrade once per hour. Two the last frame 15000b altogether. The content of navigating in the text has telemeter measurement yard, changes yard, the 1st, 2nd, 3rd data one mainly, among them the most important one goes through the data for the star. When users accept to the text of navigating, draw out satellite time and make and compare with one's own clock with can learn the distance between satellite and user it, and then utilize the satellite star navigating in the text to go through the data and calculate that publish satellites in the present position while launching texts, user earth position speed, etc. information of the system of coordinates can learn in WGS-84.  
    It is obvious the function of the part of the navigation system satellite of GPS is to launch the text of navigating constantly. However, because the clock can not always move ahead simultaneously in the clock that user's accepting machine uses and satellite year, so besides users' three-dimensional coordinate x, y, z, it is a time difference between satellite and receiver as the unknown number to introduce one t, then solve this 4 uncertainly out with 4 equations. So if want to know the position where the receiver is in, can receive to the signals of 4 satellites at least.
     GPS receiver can receive to the accuracy used in time service to the time message of receiving second; The prediction staining the outline position of the satellite goes through in months how much is used and predicted in the future; The broadcast star who is use for calculating the necessary satellite coordinate while orientating goes through, the precision is that from several meters to dozens of meters (each satellite is different, change at any time)  ; And GPS systematic information, for instance state of the satellite, etc..  
    The quantity to yard of GPS receiver can get the distance to the receiver of satellite when being examined, because the error and atmosphere with receiver satellite clock propagates the error, so called the false distance. Call UA yards of false distance by yards of false distance that must examine to 0A, precision about 20 about, call P one yard of false distances to P yards of false distance that must examine, the precision is about 2 meters.  
    GPS receiver decodes or adopts other technology to the satellite signal that is received, after the information that will be modulated on the signal carrier is removed, can resume the signal carrier. Rigorously enforce but the speech, the phase place of signal carrier should be known as the signal carrier and strike the phase place frequently, it receive satellite signal carrier phase place and receiver copies of machine influenced to move is it produce difference, signal of phase place to shake frequently Doppler. Clock confirmed calendar Yuan’s of moment quantity examine in receiver generally, is it follow to satellite signal to keep, can note change value of phase place, is it observe receiver and phase place initial value, satellite of oscillator when know to begin, initial to go through phase place integer of Yuan be known too, namely ambiguity, can only is it charge to solved as the parameter of data processing. The precision of the observed value of phase place is high to mm., but the prerequisite solves out the ambiguity in whole week, so use the observed value of phase place when make a reservation, and have a section of continuous observed value relatively, if and reaching, can only adopt the observed value of phase place in the precision of localization of grade of rice.   
    According to the way of orientating, the GPS's positioning is divided into and ordered and orientated and makes a reservation relatively only (difference divide the localization). It is the way positioning receiver according to the observation datum of a receiver to is it orientate to order only, it can only adopt the observing amount of the false distance, the localization that navigate in outline that can be used in type, etc.. As to making a reservation (Difference divides the localization) Method fixing the relative position between the observation stations comes according to the observation data of more than two receivers, it can adopt the observing amount of the false distance and can adopt the observing amount of phase place, earth measurement or the project measurement should adopt the observed value of phase place to make a reservation relatively.
    The clock including the satellite and receiver is bad, the atmosphere propagates such errors as delaying, much routes effect, etc. in GPS observing amount, be influenced by the fact that the satellite broadcasting star went through the error while making a reservation and calculating, most public errors are off-site or weakened while making a reservation relatively, orient precision improve greatly, pair receiver can offset main part, ionosphere of error in the atmosphere according to two observation amount of frequency frequently, expecting much in the precision, when the distance among the receivers is farther (atmosphere has obvious differences)  ,Should select one pair of receivers frequently for use.
  
Theory of Relativity has offered necessary revision for GPS

   The timing signal of the global positioning system GPS satellite offers the information of the latitude, longitude and height, accurate distance measurement needs accurate clock. So accurate GPS accepting device will use the Theory of Relativity effect soon.
   GPS accepting device within 30 meters of accuracy means it has already utilized the Theory of Relativity effect. Physicist of University of Washington Clifford M. Will explain in detail: "If does not consider the Theory of Relativity effect, the step different from clock on the earth of clock on the satellite.”  Theory of Relativity thinks that it is slower than the static one to move objects with the passage of time fast. Will is calculated out, each GPS satellite stride kilometer of journeys per hour, this mean star will it be every day such as clock such as atom year of it than clock 7 microseconds slowly of the earth.
     And the gravitation has exerted greater Theory of Relativity effect to time. The high altitude of about 20,000 kilometers, the gravitation pulling force that GPS satellite stands is probably equivalent to 1/4 on the ground. The result is that clocks are nearly 45 microseconds in year in a star, GPS should charge to and amount to the deviation for 38 microseconds. Ashby explains: "If there is no frequency to compensate on the satellite, will increase 11 kilometers of errors every day.”  (More complicated on this kind of effect practical thing, because the satellite is along a partial track, relatively close to the earth sometimes, sometimes from relatively far.)