Research On Determination Method Of Real-time Precise Satellite Clock Offsets

The development of GNSS Precise Point Positioning(PPP) technology, is changing thetraditional mode of precise relative positioning,and has made extensive contribution to boostingthe wide adaption of sophisticated positioning technology. The main advantage of PPPtechnology lies in real-time PPP application. Real-time PPP technology has already became oneof the hotspots in research of GNSS. The main reason that restricts real-time PPP application isthe low accurate estimation of precise satellite clock offsets and a delay of clock offsetsdistribution. Therefore, systematically study on real-time precise satellite clock offsets estimationmethod, develop coordinating estimation software, improve satellite clock offsets accuracy,andresearching area precise satellite clock offsets estimation method, are of great institutingimportance and practical value on GNSS PPP technology real-time application.This paper aims at realizing real-time precise satellite clock offsets estimation, the basictheories and methods of precise satellite clock offsets estimation are systematically investigated.a program for the precise satellite clock offsets estimation is developed. by field surveying data,the validity of the method and model are proved. Precision of calculation basically meet therequirement for PPP at subnanosecond. The main contents of this paper are summarized asfollows:（1）Current development condition of GNSS and PPP is introduced,the importance ofprecise satellite clock offsets in PPP is pointed out, and the researching status of precise satelliteclock offsets estimation methods domestic and foreign is analysised. organization of IGS and itsexisting main products and its precision characteristic are introduced. Based on this, theresearching object,importance and structure of this paper is outlined.（2）Basic theory of precise satellite clock offsets estimation is concluded:The methods and characteristics of several combination of code and phase observationswitch are used in this paper are introduced, including the ionosphere-free combination inobservation equation,and the M-W combination and ionosphere residual combination incycle-slip detection.Based on observations of ionosphere-free combination and non-difference observationmodel, the difference observation model among the satellites, the difference observation modelamong the epoch and the non-ambiguity observation model among the atellite and epoch aregradually established. Through analysis of the comparison of non-difference observation modeland non-ambiguity model, proposed that non-ambiguity observation model will be moreapplicable to precise satellite clock offsets estimation. Related error correction method and its mathematic model in precise satellite clock offsetsestimation are specifically interpreted. The application of the sequential least squares method andclassic linear discrete kalman filter method in clock offsets estimation are studied. Through testcalculation, the precision in satellite clock offsets estimation with these two methods’iscompared, the result shows that these two methods’results are close each other.Analyzed the influence of satellite clock systematical deviation towards PPP precision,andbased on this,a method was proposed to through the epoch difference and through doubledifferences to assess the accuracy of the satellite offset（3）Introduced the process of satellite clock offsets estimation and model design, andintroduced related algorithm and mathematical model. Noted the detailed parameter settings inestimation. The paper introduced current GPS satellite constellation and clock types. Furtherdiscussed the selection of reference satellite. Specifically explained non-ambiguity model. Basicon this, a precised satellite clock offsets estimation program was designed and implemented.（4）Through the estimation program for precise satellite clock offsets, all the relativeclock offsets in24hour for32satellites in Nov.15th,2012are calculated. Take the relative resultof IGS as compare standard, the estimation result are compared and analyzed with epochdifference and double difference. Compare the result in the four values: maximum, minimum,average, and mean square error. The statistic result shows that, the accuracy of relative satelliteclock offsets estimation among the epoch is0.02ns, the accuracy of relative satellite clockoffsets estimation is0.8, thus, basically satisfy the precision requirement of real-time PPP atsubnanosecond level.（5）The accuracy of satellite clock offsets estimated with the surveyed data recorded fromregional distributed tracking station is discussed; With the surveyed data collected from part ofregional tracking station,precise satellite clock offsets are estimated.The result indicates that,within valid survey period, the relative clock offsets calculated by real-time regional trackingsegment data, can arrive at the precision respectively0.03ns in epoch difference and0.8ns insatellite relative clock offsets.It shows that the surveyed data recorded from regional distributedtracking station can also be used for real-time estimation in precise satellite clock offsets.