Application of network adjustment to the GPS common-view time links for TAI computations

In recent decades the GPS has served the principal national timing laboratories for the TAI calculation by regular comparisons of remote atomic clocks. Up to now, the TAI common-view time links are organized around the three central stations, CRL, OP and NIST, which connect with about 50 time laboratories around the world. The present method of fixed GPS common-view time links was artificially devised for the convenience of the TAI calculation. It has the features of simplicity and low work load, but the calculated results depend heavily on the observational qualities of the three central laboratories. Should one of them fail to function properly, the TAI calculation would be badly affected. From the point of view of the GPS common-view technique itself, any form of time links is feasible. If a slightly more complicated network could be formed in which all the time laboratories send their GPS timing data to the BIPM, then the effect of any imperfections in a closed loop could be greatly minimized by using the method of network adjustment. This method will provide more reliable time comparison results for the TAI calculation, and avoid the an entire regionʹs non-participation because of some failure of its central station. In this paper we present an experimental calculation with the method of network adjustment and the results obtained.