jgg     2013 33 (5):  124-128    ISSN: 0412-1961  CN: 21-1139/TG PHASE BIAS ESTIMATION AND ITS APPLICATION IN  PPP AMBIGUITY FIXING School of Geodesy and Geomatics, Anhui University of Science & Technology, Huainan 232001 Received: 2013-03-18  Revised: null  Online: 2013-10-13 Supporting info