A new method for GLONASS inter-frequency bias estimation based on long baselines

Frequency division multiplexing of GLONASS signals causes inter-frequency bias (IFB) in receiving equipment. IFB significantly increases the difficulties of fixing GLONASS ambiguities and limits the accuracy and reliability of GLONASS positioning and orbit determination. Accurately estimating and calibrating IFB can effectively solve such a problem. However, at present, most methods of IFB estimation are based on zero and short baselines, in which case it is not only difficult to realize fast and efficient IFB estimation but also one cannot fully utilize publicly available IGS and CORS data. Therefore, we present a new method for GLONASS IFB estimation based on long baselines. First, to weaken the influence of inter-frequency code bias, the wide-lane ambiguities are calculated directly based on the wide-lane combinations of observations. Then, according to the range of inter-frequency phase bias (IFPB) rates, a IFPB defined as the difference in IFPBs between adjacent frequencies, a step-by-step search schedule is designed to remove the impacts of IFPB on wide-lane and narrow-lane ambiguity resolution. Finally, after fixing integer wide-lane and narrow-lane ambiguities, the IFPB rate can be estimated. An experimental network is set up to verify the validity of this method; the experiment includes the data observed for 31 days at 542 stations in Europe and North America. The IFPB rates of 38 receiver types from nine manufacturers are successfully determined. Experimental results show that the estimated IFPB rates for the same receiver type stabilize within a month with a standard deviation of less than 1.4 mm/a dagger f (millimeters per frequency number increment, a dagger f denotes the frequency difference of adjacent GLONASS frequencies with frequency number increment of 1). Generally, the difference in IFPB rates of receiver types from the same manufacturer does not exceed 2.5 mm/a dagger f. However, the estimated IFPB rates of Septentrio's newly produced receivers, as compared with that of the old receiver types, show a rate difference of up to 50 mm/a dagger f. This significant difference should be considered for practical applications.