LAUSR

An improved cycle-slip repair model is proposed for BDS triple-frequency undifferenced observations. Two extra-wide-lane code-phase combinations and one additional geometry-free (GF) carrier-phase combination are employed. To ensure the GF phase combination follows a normal distribution, the residual ionospheric variation of the GF phase combination is corrected in real-time using the previous observation sequence without cycle slip. The integer least squares principle, based on the least-squares ambiguity decorrelation adjustment, is used to solve the fixed value of cycle slip. The corresponding covariance matrix of floating cycle-slip estimations used for construction is updated in real time to improve the fixed efficiency of cycle slip. Moreover, for reliable repair of cycle slip for triple-frequency observations, the critical ratio value between the second-best and best cycle-slip candidates for different residual ionosphere accuracies and different repair success rates are given based on large amounts of simulated data. Lastly, a set of active ionosphere and low-sampling-rate real data was used for evaluation and analysis of the algorithm. Results showed the success rate of cycle-slip repair is 99.997%, even under active ionosphere conditions, with low satellite elevation and low sampling rate. Unfortunately, one cycle-slip group (1, 1, 1) of the C14 satellite was not detected successfully and repaired correctly because of insensitivity to the GF phase combination under bad observation conditions.