A method of GPS/BDS/GLONASS combined RTK positioning for middle-long baseline with partial ambiguity resolution

As China's BeiDou Navigation Satellite System (BDS) has become operational in the Asia-Pacific region, it is important to demonstrate the capabilities that a combination of GPS, BDS and GLONASS to high-precision positioning. Multi-constellation combination increases the available satellites and thus improves the positioning reliability. However at the same time, it will bring some challenges to the high-dimension ambiguity resolution (AR). In this contribution, a GPS/BDS/GLONASS combined real time kinematic (RTK) positioning method for middle-long baseline is proposed. In order to reduce the influence of troposphere and ionosphere delays on AR, a two-step AR strategy is adopted, where wide-lane and ionosphere-free observation model are used respectively. In the integer ambiguity search process, a partial ambiguity resolution (PAR) method is proposed to improve the AR performance. In the PAR method, satellite cutoff elevation, satellite number, AR success rate and ratio are used together to determine the ambiguity subset, which can be fixed reliably. A set of baselines ranging from about 30 to 60 km, which all contain GPS/BDS/GLONASS observations, are used to test RTK positioning performance. Experiment results demonstrate that GPS/BDS/GLONASS combined RTK positioning with partial ambiguity resolution can get much improved performance for middle-long baseline both in positioning speed and accuracy, as within about 20 sand 5 cm, respectively.