Gao Wang, Gao Chengfa, Pan Shuguo, Wang Denghui, Deng Jiadong
School of Transportation, Southeast University, Nanjing 210096, China.
School of Instrument Science and Engineering, Southeast University, Nanjing 210096, China.
Sensors (Basel). 2015 Oct 30;15(11):27525-42. doi: 10.3390/s151127525.
The regional constellation of the BeiDou navigation satellite system (BDS) has been providing continuous positioning, navigation and timing services since 27 December 2012, covering China and the surrounding area. Real-time kinematic (RTK) positioning with combined BDS and GPS observations is feasible. Besides, all satellites of BDS can transmit triple-frequency signals. Using the advantages of multi-pseudorange and carrier observations from multi-systems and multi-frequencies is expected to be of much benefit for ambiguity resolution (AR). We propose an integrated AR strategy for medium baselines by using the combined GPS and BDS dual/triple-frequency observations. In the method, firstly the extra-wide-lane (EWL) ambiguities of triple-frequency system, i.e., BDS, are determined first. Then the dual-frequency WL ambiguities of BDS and GPS were resolved with the geometry-based model by using the BDS ambiguity-fixed EWL observations. After that, basic (i.e., L1/L2 or B1/B2) ambiguities of BDS and GPS are estimated together with the so-called ionosphere-constrained model, where the ambiguity-fixed WL observations are added to enhance the model strength. During both of the WL and basic AR, a partial ambiguity fixing (PAF) strategy is adopted to weaken the negative influence of new-rising or low-elevation satellites. Experiments were conducted and presented, in which the GPS/BDS dual/triple-frequency data were collected in Nanjing and Zhengzhou of China, with the baseline distance varying from about 28.6 to 51.9 km. The results indicate that, compared to the single triple-frequency BDS system, the combined system can significantly enhance the AR model strength, and thus improve AR performance for medium baselines with a 75.7% reduction of initialization time on average. Besides, more accurate and stable positioning results can also be derived by using the combined GPS/BDS system.
北斗导航卫星系统（BDS）区域星座自2012年12月27日起一直在提供连续的定位、导航和授时服务，覆盖中国及周边地区。利用BDS和GPS观测数据进行实时动态（RTK）定位是可行的。此外，BDS的所有卫星均可传输三频信号。利用多系统、多频率的多伪距和载波观测优势，有望对模糊度解算（AR）大有裨益。我们提出了一种利用GPS和BDS双频/三频组合观测数据的中长基线综合AR策略。该方法首先确定三频系统（即BDS）的超宽巷（EWL）模糊度。然后，利用基于几何模型的BDS固定模糊度EWL观测值，解算BDS和GPS的双频宽巷模糊度。之后，利用所谓的电离层约束模型，联合估计BDS和GPS的基本（即L1/L2或B1/B2）模糊度，并加入固定模糊度的宽巷观测值以增强模型强度。在宽巷和基本AR过程中，均采用部分模糊度固定（PAF）策略，以减弱新升起或低仰角卫星的负面影响。进行并展示了相关实验，在中国南京和郑州采集了GPS/BDS双频/三频数据，基线距离约为28.6至51.9公里。结果表明，与单三频BDS系统相比，组合系统可显著增强AR模型强度，从而提高中长基线的AR性能，平均初始化时间减少75.7%。此外，使用GPS/BDS组合系统还可获得更精确、稳定的定位结果。
