中文摘要：

现阶段BDS卫星和地面跟踪站数量较少，用BDS单系统获取的DCB精度有限，针对此问题，本文基于CODE GIM，采用两种不同的“零均值”基准约束方案（分别称为约束1和约束2），选取2015年（DOY002-090）MGEX的BDS数据，求解BDS的DCB，并对其进行精度评估。结果表明，两种约束方案下，卫星DCB差值整体趋势一致，DCBC2I-C7I、DCBC2I-C6I的系统性偏差分别约为-3.3 ns和1.2 ns，接收机DCB的系统性偏差与卫星DCB大小相同，符号相反。相对于约束1，施加约束2后，IGSO和MEO卫星DCB估值更加稳定（DCBC2I-C7I STD最大改善21%，DCBC2I-C6I STD最大改善13%），IGSO和MEO卫星的稳定性（分别在0.1 ns和0.2 ns左右）优于GEO卫星（0.15~0.32 ns）。约束2的DCB估值效果不仅与CAS/DLR产品有较好的一致性（Bias：-0.4~0.2 ns），而且顾及了BDS卫星DCB间的稳定性差异。两种约束方案下，BDS接收机DCB的STD无明显变化，说明约束的选择对BDS接收机DCB的稳定性无明显影响。BDS接收机DCB稳定性整体上优于1 ns，中高纬度区域较好（STD 0.4 ns左右），低纬度区域稍差（STD 0.8~1 ns）。

英文摘要：

As the limited number of the BeiDou Navigation Satellite System （BDS） satellites and tracking stations currently, it＇s difficult to attain daily DCBs solution with precisely high accuracy based on BeiDou single system. In order to overcome the weakness above, two different zero-mean constraints for BDS satellites, called constraint one and constraint two, respectively, are used to estimate DCBs of BDS based on BeiDou observations from the multi-GNSS experiment （MGEX） network and global ionosphere maps （GIM） from the Center for Orbit Determination in Europe （CODE）. The results show that the systematic difference of the overall trend under two different constraints is consistent, and the systematic difference of DCBC2I-C7I and DCBC2I-C6I is -3.3 ns and 1.2 ns, respectively. The systematic difference between BDS satellite DCBs and receiver DCBs has the same absolute value, but opposite signs instead. Compared to constraint one, The DCBs estimation of IGSO/MEO satellites under constraint two are more stable （the improvement of satellites DCBC2I-C7I and DCBC2I-C6I STD are up to 21%, 13%, respectively）, the stability of IGSO and MEO satellites （STDs are within 0.1 ns, 0.2 ns, respectively） is better than that of GEO satellites （STDs are 0.15~0.32 ns）. DCB estimation of constraint one is not only consistent with the CAS/DLR products （Bias：-0.4~0.2 ns）, but also takes into account the stability of BDS satellites DCB. Under the two different constraints, there is no obvious change in BDS receiver DCBs, meaning that the selection of constraints has no obvious influence on the stability of BDS receivers DCBs. The overall stability of BDS receiver DCBs is better than 1 ns. Due to the accuracy discrepancy of GIM in different latitudes, the stability of BDS receiver DCBs in the middle-high latitude （STDs are within 0.4 ns） is better than that in low latitude region （STDs are 0.8~1 ns）.