在全球导航卫星系统（GNSS）应用中，垂向总电子含量（VTEC）是电离层反演的一类重要参数，卫星差分伪距偏差（DCB）则是实现精密定位等服务的一类必要改正。分别采用单频“伪距减相位”和双频“无几何影响”组合观测值的单、双频方案均可用于估计VTEC，且优点互补：单频方案的接收机硬件成本低，双频方案能同步估计卫星DCB。为此，本项目提出一种“单频改进方案”：其出发点是经精密卫星轨道和卫星钟差改正后的单频多GNSS非组合观测值，其中包含了卫星DCB信息；其核心技术是实现“单频多GNSS”非组合PPP的滤波算法，作为获取电离层斜延迟的手段；其特色是可同步估计VTEC和卫星DCB；其优势是硬件投入少、软件实现简单。研究成果将可丰富非组合PPP的模型，拓展非组合PPP的应用，发展GNSS数据处理理论；也可为GNSS电离层反演提供新思路，为包含我国BDS在内的多GNSS卫星DCB标定贡献新方法。

In the context of GNSS-based applications, Vertical Total Electron Content (VTEC) is one of the key parameters for ionosphere monitoring, while satellite Differential code biases (DCB) account for one type of correction that is of necessity to the realization of services including precise positioning. At present, the single- and dual-frequency schemes employing, respectively, “code-minus-phase” and “geometry-free” linear combinations, can both serve the needs of VTEC estimation with complementary advantages. Single-frequency scheme corresponds to fairly low expense in relation to receiver hardware. At the same time, dual-frequency scheme is in support of joint estimation of satellite DCB, along with VTEC. ..With these facts in mind, this proposal presents a so-called “modified single-frequency scheme”: its point of departure is the single-frequency, multi-GNSS observations that have been corrected using the precise satellite orbit and clock products, in which information about the satellite DCB shall show up; its key technique is the realization of Kalman-filtered-based “single-frequency, multi-GNSS” uncombined precise point positioning (PPP), serving as a tool for extracting the ionospheric delays; its main feature is the possibility of joint estimation of VTEC and satellite DCB; its advantage is low hardware expense and simple software implementation. ..The outcomes of this proposal shall enrich the model and applicability of uncombined PPP, and further GNSS data processing theory. In the meantime, they can also provide a novel idea for GNSS-based ionosphere monitoring, and contribute a new method to multi-GNSS (including Chinese BDS) satellite DCB calibration.