2019-10-26

Thereafter, in the same way as for the wide-lane, the narrowlane ambiguity can be fixed to integer if the fractional part of the narrow-lane UPD in Eq. (28), which is actually the mixture of the fractional parts of both wide- and narrow-lane,can be estimated precisely. 

因此，和宽巷一样，如果精确估计出式（28）中的窄巷UPD，窄巷模糊度即可固定为整数，其中窄巷UPD实际上同时包含了宽巷和窄巷的小数部分。

Through this reformulation, the estimated wide-lane UPD is only needed for making the fixing decision, but not for the deriving of narrow-lane ambiguities and reconstructing of the fixed ionosphere-free ambiguities. 

基于该公式，只需基于宽巷UPD的估计值确定是否固定，不需要获取窄巷模糊度和重构固定的无电离层模糊度。

Thus, only biases in the estimated narrow-lane UPDs enter into the reconstructed fixed ambiguities and contaminate estimated parameters and have therefore to be estimated as precisely as possible. One must be aware of that if the estimated wide-lane UPD is biased, which is inevitable because the integer parts are not separable with the ambiguities, the fixed values for all the ambiguities of the same satellite pair will be shifted by a common integer value [see Eq. (25)]. 

因此，仅窄巷UPD估值中的偏差会进入到重构的模糊度并影响估值参数，因而必须尽可能的估计准确。必须知道，由于宽巷UPD与模糊度不可分离，如果宽巷UPD不可避免地出现了偏差，基于同一卫星对的所有模糊度的固定值都将平移一个整数值。

Such a common shift in wide-lane will result in a constant change in their narrowlane ambiguities according to Eqs. (27)–(29), and can be absorbed by the narrow-lane UPDs. Therefore, for the ambiguity fixing, the knowledge of the fractional parts of the UPD corrections is sufficient. For the same reason, the constant pseudo-range biases in satellites have also no impact on the ambiguity fixing.

由式27-29可知，在宽巷中的这一平移会导致窄巷模糊度的也产生常数的改变，这一个变化会被吸收到窄巷UPD当中。因此，对于模糊度固定来说，已知UPD改正数的小数部分就已足够。同样，卫星的伪距常数偏差对模糊度固定也没有影响。

In summary, an ambiguity can be fixed on the SD-level for PPP in the similar way as on the DD-level, if the fractional parts of the SD-UPDs can be estimated and applied as corrections to SD-ambiguities

总之，对于PPP，如果能估计出SD-UPD的小数部分并作为改正值应用于单差模糊度，模糊度即可在单差的层面上固定，