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Carrier-Smoothed-Code(CSC) can effectively suppress the multipath effect and receive noise in the code based differential positioning,which is widely adopted by the Ground Based Augmentation System (GBAS).Since the BeiDou Navigation Satellite System (BDS) code measurement suffers from the severer measurement noise,the CSC is necessary for the BDS based GBAS.However,the accuracy of smoothing pseudorange can be degraded significantly by the ionospheric delay error,which caused by the Code-Carrier Divergence (CCD) effect.The theoretical analysis shows that the CCD will greatly affect the precision of the smoothed pseudorange,thus,ionospheric delay error has to be considered for the services related to the safety-of-life (SoL).Based on the traditional CCD monitoring techniques,this paper proposed a new two first-order linear time invariant filter sequentially to improve the CCD performance.Meanwhile,sigma-inflation method is used to obtain the CCD detection threshold considering the impact from the non-ideal distribution of the constructed statistic.The real-world experiment result has shown that the proposed method can suppress the measurement noise more effectively when compared with the traditional first-order linear monitoring method with satisfying the predefined false alarm requirement,which make the proposed method more adaptable to the small bias from CCD.