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The autocorrelation function of Composite BOC(CBOC) signals has many side-peaks, which leads to the ambiguous problem. To solve this problem, an improved two-stage unambiguous tracking scheme is proposed in this paper. In the first stage, an unambiguous correlation function with narrow main peak is constructed by combining four out of twelve sub-correlation functions. In the second stage, by adding the rest of sub-correlation functions, the final correlation function with sharper and higher main-peak is developed based on the preparatory function from the first step. Numerical results demonstrate that compared to the original methods, the proposed scheme has a better tracking performance and can effectively suppress the short delay multipath.

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The multipath in the inter-spacecraft microwave ranging system is the short-delay multipath generally. The performance of existing multipath mitigation algorithms degrade in the short-delay scenario, and therefore an adaptive filtering algorithm based on variable step-size LMS is exploited for estimating the parameters of multipath signals. Firstly, the equation of variable step-size LMS is deduced. Then, the signals parameters are estimated recursively though the adaptive filtering algorithm. Multipath elimination is performed by substracting the estimated multipath effects from the measured correlation function. Simulation results validate that the proposed method is superior to the existing algorithms in the aspect of convergence rate and ranging accuracy for the short delay multipath. Therefore, it is a viable solution for achieving high accuracies measurements in microwave ranging system with short-delay multipath.