The vulnerability of its own may degrade or even invalid the service of GNSS. Researchers from related fields have paid high attention to this problem. In this new subject, it has an obligation to establish the concept, intension and extension of the vulnerability, to record the vulnerability events and analyze its causes and influences, to weight the vulnerability level, to seek the countermeasures out, and to improve the performance of GNSS. In this paper, the GNSS vulnerability issues were described and then its quantitative assessment method was investigated. A model was proposed to quantitatively assess the impact of vulnerability on service availability, and the key of the model rely on finding several service intrinsic parameters which share comprehensive as well as unrelated as possible as they can to reflect the service availability. In this paper we chose predefined but concrete parameters such as carrier-to-noise ratio deviation, relative pseudorange measurement error, geometric dilution of precision deviation, code-minus-carrier (CMC), etc., and used the method of principal component analysis to get the assessment parameters. The upper and lower threshold values of the assessment parameters were settled to evaluate corresponding service quality. Then the theory of Dempster-Shafer evidence reasoning was used to fuse these parameters of vulnerability performance into the vulnerability index which characterizes the vulnerability state of service availability.

Keywords: GNSS vulnerability, quantitative assessment, D-S evidence