A model of function-level fault tolerance of navigation signals provision processes in adverse conditions

Abstract

The aim of this article is to develop a model that would allow quantitatively evaluating the function-level fault tolerance of navigation signals provision processes in adverse reception conditions using consumer navigation equipment (CNE). The article also substantiates the relevance and importance of evaluation of the function-level fault tolerance of consumer navigation systems in those cases when the reception of the signals is affected by industrial interference, pseudo-satellites, rereflections from urban structures and terrain features. The function-level fault tolerance of the processes of navigation signals (of CNE) provision to consumers in adverse conditions is understood as their ability to fulfil their functions and retain the allowed parameter values under information technology interference within a given time period. The adverse conditions of provision of navigation data (signals) to consumers are understood as a set of undesirable events and statuses of reception and processing of navigation data with possible distortions. The article analyzes a standard certificate of vulnerabilities of navigation signal (by the example of distortion of pseudorange and pseudovelocity values distortion) that defines the input data for the analysis of CNE equipment fault tolerance. The model is based on the following approaches: the navigation signal parameters are pseudorange and pseudovelocity, system almanac data and ephemeris information; quantitative evaluation of function-level fault tolerance of the processes of navigation signals provision to users is based on the probability of no-failure of CNE in adverse conditions; function-level fault tolerance of the above processes is ensured by means of integrated use of functional, hardware, software and time redundancy; the hardware and software structure of the CNE fault tolerance facilities has the form of a three-element hot and cold standby system; the allowable level of functionlevel fault tolerance violation risk is defined according to the ALARP principle. It is shown that CNE fault tolerance and jamming resistance is based on the following: use of multisystem navigation receivers; navigation signal integrity supervision; spatial and frequency-time selection of signal; precorrelation processing of signal and interference mixture; postcorrelation signal processing; processing of radio-frequency and information parameters of the signal; cryptographic authentication; integration with external sources of navigation information and within a single signal processing system of a number of methods of interference countermeasures and pseudo-satellite navigation signals. The proposed model defines the CNE function-level fault tolerance as two variants of dynamic dependability models, in which the values of probability of no-failure are time-dependent: a hot standby system that includes three additional countermeasure modules and a cold standby system with a switch to three additional countermeasures modules. The model allows visualizing the processes of navigation signals provision to users in adverse conditions, quantitatively evaluating the probability of no-failure for hot and cold standby systems with three modules of information technology interference countermeasures, probability of recovery and CNE availability coefficient, as well as the allowable risk of CNE fault tolerance violation.