Probabilistic timing analysis: An approach using copulas

  • Authors:

  • Guillem Bernat;Alan Burns;Martin Newby

  • Affiliations:

  • Real-Time Systems Research Group. University of York, England UK (Corresponding author. E-mail: bernat@cs.york.ac.uk);Real-Time Systems Research Group. University of York, England UK;Centre for Risk Management, Reliability and Maintenance School of Engineering and Mathematical Sciences, City University, London, UK

  • Venue:
  • Journal of Embedded Computing - Real-Time Systems (Euromicro RTS-03)
  • Year:
  • 2005

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Abstract

Timing analysis and scheduling for complex systems now requires tools to deal with the fact that systems behaviour is stochastic and contains dependencies which are difficult to determine analytically. This paper introduces copulas, a general statistical tool for constructing multivariate distributions and describing dependence structures of random variables. Copulas are used to solve the problem of determining the probability distribution of the worst-case execution time of a real-time program. The common assumption of statistical independence is generally incorrect for real-time systems and results in severe underestimation of the probability of the worst case. Copulas allow the description of the dependence structure between blocks of a program, and whenever that dependence can not be determined it is possible to provide lower bounds for the distribution of the worst case execution time for any possible dependence between them. The method is illustrated through a case study.