On Voting Strategies for Loosely Synchronized Dependable Real-Time Systems

Hard real-time applications typically have to satisfy high dependability requirements in terms of fault tolerance in both the value and the time domains. Loosely synchronized real-time systems, which represent many of the systems that are developed, make any form of voting difficult as each replica may provide different outputs independent of whether there has been an error or not. This can also lead to false positives and false negatives which makes achieving fault tolerance, and hence dependability, difficult. We have earlier proposed a majority voting technique, Voting on Time and Value (VTV) that explicitly considers combinations of value and timing errors, targeting loosely synchronised systems. In this paper, we extend VTV to enable voter parameter tuning to obtain the desired user specified trade-offs between the false positive and false negative rates in the voter outputs. We evaluate the performance of VTV against Compare Majority Voting (CMV), which is a known voting approach applicable in similar contexts, through extensive simulation studies. The results clearly demonstrate that VTV outperforms CMV in all scenarios with lower false negative rates.