N-version Programming for Railway Interlocking Systems: Synchronization and Voting Strategy

The main issue in controlling safety-critical systems such as nuclear power reactors or railway signalization systems where risk ratio is at the highest level because small errors might result in hazardous accidents (e.g. death or injury of several people) is to satisfy safety-related standards and provide high-safety with high-reliability. In order to improve reliability and safety of such systems to the required level by decreasing common-cause failures at the same time, diverse programming (or N-version programming) technique where N-different independently designed modules run in parallel on the same input output specifications can be used. In this study, a new bitwise voting strategy based on safe-states of variables is proposed and possible critical races between modules those run in a parallel manner are determined. Solutions for critical races are also explained.