Limited lookahead policies in supervisory control of discrete event systems

A supervisory control scheme which is based on limited lookahead control policies is proposed, using an online scheme where after the occurrence of an event, the next control action is determined on the basis of an N-step-ahead projection of the behavior of the process (represented as an N-level tree). This procedure then repeats after the execution of the next event. Different attitudes can be adopted to calculate a control action for the given N-level tree in order to resolve uncertainties about the process behavior beyond N steps. Two such attitudes, termed conservative and optimistic. are studied. Results are presented pertaining to monotonicity and convergence properties of the optimistic and conservative N-step policies in terms of N, and comparison of these policies with the optimal offline solution; closed-form expression for the language generated by the N-step conservative policy for prefix-closed legal languages; and lower bounds for N that guarantee that the online scheme performs as well as an offline scheme with complete information