On a notion of entropy for reachability properties

In this work, we introduce a notion of reachability entropy to characterize the smallest data rate which is sufficient enough to enforce reach-while-stay specification. We also define data rates of coder-controllers that can enforce this specification in finite time. Then, we establish the data-rate theorem which states that the reachability entropy is a tight lower bound of the data rates that allow satisfaction of the reach-while-stay specification. For a system which is related to another system under feedback refinement relation, we show that the entropy of the former will not be larger than that of the latter. We also provide a procedure to numerically compute an upper bound of the reachability entropy for discrete-time control systems by leveraging their finite abstractions. Finally, we present some examples to demonstrate the effectiveness of the proposed results.