Reachability analysis of linear hybrid automata (LHA) is an important problem. Classical model checking (CMC) technique is not scalable and not guaranteed to terminate. On the other hand, bounded model checking (BMC) is more cost-effective to conduct but can not guarantee the safety beyond the bound. In this paper, we seek to bridge the gap between BMC and CMC for reachability analysis of LHA. During BMC of LHA, typical procedures can discover sets of unsatisfiable constraint cores, which can be mapped back to path segments in the graph structure of LHA. If every path connecting the initial and target location has to go through such infeasible path segment, the target location is entirely not reachable. Based on this characteristic, we propose a LTL model checking based approach to check whether the target location is blocked. To further optimize the performance, we propose an automata based solution to check the LTL specification incrementally and adopt an on-the-fly algorithm to check the accepting condition to avoid an explicit construction of product automata.

The behavior space of real time hybrid systems is very complex and hence expensive to conduct the classical full state space model checking. Compared to the classical model checking, bounded model checking (BMC) is much cheaper to conduct and has better scalability. This work presents a technique that can derive, in some cases, a proof of unbounded reach ability argument of Linear Hybrid Automata (LHA) from a BMC procedure. During BMC of LHA, typical procedures can discover sets of unsatisfiable constraint cores, a.k.a. UC or IIS, in the constraint set according to the bounded continuous state space of LHA. Currently, such unsatisfiable constraints are only fed back to the constraint set to accelerate the BMC solving. In this paper, we propose that such unsatisfiable constraint core can be exploited to give general unbounded verification result of the system model. As each constraint can be mapped back to certain semantical elements of the system model, the unsatisfiable constraint cores can be mapped back into path segments, which are not feasible, in the graph structure of the LHA model. Clearly, if all the potential paths to reach the target location in the graph structure have to go through such infeasible path segments, the target location is not reachable in general, not only in the given bound. Based on this observation, we propose to encode the infeasible path segments as linear temporal logic (LTL) formulas, and present the graph structure, the discrete part, of the LHA model as a transition system. Then, we can take advantage of the mature off-the-shelf LTL model checking techniques to verify whether there exists a path to reach the target location without touching any detected IIS path segment in the graph structure of the LHA model. We implement this technique into a bounded LHA checker BACH. The experiments show that most of the benchmarks can be verified by the enhanced BACH with a clearly better performance and scalability.