The open family of temporal logics: annotating temporal operators with input constraints

Assume-guarantee style verification of modules relies on the appropriate modeling of the interaction of the module with its environment. Popular temporal logics such as Computation Tree Logic (CTL) and Linear Temporal Logic (LTL) that were originally defined for closed systems (Kripke structures) do not make any syntactic discrimination between input and output variables. As a result, these logics and their recent derivatives (such as System Verilog, Sugar, Forspec, etc) permit the specification of properties that have some semantic problems when interpreted over open systems or modules. These semantic problems are quite common in practice, but are computationally hard to detect within a given specification. In this article, we propose a new style for writing temporal specifications of open systems that helps the designer to avoid most of these problems. In the proposed style, the basic temporal operators (such as next and until) are annotated with assume constraints over the input variables. We formalize this style through an extension of LTL, namely Open-LTL and an extension of CTL with fairness, called Open-CTL. We show that this simple syntactic separation between the assume and the guarantee achieves the desired results. We show that the proposed style can be integrated with traditional symbolic model-checking techniques and present a complete tool for the verification of Verilog RTL modules in isolation

Service Level Guarantee for Mobile Application Offloading in Presence of Wireless Channel Errors

Mobile cloud computing is increasingly being used in recent times to offload parts of an application to the cloud to reduce its finish time. However, quality of offloading decisions depend on network conditions and hence many offloading solutions assume that MAC layer retransmissions will tackle transient frame errors. This can lead to suboptimal solutions, as well as, degrade service level guarantee of reducing finish time compared to execution without offloading. In this work, we propose an error-aware solution that uses run-time channel conditions to adapt the offloading decisions. We guarantee that given a failure rate bound (ϵ), offloading decisions will achieve application execution in less time than that of local execution with a probability of (1-ϵ) while operating in networks with unpredictable error characteristics. Simulation results show that at channel error rate of 20%, our heuristic provides 90% guarantee of better performance than on-device computation and reduces the mean finish time by 18% compared to execution without any offloading