Wireless Sensor Networks (WSN) are gaining popularity as a flexible and economical alternative to field-bus installations for monitoring and control applications. For missioncritical applications, communication networks must provide endto-end reliability guarantees, posing substantial challenges for WSN. Reliability can be improved by redundancy, and is often addressed on the MAC layer by re-submission of lost packets, usually applying slotted scheduling. Recently, researchers have proposed a strategy to optimally improve the reliability of a given schedule by repeating the most rewarding slots in a schedule incrementally until a deadline. This Incrementer can be used with most scheduling algorithms but has scalability issues which narrows its usability to offline calculations of schedules, for networks that are rather static. In this paper, we introduce SchedEx, a generic heuristic scheduling algorithm extension which guarantees a user-defined end-to-end reliability. SchedEx produces competitive schedules to the existing approach, and it does that consistently more than an order of magnitude faster. The harsher the end-to-end reliability demand of the network, the better SchedEx performs compared to the Incrementer. We further show that SchedEx has a more evenly distributed improvement impact on the scheduling algorithms, whereas the Incrementer favors schedules created by certain scheduling algorithms.

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A natural and often used strategy when testing software is to use input values at boundaries, i.e. where behavior is expected to change the most, an approach often called boundary value testing or analysis (BVA). Even though this has been a key testing idea for long it has been hard to clearly define and formalize. Consequently, it has also been hard to automate. In this research note we propose one such formalization of BVA by, in a similar way as to how the derivative of a function is defined in mathematics, considering (software) program derivatives. Critical to our definition is the notion of distance between inputs and outputs which we can formalize and then quantify based on ideas from Information theory. However, for our (black-box) approach to be practical one must search for test inputs with specific properties. Coupling it with search-based software engineering is thus required and we discuss how program derivatives can be used as and within fitness functions. This brief note does not allow a deeper, empirical investigation but we use a simple illustrative example throughout to introduce the main ideas. By combining program derivatives with search, we thus propose a practical as well as theoretically interesting technique for automated boundary value (analysis and) testing.

We propose novel strategies for end-to-end reliability-aware scheduling in Industrial Wireless Sensor Networks (IWSNs). Because of stringent reliability requirements in industrial applications where missed packets may have disastrous or lethal consequences, all IWSN communication standards are based on Time Division Multiple Access (TDMA), allowing for deterministic channel access on the MAC layer. We therefore extend an existing generic and scalable reliability-aware scheduling approach by the name of SchedEx. SchedEx has proven to quickly produce TDMA schedules that guarantee a user-defined end-to-end reliability levelρ_for all multihop communication in a WSN. Moreover, SchedEx executes orders of magnitude faster than recent algorithms in the literature while producing schedules with competitive latencies. We generalize the original problem formulation from single-channel to multichannel scheduling and propose a scalable integration into the existing SchedEx approach. We further introduce a novel optimal bound that produces TDMA schedules with latencies around 20% shorter than the original SchedEx algorithm. Combining the novel strategies with multiple sinks, multiple channels, and the introduced optimal bound, we could through simulations verify latency improvements by almost an order of magnitude, reducing the TDMA superframe execution times from tens of seconds to seconds only, which allows for a utilization of SchedEx for many time-critical control applications.