# Special Issue: Quality of Service in Wireless Sensor/Actuator Networks and Systems
## 2 Summary of Contributions  
This special issue gathers together an extremely rich set of contributions, addressing several WSAN domains and sharing QoS as a common denominator. Eight papers have made it through a rigorous and iterative peer-reviewing process (three reviews per paper, at least two review rounds), involving 38 authors from all over the world (North and South America, Europe, Asia, and Australia) from academia, industry, and the military. Each paper features at least one reference author which is highly reputed in this scientific domain, totaling over one hundred thousand citations altogether. Papers cover a wide range of topics, namely the optimization of retransmission scheduling in IEEE 802.15.4e WSANs [1], an experimental evaluation of LoRa reliability [2], the estimation of WSAN lifetime based on innovative battery models [3], a novel radio interference classification method for WSANs [4], a dynamic QoS-aware MAC that can be boosted for long-range communications [5], an RSSI-based model-learning for target localization/tracking [6], using sensor network calculus for designing WSANs with predictable e2e delays [7], and decision-centric WSAN resource management [8]. A brief summary of each paper is provided here. The first paper to be published in this special issue, [1], investigates how the reliability of Industrial WSANs based on the IEEE 802.15.4e LLDN (low-latency deterministic network) protocol can be increased. The authors explore the inherent characteristics of the protocol to reschedule predetermined retransmission slots in a clever way, improving the reliability of uplink (sensor nodes -> coordinator) traffic and maximizing the probability of correct packet delivery. Importantly, two basic retransmission scheduling mechanisms are proposed that are backward compatible with the standard protocol, while two other approaches relying on cooperative relayers lead to more substantial gains but require minor changes to the standard. The authors build on two channel models: one static (fixed randomly chosen PER) and another one time-varying (hopping between two randomly chosen PERs) and evaluate the performance (essentially the superframe packet success rate) using a custom-made simulator. The authors of [2] report the main results of an extensive experimental evaluation of the reliability of LoRa, one of the most prominent long-range low-power WSAN to date, along with SigFox and Narrowband-IoT. The authors focus on the impact of physical layer settings and ambient temperature on effective data rate and energy efficiency. The authors build on indoor, outdoor, and underground experiments, concluding, e.g., that, when sensor nodes are at the boundaries of their communication range, it is better to use higher bit rates together with a retransmission scheme, rather than selecting a slower setting that maximizes PDR. It is also systematically shown that there is a direct correlation between ambient temperature, PDR, and received radio signal strength, for different LoRa radios. Over a range of 60 \({}^{\circ}\)C, the received signal strength consistently decreases 1 dBm/10 \({}^{\circ}\)C, which has a great impact for nodes at the edge of the communication range: a perfectly good link at 15 \({}^{\circ}\)C becomes unusable at 60 \({}^{\circ}\)C.  
WSANs are typically dependent (at least partially) on battery-powered devices. Therefore, estimating their current energy capacity and their lifetime may be of paramount importance, namely for energy-aware protocols and resource management. However, operating temperature and discharge current variations have a great impact on most electrochemical batteries' capacity, rendering the estimation of their voltage/charge behavior over time a tricky task. The authors of [3] propose an analytical model to estimate the state-of-charge and voltage of batteries based on their temperature, avoiding more expensive and energy-consuming hardware-based solutions that may compromise WSANs scalability.