## 6 Conclusions  
The evolution of WSNs towards the IoT in general, and the edge and fog computing approaches in particular, has had a significant impact on the computational load of the end-devices. As a result, current and future sensor devices are expected to provide more highly-processed information compared to traditional WSN nodes, which highly increases their computational loads.  
In this work, we have carried out an empirical study of the cross-influence that the computational load of processing tasks has in the communication performance when using an OS for IoT sensor devices. The main conclusion drawn from this work is that the increase in computational load results in the appearance of a series of cross-effects between the processing and communication tasks that can significantly affect their performance. It is important to emphasize that this circumstance can cause the complete malfunctioning of an application. Future designs must therefore take into account both aspects in order to reach a compromise between their requirements, especially when both the processing and communication tasks have strict timing constraints. This poses a series of new challenges that will have to be faced at multiple levels: OS process management, communication protocols, hardware architecture of end-devices, microcontroller features, etc.  
To draw these conclusions, in this empirical study real IoT sensor devices have been used to conduct multiple tests with different levels of computational load, various priority schemes, different scenarios, etc. This study was performed with a specific set of tools: an OS with a round-robin priority scheduler and a layered network stack with a TDMA-based MAC. These features are present in many other IoT sensor devices, so the results can be extrapolated to other cases in which the characteristics of the OS and the communication protocols are similar.  
However, it is convenient to go deeper into this study to better understand the influence on the observed effects of other aspects that, due to the scope of this preliminary work, have not been considered. Along these lines, it would be interesting to experiment with a connection-oriented reliable communication protocol (TCP-like), different MAC schemes, multiple payload lengths, more complex scenarios with a greater spectrum occupancy, etc. In addition, it would also be useful to replicate these experiments with other reference IoT OSs and platforms. The realization of these studies will constitute a necessary basis for the development of new mechanisms to reduce the cross-effects between the processing and communication tasks.  
Conceptualization, R.R.-Z. and R.U.; methodology, R.R.-Z., R.U. and A.A.; software, R.R.-Z. validation, A.R. and A.A.; formal analysis, R.R.-Z. and R.U.; investigation, R.R.-Z.; resources, R.R.-Z. and R.U.; data curation, R.R.-Z. and R.U.; writing--original draft preparation, R.R.-Z., R.U. and A.R.; writing--review and editing, A.R. and A.A.; supervision, A.A.; project administration, A.A.; funding acquisition, A.A.  
This research was partially funded by the Spanish Ministry of Economy and Competitiveness, under RETO COLABORACION program (Reference grant: All-in-one: RTC-2016-5479-4), and CIEN program (ROBIM Project), and the Spanish Ministry of Industry, Energy, and Tourism through the Strategic Action on Economy and Digital Society (AEESD) under SENSORIZA: TSI- 100505-2016-10 project.