## 3 The SensoTube Architecture  
Taking into consideration the constraints mentioned in the previous section, the prospect of a new scalable architecture which, on one hand, can maintain the obvious advantages of the OSH expandable architectures, and, on the other hand, can help OSH concept take the next step towards optimization and reliability by provide the mechanisms for avoiding the existing limitations can be reasonably raised. Hence, the OSEP concept can be fully exploited in the WSAN applications even in the demanding domain of agriculture. Therefore, a new architecture, namely the SensoTube, is proposed and described in this section. The grand aim of the SensoTube architecture is to enable a WSAN hardware system to:  
1. _Escape from the structural restrictions of the existing architectures_: The adhesion to the traditional architecture together with the persistence for miniaturization seems to be rather inappropriate for real-life applications in agriculture. Actually, the size of a WSAN node doesn't matter [90], and for the case of agriculture, this is evident from the trend to use large-sized OSH platforms. * _Keep the advantages of OSH expandable concept:_ The new architecture should maintain the reasons for which the Arduino-like OSH architectures became popular, i.e., the simplicity, the expandability, the reconfigurability and the reusability of hardware. * _Avoid existing OSH architectures' implementation constraints:_ The new architecture should provide new mechanisms, in order to avoid the constraints of existing expandable architectures (see Section 2) and, on the other hand, ensure the highest versatility and flexibility. * _Satisfy all the applications' stakeholders:_ The new architecture should allow designers of different design fields (e.g., power electronics, communications, data acquisition etc.) to easily adapt their contributions. Also, the end-users should have clear and reusable building blocks for their present and future integrations. * _Support the \"separation of concern\":_ Regarding the research efforts to study new challenging technologies with potential benefits for WSAN systems, there is a trend for decoupling the WSAN from the application [91]. Also, several other studies, e.g., for WSAN nodes' scenario reconfiguration [92; 93], for strategies on WSAN power management [94], for data acquisition development, or for implementing technologies like Wakeup-Radio (WuR) [95], and many others, are indicators cases where the decoupling from the wireless networking is required. This decoupling is practically achieved either by the addition of more than one MCU on-board, or by the usage of FPGAs, or by the addition of extra RF communication circuits or modules. Such modifications are necessary to overcome the limited boundaries of the traditional architectures, in order to implement the pilots. On the other hand, they may be considered as custom closed-architecture designs. Therefore, the new architecture should ensure the accommodation of research in new and challenging technologies. * _Support modeling:_ The new architecture should allow for modeling of the WSAN hardware system. To meet this target the architecture should provide the highest scalability and standardization. In this way, the WSAN systems could be seen from the middleware infrastructure as well-defined functional multi-class objects. * _Ensure optimization:_ The systems based on the new architecture should combine the performance level required in real-world WSAN applications [10] with the vagaries of the agricultural domain. Ideally, the systems should have the optimization level of the commercial end-systems, but with the flexibility of a testbed. Furthermore, a provision should be made in terms of the form factor of the WSAN systems and their encapsulation, in order to cover the specific requirements in the open agricultural field. Actually, the name SensoTube reflects the idea of using plastic tubes for the encapsulation of the WSAN systems in the agricultural fields.