## 2 Challenges, Trends and Constraints in WSAN Hardware Design  
Designing hardware systems for WSAN is always an arduous work. Knowledge, skills, and experience have to be demonstrated in fields such as digital and analog electronics, embedded systems,MCUs' firmware development, power electronics, sensors, radio frequency (RF) communications, wireless networking, printed circuits board (PCB) design, prototyping, testing and evaluation. Furthermore, it is necessary to have a keen awareness of updated solutions launched by the microelectronics industry, which can benefit new systems' designs (i.e., new integrated semiconductors (ICs), systems-on-chip [54] and other electronic components, in general). Diving deep into such fields is very often out of scope, for example, in cases where the aim is to monitor a particular physical phenomenon using WSAN technology in-situ. Although the aforementioned requirements are critical preconditions to WSAN systems, they are not included in the training courses for WSAN systems and applications [55]. The view perspectives of what is a WSAN system may vary among different areas of interest [6]. In particular, for the agricultural domain, the various differences in perspectives of a WSAN node are summarized in Table 1.  
Design inefficiencies like the fragmentation and limitations caused by the lack of skills can jeopardize the anticipated full-scale commercialization and popularization of WSAN systems. In order to build successful systems that can face the difficulties and the requirements of real-life applications, each stakeholder has to take into consideration other stakeholders' needs and idiocyncracies. As depicted in Figure 2, there are five major stakeholder groups, namely the application experts, the systems designers, the end-users, the industry/market, and the authorities (the external circle in Figure 2). The arrows illustrate the influence between different parts. Practically, this influence is based on the flow of tangibles (e.g., technologies, systems, tools, documents, etc.) and intangibles (e.g., skills, ideas, needs, expectations, etc.).  
Obviously, the typical architecture of Figure 1 or the COTS approach cannot support the design of systems that will meet all the expectations of everyone that has a vested interest in a WSAN application. On the other hand, the reaction of the expandable multi-board systems' designers and developers signals the direction for future architectures, in order to confront the changing, demanding, and complex applications' ecosystems.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Area of Interest** & **What a WSAN Node Means** \\ \hline Embedded Electronics & A fast, miniaturized, MCU-based board \\ Communications & A protocol-powered machine \\ Information Technology (IT) & A client \\ Electronics Industry & A development tool \\ Agriculture original equipment manufacturing (OEM) & A proprietary, closed, turn-key solution \\ Agricultural Science & A remote sensor/actuator \\ Farmers & An expensive telemetry equipment \\ \hline \hline \end{tabular}
\end{table}
Table 1: Different perspectives of WSAN node in the agricultural domain.  
Figure 2: Interactions among different stakeholders in WSAN hardware systems design.