## 1 Introduction
EH converts every possible available energy source existing in a specific environment into power to supply the device. An optimum implementation of this approach requires an accurate identification of both spatial and temporal energy distribution in the operation environment in order to power up the devices in accordance with the functional requirements [11]. As a consequence, the knowledge of these parameters drives the overall system design in term of performance, complexity and functionalities [12]. Recently an EH approach based on the use of renewable energy sources has been proposed to achieve long-term and self-sustainable operations for nodes. This translates in prolonging the lifetime of IoT network especially if operating in extreme environments where the replacement of batteries can be difficult. The latter represents a great improvements with respect of applications where a mobile charger is usually employed to provide the energy replenishment through energy downlink collecting surplus power from energy-rich nodes and transfer it to energy-deficient nodes. An EH system consists of two processes: (1) energy harvesting and (2) data transmission. Since data communications modify the nodes energy, an optimal control of data and related energy flows represents a critical issue for effective communications. On the other hand, WPT supports both battery-less and backup-battery approach, giving a higher degree of freedom for the system designers [13]. In particular, WPT enables the energy supply with a direct device activation, or the device battery recharge, respectively. The second approach relies on an infrastructure dedicated to the energy transfer embodied in the communications topology, requesting specific routing strategies to optimise both aspects [14]. The present work is focused on an overall system architecture design for application over an IIoT scenarios. In particular, we consider that industrial devices (i.e., sensor and actuators) are expected to act as a group to perform homogeneous operations in terms of manufacturing and quality assessment. Then they can be logically clustered and the possible interactions among clusters needs to be optimised mostly under energetic constraints which affects their availability and life-time. In order to establish intra- and inter-cluster(s) communications, we resorted to a WoT protocol, in particular, following the publish-and-subscribe pattern, according to the MQTT-SN framework. This allows to set-up extremely flexible end -to-end (e2e) sessions; to this purpose, we derived a solution that allows the joint management of the data flows and power budget management. Specifically, the aim is to evaluate e2e paths among Publisher(s) and Subscriber(s) minimising the power consumption. Accordingly, we characterised the proposed architectures and interfaces, further extending this approach by taking into account also the presence of a subnetwork to handle the WPT procedure, that is aimed to dynamically distribute the available power to that nodes involved in communications. The involved functional modules and the device level architectures have been described and harmonised within the overall system. Summarising, the main contribution of this paper consists in:  
* an high-level architecture design, integrating a typical IIoT scenario on a publish-subscribe oriented messaging framework through proper interfaces and protocols
* individual module modelling and design, with a specific focus on the power supplying process, both on a component and procedure point of view. * development of an ad hoc simulation framework including different approaches performed over realistic scenarios. The paper structure is at it follows: after introducing the specific features, the related literature and the open issue of IIoT domain in Section 1, the reference system model is presented in Section 2, in terms of both the general architecture and specific communications and control protocols, with a characterisation of hardware components.