# Predictive Energy-Aware Routing Solution for Industrial IoT Evaluated on a WSN Hardware Platform
## 3 Energy Awareness and Prediction Model for IWSNs
### Problem Definition and Prerequisites  
The PEAR solution was designed to respect the requirements, constraints and use of IWSNs deployed in real harsh and demanding environments such as oil and gas platforms and renewable energy plants. Moreover, PEAR aims to provide field device lifetime predictability and to discover the energy management potential within a standard ISA100.11a network without affecting its performance or stability.  
The PEAR design and performance criteria are based on the requirements for control and predictability of the sensor lifetime within an industrial ISA100.11a network. These requirements reflect the concerns of industrial plants for predictable availability of sensors, especially when critical or safety processes are involved and for predictable maintenance operation, such as battery replacement, to avoid high operational cost caused by frequent and unplanned maintenance procedure. The predictable lifetime and availability of IWSN sensors further prevent production discontinuity and lowers the facility downtimes.  
Within an ISA100.11a network, the field device consumption and lifetime mainly depend on the battery capacity, acquisition rate and the position in the network topology. While the battery capacity is known and the acquisition rate is configurable in a dynamic mesh network, the energy consumption is dependent on the network topology. This results in a real-life case where there is a theoretical lifetime specified by the sensor manufacturer based on a standalone operation at a specific acquisition rate. However, the actual sensor lifetime cannot be controlled or predicted at sensor level when deployed within a dynamic ISA100.11a mesh network.  
To accommodate such real deployment requirements, PEAR considers the following design constraints: ISA100.11a standard compatibility and IWSN hardware platform resources.  
PEAR is designed to use the ISA100.11a standard attributes, objects, and mechanisms to preserve the compatibility with the ISA100.11a field devices irrespective of the manufacturer. This enhances its applicability and ease of integration with sensors from vendors such as Yokogawa [33], Honeywell [34], Draeger [35] and SpiraSarco [36]. Moreover, PEAR uses the ISA100.11a routing and resource allocation mechanisms. To avoid a negative impact on the network performance PEAR uses the ISA100.11a standard network formation mechanism to trigger topology changes that reflect the energy constraints. This limits the PEAR possibilities to make topology changes. Therefore, PEAR does not propose a theoretical best solution approach towards energy management bur rather it provides energy awareness in the presence of routing constraints corresponding to a dynamic ISA100.11a mesh network formation.  
The PEAR algorithm runs on the CDS VR950 embedded hardware platform [10] sharing processing and memory resources with other software modules, more specifically, the ISA100.11a management modules such as the system manager (SM), gateway (GW) and security manager. The topology changes triggered by PEAR consider the hardware processing limitations and do not affect the ISA100.11a network stability and performance in terms of sensor update rate.