# Cross-Layer Energy Optimization for IoT Environments: Technical Advances and Opportunities
###### Abstract  
Energy efficiency is a significant characteristic of battery-run devices such as sensors, RFID and mobile phones. In the present scenario, this is the most prominent requirement that must be served while introducing a communication protocol for an IoT environment. IoT network success and performance enhancement depend heavily on optimization of energy consumption that enhance the lifetime of IoT nodes and the network. In this context, this paper presents a comprehensive review on energy efficiency techniques used in IoT environments. The techniques proposed by researchers have been categorized based on five different layers of the energy architecture of IoT. These five layers are named as sensing, local processing and storage, network/communication, cloud processing and storage, and application. Specifically, the significance of energy efficiency in IoT environments is highlighted. A taxonomy is presented for the classification of related literature on energy efficient techniques in IoT environments. Following the taxonomy, a critical review of literature is performed focusing on major functional models, strengths and weaknesses. Open research challenges related to energy efficiency in IoT are identified as future research directions in the area. The survey should benefit IoT industry practitioners and researchers, in terms of augmenting the understanding of energy efficiency and its IoT-related trends and issues. Internet of Things; energy efficiency; smart technologies; green computing; heterogeneous networks +
Footnote †: journal:  
_Renormalization and Computing_  
four times the world's population. This estimated steep growth shows both the exponential expansion rate of IoT in the world and our dependence on IoT enabled devices [8; 9]. Towards realizing a smarter world via IoT enabled connected devices, there are two major constraints for tiny and smarter devices, namely, communication and computing power constraints due to the limitation of energy resources. The main power supply resource in most sensor-enabled IoT devices is a battery, whereby operating sensors consume battery power for collection and transmission of data among neighborhood devices. The accuracy of sensed and collected information is enhanced via analysis of the data. However, the analysis increases the energy consumption in IoT devices [10]. The sensor-enabled smart devices operate, i.e., they sense, receive, compute and disseminate information continuously, to facilitate automating intelligent decisions. The optimization of energy consumption in sensor-enabled IoT devices has become one of the fundamental issues due to the integration of sustainability in recent greener, and smarter world research [11]. Technical standardization bodies such as the Institute of Electrical and Electronics Engineering (IEEE), 3 rd Generation Partnership Projects (3 GPP) and the European Telecommunications Standard Institute (ETSI) have introduced various energy efficient approaches for sensor-enabled IoT devices [12]. In the related literature, various techniques have been suggested for optimizing energy consumption in sensor-enabled IoT devices. The techniques span focusing different aspects of IoT communication and computation for optimizing energy consumption in specific use cases. This energy-oriented diverse IoT domain can be systematically explored using a five-layered architecture (see Figure 1). The cross layer optimizations have been proven better in the literature due to the consideration of diverse aspects of communication and computing for scalable IoT use case implementation environments. Figure 1 shows a communication architecture of different IoT use case implementations focusing on the energy consumption aspects. It consists of five layers including sensing layer (SL), local processing and storage layer (LPSL), network/communication layer (NCL), cloud processing and storage layer (CPSL) and application layer (AL). The layer wise issues have been also highlighted. Figure 1: Energy consumption-oriented layered architecture for IoT.