Wake-up radio is a promising approach to mitigate the problem of idle listening, which incurs additional power consumption for the Internet of Things (IoT) wireless transmission. Radio frequency (RF) energy harvesting technique allows the wake-up radio to remain in a deep sleep and only become active after receiving an external RF signal to ‘wake-up’ the radio, thus eliminating necessary hardware and signal processing to perform idle listening, resulting in higher energy efficiency. This review paper focuses on cross-layer; physical and media access control (PHY and MAC) approaches on passive wake-up radio based on the previous works from the literature. First, an explanation of the circuit design and system architecture of the passive wake-up radios is presented. Afterward, the previous works on RF energy harvesting techniques and the existing passive wake-up radio hardware architectures available in the literature are surveyed and classified. An evaluation of the various MAC protocols utilized for the novel passive wake-up radio technologies is presented. Finally, the paper highlights the potential research opportunities and practical challenges related to the practical implementation of wake-up technology for future IoT applications.

The narrowband Internet of Things (NB-IoT) is a new wireless protocol proposed by the 3rd Generation Partnership Project intending for low data rate IoT applications. The general objectives of the NB-IoT include supporting massive connections, enhanced coverage, reduced cost and complexity, ultra-low power consumption, and flexible delay characteristics. To lower energy consumption while providing reliable connections, extended discontinuous reception and power saving mode (PSM) mechanism are applied in the NB-IoT. To evaluate the energy consumption and delay performance under periodic uplink reporting, which is common among cellular IoT applications, this paper develops a semi-Markov chain with four states, namely, PSM, idle, random access (RACH), and transmission (Tx) states. RACH and Tx states are introduced from the well-known CONNECTED STATE to account for the extra power consumed due to increased access collisions under massive synchronous connections. Furthermore, an optimization model is introduced to find the best PSM duration, which is configured to minimize energy consumption and average delay according to user's preference. The numerical results show that setting higher limits for the number of possible RACH request transmission can make the user equipment (UE) more tolerant to delay and energy consumption in massively deployed concurrent communication UEs. Extending the PSM duration to longer period will cause excessive increase in delay without much impact on energy saving improvement. INDEX TERMS Narrowband-Internet of Things, extended discontinuous reception, power saving mode, energy consumption, semi-Markov chain.

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In this paper, we evaluated several network routing energy models for smart farm application with consideration of several factors, such as mobility, traffic size and node size using wireless ZigBee technology. The energy models considered are generic, MICA and Zigbee compliant MICAz models. Wireless sensor networks deployment under several scenarios are considered in this paper, taken into account commercial farm specification with varying complex network deployment circumstances to further understand the energy constraint and requirement of the smart farm application. Several performance indicators, such as packet delivery ratio, throughput, jitter and the energy consumption are evaluated and analysed. The simulation result shows that both throughput and packet delivery ratio increases as the nodes density is increased, indicating that, smart farm network with higher nodes density have a superior Quality of Service (QoS) than networks with sparsely deployed nodes. It is also revealed that traffic from the mobile nodes causes increase in the energy consumption, overall network throughput, average end-to-end delay and average jitter, compared to static nodes traffic. Based on the results obtained, the Generic radio energy models consumed the highest total energy, while MICAz energy consumption model offers the least consumption, having the lowest ‘Idle’ and ‘receive’ modes consumption. The MICAz model also has the lowest total consumed energy as compared with the other energy models, suggesting that it is the most suitable energy model that should be adopted for future smart farm deployment.