Research Article Energy-Efficient Asynchronous QoS MAC Protocol for Wireless Sensor Networks Sohail Sarang , 1 Goran M. Stojanović, 1 Stevan Stankovski, 1 Željen Trpovski, 1 and Micheal Drieberg 2 1 Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovića 6, 21000 Novi Sad 21000, Serbia 2 Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak, Malaysia Correspondence should be addressed to Sohail Sarang; sohailsarang109@gmail.com Received 23 May 2020; Revised 1 September 2020; Accepted 4 September 2020; Published 24 September 2020 Academic Editor: Jaime Lloret Copyright © 2020 Sohail Sarang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In recent years, wireless sensor networks (WSNs) have gained significant attention in both industry and academia. In WSNs, each sensor node is normally equipped with a small-size battery with finite capacity. Hence, energy-efficient communication is considered a key factor for the extension of network lifetime. Formerly, a large number of medium access control (MAC) protocols have been proposed to improve energy efficiency to prolong the network lifetime. There are applications that generate different types of data packets and require quality of service (QoS) without any disruption in network operation. Therefore, these applications need an energy-efficient QoS MAC protocol that can support QoS by considering energy efficiency as the primary goal to avoid any failure in the network. This article proposes an energy-efficient asynchronous QoS (AQSen) MAC protocol, called AQSen-MAC. The AQSen-MAC considers different types of data packets and uses two novel techniques: self- adaptation and scheduling to enhance energy efficiency, packet delivery ratio, and network throughput. Furthermore, in the protocol, the receiver adjusts its duty cycle according to the remaining energy to prolong the network operation. Finally, the performance of the AQSen-MAC protocol has been evaluated through detailed simulation using Castalia and compared with MPQ-MAC, PMME-MAC, and QAEE-MAC protocols. The simulation results indicate that the AQSen-MAC protocol significantly reduces the energy consumption at the receiver of up to 13.4%, consumption per bit of up to 3% and improves the packet delivery ratio and network throughput of up to 12% in the network. 1. Introduction Internet of things (IoT) is a fast-growing technology and is playing a vital role in many applications such as smart home infrastructure [1], wearable devices [2], and building automa- tion [3]. The wireless sensor network (WSN) is a key compo- nent for the IoT [4–7]. A WSN consists of low-power, low- cost, and small-in-size sensor nodes, which have the ability to sense, measure, gather, and process information (i.e., conduc- tivity, temperature, and pressure) gathered from the sensor coverage area [8, 9]. The sensor nodes can communicate wire- lessly with each other. WSNs have a wide range of advantages in terms of scalability, deployment, simplicity, self-organizing capabilities, and others [10] and have many applications including smart cities, food quality, and environment monitor- ing, industrial process monitoring, and health-care [11–13]. In WSNs, sensor nodes are traditionally powered by small batteries with limited capacity [14–17]. Hence, energy efficiency plays an essential role in the lifetime extension [18–20]. This is due to some scenarios, for instance, volcano monitoring [21], where it is difficult to replace the battery; hence, it requires a longer operational time [22]. This has motivated the researchers to introduce energy-efficient schemes to prolong the network lifetime [7, 17]. The network lifetime is defined as the time elapsed until the failure of the first node due to energy depletion in the network [23]. For example, the wake-up radio approach helps the node to save energy by putting its main radio in the deep sleep mode [7, 24, 25]. The packet aggregation routing scheme proposed that reduces the transmission delay, amount of redundant data, and energy consumption by adjusting the forwarder nodes and duty cycle in body sensor networks [22]. Recently, Hindawi Wireless Communications and Mobile Computing Volume 2020, Article ID 8860371, 13 pages https://doi.org/10.1155/2020/8860371