Wireless sensor networks (WSN) are rapidly emerging as an interesting and challenging area of research in the field of communication engineering. This review work is different from other state-of-the-art literature as the MAC protocols discussed here are applicable both for homogeneous and heterogeneous networks. Performances like energy efficiency, cost optimization, throughput, bandwidth utilization, and scalability of the sensor network depend on MAC protocols, which are application-based. In the study, the authors have surveyed different MAC protocols with different merits and demerits. Based on the study, it is very hard to recommend any particular protocol as a standard for implementation as these are exclusively application dependent. The work can be further extended in terms of hybrid protocols, which may carry the advantages of the respective protocols along with energy-efficient criteria for practical implementation. Further cooperative WSN communication can be used for internet of things (IoT)-based systems, where the node placements and multi-operations concepts are of main concern.
TopIntroduction
Wireless Sensor Network (WSN) consists of distributed autonomous sensor nodes which are used to monitor different environmental conditions like temperature, pressure, humidity, noise level, light intensity, etc. These nodes cooperatively send their information to the central unit or base station. WSN finds applications in remote monitoring, target tracking, automation and traffic control (Pegatoquet et.al 2018, Salman 2014, Heidemann & Estrin 2004, Qian & Waltenegus 2012). A WSN consists of wireless units called nodes. Each sensor node incorporates a processing unit, a power unit and a communication unit as illustrated in Figure 1.
Sensor nodes located in monitored areas coordinate to form a network through the access mechanism of self-organization. These nodes transmit the monitored data through other nodes one after another (Demirkol et.al. 2006). Figure 2 shows the architecture of WSN, which consists of a source (as of end-user) and a sink connected through the internet and the sensing operation is performed using the wireless sensors.
As the sensor nodes used in most of the applications are battery-powered devices, most of the challenges are focused on how to increase the lifetime of each sensor node and how to reduce energy consumption in the nodes, thus implicating greater network energy efficiency. Network lifetime is represented as the time passed from the path operation starts till the first node (or last node) in the path expends its energy (dies). Generally, the activity of the nodes depends upon its transmission and reception of information. On the other way, it performs other activities like redundant control packets broadcast, re-transmission due to collision, overhearing, and idle listening. These unnecessary node operations increase energy consumption and hence reduce the network lifetime. So, to avoid these unnecessary activities, many energy-efficient MAC protocols are proposed. Here, WSN multiple nodes may transmit information on the same shared channel at the same time. In such a situation, the transmitted information would get distorted unless a suitable medium access attribution scheme is deployed. Usually to perform this task MAC protocols are implemented in the data link layer. The traditional wireless MAC protocols (IEEE 802.11) are having many constraints. The main problem is that the nodes used are battery-driven, so sensor network applications are limited (Yang et al. 2018, Liu et al. 2018, Halkes et al. 2005).
This review work is different from other state-of-the-art review papers as the MAC protocols discussed here are applicable both for homogeneous and heterogeneous networks. In this paper, we discussed the different MAC protocols and their classifications. The rest of the paper is organized as follows. In section 2, we discuss the different challenges of MAC protocols in WSNs. Different merits and demerits of MAC are described in section 3. Then a comparison of all protocols is discussed in section 4. Finally, the behavioral analysis of MAC protocols is explained and concluded in section 5.
TopMedium Access Protocols
MAC protocols play an important role in accessing the same channel in the wireless communication system. For the design of MAC Protocols, there are many factors like collisions, overhead, overhearing, complexity, idle listening, Quality of Service (QoS), etc. where maximum energy consumption is required. Since energy consumption is very important for sensor nodes as they are battery powered, the design of MAC protocols throughput, fairness, and the end to end delay are relevant to the Quality of Service(Enz et al. 2004, Ray & Turuk 2009, Li et al. 2018).