MAC Protocols for WuR Enabled WSNs : Design and Performance Evaluation

Master's thesis Information- and communication technology IKT591 - University of Agder 2017Increasing energy efficiency is a challenging task for protocol design in wireless sensor networks (WSNs) as well as in Internet of things (IoT). Traditionally, duty-cycled (DC) protocols have been widely adopted for data transmissions in WSNs for energy conservation by reducing idle listening and overhearing. Recently, wake-up radio (WuR) has merged as a promising technique to replace DC protocols thanks to its superior performance in both network lifetime and transmission latency. This thesis work focuses on the design and performance evaluation of WuR-enabled MAC protocols considering various traffic conditions and network topologies. As the first step, we investigate the niche of WuR by putting forward a question: Does WuR always consume lower energy than DC protocols? Through in-depth analysis, we ascertain the outstanding energy performance of WuR at light traffic loads. At the same time, we reveal its disadvantages at heavy traffic loads. Secondly, we propose a WuR protocol that is capable of avoiding WuC collisions by enabling a contention-based collision avoidance mechanism for WuC transmissions. The performance of the proposed protocol is evaluated by a Markov chain based mathematical model. Numerical results indicate that our proposed protocol achieves higher packet delivery radio (PDR) and network throughput, with the cost of slightly longer packet delay, compared with an existingWuR protocol. Thirdly, we propose another WuR protocol, referred to as EHA-WuR, which is designed to avoid energy hole in multi-hop networks for multipoint-to-point transmissions. Three operation modes are designed for EHA-WuR. The proposed protocol is implemented in Omnet++ simulator. Numerical results indicate that EHA-WuR significantly extends network lifetime compared with the traditional hop-by-hop operation mode. Key words: Wireless sensor networks, Internet of things, Wake-up radio, Collision avoidance, Energy hole proble

Energy Efficiency inWireless Sensor Networks: Transmission Protocols and Performance Evaluation

Doktorgradsavhandling, Fakultet for teknologi og realfag, Universitetet i Agder, 2016Energy efficiency is one of the major goals for achieving green wireless communications. The recent growth in ubiquitous wireless connections and multimedia applications demands higher energy efficiency for wireless communications. As a part of this picture, wireless sensor networks (WSNs) need to be more energy efficient since the battery capacity of nodes in such networks is limited in the absence of energy harvesting sources. In general, an energy efficient protocol should perform as few as possible operations when delivering user information successfully across the network. Energy efficient data transmission schemes could utilize network resources more effectively to lower down the energy consumption level. In this dissertation research, we focus on improving energy efficiency for data transmission and medium access control (MAC) protocols in WSNs. While energy consumption is inevitable for transmitting and receiving data in a WSN, the other typical and dominant energy consumption activities are idle listening, overhearing, and retransmissions due to unsuccessful transmission attempts. An energy efficient MAC protocol conserves energy by minimizing all these auxiliary operations in order to prolong network lifetime. On the other hand, balanced energy consumption among nodes which mitigates energy hole across a WSN also helps to extend network lifetime. In this context, we propose two cooperative transmission (CT) based energy balancingMAC protocols for the purpose of WSN lifetime prolongation. The first one is an asynchronous cooperative transmission MAC protocol, in which nodes generate their own wakeup schedules based on their level number in a WSN topology. The second one is a receiver initiated cooperative transmission MAC protocol in which the CT is initiated by a relay node. It is demonstrated that both proposed CT MAC protocols are able to achieve significantly extended network lifetime. In addition, an energy conserving sleeping mechanism for synchronous duty cycling MAC protocols is also proposed in this thesis. It is an eventtriggered sleeping (ETS) mechanism, which triggers the sleep mode of a node based on the incoming traffic pattern to that node. The ETS mechanism eliminates overhearing in a WSN and achieves higher energy efficiency. Furthermore, we apply packet aggregation at the MAC layer in WSNs for achieving more energy efficient data transmission. In aggregated packet transmission (APT), multiple packets are transmitted as a batch in a frame within a single duty cycle instead of transmitting merely one packet per cycle. Numerical results demonstrate that APT achieves higher throughput and shorter delay, in addition to higher energy efficiency. To evaluate the performance of the proposed MAC protocols and transmission schemes, we develop discrete time Markov chain (DTMC) models and verify them by comparing the results obtained from both analysis and discrete-event based simulations. The analytical and simulation results match precisely with each other, confirming the effectiveness of the proposed protocols and schemes as well as the accuracy of the developed models