In a wireless sensor network, energy is almost always the greatest limitation. Energy sources are restricted in many of the environments where nodes are deployed, limiting them to the use of batteries for power. Therefore, conserving energy is supremely important, however, such a task poses many challenges to hardware and protocol design. One of the greatest problems faced is reducing the energy consumption of the communications systems, which represents a substantial amount of the total consumption. This paper surveys the most recent schemes designed to reduce the communications module energy consumption with a focus on novel MAC protocols for ad-hoc wireless sensor networks. It initially describes the many challenges involved, then it analyses each protocol individually. Finally, the presented protocols are compared and the issues that remain open are raised for further research.

Wireless sensor networks are an emerging technology that is used to monitor points or objects of interest in an area. Despite its many applications, this kind of network is often limited by the fact that it is difficult to provide energy to the nodes continuously, forcing the use of batteries, which restricts its operations. Network density may also lead to other problems. Sparse networks require stronger transmissions and have little redundancy while dense networks increase the chances of overhearing and interference. To address these problems, many novel medium access control (MAC) protocols have been developed through the years. The objective of this study is to assess the effectiveness of the T-MAC, B-MAC, and RI-MAC protocols in a variable density network used to collect data inside freight trucks carrying fruits that perish quickly. This article is part of the PrunusPós project, which aims to increase the efficiency of peach and cherry farming in Portugal. The comparison was done using the OMNET++ simulation framework. Our analysis covers the behavior and energetic properties of these protocols as the density of the network increases and shows that RI-MAC is more adaptable and consumes less energy than the alternatives.

O estudo e implementação de redes de sensores sem fios é um campo emergente da eletrônica que está muito interligado com a internet das coisas. Juntas essas duas tecnologias possibilitam a recolha e transmissão de dados em cenários ondes redes comuns não são adequadas. Entretanto, devido às limitações usuais que são impostas aos equipamentos usados, a conservação de energia se torna indispensável para a sua utilização. Por conta disso, foram criados diversos mecanismos para redução no consumo de energia, uma grande parte das quais passa pela implementação de novos protocolos MAC. Este artigo explica como podem ser feitas implementações desse tipo de protocolo em um simulador, o que permite que se avalie o seu desempenho sem os custos associados com estudos no mundo real. Para tanto, foram comparados os simuladores mais comuns usados neste campo de estudo e o OMNeT++ foi escolhido como o mais adequado. Depois disso foi feita uma demonstração prática de como implementar um protocolo MAC nesse simulador e os resultados da simulação foram analisados.