Article Preview
Top1. Introduction
During the last decade, the emphasis was on finding a method that saves energy in WSNs by employing different techniques. DC is the most important among the proposed ones, which is broadly used by different hardware levels and protocol layers. Despite the numerous types of DC, none is applicable for all scenarios. For instance, some applications need fast and timely responsiveness, as in health-care domain, while others do not put strict conditions on delay as in agriculture. Thus, in the former type, dynamic DC is required while in the later low DC is needed. Indeed, there is still much research going on, mostly to optimize DC usage while taking into account different limitations in such networks.
1.1. Contributions
Contrary to the existing work that discuss DC schemes, the present work gives a detailed review on each scheme. Furthermore, it proposes a new DC classification according to different points of view including synchronization time, implementation level, schedule behavior and DC behavior. Thanks to a detailed analysis, the first objective of the present study is to help to better understand the difference between each DC type.
Furthermore, many works have focused recently on shortening DC length, and today different protocols operate with low DC. Most recently extremely low DC is considered. So, we believe that investigating the impact of low DC while taking into consideration the requirements of QoS is still be needed.
Recalling that almost all applications of WSNs need to forward data to a sink, it is necessary to find an awakened forwarder anytime. In other words, there is an urgent requirement to keep nodes connected all over time. For that, several network tasks will be concerned by this requirement, especially the neighbor discovery and the routing ones. Hence, low DC gives them a real challenge to keep the network operational. So, we are seeking to answer the following questions:
- 1.
How low DC affects the network?
- 2.
Will lowering DC for nodes over time be advantageous?
- 3.
How DC scheme can be efficient?
In summary, this paper studies and analysis how low DC affects the network layer behavior. Consequently, it helps to design better solutions. For this purpose, we analyze its position versus different QoS properties. Then, we try to find what are the types of DC that are commonly used in diverse application domains.
1.2. Paper Organization
The remainder of this paper is organized as follows: section 2 reviews the different energy saving techniques. Section 3 discusses the main properties of an efficient DC scheme. Section 4 proposes a taxonomy for different DC schemes that exist in the literature. The position of DC versus different QoS parameters is studied in section 5. In section 6, low DC is presented then its impact on the network and application layers is discussed. Finally, the section 7 concludes the paper.
2. Energy Saving Techniques
Energy saving is a major challenge in WSNs, as the nodes have limited power resources. Such purpose which is recently a hot research interest topic may be achieved by applying energy conservation schemes such as DC. In the literature many works have been proposed, in (Anastasi, 2009b) an interesting taxonomy of energy conservation schemes is given. However, in (Rault, 2014) the authors argue that such taxonomy mainly focuses on duty cycling and data-reduction. Thus, they gave and discuss a new classification of energy conservation schemes from recent literature. Different approaches are employed, and each one uses a specific mechanism which we classify in two main classes including hardware and software based solution, as summarized below.