Networking Issues in wireless sensor networks and the Data Aggregation problem: A survey

In recent years, a great deal of research has been devoted to wireless sensor networks (WSNs). WSNs are networks consisting of small self-powered devices that communicate with each other over the wireless medium and coordinate their operation in order to perform distributed sensing near physical phenomena. The total lifetime of the network is a major design factor for protocols, applications and in general algorithms used by a WSN. Therefore, it is always a good choice to avoid the transmission of big amounts of data. Each sensor node produces locally raw data upon sensing events. These data usually flow to a central node (called sink) that collects them for further processing. Such a traffic pattern tends to exhaust the limited resources of the sensor network (including the energy). In-network processing and in particular the data aggregation techniques, try to reduce the traffic inside the network by trading the expensive, in terms of energy, communication for local computation at each node. In this paper, we firstly point out the main networking challenges for a WSN and give an overview of the data aggregation problem. Then we continue by presenting a taxonomy of the most representative aggregation techniques. We finally discuss the main trade-offs that result from the use of data aggregation and conclude our work.