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A Wireless sensor network (WSN) has important applications such as remote ecological monitoring and target tracking. This has been enabled by the availability, particularly in recent years, of sensors that are smaller in size and smart. These sensors are equipped with wireless interfaces with which they can communicate with one another to form a network. Wireless sensor networks consist of sensor nodes with sensing and communication capabilities. As sensor nodes are generally battery-powered devices, the critical aspects to face concern how to reduce the energy consumption of nodes, so that the network lifetime can be improved to reasonable times. In this paper we first describe the energy consumption for components of a typical sensor node, and discuss the main directions to energy saving methods in wireless sensor networks. Then we present a methodical and comprehensive taxonomy of the energy optimization methods in wireless sensor networks. The main goal of energy optimization methods is to collect and aggregate data in an energy efficient manner so that network life time is enhanced. We conclude with possible future research directions. KeywordsWireless sensor network (WSN), Multiple-input Multipleoutput, Energy efficiency, Alamouti diversity schemes.

Precision agriculture is a process in which information and technology is used for collection of high resolution spatio-temporal data regarding atmospheric and soil conditions from farm land. With the help of farm land data and an appropriate crop-growth model, a decision support system regulates the agricultural needs precisely in order to gain maximum benefits for farmer. Application of Wireless Sensor Networks (WSN) provides a low cost and easy to implement solution for automatic data collection from farmlands. Various design issues for WSN in context of precision agriculture have been reviewed in this paper. Humidity (RH) sensors play a crucial role for WSN for precision agriculture applications. This paper also reviews various requirements of Humidity sensors characteristics in context of WSN application for precision agriculture. In the later section of the paper, in depth comparative review of recent research work done in field of design and performance modeling of humidity sensor has been given.

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