Sensors_**2009**, \(9\), 6869-6896; doi:10.3390/s90906869  
[1]_Sensors_**ISSN 1424-8220**  
www.mdpi.com/journal/sensors  
_Review_  
[2] An Overview on Wireless Sensor Networks Technology and Evolution  
[3] [PERSON] \({}^{1,\star}\), [PERSON] \({}^{2}\), [PERSON] \({}^{1}\) and [PERSON] \({}^{1}\)  
[4] WiLAB, DEIS at University of Bologna, Bologna, Italy; E-Mails: [EMAIL_ADDRESS] (D.D. ); [EMAIL_ADDRESS] (R.V.) [5] WiLAB, ENDIF at University of Ferrara, Ferrara, Italy; E-Mail: [EMAIL_ADDRESS] (A.C.)  
[6]Author to whom correspondence should be addressed; E-Mail: [EMAIL_ADDRESS]; Tel. : +39-051-2093549; Fax: +39-051-2093540. _Received: 25 July 2009; in revised form: 24 August 2009 / Accepted: 25 August 2009 / Published: 31 August 2009_  
[7]**Abstract:** Wireless sensor networks (WSNs) enable new applications and require non-conventional paradigms for protocol design due to several constraints. Owing to the requirement for low device complexity together with low energy consumption (i.e., long network lifetime), a proper balance between communication and signal/data processing capabilities must be found. This motivates a huge effort in research activities, standardization process, and industrial investments on this field since the last decade. This survey paper aims at reporting an overview of WSNs technologies, main applications and standards, features in WSNs design, and evolutions. In particular, some peculiar applications, such as those based on environmental monitoring, are discussed and design strategies highlighted; a case study based on a real implementation is also reported. Trends and possible evolutions are traced. Emphasis is given to the IEEE 802.15.4 technology, which enables many applications of WSNs. Some example of performance characteristics of 802.15.4-based networks are shown and discussed as a function of the size of the WSN and the data type to be exchanged among nodes. **Keywords:** wireless sensor networks; enabling technologies; applications; IEEE 802.15.4 Introduction  
Since the start of the third Millennium, wireless sensor networks (WSNs) generated an increasing interest from industrial and research perspectives [1; 2; 3; 4; 5; 6; 7]. A WSN can be generally described as a network of nodes that cooperatively sense and may control the environment enabling interaction between persons or computers and the surrounding environment [8]. On one hand, WSNs enable new applications and thus new possible markets, on the other hand, the design is affected by several constraints that call for new paradigms. In fact, the activity of sensing, processing, and communication under limited amount of energy, ignites a cross-layer design approach typically requiring the joint consideration of distributed signal/data processing, medium access control, and communication protocols [9]. This paper provides a survey of WSNs technologies, main applications and standards, features in WSNs design with case study, and evolutions. In particular example of performance based on experimental results will be reported. With respect to the literature [1; 2; 10] this paper deals not only with applications and features of WSNs, or only on design of WSNs, but puts together all these aspects, focusing also the attention on technologies and standards. WSNs have several common aspects with wireless ad hoc network [11] and in many cases they are simply considered as a special case of them. This could be lead to erroneous conclusions, especially when protocols and algorithms designed for ad hoc networks are used in WSN. For this reason in Section 2 an appropriate definition of WSN and discussion is provided. In Section 3, the main application areas for WSNs are categorized according to the type of information measured or carried by the network. Applications, on top of the stack, set requirements that drive the selection of protocols and transmission techniques; at the other end, the wireless channel poses constraints to the communication capabilities and performance.