Sensors_**2010**, _10_, 6662 - 6717; doi:10.3390/s100706662  
_Series_  
**ISSN 1424-8220**  
www.mdpi.com/journal/sensors  
_Article_  
**Wireless Multimedia Sensor Networks: Current Trends and Future Directions**  
**[PERSON] \({}^{1,\star}\), [PERSON] \({}^{1}\), [PERSON] \({}^{2}\) and [PERSON] \({}^{1}\)**  
\({}^{1}\) Computer Architecture Department, Technical University of Catalunya, Barcelona, Spain;  
E-Mails: [EMAIL_ADDRESS] (M.G.Z. ); [EMAIL_ADDRESS] (J.M.P.) \({}^{2}\) Computer Engineering Department, The Hashemite University, Zarqa, Jordan;  
E-Mail: [EMAIL_ADDRESS] (J.N.A.-K.)  
\(\star\) Author to whom correspondence should be addressed; E-Mail: [EMAIL_ADDRESS];  
Tel. : +34 9340 11655  
_Received: 27 May 2010; in revised form: 20 June 2010 / Accepted: 25 June 2010 / Published: 9 July 2010_  
**Abstract:** Wireless Multimedia Sensor Networks (WMSNs) have emerged and shifted the focus from the typical scalar wireless sensor networks to networks with multimedia devices that are capable to retrieve video, audio, images, as well as scalar sensor data. WMSNs are able to deliver multimedia content due to the availability of inexpensive CMOS cameras and microphones coupled with the significant progress in distributed signal processing and multimedia source coding techniques. In this paper, we outline the design challenges of WMSNs, give a comprehensive discussion of the proposed architectures, algorithms and protocols for the different layers of the communication protocol stack for WMSNs, and evaluate the existing WMSN hardware and testbeds. The paper will give the reader a clear view of the state of the art at all aspects of this research area, and shed the light on its main current challenges and future trends. We also hope it will foster discussions and new research ideas among its researchers. **Keywords:** wireless multimedia sensor networks; wireless sensor networks; multimedia delivery; survey Introduction  
The field of Wireless Sensor Networks (WSNs) is receiving much attention in the networking research community and as an interdisciplinary field of interest. WSNs are becoming more low-cost, low-power, multi-functional, and viable due to the advances in micro-electro-mechanical systems (MEMS), low power and highly integrated digital electronics, and proliferation of wireless communications [1]. Wireless sensor networks (WSNs) typically consist of a large number of intelligent battery-powered sensor nodes with sensing, processing and wireless communicating capabilities [2]. The sensing circuitry measures simple ambient conditions, related to the environment surrounding the sensor such as temperature, humidity or light, and transforms them into an electric signal. Processing such a signal reveals some properties about objects located and/or events happening in the vicinity of the sensor. The sensor sends such collected data (called as scalar data), usually via radio transmitter, to a command center (sink) either directly or through multiple wireless hops [1; 3; 4]. WSNs have wide and varied applications such as real time tracking of objects, monitoring of environmental conditions, monitoring of health structures, and preparing a ubiquitous computing environment, _etc._[1]. The above mentioned characteristics impose a lot of restrictions on the WSNs design such as fault tolerance, scalability, production costs, network topology, operating environment, hardware constraints, power consumption, _etc._ These challenges have led to an intensive research in the past few years that addresses the potential collaboration among sensors in data gathering and processing. In most applications, the deployment area has no existing infrastructure for either energy or communication. Therefore, a basic requirement for sensor nodes is to be able to survive with a limited source of energy which is usually a small battery [5]. The network should stay alive and active for a duration of time that depends on the application of the deployed network, and that may last from several weeks to a few years.