This chapter presents an overview of multimedia information transmission over Wireless Sensor Networks (WSNs). These WSNs have evolved since the 1980s and their evolution can be divided into three generations. Wireless Multimedia Sensor Networks (WMSNs) have become viable in recent years with the availability of inexpensive video cameras, increase in procession power and memory capacity of nodes, and better power sources and their management. Multimedia information requires higher bandwidth and lower delay and delay jitter to provide the required Quality of Service (QoS) for multimedia transmission. Further research is being conducted, and can be taken even further, in the areas of advanced algorithms for content capture, compression and communication of multimedia information over WSNs.
TopIntroduction
A Wireless Sensor Network (WSN) is a system of distributed nodes connected by wireless communication technologies. Each node performs the function of sensing some physical parameter, such as temperature and pressure, and passing on the captured information to one or more destination nodes. Each node in the WSN can also be involved in routing the information from the source to the destination.
While early WSNs tended to capture and transmit only low volume data, newer systems are being developed to capture and transmit multimedia information as well. In general, multimedia information requires much higher bandwidth for timely transmission. Furthermore, multimedia content, in general, and video in particular, is adversely affected by transmission impairments such as delay and jitter.
The objectives of this chapter are to:
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Present an overview of the evolution of Wireless Sensor Networks, and multimedia transmission in such networks.
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Discuss factors such as bandwidth, delay and delay jitter and how these influence the Quality of Service (QoS) in the delivery of multimedia information.
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Explore the special issues and limitations related to Wireless Sensor Networks, such as limited energy, computational power, and bandwidth.
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Discuss current and further research directions in coding, compression and communication of multimedia information.
TopWireless Sensor Networks Overview
Wireless Sensor Networks (WSNs) are essentially wirelessly connected sensors that can monitor the physical environment in which these are deployed. The parameters monitored by these sensors can include temperature, sound volume, vibration, pressure, motion, machine wear, and even the concentration of pollutants in the environment.
Originally WSNs were developed for military applications such as the surveillance of a battlefield. As often happens, these have now found many industrial as well as civilian application, such as: industrial process monitoring, machine health monitoring, environment and habitat monitoring, healthcare, home automation, and traffic control (Kay & Mattern, 2004).
Each node in a WSN contains one or more sensors. Some nodes are designed such that different sensors can be plugged in a motherboard, as required. Each note also comprises a radio transceiver linked to other wireless communications components, a low power microcontroller, and some power source, such as a battery or a solar cell (Kay & Mattern, 2004).
These sensor nodes can vary considerably in terms of size and complexity. Often the size and the cost of the node are linked to the node’s performance and properties such as: power source, its capacity, memory size, computational speed and communication bandwidth (Kay & Mattern, 2004).
A complete WSN if built using a wireless ad-hoc network, i.e. a network in which the routing of data from a source to a destination node is based on a multi-hop routing algorithm, in which the same data packet may be forwarded via multiple routes to the destination nodes. Such protocols are not the best for transmitting multimedia information. Therefore, many new communication protocols have been developed to address issues related to the environment and applications where WSNs are deployed.