An Introduction to Wireless Multimedia Sensor Networks

Wireless multimedia sensor networks (WMSNs) are a new and emerging type of sensor networks that contain sensor nodes equipped with cameras, microphones, and other sensors producing multimedia content. These networks have the potential to enable a large class of applications, ranging from assisting elderly in public spaces to border protection, that benefit from the use of numerous sensor nodes that deliver multimedia content. In this chapter, we investigate some of the new technology’s potential and describe typical characteristics of WMSNs. Then, we introduce the primary challenges in the state-ofthe-art in WMSNs. Finally, we discuss the existing solutions and possible future research trends. An Introduction to Wireless Multimedia Sensor Networks Krishanamachari, Estrin, & Wicker, 2002). Sources are data generators, which detect events and provide observations or measurements of physical phenomena. Sinks are designed to receive data sent by sources. Therefore, such nodes can monitor and act in the network performing some management functions. Besides, sinks can act as gateways between the WSN and an infrastructure network. Thus, sinks may also provide an interface to the user, allowing a manager to decide and act based on the data provided. This interface can be textual or multimedia, becoming a useful tool to network managers. Wireless multimedia sensor networks (WMSNs) are a new and emerging type of sensor network that contains sensor nodes equipped with cameras, microphones, and other sensors producing multimedia content; hence, quantified multimedia management is required. Multimedia management faces new challenges in WSNs concerned with provision of scalable quality of service (QoS) through the management of metrics, such as coverage (Tian & Georganas, 2002), exposure (Megerian et al., 2002), energy consumption (Zhao, Govindan, & Estrin, 2002) and application specific metrics (e.g., for target detection, possible metrics are miss detection and false detection ratios). Due to the ad hoc nature of WSNs -which might be deployed in hostile environments with fairly unpredictable conditions — multimedia management must be scalable, self-configurable and adaptive to handle such challenges. A classic approach is the data-centric design of WMSNs, which aims for the integration of applicationlevel and network-level operations to provide power-efficient solutions. These networks have the potential to enable a large class of applications. The following paragraphs describe some of these applications. Multimedia surveillance sensor networks. Video-based wireless sensor networks are composed of interconnected, battery-powered miniature video cameras, each video and audio sensor camera packaged with a low-power wireless transceiver that is capable of processing and transmitting sensing video signals. This integration of video technology and sensor networks constitutes the fundamental infrastructure for new generations of multimedia surveillance systems, where many different media streams (audio, video, images, textual data, sensor signals) are concurred to provide an automatic analysis of the controlled environment and a real-time interpretation of the scene. Video and audio sensors are utilized as multimedia facilities to enhance and complement existing surveillance systems against crime and terrorist attacks. Dependable and large-scale video and audio sensor networks, to some extent, extend the ability of law enforcement agencies to monitor areas, public events, private properties, and borders. Traffic monitoring. Transportation is a sector that is expected to benefit from increased monitoring and surveillance. Traffic in the United States is growing at three times the rate of population growth and causing an estimated $75 billion loss annually due to traffic congestion; therefore, it might be possible to monitor traffic flow in major cities or highways and deploy services that offer traffic routing advice to avoid congestion. Wireless magnetic sensor networks offer a very attractive, low-cost alternative to current technologies such as inductive loops, video cameras and radar for traffic measurement in freeways, urban street intersections, and presence detection in parking lots. In addition, smart parking advice systems (Campbell et al., 2005) WMSNs also allow for monitoring available parking spaces and provide drivers with automated parking advice; thus improving mobility in urban areas. Furthermore, multimedia sensors are installed along major highways; the digital multimedia sensor network gathers lane-by-lane data on travel speeds, lane occupancy, and vehicle counts. Besides, these sensors could also detect violations and autonomously report video streams. These basic data elements An Introduction to Wireless Multimedia Sensor Networks make it possible for law enforcement agencies to identify the violator, to calculate average speeds and travel times, or to buffer images and streams in the case of accidents for subsequent accident scene analysis. Biomedical applications. A prodigious amount of hospital centers are exploring applications of WMSNs technology to a range of medical applications, including pre-hospital and in-hospital emergency care, disaster response, and stroke patient rehabilitation. WMSNs have the potential to affect the delivery and study of resuscitative care by allowing vital signs to be collected and integrated automatically into the patient care record and used for real-time triage, correlation with hospital records, and long-term observation (Shnayder et al., 2005). For instance, patients may carry medical sensors, with the remote access to 3G multimedia networks, to monitor vital parameters such as body temperature, blood pressure, pulse oximetry, oxygen saturation ECG, and breathing activity. Then, these heterogeneous medical sensors relay patients’ medical data over a short-range wireless network to any number of receiving devices, including PDAs, laptops, or ambulance terminals. Furthermore, remote medical centers will perform advanced remote monitoring of their patients via video and audio sensors, location sensors, and motion or activity sensors (Hu et al., 2005). An attempt has been made to implant 100 microsensers within the human eye. This allows the patients with no vision to gain limited vision to see at an acceptable level ( Schwiebert, Gupta, & Weinmann, 2001). Researchers have made limited efforts in the field of biomedical, using multimedia such as data acquisition glove (PI Lawrence Hermansen, 2001) and body wearable sensors (PhiloMetron, 2002), as shown in Figure 1a and 1b, respectively. Habitat sensing and seismic monitoring. Several projects on habitat monitoring that use acoustic and video feeds are being envisaged, in which information has to be conveyed in a time-critical fashion. One collaborative project has been initiated between the University of New South Wales, Portland State University, and National ICT Australia aimed to deploy wireless acoustic sensor networks on tropical Queensland in Northern Australia. These networks used automatic recognition of animal vocalizations to census the populations of native frogs and the invasive toads (Hu et al., 2005). The goal of this project was to develop a habitat-monitoring kit (see Figure 2a) that enabled volunteers to determine which areas they needed to target and which areas could be left alone, allowing for workers to be used more efficiently rather than spending time doing broad sweeps of the area in search of the toad. More than a thousand audio sensors were deployed in Northern Queensland. Each sensor has a microcontroller, a Figure 1. Sensors for biomedical applications (a) Human Body an Internet Data Source (b) Data Acquisition Glove (DAG) An Introduction to Wireless Multimedia Sensor Networks low-power radio, memory, and batteries. Not only were audio sensors scattered to collect acoustic samples, but they also performed preliminary processing on the samples to reduce the transmission size and environmental noise of the data that are periodically sent to computer base stations. In 2002, Intel Research Laboratory at Berkeley initiated a collaborative project with the College of the Atlantic in Bar Harbor and the University of California at Berkeley to deploy wireless sensor networks on Great Duck Island, Maine. Their goal was to establish habitat-monitoring kit for researchers worldwide. Reconnaissance and surveillance. WMSNs could replace single high-cost sensor assets with large arrays of distributed sensors for both security and surveillance applications. The WMSNs sensors that allow retrieving video stream and audio signals are smaller and more powerful than sensor assets presently in the inventory. The extensions concerning video and audio signal processing make WMSNs deployable by untrained troops in essentially any situation. Over the past several years, the primary challenge facing military wireless sensor networks is accurate identification of signal being sensed. At the very beginning, military wireless sensor networks run vibration detection algorithms based on energy threshold (Li et al., 2002). Although this is a concise technique, it is subject to false alarms, leading to a desire for more sophisticated spectral signature algorithms. Currently, with the large-scale deployment of multimedia sensors, the inclusion of multiple sensors enables fusion of different sensed phenomenology, leading to higher-quality information and decreased false alarm rates. Person locator service in fire detection and tracking application. Collecting real-time data from wildfires is important for life safety considerations and allows predictive analysis of evolving fire behaviour. One way to collect such data is to deploy sensors in the wildfire environment and thus estimate fire behaviour based on temperature reading retrieved from temperature sensors. Agilla is a small sensor-based system with mobile-agent paradigm, which is based on TinyOS that self-organize into networks for collecting real-time data in wildfire environments (Fok, Roman, & Lu, 2005). Furthermore, multimedia content such as video streams and still images, along with advanced signal processing techniques, can be used to locate missing persons in a wildfire environment. Efficient industrial process control. As surveyed in Akyildiz, Melodia, & Chowdhury (2007), multimedia content including imaging, temperature, or pressure readings may be used for time-critical industrial process control. One of them is the chemical plants inventory management application area, which has benefited from multimedia sensor deployments. Tank management system Figure 2. Sensor for habitat sensing (a). Acoustic Sensors (b). Sensor deployment in Great Duck Island An Introduction to Wireless Multimedia Sensor Networks using sensor networks unlocks the value hidden within the supply chain by providing instant access to real-time tank inventory data, enabling both producers and their suppliers to more efficiently manage, schedule, and replenish inventory stocks to ensure a constant supply of raw materials and no interruptions to business operations (Xsilagy Inc., 2004). Another common industrial process profiting from WMSNs is monitoring machines for diagnostic and preventative maintenance purposes. As an example, the rolling machines at pulp and paper mills are massive, complex mechanisms. The smallest variations in the speed, temperature or alignment of the rollers can have serious effects on quality or operation. Wireless multimedia sensor networks equipped with acoustics sensors offer an ideal solution for investigating and resolving circumstances such as unanticipated variations in output quality, unusual vibration or noise, or other signs of potential problems. These ad hoc or overlay systems can be quickly installed and rapidly removed once problems are identified and resolved (Crossbow Technology, 2007). As investigated in the work proposed by Akyildiz, Melodia, & Chowdhury(2007), the growing interest in WMSNs has extended the horizon of traditional monitoring and surveillance systems. Firstly, the field of view of a single fixed camera to a certain extent is limited. In contrast, a distributed computing environment consists of various cameras and sensors that efficiently achieved perception of the environment from multiple disparate viewpoints. Secondly, the redundancy caused by various heterogeneous and overlapped sensors not only enhances the monitoring of an environment but also provides the same monitoring target or region with disparate viewpoint. Also, the joint operation of cameras and audio or infrared sensors can help to accurately identify disparate monitoring target. Thirdly, heterogeneous media streams can be acquired from the same point of view to provide a multi-resolution description of the scene and multiple levels of abstraction. As an illustrative case, a static medium camera with low-quality views can be enriched by views from zoom camera, which provides a high-quality view of a region of interest. Most applications introduced above require the traditional sensor network paradigm to be rethought in view of the need for mechanisms to deliver multimedia content with a certain level of quality of service (QoS). Since current research mainly concentrates on minimizing the energy consumption in wireless sensor networks, mechanisms to efficiently deliver application level QoS, and to map these requirements to network layer metrics such as latency and jitter, have not been primary concerns in mainstream research on classical sensor networks (Akyildiz, Melodia, & Chowdhury, 2007). In this chapter, we survey the state-of-the-art in deployment architecture and related novel protocols for the development of WMSNs. Furthermore, we discuss open research issues and emerging trends in details. In particular, in the second section we point out the heterogeneous characteristics of WMSNs. The third section describes a possible deployment architecture and discusses existing solutions for WMSNs. In the fourth section, we discuss future and emerging trends. Finally, we conclude the chapter.