Abstract
When camera-enabled sensors are deployed for visual monitoring, a new set of innovative applications is allowed, enriching the use of wireless sensor network technologies. In these networks, energy-efficiency is a highly desired optimization issue, mainly because transmission of images and video streams over resource-constrained sensor networks is more stringent than transmission of conventional scalar data. Due to the nature of visual monitoring, that follows a directional sensing model, camera-enabled sensors may have different relevancies for the application, according to the desired monitoring tasks and the current sensors’ poses and fields of view. Exploiting this concept, each data packet may be associated with a priority level related to the packet’s origins, which may be in turn mapped to an energy threshold level. In such way, we propose an energy-efficient relaying mechanism where data packets are only forwarded to the next hop if the associated energy threshold level is below the current energy level of the relaying node. Thus, packets from low-relevant source nodes will be silently dropped when the current energy level of intermediate nodes run below the pre-defined thresholds. Doing so, energy is saved potentially prolonging the network lifetime. Besides the sensing relevancies of source nodes, the relevance of DWT subbands for reconstruction of original images is also considered. This allows the creation of a second level of packet prioritization, assuring a minimal level of image quality even for the least relevant source nodes. We performed simulations for the proposed relaying mechanism, assessing the expected performance over a traditional relaying paradigm.
Highlights
In recent years, Wireless Sensor Networks (WSNs) have raised a lot of attention of both industry and academic communities
We propose in this paper an energy-efficient packet relaying mechanism, where packets are relayed to the hop according to the residual energy level of intermediate nodes and predefined energy thresholds
The standard relaying functionality in the framework Castalia [37] was adapted to execute our packet selection algorithms. They read the SR(s) included in each data packet to decide if it will be forwarded to the hop or silently dropped, according to the current energy level and predefined energy thresholds
Summary
Wireless Sensor Networks (WSNs) have raised a lot of attention of both industry and academic communities. WSNs are composed of self-organizing electronic devices equipped with a short-range wireless transceiver, limited energy supply (usually batteries), a sensing unity and processing and memory resources [1,2], addressing applications as surveillance, tracking, disaster monitoring, home automation, industrial control, battlefield surveillance, among others. VSNs are composed of one or more camera-enabled source nodes for a series of innovative multimedia sensing functions, where visual information retrieved from the monitored field in the form of video streaming, conventional snapshots, infrared or thermal images can significantly enhance a large set of monitoring applications [5,6]. Images captured by visual sensors are packetized and transmitted to the sink of the network, where data packets are relayed by intermediate nodes in a hop-by-hop many-to-one manner. As packet relaying consumes energy and transmission paths may be disabled due to energy depletion of intermediate nodes, the total amount of information transmitted over the network should be minimized, saving energy with reduction of packet relaying and potentially prolonging the network lifetime
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