Wireless Multimedia Sensor Networks (WMSNs) are attracting attention from both academic and industrial environments due to the rapid development of low-cost multimedia sensors. With the enhancement... Show More

Wireless Multimedia Sensor Networks (WMSNs) are attracting attention from both academic and industrial environments due to the rapid development of low-cost multimedia sensors. With the enhancement of the multimedia content captured by multimedia devices, WMSNs play an important role in pervasive and ubiquitous systems. The multimedia content in these networks has the potential to enhance the level of collected information, by enlarging the range of coverage, and enabling multi-view support. In the case of WMSN applications, the multi-tier network architecture has proved to be more beneficial than single-tier architecture in terms of energy-efficiency, scalability, functionality and reliability. In this context, a multimedia event detection application is a promising application for multi-tier WMSNs, where the lower-tier nodes detect an event occurrence by means of scalar measurements, and the higher-tier nodes will be woken up to send real-time video flows from the event area. The transmission of multimedia content requires a certain quality level from the user's perspective, while energy consumption and network overhead should be minimized. Among the existing mechanisms for improving video transmissions, application-level Forward Error Correction (FEC) is regarded as a suitable solution to improve video quality level from the user´s standpoint. In this work, the authors propose an adaptive cross-layer approach, which includes a Quality of Experience (QoE)-aware FEC mechanism for WMSNs by generating redundant packets, based on frame importance from user's experience. Additionally, the aothors introduce a multi-tier routing protocol to select the best route to transmit multimedia data. According to the simulation results, the proposed cross-layer approach achieved high video quality level with reduced transmission of redundant packets, which will bring many benefits to a resource-constrained system.

In this paper the authors present an approach to provide efficient low-complexity encoding for the block-based video coding scheme. The authors present a method based on removing the most... Show More

In this paper the authors present an approach to provide efficient low-complexity encoding for the block-based video coding scheme. The authors present a method based on removing the most time-consuming task, that is motion estimation, from the encoder. Instead the decoder will perform motion prediction based on the available decoded frame and send the predicted motion vectors to the encoder. The results presented are based on a modified H.264 implementation. The results show that this approach can provide rather good coding efficiency even for relatively high network delays.

Traditional transport layer protocols have been designed to perform end-to-end error control transparently to the intermediate nodes (e.g., TCP). To address the severe resource constraints featured... Show More

Traditional transport layer protocols have been designed to perform end-to-end error control transparently to the intermediate nodes (e.g., TCP). To address the severe resource constraints featured by Wireless Sensor Networks (WSN), new paradigms have been developed such as intermediate caching where intermediate nodes are able to cache packets and if possible retransmit them on-demand to avoid incurring costly end-to-end retransmissions. Lately, Wireless Multimedia Sensor Network (WMSN) has been considered as a new research area whereby WSNs are targeted for the delivery of multimedia traffic. In this paper, we propose a NACK-based repair mechanism coupled with an adaptive MAC layer retransmission scheme in order to improve the performance of caching-based WMSN transport protocols. Specifically, our goal is to be able to reduce real-time end-to-end delay while maintaining reliability and energy efficiency in the presence of high channel error rates. Our simulation results show that the ensemble of both mechanisms provides better good put performance while simultaneously improving energy efficiency. Furthermore, the improved protocol also achieves lower deadline miss ratios making it suitable for multimedia transport. While we demonstrate the effectiveness of the mechanisms by incorporating them into the basic Distributed Transport for Sensor Networks (DTSN) protocol, they are generic enough to be applicable to other WSN and WMSN transport protocols.

Prolongation of the lifetime has become a key challenge in design and implementation of Wireless Multimedia Sensor Networks (WMSNs). The energy consumed in multimedia sensor nodes is much more than... Show More

Prolongation of the lifetime has become a key challenge in design and implementation of Wireless Multimedia Sensor Networks (WMSNs). The energy consumed in multimedia sensor nodes is much more than in the scalar sensors; a multimedia sensor captures images or acoustic signals containing a huge amount of data while in the scalar sensors a scalar value is measured (e.g., temperature). On the other hand, given the large amount of data generated by the visual nodes, both processing and transmitting image data are quite costly in terms of energy in comparison with other types of sensor networks. Therefore, energy efficiency is a main concern in WMSNs. In this paper an energy efficient collaborative mechanism for monitoring is proposed. The proposed scheme employs a mixed random deployment of acoustic and visual sensor nodes. Acoustic sensors detect and localize the occurred event/object(s) in a duty-cycled manner by sampling the received signals and then trigger the visual sensor nodes covering the objects to monitor them. Hence, visual sensors are warily scheduled to be awakened just for monitoring the object(s) detected in their domain, otherwise they save their energy.