# On the Feasibility of Wireless Multimedia Sensor Networks over IEEE 802.15.5 Mesh Topologies
## 1 Introduction  
Wireless Sensor Networks (WSNs) [1] consist of a large number of low-cost and energy-constrained devices. These devices transmit data acquired by a number of in-built sensors to one or several data collection units, named data sinks, which are in charge of sending data to remote database servers for further data processing and storage. Wireless Multimedia Sensor Networks (WMSNs) [2] are regarded as a particular type of WSN where nodes are interfaced with sensors for visual and sound data acquisition, such as Complementary Metal Oxide Semiconductor (CMOS) cameras and microphones. This technology has drawn the attention of the WSN research community, encouraged by the challenge of providing support applications such as video surveillance, environmental monitoring, target tracking and traffic management, where multimedia services are required. Compared with low-data-sampling, low-data-transmission rate WSN applications, multimedia applications impose stringent requirements in terms of high sampling rate, data transmission reliability, data latency and data throughput. Reliable transmission of multimedia data in WMSNs is challenging due to the inherent technology limitations, such as interference between devices orlimited data transmission bandwidth. Multimedia communications also require a high utilization of the transmission channel, increasing communication activity within the network and considerably decreasing the operational lifetime of battery-powered nodes. This clearly contrasts with the traditional WSN/WMSN requirements imposed by, on the one hand, the use of short-range communications over low-bandwidth links (maximum bitrate of 250 kbps at 2.4 GHz) and, on the other hand, the energy constraints of sensor devices. Traditional routing in WSNs is also a problem in WMSNs. Many state-of-the-art multi-hop proposals for WSNs consider tree-based topological configurations where only a few number of nodes are likely to forward all the data traffic. Because of the intensive use of these nodes, the network may not fulfil the Quality of Service (QoS) required by the multimedia application and, more importantly, it will lead to the overuse and depletion of the batteries of nodes in the path. In addition, traditional routing mechanisms usually only deal with the transmission to a sink node and not to any arbitrary node of the network, which hampers the development of collaborative applications or the use of multiple sinks. Mesh topologies, in addition to enabling multiple routing paths between two nodes outside of radio communication range with each other, have proven advantages against other topological configurations, such as tree-based or cluster-based topologies, which include data transmission reliability, network robustness against node failures, and potential reduction in energy consumption [3]. Nodes arranged in a mesh topology are generally easier to deploy and potentially easier to maintain as they are able to reconfigure themselves in order to adapt to the conditions brought by the deployment environment. Among the different mesh solutions available for low-power wireless networks, the low-rate part of the IEEE 802.15.5 (hereafter IEEE 802.15.5) [4] offers suitable functionalities for enabling multimedia applications compared with other state-of-the-art network/MAC layer standards. This standard assures that any node is able to communicate with any other node of the network through different routes, enhancing data transmission reliability and robustness against node failures. It also emphasizes simplicity, adding, for low-rate WPAN, a thin mesh sublayer on top of the IEEE 802.15.4 MAC sublayer, the most widely adopted point-to-point communication standard for low-rate wireless personal area networks (LR-WPANs). This results in an easy migration of applications using the 802.15.4 standard and in a greater scalability, enabling large-scale deployments. In addition, the standard provides two radio duty-cycle mechanisms, named Asynchronous Energy Saving (ASES) and Synchronous Energy Saving (SES).