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A breakthrough in multi-hop wireless multimedia sensor networking protocols

Beyond the conventional wireless sensor networks (WSNs) transmitting mainly small sensed and non-time-constrained data, the emerging hardware technologies such as complementary metal-oxide semiconductor (CMOS) cameras and microphones have fostered the development of wireless multimedia sensor networks (WMSNs), that is, networks of wirelessly interconnected heterogeneous devices that are able to ubiquitously retrieve multimedia content such as video and audio streams, still images, and scalar sensor data from the environment. Because of such enhanced capabilities, WMSN has been considered as an essential new technology with great potential for strengthening the traditional WSN applications, as well as creating new multimedia-data-oriented applications such as multi-camera surveillance, visual target/location tracking, location-based multimedia services, and situation/ context awareness. Furthermore, as tactical and mission critical environment intends to utilize more unmanned systems such as unmanned vehicles, aerial vehicles, drones, and robots, importance of reliable WMSNs is increasing. Recently, the standard activities for fifth-generation (5G) cellular communication, officially named ‘‘IMT-2020,’’ has been actively in progress and it plans to specify various communication/networking technologies for supporting a Massive Machine Type Communication (mMTC) targeting on Internet of Things (IoT) services and ultra-reliable and low-latency communications (uRLLC) targeting multimedia communications. With the deployment of IMT2020 which provides the majority of hardware infrastructure support for mMTC and uRLLC, WMSN has become an important supportive platform for sensing and transmission of Internet of Multimedia Things (IoMT). Many applications in IoMT benefit from WMSN technology, such as massive or wearable sensing devices. The recent survey paper, named ‘‘Routing in wireless multimedia sensor networks: A survey and challenges ahead,’’ shows that according to the Google, the research activities with video sensors and camera sensors are continuously increasing. In spite of aforementioned trends heading toward for WMSN, WMSN needs lots of issues to be resolved and enhanced. The objective of this Special Issue is to answer various open issues to provide more practical feasibility on WMSN. Due to the great effort made in publicity, we received 14 submissions from both academia and industry in the relevant fields. Following a strict review process, we accepted only five papers for this Special Issue. Each of the papers was peer-reviewed by at least two experts in the field. In the following, we provide a brief introduction to each paper. Multimedia data are playing an increasing role in WSN applications including target tracking, environmental video/imaging surveillance, telemedicine, video vehicle detection, and battlefield intelligence, in which users have specific quality of service (QoS) requirements on bandwidth, delay, and/or packet loss. Softwaredefined networking (SDN) primarily moves network control functions away from traditional routers to an external software entity called the controller. This simple abstraction makes for easy optimal path detection and on-demand resource allocation through the centralized control plane, thereby offering new opportunities for addressing QoS supporting problems in WMSNs. The paper ‘‘QoS-Aware Routing Mechanism in OpenFlow-Enabled Wireless Multimedia Sensor Networks’’ by L Han et al. introduces SDN technology (e.g. OpenFlow-enabled wireless networking) to design QoS-aware routing mechanism for cluster-based WMSNs. In the proposed routing scheme, OpenFlowenabled nodes (OFNs) act as cluster headers, maintain connections with neighbor OFNs, and forward packets on behalf of sensor nodes. Each OFN also detects link states among OFNs and determines flow’s QoS requirements. The SDN controller then seeks the feasible paths that satisfy QoS requirements of a flow. If there is no path which satisfies the required QoS, the path will be decided by the proposed algorithms depending on the flow types, such as delay-sensitive, bandwidth-sensitive, or best-effort traffic. An SDN overlay network testbed is built with OFNs using Open vSwitch and an SDN controller using Ryu controller. A series of experiments