Within the last 20 years, wireless communication and network has been one of the fastest-growing research areas. Significant progress has been made in the fields of mobile ad hoc network (MANET) and wireless sensor networks (WSN). Very recently, the cyber-physical system (CPS) has emerged as a promising direction to enrich human-to-human, human to-object, and object-to-object interactions in the physical world as well as in the virtual world. The possibilities are enormous, such that CPS would adopt, and even nurture, the areas of MANET and WSN because more sensor inputs and richer network connectivity are required. The chapter reviews what has been developed in these fields, outlines the projection of what may happen in the field of CPS, and identifies further works. The authors identify the unique features of WSN, raising some CPS critical examples, and then directing the future challenges of CPS. In order to fully comprehend the connection of WSN to CPS, the authors provide some preliminaries of WSN and establish their necessary connections.
TopIntroduction
Advanced design in microelectronics, material sciences and networking capability are driving the deployment of large scale WSN and Wireless Actuator Network (WAcNet). These technologies actually enabled the low cost WSN, low power, micro devices with multifunctional characteristics connected to multiple sensors (Dargie & Poellabauer, 2010). These micro devices accumulate sensed data from the environment and transmitted it over certain distance and further routed by multi hopping to a typical gateway. The data can then be aggregated and streamed over the region through the cloud. Nowadays WSN can be seen almost everywhere, where data need to actually being monitored and managed. Significant research contributions have made WSN communications more reliable for realtime applications (Akyildiz et. al., 2002). With the maturity of WSN, networks require the extended functionality and formal interaction with other networked system, with additional reliability. Hence the Cyber Physical Systems (CPS) paradigm comes into the sensing applications as a platform to provide extended interactive functionality, thus bridging real time and virtual environments. With an additional WAcNet scenario, it will produce a very comprehensive system.
Wireless sensor networks (WSN), and actuator networks (WAcNet), are spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, gaseous, electricity usage, sensing people, and so on. The nodes cooperatively pass their data through the network to other locations. Currently the networks are bi-directional, also enabling control of sensor activity, resulting what we may called as WAcNet, such networks are used in many industrial and consumer applications. WSN is built of nodes, from a few in numbers to thousands, where each node is connected to one or several sensors. Each node has typically several parts: a radio transceiver with an internal antenna, a microcontroller, an interfacing with the sensors and an energy source, usually a battery or an embedded form of energy harvesting mechanism. A sensor node might vary in size from that of a matchbox down to the size of a grain of dust, although functioning motes of microscopic dimensions have yet to be manufactured. Size and cost constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and communications bandwidth. The WSN topology can vary from a simple star network to an advanced multi-hop wireless mesh network. The radio propagation technique between the hops of the network is accomplished by routing mechanism.
A mobile ad hoc network (MANET) is generally defined as a network that has many free or autonomous nodes, often composed of mobile devices, which can arranged themselves in various ways and operate without strict top-down network administration. The communication maybe achieved through multi hop mechanism. MANET, now a topic of commercial research, was originally used in military projects, including in tactical networks and defense projects. Some use 4G networks and other wireless systems as examples of a potential topology for a MANET, while others refer to a vehicular ad-hoc network (VANET), where the free network nodes are installed in cars and other vehicles. MANET has the potential but face various challenges, including signal protection and the reliability of mobile or dynamic nodes. In addition there’s an issue of limited processing power, especially mobile nodes within MANET. Smart phones as an example of node within MANET may experience this power constraint.
Cyber-Physical Systems(CPS) is integrations of element of computations with some physical processes. Networked embedded computers are used to monitor and control physical processes based upon local network and remote computation (Akella & McMillin, 2009). The main features of CPS are that it is tightly coupled between physical and software components. CPS may operate on different spatial and temporal scales and exhibiting multiple and distinct behavior. Furthermore, CPS is continuously interacting with the physical world, causing the behavior of a CPS changes with the operational scheme. Hence, CPS actually is a system to provide a virtual environment that incorporates an interacting network of elements with physical inputs and outputs at both ends as shown in Figure 1. It provides an intuitive interconnection mechanism for human-to-human, human-to-machine and machine-to-machine interactions through seamless network connectivity (Edward A. Lee, 2006).