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2009 Seventh Annual Communications Networks and Services Research Conference 2009 Seventh Annual Communication Networks and Services Research Conference

RACE: A Real-Time Scheduling Policy and Communication Architecture for Large-Scale Wireless Sensor Networks
Kambiz Mizanian, Reza Hajisheykhi, Mohammad Baharloo, Amir Hossein Jahangir
Department of Computer Engineering, Sharif University ofTechnology, Tehran, Iran,,,

Abstract—In wireless sensor networks (WSN), individual sensor nodes are inherently unreliable and have very limited capabilities to ensure real-time properties. In fact, one of the most predominant limitations in wireless sensor networks is energy consumption, which hinders thecapacity of the network to provide real-time guarantees (e.g. low duty-cycles, low transmission range). Many approaches have been proposed to deal with energy/latency trade-offs, but they are likely to be insufficient for the applications where reduced delay guarantee is the main concern. We present and evaluate a packet scheduling policy and routing algorithm called RACE that inherently accountsfor time constraints. We show that this algorithm is particularly suitable for communication in sensor networks in which a large number of wireless devices are seamlessly integrated into a physical space to perform realtime monitoring and control. Detailed simulations of representative sensor network environments demonstrate that RACE significantly reduces the end-to-end deadline and miss ratio inthe sensor network. Also RACE will balance load and energy consumption of network and life time of network will be increased. Keywords-Real-time; Wireless Sensor Networks; BellmanFord; EDF; QoS;

typically interacts with a physical environment, thus it has to meet timing constraints. Time requirements are generally in the form of end-to-end deadlines of sensory data packets from sensor nodestoward a control station. The primary real-time requirement is to guarantee bounded end-to-end delays or at least statistical delay bounds. Many approaches have dealt with providing delay bounds in a multi-hop sensor network. This has been basically achieved by means of Medium Access Control (MAC) protocols such as LEACH [1], D-MAC [2], and DBMAC [3], which guarantee that every node gains mediumaccess rights within a bounded time interval. Other solutions have targeted the Network Layer protocols to support realtime communications, such as SPEED [4]. The rest of this paper is organized as follows: in Section II we explain our design goal. In Section III our algorithm is clarified. Section IV presents the simulation results and Section V provides some conclusions. II. DESIGN GOALS


Typically, a Wireless Sensor Network (WSN) is composed of a large number of nodes having processing, sensing and radio communication capabilities, scattered throughout a certain geographical region, where the sensory data is routed in a multi-hop ad-hoc fashion from the originator sensor node to a remote control station. In this paper, we refer to large scale sensor network, as anetwork with large number of sensor nodes. WSNs differ from other types of wireless networks due to their tight interaction with the physical environment and to the hardware limitations of the low-cost sensor nodes. The latter feature has an important implication on the networking performance of individual sensor nodes due to their limited capacities in terms of energy, CPU speed, memory andbandwidth. These features make sensor nodes naturally unreliable, raising additional challenges for sensor networks to support realtime and reliable communications. While low energy consumption has been considered as the most predominant requirement in the design of wireless sensor networks, supporting real-time communications is nonetheless increasingly important. In fact, a sensor network

Our design...
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