Published in IET Communications Received on 1st July 2010 Revised on 7th January 2011 doi: 10.1049/iet-com.2010.0580 In Special Issue on Distributed Intelligence and Data Fusion for Sensor Systems ISSN 1751-8628 Towards intelligent contention-based geographic forwarding in wireless sensor networks L. Cheng 1,2 J. Cao 2 C. Chen 3 H. Chen 4 J. Ma 1,5 1 State Key Lab of Networking and Switching Technology, Beijing University of Posts and Telecommunications, People’s Republic of China 2 Department of Computing, Hong Kong Polytechnic University, Hong Kong, People’s Republic of China 3 Nokia Research Center, Beijing, People’s Republic of China 4 Institute of Industrial Science, The University of Tokyo, Tokyo, Japan 5 Wuxi Sensingnet Industrialization Research Institute, Wuxi, People’s Republic of China E-mail: chenglong@bupt.edu.cn Abstract: Contention-based geographic forwarding (CGF) is a state-free communication paradigm for data delivery in multihop wireless sensor networks. CGF is robust to frequent topology changes, scalable to large-scale node deployment and applicable to data-centric applications and resource constrained networks. However, CGF may experience significant performance degradation under unreliable links. In this work, we present the intelligent CGF (ICGF) to combat the channel variation. IGCF combines the advantages of both cooperative and contention-based forwarding, involving multiple neighbours of the sender into the local forwarding to improve the transmission reliability. ICGF differs from existing work in that it extends the cooperation scope intelligently, by sending one additional control message on demand. For this reason, the probability of cooperation void in ICGF is decreased and the single-hop packet progress is increased. The authors conduct extensive simulations to study the performance of the proposed ICGF compared with existing protocols. Simulation results demonstrate that ICGF improves the end-to-end data delivery delay, energy efficiency and data delivery ratio. 1 Introduction With the advances in computing and communication technologies, wireless sensor networks (WSNs) have attracted a great deal of attention owing to their wide variety of potential applications, such as environmental and habitat monitoring [1], healthcare [2] and ambient intelligence [3]. For most WSNs applications, the information obtained from sensors would be meaningless without the location of the sensor nodes. Therefore the geographic location information of sensor nodes is important and is always assumed available in the literature, either by a priori configuration or by the global positioning system (GPS) receiver or through some self-configuring localisation techniques [4]. Geographic routing (or location-based, position-based routing) is quite commonly adopted for information delivery in WSNs, where the location information of sensor nodes is always assumed available. Traditionally, in geographic routing, nodes need to know only the location information of their direct neighbours and where the destination is. The basic idea for geographic routing is greedily forwarding data packets to the neighbour geographically closest to the destination [5], so that data packets gradually approach and eventually arrive at the intended destination. This simple forwarding method can be an efficient and scalable data delivery scheme for large-scale sensor networks if it is reasonable to assume: (i) sufficient network density; (ii) accurate localisation; (iii) infrequent topology change and (iv) high link reliability independent of distance within the radio range [6]. To better adapt to the frequent topology changes, for example, nodes mobility or unavailability, a communication paradigm, contention-based geographic forwarding (CGF) has been proposed in recent years [7–10]. CGF allows nexthop candidate nodes to contend to take the data forwarding task, and a specific nexthop node is decided at the transmission time in a distributed manner. The contention mechanism releases the need to keep neighbourhood location information updated, thus avoiding sending beacons periodically. Nodes employing CGF only need to know their own locations and that of the destination. So, CGF has been considered to be robust to frequent topology changes, scalable to large-scale node deployment and applicable to data-centric applications and resource constrained networks [11]. In CGF, once the nexthop node is decided, the unicast between the sender and the specific nexthop node follows. However, several recent studies [12, 13] have stressed that the realistic link conditions in wireless networks can be highly unreliable because of many factors such as interference, attenuation and fading. The small control messages, such as request to send (RTS), clear to send (CTS), always have higher packet reception ratio than the IET Commun., 2011, Vol. 5, Iss. 12, pp. 1711–1719 1711 doi: 10.1049/iet-com.2010.0580 & The Institution of Engineering and Technology 2011 www.ietdl.org