IEICE TRANS. COMMUN., VOL.E94–B, NO.1 JANUARY 2011 297 LETTER One-Hop Neighbor Based Broadcast Scheduling in Wireless Sensor Networks * Taehong KIM †a) , Student Member, Daeyoung KIM † , Member, and Chong Poh KIT † , Nonmember SUMMARY For wireless sensor networks in which resources are lim- ited and network topology dynamically changes, we propose the one-hop neighbor based broadcast scheduling (ONBS) algorithm to provide reliable delivery service of broadcast packets. The proposed algorithm reduces the scheduling overhead by allowing each joining node to decide its broad- cast schedule based on only its one-hop neighbor information in an on-line and distributed manner. Also, once the broadcast schedule is decided, it is not changed to accommodate a newly joining node in order to prevent the consecutive changes of existing schedules. The network simulation results show that the proposed algorithm provides low latency and high reachabil- ity despite low overhead and on-line algorithm design. key words: broadcast scheduling, 1-hop neighbor, sensor network 1. Introduction In wireless sensor networks, the base station disseminates many important messages, such as network reconfiguration, security key renewal, and queries, which have to be deliv- ered to all the nodes in a network. These messages are critical for the network operation. For example, nodes that fail to receive the channel reconfiguration message from the base station cannot communicate with others and remain isolated from the network. In order to prevent such prob- lems, broadcast scheduling is an essential requirement to avoid the packet loss from collisions and contention. There have been many studies on broadcast scheduling in wireless ad hoc and sensor networks [1]–[3]. Lloyd [1] proposes to use 2-hop neighbor information for their dis- tributed scheduling algorithm. Gandhi et al. [2] prove that the optimization algorithm for the minimum latency broad- cast scheduling is NP-hard, and they propose an approxi- mation algorithm based on topology information. Wang [3] and Shen [4] also suggest exploiting the network topology to apply to their GWMIN2 and FHNN algorithm respectively. Since those algorithms focus on improving scheduling per- formance, they do not care much about the heavy traffic load for exchanging 2-hop neighbor information [1] and gather- ing topology information [2]–[4], which is burdensome in resource limited wireless sensor networks. In addition, it is not realistic to use centralized scheduling algorithms [2]– [4], because they need to change the whole schedules for the Manuscript received March 9, 2010. Manuscript revised July 13, 2010. † The authors are with Korea Advanced Institute of Science Technology, Daejeon 305-701, Republic of Korea. ∗ This research was supported by the ICT Standardization pro- gram of MEK (The Ministry of Knowledge Economy). a) E-mail: damiano@kaist.ac.kr DOI: 10.1587/transcom.E94.B.297 dynamic topology changes that frequently occurs in wireless sensor networks. In this letter, we propose a broadcast scheduling algo- rithm to provide reliable delivery service of broadcast pack- ets by considering not only scheduling performance but also the characteristics of wireless sensor networks. First, the proposed scheduling is designed to optimize the reachability and latency of broadcast packet initiated by the base station, since the base station administrates network and dissemi- nates many system critical messages. Second, to reduce the overhead of obtaining prior knowledge, we design the distributed scheduling algorithm based on 1-hop neighbor information. Each node dynamically decides the collision- free broadcast schedule within its 2-hop coverage using in- formation from 1-hop neighbors that already know their 1- hop neighbor’s broadcast schedule. Third, we prevent the existing broadcast schedule from being changed by newly joining nodes in order to avoid consecutive changes of ex- isting schedules in dynamic wireless sensor networks. 2. One-Hop Neighbor Based Broadcast Scheduling Since the network join operation is a mandatory function to establish membership and assign network address in wire- less sensor networks, every node decides its collision-free broadcast schedule when joining the network in the pro- posed algorithm. Thus, a joined node is one that has already decided its broadcast schedule, whereas a joining node is in progress of scheduling. Figure 1(a) shows an example of the proposed broad- cast scheduling algorithm. The arrow represents the join- ing process, and the value on the arrow indicates the join- ing order of each node. The information used in broadcast schedule is the rebroadcast time (RT) and highest rebroad- cast time in its 1-hop neighbor (HRT). Base station has RT (a) (b) Fig. 1 Proposed broadcast scheduling (a) and rebroadcast (b) algorithms. Copyright c  2011 The Institute of Electronics, Information and Communication Engineers