JOURNAL OF INFORMATION SCIENCE AND ENGINEERING 20, 517-534 (2004) 517 Modeling and Tracking Complexly Moving Objects in Location-Based Services * MOONBAE SONG, KWANGJIN PARK, JEHYOK RYU AND CHONG-SUN HWANG Department of Computer Science and Engineering Korea University Seoul 136-701, Korea E-mail: {mbsong, kjpark, jhryu, hwang}@disys.korea.ac.kr One of the most important issues in location-based services is tracking moving ob- jects efficiently. To achieve this goal, an efficient protocol which updates location in- formation in a location server is primarily needed. In fact, the performance of a location update strategy highly depends on the assumed mobility pattern. In most existing studies, however, the mobility issue has been disregarded and oversimplified as a linear function of time. In this paper, we propose a new mobility model, called state-based mobility model (SMM) to provide a more generalized framework for describing both the mobility and updating location information of complexly moving objects. We also introduce the state-based location update protocol (SLUP) based on this mobility model. Keywords: mobility modeling, location tracking, moving objects, location-based services, location update protocol 1. INTRODUCTION In mobile computing environments, mobile terminals (MTs) are emerging in many forms and applications, such as databases, networks and so on. MTs, like cellular phones, PDAs, and mobile PCs, can dynamically change their locations over time. Objects which continuously change their location and extent are called moving objects. Thus, what is important in the mobile computing environment is how to model the location and move- ment of moving objects efficiently. Therefore, a software infrastructure providing loca- tion-based services, called a moving objects database (MOD), is greatly needed. Recently, many studies has been done on the representation and management of moving objects [5, 13, 14]. Wolfson et al. presented the well-known data model called Moving Object Spatio-Temporal (MOST) for representing moving objects [18]. In the MOST model, the location of a moving object is simply given as a linear function of time, which is specified by two parameters: the position and velocity vector of the object. Thus, without frequent update messages, the location server can compute the location of a moving object at a given time t through linear interpolation: yt y vt t () ( ) = + - 0 0 at time Received October 15, 2003; accepted November 15, 2003. Communicated by Ten-Hwang Lai, P. Sadayappan, Yu-Chee Tseng and Yi-Bing Lin. * This work was supported by grant No. R01-2002-000-00235-0 from the Basic Research Program of the Korea Science & Engineering Foundation.