In forthcoming personal communication systems (PCSs), small cells are deployed to achieve high spectral efficiency. This has significant impacts on location tracking of mobile users. The increase in location update (LU) load leads to more contention on the reverse control channel. Thus, many algorithms are designed to distribute the LU load to a larger number of cells. This avoids the inefficiency of random accessing due to high offered load. In an alternative approach [3], a contention-free LU

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... algorithm is proposed. Two or more mobile units are permitted to register with a base station simultaneously without contention. A probabilistic paging mechanism called Bloom filtering is used to select cells to be paged. Since there is no contention in LU, inefficiencies due to random accessing are bypassed. In this paper, we present another contention-free LU algorithm. It is hybrid in the sense that LUs are temporally or geographically triggered. The use of hybrid LU alleviates inefficiencies inherent to temporal triggered LU in [3]. Three selective paging schemes are considered in this paper. Tradeoff between paging delay and paging bandwidth is addressed. The performance of this algorithm is compared to [3] and other conventional strategies. Numerical results shows that the new algorithm compares favorably with previous proposed strategies. His research interests include mobility management, power control, rate management for cellular, and ad hoc networks. Wing Shing Wong (M'81-SM'90) received the M.A.B.A. degree (summa cum laude) from Yale University, New Haven, CT, in 1976 and the M.S. and Ph.D. degrees from Harvard University, Cambridge, MA, in 1978 and 1980, respectively. He joined AT&T Bell Laboratories in 1982. From 1987 to 1992, he managed a group of technical staff working on a number of research and development projects and consulting activities. He joined the Chinese University of Hong Kong in 1992 and is now Professor of information engineering. He has been the Chairman of the Information Engineering Department since 1995. He is actively involved in a variety of R&D projects, including topics such as mobile communication systems, Web technology development, and information issues in estimation and control. He has published more than 85 refereed journal and conference papers and is the recipient of multiple competitive R&D grants from the Hong Kong