在行動通訊網路中，系統利用註冊位置更新(registration area update，RAU)之方式以追蹤目前行動用戶(mobile station，MS)所在位置。然而，當MS在兩個註冊區域(registration areas，RAs)的邊界來回移動時，MS必須頻繁地執行位置更新動作，即產生不必要的位置更新成本(location update cost)，造成系統網路資源嚴重負擔，此現象被稱為乒乓效應(Ping-Pong Effect)。為了解決此現象，我們採用重疊註冊區域方法(overlapping registration area scheme)，以降低位置更新所造成的網路負擔。在重疊位置區域方法中，RA會與相鄰之RA重疊，因此邊界的cell會同時屬於兩個或兩個以上的RAs。當MS移動到一個新的cell，且此cell同時屬於兩個以上的註冊區域， MS必須和其中一個RA做註冊的動作，因而我們利用選擇註冊區域之策略(RA selection policy)，以表示如何在這些註冊區域選擇其中一個註冊區域執行註冊程序。在這篇論文中，我們提出兩套對於重疊位置區域的相關研究。第一個部份，我們介紹四種選擇註冊區域的策略，並採用二維六邊形cell的結構及隨機移動模型(random walk model)，提出一套數學分析模型來研究在重疊位置區域下的位置更新成本。第二個部份，我們根據MS移動的特性和call arrival的特性，提出一套動態調整重疊位置區域的演算法，藉以決定是否重疊加入cell至位置區域(或從重疊位置區域中移除cell)。最後，我們利用模擬實驗來驗證數學分析之正確性，並利用實驗結果，比較採用重疊位置區域和未採用重疊位置區域之優劣。

In a mobile telecommunications network, the registration area (RA) of a mobile station (MS) is tracked by the registration area update (RAU) mechanism. To reduce the RAU traffic caused by the ping-pong effect, the overlapping RA concept is introduced. In the overlapping RA configuration, an RA selection policy is required to select the new RA at an RAU when the MS enters a new cell covered by multiple RAs. According to overlapping RA configuration, we make two parts of mechanisms to study in this paper. First, we describe four RA selection policies and develop an analytic model to study the performance of these RA selection policies. Second, according to the user mobility and call arrival patterns, we propose a dynamic RA adjustment algorithm with overlapping RA configuration. The algorithm is used to decide whether to add cells into an RA or remove cells from an RA. Finally, our study provides the simulation result to validate the analytic result and compare performances of overlapping and non-overlapping RA configurations. Moreover, we propose a simulation experiment to implement the dynamic RA adjustment algorithm and compare with the static scheme in terms of the total RAU cost and the total paging cost.

[1]　Gu, D. and Rappaport, S. S. Mobile User Registration in Cellular System with Overlapping Location Areas. IEEE Vehicular Technology Conference, 1:802-806, May 1999.
[2]　Chiang, K.-H. and Shenoy, N. Performance of an Overlapped Macro-cell Based Location Area Scheme. International Conference on Communications (ICC '03), 1:475-481, May 2003.
[3]　Chiang, K.-H. and Shenoy, N. A 2-D Random-Walk Mobility Model for Location Management Studies in Wireless Networks. IEEE Transactions on Vehicular Technology, 53(2):413-424, June 2004.
[4]　Varsamopoulos, G. and Gupta, S. K. S. Dynamically Adapting Registration Areas to User Mobility and Call Patterns for Effcient Location Management in PCS Networks. IEEE/ACM Transactions on Networking, 12(5):837-890, Oct. 2004.
[5]　Bar-Noy, A., Kessler I. and Sidi, M. Mobile Users: To Update or Not to Update. Wireless Net, 1(2):175-186, 1996.
[6]　Castelluccia, C. Extending Mobile IP with Adaptive Individual Paging: A Performance Analysis. ACM Mobile Computing and Communications Review, 2:1-13, Feb. 1997.
[7]　Das, S. K. and Sen, S. K. Adaptive Location Prediction Strategies Based on a Hierarchical Network Model in a Cellular Mobile Environment. Computer Journal, 42(6):473-486, June 1999.
[8]　Ho, J. S. M. and Akyildiz, I. F. Dynamic Hierarchical Location Management in PCS Networks. IEEE/ACM Trans. Networking, 5:646-660, Oct. 1997.
[9]　Okasaka, S. and Onoe, S. A New Location Updating Method for Digital Cellular Systems. Proc. IEEE Vehicular Technology Conf., St. Louis, MO, pages 345-350, May 1991.
[10]　Xie, H., Tabbane, S. and Goodman, D. J. Dynamic Location Area Management and Performance Analysis. Proc. IEEE Vehicular Technology Conf. (VTC93), Seacaucus, NJ, pages 536-539, May 1993.
[11]　Zhang, X., Gomez Castellanos, J. and Campbell, A. T. P-MIP: Paging Extensions for Mobile IP. Kluwer Mobile Networks and Applications, 2(7):127-141, Apr. 2002.
[12]　Akyildiz, I.F., Lin, Y.-B., Lai, W.-R., and Chen, R.-J. A New Random Walk Model for PCS Networks. IEEE Journal on Selected Areas in Communications, 18(7):1254-1260, July 2000.
[13]　Kernighan, B. W. and Lin, S. An Efficient Heuristic Procedure for Partitioning Graphs. The Bell system technical journal, 49(1):291-307, 1970.
[14]　Manber, U. Introduction to Algorithms: A Creative Approach, chapter 7. Addison-Wesley Publishing Company, 1989.
[15]　Fiduccia, C. M. and Mattheyses, R. M. A Linear-Time Heuristic for Improving Network Partitions. Proc. of DAC, pages 175-181, 1982.
[16]　Wodziak, J. R., Fadel, G. M. and Kirschman, C. A Genetic Algorithm for Optimizing Multiple Part Placement to Reduce Build Time. Proceedings of the Fifth International Conference on Rapid Prototyping, Dayton, Ohio, June 1994.
[17]　Demirkol, I., Ersoy, C., Ufuk Caglayan, M. and Delic, H. Location Area Planning in Cellular Networks Using Simulated Annealing. Proceedings of IEEE Infocom,The Conference on Computer Communications 2001, Anchorage, Ak., pages 22-26, Apr. 2001.