我們提出一分配通話頻道的機制，應用在無線通訊網路雙層架構下，所有可使用頻道由高層微細胞基地台及低層微細胞基地台共享。此機制主要運用動態分配頻道的方式，整合其他機制包括:通話中使用者的優先權、區域性最密堆積法(local-packing)、被保留頻道可與被相互干擾鄰近基地台(interference cell)共用、從低層微細胞基地台溢出(overflow)至高層微細胞基地台。
在基地台分散的網路環境裡，這些機制透過各基地台所維護的資料庫表(ACOR table)，獲得頻道使用狀況而運作。此資料庫表儲存基地台本身頻道使用狀況及相互干擾的基地台頻道使用狀況，並由基地台彼此交換訊息而更新。
我們從模擬的結果可看出，在雙層網路架構下，此整合機制對於降低通話中使用者被中斷的機率有較好的成效，但不造成嘗試通話的使用者增加過多失敗的機率。影響此結果的因素有二：通話中使用者在不同方向非等機率移動的模式，以及通話中使用者在高層微細胞基地台與低層微細胞基地台所待時間的不同。
此外，我們設計從低層微細胞基地台溢出至高層微細胞基地台的機制已包含在被保留頻道可與相互干擾鄰近基地台共用的機制中，因此不需要額外增加流程即達到此效果。

We propose a channel assignment strategy, called Hierarchical cellular system - Prioritized Handoff Dynamic Channel Allocation strategy (HPHDCA), for use in hierarchical cellular networks, in which channel resources are shared by both tiers of cells. The HPHDCA is essentially a DCA scheme with additional operational features including prioritized-handoff, local-packing, reservation-sharing and overflow. In distributed operation environment, these features are achieved through looking up channel status maintained in an ACOR table. The ACOR table is developed to support enough information of channel usage patterns of interference cells sufficient for each cell to determine channel allocation by itself. By the mobility of nonuniform transition probability between cells and different dwell time distribution in microcells and macrocell-only areas, simulations show that the HPHDCA in macrocell/microcell overlay is able to yield favorable performance on handoff call blocking over new call blocking, at the cost of new call blocking probability. One additional feature is found that HPHDCA takes the conventional overflow technique completely into the reservation-sharing scheme, with no need to crank up a new overflow mechanism.

[1] D. C. Cox and D. O. Reudink, “Increasing channel occupancy in large-scale mobile radio system: dynamic channel reassignment,” IEEE Trans. Veh. Technol., vol VT-22, pp. 218-222, Nov. 1973.
[2] T. J. Kahwa and N. D. Georganas, “A hybrid channel assignment scheme in large-scale, cellular-structured mobile communication systems,” IEEE Trans. Commun., vol COM-26, pp.431-438, Apr. 1978.
[3] M. Murata and E. Nakano, “Enhancing the performance of mobile communications systems,” Proc. IEEE Int. Conf. Universal Personal Communications, pp. 732-736, 1993.
[4] R. Steele and M. Nofal, “Teletraffic performance of microcellular personal communication networks,” Proc. Inst Elec. Eng., vol, 139, pp. 448-461, Aug. 1992.
[5] S. A. El-Dolil, W.-C. Wong, and R. Steele, “Teletraffic performance of highway microcells with overlay macrocell,” IEEE J. Selected Areas Commun., vol. 7, pp. 71-78, Jan. 1989.
[6] C.-L. I, L. J. Greenstein, and R. D. Gitlin, “A microcell/macrocell cellular architecture for low- and high-mobility wireless users,” IEEE J. Selected Areas Commun., vol. 11, pp. 885-891, Aug. 1993.
[7] S. S. Pappaport and L. R. Hu, “Microcellular communication systems with hierarchical microcell overlays: traffic performance models and analysis,” Proc. IEEE, vol. 82, no. 9, pp. 1383-1397, Sep. 1994.
[8] ------, “Personal communication systems using multiple hierarchical cellular overlays,” IEEE J. Selcted Areas in Commun., vol. 13, no. 2, pp. 406-415, May 1995.
[9] Y.-B. Lin, S. Mohan, and A. Noerpel, “PCS channel assignment strategies for hand-off and initial access,” IEEE Personal Commun. Mag., vol. 1, no. 3, pp. 47-56, 1994.
[10] V. O. K. Li and X. Qiu, “Personal communication systems (PCS),” Proc. IEEE, vol. 1, no. 3, pp. 47-56, 1994.
[11] S. –H. Oh et al., “Prioritized Channel Assignment in a Cellular Radio Network,” IEEE Trans. Commun., vol. 40, pp. 1259-69, 1992.
[12] D. Hong and S. Rappaport, “Traffic Modelling and Performance Analysis for Cellular Mobile Radio Telephone Systems with Prioritized and Nonprioritized Handoff Procedures,” IEEE Trans. Vehicular Tech., vol. VT-35, pp. 77-92, 1986.
[13] S. Tekinay, “A Measurement-Based Prioritization Scheme for Handovers in Mobile Cellular Networks,” IEEE JSAC, vol. 1, pp. 1343-50, 1992.
[14] C. Posner and R. Guerin, “Traffic Policies in Cellular Radio that Minimize Blocking of Handoffs,” ITC-II, pp. 2.4B.2.5, 1985.
[15] R. Guerin, “Queuing Blocking System with Two Arrival Streams and Guard Channels,” IEEE Trans. Commun., vol. 36, pp. 153-63, 1988.
[16] I. Katzela and M. Naghshineh, “Channel Assignment Schemes for Cellular Mobile Telecommunication Systems: A Comprehensive Survey,” IEEE Personal Commun., pp. 10-31, June 1996.
[17] R. Beck and H. Panzer, “Strategies for Handover and Dynamic Channel Allocation in Micro-Cellular Radio Telephone Systems,” IEEE VTC, vol. 1, pp. 178-185, 1989.
[18] D. Everitt and N. W. MacFadyen, “Analysis of Multicellular Mobile Radio Telephone Systems with Loss,” BT TECH. J., vol. 2, pp. 37-45, 1983.
[19] Chih-Lin I and Pi-Hui Chao, “Local-Packing – Distributed Dynamic Channel Allocation at Cellular Base Station,” Proc. IEEE, pp. 293-301, 1993.
[20] Chih-Lin I and Pi-Hui Chao, “Distributed Dynamic Channel Allocation Algorithms with Adjacent Channel Constraints,” PIMRC, vol. B2.3, pp. 169-175, 1994.
[21] K. Okada and F. Kubota, “Performance of a Dynamic Channel Assignment Algorithm with Information of Moving Direction in Mobile Communication Systems,” Proc. IEICE Spring Nat’l. Conv., 1991, p.334.
[22] K. Okada and F. Kubota, “A Proposal of a Dynamic Channel Assignment Strategy with Information of Moving Directions,” IEICE Trans. Fundamentals, vol. E75-a, pp. 1667-1673, 1992.
[23] Chih-Lin I, “Distributed Dynamic Channel Allocation Algorithms in Microcells Under Light Traffic Loading,” Proc. IEEE ICC, 1993.
[24] L. J. Clmini, G. J. Foschini, and Chih-Lin I, “Call Blocking Performance of Distributed Algorithms for Dynamic Channel Allocation in Microcells,” Proc. IEEE ICC, 1992.
[25] W. C. Y. Lee, Mobile Cellular Communication Systems, 1989.
[26] Jung-Tsung Tsai, “A Prioritized Handoff Local-Packing Distributed Dynamic Channel Allocation Strategy for Cellular Network,” submitted for GLOBECOM 2000 general conference.
[27] Lauro Ortigoza-Guerrero, “A Self-Adaptive Prioritised Hand-off Strategy for a Microcellular Environment,” IEEE Trans. Veh. Technol., pp. 401-405, 1997.
[28] Lauro Ortigoza-Guerrero, “A Prioritized Handoff Dynamic Channel Allocaion Strategy for PCS,” IEEE Trans. Veh. Technol., vol. 48, no. 4, pp. 1203-1215, 1999.
[29] Kuen-Rong Lo etc., “A Combined Channel Assignment Strategy in a Hierarchical Cellular Systems,” VTC-99, 1999.
[30] S. S. Rappaport, “Blocking, handoff and traffic performance for cellular communication systems with mixed platforms,” Proc. Inst. Elec. Eng., vol.140, pt. I, pp. 389-401, Oct. 1993.
[31] R. Deck and H. Panzer, “Strategies for handover and dynamic channel allocation in micro-cellular mobile radio systems,” Proc. of IEEE Veh. Tech. Conf., 1989.
[32] L. J. Cimini and G. J. Foschini, “Distributed algorithms for dynamic channel allocation in microcellular systems,” Proc. IEEE Veh. Tech. Conf., pp. 641-644, 1992.
[33] H. Panzer and R. Deck, “Adaptive resource allocation in metropolitan area cellular mobile radio systems,” Proc. IEEE Veh. Tech. Conf., 1990.
[34] Kwan L. and Sanjiv, “Channel Management in Microcell/Macrocell Cellular Radio Systems,” IEEE Trans. Commun., vol. 45, no. 4, pp. 153-63, 1996.