LTE 為了改良室內的無線網路覆蓋率，透過建置低功耗小服務範圍的femtocells，
把femtocells 加入原本的網路架構中是最有可能實踐的方法。然而加入了femtocell
的網路架構會產生許多原本沒有的問題，例如：頻譜分配、跨層干擾、同層干
擾...... 等的問題，如果這些問題沒有妥善解決則網路效能將不會有所提升。而在
這邊要特別提出來的就是femtocell 的作弊行為所產生的問題，macrocell 是由電
信商經過精密量測結果而選定位置建造，相反的femtocell 是由使用者自行安裝。
人類自私的天性導致部分使用者為了自身利益在初次安裝後再次移動femtocell 的
位置，這樣的行為將會在成整體網路的影響。所以我們將針對此種行為設計一套
機制，在考量到安全性的情形下去防範作弊行為的發生。最後透過OpenCellID 網
站上面所提供的基地台資料以及不同撒點模型(PPP、MCP) 來模擬在異質網路
下作弊行為所造成的影響，以及使用我們機制後的效能回升，說明在異質蜂巢式
網路上位置追蹤的機制是必需的。

To improve indoor coverage and network capacity, deploying low-power and small-coverage femtocells in the coverage of a macrocell as two-tier heterogeneous network is regarded as the most promising approach. Since femtocells share the same licensed spectrum with macrocell, severe cross-tier and intra-tier interference from concurrent transmissions, which causes performance degradation.

However, the owner of femtocell might install or move it anywhere without the operator's awareness and permission for high quality indoor transmission. Such cheating behaviors destruct the extensive planning and explicitly suggest the existence of femtocell positioning mechanism. By examining the existing mechanisms and consider the security factor, we observe that macrocell shall assist in measuring and protecting location and timing information of femtocells to prevent the cheating.

We design a secure femtocell location tracking scheme with tolerable precision. Finally, we use the macro-BSs location information provided by OpenCellID and different point process (PPP, MCP) to simulate the effect of cheating behavior in heterogeneous network. Performance evaluations show that considerable performance improvement can be generally achieved, and thus demonstrate the necessity of applying location tracking on planned femtocells for interference control.

[1] A. Damnjanovic, J.Montojo, Y. Wei, T. luo, M. Vajapeyam, T. Yoo, O. Song, and D. Malladi, “A survey on 3gpp heterogeneous networks,” IEEE Commun. Soc. Mag., vol. 18, no. 3, pp. 10–21, June 2011.

[2] J. Andrews and A. Gatherer, “Femtocell networks: a survey,” IEEE Commun.
Soc. Mag., vol. 46, no. 9, pp. 59–67, Sept. 2008.

[3] A. Ghosh, N. Mangalvedhe, R. Ratasuk, B. Mondal, M. Cudak, E. Visotsky,
T. A. Thomas, N. S. Networks, J. G. Andrews, P. Xia, H. S. Jo, H. S. Dhillon, and T. D. Novlan, “Heterogeneous cellular networks: From theory to practice,” IEEE Computer, vol. 50, no. 5, pp. 54–64, June 2012.

[4] D. Lopez-Perez, A. Valcarce, G. de la Roche, and J. Zhang, “OFDMA femtocells: A roadmap on interference avoidance,” IEEE Commun. Mag., vol. 47, no. 9, pp. 41–48, Sept. 2009.

[5] J. Andrews, “Femtocells: Past, present, and future,” IEEE J. Sel. Areas Commun., vol. 30, no. 3, pp. 497–508, Apr. 2012.

[6] J. M. Dietrich Stoyan, Wilfrid S Kendall, Stochastic Geometry and Its Applications, 2nd ed. Wiley, 1996.

[7] J. G. Andrews, R. K. Ganti, M. Haenggi, N. Jindal, and S. Weber, “A primer on spatial modeling and analysis in wireless networks,” IEEE Commun. Mag., vol. 48, no. 11, pp. 156–163, Nov. 2011.

[8] R. W. H. Jr. and M. Kountouris, “Modeling heterogeneous network interference using poisson point processes,” IEEE Trans. Signal Process., vol. 61, no. 16, pp. 4114 – 4126, Aug. 2013.

[9] J. G. Andrews, F. Baccelli, and R. K. Ganti, “A tractable approach to coverage and rate in cellular networks,” IEEE Trans. Commun., vol. 59, no. 11, pp. 3122–3134, 2011.

[10] C.-H. Lee, C.-Y. Shih, and Y.-S. Chen, “Stochastic geometry based models for
modeling cellular networks in urban areas,” Wireless Networks, vol. 19, no. 6,
pp. 1063–1072, Aug. 2013.

[11] 3GPP, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved
Universal Terrestrial Radio Access (E-UTRAN); Overall description; Stage 2,”
3GPP TS 36.300, Sept. 2010.

[12] S.-M. Cheng, S.-Y. Lien, F.-S. Chu, and K.-C. Chen, “On exploiting cognitive radio to mitigate interference in macro/femto heterogeneous networks,” IEEE Wireless Commun. Mag., vol. 18, no. 3, pp. 40–47, June 2011.

[13] 3GPP, “Security of Home Node B (HNB) / Home evolved Node B (HeNB),”
3GPP TS 33.320 v9.5.0, Mar. 2011.

[14] ——, “Home enhanced Node B (HeNB) Operations, Administration, Maintenance and Provisioning (OAM&P); Procedure flows for Type 1 interface HeNB to HeNB Management System (HeMS),” 3GPP TS 32.593 v8.3.0, Dec. 2009.

[15] S. Communications, “An overview of LTE positioning,” Feb. 2012. [Online]. Available: http://www.opencellid.org/

[16] 3GPP, “E-UTRAN; Stage 2 functional specification of User Equipment (UE)
positioning in E-UTRAN,” 3GPP TS 36.305 v11.3.0, Mar. 2013.

[17] ——, “LTE Positioning Protocol (LPP),” 3GPP TS 36.355 v11.2.0, Mar. 2013.

[18] J. T. Chiang, J. J. Haas, J. Choi, and Y.-C. Hu, “Secure location verification using simultaneous multilateration,” IEEE Trans. Wireless Commun., vol. 11, no. 2, pp. 584–591, feb 2012.

[19] I. Instrumentation and M. Society, “IEEE 1588 standard for a precision clock synchronization protocol for networked measurement and control systems,”IEEE Std 1588, 2008.

[20] 3GPP, “E-UTRA; Physical Channels and Modulation,” 3GPP TS 36.211 v9.1.0,Mar. 2010.

[21] “OpenCellID.” [Online]. Available: http://www.opencellid.org/

[22] 3GPP, “E-UTRA: Further Advancements for E-UTRA Physical layer aspects,”
3GPP TR 36.814 v9.0.0, Mar. 2010.