智慧行動裝置變得普及，資料流量也急遽增加，在長期演進系統中，傳統大型基地台的負擔越來越重，為了分擔大型基地台的負載，低功率基地台將相對應地被部屬，例如: 小型基地台，這樣包含大型基地台以及小型基地台的異質網路是本論文所考量的。對於這樣的異質網路，我們將討論如何適當地選擇基地台以改善換手效能，尤其是在高速的環境下。在我們的設計中，基地台預選策略提出了根據預先定義的速度門檻值與服務品質需求將使用者設備進行分類。對於不同類型的使用者設備，不同的偏好被設定，使得高速的使用者設備主要被大型基地台所照料，同時低速或服務品質需求較低的使用者設備則被卸載到小型基地台的服務區域，以減輕大型基地台的負擔。此外，還提出一個動態換手參數調整的機制，藉由考量換手失敗率、乒乓效應率、速度以及使用者移動的歷史紀錄等。最後，透過大量的模擬，在換手次數、失敗率以及乒乓率方面，顯示了我們的設計優於其他文獻中的相關機制。

As personal intellectual mobile devices become pervasive, data traffic increases drastically, causing a much heavier burden to the traditional macro eNode B (eNB) in the long term evolution (LTE) system. To share the load of macro eNBs, lowpower base stations, e.g., pico eNBs, are deployed accordingly. Such a heterogeneous network (HetNet) with macro and pico eNBs is then considered in this thesis. For such a HetNet, we will address how to appropriately select an eNB to improve handover performance, especially in the high-speed environment. In our design, a base station pre-selection strategy is proposed to classify user equipments (UEs) according to the pre-defined thresholds of speed and quality of service (QoS) requirements.For different types of UE, different preferences are then set so that high-speed UEs are primarily taken cared by macro eNBs while lowspeed or low QoS UEs are offloaded to the service area of pico eNBs to share the load of macro eNBs. Additionally, a dynamic handover parameter adjustment mechanism is proposed by considering the handover failure ratio, ping-pong effect ratio, speed, and mobility history etc. Finally, we show the superiority of our design over some related mechanisms reported in the literature in terms of number of handover, radio link failure ratio, and ping-pong ratio via extensive simulations.

[1] A. Larmo, M. Lindstrom, M. Meyer, G. Pelletier, J. Torsner, and H. Wiemann,“The LTE link-layer design,” IEEE Communications Magazine, vol. 47, no. 4,pp. 52–59, Apr. 2009.
[2] 3GPP, TS 36.300 V10.4.0,“Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN);
Overall description; Stage 2 (Release 10),” 2011.
[3] Cisco Visual Networking Index,“Global mobile data traffic forecast”. Feb.2015.
[4] S. Deb, P. Monogioudis, J. Miernik, and J. P. Seymour, “Algorithms for enhanced inter-cell interference coordination (eICIC) in LTE HetNets,” IEEE/
ACM Transactions on Networking (TON), vol. 22, no. 1, pp. 137–150, Feb.
2014.
[5] Z. Wei, “Mobility robustness optimization based on UE mobility for LTE system,”in Proc. IEEE International Conference on Wireless Communications
and Signal Processing (WCSP), pp. 1–5, Oct. 2010.
[6] S. Barbera, P. H. Michaelsen, M. Säily, and K. Pedersen, “Mobility performance of LTE co-channel deployment of macro and pico cells,” in Proc. IEEE Wireless Communications and Networking Conference (WCNC), pp. 2863–
2868, Apr. 2012.
[7] Y. Peng, W. Yang, Y. Zhang, and Y. Zhu, “Mobility performance enhancements for LTE-advanced heterogeneous networks,” in Proc. IEEE 23rd International Symposium on Personal Indoor and Mobile Radio Communications
(PIMRC), pp. 413–418, Sept. 2012.
[8] M. Peng, D. Liang, Y. Wei, J. Li, and H. H. Chen, “Self-configuration and self-optimization in LTE-advanced heterogeneous networks,” IEEE Communications Magazine, vol. 51, no. 5, pp. 36–45, May 2013.
[9] M. Peng, Y. Liu, D. Wei, W. Wang, and H. H. Chen, “Hierarchical cooperative relay based heterogeneous networks,” IEEE Wireless Communications,vol. 18, no. 3, pp. 48–56, June 2011.
[10] 3GPP TR 36.842 (V0.1.0),“Evolved universal terrestrial radio access (EUTRA):Small cell enhancements for E-UTRA and E-UTRAN –higher layer
aspects (Release 12),” 2013.
[11] A. Damnjanovic, J. Montojo, Y. Wei, T. Ji, T. Luo, M. Vajapeyam, T. Yoo,O. Song, and D. Malladi, “A survey on 3GPP heterogeneous networks,” IEEE
Wireless Communications, vol. 18, no. 3, pp. 10–21, June 2011.
[12] A. Barbieri, A. Damnjanovic, T. Ji, J. Montojo, Y. Wei, D. Malladi, O. Song,and G. Horn, “LTE femtocells: system design and performance analysis,”
Proc. IEEE Journal on Selected Areas in Communications, vol. 30, no. 3,
pp. 586–594, Apr. 2012.
[13] 3GPP TR 36.839 V0.5.0, “Mobility Enhancements in Heterogeneous Networks
(Release 11),” 2012.
[14] 3GPP RP-110709, “Revised WID on Study on for Hetnet Mobility Enhancements for LTE,” 2011.
[15] 3GPP TR 36.814, “Evolved Universal Terrestrial Radio Access (EUTRA); further advancements for E-UTRA physical layer aspects,” 2010.
[16] 3GPP TR 36.902,“Self-configuring and self-optimizing network (SON) use
cases and solutions (Release 9),” 2011.
[17] J. Han and B. Wu, “Handover in the 3GPP long term evolution (LTE) systems,” in Proc. IEEE Global Mobile Congress (GMC), pp. 1–6, Oct. 2010.
[18] D. Lopez Perez, İ. Güvenc, and X. Chu, “Mobility management challenges in 3GPP heterogeneous networks,” IEEE Communications Magazine, vol. 50,
no. 12, pp. 70–78, Dec. 2012.
[19] A. K. Mahima Mehta, Nadeem Akhtar, “Impact of handover parameters on
mobility performance in LTE HetNets,” in Proc. IEEE Twenty First National
Conference on Communications (NCC), pp. 1 – 6, Feb. 2015.
[20] H. Hu, J. Zhang, X. Zheng, Y. Yang, and P. Wu, “Self-configuration and selfoptimization for LTE networks,” IEEE Communications magazine, vol. 48,
no. 2, pp. 94–100, Feb. 2010.
[21] S. Feng and E. Seidel, “Self-organizing networks (SON) in 3GPP long term evolution,” Nomor Research GmbH, Munich, Germany, May 2008.
[22] H. Zhang, “Peer to peer technologies in future LTE self-organizing networks,” in Proc. IEEE Computing, Communications and Applications Conference (ComComAp), pp. 127–132, Jan. 2012.
[23] A. Schröder, H. Lundqvist, and G. Nunzi, “Distributed self-optimization of handover for the long term evolution,” Springer, Dec. 2008.
[24] W. Gao, B. Jiao, G. Yang, W. Hu, L. Chi, and J. Liu, “Mobility robustness improvement through transport parameter optimization in HetNets,” in Proc. IEEE 24th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC Workshops), pp. 101–105, Sept. 2013.
[25] Y. Lee, B. Shin, J. Lim, and D. Hong, “Effects of time-to-trigger parameter on handover performance in SON-based LTE systems,” in Proc. IEEE 16th Asia-Pacific Conference on Communications (APCC), pp. 492–496, Oct. 2010.
[26] J. Puttonen, N. Kolehmainen, T. Henttonen, and J. Kaikkonen, “On idle
mode mobility state detection in evolved utran,” in Proc. IEEE ITNG’09.
Sixth International Conference on Information Technology: New Generations,
pp. 1195–1200, Apr. 2009.
[27] N. Kolehmainen, J. Puttonen, T. Henttonen, and J. Kaikkonen, “Performance of idle mode mobility state detection schemes in evolved utran,” in Proc. IEEE International Symposium on Wireless Pervasive Computing (ISWPC), pp. 584–588, May 2010.
[28] Y. Lei and Y. Zhang, “Enhanced mobility state detection based mobility optimization for femto cells in LTE and LTE-advanced networks,” in Proc. IET
International Conference on Communication Technology and Application (ICCTA
2011), pp. 341–345, Oct. 2011.
[29] S. Barbera, P. H. Michaelsen, M. Saily, and K. Pedersen, “Improved mobility performance in LTE co-channel hetnets through speed differentiated enhancements,” in Proc. IEEE Globecom Workshops (GC Wkshps), pp. 426–
430, Dec. 2012.
[30] S. S. Mwanje, N. Zia, and A. Mitschele Thiel, “Self-organized handover parameter configuration for LTE,” in Proc. IEEE International Symposium on
Wireless Communication Systems (ISWCS), pp. 26–30, Aug. 2012.
[31] G. Piro, L. A. Grieco, G. Boggia, F. Capozzi, and P. Camarda, “Simulating LTE cellular systems: An open-source framework,” IEEE Transactions on Vehicular Technology, vol. 60, no. 2, pp. 498–513, Nov. 2011.