隨著科技的發展與進步，越來越多人擁有移動設備，進而導致對流量和服務的需求不斷增長，為了滿足這些需求，異質性網路是一個有前景的解決方案，但也因此引入了兩個問題：無縫的複雜性以及能源損耗的問題。為了解決這兩個問題，在本文中，我們分析了在異質性網路的省電睡眠方案中的垂直交遞，垂直交遞是在無線異質性網路中無縫服務的重要議題，而省電睡眠方案顧名思義則可使基地臺進入睡眠以達到省電的目的。另外為了解決小基地臺拓撲的隨機性使得它們難以分析，所以我們在我們的模型中利用隨機幾何的方法幫小基地臺建模，並且利用隨機幾何的方法去分析現有的兩種省電睡眠方案以及我們提出的新方案垂直交遞的過程，接著推導出垂直交遞次數期望值的近似表達數學式。
模擬實驗驗證了我們分析結論的正確性，我們所提出的數學式子平均誤差小於5%，而對比現有論文的數學式的誤差約34%，我們的精準度提升了29%。此外，模擬實驗的結果也表明我們所提出的省電睡眠方案比現有的兩個方案還省電，以每單位流通量可以省多少能源當效能指標，我們的方案的效能指標是隨機睡眠方案的2.28倍，是省電圈方案的3.53倍。

With the development and advancement of technology, more and more people own mobile devices, which in turn leads to the increasing demand for traffic and services. To meet these demands, the heterogeneous networks are a promising solution, but they also introduce two problems: seamless complexity and energy consumption. To solve these two problems, in this thesis, we analyze the vertical handover in the energy efficient sleep mode schemes for heterogeneous networks. Vertical handover is an important issue for seamless service in wireless heterogeneous networks. The energy efficient sleep mode scheme, as the name suggests, allows the base station to sleep for power saving purposes. In addition, to solve the problem that the randomness of the small cell topology makes them difficult to analyze, we use stochastic geometry to model the small cells. We also use stochastic geometry to analyze the vertical handover process of two existing energy efficient sleep mode schemes and the vertical handover process of our proposed new schemes and then derive an approximate mathematical expression for the expected number of vertical handovers.
The simulation experiment verifies the correctness of our analytical conclusion. The average error of our proposed mathematical equation is less than 5%, and compared with the error of the mathematical equation of the existing paper, which is about 34%, our accuracy is improved by 29%. In addition, the simulation results also show that our proposed new scheme is more energy-efficient than the existing two schemes, and our scheme is 2.28 times more efficient than the random sleep scheme and 3.53 times more efficient than the sleep circle scheme in terms of energy savings per unit of throughput.

[1] Cisco, “Cisco annual internet report, 2018–2023 white paper, accessed on march 9, 2020.”
[2] J. G. Andrews, S. Buzzi, W. Choi, S. V. Hanly, A. Lozano, A. C. K. Soong, and J. C. Zhang, “What will 5g be?,” IEEE Journal on Selected Areas in Communications, vol. 32, no. 6, pp. 1065–1082, 2014.
[3] D. Liu, L. Wang, Y. Chen, M. Elkashlan, K. Wong, R. Schober, and L. Hanzo,“User association in 5g networks: A survey and an outlook," IEEE Communications Surveys Tutorials, vol. 18, no. 2, pp. 1018-1044, 2016.
[4] M. F. Tuysuz and R. Trestian,“Energy-ecient vertical handover parameters, classication and solutions over wireless heterogeneous networks: a comprehensive survey," Wireless Personal Communications, vol. 97, no. 1, pp. 1155-1184, 2017.
[5] J. Marquez-Barja, C. T. Calafate, J.-C. Cano, and P. Manzoni,“An overview of vertical handover techniques: Algorithms, protocols and tools," Computer communications, vol. 34, no. 8, pp. 985-997, 2011.
[6] M. Stemm and R. H. Katz, " Vertical handos in wireless overlay networks," Mobile Networks and applications, vol. 3, no. 4, pp. 335-350, 1998.
[7] T. M. Duong and S. Kwon, " Vertical handover analysis for randomly deployed small cells in heterogeneous networks," IEEE Transactions on Wireless Communications, vol. 19, no. 4, pp. 2282-2292, 2020.
[8] S. Cai, Y. Che, L. Duan, J.Wang, S. Zhou, and R. Zhang, " Green 5g heterogeneous networks through dynamic small-cell operation," IEEE Journal on Selected Areas in Communications, vol. 34, no. 5, pp. 1103-1115, 2016.
[9] A. S. Andrae and T. Edler, “On global electricity usage of communication technology: trends to 2030,”Challenges, vol. 6, no. 1, pp. 117–157, 2015.
[10] L. Belkhir and A. Elmeligi, “Assessing ict global emissions footprint: Trends to2040 & recommendations,”Journal of cleaner production, vol. 177, pp. 448-463,2018.
[11] A. Racz, A. Temesvary, and N. Reider,“Handover performance in 3gpp long termevolution (lte) systems,”in2007 16th IST Mobile and Wireless CommunicationsSummit, pp. 1–5, IEEE, 2007.
[12] W. K. Lai and J. C. Chiu, “Improving handoff performance in wireless overlaynetworks by switching between two-layer ipv6 and one-layer ipv6 addressing,”IEEE Journal on Selected Areas in Communications, vol. 23, no. 11, pp. 2129–2137, 2005.
[13] K. I. Pedersen, P. H. Michaelsen, C. Rosa, and S. Barbera,“Mobility enhance-ments for lte-advanced multilayer networks with inter-site carrier aggregation,”IEEE Communications Magazine, vol. 51, no. 5, pp. 64–71, 2013.
[14] K. Dimou, M. Wang, Y. Yang, M. Kazmi, A. Larmo, J. Pettersson, W. Muller,and Y. Timner,“Handover within 3gpp lte: Design principles and performance,”in2009 IEEE 70th Vehicular Technology Conference Fall, pp. 1–5, IEEE, 2009.
[15] M. M. Hasan, S. Kwon, and J.-H. Na,“Adaptive mobility load balancing algorithm for lte small-cell networks,”IEEE transactions on wireless communications,vol. 17, no. 4, pp. 2205–2217, 2018.
[16] M. M. Hasan, S. Kwon, and S. Oh,“Frequent-handover mitigation in ultra-denseheterogeneous networks,”IEEE Transactions on Vehicular Technology, vol. 68,no. 1, pp. 1035–1040, 2018.
[17] V. K. Shaw and S. D. Roy, “Handoff analysis in 5g small cell network,” in 2020 International Conference on Electronics and Sustainable Communication Systems(ICESC), pp. 655–659, IEEE, 2020.
[18] R. Arshad, H. ElSawy, S. Sorour, T. Y. Al-Naffouri, and M.-S. Alouini, “Handovermanagement in 5g and beyond: A topology aware skipping approach,”IEEEAccess, vol. 4, pp. 9073–9081, 2016.
[19] A. Merwaday and I. G ̈uven ̧c, “Handover count based velocity estimation and mo-bility state detection in dense hetnets,”IEEE Transactions on Wireless Commu-nications, vol. 15, no. 7, pp. 4673–4688, 2016.
[20] C.-H. Lee and Z.-S. Syu, “Handover analysis of macro-assisted small cell net-works,” in2014 IEEE International Conference on Internet of Things (iThings),and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber,Physical and Social Computing (CPSCom), pp. 604–609, IEEE, 2014.
[21] X. Xu, Z. Sun, X. Dai, T. Svensson, and X. Tao, “Modeling and analyzing the cross-tier handover in heterogeneous networks,”IEEE Transactions on WirelessCommunications, vol. 16, no. 12, pp. 7859–7869, 2017.
[22] J. Wu, Y. Zhang, M. Zukerman, and E. K.-N. Yung,“Energy-efficient base-stations sleep-mode techniques in green cellular networks: A survey,”IEEE communications surveys & tutorials, vol. 17, no. 2, pp. 803–826, 2015.
[23] O. Arnold, F. Richter, G. Fettweis, and O. Blume,“Power consumption modeling of different base station types in heterogeneous cellular networks,”in 2010 Future Network & Mobile Summit, pp. 1–8, IEEE, 2010.
[24] C. Han, T. Harrold, S. Armour, I. Krikidis, S. Videv, P. M. Grant, H. Haas, J. S.Thompson, I. Ku, C.-X. Wang,et al.,“Green radio: radio techniques to enable energy-efficient wireless networks,”IEEE communications magazine, vol. 49, no. 6,pp. 46–54, 2011.
[25] Y. Zou, Y.-D. Yao, and B. Zheng,“Opportunistic distributed space-time coding for decode-and-forward cooperation systems,”IEEE Transactions on Signal Processing, vol. 60, no. 4, pp. 1766–1781, 2011.
[26] D. Feng, C. Jiang, G. Lim, L. J. Cimini, G. Feng, and G. Y. Li,“A survey of energy-efficient wireless communications,”IEEE Communications Surveys &Tutorials, vol. 15, no. 1, pp. 167–178, 2012.
[27] F. Richter, A. J. Fehske, and G. P. Fettweis,“Energy efficiency aspects of basestation deployment strategies for cellular networks,”in 2009 IEEE 70th VehicularTechnology Conference Fall, pp. 1–5, IEEE, 2009.
[28] W. Guo and T. O Farrell,“Green cellular network: Deployment solutions, sensitivity and tradeoffs,”in2011 Wireless Advanced, pp. 42–47, IEEE, 2011.
[29] S. Zhang, J. Gong, S. Zhou, and Z. Niu,“How many small cells can be turned off via vertical offloading under a separation architecture?,”IEEE Transactions on Wireless Communications, vol. 14, no. 10, pp. 5440–5453, 2015.
[30] R. Tao, W. Liu, X. Chu, and J. Zhang,“An energy saving small cell sleeping mechanism with cell range expansion in heterogeneous networks,”IEEE Transactions on Wireless Communications, vol. 18, no. 5, pp. 2451–2463, 2019.
[31] M. R. Celenlioglu, D. G ̈oz ̈upek, and H. A. Mantar,“A survey on the energy efficiency of vertical handover mechanisms,” inProc. of the International Conferenceon Wireless and Mobile Networks (WiMoN), 2013.
[32] X. Pons, A. Mesodiakaki, C. Gruet, L. Naviner, F. Adelantado, L. Alonso, and C. Verikoukis,“An energy efficient vertical handover decision algorithm,”in 2014 IEEE Globecom Workshops (GC Wkshps), pp. 1145–1150, IEEE, 2014.
[33] B. Narwal and A. Mohapatra,“Energy efficient vertical handover algorithm for heterogeneous wireless networks,”Int. J. Control Theor. Appl, vol. 9, no. 19, pp.9221–9225, 2016.
[34] A. Prasad, A. Maeder, and C. Ng,“Energy efficient small cell activation mechanism for heterogeneous networks,” in2013 IEEE Globecom Workshops (GC Wkshps), pp. 754–759, IEEE, 2013.
[35] S. C. Forum, “Precision planning for 5g era networks with small cells, version :Scf230.10.01, release on october 30, 2019.”