隨著可攜式終端設備的發展，人類越來越依賴無線通訊技術來進行社交、商業等行為。若在建築物密集的都市當中，基地台之訊號可能會因建築物的遮蔽導致較差的收訊；而在人口稀少的郊區，用戶則可能處於基地台通訊範圍的邊緣或外部，導致訊號薄弱甚至沒有訊號。無線訊號透過使用中繼技術可以獲得通訊範圍的延伸，當訊號傳遞途中遭遇遮蔽物干擾時，亦可透過中繼站的訊號轉發來達到繞送的效果，進而解決收訊不良的問題。在本文中，我們考量到用戶具有移動性，並因而導致換手過程的差異，因此假設了可能的幾種情境，並整合分析，探討路徑差異導致延遲時間的差異，進而知曉如何選擇較佳的路徑以及基地台之間如何佈署較適當的情境。

With the fast development of mobile networks and technologies, many people have highly relied on wireless communication to carry out their everyday activities, like communicating with their family members or online shopping. However, in the downtown of a city, the radio signals that the user equipment (UE) receives from its nearby eNBs may be sheltered by its surrounding high buildings, resulting in poor mobile QoS. In a rural area, the user staying at the border of an eNB's communication range may also receive weak radio signals from the eNB. In fact, wireless signals emitted by an eNB, e.g., B, can be forwarded by a relay station so as to extend the communication range of B. When the signals radiated by B are interfered or sheltered, a relay station can also help to bypass the interference and shelters, thus effectively solving the problems of poor radio signals reception. In this paper, we deal with handover processes between two relay stations and between a relay station and an eNB, both of which are different from that between two eNBs. But handover concerning relay stations has its problems, e.g., if the base stations before and after handover are two relation stations and they belong to two neighbor eNBs, how to proceed the handover? Should the handover go through the two eNBs? Several handover scenarios are also explored in this study.

1. Introduction
2. Background and Related Work
2.1 Network Interfaces
2.2 LTE-Advanced (LTE-A)
2.3 Relay node (RN)
2.4 LTE-Femto (HeNB)
2.5 Related Studies
3. The Proposed of Possible Scenarios
3.1 Scenario 1: DeNBsrc - to – RNsrc
3.2 Scenario 2: RNsrc - to - DeNBsrc
3.3 Scenario 3: RNsrc - to - RNsrc’
3.4 Scenario 4: DeNBsrc - to - RNtar
3.5 Scenario 5: RNsrc - to - DeNBtar
3.6 Scenario 6: RNsrc- to - RNtar
3.7 Signaling Cost of Scenarios
4. Simulations and Discussions
4.1 Experiment on Different Paths
4.2 Experiment on Different Moving Speeds
4.3 Experiment on Different Numbers of UEs
4.3.1 Handing over individually
4.3.2 UEs moving along different paths with the same speed
4.3.3 UEs moving along the same path with different speeds
4.4 Experiment on Random Moving Model
5. Conclusions and Future Studies
6. Acknowledgement
References

[1].3GPP TS 8401 V10.4.0 (2012–06): Evolved Universal Terrestrial Radio Access Network (EUTRAN); Architecture description.
http://www.3gpp.org/ftp/specs/archive/36_series/36.401/
[2].A.M. Linoh, H.A. Chan and E.F. Olabisi, "Handover Coordination with a Relay-based Design for Heterogeneous Wireless Networks," IEEE Conference on Local Computer Networks (LCN), 2010, PP. 380-383.
[3].3GPP TS 36.424 V10.1.0 (2011-06): Evolved Universal Terrestrial Access Network (E-UTRAN); X2 data transport.
http://www.3gpp.org/ftp/specs/archive/36_series/36.424/
[4].Y.C. Sung, M.H. Tsai, and H.Y. LEE, "An Efficient Robust Header Compression Mechanism for Long Term Evolution Advanced Relay Architecture," Asia-Pacific Network Operations and Management Symposium (APNOMS), 2012, PP. 25-27.
[5].3GPP TR 36.808 V10.1.0 (2013-07): Evolved Universal Terrestrial Radio Access (E-UTRA); Carrier Aggregation; Base Station (BS) radio transmission and reception.
http://www.3gpp.org/ftp/specs/archive/36_series/36.808/
[6].3GPP TR 36.819 V11.2.0 (2013-09): Coordinated multi-point operation for LTE physical layer aspects (Release 11).
http://www.3gpp.org/ftp/specs/archive/36_series/36.819/
[7].3GPP TS 26.346 V14.3.0 (2017-06): Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs (Release 14).
http://www.3gpp.org/ftp/specs/archive/36_series/36.819/
[8].X.C. Zhang, and X.J. Zhou, LTE-Advanced Air Interface Technology, 1st ed. London: CRC Press; 2012.
[9].S. Kasera, and N. Narang, 3G Networks: Architecture, Protocols and Procedures, McGraw Hill Education; 17 March 2004, PP. 83.
[10].3GPP TR 36.828 V11.0.0 (2012-06): Further enhancements to LTE Time Division Duplex (TDD) for Downlink-Uplink (DL-UL) interference management and traffic adaptation (Release 11).
http://www.3gpp.org/ftp/specs/archive/36_series/36.828/
[11].A. Ulvan, R. Bestak and M. Ulvan, "The study of Handover Procedure in LTE-based Femtocell Network," Third Joint IFIP, Wireless and Mobile Networking Conference (WMNC), 2010, PP. 1-6.
[12].NS-3 Project. ns-3. https://www.nsnam.org/.
[13].Wikipedia. Friis transmission equation.
https://en.wikipedia.org/wiki/Friis_transmission_equation.
[14].3GPP. Radio link management in hierarchical networks. TS 45.022, 3rd Generation Partnership Project (3GPP), 12 2009.
http://www.3gpp.org/ftp/specs/archive/45_series/45.022/
[15].“ns-3-user” mailing list. Why srs periodicity value of 80 is not enough for 70 ues in lena lte. https://groups.google.com/forum/#!topic/ns-3-users/afDcL8knL_Q.
[16].“ns-3-user” mailing list. Lte (lena) model handover problem.
https://groups.google.com/forum/#!topic/ns-3-users/N5xmmBXjKzo.
[17].3GPP. Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification. TS 36.331, 3rd Generation Partnership Project (3GPP), 06 2011.
http://www.3gpp.org/ftp/specs/archive/36_series/36.331/
[18].ShareTechnote. SRS (sounding reference signal).
http://www.sharetechnote.com/html/Handbook_LTE_SRS.html.
[19].R. Raheem, A. Lasebae, and J. Loo, "Performance Evaluation of LTE network via using Fixed/Mobile Femtocells," Advanced Information Networking and Applications Workshops (WAINA), 2014, PP. 255-260.
[20].O. Teyeb, V.V. Phan, B. Raaf, and S. Redana, "Handover Framework for Relay Enhanced LTE Networks," IEEE International Conference on Communications Workshops, 2009 PP. 1-5.
[21].Y.Y. Chen, and X. Lagrange, "Analysis and Improvement of Mobility Procedures for Mobile Relays in LTE networks," Personal, Indoor, and Mobile Radio Communications (PIMRC), 2015, PP. 1769-1774.
[22].Y.T. Mai, and J.Y. Chen, "IP Multimedia Relay Architectures with Multi-RAT Support in LTE-Advanced Wireless Network," Asia Modelling Symposium, 2013, PP. 283-288.
[23].A. Kamal, and V. Mathai, "A Novel Cell Selection Method for LTE HetNet," International Conference on Communication and Signal Processing, 2014, PP. 738-742.
[24].Y.S. Huang, F.Y. Leu, J.C. Liu, Y.L. Huang, and C.C. Chu, "A Handover Scheme for LTE Wireless Networks under the Assistance of GPS," Broadband and Wireless Computing, Communication and Applications (BWCCA), 2013, PP. 399-403.
[25].F.Y. Leu, P.Y Tsai, I. You, and H.C. Chen, "IP-based Seamless Handover Scheme using ANDSF in an Untrusted Environment," IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS), 2017, PP. 595-600.
[26].F.Y. Leu, and C.C. Cheng, "MIH-Based Congestion Control with Seamless Handover in Untrusted Networks," International Conference on Innovative Mobile and Internet Services in Ubiquitous Computing, July 2017, pp.502-512.
[27].Worlds first femtocell standard published by 3GPP.
http://www.3gpp.org/news-events/partners-news/1203-world-s-first-femtocell-standard
[28].Z.Y. Yang, F.Y. Leu "Relay Base-Station Handover in a 5G Environment," Advances on Broad-Band Wireless Computing, Communication and Applications (BWCCA), 2017, pp. 803-810.
[29].F.Y. Leu, C.Y. Liu, J.C. Liu, and F.C. Jiang "S-PMIPv6: an Intra-LMA model for IPv6 Mobility, " Journal of Network and Computer Applications, Vol. 58, December 2015, pp. 180–191.
[30].L.W. Chen, Y.L. Huang, "An Enhanced Handover Scheme Adopting Mobile Relays in a LTE-A Network for High-Speed Movements," Software Quality, Reliability and Security Companion (QRS-C), 2017, pp.567-568.
[31].J.Y. Chen, C.C. Yang, and Y.T. MAI, "A Novel Smart Forwarding Scheme in LTE-Advanced Networks," China Communications, 2015, pp.120-131.
[32].Cisco 5G Vision Series: Small Cell Evolution.
https://www.cisco.com/c/dam/en/us/solutions/collateral/service-provider/ultra-services-platform/5g-vision-series-small-cell-evolution.pdf
[33].3GPP. Further advancements for E-UTRA physical layer aspects. TR 36.814, 3rd Generation Partnership Project (3GPP), 03 2010.
http://www.qtc.jp/3GPP/Specs/36814-900.pdf