臺灣博碩士論文加值系統

5G雙層細胞架構(Two-layer 5G Cellular Architecture)的構想被許多國際大廠[1,2]的白皮書中提出來，此架構可能成為5G的規格。此架構分成大細胞與小細胞，大細胞為現行的4G架構，小細胞則為5G高傳輸量的架構；當使用者要進入網路時，必須先透過競爭模式隨機接入(Contention-based Random Access)進入大細胞中，當使用者有高資料量需求時，再經由非競爭模式隨機接入(Contention-Free Random Access)進入5G。由於5G人數眾多，現行的4G隨機接入機制是否能滿足5G的需求，是本論文探索的議題。
由於目前並無5G話務模型，因此本論文使用3GPP MTC話務模型，並考慮實際的通道情況，包括:路徑衰減、遮蔽效應、衰弱、錯失偵測機率。並針對此模型進行效能分析，包含成功接入機率、碰撞機率、接入延遲時間與總功率的消耗，發現當使用者數量多時，現行的4G隨機接入機制並不能達到5G的需求，會造成碰撞機率過高的問題，使得使用者必須花費更多時間與額外的功率消耗才能進入系統。然而當target power設定越高，使用者所消耗的功率也越多，因此本論文對不同target power的設定值進行隨機接入模擬，並結合四項效能指標做分析，提出建議的target power設定值。此外，本篇論文亦針對增加隨機接入機會(Random Access Opportunities)的隨機接入效能分析，以此改善碰撞機率過高、成功接入機率過低的問題；因此當RAO增加為三倍時，成功接入機率達96%，碰撞機率降至17%，在實際系統獲得明顯改善。

Two-layer cell architecture has been proposed as a candidate for future 5G systems, where the system constitutes of macro cells and small cells. Macro cells use the existing 4G system while small cell use 5G technology to provide higher high data rate and system capacity. A user first camps 4G systems through contention-based random access mechanism, and when very high data rate is needed it is handed over to 5G systems via contention-free random access. Whether the current 4G random access design is able to cope with the very large number of users anticipated in the future 5G systems is theme of this research.
In this thesis, the performance of random access in the two-layer cell architecture is studied in realistic channel environment, with MTC (Machine-Type Communications) traffic model proposed by 3GPP. The performance indexes include access success probability, collision probability, the access delay and total power consumption. Numerical results show that the current 4G random access design is not able to achieve the 5G requirements because of high collision probability, and excessive access delay and power consumption. One remedy is to increase the random access opportunity (RAO). Our results show that with 3-times RAO, access success rate is increased to 96%, and collision probability is decreased to 17%, and that significantly improves the random access performance.

致謝 i
摘要 ii
Abstract iii
目錄 iv
圖目錄 vi
表目錄 viii
第一章 導論 1
1.1 前言 1
1.2 研究動機 1
1.3 論文架構 3
第二章 5G細胞架構介紹 4
2.1 雙層細胞架構 4
2.2 隨機接入的時機與目的 4
第三章 4G隨機接入之程序介紹 6
3.1 PRACH 6
3.2 PRACH時頻域結構與ZC序列 11
第四章 話務模型的分析 17
4.1 3GPP MTC話務模型 17
第五章 隨機接入之效能分析 19
5.1 效能指標 19
5.2系統參數設定 20
5.2.1 分頻雙工參數設定 20
5.2.2 分時雙工參數設定 25
5.3 3GPP效能分析的驗證 27
5.4 實際系統下的效能分析 28
5.4.1 模擬環境設定 29
5.4.2路徑衰減模型 30
5.4.3 遮蔽效應模型 31
5.4.4 衰弱效應模型 32
5.4.5 錯失偵測機率 32
5.4.6 開迴路功率控制 33
5.5 實際系統的效能分析 36
5.6不同數量前導碼的效能分析 44
第六章 結論與未來展望 49
參考文獻 50

[1] NTT DOCOMO INC., “DOCOMO 5G White Paper, 5G Radio Access: Requirements, Concept and Technologies,” Jul. 2014.
[2] METIS Deliverable D8.4, Mobile and wireless communications Enablers for the Twenty-twenty Information, Mar. 2015.
[3] 3GPP TR 37.868, “RAN improvements for machine-type communications,” v.11.0.0, Oct. 2011.
[4] 3GPP TS 22.368, “Service Requirements for Machine-Type Communications,” V10.1.0, Jun. 2010.
[5] R.G. Cheng, C.H. Wei, S.L. Tsao, and F.C. Ren, ”RACH collision probability for machine-type communications”, Proc. IEEE VTC, Yokohama, Japan, May 2012, pp.1-5.
[6] E. Dahlman, S. Parkvall, and J. Sköld, 4G LTE/LTE-Advanced for Mobile Broadband, Cambridge University Press, 2009.
[7] Farooq Khan, LTE for 4G Mobile Broadband Air Interface Technologies and Performance, 1st Edition, Cambridge University Press New York, NY, USA 2009.
[8] 3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (EUTRA), Physical layer procedures,” v10.6, Jun. 2012.
[9] 李靜，「基於LTE系統的PRACH仿真鏈路平台設計和Preamble檢測算法研究」，武漢理工大學信息工程學院碩士位論文2011年6月。
[10] 3GPP TS 36.321, “Medium Access Control (MAC) protocol specification,” v12.6.0 Jun. 2015.
[11] 3GPP TS 36.211, Evolved Universal Terrestrial Radio Access (EUTRA), Physical Channels and Modulation, v10.5.0, Jun. 2012.
[12] 3GPP RAN R4-071591, “Evolved Universal Terrestrial Radio Access (EUTRA), LTE UL Simulation Results for PRACH,” Oct. 2007.
[13] 3GPP. TSG RAN: TS36.212v8.9.0 E-UTRA, Physical Channels and Modulation, Dec. 2009.
[14] K. Zhou and N. Nikaein, “Packet aggregation for machine type communications in LTE with random access channel,” IEEE WCNC, Shanghai, China, Apr. 2013, pp. 262-267.
[15] IEEE 802.16 Broadband Wireless Access Working Group “Proposed performance requirements for network access with large number of devices,” Jan. 2011.
[16] G.-Y. Lin, H.-Y. Wei, and A.C.-C. Hsu, “Overload control for machine-type-communications in LTE-advanced system,” IEEE Commun. Mag., vol. 50, no. 6, pp. 38-45 Jun. 2012.
[17] 3GPP TS 36.331, “Evolved Universal Terrestrial Radio Access (EUTRA), Radio Resource Control (RRC), Protocol specification” v13.0.0 Dec. 2015.
[18] 3GPP TR 36.912, “Feasibility study for Further Advancements for E-UTRA (LTE-Advanced)” v12.0.0 Sep. 2014.