BBU BBU CRAN L 1 BBU Radio Resource
BBU 的功能介紹 • BBU 的功能視 C-RAN 功能切割方式而異 • 包含完整 L 1 的 BBU 主要功能為無線資源控制 (Radio Resource Control; RRC)、 媒 介 存 取 控 制 (Media Access Control; MAC) 與通訊實體層 (Physical Layer; PHY) 以提供 或接受與 RRH 之介面的 I/Q 數位基頻訊號 5 … CPRl/OBSAl/ORl l. FFT/FFT De-/Modulation De-/sampling Antenna Mapping-Ml. MO Resource-block Mapping . . De-/Quantization . . Channel de-/ coding Transport-MAC … L 1 el. C L 2 Co. MP L 3 Control-RRC RRH l. Q DL l. Q UL
BBU 的功能介紹 • Layer 3 – Radio Resource Control (RRC) e. NB • 無線資源管理 • RRC 之下各層的設定 Layer 3 RRC • Layer 2 – Packet Data Convergence Protocol (PDCP ) • 處理標頭壓縮 • 加密運算 PDCP RLC – Radio Link Control (RLC) MAC • ARQ 與 HARQ 等重傳 • 封包分割與重組 PHY – Medium Access Control (MAC) • Qo. S (Quality of Service) 排程 6 Layer 2 Layer 1
BBU 的功能介紹 • Layer 1 – Physical (PHY) • 將資料轉為實體訊號發送 • 通道編碼 (以 LTE 為例含冗餘碼、渦輪碼、交織器) • 以 LTE 為例下行為正交分頻多重存取 (Orthogonal Frequency Division Multiple Access; OFDMA) • 以 LTE 為例上行為單載波分頻多重存取 (Single-Carrier Frequency-Division Multiple Access; SC-FDMA) • 多輸入多輸出 (Multiple Input Multiple Output; MIMO) 技術 • 加強型細胞間干擾消除 (enhanced Inter-Cell Interference Coordination; e. ICIC) • 多點協調 (Coordinated Multi-Point; Co. MP) 7
BBU 的功能介紹 • 以 LTE 規格的下行 PHY 為例 CRC-24 insertion Code block segmentation Turbo coding Sub block interleaver Bit collection / selection / transmission Sub block interleaver Bits Resource element mapper Scrambler Symbol mapper Antenna mapper 8 OFDM Symbols Resource element mapper OFDM
BBU 的核心技術 Coordinated Scheduling / Beamforming (CS/CB) Joint Processing (JP) Coordinated Scheduling / Beamforming Joint Transmission Dynamic Cell Selection • Tx point is the serving cell • • • UE scheduling / BF decisions are A couple of BSs serve one UE by subframe made with coordination among cells 17 圖片來源: 引用自 [5] Tx point can switch subframe
C-RAN 架構下的 BBU Pool 技術 • Single BBU v. s. BBU Pool BBU System-specific Baseline I/O S 1 -X 2 Control unit General Processing L 3 Alarm unit BB processing L 1 -12 I/O FH Cooling / fans Legend: I/O:input / output interface BB:baseband FH:fronthaul Power supply & conversion BBU Pool I/O S 1 -X 2 Control unit Alarm unit BB processing L 1 -L 2 Low latency switch 29 General Processing L 3 I/O (FH) Cooling / Fans Power conversion
C-RAN 架構下的 BBU Pool 技術 • Virtualized BBU Cloud 30
C-RAN 架構下的 BBU Pool 技術 • BBU 功能的實現:DSP vs. GPP DSP GPP Flexibility dedicated solution general purpose Vendor compatibility vendor specific, proprietary higher compatibility between vendors Backward compatibility limited assured Power consumption lower higher Real-time processing optimized, achieved only possible with high power hardware Virtualization of BBU possible 33
參考資料 [1] LTE-A 強化行動通訊品質 http: //www. 2 cm. com. tw/technologyshow_content. asp? sn=1311050004 [2] ICIC and e. ICIC http: //www. simpletechpost. com/2012/06/icic-and-eicic. html [3] LTE Quick Reference: ICIC(Inter-Cell Interference Coordination) http: //www. sharetechnote. com/html/Handbook_LTE_ICIC. html [4] Moving to LTE-Advanced. . . before LTE arrives! https: //www. electronicproducts. com/Test_and_Measurement/Benchtop_Rack_ Mountable/Moving_to_LTE-Advanced_before_LTE_arrives. aspx [5] 3 GPP LTE-A下行傳輸之多點協調技術介紹 http: //www. teema. org. tw/upload/ciaupload/1_62160. doc 35
參考資料 [6] A. Checko, Cloud Radio Access Network architecture - Towards 5 G mobile networks, Ph. D. thesis, Department of Photonics Engineering, Technical University of Denmark, 2016. [7] C. -L. I, et al. , “Recent Progress on C-RAN Centralization and Cloudification, ” IEEE Access, 2014. [8] M. D. Andrade, et al. , “Cost Models for Baseband Unit (BBU) Hotelling: from Local to Cloud, ” IEEE International Conference on Cloud Networking, 2015. [9] BBU 池技术研究及干扰抑制性能验证 http: //www. ydsjjs. com/oa/pdfdow. aspx? Sid=2017060004 36
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