Focus Group on IMT-2020, IMT-O-016, October 2015. 3GPP Specifications3 [13] 3GPP TR 23.799: Study on Architecture for Next Generation System (Release 14), December 2016. [14] 3GPP TR 38.913: Study on Scenarios and Requirements for Next Generation Access Technologies (Release 14), March 2017. [15] 3GPP TR 38.912: Study on New Radio (NR) Access Technology (Release 14), March 2017. [16] 3GPP TR 38.801: Study on New Radio Access Technology: Radio Access Architecture and Interfaces (Release 14), March 2017. [17] 3GPP TS 38.300: NR; NR and NG-RAN Overall Description, Stage 2 (Release 15), April 2019. [18] 3GPP TR 38.802: Study on New Radio Access Technology, Physical Layer Aspects (Release 14), March 2017. [19] 3GPP TR 38.803: Study on New Radio Access Technology, RF and Co-existence Aspects (Release 14), March 2017. 3GPP TR 38.804: Study on New Radio Access Technology, Radio Interface Protocol Aspects (Release 14), March 2017. [21] 3GPP TS 22.261: Service Requirements for the 5G system, Stage 1 (Release 16), June 2017. [22] 3GPP TR 38.900: Study on Channel Model for Frequency Spectrum Above 6 GHz (Release 14), December 2016. Articles, Books, White Papers, and Application Notes [23] China Mobile Research Institute, C-RAN: The Road Towards Green RAN (Version 3.0), June 2014. [24] China Mobile Research Institute, NGFI: Next Generation Fronthaul Interface (Version 1.0), June 2015. ITU-R specifications can be accessed at the following URL: http://www.itu.int/en/ITU-R/study-groups/rsg5/ rwp5d/imt-2020/. 3GPP specifications can be accessed at the following URL: http://www.3gpp.org/ftp/Specs/archive/. Introduction and Background xcvii [25] NGMN Alliance, NGMN 5G White Paper v1.0, February 2015. [26] NGMN, Further Study on Critical C-RAN Technologies, April 2015. D. Bojic et al., Advanced wireless and optical technologies for small cell mobile backhaul and dynamic software-defined management, IEEE Commun. Mag., 51 (9) (2013). [28] M. Dohler, et al., Beyond 5G Challenges: White Paper, The University of Sheffield, March 2015. [2