IEEE TRANSACTIONS ON BROADCASTING 1 5G Radio Access Network Architecture for Terrestrial Broadcast Services Mikko Säily, Carlos Barjau Estevan, Jordi Joan Gimenez, Fasil Tesema, Wei Guo, David Gomez-Barquero and De Mi Abstract — The 3rd Generation Partnership Project (3GPP) has design. Rel-15 and Rel-16 only cover unicast, or Point-to-Point defined based on the Long Term Evolution (LTE) enhanced (PTP), transmissions. However, benefits of multicast and Multicast Broadcast Multimedia Service (eMBMS) a set of new broadcast, or Point-to-Multipoint (PTM), have been already features to support the distribution of Terrestrial Broadcast assessed as beneficial for some 5G use cases [1], [2]. services in Release 14. On the other hand, a new 5th Generation (5G) system architecture and radio access technology, 5G New The support of PTM communications is not new in 3GPP. Radio (NR), are being standardised from Release 15 onwards, Mobile broadcast as a service is already included in Long Term which so far have only focused on unicast connectivity. This may Evolution (LTE) as per the enhanced Multicast/Broadcast change in Release 17 given a new Work Item set to specify basic Multimedia Service (eMBMS). The set of specifications have Radio Access Network (RAN) functionalities for the provision of been updated to support new services such as public safety, multicast/broadcast communications for NR. This work initially Internet of Things (IoT) or Vehicle-to-Everything (V2X) [3]. excludes some of the functionalities originally supported for Terrestrial Broadcast services under LTE e.g. free to air, receive- Its most recent update comes in Rel-14 [4] and Rel-16 [5], [6] only mode, large-area single frequency networks, etc. This paper in order to support the 5G requirements for broadcast, and in proposes an enhanced Next Generation RAN architecture based particular for the provision of Terrestrial Broadcast services. on 3GPP Release 15 with a series of architectural and functional This has implied severe changes at the air-interface to enhancements, to support an efficient, flexible and dynamic implement larger Single Frequency Networks (SFNs) or the selection between unicast and multicast/broadcast transmission introduction of carriers with dedicated broadcast content. The modes and also the delivery of Terrestrial Broadcast services. The paper elaborates on the Cloud-RAN based architecture and architecture relies on the existing for eMBMS with the proposes new concepts such as the RAN Broadcast/Multicast introduction of the so-called receive-only mode for Subscriber Areas that allows a more flexible deployment in comparison to Identification Module (SIM)-free operation even without eMBMS. High-level assessment methodologies including uplink, or a new xMB interface between the eMBMS system complexity analysis and inspection are used to evaluate the and service providers. So far, eMBMS has proven limited feasibility of the proposed architecture design and compare it with success among mobile network operators due to a demanding the 3GPP architectural requirements. implementation both at the network architecture and user Index Terms — 5G, architecture, broadcast, multicast, point-to- equipment. point, point-to-multipoint, radio access network, single frequency Under the 5G System (5GS) and NG-RAN architectures, network, signal synchronisation. basic support for multicast/broadcast is expected to be introduced in Rel-17. This includes Multicast/Broadcast I. INTRODUCTION support at 5G Core Network [7] and NR-based Mixed Mode HE 3rd Generation Partnership Project (3GPP) finalised the transmissions at RAN [8]. The support of Terrestrial Broadcast T first set of 5th Generation (5G) specifications for Release 15 services is not in the scope of these specifications. However, a (Rel-15) in December 2018. This defines a new Radio Access generic architectural solution that could allocate requirements Technology (RAT) known as New Radio (NR), the Next from different domains would be beneficial to increase Generation Radio Access Network (NG-RAN) and the 5G Core deployment opportunities. Network which embrace several design principles such as: (i) One of the 3GPP system requirements for 5G is a flexible forward compatibility with future releases; (ii) control-user broadcast/multicast service for three types of devices, be they plane separation (CUPS); (iii) lean and cloud-native system enhanced Mobile Broadband (eMBB), Ultra Reliable and Low This work was supported in part by the European Commission under the Politecnica de Valencia, 46022 Valencia, Spain (e-mail: {carbare1, 5GPPP project 5G-Xcast (H2020-ICT-2016-2 call, grant number 761498). The dagobar}@iteam.upv.es). views expressed in this contribution are those of the authors and do not J. J. Gimenez is with the Future Networks Department, Institut für necessarily represent the project. Part of the material in this paper was presented RundfunktTechnik GmbH, 80939 Munich, Germany (e-mail: at the IEEE International Symposium on Broadband Multimedia Systems and [email protected]). Broadcasting (BMSB) 2019 [20]. F. Tesema is with Nomor Research GmbH, Munich, 81541 Germany (e- M. Säily is with the Standardization and Research Lab, Network & mail: [email protected]) Architecture Group, Nokia Bell Labs, Espoo, 02610 Finland (e-mail: W. Guo is with Samsung R&D Institute UK, Staines-upon-Thames TW18 [email protected]). 4QE, U.K. (e-mail: [email protected]). C. Barjau Estevan and D. Gomez-Barquero are with the Institute of D. Mi is with the 5G Innovation Centre (5GIC), Institute for Communication Telecommunications and Multimedia Applications (iTEAM), Universitat Systems, University of Surrey, Guildford GU2 7XH, U.K. (e-mail: [email protected]). IEEE TRANSACTIONS ON BROADCASTING 2 Latency Communications (URLLC) and massive Machine Type Communications (mMTC) [9]. 5G should be envisioned as a system of systems, where the Core and Transport Network Data Network alongside the RAN must accommodate a plethora of different SMF services, with stringent requirements, ranging from several N6 N4 N11 gigabits/sec (think of Augmented/Virtual reality - AR/VR) to UPF AMF low kilobits/sec throughput (think of mMTC), latencies ranging 5GC from 1 millisecond (e.g., industrial IoT) up to several seconds NG-RAN N3 N2 gNB (e.g., best-effort data delivery), mobility support to moving gNB-CU-UP E1 gNB-CU-CP Xn gNB devices, from static equipment (e.g., roof-top antennas) up to (SDAP, PDCP) (SDAP, PDCP) 500 kilometre per hour (e.g., V2X) and support for millions of F1-U F1-C users per square kilometre (e.g., massive IoT) [10]-[12]. F1-C F1-U The 5G Infrastructure Public Private Partnership (5G-PPP) gNB-DU gNB-DU project 5G-Xcast has developed a holistic implementation of (RLC, MAC, PHY) (RLC, MAC, PHY) eCPRI/xRAN 5G PTM systems [13], covering Core Network [14]-[16] and interface RAN developments from air interface [17], [18] to architecture RU RU RU RU [19]-[21] and protocols [21], [22]. This can facilitate the (PHY) (PHY) (PHY) (PHY) fulfilment of requirements from different applications [23], including traditional Terrestrial Broadcast deployments, which Fig. 1. Rel-15 NG-RAN architecture with a CU-DU split deployment. are the scope of this work. The main contributions of this work are listed as follows: Central Units (CUs) and Distributed Units (DUs) in 5G • We develop a dynamic RAN Broadcast/Multicast Areas architecture enables dynamic adaptation of QoS functions mechanism that allows the delivery of multicast/broadcast depending on the real-time radio conditions, user density and services wherever needed without the fixed deployment on dynamically controlled geographical area. top of the existing RAN. As shown in Fig. 1, the gNB functions are split into CU and • Our proposed RAN architecture design supports multi-cell DU, where CU covers higher layer protocol functions of and SFN transmissions using NG-RAN based Service Data Adaptation Protocol (SDAP) and Packet Data synchronization method fulfilling Quality of Service (QoS) Convergence Protocol (PDCP), and DU entails lower layer targets defined for traffic flows. protocol functions of Radio Link Control (RLC), Medium • We introduce a new RAN interface design to support Access Control (MAC) and Physical Layer (PHY). In a typical Terrestrial Broadcast and multicast with the minimal Cloud-RAN deployment, the CUs are placed in a computing impact on the current 5G system. hardware pool and thus form the cloud. The gNBs are inter- • We propose a detailed procedure and deployment strategy connected through an Xn interface. for our architecture design, together with high-level The F1 interface provides control (F1-C) and user (F1-U) evaluations including complexity analysis and inspection, plane connectivity between the CU and DU, enabling providing insightful and practical instructions on the deployments with C/U-plane separation. The E1 interface feasibility of our design. provides connectivity between the user plane CU-UP and The rest of this paper is structured as follows. First, the RAN control plane CU-CP, enabling deployments with C/U-plane architecture evolution to 3GPP Rel-15 is discussed in Section separation on the CU level. The interface also provides II. Next, it details in Section III our design on the new RAN separation between the radio network and transport network architecture for the Terrestrial Broadcast. Then, deployments layers, enabling the exchange of User Equipment (UE) and non- and procedures of the proposed architecture are presented in UE