Point-to-Multipoint services on Fifth-Generation Mobile Networks
Carlos Salvador Barjau Estevan
Point-to-multipoint services over mobile networks have always been of interest to several verticals. They are not only limited to the delivery of television, but other applications such as Internet of Things (IoT), Vehicular-to-Everything, Public Warning Services (PWS); which can efficiently leverage the capacity that the use of point-of-multipoint provides. In this regard, mobile networks had their first version of a Broadcast/Multicast extension in 3G, known as Multicast/Broadcast Multimedia Services (MBMS). However, this technology was considered limited in technical and economical terms and did never successfully take off. The 4G Long Term Evolution (LTE) version, enhanced MBMS (eMBMS), provided the much needed enhancements by listening to the requirements of the broadcast industry. Broadcasters, specially in Europe, see in this technology a potential terrestrial broadcast standard able to provision point-to-multipoint services for both rooftop antennas, pedestrian devices and moving vehicles. Yet, the requirement of New Radio based point-to-multipoint mode was defined in the early stages of 5G, but it was not until Release 17 that this requirement started to get addressed, in the form of 5G Multicast Broadcast Services (5MBS). These point-to-multipoint mobile standards compete against the existing European standard DVB-T2 and the American ATSC 3.0, already deployed commercially. It remains to be seen what will happen to the lower band of the UHF, which is currently allocated to primary broadcast services in ITU region 1 and an agenda topic for the World Radio Congress of 2023. In other regions, part of the band has been allocated to 5G communications.
This dissertation covers the state-of-the-art in LTE eMBMS Release 14, also known as Enhanced Television Services (ENTV). ENTV provided a suite of radio and core enhancements that made eMBMS into a viable terrestrial broadcast standard. The latest iteration of this technology is known as LTE-based 5G Broadcast; even though it is not New Radio or 5G Core based. To bridge this gap, research efforts by academia, public and private enterprises evaluated how to provide a 5G-based solution for point-to-multipoint services. The most notable effort in this regard is the Horizon 2020 project 5G-Xcast, which ran from 2017 to 2019. 5G-Xcast provided several architectural solutions, from the content delivery perspective down to air interface specifics; providing new waveforms based on New Radio and Network Functions interoperable with a Release 15 5G Core. The findings are summarized in this thesis. Two examples of eMBMS applied to different verticals are included in the thesis, one for the use of eMBMS in industrial environments, and the other using eMBMS as a PWS technology.
Providing point-to-multipoint services as another cellular service poses some problems, as the standardization process of eMBMS showed: the broadcast infrastructure is different than the cellular one. Having a waveform that is suited for both scenarios is a difficult endeavour. The thesis provides a new perspective into this problem: Having existing Terrestrial Broadcast standards and infrastructure be the point-to-multipoint solution of 5G, where mobile operators and broadcasters collaborate together. This is defined in the dissertation as Convergence of Terrestrial and Mobile Networks. The technologies chosen to be converged together were ATSC 3.0 and 5G; using the existing Release 16 framework known as Advanced Traffic Steering, Switching and Splitting (ATSSS). ATSSS is a series of procedures, interfaces, new Network Functions, to allow the joint use of a 3GPP Access Network alongside a non-3GPP one, like Wi-Fi. However, the use of ATSSS for cellular plus broadcast brings challenges, as the ATSSS technology was not designed to be used with a unidirectional access network like ATSC 3.0. These limitations are described in detail, and an architectural proposal that overcomes the limitations is proposed. This solution is based on Quick UDP Internet Connections (QUIC), and how to provide Convergent Services (i.e File Repair and Video Offloading) is shown.
The thesis concludes with a description of Release 17 5MBS, including the new concepts introduced. 5MBS features the capacity of switching between unicast, multicast and broadcast; depending on the service addressed, the geographical location of the users, and the capability of the RAN infrastructure targeted. In order to evaluate 5MBS, a performance study of the use of multicast inside the 5G Core has been carried out. The 5MBS prototype was developed as part of the VLC Campus 5G laboratory, using the commercial software Open5GCore which provides the libraries and Network Functions to deploy your own 5G Private Network in testing environments. The system model of the experiment is formed by a video server, connected to the Open5GCore and the 5MBS enhanced functions; which will deliver the content to an emulated RAN environment hosting virtual gNBs and devices. The results obtained reinforce the objective of the thesis, positioning point-to-multipoint as a scalable way to deliver live content.