IBC2023 Tech Papers: 5G Broadcast Receivers: Optimizing Performance under Implementation Constraints

Abstract

The holy grail of making broadcast services ubiquitously available to the broadest set of users is to enable reception directly to smartphones, while reusing the silicon of cellular modems, with minimal compromises towards efficiency for a broad set of use cases.

5G Terrestrial Broadcast, as specified in 3GPP and profiled in ETSI TS 103 720, is realizing this promise. In the first part of our paper, we provide an overview of the design philosophy behind 5G Broadcast, mainly re-use of existing cellular modem silicon and protocol stack. For efficiency demonstration, we provide comparative simulations against other broadcasting standards under several practical deployment scenarios, further backed by multiple successful demos and trials of the technology.

Next, we highlight that, while maintaining the constraint of hardware reuse, further enhancements to the technology can be introduced by carefully exploiting existing features in cellular modems – for instance, time interleaving can be realized by reusing the building blocks of HARQ combining. Along with the incorporation of a codeblock-spreading frequency interleaver, we demonstrate considerable performance improvements in high-mobility scenarios, when such time interleavers are used.

We finally evaluate how some basic features of cellular modems (e.g., receive diversity) can greatly improve the performance of 5G Broadcast beyond the basic broadcast-specific feature set.

Introduction

3GPP-based Multimedia Broadcast Multicast Services (MBMS) for mobile network operators (MNO) has been part of 3GPP specifications for more than 20 years. In Release 9, an LTE-based MBMS, referred to as “eMBMS” was created and further enhanced until Release-12. In the last decade, several MNOs deployed eMBMS within operators’ networks and eMBMS modems and service layers are prominently available on mobile chipsets and mainstream mobile devices – primarily also because they are hardware- compatible with LTE modems. Meanwhile, with the 3GPP expansion to verticals and the migration to 5G, broadcasters showed significant interest in using 3GPP-based technologies to be operated on dedicated broadcast networks and a set of dedicated requirements of broadcast service providers finally resulted in the definition of 5G Broadcast requirements documented in clause 6.13 of 3GPP TS 22 261.

Based on these requirements, 3GPP specifications have gradually evolved (through to Release 16) to meet the use cases and requirements in order to support broadcasting of linear television and radio services, taking into account among others, support of free-to- air (FTA) services over 3GPP with no MNO broadcast subscription; support of receive-only mode devices (ROM); decoupling of content, MBMS service and MBMS transport functions; support of dedicated, downlink-only networks; and support of single frequency networks (SFNs) with large inter-site distances. Finally, in Rel-17 and Rel-18 of 3GPP, additional specific needs for broadcast channel bandwidths of 6/7/8 MHz, support for UHF spectrum and the addition of public warning and emergency alerts are addressed.

While 3GPP could have taken a radical approach to define a clean slate radio system to meet the broadcasters’ requirements, a more pragmatic route was chosen: experiences from the past with dedicated modems such as MediaFLO or DVB-H, and the need for easy integration into mainstream mobile devices, led to the decision to evolve eMBMS to LTE- based 5G Broadcast instead of any radical new designs. The term hardware-compatible feature was coined in the process, i.e., LTE-based 5G Broadcast was developed with the cellular modem architecture in mind: the new features added to the physical and higher layers were carefully designed to be compatible with the cellular modems that are in our smartphones today. To support reception from broadcast networks, such as a high-power high-tower downlink-only infrastructure, existing hardware in smartphones can be entirely reused. With this integration, typical commercial assessments before adding a new modem technology to a mainstream mobile chipset can be cut short or completely bypassed: for example, a detailed analysis of the technology in terms required area size, hardware availability, power consumption, integration with the apps and operating systems, global harmonization, development timescales, co-existence and re-use of existing functions, testing and interoperability testing, and many more.

Based on all these considerations, 5G Broadcast can be viewed as a modem feature, like many other technology enhancements in 3GPP, that reuses the basic building blocks of a cellular modem. With this, many new opportunities may arise. For example, this could almost instantly expand the reach that broadcasters can have, in terms of access to the millions of (3GPP standards’ compliant) smartphones all over the world, that are—and will be—in people’s pockets now and for the years and decades to come.

Based on this introduction, this paper addresses the following main contributions:

1. Provide a summary of the technology extensions to meet the broadcast requirements for LTE-based 5G Broadcast, to meet the main design target & “reason for being” of 5G broadcast, namely, to enable operation of a broadcast network (including high-power high-tower) where the receivers are hardware- compatible with cellular modems.

2. Providing an analysis of 5G Broadcast over different physical environments of practical interest for broadcasters. To evaluate the performance of a hardware- compatible design compared to an unconstrained design, we provide an estimate of the gains that certain features would provide, as compared to currently specified 5G Broadcast.

3. We provide examples of how additional enhancements can be added to 5G Broadcast in a hardware-compatible manner by reusing some cellular building blocks (e.g., HARQ combining) to realize features present in broadcast standards (e.g., time-interleaving). We also assess the performance impact of utilizing the basic cellular feature of receiver antenna diversity on broadcast performance.