ATSC 3.0 Backward Compatible SFN In-Band Distribution Link and In-Band Inter-Tower Communications Network for Backhaul, IoT and Datacasting Yiyan Wu, Liang Zhang, Wei Li, Sébastien Laflèche Communications Research Centre Canada, Ottawa, Canada Sung-Ik Park, Jae-young Lee, Heung-Mook Kim, Namho Hur Electronics and Telecommunications Research Institute, Daejeon, Korea S. Merrill Weiss Merrill Weiss Group LLC, Metuchen, NJ, USA Eneko Iradier, Pablo Angueira, Jon Montalban University of Basque Country, Bilbao, Spain Abstract – In a previous paper [1][1], we proposed an approach for providing ATSC 3.0 Studio-to- Transmitter Link (STL) data delivery for SFN operation using In-band Distribution Link (IDL – a.k.a. in- band backhaul) over the air in a 6 MHz broadcast channel. In this paper, we present detailed analysis of the backhaul issues and implementation considerations. We also exhibit field measurement results that support viability of the IDL system implementation using full-duplex transmission. We further present a full-duplex Inter-Tower Communication (ITC) system – a scalable and re-configurable wireless network for SFN broadcasting, in-band inter-tower communications, and IoT/datacasting applications – that is backward compatible with ATSC 3.0. The method uses Layered Division Multiplexing (LDM) transmission to carry STL data alongside broadcast data intended for public reception. IDL is able to offer better performance and more robust operation than on-channel repeater (OCR) technologies. It offers the possibility of delivering backhaul data for future applications – such as for IoT and data delivery to connected vehicles – over DTV infrastructure. IDL and ITC are enabling technologies for achieving convergence of broadcast services with broadband and other wireless services on the DTV spectrum. Introduction Deployment of the ATSC 3.0 Digital TV (DTV) broadcasting system, a.k.a., NextGenTV, is beginning in North America. In addition to delivering Ultra-High-Definition (UHD) TV broadcasting services to fixed receivers with rooftop, or even indoor, antennas, ATSC 3.0 also is capable of distributing robust mobile services to portable and handheld devices and of supporting localized datacasting services. To achieve these results, ATSC 3.0 is designed with the latest transmission technologies such as Layered- Division-Multiplexing (LDM) [2], Low-Density-Parity-Check (LDPC) coding, Non-Uniform Constellation (NUC) modulation, and Multiple-Input-Multiple-Output (MIMO) transmission [3]. Single-Frequency Networks (SFNs) [4] have been shown to be an effective deployment solution for achieving good Mobile Broadcast Service (MBS) distribution. SFNs also contribute to greatly improved signal strength and uniformity for Fixed Broadcast Service (FBS) distribution, enabling delivery of much higher data rates, with consequent improvements in spectrum utilization efficiency. In ATSC 3.0, a wide range of operation modes are defined with different Cyclic Prefix (CP) lengths, which allow flexible SFN deployments to provide broadcast services meeting particular quality requirements over specific geographic regions. For example, SFN deployment could begin with an existing single transmitter and gradually deploy additional SFN transmitters at locations that provide the best improvements in service coverage and quality. For each new SFN transmitter, a studio-to-transmitter link (STL) connection would be needed to transfer data from the network’s Broadcast Gateway (BGW) to the transmitter. As more SFN transmitters are deployed, the number of required STL connections will grow correspondingly. Consequently, in deploying an SFN, a capable, scalable, and cost-effective STL solution plays a significant role in the real success of such a system. Current solutions, which depend on fiber links or dedicated microwave links, suffer not only from potential accessibility limitations but also from high infrastructure and operational costs. An effective alternative, possible only with ATSC 3.0 or a similar system, is to use In-band Distribution Link (IDL), a.k.a. in-band backhaul, technology, which transmits STL data via wireless connections from the BGW to the SFN transmitters using the same spectrum as carries broadcast services to the public. This is a spectrum reuse method that makes more efficient use of the spectrum. The In-band Distribution Link (IDL) Approach An approach for providing ATSC 3.0 STL data delivery for SFN operation using in-band distribution over the air in the 6 MHz broadcast channel was introduced in a previous paper [5]. The basic concept, shown in Figure 1, includes a hub transmitter, Tx-A, which presumably is an existing, relatively high- power transmitter, having a dedicated, conventional STL connection from the BGW. Tx-A receives over the STL, on an IDL data stream delivered as an ordinary PLP (Physical Layer Pipe) stream using the STL Transport Protocol (STPTP), the STL data for the other transmitters in the SFN. The other User Device EL fixed services + STL CL mobile services Tx-B Relay Relay Rcvr Exciter EL fixed services ONLY CL mobile services User Device Tx-C Relay Relay Rcvr Exciter Broadcast ATSC 3.0 Gateway STL Exciter w/IDL Stream User Tx-A Device Tx-D Relay Relay Rcvr Exciter User Device FIGURE 1: USING LDM TO IMPLEMENT IN-BAND DISTRIBUTION LINKS 2 transmitters are Tx-B, Tx-C, and Tx-D – also termed Relay Locations – each comprising a Relay Receiver (RL-Rx) and a Relay Transmitter (RL-Tx) in this discussion. Tx-A modulates the STL data for the other transmitters onto a PLP for ATSC 3.0 over-the-air transmission. This yields an in-band solution since the STL data distribution to the Relay Locations shares the same spectrum as the broadcast services from all transmitters in the SFN. LDM is preferred for combining STL Transport Protocol (STLTP) data and broadcast-service data within one RF TV channel. In the simplest case, Tx-A, transmits a two-layer LDM signal in which the Core Layer (CL) delivers robust mobile services and part of the Enhanced Layer (EL) capacity delivers STLTP data for the RL-Tx’s. At each RL-Tx, an associated RL-Rx is implemented to decode the STLTP data from the received EL signal. The decoded STLTP data then is fed to an ATSC 3.0 Exciter to generate the SFN broadcast-service signal for emission to the public and for potential further relaying of the STLTP data stream. Backward-Compatible In-band Distribution Link (IDL) Implementation Considerations The proposed IDL is fully backward compatible and has no impact on existing services for consumer receivers. Figure 2 shows a block diagram of the STL signal reception at Tx-B. The received signal from Tx-A contains both the SFN service components (MBS+FBS) and the STL component. The signal from Tx-A is referenced as the Forward Signal (FWS). At Tx-B, the RL-Rx recovers the STLTP data and feeds it into the RL-Tx exciter for generation of the SFN service signal and its emission. To achieve a high-SNR condition for STL data recovery in the RL-Rx, a high-gain, directional receiving antenna is installed at Tx-B. Figure 2 also depicts a design challenge at the RL-Rx for STL recovery. The receiving antenna collects not only the FWS from Tx-A but also the emitted signal from the RL-Tx transmitting antenna, which is called a loopback signal (LBS) at the RL-Rx input. Since the transmitting antenna and the receiving antenna both are usually installed on the same tower and both at high elevations, they are closely coupled. This results in a very high LBS signal power received at the RL-Rx input relative to the FWS. Tx-A MBS + FBS STL Signal Isolation RL-Rx RL-Tx Tx-B FIGURE 2: IN-BAND DISTRIBUTION LINK SIGNAL RECOVERY AT RL-RX 3 In Figure 3, structures of the FWS and LBS received at the RL-Rx input are illustrated for an ATSC 3.0 SFN system with IDL using STL-TDM. In the FWS, MBS and FBS are delivered in a two-layer LDM configuration in a specific time slot, while the STLTP data for both services are delivered in a different time slot. CL CL MBS STLTP MBS Training (MBS+FBS) Sequence EL FBS EL FBS (a) (b) FIGURE 3: SIGNAL STRUCTURE MODEL AT RL-RX INPUT; (A) FWS; (B) LBS During the time slot allocated for broadcast services, the LBS waveform is the same as the FWS, although possibly slightly offset in time, because Tx-A and the Tx-B RL-Tx deliver synchronized SFN services. During the STLTP time slot, however, the FWS and LBS are different since the STLTP data has been delayed at Tx-B from the advanced data that was received in the FWS at its input. Therefore, the LBS becomes a strong interferor to STLTP recovery in the RL-Rx. This interference is also called self-interference in the in-band, full-duplex relay for LTE/5G [6]. IDL implementation requires consideration of the following design characteristics: Transmitter Timing Control for SFN Operation In an SFN of the sort shown in Figure 1, all the transmitters must deliver the same (MBS + FBS) service signals, and the waveform emissions from the different transmitters must be time-synchronized. When using IDLs, this requires that the STL data embedded in the Tx-A transmission must have a time advance relative to the service data transmitted by Tx-A. The time advance is needed to allow each RL-Rx to receive and recover the STLTP data and each RL-Tx to generate the service waveform for emission. Consequently, a timing control mechanism must be included in the Broadcast Gateway of an SFN employing IDLs to synchronize the relative timing between the STLTP data for relay by Tx-A and the STLTP data for service emission by Tx-A to align the operations of the different transmitters.