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

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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

Relay

Exciter

Tx-B

Broadcast

Gateway

w/IDL Stream

ATSC 3.0

ExciterSTL

Tx-A

Relay

Exciter

Tx-C

Relay

Exciter

Tx-D

Relay

Rcvr

EL fixed services + STL

CL mobile services

EL fixed services ONLY

CL mobile services

User

Device

User

Device

User

Device

User

Device

Relay

Rcvr

Relay

Rcvr

FIGURE 1: USING LDM TO IMPLEMENT IN-BAND DISTRIBUTION LINKS

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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.

RL-Rx

RL-Tx

Signal

Isolation

Tx-A

Tx-B

MBS + FBS

STL

FIGURE 2: IN-BAND DISTRIBUTION LINK SIGNAL RECOVERY AT RL-RX

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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.

(a)

FBS

MBS STLTP

(MBS+FBS)

EL

CL

FBS

MBS Training

Sequence

(b)

EL

CL

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. A simple timing control method for SFNs employing IDLs is illustrated in Figure 4. The figure assumes that multiple tiers of Relay Locations can be cascaded in a network and is explained as follows:

• In the transmission signal from the nth hop Tx-A, the STLTP data, X(t−nT), is transmitted with a time advance of nT relative to the service data, X(t).

• The loopback signal, carrying X(t−nT+T) data, is relatively much higher in signal strength at the

RL-Rx input than is the STL FWS signal carrying X(t−nT) data.

• The SFN time-synchronized stronger LBS signal and the weaker FWS signal, carrying the

X(t−nT+T) data and the X(t−nT) data, respectively, behave like a two layer LDM signal.

• Since the LBS carrying X(t-nT+T) data is a known signal to the RL-Rx, it can be successfully

cancelled to recover the X(t−nT) data from the FWS. In typical service scenarios, a time-advance T of one ATSC 3.0 frame duration is sufficient for SFN operation using IDLs.

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FIGURE 4: ATSC 3.0 SFN TIMING CONTROL

Loopback Signal Isolation (SI) The first step in easing the process of STLTP recovery from the FWS in the presence of a strong LBS is Signal Isolation (SI) between the RL-Tx transmitting antenna and the RL-Rx receiving antenna. The objective of SI is to minimize the LBS power arriving at the RL-Rx receiving antenna and the RL-Rx input. SI can be achieved through several methods: 1) Increasing antenna spacing: At a Relay Location, both the RL-Tx transmitting antenna and the RL-Rx receiving antenna are likely to be installed on the same tower at high elevations. The LBS propagation channel between these two antennas is fundamentally a line-of-sight (LOS) channel. The distance between the antennas is at most a few hundred meters. For such a distance, the propagation loss can be well modeled as free space path loss (FSPL), which is calculated as,

( ) ( )20log 20log( ) 32.44FSPL dB d f= + +

where d is the distance in km and f is the frequency in MHz. Therefore, an antenna separation distance of 100 meters results in an LBS power 20 dB lower than that from a separation distance of 10 meters.

FIGURE 5: LOOPBACK SIGNAL ISOLATION METHODS BETWEEN RL-TX AND RL-RX ANTENNAS

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2) Blocking the Loopback Signal: Either metal shielding or RF absorbent material can be installed above the lower antenna (presumably the RL-Rx receiving antenna), as shown in Figure 5, to obstruct the path between the two antennas. This can be especially useful for some antennas with small form factors, such as panel antennas using few panels, which may not have much signal suppression along the axis of the antenna. In [7][7], a metal mesh installed on top of a panel antenna is shown to be quite effective to block the loopback signal. 3) Increasing receiving antenna directivity: Modern antenna design techniques can be applied to the receiving antenna to increase its gain in the direction of Tx-A, thereby increasing the FWS strength, and to create a null in its pattern in the direction of the associated RL-Tx transmitting antenna, further reducing the received LBS power. It should be noted, however, that this scheme may require more engineering effort, installation of multiple antenna components, and a larger space for the antenna on the tower.

Loopback Signal Cancellation Whatever LBS signal power has not been sufficiently reduced before reaching the input of the RL-Rx to enable reception of the FWS signal must be cancelled in the RL-Rx itself. To cancel the LBS, the RL-Rx first must estimate the loopback channel and its channel response. To reduce the proportion of channel capacity required for STLTP data delivery, it is desirable to use a high-throughput signal configuration to carry the STL data, i.e., high-order modulation, high coding rate, MIMO, and the like. Such a configuration requires high SNR to decode and puts a premium on loopback channel-estimation accuracy. Because the RL-Rx can have as an input the signal being transmitted during the STLTP time slot, as shown in Figure 3, the loopback channel can be estimated using decision-directed channel-estimation (DD-CE) algorithms. To perform DD-CE, the frequency-domain (FD) least square (LS) channel estimation is first obtained as,

( )( )

( )

( )( ) ( ) ( )

( )0

RL

LB

LB

STL FWS

LB

LB

Y kH k

X k

X k H k N kH k

X k

=

+= +

Where XSTL(k)*HFWS(k) is the received FWS from Tx-A. Filtering in two-dimensions (2D-Filt) can be used to enhance the channel estimation accuracy. A frequency-domain filter (FD-Filt) is first applied to the LBS estimates,

ˆLB FD F LBH H− =

where F could be a minimum mean square error (MMSE) filter [8], a singular value decomposition (SVD)-based filter[9], a DFT-Filter [10][10], a Wiener filter, or simply a smooth windowing function. A time-domain (TD) subsequently is applied to further improve the accuracy of the channel estimate:

2ˆ ˆ

LB D T LB FDH H− −=

7

where T usually is implemented using a Wiener filter or a smooth windowing function. Computer simulations were conducted to evaluate achievable LBS cancellation performance, assuming a low-complexity DD-CE with 2D-Filt, which consists of a FD Wiener filter followed by TD average windowing. Since the RL-Rx receiving antenna and the RL-Tx transmitting antenna are assumed to be installed on the same tower and to be closely located, the loopback channel could well be approximated as an LOS channel. For cases in which there are obstacles surrounding the tower or reflections within the tower, however, the channel could be modeled as a multipath channel having very short delay spread. Therefore, two channel models were tested in simulations – a typical LOS channel and a rare multipath channel, which was modeled as a Typical Urban channel [11] with a mean delay spread (DS) of

0.1 sec, and a maximum DS of 0.7 sec. An ATSC 3.0 system operating in the 16k transmission mode was used in simulations. It was assumed that the FWS has an SNR of 25 dB at the RL-Rx receiver. Four loopback signal/forward signal (LBS/FWS) power ratios – 0, 10, 20, and 30 dB – were tested to evaluate LBS cancellation performance under a wide range of operational conditions. Since the power ratio was based on LBS power after signal isolation, a 30 dB LBS/FWS result is a rather pessimistic condition. Figure 6 shows the LBS cancellation performance for an LOS channel. For the simulations of such a channel, a Wiener filter was applied in the frequency-domain, becoming an averaging window in which a window size of 500 taps was used. In the time-domain, an averaging window of 40-taps was used. The upper subplot shows the MSE of the channel estimation after the 2D-Filt, while the lower subplot shows the SNR of the STL signal after the LBS cancellation.

FIGURE 6: LBS CANCELLATION PERFORMANCE IN LOS CHANNEL

For LOS channels, for all LBS/FWS power ratios, using the simple 2D channel estimator achieved a residual LBS power over 40 dB below the FWS power. Considering the required SNR for high-throughput STL signal detection from the FWS being from 25 to 30 dB, this LBS cancellation performance is more than sufficient, with 10 dB or greater margin. Figure 7 shows the LBS cancellation performance in a more challenging, short TU channel, which can serve as a worst-case scenario. Due to its frequency selectivity, a 50-tap Wiener filter was used in the frequency-domain, and a large 100-tap window was used in the time-domain.

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Even for this multipath channel, for all scenarios, the loopback signal cancellation was able to reduce the LBS power to 30 dB lower than the FWS power, which provides enough margin for STLTP recovery in waveform configurations requiring an SNR of 25 dB.

FIGURE 7 : LBS CANCELLATION PERFORMANCE, SHORT TU CHANNEL

It should be pointed out that loopback signal power only impacts IDL signal reception. It has absolutely no impact on broadcast service reception by ATSC 3.0 consumer receivers. IDL signals simply are ignored by consumer receivers. To achieve higher combined STL and broadcast-service throughput, LDM is used to combine STL Transport Protocol (STLTP) data and broadcast-service data within one RF TV channel. In this case, the hub transmitter, 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 downstream SFN Relay Tx’s.

Relay Receiver Dynamic Range Requirement The preceding analysis assumes that the RL-Rx has sufficient dynamic range to receive a signal comprising the sum of the FWS and LBS powers. When the LBS power is much higher than that of the FWS, the required dynamic range also is increased.

The dynamic range requirement for the RL-Rx is illustrated in Figure 8. Assuming the LBS is dB

higher than the FWS and the required SNR to decode the STL signal is dB, the dynamic range of the

RL-Rx, , should be larger than +. For example, for an LBS/FWS power ratio of 30 dB and a required SNR of 25 dB for STL detection, the receiver must have a dynamic range of at least 55 to 60 dB. While such a dynamic range is not impossible to achieve, it is quite challenging to implement. To reduce the dynamic range requirement, the LBS power level at the RL-Rx input must be reduced. This can be achieved by designing a more effective signal isolation implementation using a combination of the methods described above including increasing antenna spacing, blocking the loopback signal, and increasing receiving antenna directivity. If an improvement that lowered the LBS power by 15 dB could be achieved, the required RL-Rx dynamic range would become 45 dB for the example just above. Such performance is quite achievable for professional equipment.

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FIGURE 8: RL-RX DYNAMIC RANGE REQUIREMENT

A second solution for reducing the LBS power at the RL-Rx tuner input would be to implement an analog LBS signal cancellation process, as proposed for on-channel repeaters (OCRs) in [12][12]. The proposed method can reduce the LBS power by up to 50 dB, at the cost of additional complexity. It should be noted that, for many multi-cell deployment scenarios, the emitted power from an RL-Tx will be much lower than that from Tx-A. In such cases, with good signal isolation implementations, LBS/FWS power ratios of 30 dB will be highly unlikely to occur and a more likely range will be from 0 to 15 dB. An example theoretical calculation of IDL received FWS signal power as a function of Tx-A effective radiated power (ERP) and IDL Tx-Rx propagation distance is illustrated in Figure 9(a). In the calculation, a free-space path loss model at 470 MHz is used. Transmitter ERPs of 40~70 dBm are considered. Similarly, received LBS signal power as a function of RL-Tx ERP and RL-Tx to RL-Rx antenna separation distance is depicted in Figure 9(b), in which the same frequency of 470 MHz is assumed. At the RL-Rx, an antenna pattern discrimination of 20 dB between RL-Tx and RL-Rx antennas is assumed. To consider a specific example using Figure 9, at a Tx-A ERP of 50 dBm and a Tx-A to Relay Location distance of 5000 m, the RL-Rx input power is -30 dBm. To obtain the same RL-Rx loopback signal power as the received FWS signal power at the same RL-Tx ERP, an RL-Tx to RL-Rx antenna separation distance of 50m is necessary. This gives an idea of the required separation distance between transmitting and receiving antennas at a Relay Location for a loopback signal power value that can guarantee a fully functioning system when received FWS and LBS power values are equal. If a loopback signal cancelation capability of 25 dB can be reached (which is feasible, as shown in the previous analysis), an RL-Tx to RL-Rx antenna separation of less than 10 m easily can be achieved.

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(a) (b)

FIGURE 9: RECEIVED IDL POWER (A) VS. RECEIVED LOOPBACK POWER (B).

Field Tests in Ottawa Area

A measurement campaign was carried out in the area of Ottawa, Ontario, Canada, to evaluate the feasibility of implementing IDL in an ATSC 3.0 SFN using an existing DTV tower as Tx-A. The DTV tower is a 229-meter tower located on top of mountain Camp Fortune, Chelsea, Quebec, with a base height above mean sea level (AMSL) of 361 meters. Six DTV channels were evaluated, for which the parameters are listed in 0(The height of each antenna AMSL is the height AGL + 361 m.)

Ch. Ch. # Fc

[MHz]

HTx*

[m]

Tx ERP

[dBm]

Global

Toronto 14 473 169.1 81.6

TVO 24 533 130.9 79.8

CBC Ottawa 25 539 197.8 84.9

Tele-Quebec 30 569 141.3 84.8

Radio Canada 33 587 197.8 83.8

V-Tele 34 593 141.3 74.8 * HTx is the height of the antenna Above Ground Level (AGL).

TABLE 1: PARAMETERS OF MEASURED DTV CHANNELS

The measurement campaign was conducted in two steps. In the first step, the received signal power was measured at different locations around the Ottawa area. The locations were carefully chosen on high ground (e.g., atop local hills) or at some locations with obvious LOS paths toward the Camp Fortune tower and without surrounding reflective obstacles. This was to ensure that the path was as close as possible to actual tower-to-tower propagation. The locations of the Camp Fortune tower and measurement points are shown in Error! Reference source not found., in which the purple point on the North is the Camp Fortune tower.

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FIGURE 10 : MEASUREMENT CAMPAIGN MAP IN OTTAWA

Next, the power levels from the different TV stations were measured just above ground level at the bottom of the transmission tower using a calibrated antenna and a spectrum analyzer in Channel Power mode. The TV stations were treated for analysis purposes as if they were SFN RL-Tx transmitters. The data collected allowed determining the LBS power that would be received by an RL-Rx antenna at any distance below the transmitting antenna through use of the formula:

( ) ( ) 01 0 10

1

20logLB LB

dP d P d

d

= +

where PLB(d1) is the LBS power at the location of the RL-Rx antenna, PLB(d0) is the power measured at ground level under the tower from a particular station’s transmitter, d0 is the height above ground level (or above the measurement antenna for more precision) of that station’s transmitting antenna, and d1 is the distance from the transmitting antenna to the RL-Rx receiving antenna, with d1 having a minimum value of 10 meters.

FIGURE 11 : RECEIVED FWS SIGNAL POWER

FIGURE 12 : LBS/FWS POWER RATIO

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Based on the first-step measurements of received signal power at the various sites and the LBS power estimation just described, the power ratios of LBS/FWS for different channels at different locations were calculated and plotted in Figure 11 for an RL-Tx emission power of 70 dBm and an RL-Tx to RL-Rx antenna distance of 30 m. It is shown that, even for a distance close to 100 km, the LBS-to-FWS power ratio is always less than 30 dB. In Figure 12, it is clearly shown that a low-complexity LBS cancellation system could achieve a residual LBS power (after LBS cancellation) 30 dB lower than the FWS power. This case study shows that IDL could be realized at all testing points, even those with elevations lower than 10 meters and with the first Fresnel zones on the paths to them partially blocked. Actual implementation with a high tower should yield much better performance.

In-Band Inter-Tower Communication Network

Figure 4 above showed some of the characteristics of a one-way In-band Distribution Link in which the IDL signal is transmitted from the left tower to the right tower. There is no restriction that prevents sending a signal in the opposite direction, from the right tower to the left tower, in the same time frame. This assertion assumes that the antennas on SFN broadcast towers are much higher than typical 10m consumer receiving antennas and that there are line-of-sight paths among the SFN towers. (See Figure 13.) As a consequence, 2-way Inter-Tower Communications can be achieved along with full duplex transmission [13][13].

FIGURE 13 : IN-BAND BI-DIRECTIONAL COMMUNICATIONS AND INTER-TOWER NETWORK

Error! Reference source not found. presents two different LDM-based In-band Distribution Link (IDL) and Inter-Tower Communications (ITC) data structures that are representative of what is possible. In Error! Reference source not found.(a), the IDL and ITC are carried on the LDM enhanced layer, and in Error! Reference source not found.(b) IDL and ITC data are Time-Division Multiplexed (TDM-ed) with the SFN broadcast signal. LDM could be applied on the ITC signal for different robustness and services.

FIGURE 14: DIFFERENT LDM-BASED IN-BAND DISTRIBUTION LINK AND INTER-TOWER COMMUNICATIONS STRUCTURES

13

In Error! Reference source not found., three different services are shown:

• An In-band Distribution Link that is a one-way, high data rate, high-SNR service for STLTP data distribution.

• Inter-Tower Communications (ITC) that are two-way, low- or medium-SNR data exchanges for network cueing and control, consumer IoT and datacasting. Each tower can transmit different contents/data in the ITC period (Fig. 4).

• SFN broadcast for TV, multimedia, and data services. All SFN transmitters broadcast the same content.

IDL, ITC, and SFN data can be multiplexed into different TDM-LDM combinations. During the ITC data transmission period, different transmission sites can broadcast different data for localized services. (See Figure 15.). Different receiving antennas might be needed at the network head-end for ITC return-link signal reception to limit co-channel interference during the ITC period. Some sites could operate as an SFN with hub transmitters, if desired. LDM can be used to achieve tiered service. A robust transmission mode can be used to improve reception in overlapping areas. ITC data can include broadcast network cueing and control data for operation and monitoring. These data are not intended for consumers. ITC data also can include consumer or professional service data, such as IoT, emergency warning, connected car, and other localized data services.

FIGURE 15: INTER-TOWER LINK DATACASTING IN DIFFERENT CELLS (REGIONALIZED IOT)

ITC can form a communications network among all broadcast towers and stations in a region, which is not necessarily limited to the transmitters of a single SFN. It could, for instance, connect all broadcast towers in a large geographic area. More importantly, these connections are independent of any non-broadcast communications infrastructure (e.g., broadband wireless, wired networks, public Internet, and the like), so they could survive natural disasters and other emergency conditions to maintain services and connectivity for broadcast operations and service to consumers. 0shows salient aspects of SFN, IDL, and ITC in ATSC 3.0 evolution on broadcast and broadband convergences.

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SFN Broadcast In-Band

Distribution Inter-Tower Communications

• Improves service

quality for mobile,

handheld and

indoor reception

• Allows new

services: IoT,

connected car,

datacasting

• Supports one-to-

many timely

services for large

rural areas for

traffic map

updates, weather

forecasts,

emergency

warnings, etc.

• Eliminates

STL

spectrum

requirements

• Reduces SFN

broadcasting

operating

costs

• Improves

spectrum

sharing and

reuse

• Provides a scalable & configurable network

embedded in a broadcast system

• Supports broadcast network cueing & control that

don’t rely on telecom & other infrastructure –

surviving emergencies and natural disasters

• Carries backhaul data services among towers: IP-

based IoT, wide-area datacasting, etc

• Permits each tower to broadcast localized content

• Enables full-duplex transmission: transmission &

reception on the same frequency at the same time –

improving spectrum efficiency

• Supports dynamic spectrum re-use & sharing +

LDM: converging broadcast and wireless services

• Works in SFN, OCR, & Multi-Frequency Network

(MFN) environments

TABLE 2: COMPARISON OF SFN, IDL, AND ITC NETWORK FEATURES

Conclusions

A wireless In-band Distribution Link for ATSC 3.0 SFN operation was further analyzed. The system uses LDM transmission to carry STL data alongside broadcast service data in a manner fully compatible with ATSC 3.0 Next Gen TV service to the public, causing no degradation of consumer reception. The IDL is designed for general SFN deployment with full SFN timing control. Implementation issues were analyzed, and solutions were proposed with respect to loopback signal isolation and cancellation. Relay facility signal reception dynamic range restrictions were considered and simulated. Preliminary field tests demonstrated the viability of IDLs in real applications. Finally, an Inter-Tower Communications network was proposed that extends IDL technology into a scalable and configurable network embedded in a broadcast system and that can be implemented independent of any non-broadcasting communications infrastructure. The only negative impact of IDL implementations is that they consume small portions of broadcast channel capacity. With application of MIMO and other advanced signal processing technologies, the proportion of such consumption can be further reduced to below 10%.

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References

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