Graziano Casale, Account Manager - Rohde & Schwarz NTA Convention – Spokane, WA

A Travel Through SFN Network

What possibilities from OFDM and what’s next for the Translators

Agenda

ı What is a Single Frequency Networkı Why SFNı How to do a SFN OFMD vs ATSC DVB-T2 and ATSC 3.0 SFN Planning What equipment would you need for a SFN

ı From translators network to SFNı Conclusion

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What is a SFN

ı One broadcast headend is the source of the multiplex signal for several transmitter stations

ı The broadcast headend inserts SFN timestamps from GPS ı Timestamps compensate the delay between the headend and the transmitter

stations. ı The transmitter also receive GPS signals to compare the timestamps

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What do we have now

4

ı Multi Frequency Network

ı A broadcast network transporting different content on different transmitter stations using differentfrequencies

ı Analog TV and ATSC using single-carrier modulation can only cope with Gaussian channels

ı Single-path reception Additional signal paths are handled like error

signals for the receiver.

May 18, 2016 A Travel Through SFN – Graziano Casale

Why SFN is good for Broadcasters

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SFN networks in a variety of use cases:

1. To cover black spots on specific areas, whenever deemed necessary

2. To increase signal coverage and quality in specific urban areas

3. To extend coverage in high power transmission areas

4. To limit or eliminate interference

5. Improve Indoor and Mobile Penetration/Coverage for Mobile Service

SFN Basics

ı SFN re-use the same frequency over a bigger coverage areaı Each SFN station creates “artificial echoes”, resulting in a multipath situation for each

receiver. But because OFDM symbols with a long guard interval, the receivers can cope with that multipath situation

ı Conditions to be fulfilled:

1. Frequency synchronization Sync via a GPS time/frequency standard receiver. Both the 10 MHz signal and the 1 pps signal are used to synchronize the SFN

transmitter.

2. Time synchronization GPS via 1 pps Synchronous in time and data. SFN timestamps are inserted in the signal by the headend

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Why no SFN in ATSC

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Symbols and channel bandwidth in ATSC

ı Why not?

ı To achieve a high data rate, the symbol duration in ATSC signals is very short. The reason behind this is the 6 MHz bandwidth and the symbol rate needs to be less than the bandwidth

ı SFN in ATSC look like multipath reception for the receiverı ATSC use the symbol duration: 93 nsı ATSC is vestigial-sideband filtered. The condition to be

fulfilled is: 2 • 93 ns = 186 ns > 167 ns

16 167

* Later solution in A/110: by using a defined modulator frame initialization and reset controlled by the ATSC headend and modern equalizers in the ATSC receiver.

93 ns ATSC symbol duration is very short in relation to the expected terrestrial echoes

OFDM and Guard Intervalı OFDM-based transmission standards are designed for multipath reception situations ı OFDM symbols are much longer than single-carrier symbols ı The OFDM symbol duration depends on the OFDM carrier distance ı The guard interval (GI) lies between the OFDM symbols It is a cyclic break or rather a cyclic repetition of the end of the following OFDM

symbol The purpose of the guard interval is to avoid intersymbol interference caused by

echoes The longest allowed echo corresponds to the length of the guard interval

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OFDM symbols with guard interval

OFDM and Guard Intervalı In the case of OFDM, a broadcast channel is divided into N subcarriers. ı The more OFDM carriers there are, the closer the carrier distance and the longer

the symbols. ı The length of the GI is an overhead in the signal that reduces the net data rate of

the transmission system. ı Typical SFN use OFDM modulation with as many OFDM carriers as possible. ı Symbol durations ~1 ms or longer have a GI of ~250 µs.

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Optical horizon of a 1,000 ft transmitter station tower

SFN in DVB-T2

ı DVB-T2 is OFDM ı The system can transport several multiplexes with different levels of robustness

in different physical layer pipes (PLP)ı The final part of a DVB-T2 headend is the T2-gateway, which combines the PLP data signals the layer 1 control signal the SFN sync signal

ı The T2-MI signal is distributed to the TX stations

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SFN in ATSC 3.0 (prediction)

ı ATSC 3.0 STL / SFN is not a Candidate Standard ı ATSC 3.0 is based on OFDM and SFNs will be similar to those in DVB-T2.ı The terms are different. The main ATSC 3.0 technical parameters are: OFDM with 8K, 16K, 32K FFT size LDPC/BCH FEC QPSK, 16QAM, 64QAM, 256QAM, 1024QAM, 4096QAM modulation Uniform and non-uniform constellations Time division multiplexing (TDM) and layered division multiplexing (LDM)

similar to the T2-PLP concept Time interleaver MISO, MIMO

ı The baseband signal is called studio transmitter link (STL), which is also used for the SFN distribution.

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SFN Planning

High-accuracy maps with geographic, topographic, morphologic information

The transmitter station details The transmitter antenna diagram and gain The transmitter output power The loss in the antenna feeding network The physical modulation and FEC parameters The network planning parameters Network planning software Parameters to calculate the robustness Planned reception conditions (Fixed vs Mobile)

What do I need for a SFN network?

ı An SFN adapter at the headend, to be defined by the standard (i.e. the T2-Gateway in DVB-T2)

ı GPS antenna and GPS antenna cable to each TX siteı GPS receiver in the exciter or external to each TX site

ı Local Content insertion for SFN area (market) Allow local advertising

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Rohde & Schwarz transmitters overview

R&S®TLU9 Air cooled

UHF/VHF transmitters and translators

Up to 200W ATSC

Medium power High powerLow power

R&S®THU9/R&S®THV9Liquid cooled

UHF/VHF transmitters

Up to 78 kW

R&S®TMU9/R&S®TMV9Air cooled

UHF/VHF transmitters

Up to 4.3 kW

R&S®THR9Liquid cooledFM / HD radio

Up to 40 kW

May 18, 2016 A Travel Through SFN – Graziano Casale

What’s next for Translators and LPTV

ı Main Transmitter and each translator are on a different channel

ı X RF IN => Y RF OUT

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ı Main Transmitter and each transmitter are on the same channel

ı X RF IN => X RF OUT

Today with ATSC 1.0 Tomorrow with ATSC 3.0?

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“I don’t pretend we have all the answers. But the questions are certainly worth thinking about”- Arthur C. Clarke

Graziano Casale – Account Manager Broadcastinggraziano.casale@rsa.rohde-schwarz.com