DVB-T2: A second generation digital terrestrial broadcast system - - PowerPoint PPT Presentation

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DVB-T2: A second generation digital terrestrial broadcast system - - PowerPoint PPT Presentation

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DVB-T2: A second generation digital terrestrial broadcast system Oliver Haffenden BBC Research & Development 3 rd July 2009 BBC MMIX Research & Development 1 Presentation Overview Background and requirements DVB-T2

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1 Research & Development  BBC MMIX

DVB-T2: A second generation digital terrestrial broadcast system

Oliver Haffenden BBC Research & Development 3rd July 2009

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2 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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3 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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4 Research & Development  BBC MMIX

DVB-T2 – background

  • 1st generation system (DVB-T) used for DTT

launch in UK (1998) and around the world

  • Desire for HDTV on terrestrial platform

– requires significant increase in capacity

  • 2nd generation system (DVB-T2)

– study mission launched by DVB in 2006 – to increase capacity, ruggedness and flexibility

  • Aim to launch ‘Freeview-HD’ in UK with switch-over

roll-out from end-2009

– an incredibly short timescale!

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5 Research & Development  BBC MMIX

Commercial Requirements for T2

  • Key requirements include

– Must be able to use existing domestic receive antenna and existing transmitter infrastructure – Should provide minimum of 30% capacity increase over DVB-T – Should provide for improved SFN performance – Should have mechanism for providing service-specific robustness – Should provide for bandwidth and frequency flexibility – Should provide means to reduce peak-to-average power ratio

  • The T2 specification has been compared to these

requirements and found to meet or exceed all of them

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6 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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7 Research & Development  BBC MMIX

T2 physical layer architecture

Input processing Bit- interleaved coding and modulation Frame builder OFDM generation Input TS or GS T2-system Very similar to DVB-S2 FEC: same as DVB-S2; modulation: based on DVB-T New Based on DVB-T

  • Common elements from DVB-T and DVB-S2 give:

– coherent family of DVB standards – easy translation between S2 and T2

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8 Research & Development  BBC MMIX

Multiple services in Physical Layer Pipes (PLPs)

Input processing (PLP 1) Bit- interleaved coding and modulation Frame builder OFDM generation Input pre- processing Input processing (PLP 2) Bit- interleaved coding and modulation Input processing (PLP N) Bit- interleaved coding and modulation

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9 Research & Development  BBC MMIX

Key features: LDPC

  • Protected by the Low Density Parity Check (LDPC)

code

– As in DVB-S2 – Code rates: 1/2, 3/5, 2/3, 3/4, 4/5, 5/6 – Performance is much closer to theoretical limits than convolutional code used in DVB-T

Data LDPC check bits

Header BCH FEC bits

BaseBand Frame

FEC frame = 16200 or 64800 bits

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10 Research & Development  BBC MMIX

Key Features: Modulation (1)

  • Constellations:

– QPSK, 16-QAM, 64-QAM, plus 256-QAM

  • 256-QAM

– carries 8 bits/data cell – cf.6 for 64-QAM – improved FEC performance of LDPC makes robustness similar to 64-QAM in DVB-T

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11 Research & Development  BBC MMIX

Key Features: Modulation (2)

  • T2 uses conventional Guard-Interval OFDM

– as in DVB-T

  • 1K, 2K, 4K, 8K, 16K, 32K FFT options are available

in T2

  • Larger FFT sizes:

– Can reduce guard interval overhead for given size of SFN – Can increase SFN capability for a given fractional GI

32K symbol GI GI 8K symbol ~6% overhead 25% overhead

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12 Research & Development  BBC MMIX

Efficiency improvements

  • Lower pilot density where appropriate (1% vs 8%)
  • Extended carrier mode (2% extra capacity)
  • Fewer Continual Pilots, sync-byte removal, …
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13 Research & Development  BBC MMIX

T2-Frame Structure

  • Typical frame duration: 150 - 250 ms

– P1 Preamble gives rapid detection and acquisition – P2 carries L1 signalling including frame structure data

  • Plus other data if space remaining

T2 Frame P1 P2 Payload L1 signalling Other data

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14 Research & Development  BBC MMIX

Single vs. Multiple PLP

  • Single PLP

– Complete transport stream is contained within single PLP

  • Multiple PLP

– Each data PLP carries a transport stream – Information common to a group of PLPs (e.g. EPG) is carried in a ‘Common PLP’ – Receiver must be able to decode Common PLP & one data PLP – Different PLPs can have different modulation/coding

  • Service-specific robustness, e.g. roof-top + portable services

Carriers Symbols

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15 Research & Development  BBC MMIX

Rotated Constellations

  • Map data onto a normal

QAM (x,y)

  • Rotate constellation (axes

now (u1,u2)

  • Ensure u1 and u2 travel in

different cells

– So that they fade independently – Gather together in receiver

  • Each of u1,u2 carries all of

the info of original x,y

– So can decode if one is erased completely

  • Simulated gains up to 7dB

u1 u2 Rotated 16-QAM constellation, showing bit 0 mapping. Blue points represent a 0 and red points represent a 1

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16 Research & Development  BBC MMIX

Other key technologies

  • Transmit diversity (Alamouti)

– could give 30% increase in coverage

  • Peak-to-average power reduction

– Could reduce peak power by 20%

  • Time interleaving

– At least 70ms – Provides protection against impulsive interference

RX TX1 TX2 So,S1

  • S1

*, S0 *

h 1 h 2

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17 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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18 Research & Development  BBC MMIX

Modulator Interface

  • In a Single Frequency Network must ensure that all

modulators generate identical T2 frames

  • T2-MI generated by central ‘T2 Gateway’
  • Transmitters generate T2 signal deterministically from T2-MI
  • Specification published as DVB BlueBook in Feb 09
  • Interoperability tests planned for late 2009

Mux Enc Enc SI etc

MODULATOR PA MODULATOR PA MODULATOR PA MODULATOR PA

T2 Gateway ASI IP

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19 Research & Development  BBC MMIX

Transmitter Identification

  • Requirements for professional monitoring receiver

– Identify if Tx within SFN has incorrect timing – Identify if Tx within SFN has incorrect frequency – Monitor channel to check for anomalous propagation

  • Several techniques have been investigated

– Use of low-level additive signal – Use of existing reserved parts of T2 signal – Use of future extension frames (FEFs)

  • Progress:

– First draft of specification produced

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20 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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21 Research & Development  BBC MMIX

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 5 10 15 20 25

C/N (dB) Effective bits per Cell

Shannon Limit DVB-T2 QPSK DVB-T2 16-QAM DVB-T2 64-QAM DVB-T2 256-QAM BICM Limit DVB-T QPSK DVB-T 16-QAM DVB-T 64-QAM

Modulation and Coding Performance

DVB-T “24 Mbit/s” mode DVB-T2 “36 Mbit/s” mode DVB-T2 “40 Mbit/s” mode DVB-T2 at failure DVB-T at QEF

  • Capacity limits for simple

Gaussian noise channel

– With LDPC can get close to theoretical limit

  • Typically 30% gain in

capacity compared with DVB-T codes.

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22 Research & Development  BBC MMIX

T2 Capacity – UK-like example

Current UK mode T2 Modulation 64QAM 256QAM FFT size 2K 32K Guard Interval 1/32 1/128 FEC 2/3 CC + RS (8%) 3/5LDPC + BCH (0.3%) Scattered Pilots 8.3% 1.0% Continual Pilots 2.0% 0.53% Frame structure overhead 1.0% 0.53% Bandwidth Normal Extended Capacity 24.1 Mbit/s 36.1Mbit/s

Capacity = DVB-T + 50%

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23 Research & Development  BBC MMIX

T2 Capacity – SFN example

Current mode T2 Modulation 64QAM 256QAM FFT size 8K 32K Guard Interval 1/4 1/16 FEC 2/3 CC + RS (8%) 3/5LDPC + BCH (0.3%) Scattered Pilots 8.3% 4.2% Continual Pilots 2.0% 0.39% Frame structure overhead 1.0% 0.65% Bandwidth Normal Extended Capacity 19.9 Mbit/s 33.2Mbit/s

Capacity = DVB-T + 67%

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24 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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25 Research & Development  BBC MMIX

On-going T2 activities within DVB

  • Validation and Verification

– 8 independent implementations compared in software – More than 30 different modes tested with full agreement – Hardware plug fest (March 09) demonstrated interoperation between 5 modulators and 6 demodulators in several modes

Photo-montage of PlugFest, thanks to RAI

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26 Research & Development  BBC MMIX

On-going T2 activities within DVB

  • Simulation

– Many simulations performed and results included in Implementation Guidelines document – Good agreement between different simulation models – Common Simulation Platform

  • MATLAB model
  • Can act as open reference implementation
  • Supports most options of the specification
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27 Research & Development  BBC MMIX

T2 Implementations

  • Software simulation platforms

– Common Simulation Platform – Several independent company implementations

  • FPGA prototypes

– Modulator: BBC, DekTec, R&S, Enensys, SSBT, Teamcast – Demodulator: BBC, Dektec, Panasonic, SIDSA, Sony

  • VLSI

– Several large VLSI companies are developing T2 demodulator chips

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28 Research & Development  BBC MMIX

T2 Implementations

  • BBC has had T2

signals on-air since June 2008

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29 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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30 Research & Development  BBC MMIX

T2 Service Plans in UK

  • UK regulator, Ofcom, has announced the UK will

launch HDTV services from December 2009

– Starting in North West of UK as part of Switch Over – Around 5 additional stations likely to be added in advance

  • f switch-over

– initial coverage in early 2010 around 50% of UK

  • Single public-service MUX to be used for HD

services

– Starting with 3 HD services

  • BBC, ITV, Ch4/S4C

– Channel 5 HD service to be added during 2010

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31 Research & Development  BBC MMIX

UK Planning for HD services

  • Ofcom coordinating UK-HD Pilot planning project
  • Participants include HD broadcasters, Arqiva,

TV/STB manufacturers

  • Lab and field trials currently underway,

– using manufacturers’ prototype equipment

  • Technical goals:

– To verify performance using real hardware (in comparison with simulations) – To verify planning parameters and choice of mode – To provide test bed with real signals to assist manufacturer developments

  • Pilot is just one part of the implementation work
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32 Research & Development  BBC MMIX

Presentation Overview

  • Background and requirements
  • DVB-T2 specification

– Key Features of the system – Related specifications

  • Performance & Simulation results
  • Implementation & Validation
  • UK plans for HDTV service launch
  • Conclusions
  • Questions
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33 Research & Development  BBC MMIX

Conclusions

  • T2 specification and documentation process

approaching completion

  • Commercial requirements easily exceeded
  • Validation & Verification activities making very good

progress

  • FPGA-based hardware prototypes already

demonstrated

  • VLSI design well underway
  • Lab tests and field trials underway
  • Intense planning activity in UK
  • Launch of T2 “Freeview-HD” services in December

2009 in UK

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34 Research & Development  BBC MMIX

Thanks for your attention! Any questions?

Oliver Haffenden

  • liver.haffenden@rd.bbc.co.uk