digital tv: an introduction gregory bensberg. uk dtt 81 main and relay sites

Digital TV: An Introduction

Gregory Bensberg

UK DTT 81Main and

Relay Sites

CP5 Before

CP5 After

Current use of grouped aerials in the UK

21 31 36 38 42 62 68

UHF - channel numbers

Group A 21 - 37

Group B 35 - 53

Group C/D 48 - 68

Group W 21 - 68

Group E 35 - 37Group K 21 - 48

London Frequencies Manchester Frequencies

Digital Satellite CoverageDSAT Study:UK coverage map.Shadow regions due to terrain

Predicted UK CoverageDSAT StudyExtrapolated UK coverage

UHF spectrum now - Winter Hill

21 31 36 38 42 62 68

Interleaved spectrumAnalogue TV DTT

DTT – other sites

Group C/D 48 - 68

3 Conversion plan

• Convert 3 analogue networks for DTT• 6 multiplexes - 3 PSB, 3 commercial• Assume 16QAM rate 3/4 or 64 QAM Rate 2/3 for all

muxes • Support regional services • Release 14 channels i.e. 32 chs retained

Post switchover - 3 conversions

21 31 36 38 42 62 68

Interleaved spectrum Converted DTT

DTT – other sites

Cleared spectrum

Group C/D 48 - 68

Alois Bock’s notes

Basic video compression techniques

Motion estimation on source or reconstructed

1 2 3 4 5 6 7 8

Bit rate (Mbit/s)

Layer 1

Layer 2

Layer 3

Layer 4

Example hierarchical ME

Example exhaustive ME

Computational cost of MENormalised CPU Time

0 10 15 20 30 40 50 60 70 80 90 100

Search Range

B frame predictions

I frame B frame B frame P frame

Display order

Adrian Turner’s notes

Single Carrier QAM

Re(M(t))

Im(M(t))

Frequency

Power Spectral Density

fc1/Ts

Constellations (2)Constellations (2)

QPSK2 bits/symbolM(n) = ±1 ±j

16 QAM4 bits/symbol

64 QAM6 bits/symbol

-1 1 re

Mapping data to the constellation

Example - Gray coded 16QAM

Time domain Frequency domain

11-1-111......

Generating OFDM (1)Generating OFDM (1)

Frequency DomainFrequency DomainModulationModulation

Symbols (QPSK example)Symbols (QPSK example)

rere imim rere imim

Time DomainTime DomainSamplesSamples

FFTFFTFFTFFT-1-1

jjjj-j-j......

Fast Fourier TransformsComputational complexity

0 2000 4000 6000 8000 10000

, mill

The DVB-T pilot structure

Modulated carrier (QAM)Scattered or Continual PilotTPS carrier

Frequency

Transport Streamsand Service Discovery

Guy Hirson, BroadLynx Limited

guy@broadlynx.co.ukDTT course

Guildford University 2005

Transport StreamMPEG: Program Specific Information(CAT, PAT, PMT, NIT (?))Information for the decoder

DVB: Service InformationBAT, EIT, NIT, RST, SDT, TDT & TOTInformation for the user and service

Services (DVB speak) orPrograms (MPEG speak)carrying Elementary streams

Private CA data in Tables

Other private data (in Tables, Elementary Streams, etc.)

Containers fordata carriageMPEG table section

PES Packets

Transport Stream Packets

Data Streams•PSI: PAT, PMT & CAT•SI: NIT, SDT, EIT•DSM-CC•MHP AIT

Media Streams•Video•Audio•Subtitles•Legacy Teletext

Protecting the Packet

header payload RS

188 bytes

204 bytes

Transport Stream Packetheader payload header payload header payload

Sync byte

Transport Error

Indicator

Payload unit start indicator

Transport priority

PID Transport Scrambling

Control

Adaptation Field

Control

Continuity Counter

Adaptation Field

8 1 1 1 2 4 N213

Adaptation field length

Discontinuity indicator

Random access

indicator

ES priority

indicator 5 flags

Optional fields

Stuffing bytes

8 1 1 NN51

PCR OPCR Splice countdown

TS private data length

adaptation field extension

length

3 flags Optional fields

42 42 8 NN58

TS private data

TS packet

PCR insertion in the multiplexer

27 MHzcounter

42 bit

hdr payload hdr payload payloadhdr hdr payload hdr payload

TS packet TS packet TS packet TS packet

Video timebase

TS packet

PCR extraction in the demultiplexer

27 MHzcounter

42 bit

hdr payload hdr payload payloadhdr hdr payload hdr payload

TS packet TS packet TS packet TS packet

Video timebase (1Hz in 27MHz, 10ppb/s)

compare42 bit

errorfilter

Frequency control

PES packets for synchronised dataheader payload header payload

Packet start code prefix

Stream_id PES packet length

Optional PES header

PES packet data bytes

24 8 N NN16

‘10’ PES priority

Data alignment indicator

Original or copy

Stuffing bytes

PES scrambling

control

copyright flags PES header data len

Optional fields

2 1 1 1 1 8 8

ESCR ES Rate Additional copy info

DSM Trick mode

Previous PES CRC

PES extension

2 1 1 1 1 8 8

MPEG sectionsTable id Section

syntax indicator

Private indicator

Private section length

8 1 121

N private data bytes

Table_id extension

Current next

indicator

Version number

Section number

Private data

5 8 32

Last Section number

The guts of an Integrated

Receiver/Decoder

AudioDecode

VideoDecode

PALEncode

RCModem

Demod FEC

1 2 34 5 67 8 9

Networks, Bouquets, Services and Events

Network

Bouquet

Service

Programs and their componentsMPEG-2 Transport Stream

Program 1 Program 2 Program nPSIData

ElementaryStream 1(Video)

ElementaryStream 2(Audio1)

ElementaryStream n(Subtitles)

The inter-linking of PSI Tables and Programs

Program 1Program 2

Program n

PAT ECMES 1ES 2ES 3

ECM 3ES 4

PMT (2)MPEG-2 TS

CAS ID 1CAS ID 1

CAS ID x

Selecting a Service byLogical Channel

Number

Demod FEC

1 2 34 5 67 8 9

ProgramSI filters

RetrieveBAT, SDT, EITs

Build tableof services

SI Processing

NIT => list of services+ tuning data

SDT => Service names

EITs => Event info

Select “channel”

Tune to TSProgramPSI filtersfor PAT

RetrievePAT

ProgramPSI filtersfor PMT

RetrievePMT

Set up toretrieve

VideoDecode

AudioDecode

Selecting an EventEvent NameDescriptionAttributes

Event NameDescriptionAttributes

Data from EIT database

Service ID etc.

Select from menu

Data Carousel

DII transaction_id

mi mi mi

DII transaction_id

mi mi mi

ModuleGroup

DSI transaction_id

Digital Terrestrial Television:Domestic and MATV

Reception

Peter BarnettConsultant

Tel: +44 (0)1794 341053E-mail: peter.barnett@mandercom.co.uk

www.dtg.org.uk

DTT reception

Domestic

MATV IRS

Typical UHF spectrum

Aerials

Group A

AnalogueDigital

Group AGroup B

Group C/D

Group EGroup K

Group W

Aerials

Group W

8Group A

Group BGroup C/D

Group EGroup K

Group W

AerialsGroup A

Group BGroup C/D

Group EGroup K

Group W

Pre-switchover

Post-switchover

Receiver operating window

30 40 50 60 70 80Signal level (dBV)

Analoguesignal

Digitalsignal

Difference inreceived levels

Marginaloperation

Effects of pre-amplifiers

30 40 50 60 70 80Signal level (dBV)

Analoguesignal

Digitalsignal

Difference inreceived levels

Upgrading systems

Digital

Analogue

Channel changing in MATV systems

Intermodulation in amplifiers

LNB interference into DTT

Low band High band

10.7GHz 11.7GHz 12.75GHz

0 950MHz 2150MHz

Local oscillator

UHF interference into satellite

Measurements

University of SurreyDTT : An Overview

Receivers (Hardware) Nov 2005 v2.0Peter Lewis

Philips Semiconductors Technology Center

SouthamptonUK

Inside a ‘Set Top Box’RF in from

aerial

Picture & Sound out to

TV set

Channel Decoding Stage

Source Decoding Stage

Demodulator

Tuner Phase Noise

1116 Hz (8k)

4464 Hz (2k)

NB Carrier Separation Phase noise spreads the carriers

So they interfere with each other

Tuner Step SizeANALOGUE DIGITAL

RF from VCRs etc is imprecise RF from digital TXs is precise but may be offset ± 1/6MHz

Therefore a fine tuning resolution is needed

Therefore a 1/6MHz tuning resolution is needed

The adjacent channel problem

Chan NChan N-1

Peak sync power

total power in channel

Up to 35dB !

Lower adjacent sound, and SAW profile

Chan N

WANTED DVB-T SIGNAL

+10 dB

+20 dB

+30 dB

SAW IF Filter Profile

FM sound NICAM sound

(Levels plotted as though

with 100kHz BW S/A)

Attenuation of NICAM by one SAW

Chan N

EFFECTIVE NICAM LEVEL WITHOUT ANY FILTERING

EFFECTIVE NICAM LEVEL WITH ONE SAW FILTER

WANTED DVB-T SIGNAL

+10 dB

+20 dB

+30 dB

The more distant channel problem

Chan N-x

Up to 50dB !

Chan N

SAW filter profile for distant channels

Chan N-x Chan N

Interference from distant channels

Chan N-x Chan N

Traditional High Quality Front-End

TUNER2 SAW FILTERS

1st IF AMP

2nd IF Filter ?

DOWN-CONVERTER &

AGC AMP

DEMODULATOR

Gain control

Modern High Quality Front-End

IF / AGC AMP, in tuner

Single SAW, in tuner

DEMODULATOR, containing digital filtering that replaces

one SAW filter

Gain control

Channel decoder stage - demod IC

Tuner IF filter

Local Oscil.

1st IF (~36MHz) 2nd IF (~5MHz)

Down conversion IC

NB Down conversion is optional. Gain control is not !

DVB-T Channel demodulator & decoder IC

ADCDigital

front endFFT

Chan est. & correct.

Error Correct.

Transport stream

AGC amp

Channel decoder stage - digital F/E

Tuner IF filter

Local Oscil.

Down conversion IC

ADCDigital

front endFFT

Error Correct.

Transport stream

AGC amp

Process that may be in the ‘Digital Front End’

Digital Frequency Adjustment

ADCDigital AGC

AGC detector

analogue or digital

correction required

Gain control to RF/IF stages

I & Q data at baseband

= correction x t

data in data out

One method of identifying the symbol start

correlation

one full symbolguard interval

threshold

current samplefuturepast

Channel decoder stage - FFT

Tuner IF filter

Local Oscil.

Down conversion IC

ADCDigital

front endFFT

Error Correct.

Transport stream

AGC amp

Conversion from time samples to frequency

values.

frequency

2048 complex values for ‘2k’

-32953213395-3232-9532

-32-32133

95-95950329532-95-95

-30-7012698080106470

-78-30-9

20-9078564012-56-4020

-491062

FFT window timing error

ideal FFT window

actual FFT window

freq component A

freq component B

one full symbol

guard interval

timing error, terr

phase error = terr x A

phase error = terr x B

OFDM demod. stage - time corrector

Digital Time AdjustmentFFT

= t correction x

data in data out

The principle is the same as for frequency adjustment in the

frequency domain

I & Q time data

I & Q frequency data

Channel decoder stage - Chan. est. & corr.

Tuner IF filter

Local Oscil.

Down conversion IC

ADCDigital

front endFFT

Error Correct.

Transport stream

AGC amp

Echoes and Pilots

Phase of echo

Effect of echo

Only first 200+ carriers shown.

Continues on ….

echo adds

echo subtracts

Continual Pilot Scattered Pilot

Example of single echo with 1 usec delay

Channel estimation from pilots

interpolate through

timeinterpolate through frequency

symbol N

symbol N+1

symbol N+2

symbol N+3

to get estimates of channel response for every carrier

scattered pilot

Channel equalisation

Channel Estimation

frequency data corrupted by

channel, etc., effects

frequency data

corrected

CPE Detection

confidence

CPE detection

Channel Estimation

frequency data

corrected

CPE Detection

confidence

Common Phase Error - CPEPhase Error

one symbol

phase noise

local oscillator

part of tunerRF IF

+1kHz-1kHz

example of cause

CPE Detection using continual pilots

Continual Pilots

mean = CPE

symbol N

symbol N + 1

etc...

phase change between symbols

etc...

CPE detection

Channel Estimation

frequency data

corrected

CPE Detection

confidence

Channel decoder stage: de-mapping, de-

interleaving & error correction

Tuner IF filter

Local Oscil.

Down conversion IC

ADCDigital

front endFFT

Error Correct.

Transport stream

AGC amp

Stages of ‘Error Correction Etc’DVB-T Channel demodulator & decoder IC

ADCDigital

front endFFT

Error Correct.

Transport stream

de-mapping, de-interleaving,

etc.de-coding

De-mapping, etc, stage

etc.de-coding

What is the basic job to be done?

DE-MAPPING, DE-INTERLEAVING, etc.

MAIN INPUT IS I & Q DATA STREAMS REPRESENTING

THE MODULTION ON ALL THE USEFUL DATA CARRIERS

confidence

MAIN OUTPUT IS A BITSTREAM WITH

CONFIDENCE INFO.

de-mapper

symbol* de-

interleaver

bit de-interleaver

De-mapping & Inner De-interleaving:

muxdataI

Qconfidence

confid-ence

order may be reversed

* data on each carrier (not OFDM symbols)

de-mappersymbol

de-interleaver

bit de-interleaver

demapper

muxdataI

Qconfidence

confid-ence

Mapping: 16QAM exampleEach point represents

4 bits

A, B, C, D

B=0D=0

C=0C=0

Note that crossing one

boundary changes only

one bitC=1

e.g. ‘0,0,1,1’

1,0,0,11,1,1,00,0,0,00,1,1,0

Demapping, to symbol vectors Simple Symbol

Value VectorI

carrier n

carrier n+1

carrier n+2

carrier n+3

1(110), 0(101), 0(011), 1(001)

Demapping, including confidenceFull Symbol Metrics Vector

Bit valuesConfidence in

each bitcarrier n

1 (100), 1 , 1 , 0(111) (010) (110)

0 (110), 0 , 0(110) (101) (101), 0

0 (011), 1 , 0(111) (100) (111), 1

Demapping: separating vectors to metric streams

Symbol VectorValue (Confidence) 1

stream 0

stream 1

stream 2

stream 3

1 (110), 0 , 0 , 1(101) (011) (001)

1 (100), 1 , 1 , 0(111) (010) (110)

0 (110), 0 , 0(110) (101) (101), 0

0 (011), 1 , 0(111) (100) (111), 1

de-mappersymbol

de-interleaver

bit de-interleaver

demapper

muxdataI

Qconfidence

confid-ence

1 0 1 0 1 1 111 0 0 0 1 1 111 1 0 0 0 1 111 1 1 0 1 1 11

x 2, 4, or 61Data

Confidence

de-mapper

symbol de-

interleaver

bit de-interleaver

Symbol de-interleaver

muxdataI

Qconfidence

confid-ence

1 0 1 0 1 1 111 0 0 0 1 1 111 1 0 0 0 1 111 1 1 0 1 1 11

Confidence

x 2, 4, or 6

‘Symbol’ de-interleaving

1512 or 6048 metrics de-interleaved to undo the corresponding process at the transmitter.

metrics (data + confidence) for one

complete OFDM symbol de-

interleaved into original order

metrics (data + confidence) for one

complete OFDM symbol as received

from de-mapper

de-mapper

symbol de-

interleaver

bit de-interleaver

Symbol de-interleaver

muxdataI

Qconfidence

confid-ence

1 0 1 0 1 1 111 0 0 0 1 1 111 1 0 0 0 1 111 1 1 0 1 1 11

Confidence

1 0 1 1 1 0 001 0 1 1 1 0 001 1 0 1 0 1 011 1 1 1 1 1 01

re-arranged

x 2, 4, or 6 x 2, 4, or 6

de-mapper

symbol de-

interleaver

bit de-interleaver

muxdataI

Qconfidence

confid-ence

1 0 1 1 1 0 001 0 1 1 1 0 001 1 0 1 0 1 011 1 1 1 1 1 01

x 2, 4, or 6

Bit de-interleaving, e.g. substreams 0 & 1.

00 01 19 20 21 22 40 41 42 43 61 62 63 64 82 83 84 85 103 104 105 106 124 125... .. .. .. .. ..

i/p stream 0 (bits b0,0 - b0,125)

o/p stream 0 (bits a0,0 - a0,125)

i/p stream 1 (bits b1,0 - b1,125)

o/p stream 1 (bits a1,0 - a1,125)

de-mapper

symbol de-

interleaver

bit de-interleaver

muxdataI

Qconfidence

confid-ence

1 0 1 1 1 0 001 0 1 1 1 0 001 1 0 1 0 1 011 1 1 1 1 1 01

0 0 1 0 1 0 001 0 1 0 1 0 000 1 1 0 1 1 010 1 0 1 0 1 10

re-arranged more

x 2, 4, or 6 x 2, 4, or 6

de-mapper

symbol de-

interleaver

bit de-interleaver

multiplexer

muxdataI

Qconfidence

confid-ence

1 0 1 1 1 0 001 0 1 1 1 0 001 1 0 1 0 1 011 1 1 1 1 1 01

2, 4, or 6 streams

0 1 1 1 1 1 010 1 1 1 1 1 001 1 0 1 1 0 111 1 1 0 1 1 11

1 0 0 1 0 1 011 0 1 1 0 0 001 1 1 1 1 1 010 0 1 1 1 0 11

0 1 1 0 1 1 000 1 1 1 1 1 100 1 0 1 0 0 111 1 1 1 1 1 10

1 stream

De-coding stage:

etc.de-coding

What is the basic job to be done?

DECODING

OUTPUT IS A TRANSPORT STREAM

confidence

MAIN INPUT IS A BITSTREAM WITH CONFIDENCE INFO.

convolutional

inner decoder

outer de-interleaver

block outer

decoder

De-coding sub-stages:

energy dispersal removal

confid-ence

MPEG2 t/s

(Viterbi) (RS)

BER less than 2 x 10-4 BER near zero

convolutional

inner decoder

block outer

decoder

Convolutional Decoder (Viterbi):

confid-ence

MPEG2 t/s

1 0 0 1 0 0 11

0 1 1 0 0 1 001 1 1 0 0 1 100 1 0 1 1 0 110 1 1 1 1 1 11

Convolutional coding used in DVB-T

1 bit delay

switches at twice input

bit rate

1 bit delay

INPUT BIT STREAM

FINAL OUTPUT BIT STREAM

(twice rate of input)

Modulo 2 adder

X OUTPUT BIT STREAM

Y OUTPUT BIT STREAM

A simple convolutional coder

switches at twice input

bit rate

1 bit delay

INPUT BIT STREAM

FINAL OUTPUT BIT STREAM

(twice rate of input)

Modulo 2 adder

Y OUTPUT BIT STREAM

X OUTPUT BIT STREAM

Example output of simple convolutional coder

Input Bits

Output Bits

0 0 1 0 1 1 0 0 1 0

10 0 0 1 1 0 0 10

0 00 0

Y YX X

1 1 0 0 1 01 0 1 0 1 1

Y Y Y Y Y YX X X X X X

Delayed Input Bits+ +

Options for ‘correcting’ an error and get a valid

sequence0 0 1 0 1 1 0 0 1 00 0 1 1 1 0 1 0 1 1

0 0 1 1 1 1 0 0 1 00 0 1 0 0 0 1 0 1 1

0 0 0 1 1 1 0 0 1 00 0 0 1 0 0 1 0 1 1

0 0 1 0 1 1 0 0 1 00 0 1 1 1 0 1 0 1 1

0 0 1 0 0 1 0 0 1 00 0 1 1 0 1 1 0 1 1

0 0 1 0 0 0 0 0 1 00 0 1 1 0 0 0 0 1 1

0 0 1 0 1 1 0 0 1 00 0 1 1 0 0 1 0 1 1Rx.

Opt. A

Opt. B

Opt. C

Opt. D

Opt. E

Y Y Y Y Y Y Y Y Y YX X X X X X X X X X

convolutional

inner decoder

block outer

decoder

Outer de-interleaver:

confid-ence

MPEG2 t/s

1 0 0 1 0 0 11

Outer de-interleaving

204 byte TS like packets

204 byte blocks, but with bytes interleaved

Fifo shift registers

1 byte per position

No delay

17 bytes delay

2 x 17 bytes delay

3 x 17 bytes delay

11 x 17 bytes delay

17 complete ‘switch rotations’ per packet

RS parity bytes are now grouped at the end of each block.

Effectively the inverse of the interleaving process at the transmitter

convolutional

inner decoder

block outer

decoder

Output of Outer de-interleaver:

confid-ence

MPEG2 t/s

1 0 0 1 0 0 11

convolutional

inner decoder

block outer

decoder

Input to Block decoder (Reed-Solomon):

confid-ence

MPEG2 t/s

204 byte (corrupted ?) blocks

Reed-Solomon Error Correction for DVB

RSinc.

The Reed-Solomon error correction process can locate and correct up to 8 corrupted bytes in the block of 204 bytes

47,00,13,08,00,00,A3,C3,C0,00,00,23,74,F2,……,46,8A,9C,00,23,00,00,4C,…..,00,04,06,00,C0,00,34,42,B9,57,...,F5,9C,A3.

Possible Implementation of RS Error Corrector

47,00,13,08,00,00,A3,C3,C0,00,00,23,74,F2,……,46,8A,9C,00,23,00,00,4C,…..,00,04,06,00,C0,00,34,42,B9,57,...,F5,9C,A3.

Syndrome Calculation Error

Location Calculation

Error Calculation

Error Correction

47,00,13,08,00,00,A3,C3,C3,00,00,23,74,F2,……,46,8A,9C,00,37,00,00,4C,…..,00,04,7C,00,C0,00,34,42,B9,43,...,F7,9C,A3.

Input Block

Output Block

Parity bytes no longer needed

convolutional

inner decoder

block outer

decoder

Output from Block decoder (Reed-Solomon):

confid-ence

MPEG2 t/s

204 byte (corrupted ?) blocks

188 byte quasi error free blocks

convolutional

inner decoder

block outer

decoder

Energy dispersion removal:

confid-ence

MPEG2 t/s

Channel Decoder Stage Summary

Tuner IF filter

1st IF (~36MHz)

ADCDigital

front endFFT

Error Correct.

Transport stream

AGC amp

digital tv: an introduction gregory bensberg. uk dtt 81 main and relay sites

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