1 - Fundamentals of the Digital TV- ITS

8/11/2019 1 - Fundamentals of the Digital TV- ITS

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G i l l e s TOQU ET

2 0 1 3

Teamcast - 2013 Teamcast - 2013


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H e r t z i a n A n a l o g i c B r o a d ca s t

ContributionNetwork

DistributionNetwork

na og c Noise sensitivity 1 prg / RF channel

na og c Digital AES 1 prg / link

Analogic source Audio content


11 December 201311 December 2013


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D i g i t a l b r o a d ca s t c h a i n

ContributionNetwork

DistributionNetwork

EditorsEditors Broadcast operatorsBroadcast operatorsMultiplex operatorsMultiplex operators

Digital Broadcast Robust 5 prg / RF channel

Mixte contributions Programmes multiplexing Digital multiplex distribution

Analogic sources Digital sources Multimdia content




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La y e r i d e n t i f i c a t i o n

Compressioncoding

Compressioncoding

Com ression Multiplexing

Distribution Modulation

coding

I/FDatas

Audio Audio

erv ce rame

Multiplex frame

COFDM frame

RF

TC

TM

TRAINING




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T r a n sm i s s i o n ch a n n e l b e h a v i o r

RECEIVER

TRANSMITTER

Modifications of the transmitted signal in Time and Frequency domains




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Ch a n n e l b e h a v i o r : t h e d i s e r s i o n

Path 1

t tTime

Echoes

Monochromatic

signal

f

F

f

requency

Dopplereffect

The response to a Dirac peak defines the transmission channel response (in time and in frequency) The many paths gives some delays (Echoes) The relative speed between antennas gives some modifications in the frequency domain (Doppler)




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Ch a n n e l b e h a v i o r :

r e q u e n c y se e c v y

BandwidthFrequency response of the

channel

The frequency response of the channel is not constant Some frequencies will be attenuated (FADING), other will be reinforced




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Pe r t u r b a t i o n s s y n t h e s i s

Echoes Doppler Noise

Echoes: The multi paths cause some delays and some Fadingeffects

e ec : e mo y causes some s gna var a ons nfrequency domain

Noise: The Hertzian transmission channel generates some noise.It is added to the use ul si nal C N ratio




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Pe r t u r b a t i o n s s t u d y :

-PerturbationsF(t) F(t)

t t

N

+C C/N(dB)

: The C N ratio de ines the minimal conditions to havegood signal decoding (QEF) Note: The noise has a random distribution




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Th e n o i s e : C/ N i l l u s t r a t i o n

Source: ETS 300 744

The DVB-T standard defines a C/N minimum level of 16,5dB, in 64-QAM-2/3 mode to obtain the QEF condition




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Th e n o i s e : B ER m e a su r e m e n t

Perturbations

0 1 1 0 0 1 0 1 0 0 0 0

corrected errors and the datas number It is the main parameter that defines a transmission quality Example: 2x10E-4 after Viterbi defines the QEF after RS (DVB-T)




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Pe r t u r b a t i o n s s t u d y : 2 - Ech o e s

The echoes are due to: Adjacent-waves reflections on various obstacles (hills,

buildings etc),

-reception of di fferent transmitters.

transmitter

Receiver

transmitter

-The roblem of the echoes remained the most im ortant-Echoes can be

-> Passive (Multipath)-> Active (Transmitter in SFN)




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Th e r o b l e m o f e ch o e s

Ampli tude Amp litudeTA A

Time FrequencyF=1/TWithout Echo

A(t) A(f)

Ampli tude Ampli tudeT

A A

Time FrequencyF=1/TWith Echo

A(t) A(f)

- Frequency is not affected by the echoes- Amplitude and phase are affected by the echoes- The answer in frequency of the terrestrial channel changes in the time in function :

- of the echoes delay,- of the echoes level.




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Ech o e s i n r u r a l e n v i r o n m e n t

Not many obstacles Short echoes




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Ech o e s i n r u r a l e n v i r o n m e n t

H(t) H(t)

0dB

- 10dB

-20dB

0dB

- 10dB

-20dB

27 ns / OdB 300 ns / OdB

t

-30dB

-40dBt

-30dB

-40dB

10dB

H(f)

10dB Fading

- 10dB

-20dB-30dB

- 10dB

-20dB-30dB

f-40dB f-40dB




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Ech o e s i n u r b a n e n v i r o n m e n t

Many obstacles Long echoes




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Ech o e s i n u r b a n e n v i r o n m e n t H(t)

H(t)

1us / OdB 5us / OdB

0dB

- 10dB

-20dB

0dB

- 10dB

-20dB

t

-30dB

-40dBt

-30dB

-40dB

10dB

H(f)

10dB

- 10dB

-20dB

-30dB

- 10dB

-20dB

-30dB

f-40dB f-40dB




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I m p u l s e r e sp o n s e o f t h e

Direct path

Echo



P b i d


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Pe r t u r b a t i o n s s t u d y :

Carriers-

V=0 km/h f

=

F1

V=300 km/h f

F

The DOPPLER effect causes frequency shifts of the transmitted signal Notion of Inter carriers interferences



Ch a n n e l r e sp o n se


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Ch a n n e l r e sp o n se

H(f)

10dB

-10dBT0

-30dB

-

fT1

In mobile rece tion the fre uenc res onse of the channel alwa s chan es So, it is necessary to realize a time prediction on the decoding This implies the implementation of Time Interleaves




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Op e r a t i n g M o d e s Ga u s s i a n

Gaussian Ricean Ra lei h Mobile

Condition to emulate Fixed receiving condition

Echoless signal

Channel Characterization

1 2 3 4 5 6 Tap One main path signal Measurements objective

Intrinsic erformance measurements

Methodology

C/N increase to reach QEF

modulation modes




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Op e r a t i n g M o d e s R i c e a n


Fixed receiving condition

Roof-antenna reception

Tap

One main path signal with 5 echoes Measurements objective

1 2 3 4 5 6

Methodology

Configure Ricean channel profile

Input level sensitivity for different modulationmodes




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Op e r a t i n g M o d e s Ra y l e i g h


Portable receiving condition

Indoor/outdoor

Tap

One main path signal with 4 echoesand 1 pre-echo

1 2 3 4 5 6

Portable receiver performances

Methodology

C/N increase to reach QEF

Input level sensitivity for different modulationmodes



Op e r a t i n g M o d e s M o b i l e


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Op e r a t i n g M o d e s M o b i l e


Mobile receiving condition

Channel Characterization

Measurements objective Handset performances in mobilty

Methodology

Configure Mobile channel profile

MFER 5%

Draw the C/N performance curve




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DV B - T e x am p l e



Source: ETS 300 744

Th t i i t i t


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Th e t r a n sm i s s i o n co n s t r a i n t s

Noise - Random phenomenon- Transmission errors

?

?

Frequency selectivity - Fading/lost of somefrequencies ?

Time selectivity- Changes of the channelresponse- Mobilit

?

Echoes

- Echoes interferences with the

main path?

DOPPLER - Spectrum changes infrequencies (DOPPLER) ?



1 - Fundamentals of the Digital TV- ITS

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