NTU Confidential

Baseband Transceiver Design for the DVBaseband Transceiver Design for the DVB-Terrestrial StandardB-Terrestrial Standard

Advisor : Tzi-Dar ChiuehStudent : Yi-Ju Chen

Date : September 29th , 2003

2NTU Confidential

OutlineOutline

• Review of DVB-T SystemReview of DVB-T System• Transmitter Block DiagramTransmitter Block Diagram• Channel ModelChannel Model

– Static ChannelStatic Channel– Dynamic ChannelDynamic Channel

• Receiver ArchitectureReceiver Architecture– Coarse Boundary DetectionCoarse Boundary Detection– Integer CFO EstimationInteger CFO Estimation– WLS Fine CFO EstimationWLS Fine CFO Estimation

• Future WorkFuture Work• ReferenceReference

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What is DVB-T ?What is DVB-T ?• DVB-T stands for Digital Video Broadcasting – Terrestrial

– Wireless video

• DVB-T uses COFDM technique• DVB-T Transmit Block Diagram

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System ParametersSystem Parameters

• Center frequency: 480MHz +ｉ *6MHz• Region: 480MHz ~ 806MHz Channel 14 ~ Channel 69

6MHz Channel

Transmission mode 8k mode 2k mode

Number of carriers K 6817 1705

Duration TFFT 1194.667 us 298.6667 us

Carrier spacing 1 / TFFT 0.837054 kHz 3.348214 kHz

Bandwidth 5.71 MHz

Modulation QPSK , 16QAM , 64QAM

Code rate 1 / 2 , 2 / 3 , 3 / 4, 5 / 6 , 7/8

Guard interval ratio 1 / 4 , 1 / 8 , 1 / 16 , 1 / 32

Data Rate 3.732 ~ 23.751 Mbps

NTU Confidential

Channel ModelChannel Model

Static ChannelDynamic Channel

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Channel Model (1/4)Channel Model (1/4)Static ChannelStatic Channel

• Fixed Reception– where a directional

receiving antenna mounted at roof level is used

– A receiving antenna height of 10m above ground level is considered to be representative

• Portable Reception – Portable receiver with atta

ched or built-in antenna – Absence of receiving anten

na gain and directivity – Generally lower reception

height

Derived from the Spec. of DVB-T [1]

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Channel Model (2/4) Channel Model (2/4) Static ChannelStatic Channel

Fixed Channel Portable Reception

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Channel Model (3/4) Channel Model (3/4) Dynamic ChannelDynamic Channel

• Typical Urban Reception(TU6) • Typical Rural Area Reception ( RA6 )

Derived from COST 207 project (GSM transmission) [2]

Tap number Delay (us) Power

(dB)Doppler

spectrum

1 0 -3 Rayleigh

2 0.2 0 Rayleigh

3 0.5 -2 Rayleigh

4 1.6 -6 Rayleigh

5 2.3 -8 Rayleigh

6 5.0 -10 Rayleigh

Tap number Delay (us) Power

(dB)Doppler

spectrum

1 0 0 Rice

2 0.1 -4 Rayleigh

3 0.2 -8 Rayleigh

4 0.3 -12 Rayleigh

5 0.4 -16 Rayleigh

6 0.5 -20 Rayleigh

[2]

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Channel Model (4/4) Channel Model (4/4) Dynamic ChannelDynamic Channel

• SFN( Single Frequency Network) Channel [2]

Tap number Delay(us) Power Doppler spectrum Frequency ratio

1 0 0 Pure Doppler -1

2 1/2 Tg 0 Pure Doppler +1

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NTU Confidential

BaseBand Channel ModelBaseBand Channel Model

Delay 1

Path Amp1Rayleigh

Fading h1

Delay 2

Path Amp2Rayleigh

Fading h2

Delay L

Path AmpL

RayleighFading hL

.

.

.

.

.

.

.AWGN

MultiPath Rayleigh Fading Channel

exp(j2/N)

ADCReSampling

Timing offset

Carrier Offset

Receiver Non-idealities

NTU Confidential

Receiver ArchitectureReceiver Architecture

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Receiver Block DiagramReceiver Block Diagram

Coarse SymbolBoundaryDetection

FFT Block

FFT Window

Fractional Freq.Offset Acquisition

Integer Freq.Offset Acquisition

De-rotator

PilotExtraction

WLS Estimation

Low PassFilerNCO

Interpolator

Integrator

Scaling

ChannelEstimation

FEQ

Finished part

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NTU Confidential

Coarse Symbol Boundary Detection Coarse Symbol Boundary Detection (1/5)(1/5)

FFT SymbolCyclic PrefixPrevious Symbol Next Symbol

GI-1*

0

(d) r(d-n) r(d-n-N)n

Correlation Sum

DVB-T System doesn’t have preamble to do symbol boundary detection, but we can utilize the cyclic prefix to implement it.

- - - - - - - -0 N-1

- - - - - - - -0 GI-1

-+ +D

+

InputSymbol Correlation

Sum

N=2048 for 2k modeN=8192 for 8k mode

GI : Guard Interval Length

| | 2Find Max Moving AverageAccumulated

by NsFFT Symbols

Auto Correlation Block

Coarse Symbol Boundary DetectionCoarse Symbol Boundary Detection

*

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NTU Confidential

Coarse Symbol Boundary Coarse Symbol Boundary Detection (2/5)Detection (2/5)

• For 1 tab Channel profile the result of Correlation Sum is as follows,

• The correlation sum appears triangle and changes slowly

• If we transmit the preamble to do auto correlation the correlation sum will be an ideal delta function

• The peak is interfered by noise seriously

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NTU Confidential

Coarse Symbol Boundary Coarse Symbol Boundary Detection (3/5)Detection (3/5)

• As for multi-path channel profile, take a 2-path channel for example• The correlation sum peak becomes ambiguous• The peak might occur in the boundary which induces ISI

1*

0

1* ** *

1 2 1 20

1 1* ** *

1 1 2 20 0

1* *

1 20

( ) ( - ) ( - - )

( ( - ) ( - - )) ( ( - - ) ( - - - ))

( ( - ) ( - - )) ( ( - - ) ( - - - ))

( ( - ) ( - - - )) (

GI

n

GI

n

GI GI

n n

GI

n

d r d n r d n N

p x d n p x d n p x d n N p x d n N

p x d n p x d n N p x d n p x d n N

p x d n p x d n N p

1

* *2 1

0

(1' ) (2' )

(1' , 2' ) (2'

( - - ) ( - - ))

, 1' )

GI

n

AutoCorr st Path AutoCorr nd Path

CrossCorr st Path nd Path

x d n p x d n

CrossCorr nd Path st Path

N

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Coarse Symbol Boundary Coarse Symbol Boundary Detection (4/5)Detection (4/5)

• In the SFN Channel Model, there is no peak (extreme example)

• Add moving average to find the max. average power position

FFT SymbolCyclic Prefix

Channel Delay Profile

Auto Correlation Sum of 1'st Path

No Peak

FFT WindowResult FFT Window

Received Signal

FFT SymbolCyclic Prefix

Auto Correlation Sum of 2'nd Path

???FFT WindowFFT Window

FFT SymbolCyclic Prefix

Channel Delay Profile

Auto Correlation Sum of 1'st Path

Result FFT Window

Received Signal

FFT SymbolCyclic Prefix

Auto Correlation Sum of 2'nd Path

FFT Window

Moving AVGWindow

Peak

ISI

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NTU Confidential

Coarse Symbol Boundary Coarse Symbol Boundary Detection (5/5)Detection (5/5)

• We can observe that the resulting boundary may induce ISI because of the delay spread of the channel

• Desired FFT window = Max Boundary Position – GI/2

FFT SymbolCyclic Prefix

No ISI

Previous Symbol

Previous Symbol

Previous Symbol

Next Symbol

Next Symbol

Next Symbol

1'st Path

2'nd Path

3'rd Path

FFT Window

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NTU Confidential

Fractional CFO EstimationFractional CFO Estimation

Coarse SymbolBoundaryDetection

FFT Block

FFT Window

Fractional Freq.Offset Acquisition

Integer Freq.Offset Acquisition

De-rotator

PilotExtraction

WLS Estimation

Low PassFilerNCO

Interpolator

Integrator

Scaling

ChannelEstimation

FEQ

Finished part

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NTU Confidential

Fractional CFO EstimationFractional CFO Estimation

• If we assume the normalized CFO is

• Can’t use this formula to calculate Integer part of

GI-1 GI-1* 2 2

0 0

(d) r(d-n) r(d-n-N) |r(d-n)| j

n n

Correlation Sum e

1*

01

*

0

Im1

arctan2

Re

GI

d n d n NnGI

d n d n Nn

r rFractional Normalized CFO

r r

22( ) ( ) ( )

j N jNr k N r k e r k e

* 2 2( ) ( ) | ( ) | jr k N r k r k e

If r(k) in the Guard Interval

FFT SymbolCyclic Prefix

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Performance of Different NsPerformance of Different Ns

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NTU Confidential

Integer CFO EstimationInteger CFO Estimation

Coarse SymbolBoundaryDetection

FFT Block

FFT Window

Fractional Freq.Offset Acquisition

Integer Freq.Offset Acquisition

De-rotator

PilotExtraction

WLS Estimation

Low PassFilerNCO

Interpolator

Integrator

Scaling

ChannelEstimation

FEQ

Finished part

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NTU Confidential

Integer CFO Estimation(1/2)Integer CFO Estimation(1/2)

• Integer Frequency Offset (Normalized by Sub Carrier Spacing) will cause the sub-carrier index shift error

• Using Continual Pilots to find the shift of the index

*1, ,

ˆ max l k l km

k Pm

f Y Y

Y : Received Signal in Freq. DomainPm : [ p1+m , p2+m , ……, pL+m ] Continual Pilots Position shift ml : l ’ th Symbol

[5]

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NTU Confidential

Integer CFO Estimation(2/2)Integer CFO Estimation(2/2)• Block Diagram

• C++ Simulation Result

- - - - - - - -0 N

N Length Shift RegisterInput

Symbol

N=2048 for 2k modeN=8192 for 8k mode

* ………p1 p2 pLpL-1

FindMax

p1 , p2 ,…… pL : Continual pilot index

| | 2

NTU Confidential

Fine CFO Estimation Loop Fine CFO Estimation Loop WLS Estimation WLS Estimation

Coarse SymbolBoundaryDetection

FFT Block

FFT Window

Fractional Freq.Offset Acquisition

Integer Freq.Offset Acquisition

De-rotator

PilotExtraction

WLSEstimation

Low PassFilerNCO

Interpolator

Integrator

Scaling

ChannelEstimation

FEQ

Finished part

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NTU Confidential

Fine CFO EstimationFine CFO Estimation Joint WLS Estimation(1/2) Joint WLS Estimation(1/2)

atan

atan

abs

abs

+

-

Divider

D

D

kth pilot in theprevios symbol

kth pilot in thecurrent symbol

To LPF

Joint WLSEPhase difference inconsecutive blocks

Weighting calculation

yk

wk

[4]

WLSE Block Diagram

Assume the source of CFO and TFO is the same, by theresult of joint WLS Estimation

k

k

y : Phase Difference between 2 Symbols of k'th sub-carrier index

w : Weighting factor of k ' th sub carrier index

GR : Guard Interval Ratio

[3]

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NTU Confidential

Fine CFO EstimationFine CFO Estimation Joint WLS Estimation(2/2) Joint WLS Estimation(2/2)

• Simulation Result

Adding extra error=0.04 to see the convergence

System Simulation result The result of fractional CFO is in the convergence region already

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NTU Confidential

Conclusion and Future WorkConclusion and Future Work• Conclusion

– Although there is no preamble, the DVB-T can exchange time for good acquisition performance

– It is the advantage of broadcast system• Future Work

– Design unfinished block– Add channel coding and outer decoding– Simulation the performance on mobile channel

Coarse SymbolBoundaryDetection

FFT Block

FFT Window

Fractional Freq.Offset Acquisition

Integer Freq.Offset Acquisition

De-rotator

PilotExtraction

WLSEstimation

Low PassFilerNCO

Interpolator

Integrator

Scaling

ChannelEstimation

FEQ

Finished part

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NTU Confidential

ReferenceReference

• [1]ETSI EN 300 744 V1.4.1(2001-01)Framing structure, channel coding and modulation for digital terrestrial television

• [2]MOTIVATE report to the 36th DVB-T Meeting (2000-01)Using DVB-T standard to deliver broadcast Services to mobile receiver

• [3]Joint weighted least squares estimation of frequency and timing offset for OFDM systems over fading channels Pei-Yun Tsai; Hsin-Yu Kang; Tzi-Dar Chiueh; Vehicular Technology Conference, 2003. VTC 2003-Spring. The 57th IEEE Semiannual , Volume: 4 , April 22-25, 2003

• [4]Design and Implementation of an MC-CDMA Baseband Transceiver Hsin-Yu Kang; July , 2003• [5] Frequency synchronization algorithms for OFDM systems suitable for co

mmunication over frequency selective fading channels Classen, F.; Meyr, H.; Vehicular Technology Conference, 1994 IEEE 44th , 8-10 June 1994 Page(s): 1655 -1659 vol.3