Upload
matthew-rodgers
View
223
Download
3
Embed Size (px)
Citation preview
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
3NTU Confidential
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
4NTU Confidential
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
6NTU Confidential
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]
7NTU Confidential
Channel Model (2/4) Channel Model (2/4) Static ChannelStatic Channel
Fixed Channel Portable Reception
8NTU Confidential
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]
9NTU Confidential
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
10
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
12
NTU Confidential
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
13
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
*
14
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
15
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
16
NTU Confidential
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
17
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
18
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
19
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
21
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
22
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]
23
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
25
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]
26
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
27
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
28
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