Progress Report in DVB-T’s Research

Progress Report in

Progress Report in

DVB-T’s Research

DVB-T’s Research

Speaker: Keng-Hsien Lin

Speaker: Keng-Hsien Lin

Advisor: Prof. Tzi-Dar Chiueh

Advisor: Prof. Tzi-Dar Chiueh

Date: December 27, 2004

Outline

Outline

• Soft Demapping for Soft Viterbi Decoding_{Soft Demapping for Soft Viterbi Decoding} • Multipath Channel Modeling_{Multipath Channel Modeling}

• Propose Two-stage Mode Detection Algorithm_{Propose Two-stage Mode Detection Algorithm} • Conclusions _Conclusions && Future Work _{Future Work} && References _References

Outline Overview

Outline Overview

• Soft Demapping for Soft Viterbi Decoding_{Soft Demapping for Soft Viterbi Decoding}

– Bit Interleaved Coded Modulation_{Bit Interleaved Coded Modulation} – Bit Log-likelihood Ratio_{Bit Log-likelihood Ratio}

– Soft Demapping Approximation in ML Sense_{Soft Demapping Approximation in ML Sense}

• Multipath Channel Modeling_{Multipath Channel Modeling}

• Propose Two-stage Mode Detection Algorithm_{Propose Two-stage Mode Detection Algorithm} • Conclusions _Conclusions && Future Work Future Work && References References

Bit Interleaved Coded Modulation

Bit Interleaved Coded Modulation

• Interleaver

– The performance is better over Rayleigh fading – Needs appropriate soft-decision metrics

• Soft bit metrics for soft-decision decoding

[1] Encoder Interleaver Modulation

Channel

Bit Log-likelihood Ratio

Bit Log-likelihood Ratio

• Bit log-likelihood ratio

, Pr( | ) ln 0 Pr( | ) j dj i d j _{j ij} r c r c  



Pr( | 0) ln Pr( |1) j j j r r   , (( 1)cdj ( 1)cij ) 0 j j i d j       



(( 1)cdj ) (( 1)cij ) j j j j     





• ML criterion

Soft Demapping Approximation

Soft Demapping Approximation

in ML Sense (1/5)

in ML Sense (1/5)

• Relation between received and transmitted signals yk, xk 2 : 0 2 : 1 max exp( | ( ) | ) ln max exp( | ( ) | ) j j k k b b j k k b b y h f b y h f b          ( ) k k k y  h f b  w : : 2 0 0 2 : 1 : 1 Pr( | ) exp( | ( ) | ) Pr( | 0) ln ln ln Pr( | 1) Pr( | ) exp( | ( ) | ) j j j j b b b b k k k k j j k j k k k b b b b y b y h f b y b y b y b y h f b              









k k y s h  ( ) k x  f b • Calculate bit log-likelihood ratio

2 2 2

: 1 : 0

Soft Demapping Approximation

Soft Demapping Approximation

in ML Sense (2/5)

in ML Sense (2/5)

2 2 2 2

0 | k | (| Re( ) 1|k | Re( ) 1| ) |k k | (4 Re( ))k

b metric  h s   s   h s

2 2 2 2 2

0 | k | (min(| Re( ) 1| ,| Re( ) 3 | ) min(| Re( ) 1| ,| Re( ) 3 | ))k k k k

b metric  h s  s   s  s 

2 2 2 2 2

2 | k | (min(| Re( ) 1| ,| Re( ) 1| ) min(| Re( ) 3 | ,| Re( ) 3 | ))k k k k

b metric  h s  s   s  s 

• For QPSK using Gray mapping

• For 16-QAM using Gray mapping

2 2 2 2

1 | k | (| Im( ) 1|k | Im( ) 1| ) |k k | (4 Im( ))k

b metric  h s   s   h s

2 2 2 2 2

1 | k | (min(| Im( ) 1| ,| Im( ) 3 | ) min(| Im( ) 1| ,| Im( ) 3 | ))k k k k

Soft Demapping Approximation

Soft Demapping Approximation

in ML Sense (3/5)

in ML Sense (3/5)

Soft Demapping Approximation

Soft Demapping Approximation

in ML Sense (4/5)

in ML Sense (4/5)

Soft Demapping Approximation

Soft Demapping Approximation

in ML Sense (5/5)

in ML Sense (5/5)

Outline Overview

Outline Overview

• Soft Demapping for Soft Viterbi DecodingSoft Demapping for Soft Viterbi Decoding

• Multipath Channel Modeling_{Multipath Channel Modeling}

– Simple Case Analysis_{Simple Case Analysis}

– Frequency Responses of Several Type Interpolators_{Frequency Responses of Several Type Interpolators} – Circular Concepts in OFDM System_{Circular Concepts in OFDM System}

• Circular Convolution_{Circular Convolution}

• Propose Circular Interpolation_{Propose Circular Interpolation}

• Propose Two-stage Mode Detection Algorithm_{Propose Two-stage Mode Detection Algorithm} • Conclusions _Conclusions && Future Work _{Future Work} && References _References

Simple Case Analysis

Simple Case Analysis

[ ] [0] [ ] [0.8] [ 0.8] y n  h x n  h x n  ( 0.8) ( jw) [0] ( jw) [0.8] ( jw) j w ( jw) ( jw) Y e  h X e  h X e e   H e X e ( 0.8) ( jw) [0] [0.8] j w [ ] jwn n H e  h h e  



h n e 2 1 [ ] [0] [ ] [0.8]( [ ] [ ]) k y n h x n h i k x n k   



 ( jw) [0] ( jw) [0.8] ( jw) ( jw) ( jw) ( jw) Y e  h X e  h I e X e  H e X e ( ) ( jw) [0] [0.8] | ( jw) | j I ejw H e  h  h I e e  | (I ejw) | 1 _e j I e_ ( jw) _{ e} j( 0.8) w • Good interpolator

Frequency Responses of

Frequency Responses of

Several Type Interpolators (1/5)

Several Type Interpolators (1/5)

Frequency Responses of

Frequency Responses of

Several Type Interpolators (2/5)

Several Type Interpolators (2/5)

Frequency Responses of

Frequency Responses of

Several Type Interpolators (3/5)

Several Type Interpolators (3/5)

Frequency Responses of

Frequency Responses of

Several Type Interpolators (4/5)

Several Type Interpolators (4/5)

Frequency Responses of

Frequency Responses of

Several Type Interpolators (5/5)

Several Type Interpolators (5/5)

Circular Convolution

Circular Convolution

1 mod 0 [ ] [ ] [ ] N N m y n  h m x n m  





( )

( ) ( )

Y k



H k X k

• Circular convolution • OFDM system

– Uses cyclic prefix (CP)

– Only needs one-tap equalizer

2 1 0 ( ) ( ) nk N _j N n Y k y n e   _  



Propose Circular Interpolation

Propose Circular Interpolation

2 1 [ ] [0] [ ] [0.8]( [ ] [ ]) k y n h x n h i k x n k      _{Y e(} jw_{)  h[0] (X e}jw_{) h[0.8] (I e}jw_{) (X e}jw₎ mod mod 2 1 [ ] [0] [ ] [0.8]( [ ] [ ] ) N N k y n h x n h i k x n k   





• Circular interpolation in OFDM system

( )

[0] ( )

[0.8] ( ) ( )

Y k



h

X k



h

I k X k

Outline Overview

Outline Overview

• Soft Demapping for Soft Viterbi DecodingSoft Demapping for Soft Viterbi Decoding

• Multipath Channel Modeling_{Multipath Channel Modeling}

• Propose Two-stage Mode Detection Algorithm_{Propose Two-stage Mode Detection Algorithm}

– Why Needs Mode Detection_{Why Needs Mode Detection}

– Critical Issues in Mode Detection of DVB-T System_{Critical Issues in Mode Detection of DVB-T System} – Two-stage Mode Detection Algorithm_{Two-stage Mode Detection Algorithm}

• FFT Mode Detection_{FFT Mode Detection}

• Guard Interval Mode Detection_{Guard Interval Mode Detection}

Why Needs Mode Detection

Why Needs Mode Detection

• DVB-T system

– Two FFT size to select: 2K-mode, 8K-mode

– Four Guard Interval to select: 1/4, 1/8, 1/16, 1/32

• Severe frequency-selective fading channel

– Select 8K-mode and 1/4 guard interval ratio

• Severe fast fading channel

– Select 2K-mode and 1/32 guard interval ratio

Critical Issues in Mode Detection

Critical Issues in Mode Detection

of DVB-T System

of DVB-T System

• Mode detection should be finished in time domain

– No preamble

– Known signals are put in frequency domain – Only CP characteristic can be used

• Total eight kinds of mode need to detect one

– ML or MMSE criterion may not work

FFT Mode Detection (1/5)

FFT Mode Detection (1/5)

1 * 0 ( , , ) GI ( ) ( ) k d N GI  r d k r d k N         63 * 2 0 1 | ( , 2 , 2 ) | | ( ) ( 2 ) | 32 K k d K K r d k r d k K            63 * 8 0 1 | ( ,8 , 2 ) | | ( ) ( 8 ) | 32 K k d K K r d k r d k K            • Delay correlation • FFT mode detection • Criterion CP CP

Either one will have peaks!

arg max ( )

FFT Mode Detection (2/5)

FFT Mode Detection (2/5)

FFT Mode Detection (3/5)

FFT Mode Detection (3/5)

FFT Mode Detection (4/5)

FFT Mode Detection (4/5)

FFT Mode Detection (5/5)

FFT Mode Detection (5/5)

Guard Interval Mode Detection (1/4)

Guard Interval Mode Detection (1/4)

1 32 * 0 1 | ( , , ) | | ( ) ( ) | 32 N k d N N r d k r d k N          

• Using the lease guard interval length to do delay correlation

• Theoretical analysis

| |

Different platform width

• Detection algorithms

– Platform width detection

Guard Interval Mode Detection (2/4)

Guard Interval Mode Detection (2/4)

• Platform width detection in 2K mode

– The best case: Through Tx to Rx

Guard Interval Mode Detection (3/4)

Guard Interval Mode Detection (3/4)

• Platform width detection in 2K mode

– The worst case: P1, SNR=3dB, 20ppm CFO&TO > 1/2 Peak > 3/4 Peak

Guard Interval Mode Detection (4/4)

Guard Interval Mode Detection (4/4)

1 32 * 0 1 | ( , , ) | | ( ) ( ) | 32 N k d N N r d k r d k N           3 1/ 4 0 5 1 max( | ( ( ), , ) |) 4 32 GR l d l N N N          _1/8 3 0 9 1 max( | ( ( ), , ) |) 8 32 GR l d l N N N         

• Different accumulated window detection

3 1/16 0 17 1 max( | ( ( ), , ) |) 16 32 GR l d l N N N          1/32 3 0 33 1 max( | ( ( ), , ) |) 32 32 GR l d l N N N          1/ 4 1/8 1/16 1/ 32 arg max _{GR i} i or or or Guard Ratio _   

Outline Overview

Outline Overview

• Soft Demapping for Soft Viterbi Decoding_{Soft Demapping for Soft Viterbi Decoding} • Multipath Channel ModelingMultipath Channel Modeling

• Propose Two-stage Mode Detection Algorithm_{Propose Two-stage Mode Detection Algorithm}

• Conclusions _Conclusions && Future Work _{Future Work} && References _References

– Conclusions_Conclusions – Future Work_{Future Work} – References_References

Conclusions

Conclusions

• Both analytical and simulation results are shown

– Soft demapping method

• Use piecewise linear approximation in ML sense

– Multipath channel modeling

• Use circular interpolation with good interpolator

– Mode detection algorithm

Future Work

Future Work

• Finish the simulation on mode detection error rate

• Transform the DVB-T code to silicon IP

– Synthesizable RTL code – Testbench

References

References

• [1] G. Caire, G. TariccoE. Biglieri, “Bit-Interleaved Coded Modulation”, IEEE Trans. Inform. Theory, vol.44, May. 1998