Channel Estimation Schemes for OFDM Relay-Assisted System Darlene - - PowerPoint PPT Presentation

▶
channel estimation schemes for ofdm relay assisted system
SMART_READER_LITE
LIVE PREVIEW

Channel Estimation Schemes for OFDM Relay-Assisted System Darlene - - PowerPoint PPT Presentation

Apr 04, 2023 577 likes •778 views

Channel Estimation Schemes for OFDM Relay-Assisted System Darlene Maciel, C. Ribeiro, A. Silva e Atlio Gameiro darlene@av.it.pt Workshop 2009 2 nd Dec, FEUP, Porto, Portugal Outline Introduction Motivation PACE Schemes

slide-1
SLIDE 1

Channel Estimation Schemes for OFDM Relay-Assisted System

Workshop 2009

2nd Dec, FEUP, Porto, Portugal

Darlene Maciel, C. Ribeiro, A. Silva e Atílio Gameiro darlene@av.it.pt

slide-2
SLIDE 2

Outline

  • Introduction
  • Motivation
  • PACE Schemes
  • Simulation Scenario
  • Results
  • Conclusion
  • Future Works

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-3
SLIDE 3

Introduction: Diversity

  • Diversity is inherent in the physical layer: PHY diversity

▫ Time, frequency, space (antenna) and polarization diversity ▫ Combat the fading channel by trying to flatten the channel

  • Diversity can also be achieved in the MAC or higher layer:

Network diversity

▫ Multiuser diversity (by scheduling or routing) ▫ Cooperative diversity (by cooperative transmission)

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-4
SLIDE 4

Introduction: Cooperation

▫ Node S cooperates with neighbors to send information to D

S D

  • Redundant transmission is realized via the cooperation of third

party devices rather than solely from the originating device;

  • AF

, DF , SDF or CF

  • Half dupplex AF: 2 phases

Simple forms of cooperation involves 3 links S RN D Transmitted signal Received signal

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-5
SLIDE 5

Introduction: Amplify-and-Forward Protocol

  • In the half duplex AF protocol receiver at D needs

▫ First phase: Estimate channel S-D:  Single link  Conventional Channel Estimation ▫ Second Phase: Estimate channel S-RN-D:  Compound Channel

S RN D

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-6
SLIDE 6

Motivation: Equivalent Channel

  • Compound Channel

S D RN

(1) (2) (1) (2) Eq Eq

( ) ( ) (t) ( ) ( ) ( ) t A t m A m m

h h h h h h

    

(1) (2) 2

(1) (2)

PDP = E{| = PDP PDP

( ) ( ) | } h t h t Maximum delay = Delay channel 1 + Delay channel 2 # Taps of the compound channel will depend on the both channels PDP

(1)( )

h t

(2)( )

h t

  • The Power Delay Profile - PDP

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-7
SLIDE 7

Motivation: Equivalent Channel

  • Two sources of Noise. The total noise at the D:

S D RN

(2) (1) (2)

( ) ( ) ( ) ( )

t

w m Ah m w m w m  

 

(1) (2)

, : 0, 1 h h ES

2

2 2 2 2

( ) ( )

{| | }

t

t n n

m w m

E A      

(1)( )

h t

(2)( )

h t

(2)

2 2 2 2

2

( )

| ( )|

t n n

m

h m

A     

The conventional channel estimation schemes should be adapted to this scenario

LS , MMSE

  • Conditioned to a specific channel realization the noise variance:

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-8
SLIDE 8

Motivation: Questions

  • Questions to be Solved:

▫ How does the statistics of the compound channel affect the performance of classical PACE in OFDM signalling? ▫ How much can be gained through the knowledge of ?

(2)

h

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-9
SLIDE 9

Classical Pilot Aided Channel Estimation Schemes

  • FD – LS (Least Square):

Equalisation Channel Estimator

LS LS

ˆ ˆP h Wh 

LS

ˆ h W: Interpolator

1 LS

ˆP

P P

h X Y

+ AWGN DFT LS Estimate FD MMSE Filter

MMSE

ˆ h

MMSE MMSE

ˆ h W 

1 MMSE HP P

W R R

P HP

Autocorrelation; Cross-correlation; R R  

LS

ˆP h

  • FD – MMSE (Mean Minimum Square Error) :

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-10
SLIDE 10

Classical Pilot Aided Channel Estimation Schemes

  • TD-MMSE

Channel Estimator Equalisation

+ AWGN CIR Group TD MMSE Filter

LS

ˆ h

MMSE

ˆ h  

2

[ ] [ ]

n

hh hh

W n

R n R n 

 

Auto-correlation Function

[ ] Channel PDP

hh

R n 

1 2 2 2

PDP PDP

PDP

n t

       CIR Estimate

CIR estimate

Example

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-11
SLIDE 11

Simulation Scenario

  • Scenario and Parameter

S RN D Modulation QPSK Sampling frequency (LTE) 15.36 MHz # Subcarriers 1024 Link Analized Compound channel For reference

  • Conv. SISO

Channels’ Noise statistics identical Channel 7 Taps Path Delay(ns) Relative Power(dB) 1 0.0 0.0 2 65.1 (T)

  • 0.7

3 260.4 (4T)

  • 0.8

4 586.0 (9T)

  • 6.0

5 1041.67 (16T)

  • 10.0

6 1627.6 (25T)

  • 14.0

7 2474.0 (38T)

  • 19.0

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-12
SLIDE 12

Simulation Scenario

  • Simulation Parameters

▫ The pilots are multiplexing in the symbol:

Nt= 1; 12 Nf= 32; 4

Frequency Time Data Pilot MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-13
SLIDE 13

Results

  • FD – LS Estimator

1 2 3 4 5 6 7 8 9

  • 12
  • 11
  • 10
  • 9
  • 8
  • 7
  • 6
  • 5
  • 4
  • 3
  • 2

Eb/N0 (dB) MSE (dB) LS Channel Estimation Nf=32, Nt=1,Relay on Nf=32, Nt=12,Relay on Nf=4, Nt=1,Relay on Nf=4, Nt=12,Relay on Nf=32, Nt=1,Conv. SISO Nf=32, Nt=12,Conv. SISO Nf=4, Nt=1,Conv. SISO Nf=4, Nt=12,Conv. SISO 1 2 3 4 5 6 7 8 9

  • 12
  • 11
  • 10
  • 9
  • 8
  • 7
  • 6
  • 5
  • 4
  • 3
  • 2

Eb/N0 (dB) MSE (dB) LS Channel Estimation

Nf=32, Nt=1,Relay on Nf=32, Nt=12,Relay on Nf=4, Nt=1,Relay on Nf=4, Nt=12,Relay on Nf=32, Nt=1,Conv. SISO Nf=32, Nt=12,Conv. SISO Nf=4, Nt=1,Conv. SISO Nf=4, Nt=12,Conv. SISO

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-14
SLIDE 14

Results

  • TD – MMSE Estimator

1 2 3 4 5 6 7 8 9

  • 28
  • 26
  • 24
  • 22
  • 20
  • 18
  • 16
  • 14
  • 12
  • 10
  • 8

Eb/N0 (dB) MSE (dB) MMSE Channel Estimation Nf=32, Nt=1,Relay on Nf=32, Nt=12,Relay on Nf=4, Nt=1,Relay on Nf=4, Nt=12,Relay on Nf=32, Nt=1,Conv. SISO Nf=32, Nt=12,Conv. SISO Nf=4, Nt=1,Conv. SISO Nf=4, Nt=12,Conv. SISO 1 2 3 4 5 6 7 8 9

  • 28
  • 26
  • 24
  • 22
  • 20
  • 18
  • 16
  • 14
  • 12
  • 10
  • 8

Eb/N0 (dB) MSE (dB) MMSE Channel Estimation

Nf=32, Nt=1,Relay on Nf=32, Nt=12,Relay on Nf=4, Nt=1,Relay on Nf=4, Nt=12,Relay on Nf=32, Nt=1,Conv. SISO Nf=32, Nt=12,Conv. SISO Nf=4, Nt=1,Conv. SISO Nf=4, Nt=12,Conv. SISO

≈ 5 dB

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-15
SLIDE 15

Example

10 20 30 40 50 0.2 0.4 Magnitude Point-to-point Channel PDP 10 20 30 40 50 0.1 0.2 Magnitude Compound Channel PDP

P2P Channel N1 = 7 Taps Compound Channel  conv (P2P Ch, P2P Ch) N2 = 27 Taps N2 can be quite larger than N1

 

1 1 1 2 2 N N N  

Taps SNR per Tap MSE

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-16
SLIDE 16

How much can be gained through the Knowledge oh h2?

5 10

  • 20
  • 18
  • 16
  • 14
  • 12

Channel Estimation MSE vs. Eb/N0 ChEst MSE (dB) Eb/N0 (dB)

n2mm n2

 

2 t

m

2 n

 

   

2 2 2 2 2 2 t n n

m m

A h     

No noticeable improvement by the knowledge of h2; Number of non-zero taps << Nc/Nf

Filter design is robust to errors in the estimate of the noise variance

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-17
SLIDE 17

Conclusion

  • In AF the equivalent channel S-RN-D has a larger delay

than point-to-point ▫

Increases the minimum pilot density that can be used;

▫

Degrades the performance of the MMSE;

  • The robustness of the TD-MMSE filter to errors in the

estimate of noise variance

  • The knowledge of individual P2P channels does not

bring any noticeable improvement;

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal

slide-18
SLIDE 18

Future Works

  • Consider a scenario which the channel statistics can

bring improvements to the channel estimate:

▫ Antenna array at the BS; ▫ Equalize-and-Forward Protocol; ▫ Power constraints at the RN; ▫ Channels with different statistics.

MAP-Tele Workshop 2009 2nd Dec, FEUP, Porto, Portugal