The inner receiver structure applied to OFDM sys

tem

Advisor: Yung-an kao

Student: Chian Young

outline

OFDM system block OFDM baseband signal model Inner receiver structure Simulink Demo Future work

Serial to

Parallel

Parallelto

Serial IFFT

D/AConver

ter

CH

Parallelto

Serial

Serialto

ParallelFFT

A/DConver

ter

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TxData

Transmitter

Receiver

RxData yn,l

xn,l

Yk,l

Xk,l

OFDM system block diagram

EqEq...

Eq

SFO

Up convert

Down convert

CFO

n: n-th sample pointk: k-th subcarrierl: l-th subcarrier

CFO in OFDM system

CFO is due to the oscillator mismatch from up convert and down convert

SFO in OFDM system

time

Receiver sample

Transmitter sample

time

RX is faster than TX.

TX is faster than RX.

SFO is caused by the oscillator mismatch

between A/D & D/A converter

OFDM baseband signal model

OFDM baseband signal after IFFT at the transmitter side

The received OFDM baseband signal after FFT

12 /

, ,0

1 Nj kn N

n l k lk

x X eN

12 /

, ,0

1 Nj kn N

k l n lk

Y y eN

n: n-th sample pointk: k-th subcarrierl: l-th subcarrier

The received OFDM signal is influenced by channel effect, residual CFO, SFO, initial symbol timing offset

Td : initial symbol timing offset

Hk : frequency response of channel : residual CFO : initial phase offset

Ts : sampling clock period at the transmitter

Ts’: sampling clock period at the receiver

OFDM baseband signal model

f

k

''( )( )

{2 [ ( ) ] }

, ,

, ,

d s s ss s k

u u

kT k T T N l Gj f N l G T

T Tk l k l k

k l k l

Y X H e

N I

CFOSFO

OFDM baseband signal model

The ICI produced by residual CFO is much smaller compared to Gaussian noise.

combine Ik,l and Nk,l to

-------- (4)

''( )( )

{2 [ ( ) ] }

, ,

arg[ ],

d s s ss s k

u u

k

kT k T T N l Gj f N l G T

T Tk l k l k

j Hk l

Y X e H

e N

,k lN

Inner receiver structure

Frame Detection

Carrier FrequencyOffset Estimation

Symbol Timing

Buffer

Frequency OffsetCompensation

Remove Prefix

S/P

Input signal

FFT

Inner receiver structure

,k ld',k lY

FFTInitial coefficient

FrequencyDomain

Equalizer

Pilot-based phase estimator

Phase compensation

Outer receiver

Hard decision

Update coefficientof equalizer

Phase compensation

Training sequenceData

Pilot

,k lY

One-tap RLS equalizer• Recursive Least Square (RLS) algorithm:

Transversal filter( )nu

Adaptive Weight-Control Mechanism

+( )n

+( )d n

ˆ ( 1) ( )n nHw uˆ ( 1)n w

OutputInput vector

ˆ( ) ( ) ( 1) ( )Hn d n n n w u

( ) ( 1) ( ) ( )Hn n n n Φ Φ u u

1 *ˆ ˆ( ) ( 1) ( ) ( ) ( )n n n n n w w Φ u

, , , 1 ,ˆ Hk l k l k l k lX w Y

*, , 1 , ,k l k k l k l k lY Y

1 *, , 1 , , ,ˆ ˆk l k l k l k l k lw w Y

One tap

λ: forgetting factor 0<λ <1.ξ: estimation error

, ,k l k ld X

Pilot-based phase estimator

After giving the

appropriate weight

Re

Im

Re

Im

Received pilots

∠1 ∠2

Maximum ratio combination (MRC) pilot

O

A

B

A’

B’

O

C

C’

Pilot-based phase estimator

After giving the

appropriate weight

Re

Im

Received pilots

∠1

Maximum ratio combination (MRC) pilot

O

A

B

C

Re

Im

∠2

A’

B’

O

C’

Inner receiver structure

,k ld

,k lY

FFTInitial coefficient

FrequencyDomain

Equalizer

Pilot-based phase estimator

Phase compensation

Outer receiver

Hard decision

Update coefficientof equalizer

Phase compensation

Training sequenceData

Pilot

',k lY

, 1 ,ˆ Hk l k lw Y

, ,k l k ld X

, , , 1 ,ˆ Hk l k l k l k lX w Y

*, , 1 , ,k l k k l k l k lY Y

1 *, , 1 , , ,ˆ ˆk l k l k l k l k lw w Y

Re

Im

∠2

A’

B’

O

C’

Future work

New algorithm Combine CSI