The inner receiver structure applied to OFDM system Advisor: Yung-an kao Student: Chian Young.
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Transcript of The inner receiver structure applied to OFDM system Advisor: Yung-an kao Student: Chian Young.
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