the inner receiver structure applied to ofdm system advisor: yung-an kao student: chian young
TRANSCRIPT
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The inner receiver structure applied to OFDM sys
tem
Advisor: Yung-an kao
Student: Chian Young
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outline
OFDM system block OFDM baseband signal model Inner receiver structure Simulink Demo Future work
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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
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CFO in OFDM system
CFO is due to the oscillator mismatch from up convert and down convert
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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
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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
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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
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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
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Inner receiver structure
Frame Detection
Carrier FrequencyOffset Estimation
Symbol Timing
Buffer
Frequency OffsetCompensation
Remove Prefix
S/P
Input signal
FFT
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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
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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
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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’
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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’
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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’
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Future work
New algorithm Combine CSI