Frequency offset estimation method in OFDM system and OFDM receiver using the same
View Patent ↗A method of estimating a frequency offset based on a training symbol in a receiver of an orthogonal frequency division multiplexing (OFDM) system, includes receiving a first training symbol having a periodicity and a predetermined second training symbol, and calculating a correlation value for the first training symbol based on a coherence phase bandwidth (CPB). The method further includes determining a position of a peak value from the correlation value for an integer multiple frequency offset candidate based on a threshold value, and calculating a correlation value for the second training symbol based on the CPB. The method further includes estimating a position corresponding to a maximum value of the correlation value for the second training symbol as the frequency offset based on the position of the peak value.
1. A method of estimating a frequency offset based on a training symbol in a receiver of an orthogonal frequency division multiplexing (OFDM) system, the method comprising:
receiving a first training symbol having a periodicity and a predetermined second training symbol;
calculating a correlation value for the first training symbol based on a coherence phase bandwidth (CPB);
determining a position of a peak value from the correlation value for an integer multiple frequency offset candidate based on a threshold value;
calculating a correlation value for the second training symbol based on the CPB; and
estimating a position corresponding to a maximum value of the correlation value for the second training symbol as the frequency offset based on the position of the peak value.
2. The method of claim 1 , wherein the determining of the position of the peak value comprises:
calculating a correlation value for a received signal of the first training symbol; and
determining a position of a first peak value from the correlation value for the received signal based on the threshold value.
3. The method of claim 2 , wherein:
the correlation value C(d) for the received signal is calculated as
C
(
d
)
=
∑
m
=
0
K
-
1
∑
k
=
0
B
c
-
1
Z
1
,
k
+
mB
c
*
R
1
,
(
k
+
mB
c
+
d
)
N
;
and
the position of the first peak value represents a value of the integer multiple frequency offset candidate,
wherein R 1,k is a k th fourier transform output value of a received OFDM first training symbol, Z 1,k is a first training symbol in a k th carrier wave, * is a complex conjugate operation, N is a size of fourier transform, ( ) N is a N-modulo operation, B c is the CPB, K=N/B c ,
η
=
1
2
n
0
t
Z
1
,
k
2
1
-
j
cot
(
π
n
0
t
N
)
,
n 0 t is a normalized time offset, and j is an imaginary number.
4. The method of claim 2 , wherein the positions of remainder peak values are periodically arranged based on an interval value, starting from the position of the first peak value.
5. The method of claim 1 , wherein the frequency offset {circumflex over (ε)} is estimated based on an equation:
ε
^
=
argmax
f
∈
candidate
{
∑
m
=
0
K
-
1
∑
k
=
0
B
c
-
1
Z
2
,
k
+
mB
c
*
R
2
,
(
k
+
mB
c
+
f
)
N
}
,
where candidate is a set of frequency offset candidates existing in the position of the peak value, R 2,k is a k th fourier transform output value of a received OFDM second training symbol, Z 2,k is a second training symbol in a k th carrier wave, * is a complex conjugate operation, N is a size of fourier transform, ( ) N is a N-modulo operation, B c is the CPB, and K=N/B c .
6. The method of claim 1 , wherein the first training symbol and the second training symbol have a relation of
Z
1
,
k
=
Z
2
,
(
k
)
N
P
,
where Z 1,k is a first training symbol in a k th carrier wave, Z 2,k is a second training symbol in a k th carrier wave, ( ) N is a N-modulo operation, N is a size of a fourier transform, and P is a period of the first training symbol.
7. A non-transitory computer-readable storage medium storing a program comprising instructions to cause a computer to perform the method of claim 1 .
8. A method of estimating a frequency offset based on a training symbol in a receiver of an orthogonal frequency division multiplexing (OFDM) system, the method comprising:
receiving a first training symbol having a periodicity and a predetermined second training symbol;
calculating a first correlation value for the first training symbol and a second correlation value for the second training symbol based on a coherence phase bandwidth (CPB);
determining a position of a peak value from the first correlation value for an integer multiple frequency offset candidate based on a threshold value; and
estimating a position corresponding to a maximum value of the second correlation value as the frequency offset based on of the position of the peak value.
9. The method of claim 8 , wherein:
the first correlation value C(d) is calculated as
C
(
d
)
=
∑
m
=
0
K
-
1
∑
k
=
0
B
c
-
1
Z
1
,
k
+
mB
c
*
R
1
,
(
k
+
mB
c
+
d
)
N
;
and
the position of the peak value represents a value of the integer multiple frequency offset candidate,
wherein R 1,k is a k th fourier transform output value of a received OFDM first training symbol, Z 1,k is a first training symbol in a k th carrier wave, * is a complex conjugate operation, N is a size of fourier transform, ( ) N is a N-modulo operation, B c is the CPB, K=N/B c ,
η
=
1
2
n
0
t
Z
1
,
k
2
1
-
j
cot
(
π
n
0
t
N
)
,
n 0 t is a normalized time offset, and j is an imaginary number.
10. The method of claim 8 , wherein the determining of the position of the peak value comprises determining positions of remainder peak values based on a number of periods of the first training symbol.
11. The method of claim 8 , wherein the frequency offset {circumflex over (ε)} is estimated based on an equation:
ε
^
=
argmax
f
∈
candidate
{
∑
m
=
0
K
-
1
∑
k
=
0
B
c
-
1
Z
2
,
k
+
mB
c
*
R
2
,
(
k
+
mB
c
+
f
)
N
}
,
where candidate is a set of frequency offset candidates existing in the position of the peak value, R 2,k is a k th fourier transform output value of a received OFDM second training symbol, Z 2,k is a second training symbol in a k th carrier wave, * is a complex conjugate operation, N is a size of fourier transform, ( ) N is a N-modulo operation, B c is the CPB, and K=N/B c .
12. The method of claim 8 , wherein the first training symbol and the second training symbol have a relation of
Z
1
,
k
=
Z
2
,
(
k
)
N
P
,
where Z 1,k is a first training symbol in a k th carrier wave, Z 2,k is a second training symbol in a k th carrier wave, ( ) N is a N-modulo operation, N is a size of a fourier transform, and P is a period of the first training symbol.
13. A non-transitory computer-readable storage medium storing a program comprising instructions to cause a computer to perform the method of claim 8 .
14. An orthogonal frequency division multiplexing (OFDM) receiver configured to estimate a frequency offset based on a training symbol, the OFDM receiver comprising:
an RF unit configured to receive a first training symbol having a periodicity and a predetermined second training symbol; and
a frequency offset processor configured to
calculate a correlation value for the first training symbol based on a coherence phase bandwidth (CPB),
determine a position of a peak value from the correlation value of an integer multiple frequency offset candidate based on a threshold value,
calculate a correlation value for the second training symbol based on the CPB, and
estimate a position corresponding to a maximum value of the correlation value calculated for the second training symbol as the frequency offset based on the position of the peak value.
15. The OFDM receiver of claim 14 , wherein the frequency offset processor is configured to:
calculate a correlation value for a received signal of the first training symbol, and
determine a position of a first peak value from the correlation value for the received signal based on the threshold value.
16. The OFDM receiver of claim 15 , wherein:
the correlation value C(d) for the received signal is calculated as
C
(
d
)
=
∑
m
=
0
K
-
1
∑
k
=
0
B
c
-
1
Z
1
,
k
+
mB
c
*
R
1
,
(
k
+
mB
c
+
d
)
N
;
and
the position of the first peak value represents a value of the integer multiple frequency offset candidate,
wherein R 1,k is a k th fourier transform output value of a received OFDM first training symbol, Z 1,k is a first training symbol in a k th carrier wave, * is a complex conjugate operation, N is a size of fourier transform, ( ) N is a N-modulo operation, B c is the CPB, K=N/B c ,
η
=
1
2
n
0
t
Z
1
,
k
2
1
-
j
cot
(
π
n
0
t
N
)
,
n 0 t is a normalized time offset, and j is an imaginary number.
17. The OFDM receiver of claim 14 , wherein the frequency offset {circumflex over (ε)} is estimated based on an equation:
ε
^
=
argmax
f
∈
candidate
{
∑
m
=
0
K
-
1
∑
k
=
0
B
c
-
1
Z
2
,
k
+
mB
c
*
R
2
,
(
k
+
mB
c
+
f
)
N
}
,
where candidate is a set of frequency offset candidates existing in the position of the peak value, R 2,k is a k th fourier transform output value of a received OFDM second training symbol, Z 2,k is a second training symbol in a k th carrier wave, * is a complex conjugate operation, N is a size of fourier transform, ( ) N is a N-modulo operation, B c is the CPB, and K=N/B c .
18. The OFDM receiver of claim 14 , wherein the first training symbol and the second training symbol have a relation of
Z
1
,
k
=
Z
2
,
(
k
)
N
P
,
where Z 1,k is a first training symbol in a k th carrier wave, Z 2,k is a second training symbol in a k th carrier wave, ( ) N is a N-modulo operation, N is a size of a fourier transform, and P is a period of the first training symbol.