Apparatus and method for estimating and compensating time offset and/or carrier frequency offset in MIMO system based OFDM/OFDMA
View Patent ↗The present invention relates to an apparatus and method for estimating and compensating for a time offset and a carrier frequency offset in a Multiple Input Multiple Output (MIMO) communication system that supports Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiplexing Access (OFDMA). According to the present invention, a phase difference of pilot signals of the same transmitting antenna, which are received through receiving antennas, is calculated. An arc tangent operation is then carried out on the phase difference of the pilot signals to calculate a time offset linear phase and/or a carrier frequency offset linear phase. Further, a time offset compensation value and/or a carrier frequency offset compensation value are found by employing the time offset linear phase and/or the carrier frequency offset linear phase. A time offset and/or a carrier frequency offset with respect to pilots and data are compensated for by employing the time offset compensation value and/or the carrier frequency offset compensation value.
1. An apparatus for estimating a time offset in a Multiple Input Multiple Output (MIMO) communication system that supports Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiplexing Access (OFDMA), the apparatus comprising:
a preamble linear phase calculator configured to calculate a preamble linear phase by employing a preamble included in a received signal frame of each of a plurality of receiving antennas;
a pilot linear phase calculator configured to receive signals transmitted from a plurality of transmitting antennas using different pilot patterns through the plurality of receiving antennas, and calculate a pilot linear phase by employing the pilot patterns of the plurality of transmitting antennas, which are received from the receiving antennas, respectively; and
a time offset operator configured to calculate a time offset by employing the calculated preamble linear phase and the calculated pilot linear phase,
wherein the preamble linear phase calculator is configured to calculate the preamble linear phase θ TO — pre according to the following equation:
θ
TO_pre
=
{
1
3
a
tan
-
1
(
Im
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
143
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
Re
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
143
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
)
for
Segment
0
1
3
a
tan
-
1
(
Im
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
142
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
Re
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
142
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
)
for
otherwise
,
wherein, in each segment, p k represents resents a preamble, k represents a sub-carrier index, m represents a receiving antenna index, W 0 represents a predetermined preamble weight, and 3a represents a sub-carrier distance between p k and p k+a .
2. The apparatus of claim 1 , wherein the preamble linear phase calculator comprises:
a preamble phase difference operator configured to calculate a phase difference with respect to the preamble included in each of the received signal frames;
a preamble phase difference accumulator configured to accumulate the phase difference to generate a phase difference accumulated value; and
a preamble linear phase operator configured to convert the phase difference accumulated value into a preamble linear phase.
3. The apparatus of claim 2 , wherein the preamble phase difference operator is configured to output a value in which the calculated phase difference is multiplied by a predetermined preamble weight.
4. The apparatus of claim 1 , wherein the preamble received by each of the receiving antennas is received from a predetermined one of the plurality of transmitting antennas.
5. The apparatus of claim 1 , wherein the pilot linear phase calculator comprises:
a pilot phase difference operator configured to calculate a phase difference per pilot basis, which is received from the same transmitting antenna, of pilots transmitted from the plurality of transmitting antennas;
a pilot phase difference accumulator configured to accumulate the phase difference to generate a phase difference accumulated value; and
a pilot linear phase operator configured to convert the phase difference accumulated value into a pilot linear phase.
6. The apparatus of claim 5 , wherein the pilot phase difference operator is configured to output a value in which the calculated phase difference is multiplied by a predetermined pilot weight.
7. The apparatus of claim 6 , wherein the pilot weight has a different value per receiving-antenna basis or per cluster basis.
8. The apparatus of claim 6 , wherein the pilot weight is set on the basis of a Carrier to Interference and Noise Ratio (CINR) value.
9. The apparatus of claim 1 , wherein the pilot linear phase calculator is configured to calculate the pilot linear phase θ TO — pil according to the following equation:
θ
TO_pil
=
1
b
tan
-
1
{
Im
{
∑
c
=
0
Num
-
1
∑
m
=
0
1
(
p
0
(
m
,
c
)
·
p
3
(
m
,
c
)
*
p
0
(
m
,
c
)
·
p
3
(
m
,
c
)
*
·
W
1
(
m
,
c
)
+
p
2
(
m
,
c
)
·
p
1
(
m
,
c
)
*
p
2
(
m
,
c
)
·
p
1
(
m
,
c
)
*
·
W
1
(
m
,
c
)
)
}
Re
{
∑
c
=
0
Num
-
1
∑
m
=
0
1
(
p
0
(
m
,
c
)
·
p
3
(
m
,
c
)
*
p
0
(
m
,
c
)
·
p
3
(
m
,
c
)
*
·
W
1
(
m
,
c
)
+
p
2
(
m
,
c
)
·
p
1
(
m
,
c
)
*
p
2
(
m
,
c
)
·
p
1
(
m
,
c
)
*
·
W
1
(
m
,
c
)
)
}
}
,
wherein p 0 and p 3 represent pilots transmitted from a second transmitting antenna p 1 and p 2 represent pilots transmitted from a first transmitting antenna m represents a receiving antenna index, c represents a cluster index, W 1 represents a predetermined pilot weight, b represents a sub-carrier distance between pilots transmitted from the same transmitting antenna according to c, and Num represents a value predetermined by a simulation.
10. The apparatus of claim 1 , wherein the pilot linear phase calculator is configured to calculate the pilot linear phase θ TO — pil according to the following equation:
θ
TO_pil
=
1
2
[
1
b
tan
-
1
(
Im
{
∑
c
=
0
Num
-
1
∑
m
=
0
1
p
0
(
m
,
c
)
·
p
3
(
m
,
c
)
*
·
W
1
(
m
,
c
)
}
Re
{
∑
c
=
0
Num
-
1
∑
m
=
0
1
p
0
(
m
,
c
)
·
p
3
(
m
,
c
)
*
·
W
1
(
m
,
c
)
}
)
+
1
b
tan
-
1
(
Im
{
∑
c
=
0
Num
-
1
∑
m
=
0
1
p
2
(
m
,
c
)
·
p
1
(
m
,
c
)
*
·
W
1
(
m
,
c
)
}
Re
{
∑
c
=
0
Num
-
1
∑
m
=
0
1
p
2
(
m
,
c
)
·
p
1
(
m
,
c
)
*
·
W
1
(
m
,
c
)
}
)
]
,
wherein p 0 and p 3 represent pilots transmitted from a second transmitting antenna p 1 and p 2 represent pilots transmitted from a first transmitting antenna, m represents a receiving antenna index, c represents a cluster index, W 1 represents a predetermined pilot weight, b represents a sub-carrier distance between pilots transmitted from the same transmitting antenna according to c, and Num represents a value predetermined by a simulation.
11. An apparatus for estimating a time offset in a MIMO communication system that supports OFDM or OFDMA, the apparatus comprising:
a preamble linear phase calculator configured to calculate a preamble linear phase by employing a preamble included in a received signal frame of each of a plurality of receiving antennas; and
a time offset operator configured to calculate a time offset by employing the calculated preamble linear phase,
wherein the preamble linear phase calculator is configured to calculate the preamble linear phase θ TO — pre according to the following equation:
θ
TO_pre
=
{
1
3
a
tan
-
1
(
Im
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
143
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
-
a
(
m
)
*
·
W
0
(
m
)
}
R
e
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
143
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
)
for
Segment
0
1
3
a
tan
-
1
(
Im
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
142
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
R
e
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
142
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
)
for
otherwise
,
wherein, in each segment, p k represents resents a preamble, k represents a sub-carrier index, m represents a receiving antenna index, W 0 represents a predetermined preamble weight, and 3a represents a sub-carrier distance between p k and p k+a .
12. The apparatus of claim 11 , wherein the preamble linear phase calculator comprises:
a preamble phase difference operator configured to calculate a phase difference with respect to the preamble included in each of the received signal frames;
a preamble phase difference accumulator configured to accumulate the phase difference to generate a phase difference accumulated value; and
a preamble linear phase operator configured to convert the phase difference accumulated value into a preamble linear phase.
13. The apparatus of claim 12 , wherein the preamble phase difference operator is configured to output a value in which the calculated phase difference is multiplied by a predetermined preamble weight.
14. A method of estimating a time offset in a MIMO communication system that supports OFDM or OFDMA, the method comprising:
calculating a preamble linear phase by employing a preamble included in a received signal frame of each of a plurality of receiving antennas;
receiving signals transmitted from a plurality of transmitting antennas using different pilot patterns through the plurality of receiving antennas, and calculating a pilot linear phase by employing the pilot patterns of the plurality of transmitting antennas, which are received from the receiving antennas, respectively; and
calculating a time offset by employing the calculated preamble linear phase and the calculated pilot linear phase,
wherein the calculating of the preamble linear phase comprises calculating the preamble linear phase θ TO — pre according to the following equation:
θ
TO_pre
=
{
1
3
a
tan
-
1
(
Im
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
143
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
R
e
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
143
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
)
for
Segment
0
1
3
a
tan
-
1
(
Im
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
142
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
R
e
{
∑
k
=
0
139
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
+
∑
k
=
142
281
∑
m
=
0
1
p
k
(
m
)
·
p
k
+
a
(
m
)
*
·
W
0
(
m
)
}
)
for
otherwise
,
wherein, in each segment, p k represents a preamble, k represents a sub-carrier index, m represents a receiving antenna index, W 0 represents a predetermined preamble weight, and 3a represents a sub-carrier distance between p k and p k+a .
15. The method of claim 14 , wherein the calculating of the preamble linear phase comprises:
calculating a phase difference with respect to the preamble included in each of the received signal frames;
accumulating the phase difference to generate a phase difference accumulated value; and
converting the phase difference accumulated value into a preamble linear phase.
16. The method of claim 15 , wherein the converting of the phase difference accumulated value comprises outputting a value in which the calculated phase difference is multiplied by a predetermined preamble weight.
17. The method of claim 16 , wherein the preamble weight is set on the basis of a CINR value.
18. The method of claim 14 , wherein the preamble received by each of the receiving antennas is received from a predetermined one of the plurality of transmitting antennas.
19. The method of claim 14 , wherein the receiving of the signals transmitted from the plurality of transmitting antennas comprises:
calculating a phase difference per pilot basis, which is received from the same transmitting antenna, of pilots transmitted from the plurality of transmitting antennas;
accumulating the phase difference to generate a phase difference accumulated value; and
converting the phase difference accumulated value into a pilot linear phase.
20. The method of claim 19 , wherein the converting of the phase difference accumulated value comprises outputting a value in which the calculated phase difference is multiplied by a predetermined pilot weight.