Integer frequency offset estimation in wireless systems
View Patent ↗Systems and techniques relating to wireless communications are described. A described technique includes receiving a plurality of symbols, observing a plurality of data samples in adjacent symbols, and calculating an estimate of an integer portion of a carrier frequency offset based on a cyclic shift and a phase shift of the data samples between symbols. Calculating the estimate can include calculating sum values corresponding to respective symbol indices. Each of the sum values can be based on a summation of max values that correspond to respective data subcarrier indices, the max values being based on a maximum of an absolute value of a real component of a base value and an absolute value of an imaginary component of the base value, where the base value is based on at least one of the data samples.
1. A method comprising: receiving a plurality of symbols; observing a plurality of data samples in adjacent symbols; and calculating, in a calculator, an estimate of an integer portion of a carrier frequency offset based on a cyclic shift and a phase shift of the data samples between symbols, wherein calculating the estimate comprises calculating sum values corresponding to respective symbol indices, wherein each of the sum values is based on a summation of max values that correspond to respective data subcarrier indices, the max values being based on a maximum of (i) an absolute value of a real component of a base value and (ii) an absolute value of an imaginary component of the base value, wherein the base value is based on a multiplication of e −j2πnα and at least one of the data samples, wherein n is a symbol index of the symbol indices, and wherein α is a cyclic prefix width ratio, wherein the symbols comprise Orthogonal Frequency Division Multiplexing (OFDM) symbols, and the plurality of data samples correspond to a plurality of data subcarriers in the OFDM symbols.
2. The method of claim 1 , wherein said calculating the estimate comprises solving the equation:
l
^
=
argmax
n
{
∑
k
∈
S
2
max
{
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
,
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
}
}
,
where k is a subcarrier index, S2 is a set of indices for data subcarriers, and V is an observation vector.
3. The method of claim 1 , wherein each of the OFDM symbols further comprise a plurality of pilot samples corresponding to a plurality of pilot subcarriers in the OFDM symbols, and
wherein said calculating comprises calculating the estimate of the integer portion of a carrier frequency offset based on a cyclic shift and a phase shift of the data subcarriers and the pilot subcarriers between OFDM symbols.
4. The method of claim 3 , wherein said calculating the estimate comprises solving the equation:
l
^
=
argmax
n
{
∑
k
∈
S
1
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
A
*
[
k
]
}
+
∑
k
∈
S
2
max
{
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
,
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
}
}
where k is a subcarrier index, S1 is a set of indices for pilot subcarriers, S2 is a set of indices for data subcarriers, V is an observation vector, and A is a known sequence.
5. The method of claim 1 , further comprising:
using the estimate of the integer portion of the carrier frequency offset to process a digital broadcast signal, wherein the digital broadcast signal comprises audio and/or video data.
6. An apparatus comprising: a receiver to receive a plurality of symbols; a framer to observe a plurality of data samples in adjacent symbols; and a calculator to calculate an estimate of an integer portion of a carrier frequency offset based on a cyclic shift and a phase shift of the data samples between symbols, wherein the calculator is operative to calculate the estimate by calculating sum values corresponding to respective symbol indices, wherein each of the sum values is based on a summation of max values that correspond to respective data subcarrier indices, the max values being based on a maximum of (i) an absolute value of a real component of a base value and (ii) an absolute value of an imaginary component of the base value, wherein the base value is based on a multiplication of e −j2πnα and at least one of the data samples, wherein n is a symbol index of the symbol indices, and wherein α is a cyclic prefix width ratio, wherein the symbols comprise Orthogonal Frequency Division Multiplexing (OFDM) symbols, and the plurality of data samples correspond to a plurality of data subcarriers in the OFDM symbols.
7. The apparatus of claim 6 , wherein the calculator is operative to calculate the estimate by solving the equation:
l
^
=
argmax
n
{
∑
k
∈
S
2
max
{
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
,
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
}
}
,
where k is a subcarrier index, S2 is a set of indices for data subcarriers, and V is an observation vector.
8. The apparatus of claim 6 , wherein each of the OFDM symbols further comprise a plurality of pilot samples corresponding to a plurality of pilot subcarriers in the OFDM symbols, and
wherein the calculator is operative to calculate the estimate of the integer portion of a carrier frequency offset based on a cyclic shift and a phase shift of the data subcarriers and the pilot subcarriers between OFDM symbols.
9. The apparatus of claim 8 , wherein the estimator is operative to calculate the estimate by solving the equation:
l
^
=
argmax
n
{
∑
k
∈
S
1
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
A
*
[
k
]
}
+
∑
k
∈
S
2
max
{
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
,
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
}
}
where k is a subcarrier index, S1 is a set of indices for pilot subcarriers, S2 is a set of indices for data subcarriers, V is an observation vector, and A is a known sequence.
10. The apparatus of claim 6 , wherein the symbols are included in a digital broadcast signal, wherein the digital broadcast signal comprises audio and/or video data.
11. The apparatus of claim 6 , further comprising:
a downconverter communicatively coupled with the calculator to compensate for a cyclic shift in a received signal by using the estimate of the integer portion of the carrier frequency offset.
12. A system comprising: an antenna to receive signals; and an estimator communicatively coupled with the antenna, the estimator including: a receiver to receive a plurality of symbols; a framer to observe a plurality of data samples in adjacent symbols; and a calculator to calculate an estimate of an integer portion of a carrier frequency offset based on a cyclic shift and a phase shift of the data samples between symbols, wherein the calculator is operative to calculate the estimate by calculating sum values corresponding to respective symbol indices, wherein each of the sum values is based on a summation of max values that correspond to respective data subcarrier indices, the max values being based on a maximum of (i) an absolute value of a real component of a base value and (ii) an absolute value of an imaginary component of the base value, wherein the base value is based on a multiplication of e −j2πnα and at least one of the data samples, wherein n is a symbol index of the symbol indices, and wherein α is a cyclic prefix width ratio, wherein the symbols comprise Orthogonal Frequency Division Multiplexing (OFDM) symbols, and the plurality of data samples correspond to a plurality of data subcarriers in the OFDM symbols.
13. The system of claim 12 , wherein the estimator is operative to calculate the estimate by solving the equation:
l
^
=
argmax
n
{
∑
k
∈
S
2
max
{
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
,
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
}
}
,
where k is a subcarrier index, S2 is a set of indices for data subcarriers, and V is an observation vector.
14. The system of claim 12 , wherein each of the OFDM symbols further comprise a plurality of pilot samples corresponding to a plurality of pilot subcarriers in the OFDM symbols, and
wherein the estimator is operative to calculate the estimate of the integer portion of a carrier frequency offset based on a cyclic shift and a phase shift of the data subcarriers and the pilot subcarriers between OFDM symbols.
15. The system of claim 14 , wherein the estimator is operative to calculate the estimate by solving the equation:
l
^
=
argmax
n
{
∑
k
∈
S
1
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
A
*
[
k
]
}
+
∑
k
∈
S
2
max
{
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
,
{
V
[
k
+
n
]
ⅇ
-
j2π
n
α
}
}
}
where k is a subcarrier index, S1 is a set of indices for pilot subcarriers, S2 is a set of indices for data subcarriers, V is an observation vector, and A is a known sequence.
16. The system of claim 12 , wherein the symbols are included in a digital broadcast signal, wherein the digital broadcast signal comprises audio and/or video data.
17. The system of claim 12 , further comprising:
a downconverter communicatively coupled with the estimator to compensate for a cyclic shift in a received signal by using the estimate of the integer portion of the carrier frequency offset.