Timing synchronization in an orthogonal frequency-division multiplexing (OFDM) system
A transmitting end of an Orthogonal Frequency-Division Multiplexing (OFDM) wireless communication system may generate a training sequence and attach the training sequence to a data sequence that contains information data. A receiving end of the OFDM wireless communication system may identify a starting position of the data sequence and further extract the data sequence.
1. A system to produce a training sequence for synchronizing timing in a wireless communication, comprising:
a transmitter configured to:
generate a first sequence,
generate a second sequence by inverting the first sequence,
generate a third sequence by complementing the first sequence,
generate a fourth sequence by complementing the second sequence,
compose the training sequence to indicate a starting position of a data sequence for synchronizing timing in wireless communication of the data sequence by combining the first sequence, the second sequence, the third sequence, and the fourth sequence successively, and
attach the training sequence to the data sequence that includes information data; and
an antenna configured to:
wirelessly transmit an output sequence that includes the training sequence and the data sequence.
2. The system of claim 1 , further comprising:
a receiver configured to:
receive one or more wireless signals that include the training sequence and the data sequence;
identify a starting position of the data sequence in the one or more wireless signals;
extract the data sequence from the one or more wireless signals;
further transmit the extracted data sequence to one or more computing devices.
3. The system of claim 1 , wherein the length of the first sequence is less than the length of the data sequence.
4. The system of claim 1 , wherein the transmitter is further configured to attach the training sequence to the beginning of the data sequence.
5. The system of claim 1 , wherein the transmitter is further configured to:
attach a cyclic prefix to the training sequence and to the data sequence before transmitting the training sequence and the data sequence.
6. The system of claim 2 , wherein the receiver is further configured to:
determine multiple sampling positions and a respectively corresponding one of multiple values of a timing function; and
offset, by a predetermined length, one of the multiple sampling positions that corresponds to the maximum of the multiple values.
7. The system of claim 6 , wherein the timing function is
M
(
d
)
=
P
(
d
)
2
(
R
(
d
)
)
2
,
wherein
P
(
d
)
=
∑
k
=
0
N
/
2
-
1
r
(
d
+
k
)
r
*
(
d
-
1
-
k
)
+
∑
k
=
0
N
/
4
-
1
r
(
d
+
k
)
r
*
(
d
-
N
2
+
k
)
+
∑
k
=
0
N
/
4
-
1
r
(
d
-
N
4
+
k
)
r
*
(
d
+
N
4
+
k
)
and
R
(
d
)
=
2
∑
k
=
0
N
/
2
-
1
r
(
d
+
k
)
2
,
and wherein
d represents one of the multiple sampling positions,
r( ) represents the one of multiple values of the timing function, and
r*( ) represents the conjugate value of the one of multiple values of the timing function.
8. A device, comprising:
a sequence generator configured to generate a first sequence;
an inverter configured to generate a second sequence by inverting the first sequence;
a first sequence convertor configured to input the first sequence, complement the first sequence, and output the complemented first sequence as a third sequence;
a second sequence convertor configured to input the second sequence, complement the second sequence, and output the complemented second sequence as a fourth sequence;
a register configured to:
generate a training sequence for synchronizing timing in wireless communication of data by combining the first sequence, the second sequence, the third sequence, and the fourth sequence successively; and
output an output sequence that includes the training sequence and the data sequence; and
an antenna configured to wirelessly transmit the output sequence that includes the training sequence and the data sequence.
9. The device of claim 8 , further comprising:
a data generator configured to generate a data sequence;
a framer configured to combine the training sequence and the data sequence; and
a coupler module configured to attach a cyclic prefix to the training sequence and to the data sequence.
10. The device of claim 8 , wherein the first sequence is a pseudo noise sequence.
11. The device of claim 9 , wherein the length of the first sequence is less than the length of the data sequence.
12. The device of claim 9 , wherein the data generator is configured to generate the data sequence in accordance with orthogonal frequency-division multiplexing (OFDM).
13. A non-transitory computer-readable medium storing instructions that, when executed, cause one or more processors to perform operations comprising:
composing a training sequence by:
generating a first sequence,
generating a second sequence by inverting the first sequence,
generating a third sequence by complementing the first sequence,
generating a fourth sequence by complementing the second sequence, and
combining the first sequence, the second sequence, the third sequence, and the fourth sequence successively;
attaching the training sequence to a data sequence;
attaching a cyclic prefix to the training sequence and to the data sequence; and
wirelessly transmitting an output sequence that includes the training sequence and the data sequence.
14. The non-transitory computer-readable medium of claim 13 , wherein the length of the first sequence is less than the length of the data sequence.
15. The non-transitory computer-readable medium of claim 13 , wherein the attaching comprises attaching the training sequence to the beginning of the data sequence.
16. The non-transitory computer-readable medium of claim 13 , wherein the first sequence is a pseudo noise sequence.
17. A non-transitory computer-readable medium storing instructions that, when executed, cause one or more processors to perform operations comprising:
receiving a wireless signal including a data sequence and a training sequence for synchronizing timing in wireless communication of the data sequence;
determining multiple sampling positions of the wireless signal and a respectively corresponding one of multiple values of a timing function;
offsetting, by a predetermined length, one of the multiple sampling positions that corresponds to the maximum of the multiple values; and
identifying the offset one of the multiple sampling positions as a synchronized starting position of the data sequence.
18. The non-transitory computer-readable medium of claim 17 , wherein the timing function is
M
(
d
)
=
P
(
d
)
2
(
R
(
d
)
)
2
,
wherein
P
(
d
)
=
∑
k
=
0
N
/
2
-
1
r
(
d
+
k
)
r
*
(
d
-
1
-
k
)
+
∑
k
=
0
N
/
4
-
1
r
(
d
+
k
)
r
*
(
d
-
N
2
+
k
)
+
∑
k
=
0
N
/
4
-
1
r
(
d
-
N
4
+
k
)
r
*
(
d
+
N
4
+
k
)
and
R
(
d
)
=
2
∑
k
=
0
N
/
2
-
1
r
(
d
+
k
)
2
,
and wherein
d represents one of the multiple sampling positions,
r( ) represents the one of multiple values of the timing function, and
r*( ) represents the conjugate value of the one of multiple values of the timing function.
19. The non-transitory computer-readable medium of claim 17 , wherein the training sequence includes:
a first sequence;
a second sequence generated by inverting the first sequence;
a third sequence generated by complementing the first sequence; and
a fourth sequence generated by complementing the second sequence.
20. The non-transitory computer-readable medium of claim 17 , further comprising detaching a cyclic prefix from the training sequence and the data sequence.