System and method for detecting known sequence in transmitted sequence
View Patent ↗A known sequence of symbols is located within a transmitted sequence of symbols by estimating the phase differences between offset symbols within a portion or more of the transmitted sequence, estimating the phase differences between offset symbols in the known sequence, and determining that the symbols within the portion or more of the transmitted sequence are the known sequence if the phase difference estimates determined from the symbols within the portion or more of the transmitted sequence are substantially equal to the phase difference estimates determined from the known sequence.
1. In a receiver, a method of locating a known sequence of symbols within a transmitted sequence of symbols comprising:
forming one or more first values from one or more symbols within a portion or more of the transmitted sequence, each of the one or more first values representing an estimated difference in phase between first and second symbols within the transmitted sequence that are offset from one another;
providing one or more second values formed from one or more symbols within the known sequence, each of the one or more second values representing an estimated difference in phase between first and second symbols within the known sequence that are offset from one another;
forming a statistic from the one or more first values and the one or more second values, wherein the statistic is computed as one of A n 2 +B n 2 , |A n |+|B n |, and max(|A n |, |B n |), where
A
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Re
(
Y
n
)
±
Im
(
X
n
)
×
Im
(
Y
n
)
,
B
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Im
(
Y
n
)
±
Im
(
X
n
)
×
Re
(
Y
n
)
,
where X n is one of the one or more first values, Yn is one of the one or more second values, N is an integer of two or more, k is an integer of one or more that is less than N, Re is an operator that returns the real part of a complex symbol, and Im is an operator that returns the imaginary part of a complex symbol; and
determining that the portion or more of the transmitted sequence is the known sequence if the one or more estimated differences in phase represented by the one or more first values are substantially equal to corresponding ones of the one or more estimated differences in phase represented by the one or more second values and identifying a frame end using the known sequence.
2. The method of claim 1 further comprising:
relatively positioning a sliding window of N or more symbols within the transmitted sequence, N comprising the number of symbols in the known sequence, the sliding window encompassing a portion or more of the transmitted sequence; and
determining that the portion or more of the transmitted sequence within the sliding window is the known sequence if the one or more estimated differences in phase represented by the one or more first values are substantially equal to corresponding ones of the one or more estimated differences in phase represented by the one or more second values.
3. The method of claim 2 further comprising:
associating the statistic with the relative position of the sliding window within the transmitted sequence;
repeating the positioning and forming steps until the sliding window has substantially covered the portion or more of the transmitted sequence, resulting in a plurality of statistics, each associated with a distinct position within the portion or more of the transmitted sequence; and
locating the known sequence within the portion or more of the transmitted sequence responsive to the plurality of statistics.
4. The method of claim 3 , wherein each of the first values represents a difference in phase between first and second symbols within the sliding window that are offset from one another by k symbols.
5. The method of claim 4 wherein each of the second values represents a difference in phase between first and second symbols within the known sequence that are offset from one another by k symbols.
6. The method of claim 5 wherein a first value X n , for each value of n in the set 0≦n≦N−k−1, is computed as x n ·x n+k *, where x n is the nth symbol within the sliding window, and x n+k * is the complex conjugate of the (n+k)th symbol within the sliding window.
7. The method of claim 6 wherein a second value Y n , for each value of n in the set 0≦n≦N−k−1, is computed as s n ·s n+k *, where s n is the nth symbol within the known sequence, and s n+k * is the complex conjugate of the (n+k)th symbol within the known sequence.
8. The method of claim 3 wherein the known sequence is determined to be located at the position in the portion or more of the transmitted sequence where the statistic achieves a resonance condition.
9. The method of claim 3 wherein the known sequence is determined to be located at the position in the transmitted sequence where the statistic achieves a local maxima or minima.
10. In a receiver, a method of synchronizing frames comprising:
receiving a portion or more of a transmitted sequence comprising a sequence of N known symbols interleaved within a sequence of unknown symbols, where N is an integer of two or more;
relatively positioning a sliding window of size N or more symbols within the portion or more of the transmitted sequence, where the sliding window encompasses a portion or more of the transmitted sequence;
forming one or more first values from symbols within the sliding window, each of the one or more first values representing an estimated difference in phase between first and second symbols within the sliding window that are offset from one another;
providing one or more second values formed from symbols within the known sequence, each of the one or more second symbols representing an estimated difference in phase between first and second symbols within the known sequence that are offset from one another, the one or more estimated differences in phase represented by the one or more second values having a correspondence with the one or more estimated differences in phase represented by the one or more first values;
forming a statistic from the one or more first values and the one or more second values, wherein the statistic is computed as one of A n 2 B n 2 , |A n |+|B n |, and max(|A n |, |B n |), where
A
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Re
(
Y
n
)
±
Im
(
X
n
)
×
Im
(
Y
n
)
,
B
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Im
(
Y
n
)
±
Im
(
X
n
)
×
Re
(
Y
n
)
,
where X n is one of the one or more first values, Yn is one of the one or more second values, N is an integer of two or more, k is an integer of one or more that is less than N, Re is an operator that returns the real part of a complex symbol, and Im is an operator that returns the imaginary part of a complex symbol;
locating the known sequence within the portion or more of the transmitted sequence at the position of the sliding window if the one or more estimated differences in phase represented by the one or more first values are substantially equal to corresponding ones of the one or more estimated differences in phase represented by the one or more second values; and
locating a frame end responsive to locating the known sequence in the portion or more of the transmitted sequence.
11. The method of claim 10 further comprising:
associating the statistic with the relative position of the sliding window within the portion or more of the transmitted sequence;
repeating the foregoing steps until the sliding window has substantially covered the portion or more of the transmitted sequence, resulting in a plurality of statistics, each associated with a distinct position within the transmitted sequence; and
locating the known sequence within the portion or more of the transmitted sequence responsive to the plurality of statistics.
12. The method of claim 10 wherein the known sequence is offset from the frame end by a offset, and the method further comprises locating the end of the frame responsive to the location of the known sequence and the offset.
13. In a receiver, a system for locating a known sequence of symbols within a transmitted sequence of symbols using logics, wherein the logics are implemented as hardware, the system comprising:
first logic for forming one or more first values from symbols within a portion or more of the transmitted sequence, each of the one or more first values representing an estimated difference in phase between first and second symbols within the transmitted sequence that are offset from one another;
second logic for providing one or more second values formed from symbols within the known sequence of N symbols, each of the one or more second values representing an estimated difference in phase between first and second symbols within the known sequence that are offset from one another;
third logic for determining that the portion or more of the transmitted sequence is the known sequence if the one or more estimated differences in phase represented by the one or more first values are substantially equal to corresponding ones of the one or more estimated differences in phase represented by the one or more second values and identifying a frame end using the known sequence; and
another logic for forming a statistic from the one or more first values and the one or more second values, wherein the statistic is computed as one of A n 2 +B n 2 , |A n |+|B n |, and max(|A n |, |B n |), where
A
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Re
(
Y
n
)
±
Im
(
X
n
)
×
Im
(
Y
n
)
,
B
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Im
(
Y
n
)
±
Im
(
X
n
)
×
Re
(
Y
n
)
,
where X n is one of the one or more first values, Yn is one of the one or more second values, N is an integer of two or more, k is an integer of one or more that is less than N, Re is an operator that returns the real part of a complex symbol, and Im is an operator that returns the imaginary part of a complex symbol.
14. The system of claim 13 further comprising:
fourth logic for relatively positioning a sliding window of size N or more symbols within the transmitted sequence, N comprising the number of symbols in the known sequence, wherein the sliding window encompasses a portion or more of the transmitted sequence;
wherein the third logic is configured to determine that the portion or more of the transmitted sequence within the sliding window is the known sequence if the one or more estimated differences in phase represented by the one or more first values are substantially equal to corresponding ones of the one or more estimated differences in phase represented by the one or more second values.
15. The system of claim 14 further comprising fifth logic for (a) associating the statistic with the relative position of the sliding window within the portion or more of the transmitted sequence; (b) relatively repositioning the sliding window and reforming the one or more first values and the statistic until the sliding window has substantially covered the portion or more of the transmitted sequence, resulting in a plurality of statistics, each associated with a distinct position within the transmitted sequence; and (c) locating the known sequence within the portion or more of the transmitted sequence responsive to the plurality of statistics.
16. The system of claim 15 wherein each of the symbols in the transmitted sequence are complex, each of the first values represents a difference in phase between first and second symbols within the sliding window that are offset from one another by k symbols, and the first logic is configured to compute a first value X n , for each value of n in the set 0≦n≦N−k−1, as x n ·x n+k *, where x n is the nth symbol within the sliding window, and x n+k * is the complex conjugate of the (n+k)th symbol within the sliding window.
17. The system of claim 16 wherein each of the symbols in the known sequence are complex, each of the second values represents a difference in phase between first and second symbols within the known sequence that are offset from one another by k symbols, and the second logic is configured to provide a second value Y n , for each value of n in the set 0≦n≦N−k−1, computed as s n+k *, where s n is the nth symbol within the known sequence, and s n+k * is the complex conjugate of the (n+k)th symbol within the known sequence.
18. The system of claim 15 wherein the fifth logic is configured to determine that the known sequence is located at the position within the transmitted sequence where the statistic achieves a local maxima or minima.
19. In a receiver, a system for locating a known sequence of symbols within a transmitted sequence of symbols comprising:
first means for forming one or more first values from symbols within a sliding window, each of the one or more first values representing an estimated difference in phase between first and second symbols within the sliding window that are offset from one another;
second means for providing one or more second values formed from symbols within the known sequence of N symbols, N being an integer of two or more, each of the one or more second values representing an estimated difference in phase between first and second symbols within the known sequence that are offset from one another;
third means for determining that the portion or more of the transmitted sequence is the known sequence if the one or more estimated differences in phase represented by the one or more first values are substantially equal to corresponding ones of the one or more estimated differences in phase represented by the one or more second values and identifying a flame end using the known sequence; and
fourth means for forming a statistic from the one or more first values and the one or more second values, wherein the statistic is computed as one of A n 2 +B n 2 , |A n |+|B n |, and max(|A n |, |B n |), where
A
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Re
(
Y
n
)
+
_
Im
(
X
n
)
×
Im
(
Y
n
)
,
B
n
=
∑
n
=
0
N
-
k
-
1
Re
(
X
n
)
×
Im
(
Y
n
)
+
_
Im
(
X
n
)
×
Re
(
Y
n
)
,
where X n is one of the one or more first values, Yn is one of the one or more second values, N is an integer of two or more, k is an integer of one or more that is less than N, Re is an operator that returns the real part of a complex symbol, and Im is an operator that returns the imaginary part of a complex symbol.