Method of initial synchronization of a communication signal
View Patent ↗The present method of initial synchronization of a communication signal includes the steps of symbol boundary search, fractional frequency offset estimation, fractional frequency offset compensation, frame boundary search, integer frequency offset estimation, integer frequency offset compensation, preamble segment ID search and preamble cell ID search. The symbol boundary search includes estimating the boundary of a present data symbol by a correlation index for the present data symbol and the correlation index for the next data symbol. The frame boundary search includes identifying the preamble symbol in the symbols found in the symbol boundary search to determine the frame boundary. The integer frequency offset estimation is derived from the pilot subcarriers of the frame control header of the frame after locating the preamble symbol.
1. A method of initial synchronization of a communication signal including the steps of symbol boundary search, fractional frequency offset estimation, fractional frequency offset compensation, frame boundary search, integer frequency offset estimation, integer frequency offset compensation, preamble segment ID search and preamble cell ID search, wherein the symbol boundary search comprises:
estimating the boundary of a present data symbol by a correlation index for the present data symbol and a correlation index for the next data symbol,
wherein the combined correlation index is
i
^
=
arg
max
i
∑
v
=
0
G
-
1
{
y
i
+
v
y
i
+
v
+
N
FFT
*
+
y
i
+
v
+
G
+
N
FFT
y
i
+
v
+
G
+
2
N
FFT
)
*
}
,
wherein the combined correlation index î is calculated iteratively as follows:
i
^
=
arg
max
i
C
(
i
)
,
where
C
(
0
)
=
∑
v
=
0
G
-
1
{
y
v
y
v
+
N
FFT
*
+
y
v
+
G
+
N
FFT
y
v
+
G
+
2
N
FFT
)
*
}
and
C
(
i
+
1
)
=
C
(
i
)
+
(
y
i
+
G
y
i
+
G
+
N
FFT
*
)
+
(
y
i
+
2
G
+
N
FFT
y
i
+
2
G
+
2
N
FFT
*
)
-
(
y
i
y
i
+
N
FFT
*
)
-
(
y
i
+
G
+
N
FFT
y
i
+
G
+
2
N
FFT
*
)
and
where î denotes the correlation index, G the cyclic prefix length, y the observed time domain samples, and N FFT the size of the symbol.
2. The method of claim 1 , wherein the frame boundary search includes identifying the preamble symbol in the symbols found in the symbol boundary search to determine the frame boundary.
3. The method of claim 2 , wherein identifying the preamble symbol includes grouping the subcarriers into K subgroups of N consecutive subcarriers, where K is the number of subcarriers that define a specific segment group of subcarriers; collecting the distributed energies on subcarriers; and making a decision if the current symbol is preamble based on a threshold that is estimated by stochastic approximation.
4. The method of claim 1 , wherein the integer frequency offset estimation is derived from the pilot subcarriers of the frame control header of the frame after locating the preamble symbol.
5. The method of claim 1 , wherein the integer frequency offset estimation is derived from the pilot subcarriers of the frame control header of the frame without decoding the down load MAP.
6. The method of claim 1 , wherein the preamble segment ID search and the preamble cell ID search are performed after the integer frequency offset compensation of the identified preamble.
7. The method of claim 6 , wherein the preamble segment ID search is performed before the preamble cell ID search.
8. The method of claim 1 , wherein the preamble segment ID search is based on:
n
^
=
arg
max
n
∈
{
0
,
1
,
2
}
{
∑
k
=
0
K
-
1
y
FFT
(
PreambleCarrierSet
n
k
)
}
where PremableCarrierSet n k =n+N·k, the group index of N groups n=0, 1, 2 . . . N−1, and the subcarrier index of a K length PN sequence k={0, 1, 2 . . . K−1}.
9. The method of claim 1 , wherein the preamble cell ID search includes estimating the symbol timing offset {circumflex over (ε)} |n r by:
ɛ
^
❘
n
r
=
arg
{
N
FFT
2
π
m
k
+
1
-
m
k
[
∑
m
k
,
m
k
=
1
∈
{
non
-
zero
subcarrier
}
(
y
FFT
(
m
k
+
1
)
×
sign
(
pilot
m
k
+
1
r
,
n
)
)
×
(
y
FFT
′
(
m
k
)
×
sign
(
pilot
m
k
1
r
,
n
)
)
*
]
}
where the group index of N groups n=0, 1, 2 . . . N−1, cell ID of R cell IDs in a segment group rε{0, 1, . . . , R−1}, m k and m k+1 are two neighboring subcarrier positions, the subcarrier index of a K length PN sequence k={0, 1, 2 . . . K−1} and pilot m r,n represents the modulated PN sample for the preamble.
10. The method of claim 9 , wherein the preamble cell ID is estimated by:
r
^
=
arg
max
r
{
∑
m
∈
{
non
-
zero
subcarriers
}
real
(
z
m
r
)
×
sign
(
pilot
m
n
^
,
r
)
2
}
where
z
m
r
=
y
FFT
′
(
m
)
×
exp
(
j
2
π
m
N
FFT
ɛ
^
❘
n
r
)
,
mε{non-zero subcarriers}, N FTT is the symbol size.
11. A method of initial synchronization of a communication signal including the steps of symbol boundary search, fractional frequency offset estimation, fractional frequency offset compensation, frame boundary search, integer frequency offset estimation, integer frequency offset compensation, preamble segment ID search and preamble cell ID search, wherein the integer frequency offset estimation is derived from the pilot subcarriers of the frame control header of the frame after locating the preamble symbol, wherein the integer frequency offset estimation is derived from the pilot subcarriers of the frame control header of the frame without decoding the down load MAP.
12. The method of claim 11 , wherein the frame boundary search includes identifying the preamble symbol in the symbols found in the symbol boundary search to determine the frame boundary, and identifying the preamble symbol comprises:
grouping the subcarriers into K subgroups of N consecutive subcarriers, where K is the number of subcarriers that define a specific segment group of subcarriers;
collecting the distributed energies on subcarriers; and
making a decision if the current symbol is preamble based on a threshold that is estimated by stochastic approximation.
13. The method of claim 12 , wherein the preamble segment ID search is based on:
n
^
=
arg
max
n
∈
{
0
,
1
,
2
}
{
∑
k
=
0
K
-
1
y
FFT
(
PreambleCarrierSet
n
k
)
}
where PremableCarrierSet n k =n+N·k, the group index of N groups n=0, 1, 2 . . . N−1, and the subcarrier index of a K length PN sequence k={0, 1, 2 . . . K−1}.
14. A method of initial synchronization of a communication signal including the steps of symbol boundary search, fractional frequency offset estimation, fractional frequency offset compensation, frame boundary search, integer frequency offset estimation, integer frequency offset compensation, preamble segment ID search and preamble cell ID search, wherein the preamble cell ID search includes estimating the symbol timing offset {circumflex over (ε)} |n r by:
ɛ
^
❘
n
r
=
arg
{
N
FFT
2
π
m
k
+
1
-
m
k
[
∑
m
k
,
m
k
=
1
∈
{
non
-
zero
subcarrier
}
(
y
FFT
(
m
k
+
1
)
×
sign
(
pilot
m
k
+
1
r
,
n
)
)
×
(
y
FFT
′
(
m
k
)
×
sign
(
pilot
m
k
1
r
,
n
)
)
*
]
}
where the group index of N groups n=0, 1, 2 . . . N−1, cell ID of R cell IDs in a segment group rε{0, 1, . . . , R−1}, m k and m k+1 are two neighboring subcarrier positions, the subcarrier index of a K length PN sequence k={0, 1, 2 . . . K−1} and pilot m r,n represents the modulated PN sample for the preamble,
wherein the preamble cell ID is estimated by:
r
^
=
arg
max
r
{
∑
m
∈
{
non
-
zero
subcarriers
}
real
(
z
m
r
)
×
sign
(
pilot
m
n
^
,
r
)
2
}
where
z
m
r
=
y
FFT
′
(
m
)
×
exp
(
j
2
π
m
N
FFT
ɛ
^
❘
n
r
)
,
mε{non-zero subcarriers}, N FTT is the symbol size.