Method, apparatus and system for detecting mode and guard interval
The present invention is directed to a method, apparatus and system for detecting the mode and the guard interval of a received orthogonal frequency division multiplexing (OFDM) symbol, which includes a guard interval with length N g , and a useful part with length N u . Mode is detected by searching for the maximum correlation or statistics value based on one (for example, the shortest one) guard interval length. Further, guard interval is detected by searching for the maximum correlation value based on all guard interval lengths.
1. A method for detecting mode and guard interval, comprising:
receiving at least an orthogonal frequency division multiplexing (OFDM) symbol, which includes a guard interval with length N g , and a useful part with length N u , wherein the received OFDM symbol is in one of a plurality of modes in accordance with the length N u of the useful part, and having one of a plurality of guard interval ratios N g /N u in accordance with the length of the guard interval;
performing a mode detection step for detecting the mode of the OFDM symbol, based on correlation of the OFDM symbol with respect to chosen one of the plurality of guard interval ratios;
performing a guard interval ratio detection step for detecting the guard interval ratio of the OFDM symbol, based on correlation of the OFDM symbol with respect to all of the guard interval ratios;
evaluating validity of the guard interval ratio detection step by comparing a timing deviation between two received OFDM symbols with a timing error tolerance constant; and
repeating the mode detection step until an absolute value of the timing deviation is less than the timing error tolerance constant.
2. The method according to claim 1 , wherein the correlation is statistics value.
3. The method according to claim 2 , after the mode detection step, further comprising:
evaluating validity of the mode detection by comparing the statistics value with a threshold value; and
repeating the mode detection step until the validity is confirmed, and followed by said performing the guard interval ratio detection step.
4. The method according to claim 1 , after the guard interval ratio detection step, further comprising:
evaluating validity of the guard interval ratio detection step by comparing a timing deviation between two received OFDM symbols with a timing error tolerance constant; and
repeating the guard interval ratio detection step until an absolute value of the timing deviation is less than the timing error tolerance constant.
5. The method according to claim 1 , wherein the mode detection step comprises:
performing correlation operation with respect to the OFDM symbol;
performing a plurality of sub-searches for each of the modes, within a moving range equal a maximum length of the useful part;
combining results of the sub-searches for each of the modes; and
determining a mode decision based on the combined results.
6. The method according to claim 5 , further comprising performing search within twice the moving range of the maximum length of the useful part.
7. The method according to claim 2 , wherein the mode detection step comprises:
performing correlation operation with respect to the OFDM symbol;
performing a plurality of sub-searches for each of the modes, within a moving range equal to a maximum length of the useful part;
combining results of the sub-searches for each of the modes;
correspondingly obtaining the statistics for each of the modes; and
determining a mode decision based on maximum of the statistics.
8. The method according to claim 1 , wherein the mode detection step comprises:
defining a mode detection variable m(i) as follows:
m
(
i
)
=
1
N
g
(
i
)
max
θ
∈
Ω
i
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where y is the received OFDM symbol; i=0, 1, 2 correspond to mode 2K, 4K, and 8K respectively; ratio of the guard interval and the useful part could be 1/4, 1/8, 1/16 or 1/32;
performing a plurality of sub-searches of the mode 2K or the mode 4K within a moving range of the mode 8K, thereby the mode detection variable being expressed as
m
(
i
,
l
)
=
max
θ
∈
Ω
i
(
l
)
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where l denotes sequence of the sub-searches; Ω i (l) denotes the l-th sub-search of the mode i;
combining results of the sub-searches as
M
(
i
)
=
C
l
=
0
L
(
i
)
(
m
(
i
,
l
)
)
where L(i)=3, 1, 0 for i=0, 1, 2 respectively; ( ) denotes a combination function; and
determining a mode decision based on maximum of the M(i), wherein the combination function has an expression of
C
0
(
m
(
i
,
l
)
)
=
∑
l
=
0
L
m
(
i
,
l
)
2
or
C
1
(
m
(
i
,
l
)
)
=
∑
l
=
0
L
m
(
i
,
l
)
2
.
9. The method according to claim 2 , wherein the mode detection step comprises:
obtaining the statistics value ρ by
θ
0
(
i
,
l
)
=
arg
θ
max
θ
∈
Ω
i
(
l
)
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
s
(
i
,
l
)
=
0.5
·
∑
n
=
θ
0
(
i
,
l
)
θ
0
(
i
,
l
)
+
N
g
(
i
)
-
1
(
y
(
n
)
2
+
y
(
n
+
N
u
(
i
)
)
2
)
S
(
i
)
=
∑
l
=
0
L
(
i
)
s
(
i
,
l
)
ρ
(
i
)
=
M
(
i
)
S
(
i
)
where y is the received OFDM symbol; i=0, 1, 2 correspond to mode 2K, 4K, and 8K respectively; ratio of the guard interval and the useful part could be 1/4, 1/8, 1/16 or 1/32; l denotes sequence of the sub-searches; Ω i (l) denotes the l-th sub-search of the mode i; and
determining a mode decision based on maximum of the statistics value ρ.
10. The method according to claim 1 , wherein the mode detection step comprises:
defining a mode detection variable m(i) as follows:
m
(
i
)
=
1
N
g
(
i
)
max
θ
∈
Ω
i
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where y is the received OFDM symbol; i=0, 1, 2 correspond to mode 2K, 4K, and 8K respectively; ratio of the guard interval and the useful part could be 1/4, 1/8, 1/16 or 1/32;
performing a plurality of sub-searches of the mode 2K or the mode 4K within a moving range of the mode 8K, thereby the mode detection variable being expressed as
m
(
i
,
l
)
=
max
θ
∈
Ω
i
(
l
)
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where l denotes sequence of the sub-searches; Ω i (l) denotes the l-th sub-search of the mode i;
repeating the previous step and combing results as
M
(
i
,
t
)
=
C
l
=
t
·
(
L
(
i
)
+
1
)
2
t
·
L
(
i
)
+
1
(
m
(
i
,
l
)
)
where t=0, 1 represent the two steps; L(i)=3, 1, 0 correspond to modes i=0, 1, 2 respectively; and
determining a mode decision based on maximum of the M(i,t).
11. The method according to claim 2 , wherein the guard interval ratio detection step comprises:
obtaining correlation with respect with the guard intervals by
g
(
j
,
l
)
=
max
θ
∈
Ω
m
0
(
l
)
∑
n
=
θ
θ
+
N
g
(
j
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
m
0
)
)
where j=0, 1, 2, 3 correspond to ratio of the guard interval and the useful part 1/4, 1/8, 1/16 and 1/32 respectively; the length of the guard interval N g (j)=N u (m 0 )/4, N u (m 0 )/8, N u (m 0 )/16, N u (m 0 )/32 for j=0, 1, 2, 3; l denotes sequence of sub-searches; Ω m0 (l) denotes the l-th sub-search of the mode i;
obtaining the statistics value ρ g (j) as follows:
θ
0
(
j
,
l
)
=
arg
θ
max
θ
∈
Ω
m
0
(
l
)
∑
n
=
θ
θ
+
N
g
(
j
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
m
0
)
)
s
(
j
,
l
)
=
0.5
·
∑
n
=
θ
g
(
j
,
l
)
θ
g
(
j
,
l
)
+
N
g
(
j
)
-
1
(
y
(
n
)
2
+
y
(
n
+
N
u
(
m
0
)
)
2
)
G
(
j
)
=
C
l
=
0
L
(
m
0
)
(
g
(
j
,
l
)
)
S
(
j
)
=
∑
l
=
0
L
(
m
0
)
s
(
j
,
l
)
ρ
g
(
j
)
=
G
(
j
)
S
(
j
)
defining a guard decision ratio constant R g to be 0.5<R g ≦1;
defining a reference value ρ r as ρ g (3) or maximum value of ρ g (j), where j=0, 1, 2, 3; and
determining a guard interval decision as follows:
g 0 =0;
for (j=0; j<3; j++)
{
if(ρ g (j)< R g . ρ r )
g 0 =j+1;
}.
12. The method according to claim 5 , further comprising:
allocating ranges of the sub-searches as follows:
for the mode 2K (i=0), the ranges of the sub-searches (l=0, 1, 2, 3) are
Ω i ( l =0)={0,1, . . . , N u ( i )·5/4−1}
Ω i ( l =1)={ N u ( i )·5/4, N u ( i )·5/4+1, . . . ,2· N u ( i )·5/4−1}
Ω i ( l =2)={2· N u ( i )·5/2,2· N u ( i )·5/4+1, . . . ,3· N u ( i )·5/4−1}
Ω i ( l =3)={3· N u ( i )·5/4,3· N u ( i )·5/4+1, . . . ,4· N u ( i )·5/4−1}
for the mode 4K (i=1), the ranges of the sub-searches (l=0, 1, 2, 3) are
Ω i ( l =0)={0,2, . . . , N u ( i )·5/4−2}
Ω i ( l =1)={1,3, . . . , N u ( i )·5/4−1}
Ω i ( l =2)={2· N u ( i )·5/4,2· N u ( i )·5/4+2, . . . ,2· N i ( i )·5/4−2}
Ω i ( l =3)={2· N u ( i )·5/4+1,2· N u ( i )·5/4+3, . . . ,2· N u ( i )·5/4−1}
for the mode 8K (i=2), the ranges of the sub-searches (l=0, 1, 2, 3) are
Ω i ( l =0)={0,4, . . . , N u ( i )·5/4−4}
Ω i ( l =1)={1,5, . . . , N u ( i )·5/4−3}
Ω i ( l =2)={2,6, . . . , N u ( i )·5/4−2}
Ω i ( l =3)={3,7, . . . , N u ( i )·5/4−1}.
13. A system for detecting mode and guard interval, comprising:
a receiver including:
symbol receiving apparatus, for receiving at least an orthogonal frequency division multiplexing (OFDM) symbol, which includes a guard interval with length N g , and a useful part with length N u , wherein the received OFDM symbol is in one of a plurality of modes in accordance with the length N u of the useful part, and having one of a plurality of guard interval ratios N g /N u in accordance with the length of the guard interval;
a detector, for detecting the mode and the guard interval, said detector performing the steps of:
performing a mode detection step for detecting the mode of the OFDM symbol, based on correlation of the OFDM symbol, with respect to chosen one of the plurality of guard interval ratios;
performing a guard interval ratio detection step for detecting the guard interval ratio of the OFDM symbol, based on correlation of the OFDM symbol with respect to all of the guard interval ratios;
evaluating validity of the guard interval ratio detection step by comparing a timing deviation between two of the OFDM symbols with a timing error tolerance constant; and
repeating the guard interval ratio detection step until an absolute value of the timing deviation is less than the timing error tolerance constant.
14. The system according to claim 13 , wherein the mode detection step comprises:
performing correlation operation with respect to the OFDM symbol;
performing a plurality of sub-searches for each of the modes, within a moving range equal a maximum length of the useful part;
combining results of the sub-searches for each of the modes; and
determining a mode decision based on the combined results.
15. The system according to claim 14 , further comprising performing search within twice the moving range of the maximum length of the useful part.
16. The system according to claim 13 , wherein the mode detection step comprises:
defining a mode detection variable m(i) as follows:
m
(
i
)
=
1
N
g
(
i
)
max
θ
∈
Ω
i
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where y is the received OFDM symbol; i=0, 1, 2 correspond to mode 2K, 4K, and 8K respectively; ratio of the guard interval and the useful part could be 1/4, 1/8, 1/16 or 1/32;
performing a plurality of sub-searches of the mode 2K or the mode 4K within a moving range of the mode 8K, thereby the mode detection variable being expressed as
m
(
i
,
l
)
=
max
θ
∈
Ω
i
(
l
)
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where l denotes sequence of the sub-searches; Ω i (l) denotes the l-th sub-search of the mode i;
combing results of the sub-searches as
M
(
i
)
=
C
l
=
0
L
(
i
)
(
m
(
i
,
l
)
)
where L(i)=3, 1, 0 for i=0, 1, 2 respectively; ( ) denotes a combination function; and
determining a mode decision based on maximum of the M(i), wherein the combination function has an expression of
C
0
(
m
(
i
,
l
)
)
=
∑
l
=
0
L
m
(
i
,
l
)
2
or
C
1
(
m
(
i
,
l
)
)
=
∑
l
=
0
L
m
(
i
,
l
)
2
.
17. The system according to claim 13 , wherein the mode detection step comprises:
defining a mode detection variable m(i) as follows:
m
(
i
)
=
1
N
g
(
i
)
max
θ
∈
Ω
i
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where y is the received OFDM symbol; i=0, 1, 2 correspond to mode 2K, 4K, and 8K respectively; ratio of the guard interval and the useful part could be 1/4, 1/8, 1/16 or 1/32;
performing a plurality of sub-searches of the mode 2K or the mode 4K within a moving range of the mode 8K, thereby the mode detection variable being expressed as
m
(
i
,
l
)
=
max
θ
∈
Ω
i
(
l
)
∑
n
=
θ
θ
+
N
g
(
i
)
-
1
y
*
(
n
)
y
(
n
+
N
u
(
i
)
)
where l denotes sequence of the sub-searches; Ω i (l) denotes the l-th sub-search of the mode i;
repeating the previous step and combing results as
M
(
i
,
t
)
=
C
l
=
t
·
(
L
(
i
)
+
1
)
2
t
·
L
(
i
)
+
1
(
m
(
i
,
l
)
)
where t=0, 1 represent the two steps; L(i)=3, 1, 0 correspond to modes i=0, 1, 2 respectively; and
determining a mode decision based on maximum of the M(i,t).
18. The system according to claim 14 , further comprising:
allocating ranges of the sub-searches as follows:
for the mode 2K (i=0), the ranges of the sub-searches (l=0, 1, 2, 3) are
Ω i ( l =0)={0,1, . . . , N u ( i )·5/4−1}
Ω i ( l =1)={ N u ( i )·5/4, N u ( i )·5/4+1, . . . ,2· N u ( i )·5/4−1}
Ω i ( l =2)={2· N u ( i )·5/2,2· N u ( i )·5/4+1, . . . ,3· N u ( i )·5/4−1}
Ω i ( l =3)={3· N u ( i )·5/4,3· N u ( i )·5/4+1, . . . ,4· N u ( i )·5/4−1}
for the mode 4K (i=1), the ranges of the sub-searches (l=0, 1, 2, 3) are
Ω i ( l =0)={0,2, . . . , N u ( i )·5/4−2}
Ω i ( l =1)={1,3, . . . , N u ( i )·5/4−1}
Ω i ( l =2)={2· N u ( i )·5/4,2· N u ( i )·5/4+2, . . . ,2· N i ( i )·5/4−2}
Ω i ( l =3)={2· N u ( i )·5/4+1,2· N u ( i )·5/4+3, . . . ,2· N u ( i )·5/4−1}
for the mode 8K (i=2), the ranges of the sub-searches (l=0, 1, 2, 3) are
Ω i ( l =0)={0,4, . . . , N u ( i )·5/4−4}
Ω i ( l =1)={1,5, . . . , N u ( i )·5/4−3}
Ω i ( l =2)={2,6, . . . , N u ( i )·5/4−2}
Ω i ( l =3)={3,7, . . . , N u ( i )·5/4−1}.
19. Apparatus for detecting mode and guard interval of an orthogonal frequency division multiplexing (OFDM) symbol, which includes a guard interval with length N g , and a useful part with length N u , the OFDM symbol is in one of a plurality of modes in accordance with the length N u of the useful part, and having one of a plurality of guard interval ratios N g /N u in accordance with the length of the guard interval, said apparatus comprising:
mode detection means for detecting the mode of the OFDM symbol, based on correlation of the OFDM symbol, with respect to chosen one of the guard intervals;
guard interval ratio detection means for detecting the guard interval of the OFDM symbol, based on correlation of the OFDM symbol with respect to all of the guard intervals;
evaluation means for evaluating validity of the guard interval ration detection step by comparing a timing deviation between two received OFDM symbols with a timing error tolerance constant; and
means for repeating the mode detection step until an absolute value of the timing deviation is less than the timing error tolerance constant.
20. A method for detecting mode and guard interval, comprising:
receiving at least an orthogonal frequency division multiplexing (OFDM) symbol, which includes a guard interval with length N g , and a useful part with length N u , wherein the received OFDM symbol is in one of a plurality of modes in accordance with the length N u of the useful part, and having one of a plurality of guard interval ratios N g /N u in accordance with the length of the guard interval;
performing a mode detection step for detecting the mode of the OFDM symbol, based on correlation of the OFDM symbol with respect to chosen one of the plurality of guard interval ratios;
performing a guard interval ratio detection step for detecting the guard interval ratio of the OFDM symbol, based on correlation of the OFDM symbol with respect to all of the guard interval ratios;
evaluating validity of the guard interval ratio detection step by comparing a timing deviation between two received OFDM symbols with a timing error tolerance constant; and
repeating the mode detection step until an absolute value of the timing deviation is less than the timing error tolerance constant.
21. A system for detecting mode and guard interval, comprising:
a receiver including:
a detector, for detecting the mode and the guard interval, said detector performing the steps of:
performing a mode detection step for detecting the mode of the OFDM symbol, based on correlation of the OFDM symbol, with respect to chosen one of the plurality of guard interval ratios;
performing a guard interval ratio detection step for detecting the guard interval ratio of the OFDM symbol, based on correlation of the OFDM symbol with respect to all of the guard interval ratios;
evaluating validity of the guard interval ratio detection step by comparing a timing deviation between two of the OFDM symbols with a timing error tolerance constant; and
repeating the mode detection step until an absolute value of the timing deviation is less than the timing error tolerance constant.