Apparatus and method for producing a signal to reduce the PAR in a multicarrier system
An apparatus produces a reduction signal for a signal having a plurality of subcarriers. The apparatus has a limiter which is designed to produce a limited signal from the signal having a plurality of subcarriers;—a coefficient ascertainment unit which is designed to determine coefficients for unused subcarriers of the signal having a plurality of subcarriers from the limited signal; and—a signal generator which is designed to generate the reduction signal from the coefficients. The reduction signal is able to be combined with the signal in order to form a reduced signal. The coefficient ascertainment unit is designed to project the limited signals onto a K-th base formula.
1. An apparatus for producing a reduction signal for an input signal having a plurality of subcarriers, comprising:
a limiter to produce a limited signal from the input signal having the plurality of subcarriers;
a coefficient determiner to determine coefficients for unused subcarriers of the input signal having the plurality of subcarriers, from the limited signal; and
a signal generator to generate the reduction signal from the coefficients, which reduction signal can be combined with the input signal to form a reduced signal, wherein
the coefficient determiner determines the coefficients from the limited signal and the input signal, and
the coefficient determiner determines the coefficients using a matrix operation on the input signal and the limited signal.
2. The apparatus as claimed in claim 1 , wherein
the apparatus further comprises an adder to combine the input signal with the reduction signal in order to form the reduced signal.
3. The apparatus as claimed in claim 2 , wherein
the coefficient determiner uses weighting factors to determine the coefficients.
4. The apparatus as claimed in claim 3 , wherein
the input signal is a modulated signal having more than two possible information states per symbol,
the limited signal comprises N sample values per symbol s n ; n=1 . . . N, and
the coefficient determiner determines the coefficients using symbol-by-symbol projection of the limited signal onto a k-th base function
e
_
+
2
πj
·
(
k
-
1
)
-
(
n
-
1
)
N
,
which is associated with a k-th unused subcarrier.
5. The apparatus as claimed in claim 4 , wherein
the coefficient determiner calculates a coefficient for the k-th unused subcarrier using the following formula:
C
k
=
1
N
·
∑
n
=
1
N
s
n
·
ⅇ
-
2
πj
·
(
k
-
1
)
-
(
n
-
1
)
N
,
1
≤
k
≤
N
.
6. The apparatus as claimed in claim 5 , wherein
the signal generator calculates the reduction signal using the formula
X
n
=
∑
k
=
unused
C
k
·
ⅇ
+
2
πj
·
(
k
-
1
)
-
(
n
-
1
)
N
,
n
=
1
,
…
N
.
7. The apparatus as claimed in claim 6 , wherein
the limiter has an adjustable limiting threshold value which defines how strongly the input signal can be limited.
8. The apparatus as claimed in claim 1 , wherein
the coefficient determiner uses weighting factors to determine the coefficients.
9. The apparatus as claimed in claim 1 , wherein
the input signal is a modulated signal having more than two possible information states per symbol,
the limited signal comprises N sample values per symbol s n ; n=1 . . . N, and
the coefficient determiner determines the coefficients using symbol-by-symbol projection of the limited signal onto a k-th base function
e
_
+
2
πj
·
(
k
-
1
)
-
(
n
-
1
)
N
,
which is associated with a k-th unused subcarrier.
10. The apparatus as claimed in claim 9 , wherein
the coefficient determiner calculates a coefficient for the k-th unused subcarrier using the following formula:
C
k
=
1
N
·
∑
n
=
1
N
s
n
·
ⅇ
-
2
πj
·
(
k
-
1
)
-
(
n
-
1
)
N
,
1
≤
k
≤
N
.
11. The apparatus as claimed in claim 10 , wherein
the signal generator calculates the reduction signal using the formula
X
n
=
∑
k
=
unused
C
k
·
ⅇ
+
2
πj
·
(
k
-
1
)
-
(
n
-
1
)
N
,
n
=
1
,
…
N
.
12. The apparatus as claimed in claim 1 , wherein
the limiter has an adjustable limiting threshold value which defines how strongly the input signal can be limited.
13. A system for producing a time-domain signal from complex input symbols, comprising:
a converter to transform the complex input symbols into an input signal with a plurality of subcarriers in accordance with a predetermined transformation; and
an apparatus for producing a reduction signal for the input signal having the plurality of subcarriers, comprising:
a limiter to produce a limited signal from the input signal having the plurality of subcarriers;
a coefficient determiner to determine coefficients for unused subcarriers of the input signal having the plurality of subcarriers, from the limited signal; and
a signal generator to generate the reduction signal from the coefficients; and
an adder to add the reduction signal to the input signal having the plurality of subcarriers to form a reduced signal, with the reduced signal corresponding to the time-domain signal, wherein
the coefficient determiner determines the coefficients from the limited signal and the input signal, and
the coefficient determiner determines the coefficients using a matrix operation on the input signal and the limited signal.
14. The system as claimed in claim 13 , wherein
the system has first and second apparatuses for producing the reduction signal, and
the first and second apparatuses are connected in series.
15. The system as claimed in claim 13 , wherein
the predetermined transformation is an inverse Fourier transformation.
16. The system as claimed in claim 13 , wherein
the system is an Orthogonal Frequency Division Multiplexing (OFDM)-based or an Orthogonal Frequency Division Multiple Access (OFDMA)-based transmission system.
17. A method for producing a reduction signal for an input signal having a plurality of subcarriers, comprising:
producing a limited signal from the input signal having the plurality of subcarriers;
determining coefficients for unused subcarriers of the input signal having the plurality of subcarriers, from the limited signal; and
generating the reduction signal from the coefficients, which reduction signal can be combined with the input signal having the plurality of subcarriers to obtain a reduced signal, wherein
the coefficients are determined from the limited signal and the input signal, and
the coefficients are determined using a matrix operation on the input signal and the limited signal.