Signal processing device, communication system, and signal processing method
A transfer function calculation unit ( 522 ) calculates a diagonal matrix G(f) on the basis of a band limit condition g(t) used in a transmission device ( 20 ). A transfer function calculation unit ( 524 ) calculates a diagonal matrix C(f) on the basis of a wavelength dispersion amount c(t) incurred in an optical transmission path. A transfer function combination unit ( 526 ) combines the diagonal matrix G(f) with the diagonal matrix C(f) so as to calculate a diagonal matrix H(f)=G(f)×C(f). An equalization coefficient calculation unit ( 528 ) calculates an equalization coefficient matrix W(f)=H(f) H (H(f) H H(f)+( 1 /E s )×Φ η ) −1 used in a multiplication unit ( 506 ) by using the diagonal matrix H(f). Here, H(f) H is a Hermitian transposed matrix of a matrix H(f), E s is power of an optical signal, and Φ η is a diagonal matrix with N rows and N columns.
1. A signal processing device comprising:
an electrical signal generation unit generating an electrical signal on the basis of an optical signal which is polarization-multiplexed and multi-value-modulated and which is transmitted through an optical transmission path; and
a compensation unit performing a compensation process on the electrical signal,
wherein the compensation unit includes:
a Fourier transform unit performing Fourier transform on the electrical signal;
an equalization processing unit performing an equalization process on the electrical signal having undergone the Fourier transform in a frequency domain;
an inverse Fourier transform unit performing inverse Fourier transform on the electrical signal having undergone the equalization process; and
an equalization coefficient setting unit setting an equalization coefficient matrix W(f) used for the equalization process, and
wherein the equalization coefficient setting unit sets the equalization coefficient matrix W(f) on the basis of the following equation:
W ( f )= H ( f ) H ( f )( H ( f ) H H ( f )+(1/E s )×Φ η −1
such that H(f)=G(f)×C(f), H H is a Hermitian transposed matrix of a matrix H, E s is power of the optical signal, and Φ is a diagonal matrix with N rows and N columns defined on the basis of colored noise, and
G(f) is a diagonal matrix set on the basis of a band limit condition during generation of the optical signal, and C(f) is a diagonal matrix set on the basis of wavelength dispersion incurred in the optical transmission path.
2. The signal processing device according to claim 1 , wherein a diagonal component Φ η [k] (where k=0, 1,. . ., N−1) of Φ η is defined on the basis of the following equation:
Φ
η
[
k
]
=
E
[
1
N
∑
m
=
0
N
-
1
η
[
m
]
e
-
j
2
π
km
N
2
]
=
N
0
N
∑
n
=
0
N
-
1
∑
m
=
0
N
-
1
g
n
-
m
e
-
j
2
π
(
n
-
m
)
k
N
.
3. The signal processing device according to claim 1 ,
wherein the compensation unit further includes:
an overlap applying unit dividing the electrical signal so as to generate block signals which are signals in a unit of process in the Fourier transform unit such that overlap occurs in the block signals adjacent to each other; and
an overlap removal unit removing the overlap from the block signals having undergone inverse Fourier transform in the inverse Fourier transform unit, and connects the block signals after the removal to each other.
4. The signal processing device according to claim 3 , wherein a magnitude of the overlap is set such that inter-symbol interference of the electrical signal is removed due to removal of the overlap in the overlap removal unit.
5. The signal processing device according to claim 3 , further comprising an overlap control unit setting a magnitude of the overlap, on the basis of the band limit condition and a compensation amount for compensating for the wavelength dispersion.
6. The signal processing device according to claim 1 ,
wherein the optical signal is transmitted according to wavelength division multiplexing communication (WDM), and
wherein a single band in wavelength division multiplexing communication is set to be narrower than in a Nyquist condition.
7. A communication system comprising:
a signal transmission device generating and transmitting an optical signal; and
a signal processing device receiving and processing the optical signal,
wherein the signal transmission device generates the optical signal through polarization multiplexing and multi-value modulation, and
wherein the signal processing device is the signal processing device according to claim 1 .
8. A signal processing method of receiving and processing an optical signal, the method comprising:
generating the optical signal through polarization multiplexing and multi-value modulation; and
processing the optical signal by using the signal processing device according to claim 1 .
9. A signal processing device comprising:
an electrical signal generation unit generating an electrical signal on the basis of an optical signal which is polarization-multiplexed and multi-value-modulated and which is transmitted through an optical transmission path; and
a compensation unit performing a compensation process on the electrical signal,
wherein the compensation unit includes:
a Fourier transform unit performing Fourier transform on the electrical signal;
an equalization processing unit performing an equalization process on the electrical signal having undergone the Fourier transform in a frequency domain;
an inverse Fourier transform unit performing inverse Fourier transform on the electrical signal having undergone the equalization process; and
an equalization coefficient setting unit setting an equalization coefficient matrix W(f) used for the equalization process, and
wherein the equalization coefficient setting unit sets the equalization coefficient matrix W(f) on the basis of the following equation:
W ( f )= W 1 ( f )× W 2 ( f )
such that W i (f)=C(f) −1 , and W 2 (f)=G(f) H (G(f)+(1/E s )×Φ −1
G(f) H is a Hermitian transposed matrix of a matrix G(f), E s is power of the electrical signal, and Φ η is a diagonal matrix with N rows and N columns defined on the basis of colored noise, and
G(f) is a diagonal matrix set on the basis of a band limit condition during generation of the optical signal, and C(f) is a diagonal matrix set on the basis of a wavelength dispersion condition incurred in the optical transmission path.