US 20110116809A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2011/0116809 A1
(43) Pub. Date:
YAN et al.
(54)
PHASE RECOVERY DEVICE, PHASE
(52)
COVERY METHOD AND RECEIVER FOR 16
(57)
QAM DATA MODULATION
(75) Inventors:
Zhenning Tao, Beijing (CN);
Shoichiro Oda, Kawasaki (JP)
Fujitsu Limited, Kawasaki (JP)
(21) Appl. No.:
12/896,476
(22)
Filed:
ABSTRACT
ing respective symbols in the symbol block based on ampli
tudes, so as to classify respective symbols in the symbol block
into a ?rst category having a large or small amplitude, and a
second category having an intermediate amplitude; a refer
ence point determination unit for determining a reference
Oct. 1, 2010
point based on categories of respective symbols in the symbol
block and their fourth poWer values; a rotation unit for rotat
Related US. Application Data
ing respective symbols in the symbol block undergone the
(63) Continuation of application No. PCT/CN2009/
073231, ?led on Aug. 13, 2009.
fourth poWer operations and being classi?ed into the second
category, based on the reference point; and a phase estimation
unit for performing phase estimations based on respective
symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the ?rst category, and
Publication Classi?cation
(51)
Us. or. ....................................... .. 398/202; 375/320
The present invention relates to a phase recovery device,
phase recovery method and receiver for 16 QAM data modu
lation. The phase recovery device comprises: a fourth poWer
calculator for calculating fourth poWer values of respective
symbols in a symbol block; a classi?cation unit for classify
Meng YAN, Beijing (CN);
(73) Assignee:
May 19, 2011
respective rotated symbols in the symbol block undergone the
Int. Cl.
H03D 1/24
(2006.01)
fourth poWer operations and being classi?ed into the second
H04B 10/06
(2006.01 )
category.
51
FOURTH POWER
CALCULATOR
52
53
REFERENCE POINT
CLASSIFICATION
UNIT
CALCULATION UNIT
55
V
PHASE
ESTIMATION UNIT
54
V
ROTATION UNIT
Patent Application Publication
May 19, 2011 Sheet 1 0f 6
US 2011/0116809 A1
Patent Application Publication
May 19, 2011 Sheet 2 0f 6
US 2011/0116809 A1
SYMBOL STREAM
I [/1301
FOURTH POWER
OPERATION
302
CLASSIFYING BASED
ON AMPLITUDES
THE FIRST AND THIRD
THE SECOND GROUP OF
GROUPS OF POINTS
POINTS (DISCARDED)
l K‘)
PHASE ESTIMATION
I
FIG.3
Patent Application Publication
May 19, 2011 Sheet 3 0f 6
START
US 2011/0116809 A1
401
V
FOURTH POWER OPERATION
402
V
CLASSIFYING BASED ON AMPLITUDES
403
V
CALCULATING REFERENCE POINT
W
404
V
ROTATING THE SECOND
GROUP OF POINTS
W
405
V
PERFORMING PHASE ESTIMATION
BASED ON THE FIRST AND THIRD
GROUPS OF POINTS AND THE
ROTATED SECOND GROUP OF POINTS
END
FIG.4
W
Patent Application Publication
May 19, 2011 Sheet 4 0f 6
51
US 2011/0116809 A1
52
53
/——
FOURTH POWER
CALCULATOR
CLASSIFICATION
UNIT
REFERENCE POINT
CALCULATION UNIT
55
V
PHASE
ESTIMATION UNIT
FIG.5
54
V
ROTATION UNIT
Patent Application Publication
May 19, 2011 Sheet 5 0f 6
52
CLASSIFICATION
UNIT
51
FOURTH POWER
CALCULATOR
US 2011/0116809 A1
53
_ REFERENCE POINT
' CALCULATION UNIT
55
54
‘I
PHASE
ESTIMATION
UNIT
<
ROTATION UNIT
Patent Application Publication
May 19, 2011 Sheet 6 0f 6
US 2011/0116809 A1
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May 19, 2011
US 2011/0116809 A1
PHASE RECOVERY DEVICE, PHASE
COVERY METHOD AND RECEIVER FOR 16
QAM DATA MODULATION
context, the meaning of the “point” in the embodiment of the
present invention is equivalent to that of the “symbol”). The
arguments of the ?rst and third groups of points are
FIELD OF THE INVENTION
[0001] The present invention relates to the optical commu
nication, and the present invention relates to a digital coherent
optical receiver.
DESCRIPTION OF THE RELATED ART
[0002]
(kIO, 1, 2, 3), and the arguments of the second group of points
are
The coherent optical communication technique is
deemed as a key technique for improving the optical commu
nication system capacity. At present, the coherent optical
communication system usually adopts a modulation format
of Quadrature Phase Shift Keying (QPSK). In order to further
improve the transmission capacity, a modulation format of
higher order, such as 16 Quadrature Amplitude Modulation
(QAM), can be used. One QAM symbol carries four bits
information, While one QPSK symbol only carries 2 bits
information, thus 16 QAM has a higher spectrum e?iciency
than the QPSK. In the coherent optical communication sys
. After calculating the fourth poWer value of the symbol, the
arguments of the ?rst and third groups of points are at and in
a negative direction of the lateral axis, While the arguments of
the second group of points may be tWo possible values (see
FIG. 2) forming an angle
tem, since a laser at the transmitting terminal and a local
oscillation laser at the receiving terminal both have certain
line Widths, a phase recovery must be carried out in order to
get a correct signal at the receiving terminal. Some methods
have been provided for 16QAM phase recovery, and the
methods can be divided into a feedforWard type and feedback
type. The method of Literature 1 is a feedforWard type
method, in Which the phase estimation of each symbol is not
dependent on phase estimation results of other symbols, thus
the phase estimations can be paralleliZed, i.e., a plurality of
digital signal processing units can be simultaneously used to
perform phase estimations of a plurality of symbols. The
paralleliZation greatly reduces the requirement on the DSP
With the negative direction of the lateral axis. As shoWn in
FIG. 3, in the current method of Literature 1, the fourth poWer
value of each symbol in a symbol block is ?rstly calculated
(step 301), then the symbols are divided into three groups
based on their amplitudes in step 302, next, the phase estima
tions in step 303 only use the symbols of the ?rst and third
groups. That is to say, in the 16QAM phase recovery method
of the prior art, only the ?rst and third groups of points are
used, and the second group of points are discarded.
processing speed. Literature 2 discloses a method based on
[0006]
decision-directed, Which is equivalent to a digital phase
locked loop. But the baud rate of the optical communication
system is very high, the delay of the phase locked loop is
strictly required, and the current DSP technique is dif?cult to
implement a phase locked loop that meets the delay require
tion, the inventor ?nds that the second group of points almost
occupies a half of an symbol block, While the second group of
points are discarded in the method of the prior art. As a result,
the noise depression degree is decreased, and the phase recov
ment. Although the method of Literature 3 is a feedforWard
[0007]
type method, it is based on pre-decision, and the phase esti
mation of the current symbol depends on phase estimation
results of previous symbols, so the paralleliZation cannot be
carried out.
[0003]
The method of Literature 1 in the prior art is brie?y
introduced as folloWs.
[0004] FIG. 1 illustrates an ideal 16QAM constellation
having no noise. FIG. 2 illustrates constellation points
obtained by performing fourth poWer operations of ideal
16QAM constellation points and maintaining their ampli
tudes. FIG. 3 illustrates a processing ?oW that uses a phase
recovery device in Literature 1.
[0005] As shoWn in FIG. 1, the 16QAM symbol has three
types of amplitudes, and the 16QAM constellation points can
be divided into three groups according to their amplitudes.
The ?rst group of points are located on the inner ring and has
a minimum amplitude R1. The second group of points are
located on the intermediate ring and has an intermediate
amplitude R2. The third group of points are located on the
outer ring and has a maximum amplitude R3 (Rl<R2<R3)
(herein the “point” refers to the constellation point, and is the
re?ection of the symbol on the I-Q plane; according to the
During the process of studying the present inven
ery accuracy is affected.
Literature 1: M. SeimetZ, Performance of coherent
optical square-16-QAM systems based on IQ-transmitter
and homodyne receivers With digital phase estimation.
OFC2006, NWA4.
[0008]
Literature 2: Y. Mori, Transmission of 40 Gb/ s
16QAM signal over 100 km standard single mode ?ber
using digital coherent optical receiver. ECOC2008, Tu.1.
E4.
[0009]
Literature 3: H. Louchet, Improved DSP algorithm
for coherent 16QAM transmission. ECOC2008, Tu. 1 E6.
[0010] Literature 4: D.-S. Ly-Gagnon, Coherent detection
of optical quadrature phase-shift keying signals With car
rier phase estimation. J. of LightWave Technol., vol. 24, no.
1, 2006.
SUMMARY OF THE INVENTION
[0011]
In vieW of the above problems, the embodiments of
the present invention are provided to eliminate or relieve one
or more problems of the prior art, and give at least one ben
e?cial selection.
[0012] In order to achieve the above object, the embodi
ments of the present invention provide the folloWing aspects.
May 19, 2011
US 2011/0116809 A1
modulation, including: a fourth power calculator for calcu
tions based on respective symbols in the symbol block under
gone the fourth poWer operations and being classi?ed into the
lating fourth poWer values of respective symbols in a symbol
block; a classi?cation unit for classifying respective symbols
?rst category, and respective rotated symbols in the symbol
block undergone the fourth poWer operations and being clas
in the symbol block based on amplitudes, so as to classify
si?ed into the second category.
respective symbols in the symbol block into a ?rst category
[0019] Aspect 7, the phase recovery method for 16 QAM
data modulation according to aspect 6, Wherein, the determin
ing determines the reference point by: determining a sum of
the symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the ?rst category, i.e., a
[0013]
Aspect 1, a phase recovery device for 16 QAM data
having a large or small amplitude, and a second category
having an intermediate amplitude; a reference point determi
nation unit for determining a reference point based on cat
egories of respective symbols in the symbol block and their
fourth poWer values; a rotation unit for rotating respective
symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the second category,
based on the reference point; and a phase estimation unit for
performing phase estimations based on respective symbols in
the symbol block undergone the fourth poWer operations and
being classi?ed into the ?rst category, and respective rotated
symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the second category.
[0014] Aspect 2, the phase recovery device for 16 QAM
data modulation according to aspect 1, Wherein the reference
point determination unit determines the reference point by:
?rst sum; determining a sum of the symbols in the symbol
block undergone the fourth poWer operations and being clas
si?ed into the second category, i.e., a second sum; and sub
tracting the second sum multiplied by a coe?icient from the
?rst sum, Wherein the coe?icient is not less than 0 and not
more than 1.
[0020] Aspect 8, the phase recovery method for 16 QAM
data modulation according to aspect 7, Wherein the coef?
cient is 0.5.
a coe?icient from the ?rst sum, Wherein the coe?icient is not
less than 0 and not more than 1.
[0021] Aspect 9, the phase recovery method for 16 QAM
data modulation according to aspect 6, Wherein the rotating
rotates the symbols in the symbol block undergone the fourth
poWer operations and being classi?ed into the second cat
egory by: determining an argument difference betWeen each
of the symbols in the symbol block undergone the fourth
poWcr operations and being classi?cd into the second cat
egory and the reference point; if the argument difference is
betWeen 0 to at, rotating corresponding symbol in the symbol
block undergone the fourth poWer operation and being clas
si?ed into the second category by —0t, 0t:rc—4><arctan(1/3); and
[0015] Aspect 3, the phase recovery device for 16 QAM
if the argument difference is betWeen —J'|§ to 0, rotating corre
determining a sum of the symbols in the symbol block under
gone the fourth poWer operations and being classi?ed into the
?rst category, i.e., a ?rst sum; determining a sum of the
symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the second category, i.e.,
a second sum; and subtracting the second sum multiplied by
data modulation according to aspect 2, Wherein the coef?
sponding symbol in the symbol block undergone the fourth
cient is 0.5.
poWer operation and being classi?ed into the second category
[0016] Aspect 4, The phase recovery device for 16 QAM
by 0t.
data modulation according to aspect 1, Wherein the rotation
unit rotates the symbols in the symbol block undergone the
fourth poWer operations and being classi?ed into the second
category by: determining an argument difference betWeen
each of the symbols in the symbol block undergone the fourth
poWer operations and being classi?ed into the second cat
egory and the reference point; if the argument difference is
betWeen 0 to at, rotating corresponding symbol in the symbol
block undergone the fourth poWer operation and being clas
si?ed into the second category by —0t, (x:rc—4><arctan(1/3); and
[0022] Aspect 10, the phase recovery method for 16 QAM
data modulation according to aspect 6, Wherein the classify
if the argument difference is betWeen —J'|§ to 0, rotating corre
sponding symbol in the symbol block undergone the fourth
ing ?rstly recovers the amplitudes of respective symbols
undergone the fourth poWer operations to those before the
fourth poWer operations, then compares the recovered ampli
tudes of respective symbols With predetermined thresholds T 1
and T3, if the recovered amplitudes are betWeen T l and T3, the
symbols are classi?ed into the second category, otherWise the
symbols are classi?ed into the ?rst category.
[0023] Aspect 11, the phase recovery method for 16 QAM
data modulation according to aspect 11, Wherein
poWer operation and being classi?ed into the second category
by 0t.
R1, R2 and R3 are amplitudes of ideal 16QAM constellation
[0017] Aspect 5, a digital coherent optical receiver,
points.
Wherein the digital coherent optical receiver includes the
phase recovery device for 16 QAM data modulation accord
[0024] The embodiment of the present invention su?i
ciently utiliZes received signals, and as compared With the
ing to any one of aspects 1 to 4.
prior art not suf?ciently utiliZing received signals (or only
[0018] Aspect 6, a phase recovery method for 16 QAM data
modulation, including: calculating fourth poWer values of
utiliZing a part thereof), the phase estimation accuracy is
improved. As proved by the results of simulations and experi
respective symbols in a symbol block; classifying respective
ments, the method in the embodiment of the present invention
symbols in the symbol block based on amplitudes, so as to
achieves a bit error rate loWer than that achieved by the
classify respective symbols in the symbol block into a ?rst
method of Literature 1 in the prior art.
category having a large or small amplitude, and a second
category having an intermediate amplitude; determining a
reference point based on categories of respective symbols in
the symbol block and their fourth poWer values; rotating
symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the second category,
based on the reference point; and performing phase estima
[0025] In reference to the folloWing descriptions and draW
ings, these and further aspects and features Will be clearer.
The descriptions and draWings concretely disclose the spe
ci?c embodiments of the present invention, and specify the
principle of the invention and the Ways that can be adopted. It
shall be understood that the scopes of the embodiments of the
present invention are not limited thereby. Within the range of
May 19, 2011
US 2011/0116809 A1
the spirit and provisions of the accompanied claims, the
T1, the symbol is judged as a ?rst group point, and also
embodiments of the present invention include various
classi?ed into the ?rst category. T1 and T3 are recommended
changes, modi?cations and equivalents.
judgment thresholds:
[0026]
Features described and/ or illustrated With respect to
one embodiment can be used in one or more other embodi
ments in the same or similar Way, by combining features in
other embodiments or replacing features in other embodi
[0039]
ments.
[0027]
R1, R2, R3 are amplitudes of ideal 16QAM constellation
points.
To be emphasiZed, the term “include/comprise” or
“including/comprising” in the text means the existence of
feature, integral, step or component, but not excluding the
existence or addition of one or more other features, integrals,
After calculating the fourth poWer values of all the
symbols in the symbol block and classifying all the symbols,
calculating reference point in step 403.
[0040] In an embodiment of the present invention, a method
for calculating reference point r is for example as folloWs:
steps or components.
BRIEF DESCRIPTION OF THE DRAWINGS
XEIJII
yell
[0028] FIG. 1 illustrates an ideal 16QAM constellation
having no noise.
[0029] FIG. 2 illustrates constellation points obtained by
performing fourth poWer operations of ideal 16QAM constel
lation points and maintaining their amplitudes.
[0030] FIG. 3 schematically illustrates a processing How of
a phase recovery method in the prior art.
[0031] FIG. 4 schematically illustrates a processing How of
a phase recovery method according to an embodiment of the
present invention.
[0032] FIG. 5 illustrates a phase recovery device according
to an embodiment of the present invention.
[0033]
FIG. 6 illustrates a phase recovery device according
to another embodiment of the present invention.
[0034] FIG. 7 illustrates an exemplary embodiment of a
phase estimation unit.
[0035] FIG. 8 illustrates the structure of a coherent optical
receiver according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS
[0036] The embodiment of the present invention is con
cretely described as folloWs in combination With the draW
ings. FIG. 4 schematically illustrates a processing How of a
phase recovery method according to an embodiment of the
present invention. As shoWn in FIG. 4, ?rstly in step 401,
fourth poWer operations are performed by for example a
fourth poWer calculator for respective symbols (mathemati
cally represented With a complex number I+jQ) in a symbol
block, then in step 402, the symbols after the fourth poWer
In the above equation, the ?rst item means adding (vector
adding) the points (symbols after the fourth poWer opera
tions) in the ?rst and third groups (i.e., the ?rst category), the
second item means adding the points (symbols after the
fourth poWer operations) in the second group (i.e., the second
category), 13 is a preset coe?icient betWeen 0 to 1, and pref
erably [3:05.
[0041] After calculating the reference point r, rotating each
point p of the second category in step 404. Concretely, the
folloWing operations are performed in an embodiment of the
present invention.
[0042] 1) Calculating an argument difference dA betWeen
point p (a symbol after the fourth poWer operation) and the
reference point r, e.g., dA:arg(p/r), Wherein arg( ) means a
calculation of argument, thus the value of dA is Within [—J'c, at].
[0043] Another method for determining argument differ
ence is to calculate dA:arg(p) —arg(r) ?rstly, and then limit the
value of dA Within [—J'c, at] by using a module of 275. A person
skilled in the art can conceive of other methods for determin
ing argument difference, and they are all Within the scope of
the present invention.
[0044] 2) If an argument difference dA is betWeen 0 and at,
rotating point p by —ot, i.e., rotating point p by —(X around a
coordinate origin on the I-Q plane (rotating by a clockWise,
0t:rc—4*arctan(1/3)). Mathematically, the rotation operation
can be indicated
as
operations are classi?ed based on their amplitudes, i.e., sym
[ I J [ cosa sina 11 J
=
Q
—sina cosa
,
Q1
bols having large (the third group of points) or small (the ?rst
group of points) amplitudes are classi?ed into a ?rst category,
and symbols having intermediate (the second group of points)
Wherein (I 1 ,Q l) are coordinates before the rotation, and (LO)
amplitudes are classi?ed into a second category.
[0037] The symbols can be classi?ed as folloWs.
are coordinates after the rotation.
[0038] According to an aspect of the present invention,
?rstly, an amplitude of a symbol after the fourth poWer opera
tion is recovered to the amplitude before the fourth poWer
operation (i.e., being divided by a cube of the module value of
the symbol before the fourth poWer operation), and then the
recovered amplitude is compared With a predetermined
threshold. If the amplitude of the received signal is betWeen
T1 and T3, the symbol is judged as a second group point, and
classi?ed into the second category. If the amplitude is larger
than T3, the symbol is judged as a third group point, and
classi?ed into the ?rst category. If the amplitude is less than
rotating point p by a around the origin on the I-Q plane
[0045]
If the argument difference dA is betWeen —J'IZ and 0,
(rotating by 0t anticlockwise).
[0046]
Under ideal conditions, after this step, the second
group of points are rotated to a negative direction of the lateral
axis, and this is equivalent to eliminating the residual angular
modulation.
[0047] Next, in step 405, performing phase estimation
based on the ?rst and third groups of points, as Well as the
rotated second group of points. The phase estimation includes
operations such as average calculation, angle calculation and
unWrapping.
May 19, 2011
US 2011/0116809 A1
The phase estimation can be performed With various
FIG. 6 illustrates a phase recovery device according to
methods known by a person skilled in the art, e.g., the tech
nique disclosed in Literature 4 can be used. To be noted, When
these methods are adopted, not only the ?rst and third groups
of points Will be used, but also the rotated second group of
[0048]
another embodiment of the present invention. The phase
points shall also be used.
[0049] According to an embodiment of the present inven
tion, the reference point is calculated and the second category
of points are rotated based on the reference point, and thus the
second category of points can be suf?ciently utiliZed to
improve the accuracy of the phase estimation.
[0050] In the above embodiment, a fourth poWer operation
is performed ?rstly, and then a symbol is classi?ed based on
the amplitudes after the fourth poWer operation. In an alter
native embodiment, a symbol can be classi?ed based on the
amplitudes of respective symbols in a symbol block before
the fourth poWer operations, and the symbol and its category
can be together transferred to a fourth poWer calculator. The
fourth poWer calculator calculates a fourth poWer value of the
symbol, and respectively sends the fourth poWer value and the
symbol category to the next step for calculating a reference
point and performing a phase estimation.
[0051] That is to say, the symbol classi?cation can be per
formed either before or after the fourth poWer operations.
According to the context, “categories of respective symbols
in a (the) symbol block” can mean symbol categories either
before or after the fourth poWer operations. In the present
invention, “classifying respective symbols in a symbol block
into a ?rst category having a large or small amplitude, and a
second category having an intermediate amplitude” includes
classifying either before or after the fourth poWer operations.
[0052] FIG. 5 illustrates a phase recovery device according
to an embodiment of the present invention. As shoWn in FIG.
5, the phase recovery device according to an embodiment of
the present invention comprises a fourth poWer calculator 51,
a classi?cation unit 52, a reference point determination unit
53, a rotation unit 54 and a phase estimation unit 55.
[0053] The fourth poWer calculator 51 calculates fourth
poWer values of respective symbols in a symbol block. The
classi?cation unit 52 classi?es respective symbols in the sym
bol block after the fourth poWer operations. The classi?cation
unit 52 ?rstly recovers the amplitudes of respective symbols
after the fourth poWer operations to those before the fourth
poWer operations, then classi?es respective symbols in the
symbol block after the fourth poWer operations into a ?rst and
third groups of points or a second group of points by com
paring the recovered amplitudes With predetermined thresh
olds. The threshold selection is shoWn in Equation 1). The
reference point determination unit 53 determines a reference
point based on categories classi?ed by the classi?cation unit
52, by utiliZing calculation results of the fourth poWer calcu
lator, e.g., utiliZing Equation 2). The rotation unit 54 rotates
the second group of points (symbols of the second category
after the fourth poWer operations) by utiliZing the reference
point. According to an embodiment, the rotation is performed
recovery device in FIG. 6 is substantially same as the phase
recovery device in FIG. 5, except that the classi?cation unit
51 classi?es the symbols before the fourth poWer values of
respective symbols being calculated by the fourth poWer cal
culator 51.
[0055] FIG. 7 illustrates an exemplary embodiment of the
phase estimation unit 55. As shoWn in FIG. 7, according to an
embodiment, the phase estimation unit 55 may comprise an
averager, an argument calculator and an unWrapper. The aver
ager is used to calculate the average of the fourth poWer values
of the ?rst and third groups of points as Well as the rotated
second group of points. The argument calculator is used to
calculate an argument of the average obtained by the averager
and divides it by 4, arg( ) means an argument calculation. The
unWrapper is used to upWrap the angle value outputted from
the argument calculator.
[0056] The phase estimation unit 55 in FIG. 7 is just exem
plary, and the invention can also use phase estimation means
in other forms.
[0057] FIG. 8 illustrates the structure of a coherent optical
receiver according to an embodiment of the present invention,
Wherein the phase restorer 801 can be the phase recovery
device in respective embodiments of the present invention.
The structure of the coherent optical receiver in FIG. 8 is just
exemplary, and the phase recovery device of the present
invention can be applied to coherent optical receivers of other
forms.
[0058] The above device and method of the present inven
tion can be implemented by hardWare, or the combination of
hardWare and softWare. The present invention relates to such
a computer readable program that enables a logic unit (e.g.,
?eld programmable gate array, microchip, CPU) to imple
ment the functions of the previously described devices and
components, or to implement the previously described meth
ods and steps, When the program is executed by the logic unit.
The present invention also relates to storage medium for
storing the above program, e.g., hard disk, magnetic disk,
optical disk, DVD and ?ash memory.
[0059] The present invention is described in combination
With the above embodiments. But a person skilled in the art
shall be clear that the descriptions are just exemplary, instead
of limitations to the protection scope of the present invention.
A person skilled in the art can make various modi?cations and
changes to the present invention based on spirit and principle
of the present invention, and those modi?cations and changes
are also Within the scope of the present invention.
1. A phase recovery device for 16 QAM data modulation,
comprising:
a fourth poWer calculator for calculating fourth poWer val
ues of respective symbols in a symbol block;
a classi?cation unit for classifying respective symbols in
the symbol block based on amplitudes, so as to classify
respective symbols in the symbol block into a ?rst cat
based on argument differences betWeen each of the second
egory having a large or small amplitude, and a second
group of points and the reference point. The calculation of
argument difference and the rotation of symbol are described
in step 401. The phase estimation unit 55 performs phase
category having an intermediate amplitude;
estimations based on the ?rst and third groups of points, as
Well as the rotated second group of points (to be described in
the folloWing text).
[0054] The classi?cation unit 52 can also classify a symbol
based on its amplitude before the fourth poWer operation.
a reference point determination unit for determining a ref
erence point based on categories of respective symbols
in the symbol block and their fourth poWer values;
a rotation unit for rotating respective symbols in the sym
bol block undergone the fourth poWer operations and
being classi?ed into the second category, based on the
reference point; and
May 19, 2011
US 2011/0116809 A1
a phase estimation unit for performing phase estimations
based on respective symbols in the symbol block under
gone the fourth poWer operations and being classi?ed
into the ?rst category, and respective rotated symbols in
the symbol block undergone the fourth poWer operations
and being classi?ed into the second category.
2. The phase recovery device for 16 QAM data modulation
according to claim 1, Wherein, the reference point determi
nation unit determines the reference point by:
determining a sum of the symbols in the symbol block
undergone the fourth poWer operations and being clas
si?ed into the ?rst category, i.e., a ?rst sum;
determining a sum of the symbols in the symbol block
undergone the fourth poWer operations and being clas
si?ed into the second category, i.e., a second sum;
subtracting the second sum multiplied by a coe?icient from
the ?rst sum, Wherein the coe?icient is not less than 0
and not more than 1.
3. The phase recovery device for 16 QAM data modulation
according to claim 2, Wherein the coef?cient is 0.5.
4. The phase recovery device for 16 QAM data modulation
according to claim 1, Wherein the rotation unit rotates the
symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the second category by:
determining an argument difference betWeen each of the
symbols in the symbol block undergone the fourth
poWer operations and being classi?ed into the second
category and the reference point;
if the argument difference is betWeen 0 to at, rotating cor
responding symbol in the symbol block undergone the
fourth poWer operation and being classi?ed into the
second category by —0t, 0t:rc—4><arctan (1/3);
if the argument difference is betWeen —J'|§ to 0, rotating
corresponding symbol in the symbol block undergone
the fourth poWer operation and being classi?ed into the
second category by 0t.
5. A digital coherent optical receiver, Wherein, the digital
coherent optical receiver comprises the phase recovery device
for 16 QAM data modulation according to claim 1.
6. A phase recovery method for 16 QAM data modulation,
comprising:
calculating fourth poWer values of respective symbols in a
symbol block;
classifying respective symbols in the symbol block based
on amplitudes, so as to classify respective symbols in the
symbol block into a ?rst category having a large or small
amplitude, and a second category having an intermedi
ate amplitude;
determining a reference point based on categories of
respective symbols in the symbol block and their fourth
poWer values;
rotating symbols in the symbol block undergone the fourth
poWer operations and being classi?ed into the second
category, based on the reference point; and
performing phase estimations based on respective symbols
in the symbol block undergone the fourth poWer opera
tions and being classi?ed into the ?rst category, and
respective rotated symbols in the symbol block under
gone the fourth poWer operations and being classi?ed
into the second category.
7. The phase recovery method for 16 QAM data modula
tion according to claim 6, Wherein, the determining deter
mines the reference point by:
determining a sum of the symbols in the symbol block
undergone the fourth poWer operations and being clas
si?ed into the ?rst category, i.e., a ?rst sum;
determining a sum of the symbols in the symbol block
undergone the fourth poWer operations and being clas
si?ed into the second category, i.e., a second sum;
subtracting the second sum multiplied by a coe?icient from
the ?rst sum, Wherein the coe?icient is not less than 0
and not more than 1.
8. The phase recovery method for 16 QAM data modula
tion according to claim 7, Wherein the coe?icient is 0.5.
9. The phase recovery method for 16 QAM data modula
tion according to claim 6, Wherein the rotating rotates the
symbols in the symbol block undergone the fourth poWer
operations and being classi?ed into the second category by:
determining an argument difference betWeen each of the
symbols in the symbol block undergone the fourth
poWer operations and being classi?ed into the second
category and the reference point;
if the argument difference is betWeen 0 to at, rotating cor
responding symbol in the symbol block undergone the
fourth poWer operation and being classi?ed into the
second category by —0t, 0t:rc—4><arctan (1/3);
if the argument difference is betWeen —J'|§ to 0, rotating
corresponding symbol in the symbol block undergone
the fourth poWer operation and being classi?ed into the
second category by 0t.
10. The phase recovery method for 16 QAM data modula
tion according to claim 6, Wherein the classifying ?rstly
recovers the amplitudes of respective symbols undergone the
fourth poWer operations to those before the fourth poWer
operation, then compares the recovered amplitudes of respec
tive symbols With predetermined thresholds T1 and T3, if the
recovered amplitudes are betWeen T1 and T3, the symbols are
classi?ed into the second category, otherWise classi?ed into
the ?rst category,
Wherein
tudes of ideal 16QAM constellation points.
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