U.S. patent application number 16/866007 was filed with the patent office on 2021-07-08 for synchronization apparatus and method for upstream system.
This patent application is currently assigned to ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE. The applicant listed for this patent is ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE. Invention is credited to Dong-Joon CHOI, Joon-Young JUNG, Kwan-Woong RYU, Jin-Hyuk SONG.
Application Number | 20210211336 16/866007 |
Document ID | / |
Family ID | 1000005666532 |
Filed Date | 2021-07-08 |
United States Patent
Application |
20210211336 |
Kind Code |
A1 |
RYU; Kwan-Woong ; et
al. |
July 8, 2021 |
SYNCHRONIZATION APPARATUS AND METHOD FOR UPSTREAM SYSTEM
Abstract
Disclosed herein are a synchronization apparatus and method for
a upstream system. The synchronization apparatus for a upstream
system includes one or more processors, and execution memory for
storing at least one program that is executed by the one or more
processors, wherein the at least one program is configured to
receive a signal and calculate a first channel estimation value for
the received signal using a predefined pilot, and calculate a
second channel estimation value using a predefined complementary
pilot and the first channel estimation value.
Inventors: |
RYU; Kwan-Woong; (Daejeon,
KR) ; SONG; Jin-Hyuk; (Daejeon, KR) ; JUNG;
Joon-Young; (Daejeon, KR) ; CHOI; Dong-Joon;
(Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE |
Daejeon |
|
KR |
|
|
Assignee: |
ELECTRONICS AND TELECOMMUNICATIONS
RESEARCH INSTITUTE
Daejeon
KR
|
Family ID: |
1000005666532 |
Appl. No.: |
16/866007 |
Filed: |
May 4, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 27/2662 20130101;
H04L 2025/03796 20130101; H04L 27/2675 20130101; H04L 27/2695
20130101; H04L 27/0014 20130101; H04L 27/2659 20130101; H04L
25/0232 20130101 |
International
Class: |
H04L 27/00 20060101
H04L027/00; H04L 25/02 20060101 H04L025/02; H04L 27/26 20060101
H04L027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 6, 2020 |
KR |
10-2020-0001527 |
Claims
1. A synchronization apparatus for an upstream system, comprising:
one or more processors; and an execution memory for storing at
least one program that is executed by the one or more processors,
wherein the at least one program when executed causes the one or
more processors to: receive a signal and calculate a first channel
estimation value for the received signal using a predefined pilot,
and calculate a second channel estimation value using a predefined
complementary pilot and the first channel estimation value, wherein
the at least one program when executed further causes the one or
more processors to extract a compensation parameter from a preset
symbol range in a symbol constellation from which the predefined
complementary pilot is extracted.
2. (canceled)
3. The synchronization apparatus of claim 1, wherein the at least
one program when executed further causes the one or more processors
to extract respective compensation parameters for at least two
complementary pilots from preset symbol ranges in symbol
constellations of the at least two complementary pilots.
4. The synchronization apparatus of claim 1, wherein the at least
one program when executed further causes the one or more processors
to compensate for an error in the predefined complementary pilot
using the compensation parameter.
5. The synchronization apparatus of claim 4, wherein the at least
one program when executed further causes the one or more processors
to calculate the second channel estimation value alternatively
using an error-compensated complementary pilot, the predefined
pilot, and the first channel estimation value, and to perform
channel equalization based on the second channel estimation
value.
6. A synchronization method for an upstream system, the
synchronization method being performed using a synchronization
apparatus for the upstream system, the synchronization method
comprising: receiving a signal and calculating a first channel
estimation value for the received signal using a predefined pilot;
and calculating a second channel estimation value using a
predefined complementary pilot and the first channel estimation
value, wherein calculating the second channel estimation value
further comprises extracting a compensation parameter from a preset
symbol range in a symbol constellation from which the predefined
complementary pilot is extracted.
7. (canceled)
8. The synchronization method of claim 6, wherein calculating the
second channel estimation value further comprises extracting
respective compensation parameters for at least two complementary
pilots from preset symbol ranges in symbol constellations of the at
least two complementary pilots.
9. The synchronization method of claim 8, wherein calculating the
second channel estimation value further comprises compensating for
an error in each of the at least two complementary pilots using the
respective compensation parameters.
10. The synchronization method of claim 9, wherein calculating the
second channel estimation value further comprises calculating the
second channel estimation value alternatively using
error-compensated complementary pilots, the predefined pilot, and
the first channel estimation value, and to perform channel
equalization based on the second channel estimation value.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Korean Patent
Application No. 10-2020-0001527, filed Jan. 6, 2020, which is
hereby incorporated by reference in its entirety into this
application.
BACKGROUND OF THE INVENTION
1. Technical Field
[0002] The present invention relates generally to cable
transmission/reception and communication technology, and more
particularly, to synchronization technology for correcting a
Carrier Frequency Offset (CFO) and a sampling clock offset, which
occur in a Data Over Cable Service Interface Specification (DOCSIS)
3.1 upstream system.
2. Description of the Related Art
[0003] In order to respond to the insufficiency of a transmission
band attributable to increased demand for implementation of
high-definition broadcasting service and ultra-high-speed Internet
service and intensification in media competition attributable to
fiber-to-the-home (FTTH)-based Gigabit-level service, DOCSIS 3.1
transmission specifications have been presented. DOCSIS 3.1 refers
to technology that enables 10 Gbps-level transmission, which was
considered to be possible only when optical cables are installed on
a subscriber's premises, to be realized over existing cable
broadcasting networks.
[0004] Among these technologies, a DOCSIS 3.1 upstream system uses
an Orthogonal Frequency-Division Multiple Access (OFDMA) frame
while aiming at a speed of 1 Gbps or more, and has a transmission
unit which is a transmission burst composed of multiple minislots.
Here, each minislot is composed of multiple sub-carrier groups, and
all sub-carriers in each minislot have the same modulation order. A
cable modem (CM) is assigned one or more minislots for a
transmission burst through a transmission profile, and acquires
information about a modulation order and a pilot pattern. The
transmission profile defines the modulation order and the pilot
pattern of the corresponding minislot on a transmission burst
basis.
[0005] Meanwhile, Korean Patent Application Publication No.
10-2018-0058621 entitled "Apparatus of Synchronization for DOCSIS
Upstream Signal Transmission through Optical-Based IP Network and
Method of the Same" discloses an apparatus and method for
transmitting a DOCSIS-based upstream signal, used in cable
broadcasting over an optical-based IP network, in synchronization
with a DOCSIS network.
SUMMARY OF THE INVENTION
[0006] Accordingly, the present invention has been made keeping in
mind the above problems occurring in the prior art, and an object
of the present invention is to provide synchronization and channel
equalization efficient for a DOCSIS 3.1 upstream system.
[0007] Another object of the present invention is to effectively
eliminate frequency and phase offsets attributable to the sampling
clock offset of the DOCSIS 3.1 upstream system.
[0008] In accordance with an aspect of the present invention to
accomplish the above objects, there is provided a synchronization
apparatus for a upstream system, including one or more processors,
and an execution memory for storing at least one program that is
executed by the one or more processors, wherein the at least one
program is configured to receive a signal and calculate a first
channel estimation value for the received signal using a predefined
pilot, and calculate a second channel estimation value using a
predefined complementary pilot and the first channel estimation
value.
[0009] The at least one program may be configured to extract a
compensation parameter from a preset symbol range in a symbol
constellation from which the predefined complementary pilot is
extracted.
[0010] The at least one program may be configured to extract
respective compensation parameters for at least two complementary
pilots from preset symbol ranges in symbol constellations of the at
least two complementary pilots.
[0011] The at least one program may be configured to compensate for
an error in the complementary pilot using the compensation
parameter.
[0012] The at least one program may be configured to calculate the
second channel estimation value using an error-compensated
complementary pilot, the predefined pilot, and the first channel
estimation value, and to perform channel equalization based on the
second channel estimation value.
[0013] In accordance with another aspect of the present invention
to accomplish the above objects, there is provided a
synchronization method for a upstream system, the synchronization
method being performed using a synchronization apparatus for the
upstream system, the synchronization method including receiving a
signal and calculating a first channel estimation value for the
received signal using a predefined pilot, and calculating a second
channel estimation value using a predefined complementary pilot and
the first channel estimation value.
[0014] Calculating the second channel estimation value may be
configured to extract a compensation parameter from a preset symbol
range in a symbol constellation from which the predefined
complementary pilot is extracted.
[0015] Calculating the second channel estimation value may be
configured to extract respective compensation parameters for at
least two complementary pilots from preset symbol ranges in symbol
constellations of the at least two complementary pilots.
[0016] Calculating the second channel estimation value may be
configured to compensate for an error in the complementary pilots
using the compensation parameters.
[0017] Calculating the second channel estimation value may be
configured to calculate the second channel estimation value using
error-compensated complementary pilots, the predefined pilot, and
the first channel estimation value, and to perform channel
equalization based on the second channel estimation value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0019] FIGS. 1 and 2 are diagrams illustrating a pilot pattern (2K
mode) of a DOCSIS 3.1 upstream system according to an embodiment of
the present invention;
[0020] FIGS. 3 to 10 are constellations illustrating the results of
performing channel equalization using pilots according to an
embodiment of the present invention;
[0021] FIG. 11 is a block diagram illustrating a synchronization
apparatus for a upstream system according to an embodiment of the
present invention;
[0022] FIG. 12 is a block diagram illustrating in detail an example
of the pilot-based channel estimation unit illustrated in FIG.
11;
[0023] FIG. 13 is a block diagram illustrating in detail an example
of the complementary pilot-based channel estimation unit
illustrated in FIG. 11;
[0024] FIG. 14 is an operation flowchart illustrating a
synchronization method for a upstream system according to an
embodiment of the present invention;
[0025] FIG. 15 is an operation flowchart illustrating in detail an
example of the complementary pilot-based channel estimation step
illustrated in FIG. 14;
[0026] FIG. 16 is a diagram illustrating the arrangement of pilots
in a pilot pattern according to an embodiment of the present
invention;
[0027] FIG. 17 is a graph illustrating a CFO compensation process
in a frequency domain according to an embodiment of the present
invention;
[0028] FIG. 18 is a diagram illustrating a channel estimation
process according to an embodiment of the present invention;
[0029] FIG. 19 is a constellation illustrating an input
complementary pilot symbol according to an embodiment of the
present invention;
[0030] FIG. 20 is a constellation illustrating a symbol range for
error compensation in a complementary pilot in a sixth symbol
according to an embodiment of the present invention;
[0031] FIG. 21 is a constellation illustrating a symbol range for
error compensation in a complementary pilot in an eighth symbol
according to an embodiment of the present invention;
[0032] FIG. 22 is a constellation illustrating a complementary
pilot in an error-compensated sixth symbol according to an
embodiment of the present invention;
[0033] FIG. 23 is a constellation illustrating a complementary
pilot in an error-compensated eighth symbol according to an
embodiment of the present invention;
[0034] FIG. 24 is a diagram illustrating a channel estimation
process using error-compensated complementary pilots according to
an embodiment of the present invention;
[0035] FIGS. 25 to 32 are constellations illustrating an
error-compensated complementary pilot according to an embodiment of
the present invention; and
[0036] FIG. 33 is a diagram illustrating a computer system
according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] The present invention will be described in detail below with
reference to the accompanying drawings. Repeated descriptions and
descriptions of known functions and configurations which have been
deemed to make the gist of the present invention unnecessarily
obscure will be omitted below. The embodiments of the present
invention are intended to fully describe the present invention to a
person having ordinary knowledge in the art to which the present
invention pertains. Accordingly, the shapes, sizes, etc. of
components in the drawings may be exaggerated to make the
description clearer.
[0038] In the present specification, it should be understood that
terms such as "include" or "have" are merely intended to indicate
that features, numbers, steps, operations, components, parts, or
combinations thereof are present, and are not intended to exclude
the possibility that one or more other features, numbers, steps,
operations, components, parts, or combinations thereof will be
present or added.
[0039] Hereinafter, preferred embodiments of the present invention
will be described in detail with reference to the attached
drawings.
[0040] FIGS. 1 and 2 are diagrams illustrating a pilot pattern (2K
mode) of a DOCSIS 3.1 upstream system (or a DOCSIS upstream system)
according to an embodiment of the present invention.
[0041] Referring to FIGS. 1 and 2, it can be seen that pilot
patterns 1 to 4 for the DOCSIS 3.1 upstream system are depicted. In
a DOCSIS 3.1 upstream frame according to an embodiment of the
present invention, pilots may be scattered in first and third
symbols of a frame, and complementary pilots may be scattered in
symbols located at first and third locations from an end symbol.
Here, each of the pilots may be a Binary Phase-Shift Keying (BPSK)
symbol of 1 or -1, which is agreed upon between a transmitter and a
receiver. Unlike the pilots, each of the complementary pilots may
transmit data other than symbols agreed upon between the
transmitter and the receiver. The complementary pilot may
correspond to a data subcarrier having a modulation order lower
than that of other data subcarriers in a minislot. If the
modulation order used in other data subcarriers in the minislot is
M, a complementary pilot may use `1` (BPSK) in a modulation order
of M-4.
[0042] In the pilot structure of the DOCSIS 3.1 upstream system
according to the embodiment of the present invention, when only
pilots are used for channel equalization and the correction of a
Carrier Frequency Offset (CFO), compensation for a sampling clock
offset and a CFO and channel equalization are desirably performed
in low-order symbols in which the pilots are present, but
degradation of performance may occur in high-order symbols in which
pilots are not present.
[0043] FIGS. 3 to 10 are constellations illustrating the results of
performing channel equalization using pilots according to an
embodiment of the present invention.
[0044] Referring to FIGS. 3 to 10, it can be seen that an
embodiment in which only pilots are used for channel equalization
and CFO correction when data symbols are 1024-Quadrature amplitude
modulation (QAM) symbols and complementary pilot symbols are 64-QAM
symbols is illustrated. When synchronization is performed using
only pilots, it can be seen that compensation for a sampling clock
offset and a CFO and channel equalization are desirably realized in
low-order symbols (symbol 1 to symbol 3) in which pilots are
present, but degradation of performance may occur in high-order
symbols (symbol 4 to symbol 8) in which pilots are not present, as
illustrated in FIGS. 3 to 10. Such performance degradation may be
more severe as the difference between frequency offsets in the
transmitter and the receiver (or transmission and reception stages)
is larger.
[0045] FIG. 11 is a block diagram illustrating a synchronization
apparatus for a upstream system according to an embodiment of the
present invention. FIG. 12 is a block diagram illustrating in
detail an example of the pilot-based channel estimation unit
illustrated in FIG. 11. FIG. 13 is a block diagram illustrating in
detail an example of the complementary pilot-based channel
estimation unit illustrated in FIG. 11.
[0046] Referring to FIG. 11, the synchronization apparatus for the
upstream system according to the embodiment of the present
invention includes a pilot-based channel estimation unit 110 and a
complementary pilot-based channel estimation unit 120.
[0047] The pilot-based channel estimation unit 110 may receive a
signal, and may calculate a first channel estimation value for the
received signal using predefined pilots.
[0048] Referring to FIG. 12, the pilot-based channel estimation
unit 110 may include a Symbol Timing Offset (STO) estimation unit
111, a Fast Fourier Transform (FFT) performance unit 112, a Carrier
Frequency Offset (CFO) estimation unit 113, and a first channel
estimation unit 114.
[0049] The STO estimation unit 111 may estimate a Symbol Timing
Offset (STO) in the time domain of the received signal.
[0050] The FFT performance unit 112 may estimate a frequency offset
after performing a Fast Fourier Transform (FFT) on the received
signal.
[0051] The CFO estimation unit 113 may compensate for a Carrier
Frequency Offset (CFO) in a frequency domain.
[0052] Here, the CFO estimation unit 113 may calculate the amount
of frequency angular rotation between symbols in the frequency
domain using the following Equation (1):
.DELTA..PHI.=.angle.[(P.sub.1).degree..times.P3]/N (1)
[0053] Here, P.sub.1 denotes N pilot symbol vectors in a first
symbol, and P3 denotes N pilot symbol vectors in a third
symbol.
[0054] The CFO estimation unit 113 may apply the amount of
frequency angular rotation between the symbols, calculated in
Equation (1), to eighth symbols, as represented by the following
Equation (2):
S.sub.k=S.sub.k.times.exp(-j.times.k.times..DELTA..PHI.) (2)
[0055] Here, k of S.sub.k denotes a k-th symbol.
[0056] The first channel estimation unit 114 may obtain the average
of channel gains using P1 and P3 pilots and apply the average to
the eight symbols in the time domain, and may interpolate the
channel gains, calculated in the time domain, and apply the
interpolated value to the frequency domain.
[0057] The complementary pilot-based channel estimation unit 120
may calculate a second channel estimation value using predefined
complementary pilots and the first channel estimation value.
[0058] Referring to FIG. 13, the complementary pilot-based channel
estimation unit 120 may include a first complementary pilot
detection unit 121, a compensation parameter detection unit 122, a
second complementary pilot detection unit 123, and a second channel
estimation unit 124.
[0059] The first complementary pilot detection unit 121 may detect
predefined complementary pilots.
[0060] For example, in the constellations of a sixth symbol and an
eighth symbol, 1024-QAM data symbols and 64-QAM complementary pilot
symbols may coexist.
[0061] Here, the first complementary pilot detection unit 121 may
extract only 64-QAM complementary pilot symbols in the sixth symbol
and the eighth symbol from input complementary pilot symbols.
[0062] The compensation parameter detection unit 122 may extract
compensation parameters from preset symbol ranges in symbol
constellations from which the predefined complementary pilot
symbols are extracted.
[0063] The extracted complementary pilot symbols may exhibit a
remarkably high error rate in high-order symbols.
[0064] Here, the compensation parameter detection unit 122 may
extract respective compensation parameters for at least two
complementary pilots from preset symbol ranges in the symbol
constellations of at least two complementary pilots.
[0065] Here, in order to correct this error rate, the compensation
parameter detection unit 122 may set low-power symbol ranges (see
blue rectangular ranges in FIGS. 20 and 21) in which errors do not
occur in the constellations of the sixth symbol and the eighth
symbol, and may extract compensation parameters based on the set
symbol ranges. The complementary pilot detection values s.sub.cp
may be represented by the following Equation (3):
s.sub.cp=|{tilde over (s)}.sub.cp-s.sub.cp|.sub.m.pi.s (3)
[0066] Here, {tilde over (s)}.sub.cp denotes sixth and eighth
complementary pilot values after first-step channel estimation and
channel equalization have been performed, and may be represented by
{tilde over (s)}.sub.cp=r.sub.cp/h.sub.cp. r.sub.cp denotes a
complementary pilot value that is input after CFO estimation and
compensation have been performed, and h.sub.cp denotes an estimated
channel value at the location of the corresponding complementary
pilot.
[0067] Here, the compensation parameter detection unit 122 may
select only complementary pilot symbols falling within a range (x)
having a predetermined size.
[0068] Here, the compensation parameter detection unit 122 may set
the range in which errors do not occur in each of the
constellations of the sixth and eighth symbols to a range of
[x<c].
[0069] For example, the compensation parameter detection unit 122
may set the range to a range of [x<0.6].
[0070] In the range of [x<0.6], each complementary pilot
detection value s.sub.cp matches a transmitted complementary pilot
value s.sub.cp without causing a symbol error. The compensation
parameters may be represented by the following Equation (4):
g ^ cp = S ~ cp [ x < 0.6 ] S ^ cp [ x < 0.6 ] = S ~ cp [ x
< 0.6 ] S cp [ x < 0.6 ] ( 4 ) ##EQU00001##
[0071] The second complementary pilot detection unit 123 may
compensate for errors in the complementary pilots using the
compensation parameters, and may detect error-compensated
complementary pilots.
[0072] The complementary pilot values {tilde over ({tilde over
(s)})}.sub.cp, which are error-compensated using the compensation
parameters, may be represented by the following Equation (5):
S ~ ~ cp = S ~ cp g ^ cp ( 5 ) ##EQU00002##
[0073] Here, when the second complementary pilot detection unit 123
detects again complementary pilots after the application of the
compensation parameters, the error rate of the complementary pilots
in the sixth and eighth symbols may be `0`.
[0074] The complementary pilot error rate of `0` may mean that the
sixth and eighth complementary pilots can be used as known signals
(i.e., signals agreed upon between transmission and reception
stages), such as pilots.
[0075] The second channel estimation unit 124 may calculate the
second channel estimation value using the error-compensated
complementary pilots, the pilots, and the first channel estimation
value, and may perform channel equalization based on the second
channel estimation value.
[0076] FIG. 14 is an operation flowchart illustrating a
synchronization method for a upstream system according to an
embodiment of the present invention. FIG. 15 is an operation
flowchart illustrating in detail an example of the complementary
pilot-based channel estimation step illustrated in FIG. 14.
[0077] Referring to FIG. 14, the synchronization method for a
upstream system according to the embodiment of the present
invention may perform pilot-based channel estimation at step
S210.
[0078] That is, at step S210, a signal may be received, and a first
channel estimation value for the received signal may be calculated
using predefined pilots.
[0079] At step S210, in the time domain of the received signal, a
Symbol Timing Offset (STO) may be estimated.
[0080] Here, at step S210, after a FFT has been performed on the
received signal, a frequency offset may be estimated.
[0081] In detail, at step S210, a Carrier Frequency Offset (CFO) in
the frequency domain may be compensated for.
[0082] Here, at step S210, the amount of frequency angular rotation
between symbols in the frequency domain may be calculated using the
above-described Equation (1).
[0083] At step S210, the amount of frequency angular rotation
between the symbols, calculated in Equation (1), may be applied to
eighth symbols, as represented by the above-described Equation
(2).
[0084] In this case, at step S210, the average of channel gains
using P1 and P3 pilots may be obtained and applied to the eight
symbols in the time domain. Also, the channel gains, calculated in
the time domain, may be interpolated, and the interpolated value
may be applied to the frequency domain.
[0085] Next, the synchronization method for the upstream system
according to the embodiment of the present invention may perform
complementary pilot-based channel estimation at step S220.
[0086] That is, at step S220, a second channel estimation value may
be calculated using predefined complementary pilots and the first
channel estimation value.
[0087] Referring to FIG. 15, in the procedure at step S220,
complementary pilots may be detected at step S221.
[0088] That is, at step S221, the predefined complementary pilots
may be detected.
[0089] For example, in the constellations of a sixth symbol and an
eighth symbol, 1024-QAM data symbols and 64-QAM complementary pilot
symbols may coexist.
[0090] Here, at step S221, only 64-QAM complementary pilot symbols
in the sixth symbol and the eighth symbol may be extracted from
input complementary pilot symbols.
[0091] Further, in the procedure at step S220, compensation
parameters may be detected at step S222.
[0092] That is, at step S222, compensation parameters may be
extracted from preset symbol ranges in symbol constellations from
which the predefined complementary pilot symbols are extracted.
[0093] The extracted complementary pilot symbols may exhibit a
remarkably high error rate in high-order symbols.
[0094] Here, at step S222, respective compensation parameters for
at least two complementary pilots may be extracted from preset
symbol ranges in the symbol constellations of at least two
complementary pilots.
[0095] In detail, at step S222, in order to correct this error
rate, low-power symbol ranges (see blue rectangular ranges in FIGS.
20 and 21) in which errors do not occur in the constellations of
the sixth symbol and the eighth symbol may be set, and compensation
parameters may be extracted based on the set symbol ranges. The
complementary pilot detection values s.sub.cp may be represented by
the above-described Equation (3).
[0096] At step S222, only complementary pilot symbols falling
within a range (x) having a predetermined size may be selected.
[0097] Here, at step S222, the range in which errors do not occur
in each of the constellations of the sixth and eighth symbols may
be set to a range of [x<c].
[0098] For example, at step S222, the range may be set to a range
of [x<0.6].
[0099] In the range of [x<0.6], each complementary pilot
detection value s.sub.cp matches a transmitted complementary pilot
value s.sub.cp without causing a symbol error. The compensation
parameters may be represented by the above-described Equation
(4).
[0100] Further, in the procedure at step S220, the complementary
pilots may be detected by applying the compensation parameters at
step S223.
[0101] In detail, at step S223, errors in the complementary pilots
may be compensated for using the compensation parameters, and
error-compensated complementary pilots may be detected.
[0102] The complementary pilot values {tilde over ({tilde over
(s)})}.sub.cp, which are error-compensated using the compensation
parameters, may be represented by the above-described Equation
(5).
[0103] Here, at step S223, when complementary pilots are detected
again after the application of the compensation parameters, the
error rate of the complementary pilots in the sixth and eighth
symbols may be `0`
[0104] The complementary pilot error rate of `0` may mean that the
sixth and eighth complementary pilots can be used as known signals
(i.e., signals agreed upon between transmission and reception
stages), such as pilots.
[0105] Furthermore, in the procedure at step S220, channel
estimation and equalization may be performed using the
error-compensated complementary pilots at step S224.
[0106] That is, at step S224, the second channel estimation value
may be calculated using the error-compensated complementary pilots,
the predefined pilots, and the first channel estimation value, and
channel equalization may be performed based on the second channel
estimation value.
[0107] FIG. 16 is a diagram illustrating the arrangement of pilots
in a pilot pattern according to an embodiment of the present
invention.
[0108] Referring to FIG. 16, the arrangement of pilots in pilot
pattern 2 of a DOCSIS 3.1 upstream system according to an
embodiment of the present invention can be seen.
[0109] FIG. 17 is a graph illustrating a Carrier Frequency Offset
(CFO) compensation process in a frequency domain according to an
embodiment of the present invention.
[0110] Referring to FIG. 17, it can be seen that the process for
compensating for a CFO in a frequency domain is illustrated.
[0111] The amount of frequency angular rotation between symbols in
the frequency domain may be calculated using the above-described
Equation (1).
[0112] FIG. 18 is a diagram illustrating a channel estimation
process according to an embodiment of the present invention.
[0113] Referring to FIG. 18, illustrated is a process for obtaining
the average of channel gains using only pilots, that is, P1 and P3
pilots, and applying the average to eight symbols in a time domain
and for interpolating the channel gains calculated in the time
domain and applying the interpolated value to a frequency
domain.
[0114] FIG. 19 is a constellation illustrating an input
complementary pilot symbol according to an embodiment of the
present invention.
[0115] Referring to FIG. 19, input complementary pilot symbols
according to an embodiment of the present invention are
illustrated.
[0116] FIG. 20 is a constellation illustrating a symbol range for
error compensation in a complementary pilot in a sixth symbol
according to an embodiment of the present invention. FIG. 21 is a
constellation illustrating a symbol range for error compensation in
a complementary pilot in an eighth symbol according to an
embodiment of the present invention.
[0117] Referring to FIGS. 20 and 21, it can be seen that the error
rate of a complementary pilot in a sixth symbol is 0.0042 and that
the error rate of a complementary pilot in an eighth symbol is 0.46
due to the influence of a sampling clock offset and a CFO
corresponding to the results of detection. That is, the drawings
show that a remarkably high error rate is exhibited in a high-order
symbol.
[0118] In order to correct this error rate, the synchronization
apparatus and method for the upstream system according to
embodiments of the present invention may set a low-power symbol
range (a blue rectangular range) in which errors do not occur in
the constellations of the sixth symbol and the eighth symbol, and
may extract compensation parameters based on the low-power symbol
range.
[0119] FIG. 22 is a constellation illustrating a complementary
pilot in an error-compensated sixth symbol according to an
embodiment of the present invention. FIG. 23 is a constellation
illustrating a complementary pilot in an error-compensated eighth
symbol according to an embodiment of the present invention.
[0120] Referring to FIGS. 22 and 23, it can be seen that, when
complementary pilots are detected again after compensation
parameters have been applied, the error rates of complementary
pilots in sixth and eighth symbols are `0`. A complementary pilot
error rate of `0` may mean that the complementary pilots in sixth
and eighth symbols can be used as known signals (i.e., signals
agreed upon between transmission and reception stages), such as
pilots.
[0121] FIG. 24 is a diagram illustrating a channel estimation
process using error-compensated complementary pilots according to
an embodiment of the present invention.
[0122] Referring to FIG. 24, it can be seen that an embodiment of
channel estimation and equalization using error-compensated
complementary pilots is illustrated.
[0123] Here, the synchronization apparatus and method for the
upstream system according to an embodiment of the present invention
may obtain the average of channel gains in a time domain using
pilots in first and third symbols indicated in the red dashed-line
rectangle, and may perform interpolation on the channel gains in a
frequency domain. Since channel estimation values using only the
pilots may be used without change, channel gain values stored in
memory may be fetched and used without an operation procedure being
performed in the channel estimation and equalization process using
the complementary pilots. However, an operation procedure must be
able to be performed on fourth to eighth symbols using newly
detected complementary pilots.
[0124] In this case, the synchronization apparatus and method for
the upstream system according to an embodiment of the present
invention may calculate the channel gain of a block indicated by a
blue dashed-line rectangle (fourth and sixth symbols) by obtaining
a time domain average using a third pilot and a sixth complementary
pilot and by obtaining a frequency domain average based on the time
domain average.
[0125] At this time, the synchronization apparatus and method for a
upstream system according to an embodiment of the present invention
may calculate the channel gain of a block indicated by a black
dashed-line rectangle (seventh and eighth symbols) by obtaining a
time domain average using sixth and eighth complementary pilots and
by obtaining a frequency domain average based on the time domain
average.
[0126] FIGS. 25 to 32 are constellations illustrating
error-compensated complementary pilots according to embodiment of
the present invention.
[0127] Referring to FIGS. 25 to 32, it can be seen that the
synchronization apparatus and method for a upstream system
according to embodiments of the present invention may perform
channel estimation and equalization based on pilots and perform
channel estimation and equalization based on error-compensated
complementary pilots. As a result, a sampling clock offset and a
Carrier Frequency Offset (CFO) in the symbol constellations
illustrated in FIGS. 3 to 10 may be compensated for, and thus
symbol constellations illustrated in FIGS. 25 to 32 may be
obtained.
[0128] FIG. 33 is a diagram illustrating a computer system
according to an embodiment of the present invention.
[0129] Referring to FIG. 33, a synchronization apparatus for a
upstream system according to an embodiment of the present invention
may be implemented in a computer system 1100, such as a
computer-readable storage medium. As illustrated in FIG. 33, the
computer system 1100 may include one or more processors 1110,
memory 1130, a user interface input device 1140, a user interface
output device 1150, and storage 1160, which communicate with each
other through a bus 1120. The computer system 1100 may further
include a network interface 1170 connected to a network 1180. Each
processor 1110 may be a Central Processing Unit (CPU) or a
semiconductor device for executing processing instructions stored
in the memory 1130 or the storage 1160. Each of the memory 1130 and
the storage 1160 may be any of various types of volatile or
nonvolatile storage media. For example, the memory 1130 may include
Read-Only Memory (ROM) 1131 or Random Access Memory (RAM) 1132.
[0130] The synchronization apparatus for the upstream system
according to an embodiment of the present invention may include one
or more processors 1110, and execution memory 1130 for storing at
least one program executed by the one or more processors 1110.
Here, the at least one program is configured to receive a signal,
calculate a first channel estimation value for the received signal
using a predefined pilot, and calculate a second channel estimation
value using a predefined complementary pilot and the first channel
estimation value.
[0131] The at least one program may be configured to extract
compensation parameters from a preset symbol range in a symbol
constellation from which the predefined complementary pilot is
extracted.
[0132] The at least one program may be configured to extract
compensation parameters for at least two complementary pilots from
preset symbol ranges in the symbol constellations of the at least
two complementary pilots.
[0133] The at least one program may be configured to compensate for
errors in the complementary pilots using the compensation
parameters.
[0134] The at least one program may calculate a second channel
estimation value using the error-compensated complementary pilots,
the predefined pilot, and the first channel estimation value, and
may perform channel equalization based on the second channel
estimation value.
[0135] The present invention may provide synchronization and
channel equalization efficient for a DOCSIS 3.1 upstream
system.
[0136] Further, the present invention may effectively eliminate
frequency and phase offsets attributable to the sampling clock
offset of a DOCSIS 3.1 upstream system.
[0137] As described above, in the synchronization apparatus and
method for a upstream system according to the present invention,
the configurations and schemes in the above-described embodiments
are not limitedly applied, and some or all of the above embodiments
can be selectively combined and configured such that various
modifications are possible.
* * * * *