U.S. patent application number 11/278274 was filed with the patent office on 2007-05-10 for communication apparatus, transmitter, receiver, and error correction optical communication system.
This patent application is currently assigned to MITSUBISHI DENKI KABUSHIKI KAISHA. Invention is credited to Seiji Kozaki, Takashi Mizuochi, Naoki Suzuki.
Application Number | 20070104225 11/278274 |
Document ID | / |
Family ID | 38003734 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070104225 |
Kind Code |
A1 |
Mizuochi; Takashi ; et
al. |
May 10, 2007 |
COMMUNICATION APPARATUS, TRANSMITTER, RECEIVER, AND ERROR
CORRECTION OPTICAL COMMUNICATION SYSTEM
Abstract
A communication apparatus includes a transmitter and a receiver,
wherein the transmitter further includes: an interleaver that
rearranges positions of bits of an information frame; an FEC
encoder that performs an error correction encoding to the
information frame whose bit positions have been rearranged; and a
selector that inserts FEC parity into predetermined positions of
the information frame, to thereby generate a transmission signal,
whereas the receiver includes: a selector that extracts an
information frame part and an FEC parity part from a reception
signal; an interleaver that rearranges positions of the bits of the
information frame part using the same rule as that used at that
transmitter side; an FEC decoder that corrects an error of bits
rearranged based on the error correction parity part; and a
de-interleaver that reproduces an information frame by returning
positions of error-corrected bits to original bit positions.
Inventors: |
Mizuochi; Takashi; (Tokyo,
JP) ; Suzuki; Naoki; (Tokyo, JP) ; Kozaki;
Seiji; (Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
MITSUBISHI DENKI KABUSHIKI
KAISHA
Chiyoda-ku
JP
|
Family ID: |
38003734 |
Appl. No.: |
11/278274 |
Filed: |
March 31, 2006 |
Current U.S.
Class: |
370/476 ;
370/392 |
Current CPC
Class: |
H03M 13/2707 20130101;
H03M 13/1515 20130101; H03M 13/17 20130101; H04L 1/0071 20130101;
H04L 1/0041 20130101 |
Class at
Publication: |
370/476 ;
370/392 |
International
Class: |
H04J 3/00 20060101
H04J003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2005 |
JP |
2005-326565 |
Claims
1. A communication apparatus that comprises a transmitting unit and
a receiving unit each of which has an error correction function,
and transmits and receives respectively a information frame
sufficiently longer than a codeword, wherein the transmitting unit
includes a first interleaver that rearranges positions of bits in
an information frame based on a predetermined rule; an error
correction encoder that carries out an error correction encoding to
the information frame whose bit positions have been rearranged; and
a transmission signal generator that inserts error correction
parities obtained by the encoding operation into predetermined
positions of the information frame, thereby generating a
transmission signal; and the receiving unit includes a reception
signal extractor that receives the transmission signal and extracts
a part corresponding to the information frame and the other part
corresponding to the error correction parities, from the thus
received transmission signal; a second interleaver that rearranges
positions of the bits in the information frame part based on the
same rule as that of the first interleaver; a decoder that corrects
an error of bits rearranged by the second interleaver, based on the
error correction parity part; and a de-interleaver that reproduces
an information frame by returning positions of the error-corrected
bits to the original bit positions.
2. The communication apparatus according to claim 1, wherein the
information frame is an Ethernet.RTM. frame.
3. The communication apparatus according to claim 1, wherein a
Reed-Solomon error correction system is used for carrying out the
error correction encoding operation.
4. A communication apparatus that comprises a transmitting unit and
a receiving unit each of which has an error correction function,
and transmits and receives respectively an information frame that
is sufficiently short to an extent that a burst error cannot be
corrected satisfactorily when the information frame is interleaved
as a single frame, wherein the transmitting unit includes a first
frame generator that generates a frame sufficiently longer than a
codeword, by combining a plurality of information frames; a first
interleaver that rearranges positions of bits in the frame
generated by the first frame generator, based on a predetermined
rule; an error correction encoder that carries out an error
correction encoding to the frame whose bit positions have been
rearranged; and a transmission signal generator that inserts error
correction parities obtained by the encoding operation, into
predetermined positions of the information frame, and the receiving
unit includes a reception signal extractor that receives the
transmission signal and extracts a part corresponding to the
information frame and the other part corresponding to the error
correction parities, from the thus received transmission signal; a
second frame generator that generates a frame sufficiently longer
than a codeword, by combining a plurality of information frames; a
second interleaver that rearranges positions of bits in the frame
generated by the second frame generator, based on the same rule as
that used by the first interleaver; a decoder that corrects an
error of bits rearranged by the second interleaver, based on the
error correction parity part; a de-interleaver that returns
positions of the error-corrected bits to the original bit
positions; and a frame divider that divides the error-corrected
frame obtained by the de-interleaver, into a plurality of the
original information frames.
5. The communication apparatus according to claim 4, wherein the
information frame is an Ethernet.RTM. frame.
6. The communication apparatus according to claim 4, wherein a
Reed-Solomon error correction system is used for carrying out the
error correction encoding operation.
7. A transmitter that transmits an information frame sufficiently
longer than a codeword, the transmitter comprising: an interleaver
that rearranges positions of bits in an information frame based on
a predetermined rule; an error correction encoder that carries out
an error correction encoding to the information frame whose bit
positions have been rearranged; and a transmission signal generator
that inserts error correction parities obtained by encoding into
predetermined positions in the information frame, thereby
generating a transmission signal.
8. A transmitter that transmits an information frame that is
sufficiently short to an extent that a burst error cannot be
corrected satisfactorily when the information frame is interleaved
as a single frame, the transmitter comprising: a frame generator
that generates a frame sufficiently longer than a codeword, by
combining a plurality of information frames; an interleaver that
rearranges positions of bits in the frame generated by the frame
generator, based on a predetermined rule; an error correction
encoder that carries out an error correction encoding to the frame
whose bit positions have been rearranged; and a transmission signal
generator that inserts error correction parities obtained by the
encoding operation, into predetermined positions of the information
frame.
9. A receiver that has an error correction function, and receives
an information frame sufficiently longer than a codeword, the
receiver comprising: a reception signal extractor that extracts a
part corresponding to an information frame and a part corresponding
to an error correction parity, from a reception signal; an
interleaver that rearranges positions of the bits in the
information frame part, based on the same rule as that used at a
transmitter side; a decoder that corrects an error of bits
rearranged by the interleaver, based on the error correction parity
part; and a de-interleaver that reproduces an information frame by
returning positions of the error-corrected bits to the original bit
positions.
10. A receiver that has an error correction function, and receives
an information frame that is sufficiently short to an extent that a
burst error cannot be corrected satisfactorily when the information
frame is interleaved as a single frame, the receiver comprising: a
reception signal extractor that extracts a part corresponding to an
information frame and a part corresponding to a plurality of error
correction parities, from a reception signal; a frame generator
that generates a frame sufficiently longer than a codeword, by
combining a plurality of information frames; an interleaver that
rearranges positions of bits in the frame generated by the frame
generator, based on the same rule as that used at a transmitter
side; a decoder that corrects an error of bits rearranged by the
interleaver, based on the error correction parity part; a
de-interleaver that returns positions of the error-corrected bits
to the original bit positions; and a frame divider that divides the
error-corrected frame obtained by the de-interleaver, into a
plurality of original information frames.
11. An error-correction optical communication system that comprises
a transmitting unit and a receiving unit each of which has an error
correction function, and transmits and receives respectively a
information frame sufficiently longer than a codeword, wherein the
transmitting unit includes a first interleaver that rearranges
positions of bits in an information frame based on a predetermined
rule; an error correction encoder that carries out an error
correction encoding to the information frame whose bit positions
have been rearranged; and a transmission signal generator that
inserts error correction parities obtained by the encoding
operation into predetermined positions of the information frame,
thereby generating a transmission signal, and the receiving unit
includes a reception signal extractor that receives the
transmission signal and extracts a part corresponding to the
information frame and the other part corresponding to the error
correction parities, from the thus received transmission signal; a
second interleaver that rearranges positions of the bits in the
information frame part based on the same rule as that of the first
interleaver; a decoder that corrects an error of bits rearranged by
the second interleaver, based on the error correction parity part;
and a de-interleaver that reproduces an information frame by
returning positions of the error-corrected bits to the original bit
positions.
12. The error-correction optical communication system according to
claim 11, wherein the information frame is an Ethernet.RTM.
frame.
13. The error-correction optical communication system according to
claim 11, wherein a Reed-Solomon error correction system is used
for carrying out the error correction encoding operation.
14. An error-correction optical communication system that comprises
a transmitting unit and a receiving unit each of which has an error
correction function, and transmits and receives respectively an
information frame that is sufficiently short to an extent that a
burst error cannot be corrected satisfactorily when the information
frame is interleaved as a single frame, wherein the transmitting
unit includes a first frame generator that generates a frame
sufficiently longer than a codeword, by combining a plurality of
information frames; a first interleaver that rearranges positions
of bits in the frame generated by the first frame generator, based
on a predetermined rule; an error correction encoder that carries
out an error correction encoding to the frame of whose bit
positions have been rearranged; and a transmission signal generator
that inserts error correction parities obtained by the encoding
operation, into predetermined positions of the information frame,
and the receiving unit includes a reception signal extractor that
receives the transmission signal and extracts a part corresponding
to the information frame and the other part corresponding to the
error correction parities, from the thus received transmission
signal; a second frame generator that generates a frame
sufficiently longer than a codeword, by combining a plurality of
information frames; a second interleaver that rearranges positions
of bits in the frame generated by the second frame generator, based
on the same rule as that used by the first interleaver; a decoder
that corrects an error of bits rearranged by the second
interleaver, based on the error correction parity part; a
de-interleaver that returns positions of the error-corrected bits
to the original bit positions; and a frame divider that divides the
error-corrected frame obtained by the de-interleaver, into a
plurality of the original information frames.
15. The error-correction optical communication system according to
claim 14, wherein the information frame is an Ethernet.RTM.
frame.
16. The error-correction optical communication system according to
claim 14, wherein a Reed-Solomon error correction system is used
for carrying out the error correction encoding operation.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an error correction optical
communication system having a forward error correction (FEC)
function, and, more particularly to an error correction optical
communication system that transmits and receives a non-interleaved
information frame.
[0003] 2. Description of the Related Art
[0004] An optical access system, a so-called "Fiber To The Home
(FTTH)", that transmits large-capacity information to houses and
offices, is being distributed rapidly. Among others, the service of
"Gigabit Ethernet (registered trademark, and hereinafter referred
to as "Ethernet.RTM.") PON (normally known as GE-PON)" that uses a
"Passive Optical Network (PON)" system is being spread rapidly as a
method of connecting Gigabit Ethernet.RTM. between a
telecommunications house and plural users, since specifications are
standardized in the IEEE Std 802.3ah.
[0005] The GE-PON has a configuration that an "Optical Line
Terminal (OLT)" as a station-side device and an "Optical Network
Unit (ONU)" as a user-side device are connected in two directions
with one optical fiber via an optical branch unit. A
point-to-multipoint connection, for example, a connection between
one OLT and 32 ONUs, is made possible by carrying out a burst
transmission and reception in which a time slot is shared among
users.
[0006] According to the GE-PON, the optical branch unit braches
power. Therefore, the optical power that each ONU receives is
attenuated to one to the number of branches, and light that the OLT
receives from each ONU is also attenuated to one to the number of
branches. Consequently, a bit error is likely to occur.
Furthermore, the fact that a laser diode having low performance is
being used to decrease the cost is also likely to cause this bit
error problem. To solve these problems, each of the OLT and the ONU
is equipped with the FEC function, and a system of correcting bit
errors whose amount is smaller than that the FEC can correct is
standardized in the IEEE Std 802.3ah.
[0007] The FEC prescribed by the "IEEE Std 802.3ah." is
Reed-Solomon (255, 239). According to this FEC, 16-byte error
correction symbols (hereinafter, "FEC parity") are added to
239-byte information data symbols, thereby structuring a block of
"239+16=255" bytes. When the Ethernet.RTM. data is smaller than 239
bytes, "zeros" are filled in the data to satisfy 239 bytes. A
starting sequence and an ending sequence are added before and after
the FEC parity to be added. When the system does not use the FEC,
the added FEC parity is disregarded, thereby carrying out
communications without changing the conventional device.
[0008] The Reed-Solomon (255, 239) error correction system has a
capacity to be able to correct up to octuple byte errors. In other
words, the Reed-Solomon (255, 239) error correction system can
correct all bit errors when the error is within eight bytes among
255 bytes. However, when a bit error occurs extending to nine
bytes, the Reed-Solomon (255, 239) cannot correct the error. In a
transmission path of actual optical communications, bit errors
occur continuously in some cases, due to a fluctuation of
polarization, non-linearity of an optical fiber, or insufficient
performance of a transmitter/receiver. Even when the total number
of bit errors that occur during a predetermined time is equal to or
smaller than the number of bit errors that the Reed-Solomon (255,
239) error correction system can correct, the errors cannot be
corrected when these bit errors are burst errors which occur during
a short period of time. To solve this problem, there is a method of
randomizing the occurrence of bit errors so that the bit errors do
not occur in burst. This method is disclosed in the ITU-T
Recommendation G.975, for example.
[0009] According to the FEC system disclosed in the ITU-T
Recommendation G.975, an FEC encoder adds the FEC parity to a
transmission information frame, and thereafter, an interleaver
changes the order of bits, at the transmission side. On the other
hand, at the reception side, a process opposite to that carried out
at the transmission side is carried out. In other words, a
de-interleaver and an FEC decoder are used to reproduce the
transmission information frame. According to the ITU-T
Recommendation G.975, the bit order is changed within 16 codewords.
For example, when a continuous burst error of 512 bits occurs in a
transmission path, 16 codewords are returned to an original bit
string in a de-interleaver at the reception side, and the error is
input as a continuous error of 32 bits (obtained by 512/16), to the
FEC decoder. In this case, the continuous 32 bits become equal to
or smaller than five bytes. Therefore, the Reed-Solomon (255, 239)
error correction system can correct all errors.
[0010] In the "IEEE Std 802.3ah" document, the standard GE-PON
device has both systems using the FEC and the system not using the
FEC. Therefore, an interleave operation of the Ethernet.RTM. data
series is not carried out. This is because when the interleave of
the Ethernet.RTM. data series is carried out, a system that does
not have a de-interleaver (not using the FEC) at the reception side
cannot receive the data. Therefore, according to the Reed-Solomon
(255, 239) error correction system that does not carry out
interleaving of the Ethernet.RTM. data series, even when one bit
error occurs for each nine bytes within one block in the
Reed-Solomon (255, 239), this block cannot be corrected in the
worst case. Consequently, the Ethernet.RTM. packet is discarded by
an Ethernet.RTM. frame check sequence. In other words, the burst
error tolerance is considerably low.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to at least solve
the problems in the conventional technology.
[0012] According to one aspect of the present invention, a
communication apparatus, which includes a transmitting unit and a
receiving unit each of which has an error correction function and
transmits and receives respectively a information frame
sufficiently longer than a codeword, is constructed such that the
transmitting unit further includes: a first interleaver that
rearranges positions of bits in an information frame based on a
predetermined rule; an error correction encoder that carries out an
error correction encoding to the information frame whose bit
positions have been rearranged; and a transmission signal generator
that inserts error correction parities obtained by the encoding
operation into predetermined positions of the information frame,
thereby generating a transmission signal, whereas the receiving
unit further includes: a reception signal extractor that receives
the transmission signal and extracts a part corresponding to the
information frame and the other part corresponding to the error
correction parities, from the thus received transmission signal; a
second interleaver that rearranges positions of the bits in the
information frame part based on the same rule as that of the first
interleaver; a decoder that corrects an error of bits rearranged by
the second interleaver, based on the error correction parity part;
and a de-interleaver that reproduces an information frame by
returning positions of the error-corrected bits to the original bit
positions.
[0013] According to another aspect of the present invention, a
communication apparatus, which includes a transmitting unit and a
receiving unit each of which has an error correction function and
transmits and receives respectively an information frame that is
sufficiently short to an extent that a burst error cannot be
corrected satisfactorily when the information frame is interleaved
as a single frame, is constructed such that the transmitting unit
further includes: a first frame generator that generates a frame
sufficiently longer than a codeword, by combining a plurality of
information frames; a first interleaver that rearranges positions
of bits in the frame generated by the first frame generator, based
on a predetermined rule; an error correction encoder that carries
out an error correction encoding to the frame of whose bit
positions have been rearranged; and a transmission signal generator
that inserts error correction parities obtained by the encoding
operation, into predetermined positions of the information frame,
whereas the receiving unit further includes: a reception signal
extractor that receives the transmission signal and extracts a part
corresponding to the information frame and the other part
corresponding to the error correction parities; from the thus
received transmission signal, a second frame generator that
generates a frame sufficiently longer than a codeword, by combining
a plurality of information frames; a second interleaver that
rearranges positions of bits in the frame generated by the second
frame generator, based on the same rule as that used by the first
interleaver; a decoder that corrects an error of bits rearranged by
the second interleaver, based on the error correction parity part;
a de-interleaver that returns positions of the error-corrected bits
to the original bit positions; and a frame divider that divides the
error-corrected frame obtained by the de-interleaver, into a
plurality of the original information frames.
[0014] According to still another aspect of the present invention,
a transmitter that transmits an information frame sufficiently
longer than a codeword is construed such that it includes: an
interleaver that rearranges positions of bits in an information
frame based on a predetermined rule; an error correction encoder
that carries out an error correction encoding to the information
frame whose bit positions have been rearranged; and a transmission
signal generator that inserts error correction parities obtained by
encoding into predetermined positions in the information frame,
thereby generating a transmission signal.
[0015] According to still another aspect of the present invention,
a transmitter that transmits an information frame, which is
sufficiently short to an extent that a burst error cannot be
corrected satisfactorily when the information frame is interleaved
as a single frame, is constructed such that it includes: a frame
generator that generates a frame sufficiently longer than a
codeword, by combining a plurality of information frames; an
interleaver that rearranges positions of bits in the frame
generated by the frame generator, based on a predetermined rule; an
error correction encoder that carries out an error correction
encoding to the frame whose bit positions have been rearranged; and
a transmission signal generator that inserts error correction
parities obtained by the encoding operation, into predetermined
positions of the information frame.
[0016] According to still another aspect of the present invention,
a receiver that has an error correction function, and receives an
information frame sufficiently longer than a codeword, is
constructed such that it includes: a reception signal extractor
that extracts a part corresponding to an information frame and a
part corresponding to an error correction parity, from a reception
signal; an interleaver that rearranges positions of the bits in the
information frame part, based on the same rule as that used at a
transmitter side; a decoder that corrects an error of bits
rearranged by the interleaver, based on the error correction parity
part; and a de-interleaver that reproduces an information frame by
returning positions of the error-corrected bits to the original bit
positions.
[0017] According to still another aspect of the present invention,
a receiver, which has an error correction function, and receives an
information frame that is sufficiently short to an extent that a
burst error cannot be corrected satisfactorily when the information
frame is interleaved as a single frame, is constructed such that it
includes: a reception signal extractor that extracts a part
corresponding to an information frame and a part corresponding to a
plurality of error correction parities, from a reception signal; a
frame generator that generates a frame sufficiently longer than a
codeword, by combining a plurality of information frames; an
interleaver that rearranges positions of bits in the frame
generated by the frame generator, based on the same rule as that
used at a transmitter side; a decoder that corrects an error of
bits rearranged by the interleaver, based on the error correction
parity part; a de-interleaver that returns positions of the
error-corrected bits to the original bit positions; and a frame
divider that divides the error-corrected frame obtained by the
de-interleaver, into a plurality of original information
frames.
[0018] According to still another aspect of the present invention,
an error-correction optical communication system includes a
transmitting unit and a receiving unit constructed as disclosed
above, each of which has an error correction function, and
transmits and receives respectively an information frame which is
sufficiently longer than a codeword.
[0019] According to still another aspect of the present invention,
an error-correction optical communication system includes a
transmitting unit and a receiving unit constructed as disclosed
above, each of which has an error correction function, and
transmits and receives respectively an information frame that is
sufficiently short to an extent that a burst error cannot be
corrected satisfactorily when the information frame is interleaved
as a single frame.
[0020] The other objects, features, and advantages of the present
invention are specifically set forth in or will become apparent
from the following detailed description of the invention when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a configuration example of an error correction
optical communication system according to the present
invention;
[0022] FIG. 2A is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0023] FIG. 2B is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0024] FIG. 2C is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0025] FIG. 2D is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0026] FIG. 2E is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0027] FIG. 2F is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0028] FIG. 3A is one example of an Ethernet.RTM. frame which is
made an FEC frame;
[0029] FIG. 3B is another example of an Ethernet.RTM. frame which
is made an FEC frame;
[0030] FIG. 4 is still another example of an Ethernet.RTM. frame
which is made an FEC frame;
[0031] FIG. 5 is a configuration example of the error correction
optical communication system;
[0032] FIG. 6A is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0033] FIG. 6B is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0034] FIG. 6C is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0035] FIG. 6D is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0036] FIG. 6E is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0037] FIG. 6F is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0038] FIG. 6G is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
[0039] FIG. 6H is an explanatory diagram of a flow of transmission
and reception processes in the error correction optical
communication system;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Exemplary embodiments of an error correction optical
communication system according to the present invention are
explained below in detail with reference to the accompanying
drawings. Note that the invention is not limited to the
embodiments.
[0041] FIG. 1 is a configuration example of an error correction
optical communication system according to a first embodiment of the
present invention. The error correction optical communication
system includes a transmitter 1 as a communication apparatus at a
transmission side, and a receiver 2 as a communication apparatus at
a reception side. The transmitter 1 includes an interleaver 11, and
an FEC encoder 12, a buffer 13 and a selector 14. The receiver 2
includes a selector 21, an interleaver 22, an FEC decoder 23 and a
de-interleaver 24. In this embodiment, communications are carried
out in one direction from the transmitter 1 to the receiver 2 to
simplify the explanation. However, in the actual system, each
communication apparatus has both a transmitter and a receiver, and
can achieve communications in both directions.
[0042] In FIG. 1, the transmitter 2 branches a received
transmission information frame into two. In those two paths, the
interleaver 11 changes the order of the bits that constitute the
transmission information frame, based on a predetermined rule, and
the FEC encoder 12 carries out an error correction encoding,
thereby generating an FEC parity. In the other path, the buffer 13
adds a delay to the transmission information frame for the time
period required to carry out the interleave and the error
correction. The selector 14 adds the FEC parity to a predetermined
position of the transmission information frame received via the
buffer 13, thereby generating a transmission signal.
[0043] On the other hand, the receiver 2 receives the transmission
signal that receives the influence of noise in the transmission
path. The selector 21 divides the received signal into an
information frame part and an FEC parity part. The interleaver 22
changes the order of bits of the information frame part in the same
order as that carried out by the interleaver 11 at the transmitter
1 side. Furthermore, the FEC decoder 23 carries out the error
correction using the FEC parity extracted in the selector 21.
Thereafter, the de-interleaver 24 returns the order of the bits of
the error-corrected information frame to the original order.
Finally, the de-interleaver 24 of the receiver 2 outputs the bits
whose positions have been rearranged, as a reception information
frame.
[0044] The operation of the error correction optical communication
system is explained in detail below with reference to the drawings.
FIGS. 2A to 2F are explanatory diagrams of a flow of transmission
and reception processes in the error correction optical
communication system. Specifically, the flow includes the encoding
of a transmission information frame, and the reproduction of the
reception information from the reception signal.
[0045] FIG. 2A depicts one example of a transmission information
frame. In this example, one transmission information frame is
divided into four sub-frames (1) to (4). FIG. 2B depicts a bit
string after the interleaver 11 and the FEC encoder 12 of the
transmitter 1 carried out the process. The interleaver 11 divides
the sub-frame into four sub-frames, and arranges the divided pieces
in the order of the sub-frames (a) to (d). The FEC parities,
corresponding to A, B, C, and D in FIG. 2B, are added respectively
to the four-piece blocks after the interleaving operation is
carried out. Each of the four-piece blocks and the FEC parities
added to each of the four-piece blocks constitute one codeword. On
the transmission path, the transmission signal (corresponding to
the output of the selector 14) is transmitted in a state that the
FEC parities are inserted into the four non-interleaved
sub-frames.
[0046] FIG. 2C depicts the output of the selector 21 of the
receiver 2. A state that a burst error has occurred in the
sub-frame (2) due to a noise on the transmission path is shown. The
selector 21 selectively outputs the sub-frame part (corresponding
to the information frame part) and the FEC parity part. FIG. 2D
depicts a state that the interleaver 22 of the receiver 2 changes
the order of the bits. The order of the bits is changed based on
the same rule as that used at the transmission side, and the burst
error that has occurred in the sub-frame (2) is allocated to four
different codewords.
[0047] FIG. 2E depicts a state that the FEC decoder 23 has
corrected all the errors. For example, even when a burst error that
cannot be corrected straight has occurred as shown in FIG. 2C, the
interleaver 22 can correct the burst error by allocating the error
to plural codewords. FIG. 2F depicts a state that the
de-interleaver 24 has reproduced original sub-frames (1) to
(4).
[0048] In the error correction optical communication system
according to this embodiment, it is important that the transmission
information frame is sufficiently longer than the error correction
codewords and those plural sub-frames can be interleaved. The
method of interleaving is not limited to that described above, and
the positions of the bits of the information frame can be
rearranged based on any rule.
[0049] As explained above, according to this embodiment, the
communication apparatus at the transmission side generates the FEC
parities using the interleaver and the FEC encoder, and inserts the
FEC parities into the transmission information frame and sends this
frame. The communication apparatus at the reception side extracts
the error information frame and the FEC parities from the received
signal. Furthermore, the interleaver rearranges the order of bits
of the extracted information frame based on the same rule as that
used at the transmission side. The FEC decoder corrects the
information frame whose bit positions are rearranged, using the
extracted FEC parities. Finally, the de-interleaver rearranges the
bits of the error-corrected reception information frame, based on
the rule opposite to the used above. The frame obtained as a result
of rearranging the bits is output as the reproduced reception
information frame. Consequently, a burst error can be corrected
satisfactorily, without requiring the communication apparatus at
the transmission side to send the interleaved signal.
[0050] An error correction optical communication system according
to a second embodiment is explained below. The error correction
optical communication system has the same configuration as that of
the first embodiment shown in FIG. 1.
[0051] FIGS. 3A and 3B depict an example of an Ethernet.RTM. frame
which is made an FEC frame (codeword). In this case, the
Ethernet.RTM. frame corresponds to the above transmission
information frame. The Ethernet.RTM. frame is prescribed by the
"IEEE Std 802.3ah."
[0052] Specifically, FIG. 3A depicts that all areas other than the
FEC parities are to be interleaved, and FIG. 3B depicts that only
the Ethernet.RTM. frame is to be interleaved. In FIGS. 3A and 3B,
S_FEC denotes a marker that expresses the head of the FEC frame,
and T_FEC denotes a marker that expresses the tail of the FEC
frame. The whole frames shown in FIGS. 3A and 3B correspond to one
codeword, i.e., correspond to one of the four codewords shown in
FIG. 2B. The FEC frames shown in FIG. 3A, FIG. 3B, and FIG. 4 are
8B-to-10B converted in the transmission path. A byte of eight bits
that constitute the FEC frame and a byte as one unit of the
8B-to-10B conversion are byte-synchronized so that the header bits
of these bytes coincide with each other. By carrying out the
byte-synchronization, propagation of a bit error that has occurred
in the transmission path to plural bytes of the FEC frames can be
prevented. When an original Ethernet.RTM. frame (the Ethernet.RTM.
frame before dividing) is not sufficiently longer than the
codeword, the area which is short is filled with dummy bits by a
virtual calculation of the FEC parity. The dummy bits are virtual,
and are not actually present in the serial bit string to be
transmitted to the transmission path.
[0053] As explained above, according to this embodiment, when the
Ethernet.RTM. frame is to be applied to the error correction
optical communication system, it is made an FEC frame (codeword) as
shown in FIGS. 3A and 3B. In other words, the Ethernet.RTM. frame
is divided into plural sub-frames, and the plural sub-frames are
interleaved as described above. Based on this arrangement, the same
effect as that achieved in the first embodiment can be also
achieved in the system using the Ethernet.RTM. frame.
[0054] An error correction optical communication system according
to a third embodiment is explained below. The error correction
optical communication system has the same configuration as that of
the first embodiment shown in FIG. 1. In this embodiment, the
Ethernet.RTM. frame that is made an FEC frame (codeword) is
explained like in the second embodiment.
[0055] In this embodiment, the Reed-Solomon (255, 239) error
correction system is used as the FEC, thereby achieving excellent
error correction capacity. FIG. 4 depicts one example in which the
Ethernet.RTM. frame is made an FEC frame (codeword). In this
example, 239 bytes include the Ethernet.RTM. frame, S_FEC, and
T_FEC, and 16 bytes include the FEC parity. Accordingly, one
codeword (corresponding to four codewords shown in FIG. 2B) is
formed in the total 255 bytes. In this embodiment, the
Ethernet.RTM. frame is divided into sub-frames, and plural
sub-frames are interleaved (as shown in FIGS. 2A and 2B), thereby
generating the FEC parities, in a similar manner to that described
above.
[0056] As explained above, in this embodiment, the Reed-Solomon
codes having a high error correction capacity are used as the FEC
to the error correction optical communication system shown in the
first embodiment. Based on this arrangement, the same effect as
that achieved in the first and the second embodiments can be also
achieved, and a general-purpose system can be obtained.
[0057] An error correction optical communication system according
to a fourth embodiment is explained below. In this embodiment, the
error correction optical communication system can achieve a similar
effect to that of the above embodiments, even in a case in which
one transmission information frame is short, and thus a
satisfactory burst error correction effect cannot be achieved when
the transmission information frame is interleaved as a single
frame. This is explained below.
[0058] FIG. 5 is a configuration diagram of the error correction
optical communication system according to the fourth embodiment of
the present invention. The error correction optical communication
system includes a transmitter 1a as a communication apparatus at a
transmission side, and a receiver 2a as a communication apparatus
at a reception side. The transmitter 1a includes a framer 15a, in
addition to the configuration of the first embodiment. The receiver
2a includes a framer 25a, and a de-framer 26a, in addition to the
configuration of the first embodiment. Configurations similar to
those explained in the first to the third embodiments are not
explained herein.
[0059] In this embodiment, even in a case in which one transmission
information frame is short, and a satisfactory burst error
correction effect cannot be achieved when the transmission
information frame is interleaved as a single frame, a frame
sufficiently longer than the codeword is formed by combining plural
transmission information frames as in the above embodiments. The
burst error is corrected using this long frame. Specifically, in
FIG. 5, for example, the framers 15a and 25a generate one frame by
combining plural short transmission frames. The de-framer 26a
disassembles the bit string, which is de-interleaved by the
de-interleaver 24 in advance, into an original short transmission
information frame, thereby generating the reception information
frame.
[0060] The operation of the error correction optical communication
system according to this embodiment is explained in detail below
with reference to the drawings. FIGS. 6A to 6H are explanatory
diagrams of a flow of transmission and reception processes in the
error correction optical communication system. Specifically, the
flow includes the encoding of a transmission information frame, and
the reproduction of the reception information from the reception
signal.
[0061] FIG. 6A depicts one example of a transmission information
frame. In this example, each of transmission information frames (1)
to (4) (shown by "Information" in FIG. 6A) has only the same length
as that of a codeword that constitutes an error correction code.
FIG. 6B depicts an output of the framer 15a that combines the four
transmission information frames to compose one frame. FIG. 6C
depicts a bit string after the interleaver 11 and the FEC encoder
12 of the transmitter 1a carry out the process. The interleaver 11
divides the frame generated by the framer 15a, into four frames,
and arranges the divided pieces in the order of (a) to (d). The FEC
parities, corresponding to A, B, C, and D in FIG. 6A, are added
respectively to the four-piece blocks after the interleaving
operation is carried out. Each of the four-piece blocks and the FEC
parities added to each of the four-piece blocks constitute one
codeword. On the transmission path, the transmission signal,
corresponding to the output of the selector 14, is transmitted in
the state that the FEC parities are inserted into the four
non-interleaved transmission information frames.
[0062] FIG. 6D depicts the output of the selector 21 of the
receiver 2a. A state that a burst error has occurred in the
information frame (2) due to a noise on the transmission path is
shown. The selector 21 selectively outputs the information frame
part and the FEC parity part. FIG. 6E depicts a state that the
interleaver 22 of the receiver 2a changes the order of the bits.
The order of the bits is changed based on the same rule as that
used at the transmission side, and the burst error that has
occurred in the information frame (2) is allocated to four
different codewords.
[0063] FIG. 6F depicts a state that the FEC decoder 23 has
corrected all the errors. Even when a burst error that cannot be
corrected straight has occurred as shown in FIG. 6D, the
interleaver 22 can correct the burst error by allocating the error
into plural codewords. FIG. 6G depicts a state that the
de-interleaver 24 has reproduced the original frame by combining
the four transmission information frames. FIG. 6H depicts a state
that the de-framer 26a divides the frame shown in FIG. 6G, thereby
generating the reception information frame.
[0064] As explained above, according to this embodiment, even in a
case in which one transmission information frame is short, and thus
a satisfactory burst error correction effect cannot be achieved
when the transmission information frame is interleaved as a single
frame, the framers 15a, 25a and the de-framer 26a can interleave
the frame as plural transmission information frames. Accordingly,
when a burst error as shown in FIG. 6D occurs, the burst error can
be corrected satisfactorily, like in the above embodiments.
[0065] According to the present invention, a burst error can be
corrected satisfactorily, without requiring the communication
apparatus at the transmission side to send the interleaved
signal.
[0066] Although the invention has been described with respect to a
specific embodiment for a complete and clear disclosure, the
appended claims are not to be thus limited but are to be construed
as embodying all modifications and alternative constructions that
may occur to one skilled in the art that fairly fall within the
basic teaching herein set forth.
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