JP2008294510A - Optical signal receiver, and receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a probability that an error correction is successful even when the error correction can not be made so far since a bit error exceeding the error correcting capability of an FEC decoder occurs to a transmission line. <P>SOLUTION: An optical receiver has a first FEC decoder 10a which corrects the error of data of each FEC frame having been synchronized using parity for error correction and decodes the data, a synchronization header correcting unit 10b which corrects the value of a synchronization header which can not be taken theoretically among values of the synchronization header whose decoding by the first FEC decoder 10a has ended in failure into the value of the synchronization header indicative of packet data and/or the value of the synchronization header indicative of idle data, and a second FEC decoder 10c which corrects the error of the FEC data and decodes the data again on the basis of the FEC frame having the synchronization header corrected by the synchronization header correcting unit 10b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical signal receiver and reception method used in a PON optical communication system.

  Using the optical data communication network between the station side equipment OLT (Optical Line Terminal: optical subscriber line terminal equipment) and a plurality of home side equipment ONU (Optical Network Unit: optical subscriber line termination equipment) In particular, there is a practical single-star network configuration in which a single optical fiber is used between the station-side device OLT and each home-side device ONU. This network configuration simplifies the system and equipment configuration, but if one home-side device ONU occupies one optical fiber and there are N home-side device ONUs, it is directly connected from the station-side device OLT. N optical fibers are required, and it is difficult to reduce the cost of the system.

Therefore, a PON (Passive Optical Network) communication system in which one optical fiber drawn from the station side device OLT is shared by a plurality of home side devices ONU has been put into practical use. The PON optical communication system is one of low-cost access methods for optical subscribers that have been applied to FTTx such as FTTH (Fiber To The Home) and FTTB (Fiber To The Building).
In the PON optical communication system, one station side is passed through a passive optical branching device (optical coupler) that splits and multiplexes the signal passively from the input signal without the need for external power supply. The device OLT and a plurality of home-side devices ONU are connected by an optical transmission line. The station-side apparatus OLT and the N-station home-side apparatus ONU are based on 1-to-N transmission connected via an optical fiber SMF and an optical coupler OC. Thereby, many home side apparatuses ONU can be allocated with respect to one station side apparatus OLT, and the whole installation cost can be held down.

  In the PON optical communication system, since the optical transmission path between the station side device OLT and the optical branching unit is shared by a plurality of home side devices ONU, the direction from the home side device ONU to the station side device OLT (hereinafter referred to as the uplink direction). ), It is necessary to take measures to avoid collision of optical signals transmitted from each home-side apparatus ONU. For this reason, the station side apparatus OLT controls the optical signal transmission timing of each home side apparatus ONU by the time division access control system.

With this time-division access control method, each home-side apparatus ONU sends out an optical signal divided at a certain time from each home-side apparatus ONU. An optical signal transmitted from each home-side apparatus ONU in this way is called a “burst optical signal”.
This burst optical signal is composed of an FEC (Forward Error Collection) frame including a parity for error correction.

The FEC decoder of the station side apparatus OLT performs error correction / decoding of the data of the FEC frame in units of FEC frames using the error correction parity included in the received burst optical signal.
JP 11-163738 A

However, in the FEC algorithm (such as Reed-Solomon code) used in the FEC encoder, the ability to correct an error is determined, and if an error exceeding that ability is included in the received FEC frame, the error cannot be corrected. Therefore, when a bit error exceeding the error correction capability of the FEC decoder occurs in the transmission path, the error cannot be corrected.
For example, in the case of the Reed-Solomon code (255, 239), an error of up to 8 data in 255 data can be corrected, but if it exceeds that, the error cannot be corrected.

  An object of the present invention is to receive an optical signal capable of increasing the probability of successful error correction even if a bit error exceeding the error correction capability of the FEC decoder has occurred in the transmission line and error correction has not been possible so far. And a receiving method.

  In the optical signal receiver of the present invention, the FEC frame is composed of a block composed of a synchronization header and packet data and / or a block composed of a synchronization header and idle data. The value of the synchronization header for the first FEC decoder that performs error correction / decoding of the data of the FEC frame using the parity for error correction and the FEC frame that has failed to be decoded by the first FEC decoder A synchronization header correction unit that corrects a synchronization header value having a theoretically impossible value to a synchronization header value indicating packet data and / or a synchronization header value indicating idle data, and the synchronization header correction unit The error correction / recovery of the FEC data is performed again based on the FEC frame after the synchronization header is corrected by the A second FEC decoder for, characterized in that it comprises a.

In the optical signal receiver having this configuration, for the FEC frame that has failed to be decoded, the value of the synchronization header having a value that cannot be theoretically taken out of the values of the synchronization header, the value of the synchronization header indicating packet data, and / or Alternatively, the number of error bits can be reduced because the synchronization header value indicating idle data is corrected.
Therefore, conventionally, when a bit error exceeding the error correction capability of the FEC decoder has occurred, error correction cannot be performed. However, in the present invention, the number of bit errors can be expected to be less than or equal to the error correction capability of the FEC decoder. Error correction capability by FEC can be improved.

The “value that cannot theoretically be taken” is a value that is neither a value of a synchronization header indicating packet data nor a value of a synchronization header indicating idle data.
The synchronization header correction unit is a synchronization header in which the synchronization header value of the block before the block or the synchronization header value of the block after the block indicates packet data with respect to the block having the value of the synchronization header that cannot be theoretically taken. If the value is, the value of the synchronization header of the block is preferably corrected to the value of the synchronization header indicating the packet data.

Also, if the value of the synchronization header of the previous block or the synchronization header of the subsequent block is the value of the synchronization header indicating idle data, the value of the synchronization header of the block is set to the value of the synchronization header indicating idle data. It is preferable to correct it.
This is because packet data and idle data rarely exist in only one block in the FEC frame, and usually exist across multiple blocks. Therefore, the synchronization header of the block before the block or the block after the block This is because the probability that it can be corrected to the correct value of the synchronization header increases if the value is corrected with reference to the value of the synchronization header.

  The optical signal receiving method of the present invention is a method according to the invention substantially the same as the invention of the optical signal receiver.

  As described above, according to the present invention, the number of bit errors can be expected to be equal to or less than the error correction capability of the FEC decoder even when a bit error exceeding the error correction capability of the FEC decoder has conventionally occurred and the error cannot be corrected. The error correction capability by FEC can be improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram illustrating a configuration example of a PON optical communication system.
In the PON optical communication system, a station side device OLT provided in a station building and a home side device ONU provided in a plurality of subscribers are connected via an optical fiber SMF and an optical coupler OC.
The home-side apparatus ONU includes a network interface for connecting a terminal for enjoying an optical network service, such as a personal computer installed in a subscriber's home.

The optical coupler OC is composed of a star coupler that passively branches and multiplexes a signal from an input signal without requiring an external power supply.
The optical fibers connected to the station-side device OLT, the optical coupler OC, the optical coupler OC, and the home-side device ONU are single mode fibers each composed of one optical fiber SMF. That is, one station side device OLT is connected to one optical coupler OC through one trunk optical fiber SMF. One optical coupler OC is connected to M second optical couplers OC (M is a number of 4 in this example) by an optical fiber SMF. The second optical coupler OC is connected to N units (N is a number of 8 or less in this example) of home-side devices ONU by branch optical fibers SMF. Therefore, a signal transmitted / received by one station-side device OLT is distributed to a maximum of 32 home-side devices ONU by 1 + M optical couplers OC. Note that the numbers of the optical couplers OC and the home-side devices ONU are merely examples.

  The communication system of the embodiment of the present invention incorporates the technology of 10 Gigabit Ethernet (Ethernet is a registered trademark) into the PON optical communication system, and is optical at a baseband speed of 10.3125 Gbps. The 10GE-PON (Gigabit Ethernet-Passive Optical Network) system that realizes fiber access section communication is adopted.

According to the 10GE-PON system, the communication between the station side device OLT and the home side device ONU is performed in units of variable length frames.
First, a downlink frame that enters the station side apparatus OLT from the higher level network is subjected to a predetermined bridge process in the station side apparatus OLT, and a logical link to be relayed is specified. Then, it is transmitted to the optical fiber SMF as an optical signal through the station side device OLT. The optical signal transmitted to the optical fiber SMF is branched by the optical coupler OC and transmitted to the home-side device ONU connected to the optical coupler OC. Only the home-side device ONU constituting the logical link receives a predetermined optical signal. Capture and relay frame to home network interface.

  On the other hand, the upstream optical signal includes an upstream frame from each home-side apparatus ONU. The upstream optical signal needs to be transmitted so that the optical signals from the respective home devices ONU do not compete with each other in time. For this purpose, the station side device OLT allocates a window (hereinafter simply referred to as a window) during which an upstream optical signal may be transmitted to each home side device ONU, and notifies it as a control frame. The home apparatus ONU to which the window is assigned transmits an upstream optical signal to the assigned window. This upstream optical signal is referred to as a “burst optical signal”. The burst optical signal is a finite-time optical signal sequence which is transmitted from each home-side apparatus ONU and whose light emission state is changed by a 10.3125 Gbps baseband signal.

Therefore, the competition of the upstream optical signal between each home-side apparatus ONU is avoided. Each home-side apparatus ONU, when given a certain window, may transmit frames continuously as long as it fits in that window.
The station apparatus OLT can receive a burst optical signal including a series of frame signals from each home apparatus ONU.

Note that the optical signal waveform and optical signal intensity received by the station side device OLT differ depending on the characteristics of the optical transmission line such as the characteristics of the light emitting element of the home side device ONU and the length of the optical fiber SMF. Therefore, the station side device OLT performs a predetermined process on the upstream burst optical signal, and then transmits the restored significant frame sequence to the upper network.
FIG. 2 is a diagram illustrating the format of the upstream burst optical signal. The burst optical signal is composed of a burst effective frame portion and a burst synchronization portion. The burst effective frame portion is composed of an FEC frame in which parity data for FEC is added to information to be sent. The burst synchronization unit includes a preamble unit (repetition of bit 01) for bit synchronization and a delimiter unit (66 bits) for FEC frame synchronization.

FIG. 3 is a diagram illustrating the structure of the FEC frame. This FEC frame is a unit for encoding and decoding error correction codes.
The FEC frame is composed of an FEC information part and an FEC parity part. Data is stored in the FEC information part, and parity data for error correction calculated from the FEC information part is stored in the FEC parity part. A unit of data included in the FEC information part and the FEC parity part is referred to as a “block”. In the embodiment of the present invention, the 64B / 66B code is used for data transmission, and hence it is referred to as a “66B block”. The 66B block consists of 66 bits, of which 64 bits are transmission data, and 2 bits are a synchronization header SH (SH) for synchronization.

In the FEC information part, a plurality of 66B blocks sent from the 64B / 66B transmission part 2 (see FIG. 4) are stored. The FEC parity part is composed of a plurality of 66B blocks for storing packet data, and this also has a structure in which two bits of the synchronization header SH (SH) are added, like the FEC information part.
Here, the concept of packet idle will be described. A packet is a unit of data contained in a burst optical signal. The length of one packet is variable from 64 bytes to 1522 bytes. One packet can be sent in one burst optical signal, and a plurality of packets can be sent. When sending multiple packets, there is an idle between the packets. The idle is a minimum of 10 bytes.

On the other hand, the FEC frame is obtained by dividing a byte sequence composed of a packet and an idle into fixed bytes (every 239 bytes if Reed-Solomon 255: 239). In other words, the FEC frame is a frame in which the transmission data string is cut into pieces at fixed lengths without being aware of the beginning or end of the packet.
FIG. 4 is a block diagram showing a simplified configuration of a PON optical communication system using the 64B / 66B code from the home side apparatus ONU of the present invention to the station side apparatus OLT. Only one home device ONU is depicted.

  The optical transmission unit of the home-side apparatus ONU includes a 64B / 66B transmission unit 2 that receives 64-bit data from an upper layer (MAC layer). The 64B / 66B transmission unit 2 adds a 2-bit synchronization header SH (SH) for each 64-bit unit data constituting the burst optical signal and converts it to 66 bits (as described above, this is called a block) Send to scrambler 3. The scrambler 3 scrambles the 64-bit data portion. The scrambler 3 sends scrambled 64-bit data and a synchronization header SH to the FEC encoder 4. These 64-bit data and the synchronization header SH constitute the FEC information section. The FEC encoding unit 4 adds the FEC parity unit to the FEC information unit, generates an FEC frame, and sends it to the parallel / serial conversion unit 5 (P / S). The parallel / serial conversion unit 5 converts a plurality of bits of parallel data into serial signals of one bit, and the converted serial signal is converted into an optical signal by an electrical / optical conversion unit 6 (E / O conversion). Sent to an optical fiber.

The optical signal receiving unit of the station side device OLT converts the burst optical signal that has entered from the optical fiber into an electric signal by the optical / electrical conversion unit 8 (O / E conversion), and the serial / parallel conversion unit 9 (S / P). ) The serial / parallel converter 9 converts the serial signal into a 66-bit parallel signal and sends it to the FEC decoder 10.
The FEC decoding unit 10 detects the FEC frame in the burst synchronization frame unit (see FIG. 2) and performs processing for synchronization. After synchronization is established, error correction of received data is performed using FEC parity for each FEC frame. The error-corrected received data is descrambled by the descrambler 11. Thereafter, the 66B / 64B receiving unit 12 performs 64B / 66B decoding processing, removes the 2-bit synchronization header SH, and passes it to the MAC layer.

The FEC decoding function according to the first invention will be described below.
FIG. 5 is a detailed functional block diagram of the FEC decoding unit 10 of the optical signal receiving unit of the station side apparatus OLT.
The FEC decoding unit 10 synchronizes with the first FEC decoder 10a that performs error correction / decoding of data having a length of 1 FEC frame from the boundary of the FEC frame using the FEC parity for each FEC frame with which synchronization has been established. An SH correction unit 10b that corrects the header SH and a second FEC decoder 10c that corrects and decodes received data again based on the FEC frame after the synchronization header correction is provided. The function of the SH correction unit 10b is realized by the computer of the station side apparatus OLT executing a program recorded on a predetermined medium such as a CD-ROM or a hard disk.

  The data of the FEC frame input to the first FEC decoder 10a is subjected to error correction processing by the first FEC decoder 10a. The error correction capability of the first FEC decoder 10a and the second FEC decoder 10b is limited. For example, if the Reed-Solomon code (255, 239) is used, as described in [Background Art], an error of 9 data or more is required. Is included in the FEC decoder, the error cannot be corrected and the FEC decoding fails.

When the first FEC decoder 10a succeeds in the FEC decoding, the first FEC decoder 10a deletes the FEC parity part and outputs the FEC data after the deletion to the descrambler 11.
When the FEC decoding fails in the first FEC decoder 10a, the FEC frame is supplied to the SH correction unit 10b.

  The SH correction unit 10b checks the value of the synchronization header SH of the 66B block. The value of the sync header SH of the 66B block is normally “01” or “10”. If “01”, it means that the packet data is contained in the next 64 bytes of the synchronization header SH. “10” means that idle data is contained in the next 64 bytes of the synchronization header SH.

  FIG. 6 shows a relationship between a packet data area constituting a packet in the FEC frame and an idle data area existing between the packets. In FIG. 6, / D / indicates packet data, and / I / indicates idle data. In the idle data / I /, since the synchronization header SH of the 66B block is “10”, the idle data area can be specified by looking at the synchronization header SH. In the packet data / D /, since the synchronization header SH of the 66B block is “01”, the packet data area can be specified based on the synchronization header SH.

On the other hand, when the synchronization header SH is “00” or “11”, it is considered that the result is an obvious bit error. Therefore, when the value of the synchronization header SH is “00” or “11”, the synchronization header is referred to by referring to the value of the synchronization header of the 66B block before the 66B block or the value of the synchronization header of the subsequent 66B block. The value of SH is changed to those values.
(A) When the value of the synchronization header SH is “00” or “11”, the value of the synchronization header of the 66B block before N (N is an integer of 1 or more) or after N is “01”. If it is, it is assumed that it was originally "01" but became "00" or "11" due to a transmission error, and is corrected to "01". (B) If the value of the synchronization header SH is “00” or “11”, if the value of the synchronization header of the 66B block before N or after N is “10”, it is originally “10”. Is considered to have become “00” or “11” due to a transmission error, and is corrected to “10”.

  Although the identification method of the integer N is not limited, For example, the following method is employable. (1) When the value of the synchronization header SH of the 66B block is “00” or “11”, first, N = 1 is set, the synchronization header of the 66B block N blocks before is referred to, and the synchronization header SH When the value is “01” or “10”, the value of “00” or “11” of the 66B block is changed to that value. (2) If the value of the sync header SH of the 66B block before N is not “01” or “10”, the sync header SH of the 66B block after N is referred to and the value of the sync header SH is “ If it is 01 "or" 10 ", the value of" 00 "or" 11 "in the 66B block is changed to that value. (3) If the value of the synchronization header SH of the 66B blocks after N is not “01” or “10”, the processing of (1) to (2) is performed with N = 2. Thereafter, N is incremented by one and the search is continued until the value “01” or “10” of the synchronization header SH is found.

  The order of reference in this way is one block before, one block behind, two blocks before, two blocks back, etc., and so on. Refer until the header is found. Instead of referring to the previous block first, the subsequent block may be referred to first. If it is not found by referring to a predetermined number of blocks, it is replaced with a value determined either "01" or "10". The predetermined number and whether to select “01” or “10” are set in advance.

  In addition, if a previous predetermined number of blocks are referred to, such as the previous block, the previous block, the previous block, and so on, and if a proper synchronization header is not found, the next block, A predetermined number of blocks behind may be referred to, such as two blocks behind. Instead of referring to the previous block first, the subsequent block may be referred to first. In this case as well, if a predetermined number of blocks are not found, the value is replaced with a value determined as “01” or “10”. The predetermined number and whether to select “01” or “10” are set in advance.

In this way, the value of the synchronization header SH of the 66B block can be corrected to “01” or “10”.
The reason why the value of the synchronization header SH of the 66B block is rewritten using the value of the synchronization header of the 66B block before or after the 66B block in this way is usually that the packet data area is 64 bytes. In many cases, it exceeds 64 bytes (as described above, the length of one packet is variable from 64 bytes to 1522 bytes). Therefore, the packet data area often exists over a plurality of 66B blocks. Therefore, if the value of the sync header SH of the 66B block is rewritten using the value of the sync header of the 66B block before or after the 66B block, the value of the sync header SH after the rewrite becomes a correct value. There are many. Since the length of the idle data area is often more than 64 bytes rather than 64 bytes, the same can be said for the packet data area.

  Therefore, if such correction is performed, the possibility of reducing the number of bit errors within the error correction capability of the FEC decoder increases. This is because, as can be seen from FIG. 6, one FEC frame actually includes a plurality of (for example, about 30) synchronization headers SH. Therefore, even if there are a considerable number of bit errors in one FEC frame, for example, about 10 to 20, if most of the bit errors are caused by the synchronization header SH, the correction of these synchronization headers SH is performed. This is because the number of bit errors may be significantly reduced.

The SH correction unit 10b sends the corrected FEC frame to the second FEC decoder 10c. The second FEC decoder 10c tries FEC decoding again.
As described above, the FEC decoding succeeds by the second FEC decoder 10c, and the probability that correct Ethernet data is decoded by error correction increases.
Next, the FEC decoding function according to the second invention will be described.

FIG. 7 is a detailed functional block diagram of the FEC decoding unit 10 of the optical signal receiving unit of the station side apparatus OLT.
The FEC decoding unit 10 includes, for each FEC frame in which synchronization is established, a first FEC decoder 10a that performs error correction / decoding of data having a length of 1 FEC frame from the boundary of the FEC frame using the FEC parity, A replacement unit 10d, a scrambler 10e, and a second FEC decoder 10c that performs error correction / decoding of received data again based on the FEC frame after replacement of idle data are provided. The functions such as the idle data identification / replacement unit 10d are also realized by the computer of the station side apparatus OLT executing a program recorded on a predetermined medium such as a CD-ROM or a hard disk.

FIG. 6 is a diagram showing the relationship between the packet data area constituting the packet in the FEC frame and the idle data area existing between the packets, as described in the previous embodiment.
In FIG. 6, in the idle data / I /, the synchronization header SH of the 66B block is “10”, so that the 64-bit area corresponding to the idle data area can be specified by looking at the synchronization header SH. .

Therefore, the idle data identification / replacement unit 10d regards the 66B block having the synchronization header SH value “10” as a block including idle data.
Since the 64-bit data of the 66B block is composed of idle data, it becomes a fixed idle pattern of 0x1E000000_00000000. As described with reference to FIG. 4, the 64-bit data of the fixed idle pattern is The scrambler 3 provided in the ONU optical transmitter is scrambled.

Therefore, the idle data identification / replacement unit 10d calculates 64-bit data that will be scrambled from the fixed idle pattern, and replaces the received 64-bit data of the 66B block with the calculated value.
Here, the reason for “calculating 64-bit data that will be scrambled from the fixed idle pattern” will be described. The scramble conversion code adopted by the transmission side scrambler 3 is not always a constant value, and feedback is applied by data transmitted in the past. That is, even if the data X is input, the scrambled value of the data X becomes a different value according to the value Y input before the X. Therefore, the idle data identification / replacement unit 10d stores the previously input value Y and the scrambled result y, predicts the scrambled conversion code from the stored contents, and the data X is input. If so, the scrambled result x is calculated.

The function of the idle data specifying / replacement unit 10d will be described with reference to a flowchart (FIG. 8) in accordance with this embodiment.
FIG. 8 is a flowchart for explaining the function of the idle data identification / replacement unit 10d. FIG. 9 is a schematic explanatory diagram showing the relationship between the descrambled data and the data after the descrambled data.

First, the idle data identification / replacement unit 10d searches for a synchronization header in the FEC frame in which FEC decoding has failed (step S1), and identifies the first 66B block B ₁ whose synchronization header SH is “10” (step S1). Step S2).
The first 66B block whose synchronization header SH is “10” is represented by B ₁ , and the idle data therein is I ₁ . If it is identified idle data I _1, based on the relationship between packet data D _n of the 66B block B ₀ received before that, sets the scramble conversion codes s ₁ used for the idle data I ₁ (step S3).

When the scrambled conversion code s ₁ is set in this way, the idle data 0x1E000000 — 00000000 (fixed idle pattern; referred to as i ₀ ) is scrambled using the code s ₁ (step S4).
Then, the data I ₁ of the 66B block B ₁ is replaced with the scrambled data s ₁ · i ₀ .

Next, the process returns to step S2, and the next 66B block B ₂ whose synchronization header SH is “10” is specified (step S2).
The next 66B block in which the synchronization header SH is “10” is represented by B ₂ , and the idle data therein is I ₂ . If idle data I ₂ is specified, based on the relationship between the idle data I ₁ of the 66B block B ₁ received before that, sets the scramble conversion code s ₂ used for the idle data I ₂ (step S3).

When the scrambled conversion code s _{2 is} set in this way, the idle data 0x1E000000_00000000 (fixed idle pattern i ₀ ) is scrambled using the code s ₂ (step S4).
Then, the data I ₂ of the 66B block B ₁ is replaced with the scrambled data s ₂ · i ₀ .

Thereafter, the same replacement process is performed for the next 66B blocks B ₃ , B ₄ , B ₅ and the like.
The reason why the idle data i ₀ that is a fixed idle pattern is used to replace the received 64-bit data of the 66B block is that if there is a data error in the idle data of the 66B block, the data This is because the data can be changed to data s ₁ · i ₀ with no data error.

Even if there is no data error, the idle data is changed to idle data s ₁ · i ₀ based on the fixed idle pattern, but there is no actual harm caused by this change.
In this manner, idle data that may contain bit errors can always be replaced with correct idle data, and as a result, a reduction in the number of errors in the FEC frame can be expected. Therefore, there is a high possibility that the number of bit errors can be accommodated within the error correction capability of the FEC decoder. The reason why the parity data is not replaced is that the content of the parity data is information to be transmitted and is not constant while the content of the idle data is a fixed idle pattern.

As a result, when the number of bit errors decreases within the error correction capability of the FEC decoder, the second FEC decoder 10c succeeds in FEC decoding, and correct Ethernet data can be acquired.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

It is the schematic which shows the structural example of the PON optical communication system which connected between the control station apparatus OLT and several terminal device ONU with the optical fiber via the optical coupler. It is a frame configuration diagram of a burst optical signal transmitted from the home side apparatus ONU to the station side apparatus OLT. It is a figure which shows the internal structure of one FEC frame. It is the block diagram showing the structure of the PON optical communication system from the home side apparatus ONU to the station side apparatus OLT. It is a detailed functional block diagram of the FEC decoding part of the optical signal receiving part of the station side apparatus OLT based on 1st invention. It is detail drawing which shows the internal structure of a FEC frame. It is a detailed functional block diagram of the FEC decoding part of the optical signal receiving part of the station side apparatus OLT based on 2nd invention. It is a flowchart for demonstrating the function of the idle data specific and replacement part 10d. It is typical explanatory drawing which shows the relationship with the data after having been descrambled data.

Explanation of symbols

2 64B / 66B Transmitter 3 Scrambler 4 FEC Encoder 5 Parallel / Serial Converter 6 Electrical / Optical Converter 8 Optical / Electric Converter 9 Serial / Parallel Converter 10 FEC Decoder 11 Descrambler 12 64B / 66B Receiver 10a First FEC decoder 10b SH correction unit 10c Second FEC decoder 10d Idle data identification / replacement unit 10e Scrambler

Claims (4)

An optical signal receiver installed in an optical communication system for transmitting an optical signal,
An optical signal transmitted through the optical transmission line includes an FEC frame including parity for error correction,
The FEC frame is composed of a block consisting of a synchronization header and packet data and / or a block consisting of a synchronization header and idle data.
A first FEC decoder that performs error correction / decoding of data of the FEC frame using the parity for error correction for each FEC frame with which synchronization is established;
For an FEC frame that has failed to be decoded by the first FEC decoder, a value of the synchronization header having a value that cannot be theoretically taken out of the values of the synchronization header, a value of the synchronization header indicating packet data, and / or idle data A synchronization header correction unit for correcting the value of the synchronization header to indicate
An optical signal receiver comprising: a second FEC decoder that performs error correction / decoding of FEC data again based on the FEC frame after the synchronization header is corrected by the synchronization header correction unit. The synchronization header correction unit
For a block having a value of the synchronization header having a value that cannot be theoretically taken, if the value of the synchronization header of the previous block or the value of the synchronization header of the subsequent block is a value of the synchronization header indicating packet data, The optical signal receiver according to claim 1, wherein the value of the synchronization header of the block is corrected to a value of a synchronization header indicating packet data. The synchronization header correction unit
For a block having a value of the synchronization header having a value that cannot be theoretically taken, if the value of the synchronization header of the block before the block or the value of the synchronization header of the subsequent block is a value of the synchronization header indicating idle data, The optical signal receiver according to claim 1, wherein the value of the synchronization header of the block is corrected to a value of a synchronization header indicating idle data. An optical signal receiving method used in an optical communication system for transmitting an optical signal,
An optical signal transmitted through the optical transmission line includes an FEC frame including parity for error correction,
The FEC frame is composed of a block consisting of a synchronization header and packet data and / or a block consisting of a synchronization header and idle data.
For each FEC frame with which synchronization has been established, using the error correction parity, error correction / decoding of the data of the FEC frame is performed,
For an FEC frame that has failed to be decoded by the first FEC decoder, a value of the synchronization header having a value that cannot be theoretically taken out of the values of the synchronization header, a value of the synchronization header indicating packet data, and / or idle data To the value of the sync header indicating
An optical signal receiving method for performing error correction / decoding of FEC data again based on the FEC frame after the synchronization header is corrected by the synchronization header correction unit.

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