JP2015056735A - Communication system and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system and a communication method, which can avoid deterioration of transmission efficiency even if an error correction encoding system is applied.SOLUTION: A communication system includes: a PON for connecting one OLT and a plurality of ONUs via an optical power splitter; hierarchical modulation means for transmitting a hierarchical modulation signal obtained by multiplexing downlink data to the ONUs from the OLT; data distribution means for distributing the downlink data to one of hierarchies of the hierarchical modulation signal; and error correction means for setting at least one of an error correction encoding system and redundancy of the error correction encoding system for each hierarchy to which the data distribution means distributes the downlink data.

Description

  The present invention relates to a communication system in which a PON is constructed and a communication method thereof.

  In the optical access network, a PON (Passive Optical Network) method is widely adopted. FIG. 7 shows an example of a PON system. Until now, in the PON system, the transmission capacity has been expanded by increasing the symbol rate and the number of wavelengths used. However, the symbol rate is limited by analog devices, and the number of wavelengths that can be used is also finite. Therefore, effective use of wavelengths is required for further expansion of transmission capacity.

  It has been studied to improve the transmission capacity without increasing the symbol rate and the number of wavelengths by using a multi-level modulation method capable of transmitting a plurality of bits with one modulation symbol. As an application example of multi-level modulation for downlink communication, a hierarchical modulation PON system has been proposed (see Patent Document 1). The hierarchical modulation PON system of Patent Document 1 includes an optical transmitter that transmits a multilevel / higher order modulation signal composed of a plurality of layers in downlink communication. This optical transmitter refers to a correspondence table in which addresses of each ONU and receivable layers are stored in association with each other, and determines the modulation layer of each frame according to the destination address of the transmission frame. Such a hierarchical modulation PON system divides a plurality of transmission frames into hierarchies so that data for a plurality of users can be transmitted simultaneously at one wavelength.

  As an example, a hierarchical modulation PON system using a star 8-QAM modulated signal will be described. The star 8-QAM modulated signal can be transmitted in 3 bits with one modulation symbol. Therefore, modulation is performed using 1 bit of each of three separate data, and three data are multiplexed on one modulation symbol. Thereby, three data can be transmitted simultaneously by one wavelength. These three data may be different destinations, or at least two or more data may have the same destination.

  Hereinafter, transmission / reception of data using the i-th bit is expressed as using the i-th lane. The modulation signal of the hierarchical modulation PON system is not limited to the star 8-QAM modulation signal, and an arbitrary modulation multilevel number QAR modulation signal and an arbitrary modulation multilevel number QAM modulation signal can be used.

  FIG. 8 shows an apparatus configuration example of the hierarchical modulation PON system.

  The optical line terminal unit (OLT) 100 is a data distribution unit that distributes downlink data addressed to each optical terminal unit (ONU) to each lane for downlink communication. 11, a buffer 12 that stores data for each lane, a multi-value signal generator 13 that creates a data signal using 1 bit from the buffer 12 of each lane, and an E / O converter that converts the data signal into an optical signal 14 The data distribution unit 11 corresponds to the bit position determination unit of Patent Document 1, the buffer 12 and the multilevel signal generation unit 13 correspond to the parallel / serial conversion and encoding of Patent Document 1, and the E / O conversion unit 14 is patented. This corresponds to the modulator of Document 1.

  The data signal is a signal generated based on the data addressed to the ONU, and is used to distinguish it from a control signal described later. The multilevel signal generation unit 13 generates a multilevel signal such as a star-QAM modulation signal or a QAM modulation signal. The number of bits that can be transmitted with one symbol of the modulation signal = the number of lanes. The E / O converter 14 converts an electrical signal into an optical signal by direct modulation or external modulation.

  The OLT 100 includes an O / E conversion unit 15 that converts a received optical signal into an electric signal and a multilevel signal decoding unit 16 that demodulates the signal for uplink communication. Regarding uplink communication, the OLT of the hierarchical modulation PON system and the OLT of the existing PON system have the same device configuration.

  Examples of data distribution by the data distribution unit 11 are shown in FIGS. 9 and 10, star 8-QAM is used, and data # i (i = 1, 2, 3) addressed to ONU # i is distributed to the 1st to 3rd lanes. Assuming that ONU # 1 can correctly receive signals from the 1-bit lane, ONU # 2 from 1 to 3 bits, and ONU # 3 from 1 to 3 lanes, the OLT 100 performs data # in the data distribution unit 11. 1 is assigned to the 1-bit lane, data # 2 is assigned to the 1st to 3rd lane, and data # 3 is assigned to the 1st to 3rd lane. When allocating data # 2 and data # 3, the buffer amount of each lane may be seen and control may be performed so as to distribute to lanes with a small buffer amount. Since ONU # 1 has few lanes that can be communicated and ONU # 2 and ONU # 3 have many lanes that can be communicated, data # 1 is assigned to lane 1 of the first bit rather than data # 2 and data # 3. By preferentially allocating, the fairness between ONUs can be improved.

  The ONU 200 includes an O / E converter 21 that converts a received optical signal into an electrical signal for downlink communication, a multi-level signal decoder 22 that outputs bits included in the multi-level signal for each lane, and a multi-level signal. A buffer 23 for storing the output of the decoding unit 22 and a data extraction unit 24 for extracting downlink data addressed to itself in the buffer and discarding downlink data of other destinations from the buffer 23 are provided. The multi-level signal decoding unit 22 performs operations such as star-QAM demodulation and QAM demodulation.

  The ONU 200 includes a multi-level signal generation unit 25 that modulates an input bit sequence and an E / O conversion unit 26 that converts an electrical signal into an optical signal for uplink communication. Regarding the uplink, the ONU of the hierarchical modulation PON system and the ONU of the existing PON system have the same device configuration.

  7 and 8 can improve the error rate by using an error correction code. For example, Reed-Solomon codes are used in GE-PON and 10G-EPON. GE-PON and 10G-EPON have the same error correction coding method but have different redundancy. Redundancy is the ratio of the number of bits before error correction coding to the number of bits after error correction coding. As the redundancy is set higher, the required reception sensitivity can be reduced, but the transmission efficiency decreases. For example, in the case of a 10G-EPON Reed-Solomon code, the transmission efficiency is reduced by about 12.5% compared to the case where no error correction code is used. If the minimum redundancy that satisfies the required communication quality is set, transmission efficiency reduction due to the use of error correction codes can be minimized.

JP 2012-222456 A

  In the PON system, the transmission quality between OLT and ONU differs for each ONU. For example, OLT-ONU communication with a long transmission distance has a large transmission loss, so the transmission quality is low, and OLT-ONU communication with a short transmission distance has a low transmission loss, so the transmission quality is high. Therefore, if redundancy is set high so that data can be correctly decoded to ONUs with relatively low transmission quality, and if redundancy can be set low for ONUs with relatively good transmission quality, the same redundancy is used for all ONUs. Compared to the case, the transmission efficiency can be improved.

  However, in the downstream communication of the PON system, the OLT broadcasts data addressed to each ONU, and each ONU demodulates and decodes all received signals and extracts only the data addressed to itself. For this reason, it is necessary to determine the redundancy so that all ONUs can correctly decode the data. Therefore, the same redundancy is used for all ONUs, leading to a reduction in transmission efficiency.

  The introduction of an error correction code into the hierarchical modulation PON system has not been studied so far, and the device configuration has not been determined. If the error correction code is directly introduced into the hierarchical modulation PON system as in Patent Document 1, the same redundancy is used for all ONUs as in the conventional PON system, so that it is expected that the transmission efficiency is lowered.

  Therefore, an object of the present invention is to provide a communication system and a communication method that can avoid a decrease in transmission efficiency even when an error correction code method is applied.

  In order to achieve the above object, according to the present invention, the encoding method and redundancy are determined for each lane of the hierarchical modulation PON system.

Specifically, the communication system according to the present invention is:
A PON that connects one OLT and a plurality of ONUs via an optical power splitter;
Hierarchical modulation means for transmitting a hierarchical modulation signal in which one or more downlink data from the OLT to the ONU is multiplexed;
Data distribution means for distributing the downlink data to any hierarchy;
Error correction means for adjusting at least one of the redundancy of the error correction coding scheme or the error correction coding scheme for each layer of the hierarchical modulation signal;
Multi-level signal decoding means for outputting a bit sequence for each hierarchy of the hierarchical modulation signal;
Error correction decoding means for error correction decoding the bit sequence for each layer; and
Is provided.

Further, the communication method according to the present invention includes:
A communication method in a PON that connects one OLT and a plurality of ONUs via an optical power splitter,
A hierarchical modulation procedure for transmitting a hierarchical modulation signal in which downlink data from the OLT to the ONU is multiplexed;
A data distribution procedure for distributing the downlink data to any one of the layers;
An error correction procedure for setting at least one of an error correction coding scheme and a redundancy of the error correction coding scheme for each of the layers to which the downlink data is sorted in the data sorting procedure;
I do.

  In the present invention, the data distribution unit distributes the downlink data to any lane (hierarchy) of the hierarchical modulation signal, the hierarchical modulation unit generates the hierarchical modulation signal in which the downlink data is multiplexed, and the error correction unit Determine the redundancy scheme. Further, the present invention provides a multi-level signal decoding procedure for outputting a bit sequence for each layer of the hierarchical modulation signal when receiving downlink data, and an error correction decoding procedure for performing error correction decoding for the bit sequence for each layer. ,I do. Therefore, the present invention can set an appropriate redundancy method for each layer, and can avoid setting an excessive redundancy method and lowering the transmission efficiency.

  Therefore, the present invention can provide a communication system and a communication method that can avoid a decrease in transmission efficiency even when an error correction code method is applied.

  The error correction means of the communication system according to the present invention adjusts at least one of the error correction coding scheme or the redundancy of the error correction coding scheme in the OLT and transmits the downlink from the OLT to the ONU. The ONU is notified of the adjusted error correction coding scheme or redundancy of the error correction coding scheme performed based on quality information. Since the present invention selects a redundancy scheme based on transmission quality information, it can flexibly cope with variations in transmission quality.

  The error correction means of the communication system according to the present invention sets at least one of an error correction coding scheme that can be decoded by all the ONUs or redundancy of the error correction coding scheme to at least one of the layers. . For example, a control signal transmitted and received between the OLT and the ONU needs to be received by all the ONUs. For this reason, any one lane is set to a redundancy system that can be handled by all ONUs, and a control signal is transmitted in the lane.

  In the communication system according to the present invention, the error correction means performs frequency multiplexing, time multiplexing, or wavelength multiplexing of at least one of the error correction coding scheme or the redundancy of the error correction coding scheme on the downlink data, and Notify ONU.

  The data distribution means of the communication system according to the present invention forms a group of ONUs based on downlink transmission quality information from the OLT to the ONU, and allocates one or a plurality of the layers to each group. Since lanes grouped with ONUs having relatively good transmission quality can communicate using lower redundancy than other lanes, transmission efficiency is improved.

  The data distribution means of the communication system according to the present invention distributes the downlink data to one of the layers based on downlink transmission quality information from the OLT to the ONU. The present invention maintains transmission quality by estimating a lane in which each ONU can correctly demodulate a signal and allocating data addressed to the ONU only to the lane even when the modulation method that each ONU can demodulate is not constant. Can do.

  The data distribution means and the error correction means of the communication system according to the present invention distribute the downlink data to the hierarchy and the error correction coding so that an average frequency use efficiency between the OLT and the ONU is maximized. At least one of the redundancy of the scheme or the error correction coding scheme is adjusted. Average frequency utilization efficiency can be increased.

  The above inventions can be combined as much as possible.

  The present invention can provide a communication system and a communication method that can avoid a decrease in transmission efficiency even when an error correction code method is applied.

It is a figure explaining the communication system which concerns on this invention. It is a figure explaining the example of the bit mapping in the communication system which concerns on this invention. It is a figure explaining the communication system which concerns on this invention. It is a figure explaining the communication system which concerns on this invention. It is a figure explaining the communication system which concerns on this invention. It is a figure explaining the communication system which concerns on this invention. It is a figure explaining PON. It is a figure explaining the communication system which performs hierarchical modulation. It is a figure explaining hierarchical modulation. It is a figure explaining hierarchical modulation.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 1 is a diagram illustrating a communication system 301 according to the present embodiment. The communication system 301 is
A PON that connects one OLT 101 and a plurality of ONUs 201 via an optical power splitter 150;
Hierarchical modulation means for transmitting a hierarchical modulation signal in which one or more downlink data from the OLT 101 to the ONU 201 is multiplexed;
Data distribution means for distributing the downstream data to any one of the tiers (lanes);
Error correction means for adjusting at least one of the redundancy of the error correction coding scheme or the error correction coding scheme for each layer of the hierarchical modulation signal;
Multi-level signal decoding means for outputting a bit sequence for each hierarchy of the hierarchical modulation signal;
Error correction decoding means for error correction decoding the bit sequence for each layer; and
Is provided.

  For downlink communication, the OLT 101 has an error correction encoding unit 31 that performs error correction encoding on an input bit sequence and an error correction that determines an error correction encoding method for each lane in the configuration of the OLT 100 in FIG. It further has an encoding method determination unit 32. The buffer 12 is notified of the error correction encoding method from the error correction encoding method determination unit 32 and outputs a bit sequence for each number of input bits of the error correction encoding method. The error correction encoding unit 31 uses the error correction encoding method notified of the error correction encoding method from the error correction encoding method determination unit 32 and performs error correction encoding on the bit sequence output from the buffer 12. Do. The error correction coding method indicates at least one of the type of error correction code and the redundancy of the error correction code.

  The OLT 101 has an error correction decoding unit 33 that performs error correction decoding on the demodulated signal in the configuration of the OLT 100 in FIG. 8 for uplink communication. With respect to uplink communication, the OLT device configuration is the same as that when an error correction code is introduced into an existing PON system.

  The ONU 201 has an error correction decoding unit 41 that performs error correction decoding on a bit sequence for each lane and an error correction that determines an error correction coding method for each lane in the configuration of the ONU 200 in FIG. 8 for downlink communication. It further has an encoding method determination unit 42. The error correction decoding unit 41 performs error correction decoding on the input bit sequence using the error correction encoding method notified from the error correction encoding method determination unit 42.

  The ONU 201 includes an error correction encoding unit 43 that performs error correction encoding on an input bit sequence in the configuration of the ONU 200 in FIG. 8 for uplink communication. With regard to downlink communication, the ONU device configuration is the same as that when an error correction code is introduced into an existing PON system.

  In the communication system 301, the hierarchical modulation means corresponds to the buffer 12 and the multilevel signal generation unit 13, the distribution means corresponds to the data distribution unit 11, and the error correction means includes the error correction encoding unit 31 and the error correction encoding. The multi-level signal decoding unit corresponds to the scheme determination unit 32, the multi-level signal decoding unit corresponds to the multi-level signal decoding unit 22, the buffer 23, and the data extraction unit 24. The error correction decoding unit corresponds to the error correction decoding unit 41 and the error correction coding determination unit. 42.

Subsequently, a method in which the error correction coding method determination unit (32, 42) determines the error correction coding method will be described.
First, a method of determining according to the ONU using each lane is conceivable. For example, in a hierarchical modulation PON system using a star 8-QAM, an existing ONU that uses an OOK modulation signal and a new ONU that uses a star 8-QAM modulation signal coexist. Since the existing ONU uses the OOK modulation signal, only the 1st bit lane is used, and the new ONU uses the 1st to 3rd lanes. Therefore, the error correction coding method determination unit (32, 42) determines the error correction coding method of the 1-bit lane in which the existing ONU exists so as to satisfy the required reception sensitivity of the existing ONU and the new ONU, and the new ONU. The error correction coding method for the 2nd to 3rd lanes, which only exists, is determined so as to satisfy the required reception sensitivity of the new ONU.

  As another method for determining the error correction coding method, a method for determining each lane according to the bit mapping of the modulation method is conceivable. For example, in a hierarchical modulation PON system using 16QAM, 4-bit transmission is possible with one modulation symbol, but the error rate of each bit may not be the same. For example, in the bit mapping example of FIG. 2, the signal points are arranged at equal intervals, but the signal points of 0 and 1 are more adjacent in the third and fourth bits than in the first and second bits. Therefore, the error rate is high. Therefore, the error correction coding method determination unit (32, 42) corrects the error so that the required reception sensitivity is satisfied in the first and second bit lanes having a relatively low error rate and the third and fourth bit lanes having a relatively high error rate. Determine the encoding method.

  In the present embodiment and the following embodiments, any error correction coding scheme can be applied. The error correction coding system refers to Reed-Solomon code, BCH code, convolutional code, turbo code, LDPC code, two or more concatenated codes, and the like.

(Embodiment 2)
In this embodiment, downlink transmission quality information is exchanged between each OLT-ONU, and an error correction coding method for each lane is determined based on the transmission quality information.

  FIG. 3 is a diagram illustrating the communication system 302 according to the present embodiment. In the communication system 302, the error correction unit described in the communication system 301 of FIG. 1 adjusts at least one of the error correction coding scheme and the redundancy of the error correction coding scheme in the OLT 102 to the downlink transmission quality. The ONU 202 is notified of the adjusted error correction coding scheme or the redundancy of the error correction coding scheme, and the data distribution means transmits the downlink data based on downlink transmission quality information. It is characterized by allocating to one of the hierarchies.

  For downlink communication, the OLT 102 has a control signal generation unit 51 for generating a control signal for notifying the ONU of the error correction coding scheme of each lane in the configuration of the OLT 101 of FIG. 1, and a control signal and a data signal. A multiplexing unit 52 for multiplexing is provided. The error correction coding method determination unit 32 determines an error correction coding method for each lane based on the transmission quality information. The multiplexing unit 52 in FIG. 3 multiplexes the data signal and the control signal by frequency multiplexing.

  For uplink communication, the OLT 102 has the configuration of the OLT 101 in FIG. 1, a separation unit 53 that separates a received signal into a data signal and a transmission quality notification signal, and transmission quality information from the transmission quality notification signal that the separation unit 53 outputs. A transmission quality information extraction unit 54 for extraction is provided.

  The ONU 202 has a configuration of the ONU 201 in FIG. 1 for downlink communication, and a separation unit 61 that separates a received signal into a data signal and a control signal, and control information extraction that extracts control information from the control signal output by the separation unit 61 Part 62. The error correction decoding unit 41 performs error correction decoding on the bit sequence from the multi-level signal decoding unit 22 using the error correction coding method notified by the control information.

  The ONU 202 generates a signal for notifying the OLT of the estimated transmission quality information and the transmission quality estimation unit 63 that estimates the transmission quality between the OLT and the ONU in the configuration of the ONU 201 in FIG. 1 for uplink communication. A transmission quality notification signal generation unit 64 and a multiplexing unit 65 that multiplexes the transmission quality notification signal and the data signal. The transmission quality estimation unit 63 estimates the transmission quality using the received signal power of the downlink communication, the average error detection number of the error correction decoding unit 41 of the downlink communication, or the like.

  The OLT 102 has a distribution lane determination unit 55. The distribution lane determination unit 55 may allocate one fixed lane to each ONU, or allocate a plurality of receivable lanes to each ONU, and the data distribution unit 11 selects a lane for each data frame and selects data. You may decide to distribute.

  In addition, the distribution lane determination unit 55 may distribute the downlink data to the lane based on downlink transmission quality information. For example, the distribution lane determination unit 55 forms a group of ONUs based on downlink transmission quality information, and allocates one or a plurality of layers to each group. Based on the transmission quality information from the transmission quality information extraction unit 54, the distribution lane determination unit 55 groups ONUs so that ONUs with similar transmission quality gather, and causes the data distribution unit 11 to set a different lane for each group. . Then, the error correction coding method determination unit 32 determines the error correction coding method for each lane so that the ONU can correctly decode the signal. In this case, since the lanes grouped by ONUs having relatively good transmission quality can perform communication using a lower redundancy than other lanes, the transmission efficiency is improved. At this time, the number of ONUs allocated to each lane may be adjusted so that the communication opportunities of each ONU are fair. Note that the distribution lane determination unit 55 may not be provided, and the error correction coding method determination unit 32 may group ONUs and instruct the data distribution unit 11.

  In FIG. 3, the data signal and the control signal are multiplexed by frequency multiplexing.

  FIG. 4 is a device configuration example of a communication system 303 that multiplexes a data signal and a control signal by wavelength multiplexing. In downlink communication, the OLT 103 converts a data signal and a control signal into optical signals of different wavelengths and multiplexes them. In downlink communication, the ONU 203 converts an optical signal into an electrical signal for each wavelength, and extracts a data signal and a control signal from each. The same applies to uplink communication.

  FIG. 5 is a device configuration example of a communication system 304 that multiplexes a data signal and a control signal by time multiplexing. The OLT 104 inputs a data signal and a control signal to the data distribution unit 11 in downlink communication. The transmission quality information extraction unit 54 of the OLT 104 may be the same as other PON control signal separation units. The ONU 204 has a data and control information extraction unit 62 c in downlink communication, extracts data and control signals addressed to itself, and inputs the control signals to the error correction decoding unit 41. In the configuration of FIG. 5, the control signal and the transmission quality information can be transmitted using the reserved bits of the GATE / REPORT frame existing in the existing PON system.

  The error correction means sets at least one of an error correction coding scheme that can be decoded by all the ONUs or redundancy of the error correction coding scheme to at least one of the layers. The control signal transmitted from the OLT must be able to be extracted by all ONUs. As a technique for this purpose, a method is conceivable in which an error correction coding method for a specific lane is set so that all ONUs can correctly extract signals, and a control signal is transmitted using that lane. In this case, the error correction coding scheme of the lane is not changed. As another method, a method of determining an error correction coding method so that the ONU can correctly extract a signal in any lane and transmitting a control signal in all lanes can be considered. The ONU can receive a control signal from any lane.

  The error correction coding method may be determined at an arbitrary timing. When the error correction coding method is periodically changed, it is necessary to have the ONU periodically transmit a transmission quality notification signal.

  The error correction encoding method at the start of operation may be set so that all ONUs can correctly extract data.

(Embodiment 3)
In downlink communication of the PON system, the modulation scheme that can be demodulated by each ONU may not be constant. A case where a QAM modulation signal is used will be described as an example. For example, an ONU with high transmission quality can demodulate 16QAM or 64QAM, but an ONU with low transmission quality can demodulate only QPSK. Here, when the OLT multiplexes M QPSK modulation signals and transmits a 2 ^2M QAM modulation signal, if the ONU performs 2 ^2N QAM demodulation (N is an integer equal to or less than M), the ONU has the 1st to 2Nth bits. Lane data can be retrieved.

  Therefore, in this embodiment, transmission quality information of downlink communication is exchanged between each OLT-ONU, and not only the OLT determines an error correction coding method based on the transmission quality information, but each ONU correctly transmits a signal. A communication system that estimates lanes that can be demodulated and distributes data addressed to the ONU only to the lanes will be described.

  FIG. 6 is a diagram illustrating the communication system 305 of the present embodiment. The communication system 305 is characterized in that the data distribution unit described in the communication system 301 of FIG. 1 distributes the downlink data to one of the layers based on downlink transmission quality information.

  For downlink communication, the OLT 105 has a configuration of the OLT 101 in FIG. 1, a distribution lane determination unit 55 that determines to which lane the data addressed to each ONU is allocated based on the transmission quality information, and each of the configurations based on the transmission quality information. An error correction coding method determination unit 32 that determines an error correction coding method of a lane, a control signal generation unit 51 that generates a control signal for notifying the determined distribution lane and the error correction coding method of each lane, It further includes a multiplexing unit 52 that multiplexes the control signal and the data signal. The buffer 12 notified of the error correction coding scheme outputs a bit sequence for each number of input bits of the error correction coding scheme. The error correction encoding unit 31 performs error correction encoding on the bit sequence from the buffer 12 in accordance with the notified error correction encoding method. The multiplexing unit 52 in FIG. 6 multiplexes the data signal and the control signal by frequency multiplexing.

  For uplink communication, the OLT 105 uses the configuration of the OLT 101 in FIG. 1 to separate the received signal into a data signal and a transmission quality notification signal, and transmission quality information from the transmission quality notification signal output from the separation unit 53. It further has a transmission quality information extraction unit 54 for extraction.

  The ONU 205 has a configuration of the ONU 201 in FIG. 1 for downlink communication, and a separation unit 61 that separates a received signal into a data signal and a control signal, and control information extraction that extracts control information from the control signal output by the separation unit 61 A portion 62 is further included. The multi-level signal decoding unit 22 performs demodulation according to the modulation scheme notified by the control information. The error correction decoding unit 41 performs error correction decoding on the bit sequence from the multilevel signal decoding unit 22 by the error correction encoding method notified by the control information.

  For uplink communication, the ONU 205 has a transmission quality estimation unit 63 that estimates the transmission quality between the OLT and the ONU in the configuration of the ONU 201 in FIG. 1 and a transmission quality that generates a signal for notifying the estimated transmission quality information. A notification signal generation unit 64 and a multiplexing unit 65 that multiplexes the transmission quality notification signal and the data signal are included.

  As described in the second embodiment, this embodiment can use not only frequency multiplexing but also wavelength multiplexing and time multiplexing. The control signal in the case of time multiplexing is transmitted in a lane using the modulation method with the lowest multi-level number so that all ONUs can be extracted.

  As a method of determining the distribution lane and the error correction coding method, a method of determining so that the average frequency use efficiency between OLT and ONU is maximized can be considered. That is, the data distribution unit and the error correction unit distribute the downlink data to the hierarchy and the error correction encoding method or the error correction encoding so that the average frequency use efficiency between the OLT and the ONU is maximized. Adjust at least one of the system redundancy.

The average frequency utilization efficiency between OLT and ONU is
_{(Σn i × (1-r} i)) / N ONU
It can be expressed as Here, _{n i} is ONU number retrieve data correctly from the i-th bit, the _{r i} redundancy of i-th bit of the _{lane, N ONU} is the ONU number under OLT. Increasing r _i increases n _i . For this reason, it is necessary to exchange information between the distribution lane determination unit 55 and the error correction coding method determination unit 32 to determine the distribution lane and the error correction coding method.

[Appendix]
The following describes the communication system of the present embodiment.
<Issues>
In the downlink communication of the PON system, since the same error correction coding method is used in each OLT-ONU communication, excessive redundancy is set in the OLT-ONU communication with good transmission quality, and the transmission efficiency is lowered. It leads to.
<Solution>
By determining the error correction coding method for each lane of the hierarchical modulation PON system, the transmission efficiency is improved.

(1):
A communication system that changes at least one of an error correction coding scheme or redundancy of an error correction coding scheme for each lane of a hierarchical modulation PON system.
(2):
OLT changes at least one of the error correction coding scheme and the redundancy of the error correction coding scheme based on downlink transmission quality information transmitted from the ONU, and the error correction coding scheme and the error are changed. The system according to (1) above, wherein the redundancy of the correction coding system is notified to the ONU.
(3):
The transmission quality information of the downlink transmitted from the ONU and the error correction coding scheme and the redundancy of the error correction coding scheme to be notified to the ONU are either frequency multiplexed, time multiplexed or wavelength multiplexed. The system according to (2) above, wherein transmission is performed using any of the above methods.
(4):
Based on the downlink transmission quality information transmitted from the ONU, the ONTs under the OLT are grouped so that ONUs with similar transmission quality gather, and one or more lanes of the hierarchical modulation PON system are assigned to each group. The system according to (2) above.
(5):
The error correction coding method and the redundancy of the error correction coding method of at least one lane among the lanes of the hierarchical modulation PON system are set so that all ONUs can correctly extract the signals, The system according to 2).
(6):
The system according to (2) above, wherein the lane to which data addressed to each ONU is distributed is changed based on the downlink transmission quality information transmitted from the ONU.
(7):
The redundancy of the error correction coding system or the error correction coding system and the lane to which the data addressed to each ONU is allocated are determined so as to maximize the average frequency utilization efficiency between the OLT and the ONU. The system according to (6) above.

<Effect>
In a hierarchical modulation PON system, transmission efficiency is improved by determining an error correction coding method for each lane.

11: Data distribution unit 12: Buffer 13: Multi-level signal generators 14, 14a, 14b: E / O converters 15, 15a, 51b: O / E converter 16: Multi-level signal decoders 21, 21a, 21b: O / E converter 22: multilevel signal decoder 23: buffer 24: data extractor 25: multilevel signal generators 26, 26a, 26b: E / O converter 31: error correction encoder 32: error correction code Encoding method determination unit 41: error correction decoding unit 42: error correction encoding method determination unit 43: error correction encoding unit 51: control signal generation units 52, 52a, 52c: multiplexing unit 53, 53a: separation unit 54: transmission quality Information extraction unit 55: distribution lane determination unit 61, 61a: separation unit 62: control information extraction unit 62c: data and control information extraction unit 63: transmission quality estimation unit 64: transmission quality notification signal generation units 65, 65a, 65c: many Part 100~105: OLT
150: Optical power splitter 200-205: ONU
300-305: Communication system

Claims (9)

A PON (Passive Optical Network) that connects one station side optical line terminator (OLT) to a plurality of subscriber side optical line terminators (ONU) via an optical power splitter;
Hierarchical modulation means for transmitting a hierarchical modulation signal in which one or more downlink data from the OLT to the ONU is multiplexed;
Data distribution means for distributing the downlink data to any hierarchy;
Error correction means for adjusting at least one of the redundancy of the error correction coding scheme or the error correction coding scheme for each layer of the hierarchical modulation signal;
Multi-level signal decoding means for outputting a bit sequence for each hierarchy of the hierarchical modulation signal;
Error correction decoding means for error correction decoding the bit sequence for each layer; and
A communication system comprising: The error correction means includes
In the OLT, the error correction coding scheme or the redundancy of the error correction coding scheme is adjusted based on downlink transmission quality information from the OLT to the ONU, and the adjusted error correction code 2. The communication system according to claim 1, wherein the ONU is notified of redundancy of the encoding method or the error correction encoding method. The error correction means includes
2. The communication system according to claim 1, wherein at least one of an error correction coding method that can be decoded by all the ONUs or redundancy of the error correction coding method is set in at least one of the layers. . The error correction means includes
The at least one of the error correction coding method and the redundancy of the error correction coding method is frequency-multiplexed, time-multiplexed, or wavelength-multiplexed to the downlink data and notified to the ONU. 4. The communication system according to any one of 3. The data distribution means includes
5. The ONU group is formed based on downlink transmission quality information from the OLT to the ONU, and one or a plurality of the hierarchies are allocated to each group. 6. Communication system. The data distribution means includes
The communication system according to any one of claims 1 to 4, wherein the downlink data is distributed to any one of the layers based on downlink transmission quality information from the OLT to the ONU. The data distribution means and the error correction means are:
Adjusting at least one of the distribution of the downlink data to the layer and the redundancy of the error correction coding method or the error correction coding method so that the average frequency use efficiency between the OLT and the ONU is maximized. A communication system according to any one of claims 1 to 6. A communication method in a PON that connects one OLT and a plurality of ONUs via an optical power splitter,
A hierarchical modulation procedure for transmitting a hierarchical modulation signal in which downlink data from the OLT to the ONU is multiplexed;
A data distribution procedure for distributing the downlink data to any one of the layers;
An error correction procedure for setting at least one of an error correction coding scheme and a redundancy of the error correction coding scheme for each of the layers to which the downlink data is sorted in the data sorting procedure;
A multi-level signal decoding procedure for outputting a bit sequence for each layer of the layer modulated signal;
An error correction decoding procedure for error correction decoding the bit sequence for each layer;
A communication method characterized by: A transmission method in a PON in which one OLT and a plurality of ONUs are connected via an optical power splitter,
A hierarchical modulation procedure for transmitting a hierarchical modulation signal in which downlink data from the OLT to the ONU is multiplexed;
A data distribution procedure for distributing the downlink data to any one of the layers;
An error correction procedure for setting at least one of an error correction coding scheme and a redundancy of the error correction coding scheme for each of the layers to which the downlink data is sorted in the data sorting procedure;
A transmission method characterized by:

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