JP6259363B2 - Station-side optical line terminator and signal generation method - Google Patents

Description

  The present invention relates to a station-side optical line termination device and a signal generation method when a multilevel / high-order modulation scheme is applied to downlink communication of a PON (Passive Optical Network) system.

  In the optical access network, the PON system is widely adopted. 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.

  In conventional PON systems such as GE-PON / 10G-EPON, communication has been performed using OOK (on-off-keying) modulation. On the other hand, the transmission capacity can be improved without increasing the symbol rate and the number of wavelengths by a multi-level modulation method capable of transmitting a plurality of bits with one symbol. In Non-Patent Document 1, in downlink communication, a first subscriber side optical line terminator (ONU # 1: Optical Network Unit) using OOK modulation and a second subscriber side optical line terminator (ONU) using multilevel modulation are used. A hierarchical modulation PON system in which # 2: Optical Network Unit) coexists at one wavelength under the same station side optical line terminal (OLT) is proposed.

  FIG. 2 is an example in the case of using 8-star QAM (quadraure amplitude modulation). As shown in FIG. 2, the OLT 100 transmits an amplitude-phase modulated signal via the optical transmission line 50, the amplitude value of the signal is used for signal transmission to the ONU # 1 (201), and the phase is ONU # 2. Used for signal transmission to (202). As a result, simultaneous communication from the OLT to a plurality of ONUs using a single time / wavelength is possible, so that the transmission capacity is improved compared to a PON system that uses only OOK modulation. The hierarchical modulation PON system of Non-Patent Document 1 can also be realized when ONU # 1 uses ASK (amplitude-shift keying) modulation instead of OOK modulation, and ONU # 2 has QPSK (quadrature phase shift keying) modulation. In addition, the present invention can also be realized when using an arbitrary modulation multi-level PSK modulation.

In addition, a method of changing the number of modulation multi-levels of the phase modulation signal according to the amplitude value of the OOK modulation signal has been proposed (Non-patent Document 2, Patent Document 1). In the method described in Non-Patent Document 1, under the assumption that the average transmission power is constant, the higher the extinction ratio of the amplitude-phase modulated signal, the more the received BER of the phase-modulated signal when the amplitude is small. Therefore, when the amplitude is small, the reception BER is improved by reducing the multi-level number of the phase modulation signal and increasing the distance between the minimum signal points. When the amplitude is large, the multi-level number of the phase modulation signal is increased. By improving the transmission rate, it is possible to improve the received code error rate (BER) while maintaining the same transmission rate as that of the non-patent document 1.
Hereinafter, the methods described in Non-Patent Document 2 and Patent Document 1 are referred to as related technologies.

JP 2014-003487 A

N. Iiyama, J .; Kani, J .; Terada, and N.A. Yoshimoto, “Feasibility study on a scheme for coexistence of DSP-based PON and 10-Gbps / λ PON using hierarchical star QAM format”. Lighttw. Technol. , Vol. 31, no. 18, pp. 3085-3092, Sep. 2013. N. Shibata, N .; Iiyama, J .; Kani, S .; Y. Kim, J. et al. Terada, and N.A. Yoshimoto, “Constellation design for next-generation hierarchically-modulated PON systems”, Proc. of SPIE, vol. 8645 864507-1, Feb. 2013.

  FIG. 3 shows an apparatus configuration example of related technology. The OLT 100 transmits data # 1 to the ONU # 1 (201) and transmits data # 2 to the ONU # 2 (202). Data # 1 and data # 2 are MAC frames. In the following, it is assumed that amplitude modulation is performed so that a small amplitude is obtained when the bit value of data # 1 is 0, and a large amplitude is obtained when the bit value is 1.

  The OLT 100 includes a buffer 11 for storing data # 2, an output bit number control unit 12 that checks data # 1 bit by bit and determines the number of bits output from the buffer according to whether the bit value is 0 or 1, A bit / symbol conversion unit 13 that generates and outputs an amplitude-phase modulation signal based on data # 1 and data # 2, a D / A conversion unit 14 that converts a digital signal into an analog signal, and an electrical signal as an optical signal An E / O conversion unit 15 for conversion is included.

  At the start of operation, the bit of data # 2 is not stored in the buffer 11. Therefore, the output bit number control unit 12 first stores the data # 2 in the buffer 11 for a certain time without sending the data # 2 to the bit / symbol conversion unit 13. After a certain period of time, the output bit number control unit 12 outputs data # 2 from the buffer 11 and sends it to the bit / symbol conversion unit 13.

  For example, when the inner PSK is BPSK and the outer PSK is 8PSK, the output bit number control unit 12 instructs the buffer to output 1 bit if the input bit is 0, and outputs 3 bits from the buffer if the input bit is 1. Command. FIG. 4 shows an operation example of the OLT 100 when the inner PSK is BPSK and the outer PSK is 8PSK.

  On the other hand, the ONU # 2 (202) is an O / E converter 21 that converts an optical signal into an electrical signal, an A / D converter 22 that converts an electrical analog signal into a digital signal, and a digitized modulation signal. A symbol / bit conversion unit (OOK) 23 for performing OOK demodulation on the basis of the obtained amplitude value and separately outputting the modulation signal when the amplitude value is high and the modulation signal when the amplitude value is low based on the obtained amplitude value; , A symbol / bit conversion unit (inner PSK) 24 that performs PSK demodulation of the first modulation multilevel number on the modulation signal when the amplitude is low, and a buffer that holds the output of the symbol / bit conversion unit (inner PSK) (Inner PSK) 25, a symbol / bit conversion unit (outer PSK) 26 that performs PSK demodulation of the second modulation multilevel number on the modulation signal when the amplitude is high, and a symbol / bit conversion unit (outer PSK) (Outside PSK) 27 that holds the output of the output and a data control unit that checks data # 1 ′ bit by bit and determines whether to output the bit sequence from the buffer (inside PSK) or the buffer (outside PSK) 28, and an output switching unit 29 for switching the output so that the output of the buffer whose output is commanded by the output control unit is taken out.

  The output control unit 28 changes the number of bits to be output from each buffer according to the format of the amplitude / phase modulation signal. For example, when the inner PSK is BPSK and the outer PSK is 8PSK, the output control unit 28 instructs to output 1 bit from the buffer (inner PSK) if the bit of the input data # 1 ′ is 0, and the input data # 1 If the bit of 'is 1, it is instructed to output 3 bits from the buffer (outer PSK).

  Note that in the OLT 100, an error correction coding unit may be placed before the bit / symbol conversion unit 13 and the output bit number control unit 12, and data # 1 may be error correction coded. At this time, the ONU # 2 (202) performs error correction decoding in the symbol / bit conversion unit (OOK) 23, and again performs error correction coding on the error correction decoded bit sequence and outputs it as data # 1 '. As the error correction coding method, any coding method such as Reed-Solomon code or LDPC code can be applied.

Further, in the OLT 100, an encoding unit may be placed in front of the bit / symbol conversion unit 13 and the output bit number control unit 12, and data # 1 may be encoded with 8B / 10B, 64B / 66B, or the like. Here, data # 1 is observed bit by bit from the start of operation, the accumulated number of bits “0” included in data # 1 is N ₀ , and the accumulated number of bits “1” included in data # 1. Let the number be N ₁ . Since the difference between N ₀ and N ₁ is reduced by 8B / 10B encoding, 64B / 66B encoding, etc., the average transmission rate of data # 2 is the transmission rate of the inner PSK signal and the transmission of the outer PSK signal. Nearly equal to the average speed. For example, as shown in FIG. 4, when the inner PSK signal is BPSK (1 bit / symbol) and the outer PSK signal is 8 PSK (3 bit / symbol), the average transmission rate is 2 bits / symbol.

  In the related art, a buffer is required on the OLT and ONU sides. The transmission rate of data input to the OLT side buffer is an average value of the transmission rates of the inner PSK and the outer PSK. On the other hand, the transmission rate of the data output from the OLT side buffer is variable. When the bit input to the output bit number control unit is “0”, the transmission rate of the inner PSK is obtained and input to the output control unit. When the bit is “1”, the transmission rate of the outer PSK is obtained.

  The transmission rate of the inner PSK is smaller than the average value of the transmission rates of the inner PSK and the outer PSK. For this reason, if the “0” bit continues in data # 1, the data stored in the buffer increases, which may cause a buffer overflow. For this reason, the related technique has a first problem that when a buffer overflow occurs and a part of the data # 2 bit sequence is lost, it is necessary to take care of error correction decoding, a retransmission procedure, and the like. These also lead to a decrease in communication efficiency.

  On the other hand, the transmission rate of the outer PSK is larger than the average value of the transmission rates of the inner PSK and the outer PSK. For this reason, if the “1” bit continues in data # 1, the data stored in the buffer decreases, the buffer becomes empty (buffer empty), and data to be temporarily transmitted may be lost. For this reason, the related art may temporarily include no information in the PSK modulation signal, but the section on which the information is not included cannot be detected on the receiving side, and therefore data # 2 is not received correctly. There are also two issues.

  The OLT buffer stores bit sequences used for the inner PSK and the outer PSK. On the other hand, the ONU has a buffer that stores a bit sequence of only the inner PSK and a buffer that stores a bit sequence of only the outer PSK. If each ONU buffer size is set to the same level as the OLT buffer size, a buffer overflow does not occur in each ONU buffer unless a buffer overflow occurs in the OLT buffer. If the OLT buffer does not become buffer empty, at least one of the ONU buffers stores bits, so there is no state in which there is no bit sequence to be extracted.

  Therefore, if buffer empty and buffer overflow of the OLT buffer can be avoided, problems caused by buffer overflow and buffer empty in the ONU buffer can be solved.

  Accordingly, an object of the present invention is to provide an OLT that can avoid buffer empty and buffer overflow of a buffer and a signal generation method thereof in order to solve the above-described problems.

  In order to solve the above problems, the present invention observes the buffer amount of the OLT buffer and adjusts the buffer amount.

Specifically, the OLT according to the present invention is connected to the first ONU and the second ONU via an optical fiber, and the first bit sequence addressed to the first ONU and the second bit addressed to the second ONU. An OLT configured to transmit an amplitude phase modulation signal from a sequence,
A buffer for storing the second bit sequence;
An output bit number control unit that determines the number of bits to be output from the buffer according to the bit type of the first bit sequence;
An amplitude modulation signal is generated based on the first bit sequence, and the amplitude modulation signal is generated based on the bits of the second bit sequence output from the buffer with the number of bits determined by the output bit number control unit. A bit / symbol conversion unit that performs phase modulation with different number of modulation levels and outputs the amplitude phase modulation signal;
A buffer amount observation unit for observing the buffer amount of the buffer;
A dummy data frame creation output unit for forming a dummy data frame according to the buffer amount observed by the buffer amount observation unit and inserting the dummy data frame into the first bit sequence;
Is provided.

The signal generation method according to the present invention is connected to the first ONU and the second ONU via an optical fiber, and the first bit sequence addressed to the first ONU and the second bit sequence addressed to the second ONU. An OLT signal generation method for constructing and transmitting an amplitude phase modulation signal from
A buffer procedure for storing the second bit sequence in a buffer;
An output bit number control procedure for determining the number of bits to be output from the buffer according to the bit type of the first bit sequence;
An amplitude modulation signal is generated based on the first bit sequence, and the amplitude modulation signal is generated based on the bits of the second bit sequence output from the buffer with the number of bits determined by the output bit number control procedure. A bit / symbol conversion procedure for performing phase modulation with different modulation multi-level numbers and outputting the amplitude phase modulation signal;
A buffer amount observation procedure for observing the buffer amount of the buffer;
A dummy data frame creation output procedure for forming a dummy data frame according to the buffer amount observed in the buffer amount observation procedure and inserting it into the first bit sequence;
I do.

  In the present invention, the buffer amount of the OLT buffer is observed, and a dummy bit string corresponding to the buffer amount is generated and inserted into the first bit sequence. That is, when the buffer amount increases and approaches the overflow, a dummy bit string including many bit types that increase the bit amount output from the buffer is inserted into the first bit sequence. Since the amount of bits output from the buffer increases, the buffer amount is reduced and overflow can be avoided. On the other hand, when the buffer amount decreases and approaches the buffer empty, a dummy bit string including many bit types that reduce the bit amount output from the buffer is inserted into the first bit sequence. Since the amount of bits output from the buffer decreases, the buffer amount increases and buffer empty can be avoided.

  Therefore, the present invention can provide an OLT and a signal generation method thereof that can avoid buffer empty and buffer overflow of the buffer.

In detail, the dummy data frame creation output unit of the OLT according to the present invention includes:
When the buffer amount exceeds a preset upper limit threshold, the second bit sequence output from the buffer is increased, and the bit type is combined so that the buffer amount is equal to or less than the upper limit threshold. Form a data frame,
When the buffer amount falls below a preset lower limit threshold, the second bit sequence output from the buffer is reduced, and the bit type is combined so that the buffer amount becomes equal to or greater than the lower limit threshold, and the dummy A data frame is formed.

In the dummy data frame creation output procedure of the signal generation method according to the present invention,
When the buffer amount exceeds a preset upper limit threshold, the second bit sequence output from the buffer is increased, and the bit type is combined so that the buffer amount is equal to or less than the upper limit threshold. Form a data frame,
When the buffer amount falls below a preset lower limit threshold, the second bit sequence output from the buffer is reduced, and the bit type is combined so that the buffer amount becomes equal to or greater than the lower limit threshold, and the dummy A data frame is formed.

  The dummy data frame creation / output unit of the OLT according to the present invention is characterized in that the destination of the dummy data frame is a destination discarded by any of the first ONUs.

  In the dummy data frame creation / output procedure of the signal generation method according to the present invention, the destination of the dummy data frame is a destination discarded by any of the first ONUs.

  Although the dummy bit string inserted in the first bit sequence is also transmitted to the ONU, since it is not the destination of any ONU, the dummy bit string is discarded in all ONUs. That is, the dummy bit string inserted into the first bit sequence in the present invention does not affect the PON.

The OLT according to the present invention further includes an encoding unit that performs predetermined encoding of the first bit sequence,
The dummy data frame creation output unit forms the dummy data frame such that the buffer amount is equal to or less than the upper limit threshold or equal to or more than the lower limit threshold in the dummy data frame encoded by the encoding unit. And

The signal generation method according to the present invention further includes an encoding procedure for performing predetermined encoding of the first bit sequence,
In the dummy data frame creation output procedure, the dummy data frame is formed such that the buffer amount is equal to or less than the upper threshold or the lower threshold in the dummy data frame encoded in the encoding procedure. And

  The predetermined encoding is error correction encoding such as Reed-Solomon code or LDPC code, or serial encoding such as 8B / 10B or 64B / 66B. The present invention can be applied even to a PON system in which such encoding is performed.

  The present invention can provide an OLT and a signal generation method thereof that can avoid buffer empty and buffer overflow of the buffer.

It is a figure explaining OLT concerning the present invention. It is a figure explaining a parallel transmission technique. This is a case where an OOK modulation signal is transmitted to ONU # 1, and a QPSK modulation signal is transmitted to ONU # 2. It is a figure explaining related technology. It is a figure explaining operation | movement of a parallel transmission technique.

  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.

FIG. 1 is a diagram illustrating the OLT 101 of the present embodiment. The OLT 101 is connected to the ONU # 1 (201) and the ONU # 2 (202) via the optical transmission line 50, and the first bit sequence (data # 1) addressed to the ONU # 1 and the first address addressed to the ONU # 2 An OLT configured to transmit an amplitude / phase modulation signal from a 2-bit sequence (data # 2),
a buffer 11 for storing data # 2, and
an output bit number control unit 12 that determines the number of bits to be output from the buffer 11 according to the bit type of data # 1,
An amplitude modulation signal is generated based on data # 1, and a multilevel modulation is performed on the amplitude modulation signal based on the data # 2 bits output from the buffer 11 with the number of bits determined by the output bit number control unit 12 A bit / symbol conversion unit 13 for performing different phase modulation and outputting the amplitude phase modulation signal;
A buffer amount observation unit 31 for observing the buffer amount of the buffer 11;
A dummy data frame creation output unit 32 that forms a dummy data frame (dummy_data # 1) according to the buffer amount observed by the buffer amount observation unit 31 and inserts it into data # 1;
Is provided.

The dummy data frame creation output unit 32 determines the following and forms a dummy data frame.
The dummy data frame creation output unit 32
When the buffer amount exceeds a preset upper limit threshold, the data # 2 output from the buffer 11 is increased, and the bit type is combined so that the buffer amount is equal to or less than the upper limit threshold, and the dummy data frame Form the
When the buffer amount falls below a preset lower threshold, the data # 2 output from the buffer 11 is decreased, and the dummy data frame is combined with the bit types so that the buffer amount becomes equal to or greater than the lower threshold. Form.
The dummy data frame creation output unit 32 may not form a dummy data frame when the buffer amount of the buffer 11 is between the lower limit threshold value and the upper limit threshold value.

  Further, the dummy data frame creation output unit 32 sets the destination of the dummy data frame as a destination to be discarded by any of the ONUs # 1.

  Further, the OLT 101 may further include an encoding unit (not shown) that performs predetermined encoding of data # 1. In this case, the dummy data frame creation output unit 32 forms the dummy data frame so that the buffer amount can be adjusted to be equal to or less than the upper threshold or the lower threshold in the dummy data frame encoded by the encoder. To do.

  When the buffer amount exceeds the upper limit threshold, the OLT 101 inserts dummy data including many bits 1 as data # 1, increases the number of bits output from the buffer 11, and reduces the buffer amount. Try to solve the first issue. Further, when the buffer amount falls below the lower limit threshold, the OLT 101 inserts dummy data including many bits 0 as data # 1, and decreases the number of bits output from the buffer 11 to increase the buffer amount. To solve the second problem. If the identifier of the MAC frame including the inserted dummy data is set so as not to point to any ONU, these dummy data are discarded in all ONUs # 1.

  Dummy_data # 1 has the same MAC frame configuration as data # 1. That is, the MAC address for the payload and the position / length of the preamble are the same. In the downlink, ONU # 1 confirms the destination from the identifier included in data # 1, and discards the frame not addressed to itself. Therefore, if the identifier of dummy_data # 1 is set so as not to point to any ONU # 1, dummy_data # 1 is discarded by all ONU # 1. Therefore, it is not necessary to modify ONU # 1 when applying this embodiment.

  Since dummy_data # 1 is discarded by all ONU # 1, the bit sequence of the payload can be arbitrarily set. For example, consider a case where the inner PSK is BPSK and the outer PSK is 8PSK. In this case, when the bit type of data # 1 is “0”, the output bit number control unit 12 outputs only one bit from the buffer 11, but when the bit type of data # 1 is “1”, the output bit number control The unit 12 outputs 3 bits from the buffer 11.

  The dummy data frame creation output unit 32 calculates the difference between the current buffer amount and the target buffer amount (or the upper limit threshold) when the buffer amount of the buffer 11 exceeds the upper limit threshold. Then, the dummy data frame creation output unit 32 determines that the total number of bit types “1” included in the payload of the dummy data frame is greater than the total number of bit types “1” included in the payload of the previous frame so as to eliminate the difference. A large number of dummy_data # 1 is generated.

  Since the total number of bit types “1” included in the payload of the dummy data frame is larger than before, the number of bits output from the buffer 11 is increased from before and the buffer amount is reduced to the target value.

  Conversely, the dummy data frame creation output unit 32 calculates the difference between the current buffer amount and the target buffer amount (may be the lower limit threshold) when the buffer amount of the buffer 11 falls below the lower limit threshold. Then, the dummy data frame creation output unit 32 determines that the total number of bit types “0” included in the payload of the dummy data frame is greater than the total number of bit types “0” included in the payload of the previous frame so as to eliminate the difference. A large number of dummy_data # 1 is generated.

  Since the total number of bit types “0” included in the payload of the dummy data frame is larger than before, the number of bits output from the buffer 11 is decreased from before and the buffer amount is increased to the target value.

  Note that the dummy data frame creation output unit 32 generates dummy_data # 1 so as to be closest to the target buffer amount when the buffer amount cannot be the target buffer amount regardless of how the payload is set.

  When the MAC frame (data # 1) is subjected to error correction encoding or encoding such as 8B / 10B before transmission, the dummy data frame creation output unit 32 performs the error correction encoding or 8B / Dummy_data # 1 is generated so that the buffer amount can be adjusted with a dummy data frame after encoding such as 10B.

  The present invention can be applied to TDM-PON, WDM-PON, or TWDM-PON that performs multiplexing using TDM, WDM, or the like.

11: buffer 12: output bit number control unit 13: bit / symbol conversion unit 14: D / A conversion unit 15: E / O conversion unit 21: O / E conversion unit 22: A / D conversion unit 23: symbol / bit Conversion unit (OOK)
24: Symbol / bit converter (inner PSK)
25: Buffer (inner PSK)
26: Symbol / bit converter (outside PSK)
27: Buffer (outside PSK)
28: Output control unit 29: Output switching unit 31: Buffer amount observation unit 32: Dummy data frame creation output unit 50: Optical transmission line 100, 101: OLT
201, 202: ONU

Claims (8)

A first subscriber side optical network unit (ONU) and a second ONU are connected via an optical fiber, and a first bit sequence addressed to the first ONU and a second address addressed to the second ONU An optical line terminator (OLT) that transmits an amplitude phase modulation signal from a bit sequence and transmits the modulated signal.
A buffer for storing the second bit sequence;
An output bit number control unit that determines the number of bits to be output from the buffer according to the bit type of the first bit sequence;
An amplitude modulation signal is generated based on the first bit sequence, and the amplitude modulation signal is generated based on the bits of the second bit sequence output from the buffer with the number of bits determined by the output bit number control unit. A bit / symbol conversion unit that performs phase modulation with different number of modulation levels and outputs the amplitude phase modulation signal;
A buffer amount observation unit for observing the buffer amount of the buffer;
A dummy data frame creation output unit for forming a dummy data frame according to the buffer amount observed by the buffer amount observation unit and inserting the dummy data frame into the first bit sequence;
OLT comprising. The dummy data frame creation output unit
When the buffer amount exceeds a preset upper limit threshold, the second bit sequence output from the buffer is increased, and the bit type is combined so that the buffer amount is equal to or less than the upper limit threshold. Form a data frame,
When the buffer amount falls below a preset lower limit threshold, the second bit sequence output from the buffer is reduced, and the bit type is combined so that the buffer amount becomes equal to or greater than the lower limit threshold, and the dummy The OLT according to claim 1, wherein the OLT forms a data frame. The dummy data frame creation output unit
The OLT according to claim 1, wherein the destination of the dummy data frame is a destination that is discarded by all of the first ONUs. An encoding unit that performs predetermined encoding of the first bit sequence;
The dummy data frame creation output unit
Claim 2 or claim 2 wherein the coding unit is characterized by forming the dummy data frame, such as the amount of the buffer in the dummy data frame subjected to coding is the upper limit threshold below or above the lower threshold The OLT according to claim 3, wherein The first ONU and the second ONU are connected via an optical fiber, and an amplitude phase modulation signal is constructed and transmitted from the first bit sequence addressed to the first ONU and the second bit sequence addressed to the second ONU. An OLT signal generation method comprising:
A buffer procedure for storing the second bit sequence in a buffer;
An output bit number control procedure for determining the number of bits to be output from the buffer according to the bit type of the first bit sequence;
An amplitude modulation signal is generated based on the first bit sequence, and the amplitude modulation signal is generated based on the bits of the second bit sequence output from the buffer with the number of bits determined by the output bit number control procedure. A bit / symbol conversion procedure for performing phase modulation with different modulation multi-level numbers and outputting the amplitude phase modulation signal;
A buffer amount observation procedure for observing the buffer amount of the buffer;
A dummy data frame creation output procedure for forming a dummy data frame according to the buffer amount observed in the buffer amount observation procedure and inserting it into the first bit sequence;
Signal generation method. In the dummy data frame creation output procedure,
When the buffer amount exceeds a preset upper limit threshold, the second bit sequence output from the buffer is increased, and the bit type is combined so that the buffer amount is equal to or less than the upper limit threshold. Form a data frame,
When the buffer amount falls below a preset lower limit threshold, the second bit sequence output from the buffer is reduced, and the bit type is combined so that the buffer amount becomes equal to or greater than the lower limit threshold, and the dummy 6. The signal generation method according to claim 5, wherein a data frame is formed. In the dummy data frame creation output procedure,
The signal generation method according to claim 5 or 6, wherein a destination of the dummy data frame is a destination to be discarded by any of the first ONUs. An encoding procedure for performing predetermined encoding on the first bit sequence;
In the dummy data frame creation output procedure,
Claim 6 or, characterized in that the buffer amount in the dummy data frame was encoded in the encoding procedure to form the dummy data frame such that less or more the lower threshold upper limit threshold 6 The signal generation method according to claim 7, wherein:

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