JP2016009931A - Station side optical line termination device, subscriber side optical line termination device, signal generation method, and signal reception method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which never cause buffer overflow or buffer underflow, in the amplitude phase modulator of an OLT(optical line terminator) consisting of an inside PSK and an outside PSK, performing phase modulation of a signal, subjected to amplitude modulation, in second bit sequence.SOLUTION: The buffer amount of an OLT buffer 11 is observed in a buffer amount observation unit 31, and when the inside PSKs of low transmission rate continue to increase the buffer amount, a transmission rate adjustment unit 32 reduces the transmission rate of a second bit sequence (data#2) input to the OLT buffer 11, or stops input thus reducing the buffer amount and preventing buffer overflow. When the outside PSKs of high transmission rate continue to decrease the buffer amount, the transmission rate adjustment unit 32 inserts dummy data into the OLT buffer, thus increasing the buffer amount and preventing buffer underflow.

Description

  The present invention relates to a station-side optical line terminator, a subscriber-side optical line terminator, a signal generation method, and a signal reception 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. 3 shows an example in the case of using 8-star QAM (quadture amplitude modulation). As shown in FIG. 3, 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 using 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 multilevel values 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). When the method described in Non-Patent Document 1 is used, under the assumption that the average transmission power is constant, the higher the extinction ratio of the amplitude phase modulation signal, the worse the reception BER of the phase modulation 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. 4 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. 5 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, when the inner PSK signal is BPSK (1 bit / symbol) and the outer PSK signal is 8 PSK (3 bits / symbol) as shown in FIG. 5, 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 buffer overflow. For this reason, the related art has a first problem that when buffer overflow occurs and part of the data # 2 bit sequence is lost, it is necessary to take care of error correction decoding and retransmission control. 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.

  SUMMARY OF THE INVENTION In order to solve the above-described problems, an object of the present invention is to provide an OLT, an OLT signal generation method, an ONU, and an ONU signal reception method that can avoid buffer empty and buffer overflow of the OLT buffer. .

  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 transmission rate adjustment unit that adjusts the transmission rate of the second bit sequence from the MAC layer to the PHY layer according to the buffer amount observed by the buffer amount observation unit;
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 transmission rate adjustment procedure for adjusting the transmission rate of the second bit sequence from the MAC layer of the OLT to the PHY layer according to the buffer amount observed by the buffer amount observation unit;
I do.

  In the present invention, the buffer amount of the OLT buffer is observed, and the transmission rate of the second bit string input to the buffer is adjusted according to the buffer amount. That is, when the buffer amount increases and approaches the overflow, the MAC layer side is instructed to lower the transmission rate of the second bit string output to the PHY layer than before. Since the amount of bits input to the buffer is smaller than before, the buffer amount is reduced and overflow can be avoided. On the other hand, when the buffer amount decreases and the buffer is approaching empty, the MAC layer is instructed to increase the transmission rate of the second bit string output to the PHY layer. Since the amount of bits to be input to the buffer is larger than before, the amount of buffer is increased, 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 OLT buffer.

Specifically, the transmission rate adjustment unit of the OLT according to the present invention includes:
When the buffer amount exceeds a preset upper threshold value, the transmission rate of the second bit sequence from the MAC layer to the PHY layer is lowered than before, or the second bit sequence is transmitted from the MAC layer to the PHY layer. Stop
When the buffer amount falls below a preset lower threshold, the transmission rate of the second bit sequence from the MAC layer to the PHY layer is increased or returned to a specified value.

Further, in the transmission rate adjustment procedure of the signal generation method according to the present invention,
When the buffer amount exceeds a preset upper threshold value, the transmission rate of the second bit sequence from the MAC layer to the PHY layer is lowered than before, or the second bit sequence is transmitted from the MAC layer to the PHY layer. Stop
When the buffer amount falls below a preset lower threshold, the transmission rate of the second bit sequence from the MAC layer to the PHY layer is increased or returned to a specified value.

The other 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 sequence addressed to the second ONU. An OLT configured to transmit an amplitude phase modulation signal from
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 output unit that inserts dummy data of a predetermined pattern into the second bit sequence to be input to the buffer when the buffer amount observed by the buffer amount observation unit falls below a preset lower threshold value When,
Is provided.

Another 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 output procedure for inserting dummy data of a predetermined pattern into the second bit sequence to be input to the buffer when the buffer amount observed in the buffer amount observation procedure falls below a preset lower threshold value When,
I do.

  According to the present invention, the buffer amount of the OLT buffer is observed, and dummy data is inserted into the second bit string input to the buffer according to the buffer amount. In other words, when the buffer amount decreases and approaches to buffer empty, dummy data is inserted into the second bit string, or the amount of dummy data to be inserted is increased. Since the amount of bits to be input to the buffer is larger than before, the amount of buffer is increased, and buffer empty can be avoided. On the other hand, when the buffer amount increases and approaches the overflow, the insertion of dummy data into the second bit string is stopped or the amount of dummy data to be inserted is reduced. Since the amount of bits input to the buffer is smaller than before, the buffer amount is reduced and overflow 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 OLT buffer.

An ONU according to the present invention is an ONU that receives an amplitude-phase modulated signal transmitted by the OLT,
An O / E converter that converts an optical signal of the amplitude phase modulation signal into an electrical analog signal;
An A / D converter that converts an electrical analog signal from the O / E converter into an electrical digital signal to obtain the amplitude and phase modulation signal;
Amplitude demodulated signal is generated by performing amplitude demodulation on the amplitude phase modulation signal from the A / D converter, and the amplitude demodulated signal is a signal when the amplitude value is higher than the reference and when the amplitude value is lower than the reference A symbol / bit converter (OOK) that separates the signal into
A symbol / bit converter (PSK) that performs PSK demodulation on each of the signals separated by the symbol / bit converter (OOK);
A buffer (PSK) for respectively holding the output of the symbol / bit conversion unit (PSK);
An output control unit that determines whether to output a bit sequence from one of the buffers (PSK) according to an amplitude value of the amplitude demodulated signal from the symbol / bit conversion unit (OOK);
An output switching unit that switches the output so that the output of the buffer (PSK) determined by the output control unit is extracted;
The bit type of the first bit sequence is determined from the amplitude value of the amplitude demodulated signal generated by the symbol / bit conversion unit (OOK), the difference in the number of bit types per unit time is calculated, and the OLT A buffer amount estimation unit for estimating the buffer amount of the buffer;
A dummy data removing unit that detects and removes the dummy data from the output of the output switching unit when the buffer amount estimated by the buffer amount estimating unit falls below the lower limit threshold;
Is provided.

The signal receiving method according to the present invention is a signal receiving method for receiving an amplitude-phase modulated signal generated by the signal generating method by an ONU,
An O / E conversion procedure for converting the optical signal of the amplitude phase modulation signal into an electrical analog signal;
An A / D conversion procedure for obtaining the amplitude and phase modulation signal by converting the electrical analog signal converted by the O / E conversion procedure into an electrical digital signal;
An amplitude demodulated signal is generated by performing amplitude demodulation on the amplitude phase modulation signal acquired in the A / D conversion procedure, and the amplitude demodulated signal is a signal when the amplitude value is higher than the reference and the amplitude value is lower than the reference. A symbol / bit conversion (OOK) procedure to separate the time signal;
A symbol / bit conversion (PSK) procedure for performing PSK demodulation on each of the signals separated by the symbol / bit conversion (OOK) procedure;
A buffer (PSK) procedure for holding each signal demodulated in the symbol / bit conversion (PSK) procedure in a buffer (PSK);
An output control procedure for determining whether to output a bit sequence from one of the buffers (PSK) according to an amplitude value of the amplitude demodulated signal generated by the symbol / bit conversion (OOK) procedure;
An output switching procedure for switching the output of the output switching unit so that the output of the buffer (PSK) determined by the output control procedure is taken out;
The bit type of the first bit series is determined from the amplitude value of the amplitude demodulated signal generated in the symbol / bit conversion (OOK) procedure, the difference in the number of bit types per unit time is calculated, and the OLT A buffer amount estimation procedure for estimating the buffer amount of the buffer;
A dummy data removal procedure for detecting and removing the dummy data from the output of the output switching unit when the buffer amount estimated in the buffer amount estimation procedure falls below the lower limit threshold;
I do.

  Since the amplitude and phase modulation signals generated by the other OLTs and other signal generation methods according to the present invention include dummy data, it is necessary to remove them. The ONU and the signal receiving method according to the present invention estimate the data amount (buffer amount) accumulated in the OLT buffer from the information (amount for each bit type) of the first bit string included in the received amplitude phase modulation signal. . The ONU and signal receiving method according to the present invention provides a second bit sequence included in an amplitude-phase modulation signal that has received a bit sequence that is determined in advance as dummy data when the estimated buffer amount is below a predetermined lower threshold. Remove from. By operating in this way, buffer empty and buffer overflow of the OLT buffer can be avoided without being affected by dummy data insertion.

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

  The present invention can provide an OLT, an OLT signal generation method, an ONU, and an ONU signal reception method that can avoid buffer empty and buffer overflow of the OLT buffer.

It is a figure explaining OLT concerning the present invention. It is a figure explaining other OLT and ONU 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.

(Embodiment 1)
FIG. 1 is a diagram illustrating the OLT 102 according to the present embodiment. The OLT 102 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 second 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 transmission rate adjustment unit 32 that adjusts the transmission rate of data # 2 from the MAC layer to the PHY layer according to the buffer amount observed by the buffer amount observation unit 31;
Is provided.
Here, the PHY layer is from the buffer 11 to the E / O converter 15.

The transmission rate adjustment unit 32 adjusts the transmission rate of data # 2 by making the following determination.
The transmission rate adjustment unit 32
When the buffer amount exceeds a preset upper threshold, the transmission rate of data # 2 from the MAC layer to the PHY layer is lowered than before, or the transmission of data # 2 from the MAC layer to the PHY layer is stopped,
When the buffer amount falls below a preset lower threshold, the data # 2 transmission rate from the MAC layer to the PHY layer is increased or returned to the specified value.
The transmission rate adjustment unit 32 may not change the transmission rate of data # 2 when the buffer amount of the buffer 11 is between the lower limit threshold value and the upper limit threshold value.

  The OLT 102 reduces the transmission rate of the data # 2 input from the MAC layer to the buffer 11 or stops the input of the data # 2 to the buffer 11 when the buffer amount exceeds the upper limit threshold. To solve the first problem. Further, when the buffer amount falls below the lower limit threshold, the OLT 102 increases the transmission speed of the data # 2 input from the MAC layer to the buffer 11 or starts input to the buffer 11 of data # 2. The buffer amount is increased to solve the second problem.

  When the buffer amount of the buffer 11 exceeds the upper limit threshold, the transmission rate adjustment unit 32 reduces the transmission rate from the data # 2 MAC layer to the PHY layer, or from the data # 2 MAC layer to the PHY layer. A command to stop transmission of is output to the MAC layer. When the transmission rate of data # 2 is reduced or the transmission is stopped, the data amount of data # 2 held in the buffer of the MAC layer increases. The transmission rate adjusting unit 32 may adjust the transmission rate by also observing the buffer amount of the MAC layer so that the buffer that stores data # 2 in the MAC layer does not cause a buffer overflow.

  The transmission rate adjustment unit 32 receives a command to return the transmission rate from the data # 2 MAC layer to the PHY layer to a specified value after a certain time has elapsed or after the buffer amount is reduced to a certain threshold value or less, or the data # 2 MAC A command to resume transmission from the layer to the PHY layer is output to the MAC layer.

  On the other hand, when the buffer amount of the buffer 11 falls below the lower limit threshold, the transmission rate adjustment unit 32 increases the transmission rate from the MAC layer of the data # 2 to the PHY layer, or from the MAC layer of the data # 2 to the PHY. A command to start transmission to the layer is output to the MAC layer. When the transmission rate of data # 2 increases or transmission starts, the data amount of data # 2 held in the buffer of the MAC layer decreases. The transmission rate adjustment unit 32 may also adjust the transmission rate by observing the buffer amount of the MAC layer so that the buffer that stores data # 2 in the MAC layer does not cause buffer empty.

  The transmission rate adjustment unit 32 receives a command to return the transmission rate from the data # 2 MAC layer to the PHY layer to a specified value after a predetermined time has elapsed or the buffer amount has increased to a certain threshold value or less, or the data # 2 MAC A command to stop transmission from the layer to the PHY layer is output to the MAC layer.

(Embodiment 2)
FIG. 2 is a diagram illustrating the OLT 103 and the ONU # 2 (203) of the present embodiment.

The OLT 103 is connected to the ONU # 1 (201) and the ONU # 2 (203) via an optical fiber, and the first bit sequence (data # 1) addressed to the ONU # 1 and the second bit addressed to the ONU # 2 An OLT configured to transmit an amplitude / phase modulation signal from a 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;
When the buffer amount observed by the buffer amount observation unit 31 falls below a preset lower threshold, dummy data (dummy_data # 2) having a predetermined pattern is inserted into data # 2 that is input to the buffer 11 A data output unit 34;
Is provided.

The ONU 203 is an ONU that receives the amplitude and phase modulation signal transmitted from the OLT 103, and
An O / E converter 21 for converting the optical signal of the amplitude phase modulation signal into an electrical analog signal;
An A / D converter 22 that converts an electrical analog signal from the O / E converter 21 into an electrical digital signal to obtain the amplitude phase modulation signal;
Amplitude demodulated signal is generated by performing amplitude demodulation on the amplitude phase modulation signal from the A / D conversion unit 22, and the amplitude demodulated signal is a signal when the amplitude value is higher than the reference and when the amplitude value is lower than the reference. A symbol / bit converter (OOK) 23 for separating the signals into
A symbol / bit converter (PSK) (24, 26) that performs PSK demodulation on each of the signals separated by the symbol / bit converter (OOK) 23;
Buffers (PSK) (25, 27) for respectively holding outputs of the symbol / bit conversion units (PSK) (24, 26);
An output control unit 28 that determines whether to output a bit sequence from one of the buffers (PSK) (25, 27) according to the amplitude value of the amplitude demodulated signal from the symbol / bit conversion unit (OOK) 23;
An output switching unit 29 that switches the output so that the output of the buffer (PSK) (25 or 27) determined by the output control unit 28 is taken out;
The bit type of the first bit sequence (data 1 ′) is determined from the amplitude value of the amplitude demodulated signal generated by the symbol / bit conversion unit (OOK) 23, the difference in the number of bit types per unit time is calculated, and the OLT 103 A buffer amount estimation unit 41 for estimating the buffer amount of the buffer 11;
A dummy data removing unit 42 for detecting and removing the dummy data from the output of the output switching unit 29 when the buffer amount estimated by the buffer amount estimating unit 41 falls below the lower limit threshold;
Is provided.

The dummy data output unit 34 determines as follows, and inputs dummy_data # 2 different from data # 2 to the buffer 11.
The dummy data output unit 34 starts input of dummy_data # 2 to the buffer 11 or increases the amount of dummy_data # 2 when the buffer amount of the buffer 11 falls below a preset lower limit threshold. Increase the buffer amount. On the other hand, the dummy data output unit 34 stops the input of the dummy_data # 2 to the buffer 11 or reduces the amount of the dummy_data # 2 to reduce the buffer amount of the buffer 11. Note that the dummy data output unit 34 may maintain the input amount of the dummy_data # 2 to the buffer 11 when the buffer amount of the buffer 11 is between the lower limit threshold value and the upper limit threshold value. The dummy data output unit 34 can arbitrarily set the bit sequence and the number of bits of dummy_data # 2. Note that it is necessary to determine a pattern of dummy_data # 2 between the OLT 103 and the ONU # 2 (203) before starting operation. This is because by determining the pattern (dummy pattern) of dummy_data # 2, ONU # 2 (203) can blindly detect and discard dummy_data # 2 as follows.

The ONU # 2 (203) performs the following operation in addition to the operation of the ONU # 2 (202) described in FIG. Buffer amount estimation unit 41 calculates the difference between the number N ₁ of bits species "0" the number N ₀ and bit type "1" of the input to the output control section 28 in a unit time data # 1 '. Then, the buffer amount estimation unit 41 estimates the buffer amount of the buffer 11 of the OLT 103 based on the calculated difference. For example, when the inner PSK is BPSK and the outer PSK is 8PSK, if the bit type of data # 1 is “0”, 1 bit is output from the buffer 11, and if the bit type is “1”, 3 bits are output from the buffer 11. estimation unit 41 may calculate the buffer amount of the buffer 11 from the difference between the number _{N 1} of bits species data # 1 'per unit time "0" the number _{N 0} and bit type "1".

  The dummy data removal unit 42 determines that the time point when the buffer amount estimated by the buffer amount estimation unit 41 falls below the lower limit threshold is the time point when the dummy data output unit 34 starts to input the dummy_data # 2 to the buffer 11. Then, the dummy data removing unit 42 detects a dummy pattern from the data series output from the output switching unit 29 from the time point and removes the dummy pattern. For this reason, dummy_data # 2 is not transmitted to the subsequent MAC layer.

  On the other hand, the dummy data removal unit 42 determines that the time when the buffer amount estimated by the buffer amount estimation unit 41 exceeds the upper threshold is the time when the dummy data output unit 34 finishes inputting the dummy_data # 2 to the buffer 11. . Then, the dummy data removal unit 42 stops blind detection of the dummy pattern from the time point.

  In addition, when the dummy data output unit 34 regularly inputs dummy_data # 2 to the buffer 11 between the upper limit threshold and the lower limit threshold, the dummy data output unit 34 also regularly detects the dummy pattern blindly.

  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: Transmission rate adjustment unit 34: Dummy data output unit 41: Buffer amount estimation unit 42: Dummy data removal unit 50: Optical transmission lines 100, 102, 103 : OLT
201, 202, 203: 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 transmission rate adjustment unit that adjusts the transmission rate of the second bit sequence from the MAC layer to the PHY layer according to the buffer amount observed by the buffer amount observation unit;
OLT comprising. The transmission speed adjustment unit is
When the buffer amount exceeds a preset upper threshold value, the transmission rate of the second bit sequence from the MAC layer to the PHY layer is lowered than before, or the second bit sequence is transmitted from the MAC layer to the PHY layer. Stop
2. The transmission rate of the second bit sequence from the MAC layer to the PHY layer is increased or returned to a specified value when the buffer amount falls below a preset lower threshold value. OLT. 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. OLT,
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 output unit that inserts dummy data of a predetermined pattern into the second bit sequence to be input to the buffer when the buffer amount observed by the buffer amount observation unit falls below a preset lower threshold value When,
OLT comprising. An ONU that receives the amplitude and phase modulation signal transmitted by the OLT according to claim 3,
An O / E converter that converts an optical signal of the amplitude phase modulation signal into an electrical analog signal;
An A / D converter that converts an electrical analog signal from the O / E converter into an electrical digital signal to obtain the amplitude and phase modulation signal;
Amplitude demodulated signal is generated by performing amplitude demodulation on the amplitude phase modulation signal from the A / D converter, and the amplitude demodulated signal is a signal when the amplitude value is higher than the reference and when the amplitude value is lower than the reference A symbol / bit converter (OOK) that separates the signal into
A symbol / bit converter (PSK) that performs PSK demodulation on each of the signals separated by the symbol / bit converter (OOK);
A buffer (PSK) for respectively holding the output of the symbol / bit conversion unit (PSK);
An output control unit that determines whether to output a bit sequence from one of the buffers (PSK) according to an amplitude value of the amplitude demodulated signal from the symbol / bit conversion unit (OOK);
An output switching unit that switches the output so that the output of the buffer (PSK) determined by the output control unit is extracted;
The bit type of the first bit sequence is determined from the amplitude value of the amplitude demodulated signal generated by the symbol / bit conversion unit (OOK), the difference in the number of bit types per unit time is calculated, and the OLT A buffer amount estimation unit for estimating the buffer amount of the buffer;
A dummy data removing unit that detects and removes the dummy data from the output of the output switching unit when the buffer amount estimated by the buffer amount estimating unit falls below the lower limit threshold;
ONU with. 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 transmission rate adjustment procedure for adjusting the transmission rate of the second bit sequence from the MAC layer of the OLT to the PHY layer according to the buffer amount observed by the buffer amount observation unit;
Signal generation method. In the transmission speed adjustment procedure,
When the buffer amount exceeds a preset upper threshold value, the transmission rate of the second bit sequence from the MAC layer to the PHY layer is lowered than before, or the second bit sequence is transmitted from the MAC layer to the PHY layer. Stop
6. The transmission rate of the second bit sequence from the MAC layer to the PHY layer is increased or returned to a specified value when the buffer amount falls below a preset lower threshold value. Signal generation method. 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 output procedure for inserting dummy data of a predetermined pattern into the second bit sequence to be input to the buffer when the buffer amount observed in the buffer amount observation procedure falls below a preset lower threshold value When,
Signal generation method. A signal receiving method for receiving an amplitude-phase modulated signal generated by the signal generating method according to claim 7 by an ONU,
An O / E conversion procedure for converting the optical signal of the amplitude phase modulation signal into an electrical analog signal;
An A / D conversion procedure for obtaining the amplitude and phase modulation signal by converting the electrical analog signal converted by the O / E conversion procedure into an electrical digital signal;
An amplitude demodulated signal is generated by performing amplitude demodulation on the amplitude phase modulation signal acquired in the A / D conversion procedure, and the amplitude demodulated signal is a signal when the amplitude value is higher than the reference and the amplitude value is lower than the reference. A symbol / bit conversion (OOK) procedure to separate the time signal;
A symbol / bit conversion (PSK) procedure for performing PSK demodulation on each of the signals separated by the symbol / bit conversion (OOK) procedure;
A buffer (PSK) procedure for holding each signal demodulated in the symbol / bit conversion (PSK) procedure in a buffer (PSK);
An output control procedure for determining whether to output a bit sequence from one of the buffers (PSK) according to an amplitude value of the amplitude demodulated signal generated by the symbol / bit conversion (OOK) procedure;
An output switching procedure for switching the output of the output switching unit so that the output of the buffer (PSK) determined by the output control procedure is taken out;
The bit type of the first bit series is determined from the amplitude value of the amplitude demodulated signal generated in the symbol / bit conversion (OOK) procedure, the difference in the number of bit types per unit time is calculated, and the OLT A buffer amount estimation procedure for estimating the buffer amount of the buffer;
A dummy data removal procedure for detecting and removing the dummy data from the output of the output switching unit when the buffer amount estimated in the buffer amount estimation procedure falls below the lower limit threshold;
Signal receiving method to do.

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