JP6513589B2 - Optical communication system and communication apparatus - Google Patents

Description

  The present invention performs waveform equalization processing of temporally intermittent burst signals in a TDM-PON optical communication system in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses. Optical communication system, communication apparatus, and waveform equalization method

  At present, in an optical subscriber access network, a PON (Passive Optical Network) system is used, which multiplexes user signals by Time Division Multiplexing (TDM). The PON system is a communication system capable of economically providing high-speed communication by using a light passive element represented by an optical coupler and sharing a part of a station side apparatus and a transmission path among a plurality of users. .

  On the other hand, in the mobile communication network, in order to accommodate the rapidly increasing mobile traffic, it is considered to make small cells in which the antennas are closely extended. In order to efficiently accommodate this small-cell mobile communication network, point-to-multipoint systems used in optical subscriber systems have been used instead of the point-to-point communication systems using dedicated lines conventionally used. Application of a PON system, which is a communication system, is under consideration. However, in view of accommodating the high-speed wireless communication standard called 5G which is scheduled to be introduced, it is indispensable to broaden the PON system.

  One of the problems in realizing a high-speed PON system is the reduction in the number of branches and the transmission distance due to the reduction in the minimum reception sensitivity. The reasons for the decrease in minimum reception sensitivity include the increase in required SNR to realize error-free transmission by broadening the bandwidth, the influence of polarization mode dispersion (PMD) and chromatic dispersion, and the band limitation of transceivers And degradation of the SNR due to waveform distortion.

  On the other hand, by applying the method using optical amplification technology and the digital coherent reception technology used in the core / metro network described in Non-Patent Document 1, by using it together with the waveform distortion equalization technology by digital signal processing. , It is considered to significantly improve the minimum reception sensitivity. Equalization processing of waveform distortion by digital signal processing includes, for example, equalization processing in the time domain and equalization processing in the frequency domain. In either method, channel characteristics or inverse characteristics are calculated from the received signal, and the received signal is filtered to compensate for waveform distortion caused by the channel condition.

  When the waveform equalization technique by digital signal processing is applied to TDM-PON (Time Division Multiplexing-Passive Optical Network), the calculation time of the waveform equalization coefficient in uplink communication becomes an issue.

  In downstream transmission of TDM-PON, each subscriber unit (ONU: Optical network unit) is assigned in advance among downstream continuous signal light transmitted from the station side apparatus (OLT: Optical line terminal) to all ONUs. The signal of the time slot corresponding to the own terminal is selectively received. Thus, the signal light received by the ONU is continuous light. On the other hand, in the upstream transmission, the signal light received by the OLT is a temporally intermittent optical signal transmitted by each ONU at the timing assigned in advance. At this time, the signal light received by the OLT has different signal light power for each signal light transmitted by the ONU due to the difference in the distance between the ONU and the OLT. Such temporally intermittent signals are generally called burst signals (shown in FIG. 1). The burst signal of the TDM-PON mainly has a burst frame configuration including a preamble, a payload and an end of burst. The preamble includes signal synchronization and a margin used for equalization of the received signal level by an AGC (Automatic-Gain control) circuit. The payload includes the real signal part. The end of burst includes a margin for falling of the laser and the like.

  The burst signal transmitted by each ONU has different signal characteristics due to the difference in frequency characteristics of the devices possessed by each ONU and the difference in transmission distance. At this time, when equalization processing is performed on signals having different characteristics based on the same coefficient, noise may be emphasized due to the difference in channel characteristics. Therefore, it is necessary to use a value derived for each reception burst signal as the waveform equalization coefficient used for waveform equalization processing in the signal processing unit that performs digital signal processing in the OLT. At this time, in uplink burst signal reception, the first method of calculating the waveform equalization coefficient adaptively for each received burst signal in the redundant part of the signal such as the preamble, or the waveform measured in advance for each burst signal, etc. There are two possible configurations of the second method of performing waveform equalization processing using the conversion coefficient.

  In the first method, the calculation of the waveform equalization coefficient used for waveform equalization processing differs in the specifications required for the signal processing unit and the overhead length of the signal used for waveform equalization processing. For example, as a method of adaptively calculating a waveform equalization coefficient used for waveform equalization processing recursively using a square component of an error between an actual transmission path state and an ideal transmission path state as an adaptive equalization algorithm, general Equalization algorithm based on least squares method (LMS) widely used (for example, CMA (Constant modulus algorithm) used in digital coherent reception of phase modulation signal such as QPSK signal in core / metro network etc. ) Can be implemented in a realistic circuit scale, but the convergence of the waveform equalization coefficient takes time, resulting in an increase in overhead and a decrease in throughput. In addition, application of an adaptive equalization algorithm that converges in a short time represented by, for example, recursive least squares (RLS) may be considered. However, while the convergence time is shortened, the amount of calculation is increased, so that the size of the mounted circuit is increased. On the other hand, if the zero forcing method etc. which estimate the transmission characteristic between ONUs and OLTs using a training sequence without recursively calculating the coefficients like LMS and RLS, etc., for calculation of waveform equalization coefficient The overhead is short compared to the above scheme. However, the stability of the waveform equalizer may be lowered because it strongly depends on the channel characteristics at the time of receiving the training sequence.

  According to the second method using the pre-computed waveform equalization coefficient, the overhead required for calculating the waveform equalization coefficient in the preamble can be largely reduced even if any adaptive equalization algorithm described above is used. Be expected. According to Patent Document 1, in upstream communication of TDM-PON using digital coherent reception, an OLT that initializes a waveform equalization coefficient to an arbitrary value at reception timing of a burst signal and calculates a waveform equalization coefficient for each reception burst signal. It is proposed to use the configuration and the waveform equalization coefficient measured in advance at initialization, but the time taken to recalculate the waveform equalization coefficient due to the polarization fluctuation of the burst signal is not taken into consideration. Is low.

JP, 2015-88821, A

Hirota Suzuki et al., "Research and Development of Digital Coherent Signal Processing Technology for Increasing Capacity of Optical Communication Network," Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 95, no. 12, pp. 1100-1116, 2012 Kazuro Kikuchi, "Evaluation of the sensitivity of the Digital Coherent Receiver", JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 26, NO. 13, pp. 1817-1822, JULY 1, 2008

  The present invention is a waveform used for waveform equalization processing of a received signal performed when a burst signal is received in a station-side apparatus (OLT) provided in an optical communication system using a TDM-PON method in which signals are transmitted and received in time division. It aims at shortening the calculation time of an equalization coefficient.

  In order to achieve the above object, according to the present invention, in the TDM-PON optical communication system, a waveform etc. in which the OLT performs waveform equalization processing of the received signal in accordance with the arrival timing of the scheduled optical signal of each ONU Initialize the parameter value of the conversion function.

Specifically, the optical communication system according to the present invention is
An optical communication system according to a TDM-PON (Time Division Multiplexing-Passive Optical Network) system, in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses,
The station-side device
A signal processing unit that performs waveform equalization processing of a burst signal received from a subscriber apparatus using a waveform equalization coefficient ;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber apparatus in a discovery process in which the communication scheduler unit authenticates a subscriber apparatus in an initial communication process for determining communication timing;
Equipped with
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit . initializing the waveform equalization coefficients used by the said signal processing unit.

The optical communication system according to the present invention is
An optical communication system according to a TDM-PON (Time Division Multiplexing-Passive Optical Network) system, in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses,
The station-side device
A signal processing unit that performs waveform equalization processing on a burst signal received from a subscriber apparatus;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber unit by using information on an initial communication process for the communication scheduler unit to determine communication timing;
Equipped with
The signal processing unit
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit the waveform equalization coefficients are initialized,
In the normal communication process after the initial communication process, calculation of the waveform equalization coefficient is started with reference to the waveform equalization coefficient held in the information holding unit at the start timing of the burst frame constituting the burst signal. And
The calculation of the waveform equalization coefficient is finished at the end timing of the burst frame constituting the burst signal, and the waveform equalization coefficient held in the information holding unit is updated.
Power saving operation of stopping the calculation of the waveform equalization coefficient in the normal communication process when the variation amount of the value of the waveform equalization coefficient calculated in the normal communication process is less than or equal to the set threshold in a set period Do.

  In the optical communication system according to the present invention, a preamble of the burst signal in the initial communication process may adopt a configuration longer than a preamble of the burst signal in a normal communication process after the initial communication process.

In the optical communication system according to the present invention,
The signal processing unit
In the normal communication process after the initial communication process,
The calculation of the waveform equalization coefficient is started with reference to the waveform equalization coefficient stored in the information storage unit at the start timing of the burst frame constituting the burst signal,
A configuration may be employed in which the calculation of the waveform equalization coefficient is completed and the waveform equalization coefficient held in the information holding unit is updated at the end timing of the burst frame constituting the burst signal.

In the optical communication system according to the present invention,
The signal processing unit calculates the waveform equalization coefficient in the normal communication process when the variation amount of the value of the waveform equalization coefficient calculated in the normal communication process is equal to or less than a set threshold in a set period. It is possible to adopt a configuration that performs a power saving operation to stop the

In the optical communication system according to the present invention,
The signal processing unit
Detecting a reception signal state of each subscriber unit in the power saving operation;
When there is a subscriber unit whose received signal state is less than or equal to the set threshold value, the calculation of the waveform equalization coefficient is started when the burst signal transmitted from the subscriber unit in the normal communication process is received. Can be adopted.

In the optical communication system according to the present invention,
The signal processing unit
Detecting a report signal transmitted from each subscriber device in the power saving operation;
In the case where there is a subscriber unit for which a report signal is not detected, a configuration may be employed in which calculation of the waveform equalization coefficient is started upon reception of a burst signal transmitted from the subscriber unit in the normal communication process.

In the optical communication system according to the present invention,
The station-side apparatus includes an optical receiving unit that receives a burst signal using a digital coherent reception method,
After compensating for the polarization state of the received signals before Symbol optical receiver for each burst signal, it may employ a configuration performs the waveform equalizing process.

Specifically, the communication device according to the present invention is
A communication apparatus functioning as the station-side apparatus in a TDM-PON (Time Division Multiplexing-Passive Optical Network) optical communication system in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses There,
A signal processing unit that performs waveform equalization processing on a burst signal received from a subscriber apparatus;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber apparatus in a discovery process in which the communication scheduler unit authenticates a subscriber apparatus in an initial communication process for determining communication timing;
Equipped with
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit . initializing the waveform equalization coefficients used by the said signal processing unit.

Specifically, the communication device according to the present invention is
A communication apparatus functioning as the station-side apparatus in a TDM-PON (Time Division Multiplexing-Passive Optical Network) optical communication system in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses There,
A signal processing unit that performs waveform equalization processing on a burst signal received from a subscriber apparatus;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber unit by using information on an initial communication process for the communication scheduler unit to determine communication timing;
Equipped with
The signal processing unit
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit Initialize the waveform equalization coefficients,
In the normal communication process after the initial communication process, calculation of the waveform equalization coefficient is started with reference to the waveform equalization coefficient held in the information holding unit at the start timing of the burst frame constituting the burst signal. And
The calculation of the waveform equalization coefficient is finished at the end timing of the burst frame constituting the burst signal, and the waveform equalization coefficient held in the information holding unit is updated.
Power saving operation of stopping the calculation of the waveform equalization coefficient in the normal communication process when the variation amount of the value of the waveform equalization coefficient calculated in the normal communication process is less than or equal to the set threshold in a set period Do.

  The above inventions can be combined as much as possible.

  According to the present invention, the calculation time of the waveform equalization coefficient at the time of receiving each burst signal can be shortened without lowering the stability of the waveform equalization function of the reception signal, and the throughput can be improved.

An example of a burst signal is shown. An example of composition of OLT concerning a first embodiment is shown. An example of composition of OLT concerning a second embodiment is shown. The 1st example of composition of OLT concerning a third embodiment is shown. The 2nd example of composition of OLT concerning a third embodiment is shown. An example of a structure of a polarization | polarized-light * phase diversity optical receiving part is shown. An example of a structure of OLT relevant to 3rd embodiment is shown. An example of the communication process which concerns on 4th embodiment is shown. The example of control of the signal processing part which concerns on 4th embodiment, and a MAC part is shown. 21 illustrates a first control example of the signal processing unit and the MAC unit according to the fifth embodiment. 21 illustrates a second control example of the signal processing unit and the MAC unit according to the fifth embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiments described below. These implementation examples are merely illustrative, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, components having the same reference numerals denote the same components.

  FIG. 2 shows an example of the configuration of the OLT according to the embodiment. The OLT 91 according to the embodiment includes a light receiving unit 11, an AD conversion unit 12, a signal processing unit 13, and a MAC (Media Access Control) unit 14 in order to receive burst signals transmitted from a plurality of ONUs. The light receiving unit 11 photoelectrically converts the received signal. The AD converter 12 converts the analog signal output from the light receiver 11 into a digital signal. The signal processing unit 13 performs arithmetic processing using the digital signal from the AD conversion unit 12. The signal processing unit 13 includes a waveform equalization unit 31, and performs waveform equalization processing of the received signal for each ONU. The MAC unit 14 performs MAC frame processing on the digital signal. The MAC unit 14 includes a communication scheduler unit 41, and performs scheduling of communication time between each ONU and the OLT.

  The received signal subjected to photoelectric conversion in the light receiving unit 11 is sampled and quantized into a digital signal in the AD conversion unit 12 and then subjected to waveform equalization processing in the signal processing unit 13. The digital signal subjected to the waveform equalization processing is input to the MAC unit 14 after being decoded and subjected to MAC frame processing. As described above, in the reception of burst signals, since the characteristics are different for each received burst signal, it is necessary to optimize the coefficients possessed in the waveform equalization processing of the signal processing unit 13 for each burst signal. Assuming that calculation processing of the waveform equalization coefficient in the signal processing unit 13 is performed at the time of reception of every burst signal, it is necessary to provide a margin for the calculation processing time in the preamble. Therefore, the throughput may be greatly reduced depending on the implemented adaptive equalization algorithm.

  On the other hand, in the upstream communication of the TDM-PON system, after passing through an initial communication process (referred to as a discovery process for convenience) performed in the initial authentication phase between the OLT 91 and each ONU, the ONU follows the communication timing scheduled by the OLT 91. Send a signal. Therefore, in the communication after the initial communication for performing the discovery process, the OLT 91 has the order of receiving the burst signal transmitted from each ONU, and timing information. Therefore, in the normal communication process (referred to as a DBA process for convenience) after the discovery process, the OLT 91 can predict, for each ONU, the reception timing of the burst signal transmitted from the ONU.

  Therefore, in the discovery process, the OLT 91 according to the embodiment obtains the waveform equalization coefficient CF of the waveform equalization unit 31 for each ONU using information that can be acquired in the discovery process, and then in advance in the subsequent DBA process. The waveform equalization processing in the waveform equalization unit 31 is performed for each ONU using the waveform equalization coefficient CF obtained for each ONU. As a result, the OLT 91 according to the embodiment can shorten the calculation time of the waveform equalization coefficient CF at the time of every burst signal reception without reducing the stability of the waveform equalization function of the received signal, thereby improving the throughput. Is possible.

First Embodiment
Focusing on the above, in this embodiment, the waveform equalization coefficient CF corresponding to the burst signal transmitted by each ONU acquired at the time of initial communication is stored in the MAC unit 14 and used as an initial value in the DBA process after the discovery process. .

  The MAC unit 14 includes a communication scheduler unit 41. The communication scheduler unit 41 has a scheduling function of allocating the communication time of each user represented by a Dynamic Bandwidth Allocation (DBA) algorithm or the like. The MAC unit 14 initializes the waveform equalization unit 31 of the signal processing unit 13 using the above-described waveform equalization coefficient CF in accordance with the reception timing of each burst signal determined by the communication scheduler unit 41. Thus, the present embodiment significantly reduces the calculation time of the waveform equalization coefficient CF after the discovery process.

  FIG. 2 shows an example of the configuration of the OLT according to the present embodiment. The OLT 91 has a path for initializing the coefficients of the waveform equalization unit 31 of the signal processing unit 13 at the reception timing of the burst signal determined by the communication scheduler unit 41 using the waveform equalization coefficient CF held in the MAC unit 14. The path may be used as a path for holding the calculated waveform equalization coefficient CF in the MAC unit 14 in the discovery process.

Second Embodiment
In the present embodiment, the OLT 91 receives the burst signal using the intensity modulation-direct detection method. FIG. 3 shows an example of the configuration of the OLT according to the present embodiment. The OLT 91 includes a linear light receiving unit 11A, an AD conversion unit 12, a signal processing unit 13, and a MAC unit 14.

  The signal processing unit 13 includes, for example, a frame detection unit 32, a waveform equalization unit 31, and a clock data recovery unit 33. The frame detection unit 32 has a function of detecting the beginning and the end of the burst frame. As a frame detection method, for example, there is a method of detecting the rise and fall of the burst frame by comparing the power of the AD converted digital signal with an arbitrary threshold value.

  The waveform equalizer 31 performs wavelength dispersion compensation on the AD converted digital signal using a time axis waveform equalization filter or a frequency axis waveform equalization filter. These filters calculate and update the waveform equalization coefficient CF by an adaptive equalization algorithm.

  The MAC unit 14 includes a communication scheduler unit 41 and an information holding unit 42. The information holding unit 42 has a logical link identifier (LLID) of each ONU and a waveform equalization coefficient CF corresponding to each ONU, and at the reception timing of the burst signal determined by the communication scheduler unit 41, the waveform of the signal processing unit 13 The filter coefficients of the quantization unit 31 are initialized. The waveform equalization unit 31 recalculates the waveform equalization coefficient CF at the end timing of the burst frame detected by the frame detection unit 32 described above, and stores the waveform equalization coefficient CF in the information holding unit 42.

  Note that in the exchange of information between the communication scheduler unit 41 and the information holding unit 42, the pull type or communication scheduler unit 41 refers to the reception timing of the burst signal transmitted by each ONU of the communication scheduler unit 41. Either of the push type for notifying the information holding unit 42 of the reception timing may be used.

Third Embodiment
In the present embodiment, the OLT 91 receives a burst signal using a digital coherent reception method. FIG. 4 shows an example of the configuration of the OLT according to the present embodiment. The OLT 91 is assumed to receive a single polarization modulated burst signal in order to simplify the ONU configuration. The OLT 91 includes a local light source for coherent reception, a polarization / phase diversity light receiver 11 B, an AD converter 12, a signal processor 13, and a MAC unit 14. The signal processing unit 13 includes, for example, a frame detection unit 32, a clock recovery unit 34, a polarization compensation unit 35, a waveform equalization unit 31, a wavelength offset / phase compensation unit 37, and a demodulation unit 38.

  The wavelength offset / phase compensation unit 37 may be located before the clock recovery unit 34. Further, as shown in FIG. 5, the clock recovery unit 34 may be an analog feedback type that adjusts the sampling phase and frequency of the AD conversion unit 12 based on the clock shift amount detected from the received digital signal. For example, the DA conversion unit 51 converts the clock restored by the clock recovery unit 34 into an analog signal, and the phase adjustment circuit 52 adjusts the phase of the AD conversion unit 12 according to the analog signal from the DA conversion unit 51.

For example, as shown in FIG. 6, the polarization / phase diversity optical reception unit 11B is a polarization splitter (PBS: polarization beam splitter) 111S, a power splitter (BS: beam splitter) 111L, an optical 90-degree hybrid 112X, 112Y, and a balanced The receiver 113XI, 113XQ, 113YI, 113YQ is provided to separate the IQ components of the respective XY polarizations and perform balanced reception. Here, _assuming that the input power of the signal light input to the polarization / phase diversity reception unit 11B is P _s and the local light power is P _Lo , the reception current detected by each balance receiver is the following equation Is represented by

Each of the above reception currents corresponds to the IQ component of each XY polarization. In the equation, α represents the ratio of power between the XY polarizations, δ represents the phase difference between the XY polarizations, θ _s (t) represents the phase of the local light and the beat signal of the signal light, and θ _n (t) represents the phase noise . When a single polarization modulation signal is received, the intensity modulation component and the phase modulation component respectively correspond to P _s and θ _s (t) in the equation.

  At this time, since the polarization state of the burst signal light received by the OLT 91 temporally changes according to the transmission path condition, the values of α and δ take different values for each of the received burst signals. In addition, due to vibration of the fiber or the like, it may also fluctuate within the burst frame.

  In the digital coherent reception configuration for continuous light related to the embodiment as shown in FIG. 7, as described in Non-Patent Document 1, the waveform equalization unit 31 of the received signal characteristics including the change in the polarization state is Follow the change. Therefore, the filter coefficient of the waveform equalization unit 31 changes according to the change of the polarization state. When a burst signal different from the polarization state of the reception burst frame in the prior measurement is received, it is preferable to recalculate the waveform equalization coefficient CF for the polarization fluctuation.

  In the present embodiment, the second stage of the waveform equalization unit 31 of the signal processing unit 13 omits recalculation of the waveform equalization coefficient CF due to the polarization fluctuation by compensating for the fluctuation or change of the polarization state. It is possible to maximize the reduction effect of the calculation time of the waveform equalization coefficient CF by inputting the pre-measured initial value. Examples of the polarization compensation unit 35 include polarization compensation using the optimal load combining method described in Non-Patent Document 2. In this method, the values of the power ratio α and phase difference δ between the above-mentioned XY polarizations are estimated, and weights proportional to the respective intensities and corrections of phase rotation components are added to the IQ signals of each XY polarization. Polarization synthesis is performed by adding algebraically. Thus, the signal input to the waveform equalization unit 31 does not depend on the polarization state.

  The waveform equalization unit 31 performs waveform equalization processing on the signal whose polarization state has been compensated by the polarization compensation unit 35, using a time axis waveform equalization filter or a frequency axis waveform equalization filter. These filters calculate and update the waveform equalization coefficient CF by an adaptive equalization algorithm.

  The MAC unit 14 includes a communication scheduler unit 41 and an information holding unit 42 as in the second embodiment. The information holding unit 42 has the LLID of each ONU and the waveform equalization coefficient CF corresponding to each ONU, and the filter of the waveform equalization unit 31 of the signal processing unit 13 at the reception timing of the burst signal determined by the communication scheduler unit 41. The coefficients are initialized with waveform equalization coefficients CF. The waveform equalization unit 31 stores the waveform equalization coefficient CF calculated again in the information holding unit 42 at the end timing of the burst frame detected by the frame detection unit 32 described above.

  Note that, in the exchange of information between the communication scheduler unit 41 and the information holding unit 42, a pull type or communication scheduler unit 41 in which the information holding unit 42 refers to the reception timing of the burst signal transmitted by each ONU of the communication scheduler unit 41. Either of the push type in which the information holding unit 42 notifies the reception timing may be used.

Fourth Embodiment
In the present embodiment, referring to FIG. 8, a discovery process in which the OLT 91 authenticates the newly connected ONU 92, and a DBA process in which communication is performed between the OLT 91 and the ONU 92 by allocating communication time of each ONU 92 according to, for example, the DBA algorithm. An example of

  The discovery process operates periodically and authenticates the ONU 92. First, the OLT 91 transmits an upstream transmission permission message S11 for authentication called a Discovery gate signal as a downstream signal to all ONUs 92. After receiving the upstream transmission permission message S11 from the OLT 91, the ONU 92 sends a registration request message S12 to the OLT called a Register request signal after a certain random time. At this time, the ONU 92 adds a preamble (referred to as long preamble for convenience) having a length sufficient for calculation processing of the waveform equalization coefficient CF by the adaptive equalization algorithm. The OLT 91 receives the registration request message S12 transmitted by each ONU 92, calculates the waveform equalization coefficient CF of the waveform equalization unit 31, and adds the LLID, and then holds the information described in the second and third embodiments. The section 42 holds the waveform equalization coefficients CF and LLID.

  In the above series of phases, in order to perform communication scheduling accurately, ranging for measuring a round trip time (RTT) between the OLT 91 and each ONU 92 is also performed simultaneously. Further, a time frame for receiving the registration request message S12 transmitted by each ONU 92 included in the OLT 91 is called a Ranging window. Here, the series of phases in the initial communication are referred to as ranging for the sake of convenience.

  Next, the OLT 91 transmits a Register signal S13 in which the assigned LLID and upstream transmission time are described, and a Gate signal S14 to the ONU 92. The ONU 92 having received the Register signal S13 and the Gate signal S14 sends a Register ACK signal S15 in accordance with the assigned upstream transmission time.

  The OLT 91 initializes the waveform equalization unit 31 using the waveform equalization coefficient CF corresponding to each ONU 92 included in the information holding unit 42 at the predicted reception time predicted from the upstream signal reception timing of each ONU 92 scheduled in advance. , Receive signal processing. At this time, since the Register ACK signal S15 transmitted by the ONU 92 uses a waveform equalization coefficient measured in advance in the OLT 91, it uses a short preamble length (referred to as a short preamble for convenience) as compared with the Register request signal S12. The series of discovery process ends with the reception of the Register ACK signal S15 in the OLT 91 described above.

  Thereafter, the ONU 92 moves to a DBA process for transmitting a report signal S17 for notifying the OLT 91 of the amount of upstream communication and a MAC frame which is upstream data at an arbitrary upstream transmission time determined by the communication scheduler unit 41 of the OLT 91. Also in the DBA process, short preamble is used as in the case of the Register ACK signal S15.

  FIG. 9 shows an example of control of the signal processing unit 13 and the MAC unit 14. First, it is determined whether it is ranging (S401). In the case of ranging (Yes in S401), after detecting the head of the burst frame (S402), the waveform equalization coefficient of the waveform equalization unit 31 is set to a common initial value common to all ONUs (S403) . Thereafter, the calculation of the waveform equalization coefficient CF by the adaptive equalization algorithm is started (S404), the end of the burst frame is detected (S405), and the calculation processing of the waveform equalization coefficient CF is ended (S406). Thereafter, the LLID provided by the MAC unit 14 is associated with the calculated waveform equalization coefficient CF (S407), and then stored in the information holding unit 42 (S408).

  Except at the time of ranging including the DBA process (No in S401), based on the information of the communication scheduler unit 41 and the information holding unit 42 (S101), the waveform equalization unit 31 is adjusted according to the predicted reception time corresponding to each ONU 92. Are initialized (S102). At this time, as the waveform equalization coefficient CF input to the waveform equalization unit 31, the waveform equalization coefficient CF corresponding to each ONU calculated at the time of ranging or at the time of reception of a burst signal one DBA cycle before is used. After detecting the beginning of the burst frame (S103), calculation of the waveform equalization coefficient CF by the adaptive equalization algorithm is started (S104), the end of the burst frame is detected (S105), and calculation processing at the timing of the end of the burst frame End (S106). The calculated waveform equalization coefficient CF is stored and updated in the information holding unit 42.

  At the timing when the end of the burst frame is detected, the waveform equalizer 31 may be initialized according to the burst signal of the ONU to be received next based on the information of the communication scheduler 41 and the user information holder 42. . The same can be applied to the following embodiments.

Fifth Embodiment
In the present embodiment, the waveform equalization unit 31 mainly compensates for waveform distortion caused by transmission characteristics between the OLT 91 and each ONU 92. Also, by continuing to update the waveform equalization coefficient CF adaptively to the received signal, it is possible to cope with the time change of the transmission characteristic. Therefore, the update period of the waveform equalization coefficient CF needs to be equal to or shorter than the period of time change of the transmission characteristic. On the other hand, it is considered that the period of time change of transmission characteristics such as wavelength dispersion and band limitation of the transceiver is longer than the burst frame length or the period of the DBA process. Therefore, after completion of the calculation process of the waveform equalization coefficient CF at the time of ranging, it is possible to reduce the calculation frequency of the waveform equalization coefficient CF and minimize the power consumption by the calculation process.

  Therefore, as shown in the control example of FIG. 10, after the ranging, the calculation processing of the waveform equalization coefficient CF is performed only in the short preamble, and as shown in FIG. The calculation process of the waveform equalization coefficient CF for each burst frame may be omitted.

  For example, as shown in the control example of FIG. 10, the waveform equalization coefficient CF is input to the waveform equalization unit 31 based on the information of the communication scheduler unit 41 and the information holding unit 42 (S201) (S202). After the head of the burst frame is detected (S203), the waveform equalization coefficient CF is calculated only within the preamble time (S204), and the waveform equalization coefficient CF held in the information holding unit 42 is updated (S205).

  For example, as shown in the control example of FIG. 11, based on the information of the communication scheduler unit 41 and the information holding unit 42 (S301), the waveform equalization coefficient CF held according to the predicted reception time corresponding to each ONU 92. Are input to the waveform equalization unit 31 (S302).

  At this time, the stop of the calculation process of the waveform equalization coefficient CF may be determined for each ONU 92. The trigger to shift to the power saving operation by stopping the calculation process of the waveform equalization coefficient CF detects the variation amount of the waveform equalization coefficient CF for a certain fixed period with respect to the burst frame transmitted by each ONU 92 and There is a configuration in which the calculation process of the waveform equalization coefficient CF is omitted in the case of. In addition, a function of monitoring the reception state of the optical signal such as Signal Detection (SD) may be used as a trigger of the power saving operation when the fluctuation amount of the reception signal characteristic is equal to or less than a predetermined threshold.

  On the other hand, if the transmission characteristics fluctuate during the above-described power saving operation, there is a possibility that the upstream signal can not be detected correctly. When the report signal S17 transmitted by the ONU 92 can not be detected, the transmission time of the upstream data signal of the ONU 92 is not allocated in the OLT 92. The ONU 92 for which such a condition has passed for a predetermined time is disconnected because the OLT 91 determines that the link is disconnected.

  Therefore, in the present embodiment, as in the case of transition to the power saving operation, the deterioration of the received signal characteristic is detected using a function such as Signal Detection (SD) that monitors the reception state of the optical signal. The calculation process of equalization coefficient CF is restarted. The above-described optical signal reception state monitoring function may be, for example, a monitor that monitors the number of error corrections of the error correction function. Further, the presence or absence of the report signal S17 transmitted by each ONU 92 is measured, and among the authenticated ONUs, calculation processing of the waveform equalization coefficient CF is resumed for the ONU 92 in which the report signal S17 has not been detected for a certain period. It is good. Thus, the power saving operation of the signal processing unit 13 is realized.

  The present invention can be applied to the information communication industry.

11: optical receiver 11A: linear optical receiver 11B: polarization / phase diversity optical receiver 12: AD converter 13: signal processor 14: MAC unit 31: waveform equalizer 32: frame detector 33: clock data Recovery unit 34: Clock recovery unit 35: Polarization compensation unit 37: Wavelength offset / phase compensation unit 38: Demodulation unit 41: Communication scheduler unit 42: Information holding unit 91: OLT
92: ONU

Claims (10)

An optical communication system according to a TDM-PON (Time Division Multiplexing-Passive Optical Network) system, in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses,
The station-side device
A signal processing unit that performs waveform equalization processing of a burst signal received from a subscriber apparatus using a waveform equalization coefficient ;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber apparatus in a discovery process in which the communication scheduler unit authenticates a subscriber apparatus in an initial communication process for determining communication timing;
Equipped with
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit . initializing the waveform equalization coefficients used by the said signal processor,
Optical communication system. The preamble of the burst signal in the initial communication process is longer than the preamble of the burst signal in a normal communication process after the initial communication process,
The optical communication system according to claim 1 . The signal processing unit
In the normal communication process after the initial communication process,
The calculation of the waveform equalization coefficient is started with reference to the waveform equalization coefficient stored in the information storage unit at the start timing of the burst frame constituting the burst signal,
At the end timing of the burst frame constituting the burst signal, the calculation of the waveform equalization coefficient is ended, and the waveform equalization coefficient held in the information holding unit is updated.
Optical communication system according to claim 1 or 2. The signal processing unit calculates the waveform equalization coefficient in the normal communication process when the variation amount of the value of the waveform equalization coefficient calculated in the normal communication process is equal to or less than a set threshold in a set period. Do the power saving operation to stop the
The optical communication system according to claim 3 . An optical communication system according to a TDM-PON (Time Division Multiplexing-Passive Optical Network) system, in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses,
The station-side device
A signal processing unit that performs waveform equalization processing on a burst signal received from a subscriber apparatus;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber unit by using information on an initial communication process for the communication scheduler unit to determine communication timing;
Equipped with
The signal processing unit
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit Initialize the waveform equalization coefficients,
In the normal communication process after the initial communication process, calculation of the waveform equalization coefficient is started with reference to the waveform equalization coefficient held in the information holding unit at the start timing of the burst frame constituting the burst signal. And
The calculation of the waveform equalization coefficient is finished at the end timing of the burst frame constituting the burst signal, and the waveform equalization coefficient held in the information holding unit is updated.
Power saving operation of stopping the calculation of the waveform equalization coefficient in the normal communication process when the variation amount of the value of the waveform equalization coefficient calculated in the normal communication process is less than or equal to the set threshold in a set period I do,
Optical communication system. The signal processing unit
Detecting a reception signal state of each subscriber unit in the power saving operation;
If there is a subscriber unit whose received signal state is less than or equal to a set threshold value, calculation of the waveform equalization coefficient is started upon reception of a burst signal transmitted from the subscriber unit in the normal communication process,
The optical communication system according to claim 4 or 5 . The signal processing unit
Detecting a report signal transmitted from each subscriber device in the power saving operation;
If there is a subscriber unit whose report signal is not detected, calculation of the waveform equalization coefficient is started upon reception of a burst signal transmitted from the subscriber unit in the normal communication process.
The optical communication system according to claim 5 or 6. The station-side apparatus includes an optical receiving unit that receives a burst signal using a digital coherent reception method,
After compensating for the polarization state of the received signals before Symbol optical receiver for each burst signal, it performs the waveform equalization process,
The optical communication system according to any one of claims 1 to 7. A communication apparatus functioning as the station-side apparatus in a TDM-PON (Time Division Multiplexing-Passive Optical Network) optical communication system in which a station-side apparatus receives temporally intermittent burst signals transmitted by a plurality of subscriber apparatuses There,
A signal processing unit that performs waveform equalization processing on a burst signal received from a subscriber apparatus;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber apparatus in a discovery process in which the communication scheduler unit authenticates a subscriber apparatus in an initial communication process for determining communication timing;
Equipped with
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit . initializing the waveform equalization coefficients used by the said signal processor,
Communication device. TDM-PON (Time Division Multiplexing- Passive Optical Network) communication device functioning as the station-side apparatus definitive optical communication system schemes station apparatus receives a temporally discontinuous burst signal to be transmitted a plurality of subscriber units And
A signal processing unit that performs waveform equalization processing on a burst signal received from a subscriber apparatus;
A communication scheduler unit that determines a communication timing for transmitting a burst signal from a subscriber unit to a station-side unit;
An information holding unit for holding a waveform equalization coefficient derived for each subscriber unit by using information on an initial communication process for the communication scheduler unit to determine communication timing;
Equipped with
The signal processing unit
The signal processing unit uses the waveform equalization coefficient for each subscriber unit held in the information holding unit in accordance with the arrival timing of the optical signal from the subscriber unit determined by the communication scheduler unit Initialize the waveform equalization coefficients ,
In the normal communication process after the initial communication process, calculation of the waveform equalization coefficient is started with reference to the waveform equalization coefficient held in the information holding unit at the start timing of the burst frame constituting the burst signal. And
The calculation of the waveform equalization coefficient is finished at the end timing of the burst frame constituting the burst signal, and the waveform equalization coefficient held in the information holding unit is updated.
Power saving operation of stopping the calculation of the waveform equalization coefficient in the normal communication process when the variation amount of the value of the waveform equalization coefficient calculated in the normal communication process is less than or equal to the set threshold in a set period I do,
Communication device.

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