JP6053163B2 - Multilevel modulation signal generation method and optical communication system - Google Patents

Description

  The present invention relates to a multi-level modulation signal generation method for coexisting subscriber premises apparatuses of different generations and an optical communication system in which subscriber premises apparatuses of different generations can coexist.

  As a current optical access system, as shown in FIG. 1, one station side device (OLT: Optical Line Terminal) 101 and a plurality of subscriber home side devices (ONU: Optical Network Unit) 201 are connected via a power splitter 150. The Passive Optical Network (PON) system 301 is widely used.

  In such an optical access system, when performing a transition that generally requires replacement of a device from one generation system to the next generation system, it is important to replace all ONUs at the same time. Difficult depending on conditions such as desired service. Therefore, as in the PON system 302 in FIG. 2, some means is required for providing services by connecting ONUs of different generations (new ONU and old ONU) to one next-generation new OLT. This means is called a coexistence method. A technique for dividing a wavelength into a service for a new ONU and a service for an old ONU using a wavelength division division multiplexing (WDM) has been proposed.

  On the other hand, multi-level modulation using digital signal processing technology can increase the speed of optical fiber communication without increasing the bandwidth, and studies for applying such technology to optical access systems have also been conducted. ing. In order to introduce this technology to the downlink communication of an access system, an old ONU that cannot receive a multilevel modulation signal and can only receive an OOK signal and a new ONU that can receive a multilevel modulation signal are connected simultaneously. Thus, a coexistence method for providing services is required. The former ONU includes only a direct detector as a receiver, and the latter includes a coherent detector and a digital signal processing unit as a receiver. As one means of the coexistence method, as shown in FIG. 3, the old ONU 201 is OOK using a Star-QAM type multi-level modulation signal (particularly, one whose amplitude is modulated at two levels) modulated by amplitude and phase. A coexistence method has been proposed in which a signal and a multilevel modulation signal including phase modulation are simultaneously transmitted to the new ONU 202 (see, for example, Non-Patent Document 1).

N. Iiyama, S-Y. Kim, T .; Shimada, S .; Kimura and N.K. Yoshimoto, “Co-existent downstream scheme between OOK and QAM signals in an optical access network using software-defined technology,”. OFC'12, paper JTh2A. 53, 2012.

As a basic characteristic of a Star-QAM type signal whose amplitude is modulated at two levels, the ratio of the two levels of amplitude can be freely set, but the signal of the component of amplitude modulation and the component of phase modulation depends on the value. The quality changes as shown in FIG. When the amplitude ratio decreases, the eye opening in the eye pattern of the signal received by the old ONU decreases, and the signal quality of the amplitude modulation component deteriorates. On the other hand, in the constellation received by the new ONU, the distance between the two circles is close and the signal quality of the amplitude modulation component is also degraded, but the minimum inter-signal distance of the phase modulation component is large, and the signal quality is improves. When the amplitude ratio is increased, the opposite is true, the signal quality of the amplitude modulation component is improved, and the signal quality of the phase modulation component is degraded. Thus, the signal quality of the amplitude modulation component and the phase modulation component is a trade-off with respect to the amplitude ratio.
The signal quality of the amplitude modulation component and the signal quality of the phase modulation component mean the signal quality of the amplitude modulation component and the signal quality of the phase modulation component detected from the received Star-QAM type multilevel modulation signal, respectively.

  In a Star-QAM type signal whose amplitude is modulated at two levels, the signal quality of the amplitude modulation component and the phase modulation component is a trade-off with respect to the amplitude ratio, so the old ONU and the new ONU depend on the set amplitude ratio. In this case, the received signal cannot satisfy the prescribed signal quality at the same time, and replacement and coexistence become difficult. The value of the amplitude ratio of the Star-QAM signal that enables replacement and coexistence has not been shown so far.

  Accordingly, an object of the present invention is to provide a multi-level modulation signal generation method and an optical communication system in which received signals in an old ONU and a new ONU can simultaneously satisfy a prescribed signal quality.

  In order to achieve the above object, the present invention adjusts the amplitude ratio at the time of modulation so that the extinction ratio of the multilevel modulation signal falls within a predetermined range when the multilevel modulation signal from the OLT is directly detected by the PD. It was decided to.

Specifically, the multi-level modulation signal generation method according to the present invention includes:
At least one first customer premises unit (ONU) capable of receiving only an on-off-keying (OOK) signal;
At least one second ONU capable of receiving a multi-level modulation signal;
One station side device (OLT: Optical Line Terminal) that transmits a multi-level modulation signal by modulating light from a light source with two levels of amplitude and phase;
An optical transmission line connecting the first ONU, the second ONU, and the OLT via a power splitter;
A multi-level modulation signal generating method for generating a multi-level modulation signal transmitted by the OLT in an optical communication system comprising:
Before SL multilevel modulation signal light receiving element: a measuring step that detects direct (PD Photo Diode), to measure the extinction ratio of the multi-level modulation signal,
A setting step of setting the generation parameter of the multilevel modulation signal in the OLT so that both the phase modulation component and the amplitude modulation component of the multilevel modulation signal have an extinction ratio that satisfies a prescribed signal quality;
Repeat in order.

The optical communication system according to the present invention is
At least one first ONU capable of receiving only an OOK signal;
At least one second ONU capable of receiving a multi-level modulation signal;
One OLT for transmitting a multi-level modulation signal by modulating light from a light source with two levels of amplitude and phase;
An optical transmission line connecting the first ONU, the second ONU, and the OLT via a power splitter;
An optical communication system comprising:
In the OLT, the generation parameter of the multilevel modulation signal is set so that both the phase modulation component and the amplitude modulation component of the multilevel modulation signal have an extinction ratio that satisfies a prescribed signal quality. .

The OLT modulates light from a light source and transmits a multilevel modulation signal. The generated parameters of the multi-level modulation signal in OLT as extinction ratio when the multilevel modulated signal obtained by detecting directly PD (may be PD Old ONU) is an amplitude ratio of the multi-level modulation signal lies in a predetermined range Adjust. The predetermined range of the extinction ratio is a range according to the communication standard. In this way, by confirming the extinction ratio and adjusting the generation parameter of the multi-level modulation signal in the OLT, it becomes possible for the received signals in the old ONU and the new ONU to simultaneously satisfy the prescribed signal quality.

  Therefore, the present invention can provide a multilevel modulation signal generation method and an optical communication system in which received signals in an old ONU and a new ONU can simultaneously satisfy a prescribed signal quality.

  The multi-level modulation signal generating method and the optical communication system according to the present invention are characterized in that, in the setting step, the extinction ratio is larger than 6.1 dB and smaller than 12.3 dB.

  Assuming that the old system is IEEE 802.3av 10G-EPON, the amplitude ratio is adjusted to 10 Gsymbol / s so that the extinction ratio is in the range of 6.1 dB to 12.3 dB when directly detecting with PD. A Star 8-QAM signal is used. As a result, as shown in FIG. 5, all signals received by the old ONU and the new ONU achieve BER <10E-03 with a receiving sensitivity of −28 dBm or less, and the old ONU of IEEE 802.3av 10G-EPON, A coherent receiver and a new ONU equipped with a DSP can coexist under the same OLT.

  The multilevel modulation signal generation method and the optical communication system according to the present invention are characterized in that, in the setting step, the extinction ratio is larger than 8.2 dB and smaller than 12.3 dB.

  ITU-T G. Assuming 987 series XG-PON, when detecting directly with PD, 10 Gsymbol / s Star 8-QAM signal with amplitude ratio adjusted so that extinction ratio is in the range of 8.2 dB to 12.3 dB Is used. As a result, as shown in FIG. 5, all signals received by the old ONU and the new ONU have achieved a BER <10E-03 with a receiving sensitivity of −28 dBm or less. It becomes possible for the 987 series XG-PON old ONU and the new ONU equipped with a coherent receiver and DSP to coexist under the same OLT.

  In the optical communication system according to the present invention, the first ONU, the second ONU, and the OLT may have a wavelength multiplexing function.

  The present invention can provide a multilevel modulation signal generation method and an optical communication system in which received signals in an old ONU and a new ONU can simultaneously satisfy a prescribed signal quality.

It is a figure explaining a PON system. It is a figure explaining a PON system. It is a figure explaining the PON system of the coexistence system which transmits an OOK signal and a multi-value modulation signal simultaneously. It is a figure explaining the change of the signal quality of the component of an amplitude modulation by the level ratio of an amplitude, and the component of a phase modulation. The minimum received light power in which the bit error rate (BER) of the amplitude modulation component and the phase modulation component of the signal received by the old ONU and the heart ONU when the multilevel modulation signal is transmitted from the OLT is smaller than 10E-03 will be described. FIG. It is a figure explaining the signal quality of each signal component of the old and new ONU with respect to the amplitude ratio of the multilevel modulation signal. It is a figure explaining the structure of new OLT. It is a figure explaining the structure of old ONU. It is a figure explaining the structure of new ONU.

  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)
As shown in FIG. 3, when switching from an old system that handles only a certain OOK signal to a new system that handles a multilevel modulation signal, the old ONU, phase modulation signal, and amplitude modulation that can receive only the OOK signal under the same PON New ONUs capable of receiving multi-level modulation signals including signals are mixed, and coexistence is realized by the OLT transmitting a Star-QAM signal. In general, in the Star-QAM signal, the amplitude modulation component and the phase modulation component have a trade-off relationship as shown in FIG. In FIG. 6, the horizontal axis represents the signal amplitude ratio, and the vertical axis represents the received light power satisfying a specified signal quality. The minimum light sensitivity defined by the old system standard is indicated by a double line. When the amplitude ratio is increased, the signal quality of the amplitude modulation component is improved, so that the specified signal quality can be satisfied with a smaller received light power. Conversely, since the signal quality of the phase modulation component deteriorates, a larger received light power is required to satisfy a specified signal quality. In addition, since the new ONU includes a coherent detector, the amplitude modulation component can satisfy the prescribed signal quality with a smaller received light power than the old ONU that receives a signal by direct detection.

  When a signal is generated with the amplitude ratio set to a value smaller than a for a system in which the quality of signal components in each ONU is represented in FIG. 6, the received signal of the old ONU does not satisfy the prescribed quality. It will be. This is because when the state of FIG. 1 is switched to the state of FIG. 2 (when the transmission signal becomes a Star-QAM type signal), the old ONU cannot receive a signal with the same quality as the state of FIG. Thus, it is indicated that the replacement of the old ONU with the new ONU by the Star-QAM type signal having the amplitude ratio smaller than a and the coexistence under the same PON are impossible. On the other hand, when the amplitude ratio is larger than b, the signal of the phase modulation component of the new ONU does not satisfy the prescribed quality. This also means that when the state of FIG. 1 is switched to the state of FIG. 2, the phase modulation component of the new ONU has not been received with a prescribed quality, and the Star-QAM type in which the amplitude ratio is greater than b. This indicates that it is impossible to replace the old ONU with the new ONU by a signal and to coexist under the same PON. That is, when the amplitude ratio is between a and b, all the signals satisfy the specified quality, so that the old ONU is replaced with the new ONU by the Star-QAM type signal with the amplitude ratio between a and b. , And coexistence under the same PON is possible.

The optical communication system of this embodiment is
At least one first ONU capable of receiving only an OOK signal;
At least one second ONU capable of receiving a multi-level modulation signal;
One OLT for transmitting a multi-level modulation signal by modulating light from a light source with two levels of amplitude and phase;
An optical transmission line connecting the first ONU, the second ONU, and the OLT via a power splitter;
An optical communication system comprising:
In the OLT, the generation parameter of the multilevel modulation signal is set so that both the phase modulation component and the amplitude modulation component of the multilevel modulation signal have an extinction ratio that satisfies a prescribed signal quality. .

The amplitude ratio of the two-level amplitude of the multilevel modulation signal is determined as follows.
Before SL multilevel modulation signal light receiving element: a measuring step that detects direct (PD Photo Diode), to measure the extinction ratio of the multi-level modulation signal,
A setting step of setting the generation parameter of the multilevel modulation signal in the OLT so that both the phase modulation component and the amplitude modulation component of the multilevel modulation signal have an extinction ratio that satisfies a prescribed signal quality;
Repeat in order.

  The optical communication system of this embodiment is characterized in that the extinction ratio is larger than 6.1 dB and smaller than 12.3 dB.

  In this embodiment, it is assumed that the old system is IEEE 802.3av 10G-EPON, and the ONU is the old ONU. The amplitude ratio of the Star 8-QAM signal that enables the old ONU and the new ONU to coexist is specified by numerical calculation. The transmitter part of the OLT 102, the receiver part of the old ONU 201, and the receiver part of the new ONU 202 are configured as shown in FIG. However, only the part directly related to the present invention is shown.

  The OLT 102 generates a 4ASK signal of an I component and a Q component by a DSP (digital signal processing unit) 11 and inputs the 4ASK signal to the IQ modulator 13 through the D / A converter 12, whereby Star 8− A QAM signal is generated. The power of the transmission signal was adjusted to +2.5 dBm. When the 4ASK signal is generated by the DSP 11, the amplitude ratio can be changed by adjusting the interval between the four amplitudes. In this specification, a parameter set in the DSP 11 in order to adjust the interval of the four-level amplitude of the 4ASK signal is referred to as a “multi-level modulation signal generation parameter”.

  The old ONU 201 includes a PD 21. The old ONU 201 receives the Star 8-QAM signal transmitted from the OLT 102 by the PD 21 and directly detects it. The old ONU 201 can receive only the OOK signal. Therefore, the old ONU 201 receives only the amplitude modulation component of the Star 8-QAM signal as the OOK signal.

  The new ONU 202 receives a signal by a coherent detector 25 including a light source, a light source 26, a 90 ° hybrid 27, and a balance PD 28, and performs restoration, demodulation, and the like of the signal by a DSP 30 through an A / D converter 29.

  The line width and output power of the light source 14 of the OLT 102 and the light source 26 of the new ONU 202 were 100 kHz and 10.0 dBm, respectively. In the above system, when a Star 8-QAM signal having a symbol rate of 10 G symbol / s is transmitted from the OLT 102, the bit error rate (BER) of the amplitude modulation component and the phase modulation component of the signal received by the old ONU 201 and the new ONU 202 is FIG. 5 shows the minimum light receiving power smaller than 10E-03.

また、１０Ｇ−ＥＰＯＮ ＯＮＵ（ｃｌａｓｓ ＰＲ３０）の最小受光感度である−２８ｄＢｍを点線で示している。 In FIG. 5, the horizontal axis represents the extinction ratio of the eye pattern when the signal is directly detected by the PD 21, and the vertical axis represents the minimum received light power at which the BER is smaller than 10E-03. The marks in FIG. 5 mean the following.
(Legend)

Further, −28 dBm, which is the minimum light receiving sensitivity of 10G-EPON ONU (class PR30), is indicated by a dotted line.

  As shown in FIG. 5, the range in which the received light power satisfying BER <10E-03 is −28 dBm or less is 6.1 dB to 12.3 dB. Therefore, the range of the extinction ratio when directly detected by the PD 21 is this range. The OLT 102 is set to transmit a Star 8-QAM signal that falls within the range. Specifically, a generation parameter capable of generating the Star 8-QAM signal is set in the DSP 11. Thereby, it is possible to replace the 10G-EPON ONU with an ONU including a coherent detector and a DSP, and coexistence under the same PON. Moreover, since the extinction ratio of the transmitter of 10G-EPON OLT is 6.0 dB or more, the range of 6.1 dB to 12.3 dB satisfies the standard.

(Embodiment 2)
The optical communication system of this embodiment is characterized in that the extinction ratio is larger than 8.2 dB and smaller than 12.3 dB.

  In the present embodiment, the old system is replaced with ITU-T G.264. Assume 987 series XG-PON. The minimum light receiving sensitivity of the ONG (class N1) of XG-PON is −27 dBm. For this reason, the OLT 102 adjusts the amplitude ratio of the Star 8-QAM signal so that the extinction ratio range when directly detected by the PD 21 falls within the range of 6.1 dB to 12.3 dB (sets a generation parameter in the DSP 11). Thus, it is possible to replace the XG-PON ONU with an ONU including a coherent detector and a DSP, and coexistence under the same PON. However, in XG-PON, since the extinction ratio standard is 8.2 dB or more, the extinction ratio range when directly detecting with PD is in the range of 8.2 dB to 12.3 dB when complying with the specification. In the OLT 102, the amplitude ratio of the Star 8-QAM signal is adjusted.

(Embodiment 3)
In the first and second embodiments, the old system is in the form of TDM-PON, but the present invention is also applied to the coexistence of the old ONU and the new ONU in the same wavelength in the WDM / TDM-PON in which these are wavelength-multiplexed. can do.

(Other embodiments)
In the above embodiment, the method of directly detecting the Star 8-QAM signal by the old ONU 201 and adjusting the amplitude ratio has been described. However, a dedicated measuring instrument for condition adjustment is connected to the subscriber side of the optical transmission line to connect the Star 8 A method of directly detecting the QAM signal and adjusting the amplitude ratio may be used. Alternatively, a method may be used in which a dedicated measuring instrument for condition adjustment is directly connected to the output port of the OLT 102, and the amplitude ratio is adjusted by directly detecting the output Star 8-QAM signal.

(Appendix)
The following is a description of the present invention.
TECHNICAL FIELD The present invention relates to a technique for smoothly and economically transitioning from an already installed system to the next generation system in an optical access system, and to specifying a range of parameters to which the technique can be applied. .
<Issues>
In introducing multi-level modulation technology using digital signal processing into an optical access system having a PON configuration, Star-QAM uses a Star-QAM type signal to coexist with an ONU that handles only an existing OOK signal. Depending on the value of the amplitude ratio of the type signal, the received signal of either the old or new ONU does not satisfy the prescribed quality, and replacement and coexistence are impossible. However, the range of the amplitude ratio of the Star-QAM type signal in which both the new and old ONUs can receive signals with the prescribed signal quality has not been clearly shown so far.

<Solution>
When a Star 8-QAM signal was transmitted under the conditions of a symbol rate of 10 Gsymbol / s and a transmission power of +2.5 dBm, the signal quality of each signal component of the old and new ONU with respect to the amplitude ratio was obtained as shown in FIG. From this result, when using the Star 8-QAM signal whose extinction ratio is in the range of 6.1 dB to 12.3 dB when directly detecting with the PD, all the signals received by the old ONU and the new ONU are all received. The signal achieves BER <10E-03 with a receiving sensitivity of −28 dBm or less, IEEE 802.3av 10G-EPON or ITU-T G. A 987 series XG-PON ONU, a coherent receiver, and a DSP, which can receive an amplitude modulation component and a phase modulation component, can be replaced and can coexist in the same OLT.

The main configuration of the present invention is as follows.
(1): Transmitter that generates Star 8-QAM such that the extinction ratio is smaller than 12.3 dB when direct detection is performed by a PD.
(2): A transmitter that generates the Star 8-QAM having the same configuration as the above (1) and further having an extinction ratio larger than 6.1 dB.
(3): Transmitter that generates Star 8-QAM with the same configuration as in (1) above, such that the extinction ratio is further greater than 8.2 dB.
(4): An OLT including the transmitter of any one of (1) to (3) above, an ONU conforming to IEEE 802.3av 10G-EPON including only a direct detector, a coherent detector, and a DSP, A PON system comprising an ONU capable of receiving an amplitude modulation signal and a phase modulation signal.
(5): OLT provided with the transmitter of any one of (1) to (3) above, and ITU-T G.1 provided with only a direct detector. 987 Series A PON system comprising an ONU that conforms to XG-PON, a coherent detector, and a DSP that can receive amplitude-modulated signals and phase-modulated signals.
(6): A PON system having the wavelength multiplexing function in the configuration of (4) or (5).

11: DPS
12: D / A converter 13: IQ modulator 14: Light source 21: PD
25: Coherent detector 26: Light source 27: 90 ° hybrid 28: Balanced PD
29: A / D converter 30: DSP
101, 102: OLT
150: Power splitter 201, 202: ONU
301, 302: PON system

Claims (2)

At least one first customer premises unit (ONU) capable of receiving only an on-off-keying (OOK) signal;
At least one second ONU capable of receiving a multi-level modulation signal;
One station side device (OLT: Optical Line Terminal) that transmits a multi-level modulation signal by modulating the light from the light source with the phase and amplitude of two levels;
An optical transmission line connecting the first ONU, the second ONU, and the OLT via a power splitter;
A multi-level modulation signal generating method for generating a multi-level modulation signal transmitted by the OLT in an optical communication system comprising:
A measurement step of directly detecting the multilevel modulation signal as a reception signal by a light receiving element (PD: Photo Diode) of the first ONU and measuring an extinction ratio of the multilevel modulation signal;
The extinction ratio of the multi-level modulation signal measured in the measurement step is made larger than 6.1 dB and smaller than 12.3 dB, and the received signals in the first ONU and the second ONU satisfy the specified signal quality at the same time. A setting step of setting a generation parameter of a multi-level modulation signal in the OLT;
A method for generating a multi-level modulation signal in order.   2. The multilevel modulation signal generation method according to claim 1, wherein, in the setting step, the extinction ratio is made larger than 8.2 dB and smaller than 12.3 dB.

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