JP5761321B2 - Station building terminal, subscriber terminal, and optical access network including station building terminal and subscriber terminal - Google Patents

Description

The present invention relates to a station terminal suitable for use in an optical network using Orthogonal Frequency Division Multiplexing (OFDM) , a subscriber terminal, and an optical access network including these station terminal and subscriber terminal. is there.

  As an optical access network, a passive optical network (PON) is known. The PON includes one station terminal (OLT: Optical Line Terminal) provided in the station and a plurality of subscriber terminals (ONU: Optical Network Unit) provided in each subscriber house. The OLT and the ONU are connected by an optical fiber via an optical multiplexer / demultiplexer called an optical splitter.

  In PON, signals transmitted from each ONU to the OLT (hereinafter also referred to as upstream signals) are combined by an optical splitter and transmitted to the OLT. On the other hand, a signal (hereinafter also referred to as a downstream signal) sent from the OLT to each ONU is demultiplexed by the optical splitter and transmitted to each ONU. Note that different wavelengths are assigned to the upstream signal and the downstream signal in order to prevent interference between the upstream signal and the downstream signal.

  In PON, various multiplexing techniques are used. The multiplexing technology used in the PON includes time division multiplexing (TDM) technology in which a short interval on the time axis is assigned to each subscriber, wavelength division multiplexing (WDM) in which different wavelengths are assigned to each subscriber (WDM: Wave Division Division Multiplex). And code division multiplexing (CDM) technology that assigns different codes to each subscriber. Among these multiplexing techniques, TDM-PON using TDM is currently most widely used. In TDM-PON, TDMA (Time Division Multiple Access) is used. TDMA is a technique in which the OLT manages the transmission timing of each ONU so that uplink signals from different ONUs do not collide with each other.

A typical PON is GE-PON using Gigabit (1 × 10 ⁹ bits / sec) Ethernet (registered trademark) technology (see, for example, Non-Patent Document 1).

  In GE-PON, the OLT periodically broadcasts a discovery gate. The discovery gate is transmitted to all ONUs regardless of whether or not the ONU is registered.

  When an unregistered ONU receives a discovery gate, it transmits a register request for requesting registration to the OLT.

  The OLT recognizes an unregistered ONU by receiving a register request. The OLT assigns a logical link identifier called LLID (Logical Link ID) to the recognized ONU and sends a register to the recognized ONU. The register includes LLID. By transmitting the register, the OLT establishes a communication link with the ONU.

  Further, following the transmission of the register, the OLT sends a gate (GATE) including information on the transmission start time and the transmission amount to the ONU. The ONU that has received the gate transmits a register ACK to the OLT. When the OLT receives the register ACK, the ONU registration is completed. In this way, when an ONU is connected to a PON, the OLT automatically discovers and registers that ONU. The process of registering an ONU newly connected to the PON in the OLT is called P2MP discovery.

  In P2MP discovery, the OLT performs frame round trip time (RTT) measurement with the ONU using a gate and a register ack, and the ONU performs time synchronization with the OLT. RTT measurement and time synchronization are periodically performed thereafter, and are corrected when a deviation occurs due to a change in transmission path conditions.

  After the ONU is registered, normal communication between the OLT and the ONU is performed.

  By the way, in the present optical access network, in addition to the request | requirement of the capacity | capacitance increase of a network by the increase in mobile traffic, the use expansion of moving image content, etc., construction of a highly efficient network is requested | required.

  As a technique for realizing such a network, attention is focused on a network in which a multi-level modulation technique and an orthogonal frequency division multiplexing (OFDM) technique that are widely used in wireless communication are applied to optical fiber transmission.

  OOK (On Off Keying) modulation is so-called binary modulation in which 1-bit data is transmitted in one symbol. On the other hand, multilevel modulation can transmit data of 2 bits or more in one symbol. As multi-level modulation, QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM, and the like are known.

  The characteristics of multilevel modulation will be described with reference to FIG. 1A to 1D are schematic diagrams for explaining the characteristics of multilevel modulation. 1A to 1D show the wavelength on the horizontal axis.

FIG. 1A shows OOK including 1-bit data in one symbol. FIG. 1B shows QPSK including 2 bits of data in one symbol. FIG. 1C shows 16QAM including 4-bit data in one symbol. FIG. 1D shows 64QAM including 6-bit data in one symbol. QPSK, 16QAM and 64QAM shown in FIGS. 1B to 1D are so-called multilevel modulation, and the number of modulation multilevels increases in the order of QPSK, 16QAM and 64QAM. Note that multilevel modulation is not limited to these, and can be 2 ⁿ QAM (n is an integer of 2 or more). As shown in FIG. 1, when the modulation multi-level number is small, the wavelength band utilization efficiency (hereinafter, band utilization efficiency) is slightly lowered, but the reception sensitivity is increased. On the other hand, when the modulation multi-level number is large, the band utilization efficiency is high, but the reception sensitivity is slightly low.

  In OFDM, band utilization efficiency can be improved by multicarrier transmission. Multi-carrier transmission will be described with reference to FIG. FIG. 2 is a schematic diagram for explaining multicarrier transmission. FIG. 2 shows the frequency on the horizontal axis. In multicarrier transmission, a plurality of subcarriers having different frequencies can be transmitted in parallel while partially overlapping. Therefore, a highly efficient network can be realized by combining OFDM and the above-described multilevel modulation technique.

  In OFDM, there is coherent detection as a technique for receiving an optical signal. In the coherent detection, an optical signal and a local oscillation light source (LO: Local Oscillator) light are caused to interfere with each other in the OLT and ONU terminal devices, and an interference signal generated thereby is detected. In coherent detection, the intensity of noise with respect to an interference signal can be relatively reduced by setting the intensity of LO light (LO light intensity) large. Therefore, it is a reception method with excellent noise resistance.

  In recent years, research and development of an elastic λ aggregation network (EλAN) has attracted attention as a network using multilevel modulation technology and OFDM (for example, see Non-Patent Document 2).

  In EλAN, a programmable OLT (P-OLT) and a programmable ONU (P-ONU) are connected via an ODN (Optical Distribution Network). In communication between the P-OLT and the P-ONU, OFDM is used. In this case, an OFDM signal is transmitted as a downlink signal, and a signal obtained by performing TDMA on the OFDM signal is transmitted as an uplink signal.

  In P-OLT and P-ONU, the modulation multi-level number, the number of subcarriers, the symbol rate, and the wavelength are variable. The P-OLT sets an optimum modulation multi-level number, subcarrier number, symbol rate, and wavelength according to the traffic situation of the network, and transmits a downlink signal to the P-ONU. The P-ONU transmits the upstream signal in accordance with the modulation format of the downstream signal transmitted by the P-OLT. In EλAN, any one of QPSK, 16QAM, and 64QAM is selected, and the downlink signal and the uplink signal are modulated.

  As a method for determining the optimum modulation multi-level number, there is a technique for calculating the distance between the P-OLT and a plurality of P-ONUs from the RTT, and calculating the SN ratio (Signal to Noise ratio) based on the distances. Yes (see Non-Patent Document 3, for example). In the technique disclosed in Non-Patent Document 3, the optimum modulation multilevel number is determined using the SN ratio, the transmission light intensity (PW) of P-OLT, and the minimum light receiving sensitivity at each modulation multilevel number. .

  In this technique, a plurality of P-ONUs connected to the P-OLT are divided into three groups of short distance, medium distance, and long distance according to the distance to the P-OLT. Since a short-distance P-ONU has a high SN ratio, it is possible to perform communication with a large modulation multi-level number with low reception sensitivity. Therefore, band utilization efficiency can be improved by selecting, for example, 64QAM having a large modulation multilevel number. On the other hand, since a long-distance P-ONU has a low SN ratio, it is necessary to perform communication with a small modulation multi-level number with high reception sensitivity. Therefore, although it is disadvantageous from the viewpoint of improving bandwidth utilization efficiency, for example, QPSK with high reception sensitivity is selected.

"Technology Basic Course GE-PON Technology" NTT Technology Journal, September 2005 Satoshi Okamoto “Retractable Optical Metro / Access Fusion Aggregation Network Technology for Realizing Various Services and Network Configurations-Elastic λ Aggregation Network-” IEICE Technical Report Hiroyuki Saito et al. “Improvement of bandwidth utilization efficiency of PON by optimizing multi-level modulation” IEICE

  Here, the traffic situation in the optical access network changes dynamically. With reference to FIG. 3, the temporal transition of traffic will be described. FIG. 3 is a diagram for explaining the temporal transition of traffic, with the time on the horizontal axis and the traffic on the vertical axis.

  As shown in FIG. 3, for example, traffic is large from day to night in a day, and traffic is small from midnight to early morning. Corresponding to such increase / decrease in traffic, the P-OLT is required to allocate a use band for each P-ONU. Furthermore, in the current optical access network, the communication quality (required quality) required by the user is diversified from low communication quality such as mail to high communication quality such as video conference. For this reason, it is necessary to change the modulation multi-level number for communication with each P-ONU as the traffic increases or decreases and the required quality is high or low.

  In a time zone when traffic is large, it is desirable that the P-OLT and each P-ONU communicate with each other with a large modulation multi-level number in order to improve the bandwidth utilization efficiency.

  However, as described above, a long-distance P-ONU has a low S / N ratio, so it is necessary to perform communication with a small modulation multi-level number with high reception sensitivity. For this reason, even in a situation where network traffic has increased, a long-distance P-ONU cannot communicate with an increased number of modulation levels. Therefore, it hinders improvement in bandwidth utilization efficiency.

  On the other hand, it is desirable to reduce power consumption in a time zone when traffic is small. In a time zone in which traffic is small, there is room in the bandwidth, so communication can be performed even with a small modulation multilevel number. Then, from the relationship between the LO light intensity and the reception sensitivity, which will be described later, it is possible to suppress a decrease in the reception sensitivity even when the LO light intensity is attenuated by decreasing the modulation multi-value number.

  However, conventionally, the ONU LO light intensity is fixed at a specific value. For this reason, even if the modulation multi-level number is lowered, the LO light intensity is not changed, so that power consumption cannot be reduced.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a central office terminal (OLT) that is advantageous in both bandwidth utilization efficiency improvement and power saving in an optical access network using OFDM , It is to provide a subscriber terminal (ONU) and an optical access network including these OLT and ONU.

In order to achieve the above-described object, in an optical access network using orthogonal frequency division multiplexing (OFDM) according to the present invention, a station terminal (OLT) connected to a plurality of subscriber terminals (ONUs) has the following characteristics. I have.

  The OLT according to the present invention includes a signal transmission unit, a signal reception unit, and a signal control unit.

Signal transmission unit, an OFDM electric signal generator for generating an OFDM electrical signal based on one or both of the input downlink data and downlink control signal, and an electrical / optical converter for converting an OFDM electrical signal to the OFDM optical signal Is included. The signal transmission unit can cope with a change in the modulation multi-level number used for communication with the ONU.

The signal reception unit includes an optical / electric conversion unit that converts an OFDM optical signal into an OFDM electrical signal, and a control signal extraction unit that extracts an uplink control signal from the OFDM electrical signal. The signal receiving unit can cope with a change in the modulation multi-level number used for communication with the ONU.

Signal control unit uses a light intensity determining unit that determines the strength of the local oscillator source light to be set to the ONU, the information of the intensity of the local oscillation light source light to be set to the ONU light intensity determining unit has determined, and the communication It includes a downlink control signal generation unit that generates a downlink control signal including information on the modulation multi-level number, and a traffic monitoring unit that monitors network traffic based on information received from a plurality of ONUs. In addition, the signal control unit determines the modulation multi-level number used for communication with the ONU.
When traffic is increasing, the downlink control signal for the ONU that is not communicating with the maximum settable modulation multi-level number is the information that increases the modulation multi-level number that is communicated, and the local oscillation that should be set by the ONU Information that increases the intensity of the light source light is included. In addition, when traffic tends to decrease, a downlink control signal for an ONU that is not communicating with the minimum settable modulation multi-level number should be set to the information that lowers the modulation multi-level number for communication and the ONU. It includes information that attenuates the intensity of the local oscillation light source light .

In the optical access network using the OFDM of the present invention, the ONU connected to the OLT of the present invention described above has the following features.

  The ONU according to the present invention includes a signal transmission unit, a signal reception unit, and a signal control unit.

Signal transmitting unit includes a OFDM electric signal generator for generating an OFDM electrical signal by adding the uplink control signal to the uplink data input and an electrical / optical converter for converting an OFDM electrical signal to the OFDM optical signal Yes. The signal transmission unit can cope with a change in the modulation multi-level number used for communication with the OLT.

The signal receiving unit has a local oscillation light source that can change the intensity of the local oscillation light source light , and an optical / electric conversion unit that converts the OFDM optical signal into an OFDM electrical signal, and extracts a downlink control signal from the OFDM electrical signal And a control signal extraction unit. The signal receiving unit can cope with a change of the modulation multi-level number used for communication with the OLT.

The signal control unit includes an uplink control signal generation unit that generates an uplink control signal, and a downlink control signal reading that reads information on the intensity of the local oscillation light source light and information on the modulation multi-level number used for communication included in the downlink control signal. And a light intensity setting unit that sets the intensity of the local oscillation light source light based on the intensity information of the local oscillation light source light included in the downlink control signal. In addition, the signal control unit sets the modulation multilevel number used for communication with the OLT.
When receiving a downlink control signal including information for increasing the intensity of the local oscillation light source and information for increasing the modulation multi-level number used for communication, the signal control unit increases the intensity of the local oscillation light source light , Increase the number of modulation multi-levels used for communication. In addition, when receiving a downlink control signal including information for attenuating the intensity of the local oscillation light source and information for reducing the modulation multi-level number used for communication, the signal control unit attenuates the intensity of the local oscillation light source light. At the same time, the number of modulation multilevels used for communication is lowered.

  The optical access network according to the present invention includes the above-described OLT and ONU.

According to the OLT, ONU, and optical access network of the present invention, the intensity of the local oscillation light source light of the ONU can be changed. Therefore, it is possible to change the modulation multi-level number without deteriorating the reception sensitivity. Therefore, it is possible to improve the bandwidth utilization efficiency in a time zone in which traffic is increasing and to reduce power consumption in a time zone in which traffic is decreasing. Furthermore, even when there is no change in traffic, the intensity of local oscillation light source light is increased to increase the reception sensitivity or the intensity of local oscillation light source light is decreased in accordance with the change in required quality of the ONU. Power consumption can be reduced.

It is a schematic diagram for demonstrating the characteristic of multi-value modulation. It is a schematic diagram for demonstrating the characteristic of OFDM. It is a figure for demonstrating the time transition of traffic. It is a schematic diagram for demonstrating an optical access network. It is a figure which shows the relationship between LO light intensity and receiving sensitivity. It is a figure which shows the database which OLT has. It is a flowchart for demonstrating the communication method of embodiment of this invention. It is a flowchart for demonstrating band efficiency improvement mode. It is a flowchart for demonstrating a power saving mode. It is a flowchart for demonstrating band efficiency maintenance mode. It is a schematic block diagram of OLT. It is a schematic block diagram of ONU.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the drawings are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, numerical conditions and the like are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(Optical access network)
An optical access network will be described with reference to FIG. 4A and 4B are schematic diagrams for explaining the optical access network. FIG. 4A is a schematic view of a PON configured similarly to that disclosed in Non-Patent Document 1. FIG. 4B is a schematic diagram of EλAN configured similarly to that disclosed in Non-Patent Document 2.

  The PON 10 includes one station terminal (OLT: Optical Line Terminal) 20 and N (N is an integer of 1 or more) subscriber terminals (ONU: Optical Network Unit) connected via an optical transmission line 40. 30-1 to N. The optical transmission line 40 includes, for example, an optical fiber 46 and an optical splitter 44 to constitute a star topology.

  The EλAN 12 includes N subscriber terminals (ONUs) connected to M (M is an integer of 1 or more) station terminals (OLT) 22-1 to M through an ODN (Optical Distribution Network) 42. ) 32-1 to N. In order to make it possible to change the service provided by EλAN12 in a programmable manner, in EλAN12, a programmable OLT (P-OLT) is used as OLT 22-1 to M, and a programmable ONU (P-ONU) is used as ONU 32-1 to N. Used. In EλAN12, the OLT to which the ONU is registered, that is, the pair of OLT and ONU is freely changed.

These optical access networks use a combination of multi-level modulation technology and OFDM. That is, as a subcarrier of the OFDM signal, a signal that is multi-value modulated by any one of QPSK, 16QAM, and 64QAM is transmitted / received. Note that, here, a case where three types of multilevel modulation of QPSK, 16QAM, and 64QAM are performed will be described, but the present invention is not limited to this and can be 2 ⁿ QAM (n is an integer of 2 or more). The number of multi-values such as 256QAM may be further increased, or a configuration in which two or more kinds of multi-value modulation are performed may be employed.

(Summary of Invention)
The inventor simulated changes in reception sensitivity with respect to changes in LO light intensity for QPSK, 16QAM, and 64QAM. In this simulation, the reception sensitivities of QPSK, 16QAM, and 64QAM were confirmed when the LO light intensity of the ONU was set to 0 dBm and 10 dBm. The simulation results will be described with reference to FIG. FIG. 5 is a diagram showing a relationship between LO light intensity and reception sensitivity in QPSK, 16QAM, and 64QAM. In FIG. 5, the horizontal axis represents the received light intensity in dBm units, and the vertical axis represents the reception error rate in the ONU on a logarithmic scale. In FIG. 5, “x” indicates the result of QPSK when the LO light intensity is set to 10 dBm. * Indicates the result of 16QAM when the LO light intensity is set to 10 dBm. ● shows the result of 64QAM when the LO light intensity is set to 10 dBm. The symbol ◇ indicates the result of QPSK when the LO light intensity is set to 0 dBm. (2) shows the result of 16QAM when the LO light intensity is set to 0 dBm. Δ indicates the result of 64QAM when the LO light intensity is set to 0 dBm.

  As shown in FIG. 5, in each modulation multilevel number, when the LO light intensity is 10 dBm, the received light intensity with respect to a certain error rate is smaller than when the LO light intensity is 0 dBm. This result means that reception is possible with a small received light intensity by increasing the LO light intensity. Therefore, it can be seen from FIG. 5 that the reception sensitivity is improved by increasing the LO light intensity. Therefore, by increasing the LO light intensity, the modulation multi-value number can be increased without degrading the reception sensitivity. Therefore, even if the ONU is far from the OLT, the modulation multi-level number can be increased by increasing the LO light intensity. By increasing the number of modulation multi-values used for communication with each ONU, the bandwidth utilization efficiency of the entire network can be improved even in a time zone when traffic is large.

  Further, from FIG. 5, even when the LO light intensity is 0 dBm, a small modulation multi-level number has a large difference in reception sensitivity compared to a large modulation multi-level number with a LO light intensity of 10 dBm. You can see that there is no. For example, QPSK when the LO light intensity is 0 dBm is less deteriorated in reception sensitivity than 64 QAM when the LO light intensity is 10 dBm. Therefore, by reducing the modulation multi-value number, it is possible to attenuate the LO light intensity while suppressing deterioration of reception sensitivity. Therefore, the power of the entire network can be suppressed by reducing the modulation multi-level number used for communication with each ONU and attenuating the LO light intensity in a time zone in which the traffic is small.

  In this embodiment, based on the relationship between the LO light intensity and the reception sensitivity shown in FIG. 5, the LO light intensity and the modulation multi-level number that the OLT is optimal in accordance with the traffic of the optical access network and the required quality from the ONU. To decide. Here, the quality of the ONU is defined by the error rate. The smaller the error rate, the better the quality.

(Database)
In this embodiment, the OLT has a database that associates the modulation multi-level number with the required quality. The OLT refers to this database to determine the LO light intensity to be set in the ONU. An example of the database is shown in FIG. FIG. 6 is an example of a database possessed by the OLT, and the values of LO light intensity are included in A to U in the figure.

In this database, the LO light intensity satisfying the required quality is shown for the set modulation multi-level number. For example, when communication is performed using QPSK and the required quality from the ONU is 10 ⁻³ , the LO light intensity is determined to be a value of A.

  Here, as already described, depending on the distance between the OLT and the ONU, the SN ratio differs in each ONU. Therefore, the optimum value of the LO light intensity for each ONU is different. Therefore, the OLT has a database optimized for each ONU based on the distance between the OLT and the ONU calculated from the RTT.

  Depending on the distance between the OLT and the ONU, it may not be possible to set the LO light intensity that satisfies both the modulation multi-level number and the required quality conditions. For example, for ONUs that are far from the OLT, it is difficult to increase the modulation multi-level number when the required quality is high. Accordingly, the LO light intensity values A to U indicated by the database may include a blank as being impossible to set.

(Communication method)
The communication method of this embodiment will be described with reference to FIG. FIG. 7 is a flowchart for explaining a process performed by the OLT in the communication method of this embodiment. In this embodiment, the OLT performs the flow shown in FIG. 7 at regular intervals.

  The OLT monitors the traffic of the entire network and the temporal transition of the traffic based on the data amount (requested data amount) requested by each ONU performing communication. The OLT determines whether there is a change in traffic (S1). In this determination, for example, the traffic at the previous LO light intensity determination (previous traffic) and the traffic at the start of the current flow (current traffic) are compared. If the difference between the previous traffic and the current traffic is equal to or greater than a certain value, it is determined that there is a change in the traffic, and the process proceeds to S2.

  When there is a change in traffic, the OLT determines whether the traffic tends to increase or decrease (S2). If the current traffic is larger than the previous traffic, it is determined that the traffic is increasing, and the mode is shifted to the bandwidth efficiency improvement mode (S3). On the other hand, when the current traffic is smaller than the previous traffic, the mode shifts to the power saving mode (S4).

  In S1, when the difference between the previous traffic and the current traffic is smaller than a certain value, it is determined that there is no change in the traffic, and the bandwidth efficiency maintaining mode (S5) is entered.

  The OLT determines the LO light intensity of each ONU in any one of the bandwidth efficiency improvement mode (S3), the power saving mode (S4), and the bandwidth efficiency maintenance mode (S5). Hereinafter, each mode will be described.

(Band efficiency improvement mode)
The bandwidth efficiency improvement mode will be described with reference to FIG. FIG. 8 is a flowchart for explaining a process performed by the OLT for the ONU in the bandwidth efficiency improvement mode. In the bandwidth efficiency improvement mode, the OLT performs the flow shown in FIG. 8 for each ONU that performs communication, and determines each modulation multi-level number and LO light intensity.

  First, the OLT determines whether or not the modulation multi-level number used in the current communication is 64QAM (S301). If the current modulation multilevel number is 64QAM, the modulation multilevel number and the LO light intensity are maintained without being changed (S302). On the other hand, if the current modulation level is not 64QAM, it is determined whether the modulation level is 16QAM (S303).

  If the result of determination in S303 is that the current modulation multilevel number is 16QAM, the database (see FIG. 6) is referred to. Then, when the modulation multi-level number is changed to 64QAM, the LO light intensity value corresponding to the required quality from the ONU is confirmed (S304). As already described, depending on the distance between the OLT and the ONU, blanks may be included in the LO light intensity values A to U indicated by the database. Therefore, the OLT determines whether or not the LO light intensity value confirmed in S304 is blank. That is, it is determined whether or not the LO light intensity can be changed (S305). As a result of the determination, if the change is possible, the modulation multi-value number is changed to 64QAM, and the LO light intensity is changed to the value confirmed by the database (S306). Here, since the modulation multi-level number increases, the LO light intensity to be set increases. If the LO light intensity value in the database is blank, that is, if it cannot be changed, the modulation multi-value number and the LO light intensity are maintained without being changed (S307).

  On the other hand, if the result of determination in S303 is that the current modulation multilevel number is not 16QAM (ie, the current modulation multilevel number is QPSK), the database is referred to. Then, when the modulation multi-level number is changed to 16QAM, the LO light intensity value corresponding to the required quality from the ONU is confirmed (S308). Next, when the modulation multilevel number is changed to 16QAM, it is determined whether or not the LO light intensity can be changed (S309). As a result of the determination, if the change is possible, the modulation multi-value number is changed to 16QAM, and the LO light intensity is changed to a value confirmed by the database (S310). Here, since the modulation multi-level number increases, the LO light intensity to be set increases. If the LO light intensity value in the database is blank, that is, if it cannot be changed, the modulation multi-value number and the LO light intensity are maintained without being changed (S311).

  In the bandwidth efficiency improvement mode, the OLT determines the modulation multi-level number and LO light intensity for one ONU, and when the flow described above is completed, the OLT starts a similar flow for the other ONU. By sequentially executing this for each ONU, the number of modulation levels and the LO light intensity of each ONU performing communication are determined.

  Further, in the band efficiency improvement mode, when the OLT changes the modulation multi-level number and the LO light intensity, it notifies the ONU of the changed modulation multi-level number and the LO light intensity. The ONU that has received the notification changes the LO light intensity in response to an instruction from the OLT, and notifies the OLT to that effect. Thereafter, the OLT and the ONU communicate with the changed modulation multi-level number.

  As described above, in the bandwidth efficiency improvement mode, the OLT increases the modulation multi-value number and sets the LO light intensity to a value that satisfies the required quality for the ONU that can change the modulation multi-value number and the LO light intensity. Increase. As a result, the bandwidth utilization efficiency of the entire network can be improved without degrading the reception sensitivity for each ONU in a time zone in which traffic tends to increase.

(Power saving mode)
The power saving mode will be described with reference to FIG. FIG. 9 is a flowchart for explaining a process performed by the OLT for the ONU in the power saving mode. In the power saving mode, the OLT performs the flow shown in FIG. 9 for each ONU performing communication, and determines each modulation multi-value number and LO light intensity.

  First, the OLT determines whether or not the modulation multilevel number used in the current communication is QPSK (S401). If the current modulation multilevel number is QPSK, the modulation multilevel number and the LO light intensity are maintained without being changed (S402). On the other hand, if the current modulation multilevel number is not QPSK, it is determined whether or not the modulation multilevel number is 16QAM (S403).

  If the result of determination in S403 is that the current modulation multilevel number is 16QAM, the OLT refers to the database (see FIG. 6). Then, when the modulation multi-level number is changed to QPSK, the LO light intensity value corresponding to the required quality from the ONU is confirmed (S404). Then, the modulation multilevel number is changed to QPSK, and the LO light intensity is changed to a value confirmed by the database. Here, since the modulation multi-level number decreases, the LO light intensity to be set attenuates.

  On the other hand, if the result of determination in S403 is that the current modulation multilevel number is not 16QAM (that is, the current modulation multilevel number is 64QAM), the database is referred to. Then, when the modulation multi-level number is changed to 16QAM, the LO light intensity value corresponding to the required quality from the ONU is confirmed (S405). Then, the modulation multi-level number is changed to 16QAM, and the LO light intensity is changed to a value confirmed by the database. Here, since the modulation multi-level number decreases, the LO light intensity to be set attenuates.

  In the power saving mode, the OLT determines the modulation multi-level number and the LO light intensity for one ONU, and when the above-described flow is finished, the OLT starts a similar flow for the other one ONU. By sequentially executing this for each ONU, the number of modulation levels and the LO light intensity of each ONU performing communication are determined.

  Further, in the power saving mode, when the OLT changes the modulation multi-level number and the LO light intensity, it notifies the ONU of the changed modulation multi-level number and the LO light intensity. The ONU that has received the notification changes the LO light intensity in response to an instruction from the OLT, and notifies the OLT to that effect. Thereafter, the OLT and the ONU communicate with the changed modulation multi-level number.

  As described above, in the power saving mode, the OLT reduces the modulation multi-level number and attenuates the LO light intensity within a range of values satisfying the required quality with respect to an ONU that performs communication using 16QAM and 64QAM. As a result, the power of the entire network can be suppressed without degrading the reception sensitivity for each ONU in a time zone in which traffic tends to decrease.

(Band efficiency maintenance mode)
The bandwidth efficiency maintenance mode will be described with reference to FIG. FIG. 10 is a flowchart for explaining a process performed by the OLT for the ONU in the bandwidth efficiency maintenance mode. In the bandwidth efficiency maintenance mode, the OLT performs the flow shown in FIG. 10 for each ONU that performs communication, and determines the LO light intensity.

  First, the OLT determines whether there is a change in the required quality from the ONU (S501).

  If the required quality is changed as a result of the determination in S501, the OLT refers to the database (see FIG. 6). Then, in the required quality after the change, the value of the LO light intensity corresponding to the current modulation multi-level number is confirmed (S502).

  Next, it is determined whether or not the LO light intensity can be changed according to the required quality after the change (S503). As a result of the determination, if the change is possible, the LO light intensity is changed to a value confirmed by the database (S504). When the required quality from the ONU decreases, the LO light intensity is attenuated based on the database. When the required quality is improved, the LO light intensity is increased based on the database. If the LO light intensity value in the database is blank, that is, if it cannot be changed, the modulation multi-value number and the LO light intensity are maintained without being changed (S505).

  On the other hand, if there is no change in the required quality as a result of the determination in S501, the LO light intensity is maintained without being changed.

  In the bandwidth efficiency maintenance mode, the OLT determines the LO light intensity for one ONU, and when the flow described above is completed, the OLT starts a similar flow for the other ONU. By executing this sequentially for each ONU, the LO light intensity of each ONU performing communication is determined.

  In addition, in the bandwidth efficiency maintenance mode, when the OLT changes the LO light intensity, it notifies the ONU of the changed LO light intensity. The ONU that has received the notification changes the LO light intensity in response to an instruction from the OLT, and notifies the OLT to that effect.

  Thus, in the bandwidth efficiency maintenance mode, the OLT can change the LO light intensity even when there is no change in traffic. For example, when the required quality from the ONU that can change the LO light intensity is improved, the reception sensitivity can be increased by increasing the LO light intensity. Further, when the required quality from the ONU is reduced, the power can be suppressed by reducing the LO light intensity.

(OLT)
The OLT will be described with reference to FIG. FIG. 11 is a schematic configuration diagram of the OLT.

  The OLT 200 includes a downlink signal transmission unit 210, an uplink signal reception unit 250, and a signal control unit 280. The OLT 200 transmits the downlink data received from the upper network 50 to the ONU via the downlink signal transmission unit 210, and transmits the uplink data received from the ONU to the upper network 50 via the uplink signal reception unit 250. Further, the signal control unit 280 generates a downlink control signal, transmits the downlink control signal to the ONU via the downlink signal transmission unit 210, and receives the uplink control signal extracted by the uplink signal reception unit 250.

  The downlink signal transmission unit 210 includes a serial / parallel conversion unit (S / P) 212, a symbol mapper 214, a control signal insertion unit 220, an inverse fast Fourier transform unit (IFFT: Inverse Fast Fourier Transformer) 230, a parallel-serial conversion unit (P / P). S) 232, a digital-analog converter (D / A) 234, and an electro-optical converter (E / O) 236 are provided in series.

  A serial bit string is input to the S / P 212 as downstream data. The S / P 212 stores a bit string. The accumulated bit string is serial-parallel converted and sent to the symbol mapper 214.

  The symbol mapper 214 converts a plurality of bits of data into corresponding complex symbols. That is, the symbol mapper 214 converts data of a plurality of bits into an in-phase (I) component and a quadrature (Q) component, respectively. For example, when the modulation multi-level number is binary, that is, in the case of QPSK, the symbol mapper 214 generates a set of I component and Q component from 2-bit data. In the case of 16QAM, the symbol mapper 214 generates a set of I component and Q component from 4-bit data. Further, in the case of 64QAM, the symbol mapper 214 generates a set of I component and Q component from 6-bit data. In the symbol mapper 214, which of QPSK, 16QAM, and 64QAM is used to convert to a complex symbol is determined by an instruction from the signal control unit 280.

  Although the configuration in which downlink data is sent to the symbol mapper 214 via the S / P 212 has been described here, the present invention is not limited to this. For example, the downlink data may be sent to the S / P 212 via the symbol mapper 214.

  A part of the OFDM symbol, which is a complex symbol, generated by the symbol mapper 214 is sent to the control signal insertion unit 220, and the others are sent to the IFFT 230. Here, a case where the number of subcarriers is two or more will be described. The OFDM symbol is divided into two or more subcarriers, and is output from the symbol mapper 214 as two systems of signals. One of the subcarriers is input to the control signal insertion unit 220 as a signal of one system. The other subcarriers are sent to IFFT 230 through the control signal insertion unit 220 as signals of the other system.

  Control signal inserting section 220 adds the downlink control signal sent from signal control section 280 to the subcarrier. The subcarrier to which the downlink control signal is added is sent to IFFT 230.

  IFFT 230 collectively performs inverse fast Fourier transform on a plurality of sets of I component and Q component received from symbol mapper 214 and control signal insertion unit 220 to generate an OFDM symbol.

  In addition, although the structure provided with IFFT as an element which performs an inverse fast Fourier transform was demonstrated here, it is not limited to this. For example, instead of IFFT, an inverse discrete Fourier transform unit (IDFT: Inverse Discrete Fourier Transformer) may be provided.

  The P / S 232 performs parallel-serial conversion on the OFDM symbol to generate a digital continuous signal that is a two-symbol sequence and sends it to the D / A 234.

  The D / A 234 converts a digital continuous signal into an analog signal.

  The E / O 236 modulates continuous light with an analog signal to generate an OFDM optical signal. The E / O 236 can be realized by those skilled in the art, and illustration and detailed description thereof are omitted here.

  The upstream signal reception unit 250 includes an optical-electric conversion unit (O / E) 276, an analog-digital conversion unit (A / D) 274, a serial-parallel conversion unit (S / P) 272, and a fast Fourier transform unit (FFT) 270. , A symbol demapper 254, a control signal extraction unit 260, and a parallel / serial conversion unit (P / S) 252.

  The O / E 276 can be configured using, for example, a coherent receiver using LO. Then, the upstream OFDM optical signal is received by the above-described coherent detection and converted into an electrical signal. As a result, an in-phase (I) component of the OFDM electrical signal and a quadrature (Q) component of the OFDM electrical signal are generated from the uplink OFDM optical signal.

  The A / D 274 converts the OFDM electrical signal into a digital signal. This digital signal is sent to S / P272. The digital signal is serial / parallel converted in S / P272. The serial / parallel converted signal is sent to a fast Fourier transform unit (FFT) 270. The FFT 270 performs a fast Fourier transform on the digital signal. A DFT can be used instead of the FFT.

  The symbol demapper 254 generates a bit string from the fast Fourier transformed digital signal. The symbol demapper 254 generates a bit string based on one of QPSK, 16QAM, and 64QAM in accordance with an instruction from the signal control unit 280. A part of the bit string generated by the symbol demapper 254 is sent to the control signal extraction unit 260, and the others are sent to the P / S 252. Here, one subcarrier to which the uplink control signal is added is input to control signal extraction section 260. The other subcarriers pass through the control signal extraction unit 260 and are sent to the P / S 252.

  The control signal extraction unit 260 extracts the uplink control signal from the subcarrier and sends it to the signal control unit 280. The subcarrier after the uplink control signal is extracted is sent to P / S 252.

  The P / S 252 accumulates the bit strings received from the symbol demapper 254 and the control signal extraction unit 260. The accumulated bit string is parallel-serial converted and sent to the upper network 50.

  The signal control unit 280 includes a downlink control signal generation unit 282, an uplink control signal reading unit 284, a traffic monitoring unit 286, and an LO light intensity determination unit 288.

  The downlink control signal generation unit 282 generates a downlink control signal. The downlink control signal includes information on the modulation multi-level number used in the next communication and the intensity of the LO light to be set by the ONU in the next communication.

  The uplink control signal reading unit 284 reads information included in the uplink control signal. The uplink control signal includes information on the currently set ONU LO light intensity, required quality, and required data amount.

  The traffic monitor unit 286 monitors the traffic of the entire network from the requested data amount of each ONU read by the uplink control signal reading unit 284.

  The LO light intensity determination unit 288 refers to the database (see FIG. 6) to determine the intensity of LO light to be set in each ONU. The database may be stored in any suitable storage unit and read by the LO light intensity determination unit 288.

  The OLT 200 executes the flow described with reference to FIGS. 7 to 10 at regular time intervals. Then, the LO light intensity and the modulation multi-value number used for communication are changed according to changes in traffic or required quality. Then, the changed LO light intensity information is notified to the ONU by the downlink control signal.

  The OLT 200 of this embodiment is different from the conventional OLT in the configuration of the signal control unit 280. Since other configurations can be configured in the same manner as a conventional OLT using OFDM, detailed description is omitted. Other conventionally well-known configurations used for transmission of OFDM signals, such as means for adding a cyclic prefix (CP) to compensate for the effects of typical multipath as distortion in the transmission path You may make it the structure provided with an element.

  The OLT can also transmit and store a database (see FIG. 6) optimized for each ONU according to the distance to each corresponding ONU. In that case, the OLT can notify the ONU of the LO light intensity to be set by an address (for example, symbols A to U in FIG. 6) in the database.

(ONU)
The ONU will be described with reference to FIG. FIG. 12 is a schematic configuration diagram of the ONU.

  The ONU 300 includes an upstream signal transmission unit 310, a downstream signal reception unit 350, and a signal control unit 380. The ONU 300 transmits uplink data received from the user terminal 60 to the OLT via the uplink signal transmission unit 310, and transmits downlink data received from the OLT to the user terminal 60 via the downlink signal reception unit 350. In addition, the signal control unit 380 generates an uplink control signal, transmits the uplink control signal to the OLT via the uplink signal transmission unit 310, and receives the downlink control signal extracted by the downlink signal reception unit 350.

  The uplink signal transmission unit 310 includes a serial / parallel conversion unit (S / P) 312, a symbol mapper 314, a control signal insertion unit 320, an inverse fast Fourier transform unit (IFFT) 330, a parallel / serial conversion unit (P / S) 332, digital An analog conversion unit (D / A) 334 and an electro-optical conversion unit (E / O) 336 are provided in series.

  The downlink signal receiving unit 350 includes an opto-electric conversion unit (O / E) 376, an analog-digital conversion unit (A / D) 374, a serial-parallel conversion unit (S / P) 372, and a fast Fourier transform unit (FFT) 370. , A symbol demapper 354, a control signal extraction unit 360, and a parallel / serial conversion unit (P / S) 352.

  The O / E 376 can be configured using a coherent receiver using LO. The LO included in the O / E 376 is configured to be able to change the LO light intensity in accordance with an instruction from the signal control unit 380.

  Other functions of the constituent elements of the upstream signal transmission unit 310 and the downstream signal reception unit 350 are the same as those of the downstream signal transmission unit and the upstream signal reception unit of the OLT, respectively, and thus redundant description is omitted.

  The signal control unit 380 includes an uplink control signal generation unit 382, a downlink control signal reading unit 384, and an LO light intensity setting unit 386.

  The uplink control signal generation unit 382 generates an uplink control signal. The uplink control signal includes information on the currently set LO light intensity, required quality, and required data amount.

  The downlink control signal reading unit 384 reads information included in the downlink control signal. The downlink control signal includes information on the modulation level used in the next communication and the LO light intensity to be set in the next communication.

  The LO light intensity setting unit 386 sets the LO light intensity based on the LO light intensity information included in the downlink control signal read by the downlink control signal reading unit 384.

  The ONU 300 changes the LO light intensity of the O / E 376 according to an instruction from the LO light intensity setting unit 386 when the OLT notifies the change of the modulation multi-value number and the LO light intensity by the downlink control signal. Then, the OLT is notified by the uplink control signal that the LO light intensity has been changed. Further, the symbol mapper 314 and the symbol demapper 354 change the modulation multi-value number to be converted to the notified modulation multi-value number according to an instruction from the signal control unit 380. As a result, the next and subsequent communications can be performed with the modulated multi-level number after the change.

  Note that the ONU 300 of this embodiment is different from the conventional ONU in that the configuration of the signal control unit 380 and the LO light intensity of the O / E 376 can be changed. Since other configurations can be configured in the same manner as a conventional ONU using OFDM, detailed description is omitted.

  As described above, according to the OLT, the ONU, the optical access network including the ONU and the OLT, and the communication method according to the present invention, the LO light intensity of the ONU can be changed. Therefore, it is possible to change the modulation multi-level number without deteriorating the reception sensitivity. Therefore, it is possible to improve the bandwidth utilization efficiency in a time zone in which traffic is increasing and to reduce power consumption in a time zone in which traffic is decreasing.

  Furthermore, even when there is no change in traffic, the power consumption can be suppressed by increasing the LO light intensity to increase the reception sensitivity or decreasing the LO light intensity in accordance with the change in the required quality of the ONU. it can.

10: PON
12: EλAN
20, 22, 200: Station terminal (OLT)
30, 32, 300: Subscriber terminal (ONU)
40: Optical transmission line 42: ODN
44: Optical splitter 46: Optical fiber 50: Upper network 60: User terminal 210: Downstream signal transmission unit 212, 272, 312, 372: Series-parallel conversion unit (S / P)
214, 314: Symbol mapper 220, 320: Control signal insertion unit 230, 330: Inverse fast Fourier transform unit (IFFT)
232, 252, 332, 352: parallel-serial converter (P / S)
234, 334: Digital-analog converter (D / A)
236, 336: electro-optical conversion unit (E / O)
250: Uplink signal reception unit 254, 354: Symbol demapper 260, 360: Control signal extraction unit 270, 370: Fast Fourier transform unit (FFT)
274, 374: Analog-digital converter (A / D)
276, 376: Opto-electric converter (O / E)
280, 380: Signal control unit 282: Downlink control signal generation unit 284: Uplink control signal reading unit 286: Traffic monitoring unit 288: LO light intensity determination unit 310: Uplink signal transmission unit 350: Downlink signal reception unit 382: Uplink control signal Generation unit 384: Downlink control signal reading unit 386: LO light intensity setting unit

Claims (7)

In an optical network using Orthogonal Frequency Division Multiplexing (OFDM) , a station terminal connected to a plurality of subscriber terminals,
And OFDM electric signal generator for generating an OFDM electrical signal based on either one or both of the input downlink data and downlink control signal,
An electrical / optical converter that converts an OFDM electrical signal into an OFDM optical signal, and a signal transmitter capable of responding to a change in the number of modulation levels used for communication with the subscriber terminal,
An optical / electrical converter for converting an OFDM optical signal into an OFDM electrical signal;
A control signal extraction unit that extracts an uplink control signal from the OFDM electrical signal, and a signal reception unit that can cope with a change in the number of modulation multilevels used for communication with the subscriber terminal,
And a light intensity determination unit for determining the intensity of the local oscillation light source light to be set in the subscriber terminal,
A downlink control signal generation unit that generates the downlink control signal including information on the intensity of the local oscillation light source light to be set in the subscriber terminal determined by the light intensity determination unit, and information on the modulation multi-level number used for communication; ,
A traffic monitoring unit that monitors network traffic based on information received from the plurality of subscriber terminals, and a signal control unit that determines a modulation multi-level number used for communication with the subscriber terminal,
In the case where the traffic is increasing,
The downlink control signal for the previous SL subscribers terminals not communicating with the maximum modulation level can be set, the information to increase the number of modulation level of communicating, and the local oscillator to be set to the subscriber terminal Contains information to increase the intensity of the source light ,
When the traffic is decreasing,
The downlink control signal for the subscriber terminal that is not communicating with the minimum settable modulation multi-level number includes information for lowering the modulation multi-level number for communication, and local oscillation light source light to be set by the subscriber terminal A station terminal characterized by including information that attenuates the strength of the station. The signal control unit further includes an uplink control signal reading unit that reads the requested quality and the requested data amount from the subscriber terminal included in the uplink control signal,
The light intensity determination unit is configured to cause the subscriber terminal to set the intensity of the local oscillation light source light to be set based on the modulation multi-level number used for communication with the subscriber terminal, the required quality, and the distance to the subscriber terminal. The station terminal according to claim 1 , wherein: The said traffic monitor part monitors the said traffic from the request | requirement data amount of these subscriber terminals which the said uplink control signal reading part read, The station terminal of Claim 2 characterized by the above-mentioned. In the case where the traffic is increasing,
The subscriber terminal that is not communicating with the maximum configurable modulation level,
When the modulation multi-level number is increased, the downlink control signal for the subscriber terminal that can set the intensity of the local oscillation light source light corresponding to the required quality and the distance is the modulation multi-level number for communication. raising information, and the station terminal according to claim 1, characterized in that it comprises information to increase the strength of the local oscillator source light to be set to the subscriber terminal. In an optical network using Orthogonal Frequency Division Multiplexing (OFDM) , a subscriber station connected to the station terminal according to any one of claims 1 to 4 ,
And OFDM electric signal generator for generating an OFDM electrical signal by adding the uplink control signal to the input uplink data,
An electrical / optical converter that converts an OFDM electrical signal into an OFDM optical signal, and a signal transmitter capable of responding to a change in the number of modulation levels used for communication with the station terminal;
A local oscillation light source capable of changing the intensity of the local oscillation light source , and an optical / electric conversion unit for converting an OFDM optical signal into an OFDM electrical signal;
A control signal extraction unit that extracts a downlink control signal from the OFDM electrical signal, and a signal reception unit that can cope with a change in the number of modulation multilevels used for communication with the station terminal,
And an uplink control signal generation unit that generates the uplink control signal;
A downlink control signal reading unit that reads information on the intensity of the local oscillation light source light included in the downlink control signal and information on the modulation multi-level number used for communication;
A light intensity setting unit for setting the intensity of the local oscillation light source light based on the information on the intensity of the local oscillation light source light included in the downlink control signal, and a modulation multi-level number used for communication with the station terminal. It has a signal control unit to set,
When receiving the downlink control signal including information for increasing the intensity of the local oscillation light source light and information for increasing the modulation multi-level number used for communication,
The signal control unit of the subscriber terminal increases the intensity of the local oscillation light source light and increases the modulation multi-level number used for communication.
When receiving the downlink control signal including information for attenuating the intensity of the local oscillation light source light and information for reducing the modulation multi-level number used for communication,
The signal control unit of the subscriber terminal attenuates the intensity of the local oscillation light source light and lowers the modulation multi-level number used for communication. The subscriber terminal according to claim 5 , wherein the uplink control signal generation unit generates the uplink control signal including information on the required quality and the required data amount. An optical access network comprising the station terminal according to any one of claims 1 to 4 and the subscriber terminal according to claim 5 or 6 .

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