JP6079909B1 - Station terminal, optical network, and bandwidth allocation method - Google Patents

Abstract

In communication using OFDM, even within a congested state, the bandwidth falls within the usable bandwidth for each ONU. In the first process, the number of loops n (n is an integer of 0 or more) is set to 0, and the initial required bandwidth is obtained for each ONU from the required quality of the ONU and the PON interval distance for the ONU. To do. In the second process, each ONU is accommodated in a plurality of OFDM bands, and a necessary bandwidth given by the sum of the OFDM band and guard band to which each ONU is allocated is calculated. In the third process, the required bandwidth is compared with the available bandwidth. If the required bandwidth is larger than the used bandwidth as a result of the comparison in the third step, the initial required bandwidth is multiplied by the usable bandwidth in the fourth step, and the initial required bandwidth and the width reduction parameter are The integer part is calculated and 1 is added to the loop count n. As a result of the comparison in the third process, the second to fourth processes are repeated until the required bandwidth is equal to or less than the used bandwidth. [Selection] Figure 12

Description

  The present invention relates to a station terminal, an optical network, and a bandwidth allocation method suitable for use in, for example, an elastic λ aggregation network.

  An example of the basic configuration of the current network will be described with reference to FIG. FIG. 1 is a schematic diagram illustrating an example of a basic configuration of a current network. The network of this basic configuration example includes an access network, a metro network, and an upper network. The access network connects users and stations. Metro networks connect access network stations. The upper network accommodates a metro network and an access network.

  The metro network is composed of, for example, a ring network that connects nodes in a ring shape. In many cases, such a ring network includes a reconfigurable optical add / drop multiplexer (ROADM: Reconfigurable Optical Add / Drop Multiplexer). An access network station is connected to this node.

  In access networks, optical access networks that enable transmission of an enormous amount of information by using optical communication are becoming mainstream. 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 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 wavelength of the downstream signal is 1480-1500 nm, and the wavelength of the upstream signal is 1260-1360 nm.

  One of the functions included in GE-PON is dynamic bandwidth allocation (DBA) implemented in OLT (see, for example, Patent Document 1). The DBA is a function in which the OLT grasps traffic generated in each ONU and allocates an upstream signal band to each ONU according to the traffic.

  The DBA will be described with reference to FIG. FIGS. 2A to 2C are schematic diagrams for explaining DBA, and the horizontal axis indicates time t. 2A to 2C, the DBA cycle is 30 msec, the no-signal interval (guard time) is 2 msec, and the number of ONUs is 4.

  The OLT calculates the allocation bandwidth of each ONU for each DBA cycle according to the traffic requested by each ONU, and allocates it to each ONU (FIG. 2A). The unit of the allocated bandwidth in GE-PON can be expressed by time. A guard time is provided between the allocated bands of each ONU.

  Here, there is a case where the bandwidth requested by each ONU is wide and the sum of bandwidths allocated to the ONU does not fit within the DBA cycle (FIG. 2B). FIG. 2B illustrates an example in which the bandwidths requested by the ONUs # 1 to # 4 are 8, 10, 12, and 6 msec, respectively.

  In such a situation, as a method of keeping the sum of the bandwidth allocated to the ONU within the DBA cycle, the bandwidth allocated to each ONU is set to the bandwidth requested by each ONU ((DBA cycle-sum of guard times) / (requested by each ONU). There is a method of multiplying and giving the sum of the bands (for example, see Patent Document 1). By this method, the allocated bandwidth of each ONU becomes 5.3, 6.7, 8, and 4 msec, respectively, and can be accommodated within the DBA cycle (FIG. 2C).

  With the increase in traffic and diversification of services, current optical access networks are required to construct highly efficient networks that efficiently use wavelengths, which are valuable network resources. Therefore, an elastic optical aggregation network (EλAN) using a multi-level modulation technique and an orthogonal frequency division multiplexing (OFDM) technique has been developed (for example, see Non-Patent Document 2).

  With reference to FIG. 3, the characteristics of multilevel modulation will be described. 3A to 3D are schematic diagrams for explaining the characteristics of multilevel modulation. 3A to 3D show the wavelength on the horizontal axis.

  FIG. 3A shows OOK (On Off Keying) in which 1-bit data is included in one symbol. FIG. 3B shows QPSK (Quadrature Phase Shift Keying) including 2 bits of data in one symbol. FIG. 3C illustrates 16QAM (Quadrature Amplitude Modulation) including 4 bits of data in one symbol. FIG. 3D shows 64QAM including 6-bit data in one symbol. QPSK, 16QAM, and 64QAM shown in FIGS. 3B to 3D are so-called multilevel modulation, and the modulation multilevel number increases in the order of QPSK, 16QAM, and 64QAM. Multi-level modulation is not limited to these, and can be 2nQAM (n is an integer of 2 or more). As shown in FIG. 3, when the modulation multi-level number is increased, the wavelength band to be used can be reduced.

  Next, the OFDM technique will be described with reference to FIG. FIG. 4 is a schematic diagram for explaining the OFDM technique. In FIG. 4, the horizontal axis shows the frequency. The OFDM technology uses frequency orthogonality and enables multicarrier transmission, thereby improving band utilization efficiency.

  Next, a configuration example of EλAN will be described with reference to FIG. FIG. 5 is a schematic diagram for explaining a basic configuration example of EλAN. EλAN is a combined metro / access network that combines a conventional metro network and an access network. In a section corresponding to a conventional metro network, a wavelength selective switch (WSS: Wavelength Selective Switch) capable of passing through various routes depending on the wavelength is used, and this section is referred to as a WSS section. A section corresponding to a conventional access network is configured in the same manner as a conventional PON (hereinafter referred to as a PON section).

  The EλAN includes an aggregation OLT in which OLTs that are conventionally installed in each station are aggregated. The aggregation OLT is provided with a logical OLT in which the OLT is programmable. A logical ONU is used as the ONU. The logical OLT and the logical ONU have programmable optical transceivers, and the optical wavelength, the modulation multi-level number, the symbol rate (SR: Symbol Rate), and the number of subcarriers (SC: Sub Carrier) are variable. In the following description, the modulation multi-value number, the SR, and the SC number are collectively referred to as an optical signal parameter.

  FIG. 6 is a schematic diagram for explaining changes in optical signal parameters. FIG. 6A shows a change in the modulation multi-level number. The left diagram in FIG. 6A is an IQ diagram in the case of QPSK with a small number of modulation multilevels, and the right diagram in FIG. 6A is an IQ in the case of 16QAM with a large number of modulation multilevels. FIG. FIG. 6B shows a change in SR. The left diagram in FIG. 6B shows a case where SR is high, and the right diagram in FIG. 6B shows a case where SR is low. When SR becomes low, the width of SC becomes narrow and the free bandwidth increases. FIG. 6C shows a change in the number of SCs. The left diagram in FIG. 6C shows a case where the number of SCs is large, and the right diagram in FIG. 6C shows a case where the number of SCs is small. As the number of SCs decreases, the available bandwidth increases.

  The aggregation OLT is equipped with an optical signal parameter control algorithm, and determines an optimum value of the optical signal parameter according to traffic, communication quality, and the like. Here, the optimum value of the optical signal parameter is a value of the optical signal parameter that satisfies a condition required by the user and has a minimum optical spectrum width.

  Thus, by determining the optimum value of the optical signal parameter, it is possible to construct a network that is excellent in band utilization efficiency. The unit of the band in EλAN is a frequency (wavelength).

  An example of a method for determining the optimum value of the optical signal parameter will be described (for example, see Non-Patent Document 3).

  In this method, a two-dimensional map is prepared in advance by taking the distance between the OLT and the ONU (PON section distance) on the horizontal axis and the transmission quality (SER: Symbol Error Rate) on the vertical axis. The two-dimensional map shows the relationship between the PON section distance and the SER for a plurality of sets of the transmission multilevel number and the SC number. For a certain PON section distance, transmission is possible if the required quality is larger than the transmission quality, and transmission is impossible if it is smaller.

  First, in the first step, a multi-value number and a bandwidth that can be transmitted are selected from the PON section distance and the required quality of the ONU. Here, the bandwidth corresponds to, for example, the product of SR and the number of SCs.

  Next, in the second step, a multi-value number and a bandwidth that can be transmitted are selected from the requested bandwidth of the ONU.

  Next, in the third step, the one having the largest multi-value number is selected from the set of multi-value number and bandwidth selected in the first and second steps. In addition, when there are a plurality of items with the largest multi-value number, the one with the largest bandwidth is selected.

  Next, in the fourth step, the allocated SC number is calculated from the multi-value number to be transmitted and the requested bandwidth of the ONU.

  Next, in the fifth step, a search is made for a combination of ONUs such that the sum of the SC numbers allocated to the bandwidth selected in the third step is close to the bandwidth.

JP 2007-129429 A

"Basic Technology Course GE-PON Technology 3rd DBA Function" NTT Technology Journal Satoshi Okamoto “Retractable Optical Metro / Access Fusion Aggregation Network Technology for Realizing Various Services and Network Configurations-Elastic λ Aggregation Network-” IEICE Technical Report CS2012-96 (2013-1) Hiroyuki Saito et al. “Basic Study on User Frequency Multiplexing in EλAN” IEICE Technical Report

  Here, in the technique of the conventional Non-Patent Document 3 described above, the optical signal parameter is determined in a non-congested state. The non-congested state is a state in which the total required bandwidth of each ONU falls within the usable bandwidth. That is, it is executed in a state where all the requests of each ONU can be satisfied.

  However, there may be a congestion state in actual network operation. The congestion state is a state in which the total required bandwidth of each ONU does not fit in the usable bandwidth, such as the usable bandwidth is limited.

  In the case of TDM, the allocated bandwidth of each ONU is accommodated in the DBA cycle by multiplying the requested bandwidth of each ONU by (DBA cycle-total of guard times) / (total of requested bandwidth of each ONU). Can do. On the other hand, in the case of OFDM, the OFDM bandwidth is fixed, and the bandwidth of each ONU is allocated to the OFDM band in which this width is fixed. When the OFDM is in a congested state, the bandwidth required by each ONU is (bandwidth-guardbandwidth) / (each ONU using the same method as TDM (hereinafter referred to as the conventional method)). In the conventional method of assigning to the OFDM band by multiplying the sum of the required bandwidth, there may be cases where the unused SC does not fit within the usable bandwidth because there is an unused SC in the OFDM band.

  FIG. 7 shows the result of calculating the initial value of the use band under the conditions described in Non-Patent Document 3. In FIG. 7A, the horizontal axis indicates the number of trials, and the vertical axis indicates the initial value of the used band. From the result shown in FIG. 7 (A), it is shown in FIG. 7 (B) whether or not the usable bandwidth is 16 nm and the bandwidth requested by each ONU is allocated by the conventional method. Show. In FIG. 7B, a case where it falls within the usable bandwidth is indicated by a circle, and a case where it does not fall is indicated by a cross. As shown in FIG. 7B, in a congested state, the conventional method may not fit in the usable bandwidth.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a bandwidth allocation method that fits in an available bandwidth in OFDM in a congested state, and a station that implements this method. It is to provide a terminal and an optical network.

  In order to achieve the above-described object, in an optical network using orthogonal frequency division multiplexing (OFDM) according to the present invention, a station terminal connected to a plurality of subscriber terminals includes an OLT receiving unit, an OLT transmitting unit, and an OLT. And a control unit.

  The OLT receiving unit receives an upstream optical OFDM signal from the ONU, performs optical / electrical (O / E) conversion on the upstream optical OFDM signal, generates an upstream OFDM signal, and is added to the upstream OFDM signal. An uplink control signal is sent to the OLT control unit.

  The OLT transmission unit generates a downlink OFDM signal, adds the control signal received from the OLT control unit to the downlink OFDM signal, performs electrical / optical (E / O) conversion on the downlink OFDM signal, and converts the downlink optical OFDM signal. Generate and send to ONU.

  The uplink control signal includes at least one of required quality and required bit rate.

The OLT control unit further includes first to fourth means. The first means sets the loop count n (n is an integer of 0 or more) to 0, and acquires the initial required bandwidth for each ONU from the required quality of the ONU and the PON interval distance for the ONU. The second means accommodates each ONU in a plurality of OFDM bands, calculates the necessary bandwidth given by the sum of the OFDM band and guard band to which each ONU is assigned, and is necessary when the number of loops n is 0 Let the bandwidth be the initial required bandwidth. The third means compares the required bandwidth with the available bandwidth. Fourth means, in comparison with the third means result, if required bandwidth is greater than the available bandwidth, multiplied by the available bandwidth in the initial request bandwidth, the initial required bandwidth and width reducing parameters Divide by the product, calculate the integer part to make the allocated bandwidth, and add 1 to the loop count n. Here, the width reduction parameter is given as a real number of 1 or more.

In addition, in the optical network using orthogonal frequency division multiplexing (OFDM) according to the present invention, the band allocation method executed by the station terminal includes the following steps. First, in the first process, the loop count n (n is an integer equal to or greater than 0) is set to 0, and for each ONU, the initial required bandwidth is acquired from the required quality of the ONU and the PON interval distance for the ONU. Next, in the second process, when each ONU is accommodated in a plurality of OFDM bands, the required bandwidth given by the sum of the OFDM band and guard band to which each ONU is assigned is calculated, and the number of loops n is 0 Uses the required bandwidth as the initial required bandwidth. Next, in the third process, the required bandwidth is compared with the available bandwidth. If the required bandwidth is larger than the usable bandwidth as a result of the comparison in the third process, the initial required bandwidth and the width reduction parameter are multiplied in the fourth process by multiplying the initial required bandwidth by the available bandwidth. And the integer part is calculated as the allocated bandwidth, and 1 is added to the loop count n. As a result of the comparison in the third process, the second to fourth processes are repeated until the required bandwidth becomes equal to or less than the usable bandwidth. Here, the width reduction parameter is a real number of 1 or more.

  According to the station terminal of the present invention, if the necessary bandwidth given by the sum of the bandwidths requested from the ONU does not fall within the usable bandwidth, the allocated bandwidth is gradually reduced so that the necessary bandwidth becomes the usable bandwidth. When it is within the width, it ends. For this reason, even in a congested state, it can be kept within the usable bandwidth. Further, the available bandwidth can be used more effectively by reducing the allocated bandwidth little by little.

It is a schematic diagram explaining the example of a basic composition of the present network. It is a schematic diagram for demonstrating DBA. It is a schematic diagram for demonstrating the characteristic of multi-value modulation. It is a schematic diagram for demonstrating OFDM technique. It is a schematic diagram for demonstrating the example of a basic composition of EλAN. It is a schematic diagram for demonstrating the change of an optical signal parameter. It is a figure which shows the result of having calculated the use band on the conditions described in the nonpatent literature 3. FIG. It is a schematic diagram for demonstrating the structure of OLT. It is a schematic diagram for demonstrating the structure of ONU. It is a figure which shows the example of a two-dimensional map. It is a figure which shows the example of the two-dimensional map at the time of changing a symbol rate. It is a figure which shows the processing flow of the band allocation method. It is a schematic diagram which shows the example using the allocation method of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component 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, the material and numerical conditions of each component 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 network)
The optical network of this embodiment can be configured in the same manner as the EλAN disclosed in Non-Patent Document 2 described with reference to FIG.

  EλAN is composed of M (M is an integer of 1 or more) station terminals (OLT) and N subscriber terminals (ONUs) connected via the WSS section. In order to make it possible to change the service provided by EλAN in a programmable manner, in EλAN, a programmable OLT (P-OLT) is used as the OLT, and a programmable ONU (P-ONU) is used as the ONU. In EλAN, the OLT registration destination OLT, that is, the pair of OLT and ONU is freely changed.

  This EλAN uses a combination of multilevel 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 and 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 2nQAM (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.

(Configuration of OLT)
The configuration of the OLT will be described with reference to FIG. FIG. 8 is a schematic diagram for explaining the configuration of the OLT. The OLT 200 includes an OLT receiving unit 210, an OLT transmitting unit 220, and an OLT control unit 230.

  The OLT receiving unit 210 receives an upstream optical OFDM signal from the ONU. The OLT reception unit 210 includes an O / E conversion unit 214 and an uplink OFDM signal demodulation unit 212. The O / E conversion unit 214 performs optical / electrical (O / E) conversion on the upstream optical OFDM signal to generate an upstream OFDM signal. Uplink OFDM signal demodulation section 212 demodulates the uplink OFDM signal and sends it to upper network (upper NW) 50. In addition, the OLT reception unit 210 sends the uplink control signal added to the uplink OFDM signal to the OLT control unit 230.

  The OLT transmission unit 220 includes a downlink OFDM signal generation unit 222 and an E / O conversion unit 224. The downlink OFDM signal generation unit 222 modulates the signal received from the upper NW 50 to generate a downlink OFDM signal. Further, the downlink OFDM signal generation unit 222 adds the downlink control signal received from the OLT control unit 230 to the downlink OFDM signal. The E / O conversion unit 224 performs electrical / optical (E / O) conversion on the downlink OFDM signal to generate a downlink optical OFDM signal. The downstream optical OFDM signal is sent to the ONU. The downlink OFDM signal generation unit 222 performs modulation according to the modulation format and symbol rate notified from the OLT control unit 230.

  The OLT control unit 230 includes an uplink control signal reception unit 232, a downlink control signal generation unit 234, a downlink control signal transmission unit 236, an OLT side modulation condition notification unit 238, and a parameter setting unit 240 as functional means. In addition, the OLT control unit 230 stores the two-dimensional map 242 in any suitable storage unit so that it can be read out.

  The uplink control signal receiver 232 receives the uplink control signal added to the uplink OFDM signal from the OLT receiver 210. The downlink control signal generation unit 234 generates a downlink control signal. The downlink control signal transmission unit 236 sends a downlink control signal to the OLT transmission unit 220. Also, the OLT side modulation condition notifying unit 238 notifies the OLT transmitting unit 220 of the modulation format and symbol rate when the OLT transmitting unit 220 modulates. The parameter setting unit 240 includes first to fourth means 244, 246, 248, and 250 that execute first to fourth processes described later, and performs bandwidth allocation.

  The OLT receiving unit 210 and the OLT transmitting unit 220 described above can be configured using any suitable conventionally known technique. Although the configuration and operation of the functional means are different from the conventional one, the OLT control unit 230 can be configured using any suitable conventionally known technique except for a program for realizing these functional means. Details of the configuration and operation of each functional unit will be described later.

(Configuration of ONU)
The configuration of the ONU will be described with reference to FIG. FIG. 9 is a schematic diagram for explaining the configuration of the ONU. The ONU 300 includes an ONU receiving unit 310, an ONU transmitting unit 320, and an ONU control unit 330.

  The ONU receiving unit 310 receives a downstream optical OFDM signal from the OLT. The ONU reception unit 310 includes an O / E conversion unit 314 and a downlink OFDM signal demodulation unit 312. The O / E converter 314 O / E converts the downstream optical OFDM signal to generate a downstream OFDM signal. The downlink OFDM signal demodulator 312 demodulates the downlink OFDM signal and sends it to the user terminal 60. Further, the ONU receiving unit 310 sends a downlink control signal added to the downlink OFDM signal to the ONU control unit 330.

  The ONU transmission unit 320 includes an uplink OFDM signal generation unit 322 and an E / O conversion unit 324. The uplink OFDM signal generation unit 322 modulates the signal received from the user terminal 60 and generates an uplink OFDM signal. Also, the uplink OFDM signal generation unit 322 adds the uplink control signal received from the ONU control unit 330 to the uplink OFDM signal. The E / O conversion unit 324 performs E / O conversion on the upstream OFDM signal to generate an upstream optical OFDM signal. The upstream optical OFDM signal is sent to the OLT. The uplink OFDM signal generation unit 322 performs modulation according to the modulation format and symbol rate notified from the ONU control unit 230.

  The ONU control unit 330 includes a downlink control signal reception unit 332, an uplink control signal generation unit 334, an uplink control signal transmission unit 336, and an ONU side modulation condition notification unit 338 as functional units.

  The downlink control signal receiving unit 332 receives the downlink control signal added to the downlink OFDM signal from the ONU receiving unit 310. The uplink control signal generation unit 334 generates an uplink control signal. The uplink control signal transmission unit 336 sends an uplink control signal to the ONU transmission unit 320. The ONU side modulation condition notifying unit 338 notifies the ONU transmitting unit 320 of the modulation format and symbol rate when the ONU transmitting unit 320 modulates.

  The above-described ONU receiving unit 310 and ONU transmitting unit 320 can be configured using any suitable conventionally known technique. The ONU control unit 330 is different from the conventional configuration and operation of the functional means, but can be configured using any suitable conventionally known technique except for a program for realizing the functional means.

(Two-dimensional map)
Before implementing the bandwidth allocation method, a two-dimensional map is prepared in which the distance between the OLT and the ONU (PON section distance) is taken on the horizontal axis and the transmission quality (SER: Symbol Error Rate) is taken on the vertical axis. . FIG. 10 is a diagram illustrating an example of a two-dimensional map. In FIG. 10, the horizontal axis indicates the distance between the OLT and the ONU (PON section distance), and the vertical axis indicates the transmission quality (SER: Symbol Error Rate). FIG. 10 shows the relationship between the PON interval distance and the SER for each of QPSK, 16QAM, and 64QAM. If the required quality is larger than the transmission quality for a certain PON section distance, transmission is possible, and if it is smaller, transmission is impossible. For example, the condition that the PON section distance is 10 km and the required quality is 10 ⁻⁵ or less is a point indicated by x in FIG. 10, so that transmission is possible with 16QAM and QPSK, and transmission is impossible with 64QAM. In this case, the optimal modulation format is 16QAM from the viewpoint of bandwidth utilization efficiency.

  FIG. 11 is a diagram illustrating an example of a two-dimensional map when the symbol rate is changed. In FIG. 11, the horizontal axis indicates the PON interval distance, and the vertical axis indicates the transmission quality (SER). FIG. 11 shows a two-dimensional map of QPSK, 16QAM, and 64QAM for each of symbol rates of 1 Gsps (symbol per second), 5 Gsps, and 10 Gsps.

Here, when the symbol rate is changed as shown in FIG. 11, the two-dimensional map changes. Therefore, in order to construct a network with excellent band utilization efficiency, it is necessary to determine an optimal modulation format in consideration of not only the PON interval distance but also the symbol rate.
The two-dimensional map shows the relationship between the PON section distance and the SER for a plurality of sets of the transmission multilevel number and the SC number. If the required quality is larger than the transmission quality for a certain PON section distance, transmission is possible, and if it is smaller, transmission is impossible.

Referring to Table 1, a case where a request for a required quality of 10 ⁻⁸ or less and a required bit rate of 5 Gbps (bit per second) or more is received as a condition a from an ONU having a PON section distance of 40 km will be described.

First, in step (hereinafter, step is represented by S) 11, a combination of modulation format and symbol rate that satisfies the required quality is selected using the two-dimensional map shown in FIG. The condition that the PON section distance is 40 km and the required quality is 10 ⁻⁸ or less is indicated by A in FIG. From FIG. 11, there are two combinations of QPSK / 1 Gsps and QPSK / 5 Gsps that can be communicated under this condition.

  Next, in S12, a combination of modulation format and symbol rate that satisfies the required bit rate is selected. In QPSK, 16QAM, and 64QAM, 2, 4 and 6 bits of data are included in one symbol, respectively. Accordingly, there are seven combinations of 64 QAM / 1 Gsps, QPSK / 5 Gsps, 16 QAM / 5 Gsps, 64 QAM / 5 Gsps, QPSK / 10 Gsps, 16 QAM / 10 Gsps, and 64 QAM / 10 Gsps with a bit rate of 5 Gbps or higher.

  Next, in S13, the combination with the lowest symbol rate is selected from the combinations selected in S11 and S12. Here, the set selected in both S11 and S12 is one set of QPSK / 5Gsps. Therefore, the modulation format and symbol rate under this condition are QPSK / 5 Gsps.

With reference to Table 2, a case where a request for a required quality of 10 ⁻⁴ or less and a requested bit rate of 5 Gbps or more is received as a condition a from an ONU having a PON section distance of 30 km.

First, in S11, a combination of modulation format and symbol rate that can be transmitted is selected using the two-dimensional map shown in FIG. The condition that the PON section distance is 30 km and the required quality is 10 ⁻⁴ or less is indicated by B in FIG. From FIG. 11, there are six combinations of QPSK / 1 Gsps, 16 QAM / 1 Gsps, 64 QAM / 1 Gsps, QPSK / 5 Gsps, 16 QAM / 5 Gsps, and QPSK / 10 Gsps that can be communicated under this condition.

  Next, in S12, a combination of modulation format and symbol rate that satisfies the required bit rate is selected. Here, there are seven combinations of 64 QAM / 1 Gsps, QPSK / 5 Gsps, 16 QAM / 5 Gsps, 64 QAM / 5 Gsps, QPSK / 10 Gsps, 16 QAM / 10 Gsps, and 64 QAM / 10 Gsps with a bit rate of 5 Gbps or more.

  Next, in S13, the combination with the lowest symbol rate is selected from the combinations selected in S11 and S12. Here, the groups selected in both S11 and S12 are four groups of 64QAM / 1Gsps, QPSK / 5Gsps, 16QAM / 5Gsps, and QPSK / 10Gsps. Among these four sets, the set with the lowest symbol rate is 64QAM / 1Gsps. Therefore, the modulation format and symbol rate under this condition A are 64QAM / 1Gsps.

  Here, an example has been described in which an optimal combination of modulation format and symbol rate is determined from three types of modulation formats and three symbol rates. However, the present invention is not limited to this. The type and number of modulation formats and symbol rates can be arbitrarily set, and a corresponding two-dimensional map may be created in advance.

(Bandwidth allocation method)
With reference to FIGS. 12 and 13, the bandwidth allocation method of the present invention will be described. FIG. 12 is a diagram showing a processing flow of the bandwidth allocation method of the present invention.

In step (hereinafter referred to as S) 1, initialization is performed. In S1, the loop count n (n is an integer of 0 or more) is set to 0. Further, the required bandwidth BW _{alloc_i} is calculated from the input parameters. The input parameters here are the required quality of the ONU and the PON section distance for that ONU. Through the process of S11 to S13 described above, the multi-value number and the initial required bandwidth BW _{alloc_initial_i} are acquired from the input parameters using the two-dimensional map. Substituting this initial request bandwidth _{BW Alloc_initial_i} the required bandwidth _{BW alloc_i.}

Next, in S2, the required bandwidth BW _{alloc_total} is calculated from the required bandwidth BW _{alloc_i} for each ONU using the OFDMA algorithm. Here, the OFDMA algorithm is an algorithm for accommodating one or a plurality of ONUs in one OFDM band. This required bandwidth BW _{alloc_total} is given by the sum of the OFDM band and guard band to which each ONU is assigned. Further, the required bandwidth BW _{alloc_total} when n = 0 is _set as the initial required bandwidth BW _{alloc_total_initial} .

Next, in S3, comparing the available bandwidth _{BW avail} required bandwidth _{BW alloc_total.} If the comparison necessary bandwidth _{BW Alloc_total} is less than the available bandwidth _{BW avail} (Yes), the process ends. On the other hand, the result of the comparison, if required bandwidth _{BW Alloc_total} is greater than the available bandwidth _{BW avail} performs update processing of S4.

The S4 update processing of the initial request bandwidth _{BW Alloc_initial_i,} multiplied by the available bandwidth _{BW avail} / (initial required bandwidth _{BW alloc_total_initial × (1 + α ×} n)), and calculates the integer portion. Further, 1 is added to n.

  Here, the constant α can take an arbitrary numerical value larger than 0, but here it is set to 0.5.

Thereafter, steps S2 to S4 are performed until the required bandwidth BWalloc_total becomes equal to or less than the available bandwidth BWavail. The first to fourth processes described above correspond to the processes of S1 to S4.

  With reference to FIG. 13, the Example of the allocation method of this invention is described. FIG. 13 is a schematic diagram showing an example using the allocation method of the present invention.

  The OFDM bandwidth of OFDM # 1 and # 2 is 11, and the OFDM bandwidth of OFDM # 3 and # 4 is 13. The usable bandwidth is 30 and the guard band is 2.

  If the bandwidths requested by the ONUs # 1 to # 4 are 8, 10, 12, and 6, respectively, they do not fall within the usable bandwidth (FIG. 13A). Therefore, when the allocated bandwidth is calculated by the conventional method, it becomes 5.3, 6.7, 8, and 4, respectively, but even in this case, it does not fall within the usable bandwidth (FIG. 13B).

On the other hand, in the band allocation method, if not fit in the required bandwidth _{BW Alloc_total} is the available bandwidth _{BW avail,} reducing the _{BW Alloc_i} slightly, if necessary bandwidth _{BW Alloc_total} is falls within the available bandwidth _{BW avail} ends To do. For this reason, as shown in FIG. 13C, the usable bandwidth can be finally accommodated.

  FIG. 13D shows a case where the bandwidth allocation is performed under the conditions described in Non-Patent Document 3, and the case where the bandwidth falls within the usable bandwidth for each of the conventional method and the bandwidth allocation method of the present invention. The case where it did not fit is indicated by x. As shown in FIG. 13D, in the congested state, the conventional method may not fit in the usable bandwidth, but if the bandwidth allocation method of the present invention is used, it will fit in the usable bandwidth in all cases. .

In the above example, with the initial required bandwidth BW _{alloc_total_initial} as a reference, the number of loops increases, the width reduction parameter (1 + α × n) is increased, and the bandwidth is narrowed by dividing by this width reduction parameter. However, it is not limited to this.

For example, in the updating process of S4 is the initial request bandwidth _{BW Alloc_initial_i,} multiply available bandwidth _{BW avail} / a (required bandwidth _{BW alloc_total} × _β), to calculate the integer portion, further, required bandwidth _{BW Alloc_total May} be newly substituted into the initial required bandwidth BW _{alloc_total_initial} . Here, the constant β, which is the width reduction parameter, can take any numerical value greater than 1.

  Increasing the constant α and the constant β increases the number of unallocated SCs and may reduce the communication efficiency, but the number of loops decreases. On the other hand, increasing the constant α and the constant β may increase the number of loops, but the number of unassigned SCs is reduced and the communication efficiency is improved.

50 Host network (Top NW)
60 User terminal
200 Station terminal (OLT)
210 OLT receiver 212 Uplink OFDM signal demodulator 214 O / E converter 220 OLT transmitter 222 Downlink OFDM signal generator 224 E / O converter 230 OLT controller 232 Uplink control signal receiver 234 Downlink control signal generator 236 Downlink Control signal transmitter
238 OLT side modulation condition notifying unit 240 Parameter setting unit 242 Two-dimensional map 244 First means 246 Second means 248 Third means 250 Fourth means 300 Subscriber terminal (ONU)
310 ONU reception unit 312 Downlink OFDM signal demodulation unit 314 O / E conversion unit 320 ONU transmission unit 322 Uplink OFDM signal generation unit 324 E / O conversion unit 330 ONU control unit 332 Downlink control signal reception unit 334 Uplink control signal generation unit 336 Uplink Control signal transmission unit 338 ONU side modulation condition notification unit

Claims (7)

In an optical network using Orthogonal Frequency Division Multiplexing (OFDM), a station terminal connected to a plurality of subscriber terminals,
An OLT receiver, an OLT transmitter, and an OLT controller;
The OLT receiving unit receives an upstream optical OFDM signal from a subscriber terminal, performs optical / electrical (O / E) conversion on the upstream optical OFDM signal, generates an upstream OFDM signal, and adds the upstream OFDM signal to the upstream OFDM signal Sent upstream control signal to the OLT control unit,
The OLT transmission unit generates a downlink OFDM signal, adds the control signal received from the OLT control unit to the downlink OFDM signal, performs electrical / optical (E / O) conversion on the downlink OFDM signal, and performs downlink optical OFDM. Generate a signal and send it to the subscriber terminal,
The uplink control signal includes at least one of required quality and required bit rate,
The OLT control unit
A first means for obtaining the initial required bandwidth for each ONU from the required quality of the ONU and the PON section distance for the ONU, while setting the loop count n (n is an integer of 0 or more) to 0,
Each ONU is accommodated in a plurality of OFDM bands, and a required bandwidth given by the sum of the OFDM band and guard band to which each ONU is assigned is calculated. When the loop count n is 0, the required bandwidth is A second means for an initial required bandwidth;
A third means for comparing the required bandwidth with the available bandwidth;
Results of the comparison in said third means, when the required bandwidth is greater than the available bandwidth, the initial request bandwidth, multiplied by the available bandwidth, the initial required bandwidth and width reducing parameters And a fourth means for adding 1 to the number of times n of the loop,
The station width terminal, wherein the width reduction parameter is a real number of 1 or more. The station terminal according to claim 1, wherein the width reduction parameter is given by (1 + α × n) using a constant α of 0 or more. The width reduction parameter is given by one or more constants β,
The station terminal according to claim 1, wherein the fourth means sets the required bandwidth as the initial required bandwidth after calculating the allocated bandwidth.   An optical network configured to include the station terminal according to claim 1. In an optical network using Orthogonal Frequency Division Multiplexing (OFDM), a station terminal having a two-dimensional map showing a relationship between a PON interval distance and communication quality for a plurality of sets of modulation formats and symbol rates. Executed,
A first process of obtaining the initial required bandwidth for each ONU from the required quality of the ONU and the PON interval distance for the ONU, while setting the loop count n (n is an integer of 0 or more) to 0,
Each ONU is accommodated in a plurality of OFDM bands, and a required bandwidth given by the sum of the OFDM band and guard band to which each ONU is assigned is calculated. When the loop count n is 0, the required bandwidth is A second process of initial required bandwidth;
A third step of comparing the required bandwidth with the available bandwidth;
Comparison of the results in the third step, the required bandwidth is performed is larger than the available bandwidth, the initial request bandwidth, multiplied by the available bandwidth, the initial bandwidth requirement and width A fourth step of dividing by the product of the decrease parameter, calculating an integer portion thereof to obtain an allocated bandwidth, and adding 1 to the loop number n;
The width reduction parameter is a real number greater than or equal to 1,
The bandwidth allocation method, wherein the second to fourth steps are repeated until the required bandwidth becomes equal to or less than the usable bandwidth as a result of the comparison in the third step. 6. The bandwidth allocation method according to claim 5, wherein the width reduction parameter is given by (1 + α × n) using a constant α of 0 or more. The width reduction parameter is given by one or more constants β,
6. The bandwidth allocation method according to claim 5, wherein, in the fourth step, after calculating the allocated bandwidth, the required bandwidth is newly set as an initial required bandwidth.

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