Communication system, relay device, and communication method

Abstract

A communication system according to the present invention comprises: one or more first communication devices; a second communication device that communicates with the one or more first communication devices; and a relay device that relays communication between the one or more first communication devices and the second communication device. The relay device transmits, to the one or more first communication devices and the second communication device, information on a transmission path necessary for the adjustment of a filter used for wavelength dispersion compensation performed during data transmission in the one or more first communication devices and the second communication device. The one or more first communication devices and the second communication device include: a filter coefficient control unit that, on the basis of the transmission path information received from the relay device, acquires a filter coefficient of the filter used for wavelength dispersion compensation; and a wavelength dispersion compensation unit that performs wavelength dispersion compensation on transmitted data using the acquired filter coefficient.　

Description

Communication system, relay device, and communication method

[0001] The present invention relates to a communication system, a relay device, and a communication method.

[0002] As broadband becomes more widespread, new network services such as autonomous driving, telemedicine, cyber-physical systems, and smart factories have been created in recent years. Autonomous driving and telemedicine services require highly real-time control, which calls for low-latency networks. To provide stable services that take scalability into account while reducing capital investment and operational costs, the increase in power consumption associated with scaling has become a major issue. As such, future networks must not only achieve high capacity, but also be protocol-independent, with even lower latency and power consumption.

[0003] To meet these demands, the Innovative Optical and Wireless Network (IOWN) has been proposed as a new service creation method. In particular, the All-Photonics Network (APN), one of the components of the IOWN, is based on the concept of optical data transfer using wavelength division multiplexing. By minimizing electrical processing in the communication path, it is expected to reduce the electrical processing required for frame reading and routing, which is conventionally performed in IP-based networks, thereby reducing power consumption and latency, and dramatically improving transmission capacity, which has previously been limited by the bandwidth of electrical switches.

[0004] On the other hand, to achieve high-speed, large-capacity communications, it is necessary to eliminate chromatic dispersion that occurs during transmission through optical fiber. There are two types of transmission methods in optical communications systems: digital coherent and IM-DD (Intensity Modulation-Direct Detection). The digital coherent method requires high equipment costs, but can completely eliminate chromatic dispersion. The IM-DD method requires low equipment costs, but has a low dispersion compensation effect.

[0005] As a method expected to eliminate chromatic dispersion, which has become increasingly significant with the recent increase in communication speed, dispersion pre-equalization technology has been proposed, which compensates for chromatic dispersion at the transmitter side by using an IQ modulator or a Mach-Zehnder modulator at the transmitter (see, for example, Non-Patent Document 1). When using dispersion pre-equalization technology, the coefficients of the filter used for dispersion compensation are calculated based on a theoretical formula using the transmission distance and communication wavelength. Therefore, it is necessary to obtain the distance to the communication partner before starting data communication. In existing electrical concentrator networks, a method has been proposed in which the transmission distance is obtained before data communication using ranging, which predicts the transmission distance from the communication delay.

[0006] P. Torres-Ferrera, G. Rizzelli, H. Wang, V. Ferrero and R. Gaudino, “Experimental Demonstration of 100 Gbps / λ C-Band Direct-Detection Downstream PON Using Non-Linear and CD Compensation with 29 dB+ OPL Over 0 Km-100 Km”, in Journal of Lightwave Technology, vol. 40, no. 2, pp. 547-556, 15 Jan.15, 2022, doi: 10.1109 / JLT.2021.3129446.

[0007] However, as the effects of chromatic dispersion increase with increasing communication speeds and longer transmission distances, communication before adjusting the filter coefficients becomes difficult, making it impossible to obtain distance using methods such as ranging, and creating the problem that dispersion pre-equalization technology, which adjusts filters through theoretical calculations, cannot be applied.

[0008] In view of the above circumstances, an object of the present invention is to provide a technique that enables dispersion pre-equalization technology for suppressing the influence of chromatic dispersion to be applied even in an optical communication system that enables high-speed transmission.

[0009] One aspect of the present invention is a communication system comprising one or more first communication devices, a second communication device that communicates with the one or more first communication devices, and a relay device that relays communication between the one or more first communication devices and the second communication devices, wherein the relay device transmits to the one or more first communication devices and the second communication devices information about the transmission path required for adjusting a filter used for chromatic dispersion compensation performed in the one or more first communication devices and the second communication devices when transmitting data, and the one or more first communication devices and the second communication devices comprise a filter coefficient control unit that acquires filter coefficients of the filter used for chromatic dispersion compensation based on the transmission path information transmitted from the relay device, and a chromatic dispersion compensation unit that performs chromatic dispersion compensation on the transmitted data using the acquired filter coefficients.

[0010] One aspect of the present invention is a relay device that relays communications between one or more first communication devices and a second communication device that communicates with the one or more first communication devices, and includes the one or more first communication devices, a network control unit that acquires transmission path information required for adjusting a filter used for chromatic dispersion compensation performed in the second communication device when transmitting data, and a communication unit that transmits the acquired transmission path information to the one or more first communication devices and the second communication device.

[0011] One aspect of the present invention is a communication method in a communication system comprising one or more first communication devices, a second communication device that communicates with the one or more first communication devices, and a relay device that relays communication between the one or more first communication devices and the second communication devices, wherein the relay device transmits to the one or more first communication devices and the second communication devices information about the transmission path required for adjusting filters used for chromatic dispersion compensation performed in the one or more first communication devices and the second communication devices when transmitting data, and the one or more first communication devices and the second communication devices acquire filter coefficients of the filters used for chromatic dispersion compensation based on the transmission path information transmitted from the relay device, and perform chromatic dispersion compensation on the transmitted data using the acquired filter coefficients.

[0012] According to the present invention, dispersion pre-equalization techniques for suppressing the effects of chromatic dispersion can be applied to optical communication systems that enable high-speed transmission.

[0013] FIG. 1 is a diagram showing an example of the configuration of a communication system in a first embodiment. FIG. 2 is a diagram showing an example of a device information database in the first embodiment. FIG. 3 is a diagram showing an example of the configuration of a transmission / reception unit in the first embodiment. FIG. 4 is a sequence diagram showing the flow of data communication start processing performed by the communication system in the first embodiment. FIG. 5 is a sequence diagram showing the flow of data communication start processing performed by the communication system in the first embodiment. FIG. 6 is a diagram showing an example of the configuration of a communication system in a second embodiment. FIG. 7 is a diagram showing an example of a filter coefficient database in the second embodiment. FIG. 8 is a sequence diagram showing the flow of data communication start processing performed by the communication system in the second embodiment.

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] (First Embodiment) Fig. 1 is a diagram showing an example of the configuration of a communication system 100 according to the first embodiment. The communication system 100 includes one user-side communication device 10, one service-provider-side communication device 20, and one relay device 30. The user-side communication device 10 and the service-provider-side communication device 20 communicate with each other via an optical transmission path and the relay device 30. The optical transmission path is configured using at least optical fiber. The optical transmission path may also include one or more optical amplifiers that amplify optical signals.

[0016] The user-side communication device 10 is a communication device used by a user receiving a service. The user-side communication device 10 performs chromatic dispersion compensation on input transmission data using dispersion pre-equalization technology. In this embodiment, the user-side communication device 10 calculates the coefficients of a filter used for chromatic dispersion compensation based on the transmission distance and wavelength notified by the relay device 30. The user-side communication device 10 is one aspect of a first communication device.

[0017] The service providing communication device 20 is a communication device that provides a service to the user of the user side communication device 10. The service providing communication device 20 performs chromatic dispersion compensation on input transmission data using dispersion pre-equalization technology. In this embodiment, the service providing communication device 20 calculates the coefficient of a filter used for chromatic dispersion compensation based on the transmission distance and wavelength notified by the relay device 30. The service providing communication device 20 is one aspect of a second communication device.

[0018] The relay device 30 relays data communication between the user-side communication device 10 and the service-providing communication device 20. Furthermore, the relay device 30 holds information about the communication device obtained by transmitting and receiving control signal light between the user-side communication device 10 and the service-providing communication device 20. The information about the communication device includes, for example, identification information of the transmitter / receiver used for communication by each of the user-side communication device 10 and the service-providing communication device 20, the transmission distance between the relay device 30, the transmission speed, the upper and lower limits of the usable wavelength, etc.

[0019] In response to a communication request, the relay device 30 establishes a communication path between the user-side communication device 10 and the service-provider-side communication device 20. Establishing a communication path includes, for example, specifying a transmission path and allocating a wavelength to be used for communication (hereinafter referred to as "used wavelength"). The relay device 30 then notifies each communication device that communicates of information to be used to calculate filter coefficients (for example, the transmission distance between the communication devices and the used wavelength). The relay device 30 is one aspect of a control device.

[0020] As described above, in this embodiment, the relay device 30 notifies the user-side communication device 10 and the service-provider-side communication device 20, with which it communicates, of information used to calculate filter coefficients. The user-side communication device 10 and the service-provider-side communication device 20 can calculate the filter coefficients used for chromatic dispersion compensation using the information used to calculate the filter coefficients notified by the relay device 30.

[0021] Next, we will explain in detail the functional units of the user-side communication device 10, the service-provider-side communication device 20, and the relay device 30. First, we will explain the configuration of the user-side communication device 10. The user-side communication device 10 includes a transceiver unit 11, a filter coefficient control unit 12, and a chromatic dispersion compensation unit 13.

[0022] The transmitter / receiver 11 communicates with the service provider communication device 20 or the relay device 30. The transmitter / receiver 11 transmits and receives control signal light to and from the relay device 30. The transmitter / receiver 11 transmits, for example, control signal light including information about the transmitter / receiver 11 (hereinafter referred to as "transmitter / receiver information") to the relay device 30, and receives control signal light including information used to calculate filter coefficients from the relay device 30. The transmitter / receiver information transmitted by the transmitter / receiver 11 includes, for example, identification information of the transmitter / receiver 11, information indicating the type of device that includes the transmitter / receiver 11, and information on the transmission speed. The transmitter / receiver 11 uses a low-speed transceiver, such as a transceiver for Gbit Ethernet, for transmitting and receiving the control signal light.

[0023] The transmitter / receiver 11 transmits and receives data signal light to and from, for example, the service provider communication device 20. The transmitter / receiver 11 uses an IQ modulator or a Mach-Zehnder modulator as the transmitter of the data signal light, and a direct detector as the receiver of the data signal light. In the following explanation, a case where an IQ modulator is used as the transmitter of the data signal light will be described. Different wavelengths are used for the control signal light and the data signal light.

[0024] The filter coefficient control unit 12 calculates filter coefficients to be used for chromatic dispersion compensation using information used to calculate filter coefficients received by the transmitting / receiving unit 11. The method of calculating the filter coefficients is the same as in the past. The filter coefficient control unit 12 sets the calculated filter coefficients in the chromatic dispersion compensator 13.

[0025] The chromatic dispersion compensator 13 includes a filter for performing chromatic dispersion compensation. An existing digital filter is used as the filter. The chromatic dispersion compensator 13 sets the filter coefficient set by the filter coefficient control unit 12 in the filter and performs chromatic dispersion compensation for the input transmission data. The chromatic dispersion compensator 13 is a digital signal processing unit.

[0026] Next, a description will be given of the configuration of the service providing communication device 20. The service providing communication device 20 includes a transmitting / receiving unit 21, a filter coefficient control unit 22, and a chromatic dispersion compensating unit .

[0027] The transmitter / receiver 21 communicates with the user-side communication device 10 or the relay device 30. The transmitter / receiver 21 transmits and receives control signal light with the relay device 30. The transmitter / receiver 21 transmits, for example, control signal light including transmitter / receiver information to the relay device 30, and receives control signal light including information used to calculate filter coefficients from the relay device 30. The transmitter / receiver information transmitted by the transmitter / receiver 21 includes, for example, identification information of the transmitter / receiver 21, information indicating the type of device that includes the transmitter / receiver 21, and information on the transmission speed. The transmitter / receiver 21 uses a low-speed transceiver, such as a transceiver for Gbit Ethernet, for transmitting and receiving control signal light.

[0028] The transmitter / receiver 21 transmits and receives data signal light to and from, for example, the user-side communication device 10. The transmitter / receiver 21 uses an IQ modulator as the transmitter of the data signal light and a direct detector as the receiver of the data signal light. Different wavelengths are used for the control signal light and the data signal light.

[0029] The filter coefficient control unit 22 calculates filter coefficients to be used for chromatic dispersion compensation using information used to calculate the filter coefficients received by the transmitting / receiving unit 21. The method of calculating the filter coefficients is the same as in the past. The filter coefficient control unit 22 sets the calculated filter coefficients in the chromatic dispersion compensator 23.

[0030] The chromatic dispersion compensator 23 includes a filter for performing chromatic dispersion compensation. An existing digital filter is used as the filter. The chromatic dispersion compensator 23 sets the filter coefficient set by the filter coefficient control unit 22 in the filter, and performs chromatic dispersion compensation for the input transmission data. The chromatic dispersion compensator 23 is a digital signal processing unit.

[0031] Next, a description will be given of the configuration of the relay device 30. The service provider communication device 20 includes a transmitter / receiver 21, a filter coefficient controller 22, and a chromatic dispersion compensator 23. The relay device 30 includes a relay unit 31 and a controller 32.

[0032] The repeater unit 31 distributes data signal light and control signal light input from the outside. For example, the repeater unit 31 relays the input data signal light to a destination communication device and forwards the input control signal light to the control unit 32. Furthermore, the repeater unit 31 forwards the control signal light output from the control unit 32 to the user-side communication device 10 or the service-provider-side communication device 20.

[0033] The control unit 32 includes a control signal transmitting / receiving unit 33, a network control unit 34, and a device information database 35. The control signal transmitting / receiving unit 33 transmits and receives control signal light to and from the user-side communication device 10 or the service-provider-side communication device 20 via the relay unit 31. The control unit 32 is one aspect of a control device.

[0034] The network control unit 34 establishes a communication path between the user communication device 10 and the service provider communication device 20 in response to a communication request from the user communication device 10 or the service provider communication device 20. Furthermore, the network control unit 34 assigns wavelengths to each communication device that will communicate. Furthermore, the network control unit 34 refers to the device information database 35, calculates the transmission distance between the communication devices, and transmits a control signal including information on the calculated transmission distance and information on the wavelength used to the user communication device 10 or the service provider communication device 20 via the control signal transmission / reception unit 33.

[0035] Information about communication devices such as the user communication device 10 and the service provider communication device 20 is registered in the device information database 35. Fig. 2 is a diagram showing an example of the device information database 35 in the first embodiment. The device information database 35 has a plurality of records representing information about the communication devices. Each record has identification information of the transmitter / receiver, the communication device type, the transmission distance, the transmission speed, and the values ​​of the upper and lower limits of the usable wavelength.

[0036] The identification information of the transmitter / receiver represents information for identifying the transmitter / receiver provided in the user communication device 10 or the service provider communication device 20. The communication device type represents a communication device provided with a transmitter / receiver identified by the identification information of the associated transmitter / receiver. Information for identifying the user communication device 10 or the service provider communication device 20 is registered as the communication device type. The transmission distance represents the distance between the user communication device 10 or the service provider communication device 20 and the relay device 30. The transmission speed represents the maximum speed at which the transmitter / receiver identified by the identification information of the associated transmitter / receiver can transmit. The upper limit of usable wavelength represents the upper limit of wavelengths usable by the transmitter / receiver identified by the identification information of the associated transmitter / receiver. The lower limit of usable wavelength represents the lower limit of wavelengths usable by the transmitter / receiver identified by the identification information of the associated transmitter / receiver.

[0037] 2, the distance between the service-providing communication device 20 and the relay device 30 is 20 km, and the distance between the user-side communication device 10 and the relay device 30 is 40 km. Therefore, the transmission distance between the user-side communication device 10 and the service-providing communication device 20 is 60 km.

[0038] Fig. 3 is a diagram showing an example of the configuration of the transmission / reception unit 11 in the first embodiment. Note that Fig. 2 illustrates an example of the configuration of the transmission / reception unit 11 provided in the user-side communication device 10, but the configuration of the transmission / reception unit 21 provided in the service-provider-side communication device 20 is similar.

[0039] The transmitter / receiver 11 is composed of a control unit 14, a control signal communication transmitter / receiver 15, a data communication transmitter / receiver 16, and an optical multiplexer / demultiplexer 17. The data communication transmitter / receiver 16 includes an IQ modulator 18 and a direct detector 19.

[0040] The control unit 14 controls the control signal communication transceiver 15 and the data communication transceiver 16. For example, the control unit 14 sets wavelengths to be used by the control signal communication transceiver 15 and the data communication transceiver 16, respectively. The control unit 14 controls, for example, the control signal communication transceiver 15 to transmit a control signal light toward the relay device 30, and controls the IQ modulator 18 included in the data communication transceiver 16 to transmit a data signal light toward a destination.

[0041] The control signal communication transceiver 15 transmits and receives control signal light to and from the repeater 30. The control signal communication transceiver 15 generates a control signal including transmitter / receiver unit information, converts the generated control signal into control signal light, and transmits it to the repeater 30 via the optical multiplexing / demultiplexing unit 17. The control signal communication transceiver 15 generates control signal light of a wavelength assigned to the control unit 14. Furthermore, the control signal communication transceiver 15 receives the control signal light transmitted from the repeater 30.

[0042] The data communication transceiver 16 transmits and receives data signal light to and from the service provider communication device 20. The IQ modulator 18 included in the data communication transceiver 16 generates data signal light by IQ modulation using transmission data whose chromatic dispersion has been compensated for by the chromatic dispersion compensator 13. The IQ modulator 18 transmits the generated data signal light to the service provider communication device 20. The IQ modulator 18 generates data signal light of a wavelength assigned to the control unit 14. The direct detector 19 directly detects the optical signal input via the optical multiplexer / demultiplexer 17. The direct detector 19 outputs received data obtained by direct detection to the control unit 14.

[0043] The optical multiplexing / demultiplexing unit 17 multiplexes or demultiplexes the input optical signals and outputs the result. The optical multiplexing / demultiplexing unit 17 is, for example, a WDM (Wavelength Division Multiplexing) filter. The optical multiplexing / demultiplexing unit 17 outputs the externally input optical signals to the control signal communication transceiver 15 or the data communication transceiver 16 depending on the wavelength. The optical multiplexing / demultiplexing unit 17 multiplexes the control signal light output from the control signal communication transceiver 15 and the data signal light output from the data communication transceiver 16 and outputs the result to the optical transmission path.

[0044] 4 is a sequence diagram showing the flow of data communication start processing performed by the communication system 100 in the first embodiment. The transmitter / receiver 21 of the service provider communication device 20 generates a control signal including transmitter / receiver information, converts the generated control signal into control signal light, and transmits it to the relay device 30 (step S101). The control signal light transmitted from the service provider communication device 20 is input to the relay device 30 via an optical transmission path.

[0045] The relay unit 31 of the relay device 30 forwards the control signal light transmitted from the service provider communication device 20 to the control unit 32. The control signal transmitting / receiving unit 33 of the control unit 32 receives the control signal light transmitted from the relay unit 31, converts the received control signal light into a control signal (electrical signal), and outputs it to the network control unit 34. The network control unit 34 registers the transmitting / receiving unit information contained in the control signal output from the control signal transmitting / receiving unit 33 and the communication device type (e.g., service side) in the device information database 35 (step S102). Furthermore, the network control unit 34 measures the transmission distance by exchanging control signals with the service provider communication device 20. The network control unit 34 registers information indicating the measured transmission distance in the device information database 35 in association with the transmitting / receiving unit information.

[0046] The transmitter / receiver 11 of the user-side communication device 10 generates a control signal including the transmitter / receiver information, converts the generated control signal into control signal light, and transmits it to the repeater 30 (step S103). The control signal light transmitted from the user-side communication device 10 is input to the repeater 30 via the optical transmission path.

[0047] The relay unit 31 of the relay device 30 forwards the control signal light transmitted from the user-side communication device 10 to the control unit 32. The control signal transmitting / receiving unit 33 of the control unit 32 receives the control signal light transmitted from the relay unit 31, converts the received control signal light into a control signal (electrical signal), and outputs it to the network control unit 34. The network control unit 34 registers the transmitting / receiving unit information contained in the control signal output from the control signal transmitting / receiving unit 33 and the communication device type (e.g., user side) in the device information database 35 (step S104). Furthermore, the network control unit 34 measures the transmission distance by exchanging control signals with the user-side communication device 10. The network control unit 34 registers information indicating the measured transmission distance in the device information database 35 in association with the transmitting / receiving unit information.

[0048] After completing the registration of the user-side communication device 10 and the service-provider-side communication device 20 in the communication system 100, it is assumed that the user-side communication device 10 desires to communicate. The control signal communication transceiver 15 of the user-side communication device 10 generates a control signal including information specifying the communication destination (hereinafter referred to as "communication destination information"), converts the generated control signal into control signal light, and transmits it to the repeater device 30 (step S105). Here, it is assumed that the communication destination information includes information indicating the service-provider-side communication device 20. The control signal light transmitted from the user-side communication device 10 is input to the repeater device 30 via an optical transmission path.

[0049] The relay unit 31 of the relay device 30 forwards the control signal light transmitted from the user-side communication device 10 to the control unit 32. The control signal transmitting / receiving unit 33 of the control unit 32 receives the control signal light transmitted from the relay unit 31, converts the received control signal light into a control signal (electrical signal), and outputs it to the network control unit 34. The network control unit 34 performs connection processing based on the communication destination information included in the control signal output from the control signal transmitting / receiving unit 33 (step S106). Here, the connection processing performed by the network control unit 34 includes specifying a transmission path between the user-side communication device 10 and the communication destination, the service-provider communication device 20, and allocating a wavelength for data communication. The network control unit 34 associates information indicating the allocated wavelength with the identification information of the transmitting / receiving unit, and registers this information in the device information database 35.

[0050] The network control unit 34 then generates connection information as a control signal, including information indicating that a communication path has been established, information about the transmission path, and information about the communication partner. The transmission path information includes information about the wavelength used and information about the transmission distance between the communication devices. Here, the information about the transmission distance between the communication devices is calculated based on the transmission distances registered in the device information database 35. For example, when the user-side communication device 10 and the service-provider communication device 20 communicate, the transmission distance between the communication devices is calculated to be 60 km (20 km + 40 km). The network control unit 34 outputs the generated control signal to the control signal transmitting / receiving unit 33. The control signal transmitting / receiving unit 33 converts the control signal output from the network control unit 34 into control signal light and transmits it to the user-side communication device 10 and the service-provider communication device 20 via the relay unit 31 (step S107).

[0051] The control signal light transmitted from the relay device 30 reaches the user-side communication device 10 and the service-provider-side communication device 20 via the optical transmission path. The transceiver 21 of the service-provider-side communication device 20 receives the control signal light transmitted from the relay device 30. Specifically, a control signal communication transceiver provided in the transceiver 21 converts the control signal light into a control signal. The control signal communication transceiver outputs connection information included in the control signal to the control unit. The control unit outputs information about the transmission path to the filter coefficient control unit 22 in accordance with information indicating that a communication path has been established, which is included in the connection information.

[0052] The filter coefficient control unit 22 calculates a filter coefficient based on the information about the transmission path output from the control unit (step S108). The filter coefficient control unit 22 sets the calculated filter coefficient in the chromatic dispersion compensating unit 23.

[0053] The transmitter / receiver 11 of the user-side communication device 10 receives the control signal light transmitted from the relay device 30. Specifically, the transmitter / receiver for control signal communication 15 included in the transmitter / receiver 11 converts the control signal light into a control signal. The transmitter / receiver for control signal communication 15 outputs connection information included in the control signal to the control unit 14. The control unit 14 outputs information about the transmission path to the filter coefficient control unit 12 in response to information included in the connection information indicating that a communication path has been established.

[0054] The filter coefficient control unit 12 calculates a filter coefficient based on the information about the transmission path output from the control unit 14 (step S109). The filter coefficient control unit 12 sets the calculated filter coefficient in the chromatic dispersion compensating unit 13.

[0055] Then, data communication is initiated between the user communication device 10 and the service provider communication device 20 (step S110). For example, when transmission data is input, the chromatic dispersion compensator 13 of the user communication device 10 performs chromatic dispersion compensation on the input transmission data using the set filter coefficient. The chromatic dispersion compensator 13 outputs the chromatic dispersion-compensated transmission data to the transmitter / receiver 11.

[0056] The control unit 14 causes the IQ modulator 18 to generate data signal light addressed to the service providing communication device 20 based on the chromatic dispersion compensated transmission data output from the chromatic dispersion compensating unit 13, information indicating the wavelength used, and information indicating the communication partner. The IQ modulator 18 IQ-modulates the chromatic dispersion compensated transmission data in accordance with instructions from the control unit 14, thereby generating data signal light of a wavelength indicated by the information indicating the wavelength used. The IQ modulator 18 transmits the generated data signal light to the service providing communication device 20 via the optical multiplexing / demultiplexing unit 17. Note that similar processing is performed when transmitting data signal light from the service providing communication device 20 to the user side communication device 10.

[0057] 5 is a sequence diagram showing the flow of data communication start processing performed by the communication system 100 in the first embodiment. Note that the processing in FIG. 5 describes a case where information on the transmission path is changed during the data communication in step S110 in FIG.

[0058] The network control unit 34 of the relay device 30 changes information about the transmission path, such as the transmission route or the wavelength used (step S201). The network control unit 34 updates the information registered in the device information database 35 based on the changed information (step S202). For example, when the network control unit 34 changes the wavelength used by the user-side communication device 10 and the service-providing communication device 20, it updates information about the wavelength (e.g., the upper and lower limits of the usable wavelength) registered in the device information database 35. For example, when the network control unit 34 changes the transmission route used by the user-side communication device 10 and the service-providing communication device 20 for communication, it updates the transmission distance registered in the device information database 35.

[0059] Then, the network control unit 34 generates, as a control signal, information indicating that the information on the transmission path has been changed and change information including information on the changed transmission path. If only the wavelength in use has been changed, the network control unit 34 generates, as a control signal, change information including information indicating that the information on the transmission path has been changed and information on the changed transmission path (for example, information indicating the wavelength in use after the change and information indicating the transmission distance between the communication devices). Note that, if only the transmission path has been changed, the network control unit 34 generates, as a control signal, change information including information indicating that the information on the transmission path has been changed and information on the changed transmission path (for example, information indicating the wavelength in use and the transmission distance between the communication devices after the change).

[0060] The network control unit 34 outputs the generated control signal to the control signal transmitting / receiving unit 33. The control signal transmitting / receiving unit 33 converts the control signal output from the network control unit 34 into control signal light and transmits it to the user-side communication device 10 and the service-providing communication device 20 via the relay unit 31 (step S203). The control signal light transmitted from the relay unit 30 reaches the user-side communication device 10 and the service-providing communication device 20 via the optical transmission path.

[0061] The transmitter / receiver 21 of the service provider communication device 20 receives the control signal light transmitted from the relay device 30. Specifically, a control signal communication transmitter / receiver included in the transmitter / receiver 21 converts the control signal light into a control signal. The control signal communication transmitter / receiver outputs change information included in the control signal to the control unit. The control unit outputs information about the changed transmission path to the filter coefficient control unit 22 in accordance with information indicating that the information about the transmission path included in the change information has been changed.

[0062] The filter coefficient control unit 22 recalculates the filter coefficient based on the information on the changed transmission path output from the control unit (step S204). If the information on the changed transmission path includes information indicating the changed wavelength to be used and information indicating the transmission distance between the communication devices, the filter coefficient control unit 22 calculates the filter coefficient based on the information indicating the changed wavelength to be used and information indicating the transmission distance between the communication devices.

[0063] If the information about the post-change transmission path includes information indicating the wavelengths used and the transmission distance between the communication devices after the change, the filter coefficient control unit 22 calculates a filter coefficient based on the information indicating the wavelengths used and the information indicating the transmission distance between the communication devices after the change.If the information about the post-change transmission path includes information indicating the wavelengths used after the change and the information indicating the transmission distance between the communication devices after the change, the filter coefficient control unit 22 calculates a filter coefficient based on the information indicating the wavelengths used after the change and the information indicating the transmission distance between the communication devices after the change.The filter coefficient control unit 22 sets the calculated filter coefficient in the chromatic dispersion compensator 23.

[0064] The transmitter / receiver 11 of the user-side communication device 10 receives the control signal light transmitted from the relay device 30. Specifically, the transmitter / receiver for control signal communication 15 included in the transmitter / receiver 11 converts the control signal light into a control signal. The transmitter / receiver for control signal communication 15 outputs change information included in the control signal to the control unit 14. The control unit 14 outputs information about the changed transmission path to the filter coefficient control unit 12 in accordance with information indicating that the information about the transmission path included in the change information has been changed.

[0065] The filter coefficient control unit 12 recalculates the filter coefficients based on the information about the changed transmission path output from the control unit 14 (step S205). The filter coefficient control unit 12 sets the calculated filter coefficients in the chromatic dispersion compensator 13. Thereafter, data communication is started between the user-side communication device 10 and the service-provider-side communication device 20 (step S206).

[0066] In the communication system 100 configured as described above, the relay device 30 transmits information about the transmission path to the user-side communication device 10 and the service-providing communication device 20, and the user-side communication device 10 and the service-providing communication device 20 each include a filter coefficient control unit 12, 22 that acquires the filter coefficient of the filter used for chromatic dispersion compensation based on the transmission path information transmitted from the relay device 30, and a chromatic dispersion compensation unit 13, 23 that performs chromatic dispersion compensation on the transmitted data using the acquired filter coefficient.

[0067] With the above configuration, the user-side communication device 10 and the service-provider-side communication device 20 can obtain the transmission path information necessary for filter adjustment before adjusting the filter. Therefore, the user-side communication device 10 and the service-provider-side communication device 20 can calculate the filter coefficients before communication. Therefore, dispersion pre-equalization technology that suppresses the effects of chromatic dispersion can be applied even in optical communication systems that enable high-speed transmission.

[0068] Furthermore, in the communication system 100, if the information on the transmission path changes during communication, the relay device 30 notifies the user-side communication device 10 and the service-provider-side communication device 20 of the information on the changed transmission path. This makes it possible to respond to the change and suppress a decrease in throughput due to processing delays during the response.

[0069] Furthermore, in the communication system 100, the relay device 30 associates the distance between itself and the user-side communication device 10 and the distance between itself and the service-providing communication device 20 with each communication device and stores them in the device information database 35, and transmits, as transmission path information, the transmission distance obtained by adding together the distance associated with the user-side communication device 10 and the distance associated with the service-providing communication device 20 with which it communicates, as well as information indicating the wavelengths assigned to the user-side communication device 10 and the service-providing communication device 20. In this way, the relay device 30 calculates the transmission distance between the communicating communication devices and notifies the user-side communication device 10 and the service-providing communication device 20. Therefore, the user-side communication device 10 and the service-providing communication device 20 can easily calculate filter coefficients using the notified transmission path information.

[0070] Second Embodiment In a second embodiment, a configuration in which a plurality of user-side communication devices are provided will be described.

[0071] 6 is a diagram showing an example of the configuration of a communication system 100a according to the second embodiment. The communication system 100a includes N (N is an integer of 2 or more) user-side communication devices 10, one service-provider-side communication device 20, one repeater device 30, and an optical multiplexer / demultiplexer 40. Each user-side communication device 10 and the service-provider-side communication device 20 communicate with each other via an optical transmission path and the repeater device 30.

[0072] 6, the present embodiment differs from the first embodiment in that multiple user-side communication devices 10 are connected to one service-provider-side communication device 20. The multiple user-side communication devices 10 are connected to a repeater 30 via an optical multiplexer / splitter 40. The optical multiplexer / splitter 40 multiplexes optical signals transmitted from each user-side communication device 10 and outputs the multiplexed optical signals to the repeater 30, and splits the optical signals output from the repeater 30 to each user-side communication device 10.

[0073] In the second embodiment, when a plurality of user-side communication devices 10 are connected to one service-provider-side communication device 20, the filter coefficient control unit 22 may store a filter coefficient database that associates information about the transmission path with filter coefficients. The filter coefficient control unit 22 may then determine the filter coefficient based on the transmission distance and wavelength used notified by the relay device 30.

[0074] The filter coefficient control unit 22 may calculate the filter coefficients in the same manner as in the first embodiment. In this case, the filter coefficient control unit 22 does not need to hold a filter coefficient database.

[0075] 7 is a diagram showing an example of a filter coefficient database in the second embodiment. The filter coefficient database has a plurality of records representing information related to filter coefficients. Each record has information about a transmission path and a filter coefficient value. The transmission path information represents a transmission distance and a wavelength used. The filter coefficient represents a filter coefficient used for chromatic dispersion compensation, which is calculated in advance based on a combination of the transmission distance and the wavelength used.

[0076] 8 is a sequence diagram showing the flow of data communication start processing performed by the communication system 100a in the second embodiment. Note that the explanation of FIG. 8 will be given for the case where a user communication device 10-N is newly connected during communication between the user communication device 10-1 and the service provider communication device 20.

[0077] A user-side communication device 10-N is newly connected to the communication system 100a (step S301). The transmitter / receiver 11-N of the user-side communication device 10-N generates a control signal including identification information of the transmitter / receiver 11-N, converts the generated control signal into control signal light, and transmits it to the repeater 30 (step S302). The control signal light transmitted from the user-side communication device 10-N is input to the repeater 30 via an optical transmission path.

[0078] The relay unit 31 of the relay device 30 forwards the control signal light transmitted from the user-side communication device 10-N to the control unit 32. The control signal transmitting / receiving unit 33 of the control unit 32 receives the control signal light transmitted from the relay unit 31, converts the received control signal light into a control signal (electrical signal), and outputs it to the network control unit 34. The network control unit 34 registers the identification information of the transmitting / receiving unit 11-N and the communication device type (e.g., user side) contained in the control signal output from the control signal transmitting / receiving unit 33 in the device information database 35 (step S303). Furthermore, the network control unit 34 measures the transmission distance by exchanging control signals with the user-side communication device 10-N. The network control unit 34 registers information indicating the measured transmission distance in the device information database 35 in association with the identification information of the transmitting / receiving unit 11-N.

[0079] Assume that after the registration of the user-side communication device 10-N is completed, the user-side communication device 10-N desires to communicate. The control signal communication transceiver 15-N of the user-side communication device 10-N generates a control signal including communication destination information, converts the generated control signal into control signal light, and transmits it to the repeater device 30 (step S304). Here, the communication destination information includes information indicating the service-provider communication device 20. The control signal light transmitted from the user-side communication device 10-N is input to the repeater device 30 via the optical transmission path.

[0080] The relay unit 31 of the relay device 30 forwards the control signal light transmitted from the user-side communication device 10-N to the control unit 32. The control signal transmitting / receiving unit 33 of the control unit 32 receives the control signal light transmitted from the relay unit 31, converts the received control signal light into a control signal (electrical signal), and outputs it to the network control unit 34. The network control unit 34 performs connection processing based on the communication destination information included in the control signal output from the control signal transmitting / receiving unit 33 (step S305). Here, the connection processing performed by the network control unit 34 includes specifying a transmission path between the user-side communication device 10-N and the communication destination, the service-provider communication device 20, and allocating a wavelength for data communication. The network control unit 34 associates information indicating the allocated wavelength with the identification information of the transmitting / receiving unit, and registers this information in the device information database 35.

[0081] The network control unit 34 then generates connection information as a control signal, including information indicating that a communication partner has been added, information indicating that a communication path has been established, information about the transmission path, and information about the communication partner. The transmission path information includes information about the wavelength used and information about the transmission distance between the communication devices. Here, the information about the transmission distance between the communication devices is calculated by adding together the distance between the user communication device 10-N and the relay device 30 and the distance between the service provider communication device 20 and the relay device 30. The network control unit 34 outputs the generated control signal to the control signal transmitting / receiving unit 33. The control signal transmitting / receiving unit 33 converts the control signal output from the network control unit 34 into control signal light and transmits it to the user communication device 10-N and the service provider communication device 20 via the relay unit 31 (step S306).

[0082] The control signal light transmitted from the relay device 30 reaches the user-side communication device 10-N and the service-provider-side communication device 20 via the optical transmission path. The transmitter / receiver 21 of the service-provider-side communication device 20 receives the control signal light transmitted from the relay device 30. Specifically, a control signal communication transmitter / receiver provided in the transmitter / receiver 21 converts the control signal light into a control signal. The control signal communication transmitter / receiver outputs connection information included in the control signal to the control unit. The control unit outputs information about the transmission path to the filter coefficient control unit 22 in accordance with information indicating that a communication path has been established, which is included in the connection information.

[0083] The filter coefficient control unit 22 selects or calculates a filter coefficient based on the transmission path information output from the control unit (step S307). For example, the filter coefficient control unit 22 refers to the filter coefficient database it holds and searches for a record that matches the information indicating the wavelength used, included in the transmission path information output from the control unit, and the information indicating the transmission distance between the communication devices. If a record that matches the information indicating the wavelength used, output from the control unit, and the information indicating the transmission distance between the communication devices is found, the filter coefficient control unit 22 acquires a value (e.g., a used filter pattern) registered in the filter coefficient field of the matching record.

[0084] On the other hand, if there is no record that matches the information indicating the wavelength used output from the control unit and the information indicating the transmission distance between the communication devices, or if the filter coefficient database is not held, the filter coefficient control unit 22 calculates a filter coefficient based on the information indicating the wavelength used output from the control unit and the information indicating the transmission distance between the communication devices. The filter coefficient control unit 22 sets the acquired or calculated filter coefficient in the chromatic dispersion compensator 23.

[0085] The transmitter / receiver 11-N of the user-side communication device 10-N receives the control signal light transmitted from the relay device 30. Specifically, the transmitter / receiver for control signal communication 15-N included in the transmitter / receiver 11-N converts the control signal light into a control signal. The transmitter / receiver for control signal communication 15-N outputs connection information included in the control signal to the controller 14-N. The controller 14-N outputs information about the transmission path to the filter coefficient controller 12-N in response to information included in the connection information indicating that a communication path has been established.

[0086] The filter coefficient control unit 12-N calculates a filter coefficient based on the information about the transmission path output from the control unit 14-N (step S308). The filter coefficient control unit 12-N sets the calculated filter coefficient in the chromatic dispersion compensating unit 13-N.

[0087] Thereafter, data communication is initiated between the user communication device 10-N and the service provider communication device 20 (step S309). For example, when transmission data is input, the chromatic dispersion compensator 13-N of the user communication device 10-N performs chromatic dispersion compensation on the input transmission data using the set filter coefficient. The chromatic dispersion compensator 13-N outputs the chromatic dispersion-compensated transmission data to the transmitter / receiver 11-N.

[0088] The control unit 14-N causes the IQ modulator 18-N to generate data signal light addressed to the service provider communication device 20 based on the chromatic dispersion compensated transmission data output from the chromatic dispersion compensating unit 13-N, information indicating the wavelength used, and information indicating the communication partner. The IQ modulator 18-N IQ-modulates the chromatic dispersion compensated transmission data in accordance with instructions from the control unit 14-N, thereby generating data signal light of a wavelength indicated by the information indicating the wavelength used. The IQ modulator 18-N transmits the generated data signal light to the service provider communication device 20 via the optical multiplexing / demultiplexing unit 17-N. Note that similar processing is performed when transmitting data signal light from the service provider communication device 20 to the user communication device 10-N.

[0089] In the second embodiment, when the information on the transmission path is changed, the same processing as that shown in FIG. 5 in the first embodiment may be performed.

[0090] According to the communication system 100a configured as above, even when a plurality of user-side communication devices 10 exist, it is possible to obtain the same effects as those of the first embodiment.

[0091] Furthermore, in the communication system 100a, if the filter coefficient control unit 22 of the service-providing communication device 20 has a filter coefficient database in which multiple pieces of information indicating filter coefficients corresponding to combinations of transmission distances and wavelengths used are registered, the filter coefficient control unit 22 can determine the filter coefficients by referring to the filter coefficient database. This eliminates the need to calculate filter coefficients even when a new user-side communication device 10 is connected. This reduces the processing load associated with an increase in the number of user-side communication devices 10 newly connected to the service-providing communication device 20.

[0092] Some of the functional units of the user communication device 10, the service provider communication device 20, and the relay device 30 in the above-described embodiments may be implemented by a computer. In this case, a program for implementing the functions may be recorded on a computer-readable recording medium, and the program may be read and executed by a computer system. Note that the term "computer system" here includes hardware such as an operating system (OS) and peripheral devices.

[0093] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs (Read Only Memory), and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients. Furthermore, the programs may be designed to implement some of the aforementioned functions, or may be capable of implementing the aforementioned functions in combination with programs already stored in the computer system, or may be implemented using programmable logic devices such as FPGAs (Field-Programmable Gate Arrays).

[0094] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0095] The present invention can be applied to an optical communication system that performs chromatic dispersion compensation.

[0096] REFERENCE SIGNS LIST 10...user-side communication device, 20...service-provider-side communication device, 30...relay device, 40...optical multiplexer / demultiplexer, 11, 21...transmitter / receiver, 12, 22...filter coefficient control unit, 13, 23...chromatic dispersion compensation unit, 14...control unit, 15...control signal communication transmitter / receiver, 16...data communication transmitter / receiver, 17...optical multiplexer / demultiplexer unit, 18...IQ modulator, 19...direct detector, 31...relay unit, 32...control unit, 33...control signal transmission / reception unit, 34...network control unit, 35...device information database, 100, 100a...communication system

Claims

1. A communication system comprising one or more first communication devices, a second communication device that communicates with the one or more first communication devices, and a relay device that relays communication between the one or more first communication devices and the second communication device, wherein: The relay device transmits information on a transmission line required for adjusting a filter used for dispersion compensation performed when transmitting data in the one or more first communication devices and the second communication device to the one or more first communication devices and the second communication device; The one or more first communication devices and the second communication device each include a filter coefficient control unit that acquires a filter coefficient of a filter used for dispersion compensation based on the transmission line information transmitted from the relay device, and a dispersion compensation unit that performs dispersion compensation on transmission data using the acquired filter coefficient.

2. The relay device holds information indicating a first distance between the relay device and the one or more first communication devices and a second distance between the relay device and the second communication device in association with the communication devices, and transmits, as the transmission line information, a transmission distance obtained by adding the first distance associated with the one or more first communication devices that perform communication and the second distance associated with the second communication device, and information indicating wavelengths assigned to the one or more first communication devices and the second communication device that perform communication. The communication system according to claim 1.

3. The relay device transmits the transmission line information after the change to the one or more first communication devices and the second communication device when it is necessary to change the transmission line information. The communication system according to claim 1 or 2.

4. When the one or more first communication devices are a plurality of first communication devices, the relay device transmits the transmission line information to the second communication device for each first communication device that communicates with the second communication device, and the filter coefficient control unit included in the second communication device acquires the filter coefficient for each first communication device that communicates with the second communication device based on the transmission line information transmitted from the relay device. The communication system according to claim 1 or 2.

5. The filter coefficient control unit included in the second communication device calculates the filter coefficient for each first communication device that communicates with the second communication device based on the information of each transmission line transmitted from the relay device, or refers to a database in which the information of the transmission line and the filter coefficient are pre-associated to obtain the filter coefficient for each first communication device that communicates with the second communication device. The communication system according to claim 4.

6. A relay device that relays communication between one or more first communication devices and a second communication device that communicates with the one or more first communication devices, the relay device including: a network control unit that obtains information on a transmission line required for adjusting a filter used for chromatic dispersion compensation performed at the time of data transmission in the one or more first communication devices and the second communication device; and a communication unit that transmits the obtained information on the transmission line to the one or more first communication devices and the second communication device.

7. The information on the transmission line includes information indicating a wavelength used for communication between the one or more first communication devices and the second communication device and information indicating a transmission distance between the one or more first communication devices and the second communication device. The network control unit obtains information indicating the transmission distance between the one or more first communication devices and the second communication device by adding up the transmission distance between the one or more first communication devices and the relay device and the transmission distance between the second communication device and the relay device. The relay device according to claim 6.

8. A communication method in a communication system including one or more first communication devices, a second communication device that communicates with the one or more first communication devices, and a relay device that relays communication between the one or more first communication devices and the second communication device, the method including: the relay device transmitting information on a transmission line required for adjusting a filter used for chromatic dispersion compensation performed at the time of data transmission in the one or more first communication devices and the second communication device to the one or more first communication devices and the second communication device; the one or more first communication devices and the second communication device obtaining a filter coefficient of a filter used for chromatic dispersion compensation based on the information on the transmission line transmitted from the relay device; and performing chromatic dispersion compensation on transmission data using the obtained filter coefficient.

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