Service provision-side device, communication device, communication system, and communication method

Abstract

Provided is a service provision-side device comprising: a distributed pre-equalization unit that performs distributed pre-equalization on control frames by using filters each having different filter coefficients for distributed pre-equalization; and a transmission unit that transmits, to the same communication device which was newly connected, each control frame that was subjected to distributed pre-equalization by the distributed pre-equalization unit using each filter.　

Description

Service providing device, communication device, communication system and communication method

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

[0002] Conventionally, dispersion pre-equalization has been performed in a service provider device that simultaneously communicates with multiple user devices, assuming a point-to-multipoint connection network as shown in Fig. 13. Dispersion pre-equalization is a technology that performs dispersion compensation in the transmitter by applying the inverse characteristics of chromatic dispersion that occurs in the transmission path to the transmitted data.

[0003] 13 is a diagram showing an example of the configuration of a conventional point-to-multipoint connection communication system S. The communication system S includes a service provider device 100 and N (N is an integer equal to or greater than 2) user devices 200. The service provider device 100 and the N user devices 200 are connected via an optical transmission path. The service provider device 100 includes a control transceiver 110, a data communication transceiver 120, a digital signal processing unit 130, and a control unit 140.

[0004] The control transceiver 110 transmits and receives control signal light to and from the newly connected user device 200 in order to establish communication with the newly connected user device 200. The control transceiver 110 uses a low-speed transceiver, such as a Gbit / s Ethernet transceiver, for transmitting and receiving the control signal light. The data communication transceiver 120 is composed of a transmitter 121 and a receiver 122. The transmitter 121 is an IQ modulator or a Mach-Zehnder modulator, and converts the transmission data that has been dispersion pre-equalized by the dispersion pre-equalization unit 132 into an optical signal and transmits it to the user device 200. The receiver 122 is a direct detector that directly detects the optical signal transmitted from the user device 200.

[0005] The digital signal processing unit 130 is composed of a dispersion compensating unit 131 and a dispersion pre-equalizing unit 132. The dispersion compensating unit 131 performs dispersion compensation on the signal received by the receiver 122. The dispersion pre-equalizing unit 132 performs dispersion pre-equalization on the transmission data. The dispersion pre-equalizing unit 132 is composed of a filter coefficient calculating unit 133, a filter coefficient storage unit 134, and a dispersion compensation filter 135. The filter coefficient calculating unit 133 calculates the coefficients of the filter used for dispersion pre-equalization. The filter coefficient storage unit 134 stores the coefficients of the filter used for communication with each user device 200. The dispersion compensation filter 135 is a filter for performing dispersion pre-equalization on the transmission data.

[0006] The control unit 140 controls communication between the control transceiver 110 and the data communication transceiver 120. The control unit 140 is composed of a discovery function unit 141 and a transmission path information acquisition unit 142. The discovery function unit 141 uses a function called P2MP discovery to detect a connection and measure the transmission distance when a new user device 200 is connected to a PON (Passive Optical Network). The transmission path information acquisition unit 142 acquires transmission path information (e.g., wavelength and chromatic dispersion coefficient of the optical transmission path) between the newly connected user device 200 and the control transceiver 110. The information indicating the transmission distance measured by the discovery function unit 141 and the transmission path information acquired by the transmission path information acquisition unit 142 are notified to the dispersion pre-equalization unit 132 and used to calculate filter coefficients.

[0007] The user device 200 includes a control transceiver 210, a data communication transceiver 220, a digital signal processing unit 230, and a control unit 240. The control transceiver 210 transmits and receives control signals to and from the service provider device 100 in order to establish communication with the service provider device 100. The control transceiver 210 uses a low-speed transceiver, such as a Gbit Ethernet transceiver, for transmitting and receiving control signal light.

[0008] The data communication transceiver 220 is composed of a transmitter 221 and a receiver 222. The transmitter 221 is an IQ modulator or a Mach-Zehnder modulator, and converts transmission data into an optical signal by modulating it, and transmits it to the service provider device 100. The receiver 222 is a receiver that performs direct detection on the optical signal transmitted from the service provider device 100. The digital signal processing unit 230 is composed of a dispersion compensating unit 231 and a dispersion compensating unit 232. The dispersion compensating unit 231 performs dispersion compensation on the transmission data. The dispersion compensating unit 232 performs dispersion compensation on the signal received by the receiver 222. The control unit 240 controls communication between the control transceiver 210 and the data communication transceiver 220.

[0009] International Publication No. 2014 / 087994

[0010] 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. 2022, doi: 10.1109 / JLT.2021.3129446. Koji Ochiai, Tsutomu Tatsuta, Yukihiro Fujimoto, Takashi Tanaka, Osamu Yoshihara, Noriyuki Ohta, and Noriaki Miki, "Development of Gigabit Ethernet-PON (GE-PON) System", NTT Technical Journal, Vol. 17, No. 3, pp. 75-80, 2005.

[0011] As described above, in order to calculate the coefficients of the filters used in dispersion pre-equalization, it is necessary to acquire transmission path information including the transmission distance. However, in the conventional communication system S, a control transceiver is required to acquire the transmission path information including the transmission distance. Therefore, in the conventional communication system S, if a control transceiver is not provided, there is a problem in that the information required to calculate the coefficients of the filters used in dispersion pre-equalization cannot be acquired.

[0012] In view of the above circumstances, an object of the present invention is to provide a technique that can acquire information necessary for calculating the coefficients of a filter used in dispersion pre-equalization without using a control transceiver.

[0013] One aspect of the present invention is a service providing device that includes a dispersion pre-equalization unit that performs dispersion pre-equalization on a control frame using filters with different coefficients used for dispersion pre-equalization, and a transmitting unit that transmits each control frame that has been dispersion pre-equalized by each filter by the dispersion pre-equalization unit to a newly connected identical communication device.

[0014] One aspect of the present invention is a communication device that, when connected to a system, receives control frames that have been dispersion pre-equalized using a filter with appropriate filter coefficients used for dispersion pre-equalization from among multiple control frames transmitted from a service providing device that provides a service; a dispersion pre-equalization unit that performs dispersion pre-equalization on a response signal to the control frame received by the receiver; and a transmitter that transmits the dispersion pre-equalized response signal to the service providing device.

[0015] One aspect of the present invention is a communication system comprising one or more user devices and a service providing device that provides services to the one or more user devices, wherein the service providing device comprises a dispersion pre-equalization unit that performs dispersion pre-equalization on a control frame using filters with different coefficients used for dispersion pre-equalization, and a transmission unit that transmits each control frame that has been dispersion pre-equalized by the dispersion pre-equalization unit with each filter to a newly connected identical user device, and the one or more communication devices comprise a reception unit that receives, from each control frame transmitted from the service providing device, a control frame that has been dispersion pre-equalized with a filter having an appropriate filter coefficient, a dispersion pre-equalization unit that performs dispersion pre-equalization on a response signal to the control frame received by the reception unit, and a transmission unit that transmits the dispersion pre-equalized response signal to the service providing device.

[0016] One aspect of the present invention is a communication method in which dispersion pre-equalization is performed on a control frame using filters with different coefficients used for dispersion pre-equalization, and each control frame dispersion pre-equalized by each filter is transmitted to the same newly connected communication device.

[0017] According to the present invention, it is possible to obtain information necessary for calculating the coefficients of a filter used in dispersion pre-equalization without using a control transceiver.

[0018] 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 the configuration of a service provider side device in the first embodiment. FIG. 3 is a diagram showing an example of the configuration of a user side device in the first embodiment. FIG. 4 is a sequence diagram showing the flow of processing performed by the communication system in the first embodiment. FIG. 5 is a diagram showing an example of the configuration of a communication system in a second embodiment. FIG. 6 is a diagram showing an example of the configuration of a user side device in the second embodiment. FIG. 7 is a sequence diagram showing the flow of processing performed by the communication system in the second embodiment. FIG. 8 is a diagram showing an example of the configuration of a communication system in a third embodiment. FIG. 9 is a diagram showing an example of the configuration of a service provider side device in the third embodiment. FIG. 10 is a diagram showing an example of the configuration of a user side device in the third embodiment. FIG. 11 is a sequence diagram showing the flow of processing performed by the communication system in the third embodiment. FIG. 12 is a sequence diagram showing the flow of processing performed by the communication system in a modified example of the third embodiment. FIG. 13 is a diagram showing an example of the configuration of a conventional one-to-many connection communication system.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] (Summary of the Invention) In the present invention, a service providing device performs dispersion pre-equalization on a GATE signal (control frame) used in P2MP discovery using filters with different coefficients for dispersion pre-equalization. For example, the service providing device generates multiple filters with different filter coefficients by temporally varying a transmission distance parameter used in filter calculation. The service providing device performs dispersion pre-equalization on the GATE signal using each generated filter. Here, performing dispersion pre-equalization means performing chromatic dispersion compensation on the signal to be transmitted. Furthermore, the GATE signal in this specification refers to a discovery GATE signal used to notify an unregistered user device of transmission timing in discovery processing.

[0021] The service providing device then transmits each dispersion pre-equalized GATE frame to the same newly connected user device at different timings. The newly connected user device can receive only the GATE frame that has been properly dispersion pre-equalized among the multiple GATE frames transmitted from the service providing device and confirm the information in the frame. The newly connected user device returns an ACK signal, which is a response signal, only if it has confirmed the information in the frame. After returning the ACK signal, communication is established between the service providing device and the newly connected user device according to the same flow as conventional discovery. At this time, dispersion pre-equalization is also performed on communication from the newly connected user device to the service providing device.

[0022] By receiving the ACK signal, the service provider device can identify the appropriate filter coefficients to be used for dispersion pre-equalization. This allows the service provider device to obtain information necessary to calculate the filter coefficients to be used for dispersion pre-equalization using the data communication transceiver and to detect newly connected user devices. Therefore, it is possible to eliminate the need for a control transceiver to obtain information necessary to calculate the filter coefficients to be used for dispersion pre-equalization. A specific configuration for realizing the above process is described below.

[0023] (First Embodiment) FIG. 1 is a diagram showing an example of the configuration of a communication system 1a according to the first embodiment. The communication system 1a includes a service provider device 100a and N user devices 200a-1 to 200a-N. The service provider device 100a and the user devices 200a-1 to 200a-N are connected via an optical branching unit and an optical transmission path. The optical branching unit branches or multiplexes input optical signals. The optical branching unit is, for example, an optical coupler. 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 the optical signals. In the following description, when there is no need to distinguish between the user devices 200a-1 to 200a-N, they will simply be referred to as user devices 200a.

[0024] The service provider apparatus 100a is a communication apparatus that provides services to the user of the user apparatus 200a. The service provider apparatus 100a performs chromatic dispersion compensation on input transmission data using dispersion pre-equalization technology. In addition, the service provider apparatus 100a transmits a GATE signal to the newly connected user apparatus 200a to establish communication with the newly connected user apparatus 200a. The service provider apparatus 100a also performs dispersion pre-equalization on the GATE signal to be transmitted to the newly connected user apparatus 200a.

[0025] In this embodiment, the service provider device 100a generates multiple filters with different filter coefficients by changing the transmission distance parameter used in the filter calculation over time. The service provider device 100a performs dispersion pre-equalization on the GATE signal using each of the generated filters. As a result, the service provider device 100a generates multiple GATE signals #1 to #N, as shown in FIG. 1. GATE signal #1 is a GATE signal that has been dispersion pre-equalized using a filter with filter coefficient #1, and GATE signal #N is a GATE signal that has been dispersion pre-equalized using a filter with filter coefficient #N. In this way, the filter coefficients used for dispersion pre-equalization are different for GATE signals #1 to #N.

[0026] The service provider device 100a includes in each GATE signal #1 to #N information indicating parameters (e.g., transmission distance) used to calculate the filter coefficients #1 to #N of the dispersion pre-equalization filter used when dispersion pre-equalizing the GATE signal. The filter coefficients #1 to #N are sufficient filter patterns to accommodate all expected user devices 200a, and using any of the filter coefficients makes it possible to appropriately compensate for chromatic dispersion in communications with all user devices 200a.

[0027] The user-side device 200a is a communication device used by a user receiving a service. The user-side device 200a performs chromatic dispersion compensation on input transmission data using dispersion pre-equalization technology. In this embodiment, the user-side device 200a calculates the coefficients of a filter used for chromatic dispersion compensation based on the transmission distance included in the GATE frame transmitted from the service-providing device 100a.

[0028] [Configuration of the service provider device 100a] Next, the functional units of the service provider device 100a and the user device 200a will be described in detail. First, the configuration of the service provider device 100a will be described using Fig. 2. Fig. 2 is a diagram showing an example of the configuration of the service provider device 100a in the first embodiment. The service provider device 100a includes a data communications transceiver 120, a digital signal processing unit 130a, and a control unit 140a.

[0029] The data communication transceiver 120 is composed of a transmitter 121 and a receiver 122. The transmitter 121 converts dispersion pre-equalized transmission data or GATE frames into optical signals and transmits them to the user device 200a. The transmitter 121 is, for example, an IQ modulator or a Mach-Zehnder modulator, and the following description will be given assuming that an IQ modulator is used. When establishing communication with a newly connected user device 200a, the transmitter 121 transmits a GATE frame to the newly connected user device 200a. After communication is established, the transmitter 121 transmits transmission data to the user device 200a.

[0030] The receiver 122 is a direct detector that performs direct detection on the optical signal transmitted from the user device 200a, and outputs the received data (electrical signal) obtained by the direct detection to the digital signal processor 130a.

[0031] The digital signal processing unit 130a is composed of a dispersion compensating unit 131 and a dispersion pre-equalizing unit 132a. The dispersion compensating unit 131 performs dispersion compensation on the received data obtained by the receiver 122. Note that if dispersion pre-equalization is performed in the user-side device 200a, the digital signal processing unit 130a does not need to include the dispersion compensating unit 131.

[0032] The dispersion pre-equalization unit 132a performs dispersion pre-equalization on the transmission data or the GATE frame, and is composed of a filter coefficient calculation unit 133a, a filter coefficient storage unit 134, and a dispersion compensation filter 135a.

[0033] The filter coefficient calculation unit 133a calculates the coefficients of the filter used for dispersion pre-equalization based on information indicating the transmission distance instructed by the control unit 140a and transmission path information acquired by the control unit 140a. When a newly connected user device 200a is detected by the control unit 140a, the filter coefficient calculation unit 133a calculates the coefficients of the filter used for dispersion pre-equalization using information indicating the transmission distance instructed at predetermined time intervals. In this way, the filter coefficient calculation unit 133a calculates the filter coefficients using information indicating different transmission distances at different times. The method of calculating the filter coefficients is the same as conventional.

[0034] Furthermore, after communication is established, the dispersion pre-equalization unit 132a acquires a filter coefficient corresponding to the user device 200a with which communication is to be performed from among the multiple filter coefficients stored in the filter coefficient storage unit 134, and outputs the filter coefficient to the dispersion compensation filter 135a.

[0035] The filter coefficient storage unit 134 stores filter coefficients (for example, filter coefficient #1 to filter coefficient #N) used for communication with each user device 200.

[0036] The dispersion compensation filter 135a sets the filter coefficients output from the filter coefficient calculation unit 133a and performs dispersion pre-equalization on the input transmission data or GATE frame. An existing digital filter is used as the filter. The dispersion compensation filter 135a outputs the transmission data or GATE frame that has been subjected to dispersion pre-equalization to the transmitter 121.

[0037] The control unit 140a controls communications of the data communications transceiver 120. The control unit 140a is composed of a discovery function unit 141a and a transmission path information acquisition unit 142. The discovery function unit 141a uses a function called P2MP discovery to detect a connection when a new user device 200a is connected to the PON. When the discovery function unit 141a detects the connection of a new user device 200a, it controls the transmitter 121 to transmit a GATE signal to the detected user device 200a.

[0038] Specifically, the discovery function unit 141a outputs information indicating different transmission distances to the dispersion pre-equalization unit 132a at predetermined time intervals, and generates a GATE signal including the output information indicating the transmission distances. As a result, the discovery function unit 141a generates multiple GATE signals #1 to #N, as shown in FIG. 1. The discovery function unit 141a outputs the generated GATE signals #1 to #N in order to the dispersion compensation filter 135a. Note that the discovery function unit 141a does not necessarily need to generate all of the GATE signals #1 to #N; if an ACK signal is not received during the ACK signal reception period after transmitting a GATE signal, it only needs to generate the next GATE signal. Therefore, the discovery function unit 141a terminates the generation of the GATE signal if an ACK signal is received.

[0039] The transmission path information acquisition unit 142 acquires transmission path information (e.g., wavelength, chromatic dispersion coefficient of the optical transmission path) between the newly connected user device 200 and the transmission path information acquisition unit 142. Specifically, the transmission path information acquisition unit 142 acquires the wavelength and chromatic dispersion coefficient of the optical transmission path based on the signal acquired by the receiver 122. The wavelength and optical transmission path may be acquired by measurement. Note that, since wavelengths are likely to be assigned in a different sequence at the start of communication, the transmission path information acquisition unit 142 may simply acquire the wavelength assigned at the start of communication. For the fiber dispersion coefficient, the transmission path information acquisition unit 142 may store a typical value (e.g., 17.0 ps / nm / km) and acquire this information. The transmission path information acquisition unit 142 outputs the acquired transmission path information to the dispersion pre-equalization unit 132a.

[0040] [Configuration of the User Device 200a] Next, the configuration of the user device 200a will be described using Fig. 3. Fig. 3 is a diagram showing an example of the configuration of the user device 200a in the first embodiment. The user device 200a includes a data communications transceiver 220, a digital signal processing unit 230a, and a control unit 240a.

[0041] The data communication transceiver 220 is composed of a transmitter 221 and a receiver 222. The transmitter 221 modulates dispersion pre-equalized transmission data or an ACK signal to convert it into an optical signal and transmits it to the service provider device 100a. The transmitter 221 is, for example, an IQ modulator or a Mach-Zehnder modulator, and the following description will be given of the case where an IQ modulator is used.

[0042] The receiver 222 is a receiver that performs direct detection on the optical signal transmitted from the service provider device 100a.

[0043] The digital signal processing unit 230a is composed of a dispersion compensating unit 232 and a dispersion pre-equalizing unit 233a. The dispersion compensating unit 232 performs dispersion compensation on the signal received by the receiver 222. Note that if dispersion pre-equalization is performed in the service providing device 100a, the digital signal processing unit 230a does not need to include the dispersion compensating unit 232.

[0044] The dispersion pre-equalization unit 233a performs dispersion pre-equalization on the transmission data or the ACK signal, and is composed of a filter coefficient calculation unit 234a, a filter coefficient storage unit 235a, and a dispersion compensation filter 236a.

[0045] The filter coefficient calculation unit 234a calculates the coefficients of a filter used for dispersion pre-equalization based on the information indicating the transmission distance acquired by the control unit 240a. The method of calculating the filter coefficients is the same as in the conventional method.

[0046] The filter coefficient storage unit 235a stores filter coefficients used for communication with the service provider device 100a. The user device 200a does not necessarily have to include the filter coefficient storage unit 235a.

[0047] The dispersion compensation filter 236a sets the filter coefficients output from the filter coefficient calculation unit 234a and performs dispersion pre-equalization on the input transmission data or ACK signal. An existing digital filter is used as the filter. The dispersion compensation filter 236a outputs the transmission data or ACK signal that has been dispersion pre-equalized to the transmitter 221.

[0048] The control unit 240a controls communication of the data communications transceiver 220. Specifically, the control unit 240a acquires information indicating the transmission distance contained in the GATE signal received by the receiver 222. The control unit 240a outputs the acquired information indicating the transmission distance to the dispersion pre-equalization unit 233a. Furthermore, the control unit 240a acquires transmission path information (e.g., wavelength, chromatic dispersion coefficient of the optical transmission path) between the service provider device 100a and the service provider device 100a. Specifically, the control unit 240a acquires the wavelength and chromatic dispersion coefficient of the optical transmission path based on the signal acquired by the receiver 222. The method of acquiring the wavelength and the optical transmission path is the same as that of the transmission path information acquisition unit 142. The control unit 240a outputs the acquired transmission path information to the dispersion pre-equalization unit 233a.

[0049] [Operation of Communication System 1a] Fig. 4 is a sequence diagram showing the flow of processing performed by the communication system 1a in the first embodiment. In the explanation of Fig. 4, the newly connected user device 200a will be described as the user device 200a-1.

[0050] When the discovery function unit 141a of the service provider device 100a detects the newly connected user device 200a-1, it generates a GATE signal #1 including information indicating the first transmission distance. The discovery function unit 141a outputs the information indicating the first transmission distance included in the GATE signal #1 to the filter coefficient calculation unit 133a, and outputs the GATE signal #1 to the dispersion compensation filter 135a.

[0051] The filter coefficient calculation unit 133a calculates a filter coefficient #1 based on the information indicating the first transmission distance output from the discovery function unit 141a and the transmission path information obtained from the transmission path information acquisition unit 142. The filter coefficient calculation unit 133a outputs the calculated filter coefficient #1 to the dispersion compensation filter 135a. The dispersion compensation filter 135a sets the filter coefficient #1 output from the filter coefficient calculation unit 133a (step S101).

[0052] The dispersion compensation filter 135a uses the set filter coefficient #1 to perform dispersion pre-equalization on the GATE signal #1 output from the discovery function unit 141a. The dispersion compensation filter 135a outputs the GATE signal #1 that has been subjected to dispersion pre-equalization to the transmitter 121. The transmitter 121 converts the GATE signal #1 output from the dispersion compensation filter 135a into an optical signal and transmits it to the newly connected user device 200a-1 (step S102).

[0053] The receiver 222 of the user side device 200a-1 directly detects the optical signal (GATE signal #1) transmitted from the service provider side device 100a. If the filter coefficients used during dispersion pre-equalization performed on the GATE signal #1 are appropriate, the receiver 222 can receive the optical signal (GATE signal #1) transmitted from the service provider side device 100a. On the other hand, if the filter coefficients used during dispersion pre-equalization performed on the GATE signal #1 are inappropriate, the receiver 222 cannot receive the optical signal (GATE signal #1) transmitted from the service provider side device 100a. Here, it is assumed that the filter coefficients used during dispersion pre-equalization were inappropriate.

[0054] In this case, the receiver 222 cannot receive the signal (step S103). The discovery function unit 141a of the service provider device 100a waits for an ACK signal during the ACK signal reception period. Because the user device 200a-1 has not received the signal, the user device 200a-1 does not transmit an ACK signal. Therefore, the service provider device 100a does not receive the ACK signal.

[0055] If the discovery function unit 141a does not receive an ACK signal during the ACK signal reception period, it generates a GATE signal #2 including information indicating a second transmission distance. The second transmission distance is a parameter different from the first transmission distance. The discovery function unit 141a outputs the information indicating the second transmission distance included in the GATE signal #2 to the filter coefficient calculation unit 133a, and outputs the GATE signal #2 to the dispersion compensation filter 135a.

[0056] The filter coefficient calculation unit 133a calculates a filter coefficient #2 based on the information indicating the second transmission distance output from the discovery function unit 141a and the transmission path information obtained from the transmission path information acquisition unit 142. The filter coefficient calculation unit 133a outputs the calculated filter coefficient #2 to the dispersion compensation filter 135a. The dispersion compensation filter 135a sets the filter coefficient #2 output from the filter coefficient calculation unit 133a (step S104).

[0057] The dispersion compensation filter 135a uses the set filter coefficient #2 to perform dispersion pre-equalization on the GATE signal #2 output from the discovery function unit 141a. The dispersion compensation filter 135a outputs the GATE signal #2 that has been subjected to dispersion pre-equalization to the transmitter 121. The transmitter 121 converts the GATE signal #2 output from the dispersion compensation filter 135a into an optical signal and transmits it to the newly connected user device 200a-1 (step S105).

[0058] The receiver 222 of the user side device 200a-1 directly detects the optical signal (GATE signal #2) transmitted from the service provider side device 100a. If the filter coefficients used during dispersion pre-equalization performed on the GATE signal #2 are appropriate, the receiver 222 can receive the optical signal (GATE signal #2) transmitted from the service provider side device 100a. On the other hand, if the filter coefficients used during dispersion pre-equalization performed on the GATE signal #2 are inappropriate, the receiver 222 cannot receive the optical signal (GATE signal #2) transmitted from the service provider side device 100a. Here, it is assumed that the filter coefficients used during dispersion pre-equalization are appropriate.

[0059] In this case, the receiver 222 can receive the signal (step S106). The receiver 222 converts the received optical signal into an electrical signal and outputs it to the control unit 240a via the digital signal processing unit 230a. The control unit 240a acquires information indicating the transmission distance contained in the received signal (GATE signal #2). The control unit 240a outputs the acquired information indicating the transmission distance to the dispersion pre-equalization unit 233a.

[0060] The filter coefficient calculation unit 234a calculates the coefficients of the filter used for dispersion pre-equalization based on the information indicating the transmission distance acquired by the control unit 240a (step S107). The dispersion compensation filter 236a sets the filter coefficients output from the filter coefficient calculation unit 234a and performs dispersion pre-equalization on the ACK signal. The dispersion compensation filter 236a outputs the ACK signal that has been subjected to dispersion pre-equalization to the transmitter 221. The transmitter 221 waits until the timing to transmit the ACK signal (step S108). At the timing to transmit the ACK signal, the transmitter 221 converts the ACK signal into an optical signal and transmits it to the service providing device 100a (step S109).

[0061] The service provider device 100a receives the optical signal (ACK signal) transmitted from the user device 200a-1. The discovery function unit 141a of the service provider device 100a, having received the ACK signal during the reception period of the ACK signal, establishes communication between the service provider device 100a and the newly connected user device 200a-1 according to the same flow as conventional discovery (step S110).

[0062] Then, the discovery function unit 141a determines the filter coefficients to be used for communication with the newly connected user device 200a-1. For example, the discovery function unit 141a determines the filter coefficients #2 used during dispersion pre-equalization of the GATE signal #2 as the filter coefficients to be used for communication with the newly connected user device 200a-1. The filter coefficient calculation unit 133a associates the determined filter coefficients #2 with the identification information of the newly connected user device 200a-1 and stores them in the filter coefficient storage unit 134.

[0063] In the communication system 1a configured as described above, the service provider device 100a includes a dispersion pre-equalization unit 132a that performs dispersion pre-equalization on a GATE frame using filters with different coefficients used for dispersion pre-equalization, and a transmitter 121 that transmits each GATE frame that has been dispersion pre-equalized by the dispersion pre-equalization unit 132a using each filter to the newly connected same user device 200a. This makes it possible to obtain information necessary for calculating the filter coefficients used for dispersion pre-equalization and detect the communication partner by using the data communication transceiver 120. In this way, the communication system 1a makes it possible to obtain information necessary for calculating the filter coefficients used in dispersion pre-equalization without using a control transceiver.

[0064] Furthermore, in the communication system 1a, the communication quality (degree of compensation for chromatic dispersion) after dispersion pre-equalization used in downstream communication can be checked simultaneously with the establishment of communication.

[0065] Second Embodiment In the first embodiment, a configuration was described in which a GATE signal transmitted by a service providing device includes information indicating a transmission distance used to calculate a filter coefficient. In contrast, in the second embodiment, a configuration will be described in which a GATE signal transmitted by a service providing device includes information indicating a filter coefficient.

[0066] 5 is a diagram showing an example of the configuration of a communication system 1b according to the second embodiment. The communication system 1b includes a service provider device 100b and N user devices 200b-1 to 200b-N. The service provider device 100b and the user devices 200b-1 to 200b-N are connected via optical branching units and optical transmission paths. In the following description, when there is no need to distinguish between the user devices 200b-1 to 200b-N, they will simply be referred to as user devices 200b.

[0067] The service providing device 100b is a communication device that provides services to the user of the user device 200b. The process performed by the service providing device 100b is the same as that performed by the service providing device 100a, except that the information included in the GATE signal is different.

[0068] The service provider device 100b generates a plurality of GATE signals #1 to #N as shown in Fig. 5. GATE signal #1 is a GATE signal that has undergone dispersion pre-equalization using a filter with filter coefficient #1, and GATE signal #N is a GATE signal that has undergone dispersion pre-equalization using a filter with filter coefficient #N. In this way, the filter coefficients used for dispersion pre-equalization for GATE signals #1 to #N are different.

[0069] The service provider device 100b includes in each GATE signal #1 to #N information indicating the filter coefficients #1 to #N of the dispersion pre-equalization filter used when dispersion pre-equalizing that GATE signal. The filter coefficients #1 to #N are sufficient filter patterns to accommodate all expected user devices 200b, and using any of the filter coefficients makes it possible to appropriately compensate for chromatic dispersion in communications with all user devices 200b.

[0070] The user-side device 200b is a communication device used by a user receiving a service. The user-side device 200b performs chromatic dispersion compensation on input transmission data using dispersion pre-equalization technology. In this embodiment, the user-side device 200b obtains the filter coefficients used for chromatic dispersion compensation from the GATE frame transmitted from the service-providing device 100a.

[0071] [Configuration of the service providing device 100b] Next, the functional units of the service providing device 100b and the user device 200b will be described in detail. The functions of the service providing device 100b are the same as those of the service providing device 100a. The only difference from the service providing device 100a is the processing of the discovery function unit 141a.

[0072] The discovery function unit 141a uses a function called P2MP discovery to detect a connection when a new user device 200b is connected to the PON. When the discovery function unit 141a detects the connection of the new user device 200b, it controls the transmitter 121 to transmit a GATE signal to the detected user device 200b.

[0073] Specifically, the discovery function unit 141a outputs information indicating different transmission distances at predetermined time intervals to the dispersion pre-equalization unit 132b. The discovery function unit 141a acquires filter coefficients using the filter coefficient calculation unit 133a and generates a GATE signal including information indicating the acquired filter coefficients. As a result, the discovery function unit 141b generates multiple GATE signals #1 to #N, as shown in FIG. 5. The discovery function unit 141a outputs the generated GATE signals #1 to #N in order to the dispersion compensation filter 135a. Note that the discovery function unit 141a does not necessarily need to generate all of the GATE signals #1 to #N; if an ACK signal is not received during the ACK signal reception period after transmitting a GATE signal, it only needs to generate the next GATE signal. Therefore, the discovery function unit 141a terminates GATE signal generation when an ACK signal is received.

[0074] [Configuration of User Device 200b] Next, the configuration of the user device 200b will be described using Fig. 6. Fig. 6 is a diagram showing an example of the configuration of the user device 200b in the second embodiment. The user device 200b comprises a data communications transceiver 220, a digital signal processing unit 230b, and a control unit 240b. The user device 200b differs in configuration from the user device 200a in that it comprises a digital signal processing unit 230b and a control unit 240b instead of the digital signal processing unit 230a and the control unit 240a. The following description will focus on the differences from the user device 200a.

[0075] The digital signal processing unit 230b is composed of a dispersion compensating unit 232 and a dispersion pre-equalization unit 233b. The dispersion compensating unit 232 performs dispersion compensation on the signal received by the receiver 222. Note that if dispersion pre-equalization is performed in the service providing device 100b, the digital signal processing unit 230b does not need to include the dispersion compensating unit 232.

[0076] The dispersion pre-equalization unit 233b performs dispersion pre-equalization on the transmission data or the ACK signal. The dispersion pre-equalization unit 233b is composed of a filter coefficient storage unit 235a and a dispersion compensation filter 236a. As such, the dispersion pre-equalization unit 233b does not include the filter coefficient calculation unit 234a.

[0077] The filter coefficient storage unit 235a stores filter coefficients used for communication with the service provider device 100b. The user device 200b does not necessarily have to include the filter coefficient storage unit 235a.

[0078] The dispersion compensation filter 236b sets the filter coefficients output from the control unit 240b or the filter coefficients stored in the filter coefficient storage unit 235a, and performs dispersion pre-equalization on the input transmission data or ACK signal. The dispersion compensation filter 236a outputs the transmission data or ACK signal that has been dispersion pre-equalized to the transmitter 221. If the dispersion pre-equalization unit 233b does not include the filter coefficient storage unit 235a, the dispersion compensation filter 236b may be set with the filter coefficients output from the control unit 240b.

[0079] The control unit 240b controls communication of the data communication transceiver 220. Specifically, the control unit 240b acquires information indicating filter coefficients included in the GATE signal received by the receiver 222. The control unit 240b outputs the acquired information indicating the filter coefficients to the dispersion pre-equalization unit 233b. For example, the control unit 240b stores the acquired information indicating the filter coefficients in the filter coefficient storage unit 235a or directly outputs it to the dispersion compensation filter 236a.

[0080] [Operation of Communication System 1b] Fig. 7 is a sequence diagram showing the flow of processing performed by communication system 1b in the second embodiment. In the explanation of Fig. 7, the newly connected user device 200b will be described as user device 200b-1.

[0081] When the discovery function unit 141a of the service provider device 100b detects the newly connected user device 200b-1, it outputs information indicating a first transmission distance to the filter coefficient calculation unit 133a. The filter coefficient calculation unit 133a calculates a filter coefficient #1 based on the information indicating the first transmission distance output from the discovery function unit 141a and the transmission path information obtained from the transmission path information acquisition unit 142. The filter coefficient calculation unit 133a outputs the calculated filter coefficient #1 to the dispersion compensation filter 135a and the discovery function unit 141a.

[0082] The discovery function unit 141a generates a GATE signal #1 including information indicating the filter coefficient #1 output from the filter coefficient calculation unit 133a. The discovery function unit 141a outputs the GATE signal #1 to the dispersion compensation filter 135a. The dispersion compensation filter 135a sets the filter coefficient #1 output from the filter coefficient calculation unit 133a (step S201).

[0083] The dispersion compensation filter 135a uses the set filter coefficient #1 to perform dispersion pre-equalization on the GATE signal #1 output from the discovery function unit 141a. The dispersion compensation filter 135a outputs the GATE signal #1 that has been subjected to dispersion pre-equalization to the transmitter 121. The transmitter 121 converts the GATE signal #1 output from the dispersion compensation filter 135a into an optical signal and transmits it to the newly connected user device 200b-1 (step S202).

[0084] The receiver 222 of the user device 200b-1 directly detects the optical signal (GATE signal #1) transmitted from the service provider device 100b. If the filter coefficients used during dispersion pre-equalization performed on the GATE signal #1 are appropriate, the receiver 222 can receive the optical signal (GATE signal #1) transmitted from the service provider device 100b. On the other hand, if the filter coefficients used during dispersion pre-equalization performed on the GATE signal #1 are inappropriate, the receiver 222 cannot receive the optical signal (GATE signal #1) transmitted from the service provider device 100b. Here, it is assumed that the filter coefficients used during dispersion pre-equalization were inappropriate.

[0085] In this case, the receiver 222 cannot receive the signal (step S203). The discovery function unit 141a of the service provider device 100b waits for an ACK signal during the ACK signal reception period. Because the user device 200b-1 has not received the signal, the user device 200b-1 does not transmit an ACK signal. Therefore, the service provider device 100b does not receive the ACK signal.

[0086] If the discovery function unit 141a does not receive an ACK signal during the ACK signal reception period, it outputs information indicating the second transmission distance to the filter coefficient calculation unit 133a. The filter coefficient calculation unit 133a calculates a filter coefficient #2 based on the information indicating the second transmission distance output from the discovery function unit 141a and the transmission path information obtained from the transmission path information acquisition unit 142. The filter coefficient calculation unit 133a outputs the calculated filter coefficient #2 to the dispersion compensation filter 135a and the discovery function unit 141a.

[0087] The discovery function unit 141a generates a GATE signal #2 including information indicating the filter coefficient #2 output from the filter coefficient calculation unit 133a. The discovery function unit 141a outputs the GATE signal #2 to the dispersion compensation filter 135a. The dispersion compensation filter 135a sets the filter coefficient #2 output from the filter coefficient calculation unit 133a (step S204).

[0088] The dispersion compensation filter 135a uses the set filter coefficient #2 to perform dispersion pre-equalization on the GATE signal #2 output from the discovery function unit 141a. The dispersion compensation filter 135a outputs the GATE signal #2 that has been subjected to dispersion pre-equalization to the transmitter 121. The transmitter 121 converts the GATE signal #2 output from the dispersion compensation filter 135a into an optical signal and transmits it to the newly connected user device 200b-1 (step S205).

[0089] The receiver 222 of the user device 200b-1 directly detects the optical signal (GATE signal #2) transmitted from the service provider device 100b. If the filter coefficients used during dispersion pre-equalization performed on the GATE signal #2 are appropriate, the receiver 222 can receive the optical signal (GATE signal #2) transmitted from the service provider device 100b. On the other hand, if the filter coefficients used during dispersion pre-equalization performed on the GATE signal #2 are inappropriate, the receiver 222 cannot receive the optical signal (GATE signal #2) transmitted from the service provider device 100b. Here, it is assumed that the filter coefficients used during dispersion pre-equalization are appropriate.

[0090] In this case, the receiver 222 can receive the signal (step S206). The receiver 222 converts the received optical signal into an electrical signal and outputs it to the control unit 240b via the digital signal processing unit 230b. The control unit 240b acquires information indicating the filter coefficient #2 included in the received signal (GATE signal #2). The control unit 240b outputs the acquired information indicating the filter coefficient #2 to the dispersion pre-equalization unit 233b.

[0091] The dispersion compensation filter 236a sets the filter coefficient to be used for dispersion pre-equalization based on the information indicating the filter coefficient #2 acquired by the control unit 240a (step S207). That is, the dispersion compensation filter 236a reflects the filter coefficient #2 acquired by the control unit 240a in the filter coefficient to be used for dispersion pre-equalization. The dispersion compensation filter 236a performs dispersion pre-equalization on the ACK signal. The dispersion compensation filter 236a outputs the ACK signal that has been subjected to dispersion pre-equalization to the transmitter 221. The transmitter 221 waits until the timing to transmit the ACK signal (step S208). At the timing to transmit the ACK signal, the transmitter 221 converts the ACK signal into an optical signal and transmits it to the service provider device 100b (step S209).

[0092] The service provider device 100b receives the optical signal (ACK signal) transmitted from the user device 200b-1. The discovery function unit 141a of the service provider device 100b, having received the ACK signal during the reception period of the ACK signal, establishes communication between the service provider device 100b and the newly connected user device 200b-1 according to the same flow as conventional discovery (step S210).

[0093] Then, the discovery function unit 141a determines the filter coefficients to be used for communication with the newly connected user device 200b-1. For example, the discovery function unit 141a determines the filter coefficients #2 used during dispersion pre-equalization of the GATE signal #2 as the filter coefficients to be used for communication with the newly connected user device 200b-1. The filter coefficient calculation unit 133a associates the determined filter coefficients #2 with the identification information of the newly connected user device 200b-1 and stores them in the filter coefficient storage unit 134.

[0094] According to the communication system 1b configured as above, it is possible to obtain the same effects as those of the first embodiment.

[0095] Furthermore, in the communication system 1b, the service provider device 100b notifies the newly connected user device 200b of the filter coefficients contained in the GATE signal. This eliminates the need for the user device 200b to calculate the filter coefficients, and instead simply uses the filter coefficients contained in the received signal. This simplifies the configuration of the user device 200b and improves its usability.

[0096] (Third Embodiment) In the first and second embodiments, a configuration has been described in which the service providing device has a direct detector as a receiver and the user device has an IQ modulator or a Mach-Zehnder modulator as a transmitter. In contrast, the present invention can also be applied to a configuration in which the service providing device has a coherent receiver as a receiver and the user device has an intensity modulator as a transmitter. Therefore, this configuration will be described in the third embodiment.

[0097] 8 is a diagram showing an example of the configuration of a communication system 1c according to the third embodiment. The communication system 1c includes a service provider device 100c and N user devices 200c-1 to 200c-N. The service provider device 100c and the user devices 200c-1 to 200c-N are connected via optical branching units and optical transmission paths. In the following description, when there is no need to distinguish between the user devices 200c-1 to 200c-N, they will simply be referred to as user devices 200c.

[0098] The service provider device 100c is a communication device that provides services to the user of the user device 200c. The processing performed by the service provider device 100c is the same as that of the service provider device 100a, except that it receives signals by coherent detection and does not include information about filter coefficients in the GATE signal.

[0099] The service provider device 100c generates a plurality of GATE signals #1 to #N as shown in Fig. 8. GATE signal #1 is a GATE signal that has undergone dispersion pre-equalization using a filter with filter coefficient #1, and GATE signal #N is a GATE signal that has undergone dispersion pre-equalization using a filter with filter coefficient #N. In this way, the filter coefficients used for dispersion pre-equalization for GATE signals #1 to #N are different.

[0100] The service provider device 100c includes in each GATE signal #1 to #N the same information as in the signal used in the PON. The filter coefficients #1 to #N are sufficient filter patterns to accommodate all expected user devices 200c, and using any of the filter coefficients makes it possible to appropriately compensate for chromatic dispersion in communications with all user devices 200c.

[0101] The user device 200c is a communication device used by a user who receives the service, and it intensity-modulates the input transmission data or ACK signal and transmits it.

[0102] [Configuration of the service providing device 100c] Next, the functional units of the service providing device 100c and the user device 200c will be described in detail. First, the configuration of the service providing device 100c will be described using Fig. 9. Fig. 9 is a diagram showing an example of the configuration of the service providing device 100c in the third embodiment. The service providing device 100c includes a data communications transceiver 120c, a digital signal processing unit 130a, and a control unit 140a.

[0103] The data communication transceiver 120c is composed of a transmitter 121 and a receiver 122c. The transmitter 121 converts dispersion pre-equalized transmission data or a GATE frame into an optical signal and transmits it to the user device 200c. The transmitter 121 is, for example, an IQ modulator or a Mach-Zehnder modulator, and the following description will be given assuming that an IQ modulator is used. When communication is established with a newly connected user device 200c, the transmitter 121 transmits a GATE frame to the newly connected user device 200c. After communication is established, the transmitter 121 transmits transmission data to the user device 200c.

[0104] The receiver 122c is a coherent receiver that performs coherent detection on the optical signal transmitted from the user device 200c, and outputs reception data (electrical signals) obtained by the coherent detection to the digital signal processor 130a.

[0105] The functional units included in the digital signal processing unit 130a and the processing performed by the digital signal processing unit 130a are the same as those in the first embodiment, and therefore a description thereof will be omitted.

[0106] The control unit 140a controls communications of the data communications transceiver 120c. The control unit 140a is composed of a discovery function unit 141a and a transmission path information acquisition unit 142. The discovery function unit 141a uses a function called P2MP discovery to detect a connection when a new user device 200c is connected to the PON. When the discovery function unit 141a detects the connection of a new user device 200c, it controls the transmitter 121 to transmit a GATE signal addressed to the detected user device 200c.

[0107] Specifically, the discovery functional unit 141a outputs information indicating different transmission distances at predetermined time intervals to the dispersion pre-equalization unit 132a and generates a GATE signal containing the same information as the signal used in the PON. As a result, the discovery functional unit 141a generates multiple GATE signals #1 to #N, as shown in FIG. 8. The discovery functional unit 141a outputs the generated GATE signals #1 to #N in order to the dispersion compensation filter 135a. Note that the discovery functional unit 141a does not necessarily need to generate all of the GATE signals #1 to #N; if an ACK signal is not received during the ACK signal reception period after transmitting a GATE signal, it only needs to generate the next GATE signal. Therefore, the discovery functional unit 141a terminates the generation of the GATE signal if an ACK signal is received.

[0108] The transmission path information acquisition unit 142 acquires transmission path information (e.g., wavelength and chromatic dispersion coefficient of the optical transmission path) between the newly connected user device 200c and the transmission path information acquisition unit 142c, and outputs the acquired transmission path information to the dispersion pre-equalization unit 132a.

[0109] [Configuration of User Device 200c] Next, the configuration of the user device 200c will be described using Fig. 10. Fig. 10 is a diagram showing an example of the configuration of the user device 200c in the third embodiment. The user device 200c includes a data communications transceiver 220c, a digital signal processor 230c, and a controller 240c.

[0110] The data communication transceiver 220c is composed of a transmitter 221c and a receiver 222. The transmitter 221c converts dispersion pre-equalized transmission data or an ACK signal into an optical signal by intensity modulation and transmits the optical signal to the service provider device 100c. The transmitter 221c is, for example, an intensity modulator.

[0111] The receiver 222 is a receiver that performs direct detection on the optical signal transmitted from the service provider device 100c.

[0112] The digital signal processing unit 230c is composed of a dispersion compensating unit 232. The dispersion compensating unit 232 performs dispersion compensation on the signal received by the receiver 222. Note that if dispersion pre-equalization is performed in the service providing device 100c, the digital signal processing unit 230c does not need to include the dispersion compensating unit 232. The digital signal processing unit 230c outputs the input transmission data or ACK signal to the data communications transceiver 220c.

[0113] The control unit 240c controls the communication of the data communication transceiver 220c. Specifically, in response to the reception of a GATE signal by the receiver 222, the control unit 240c instructs the data communication transceiver 220c to transmit an ACK signal.

[0114] [Operation of Communication System 1c] Fig. 11 is a sequence diagram showing the flow of processing performed by the communication system 1c in the third embodiment. In the explanation of Fig. 11, the newly connected user device 200c will be described as the user device 200c-1.

[0115] When the discovery function unit 141a of the service provider device 100c detects the newly connected user device 200c-1, it outputs information indicating a first transmission distance to the filter coefficient calculation unit 133a. Furthermore, the discovery function unit 141a generates a GATE signal #1 and outputs the generated GATE signal #1 to the dispersion compensation filter 135a. The filter coefficient calculation unit 133a calculates a filter coefficient #1 based on the information indicating the first transmission distance output from the discovery function unit 141a and the transmission path information obtained from the transmission path information acquisition unit 142. The filter coefficient calculation unit 133a outputs the calculated filter coefficient #1 to the dispersion compensation filter 135a.

[0116] The dispersion compensation filter 135a sets the filter coefficient #1 output from the filter coefficient calculation unit 133a (step S301). The dispersion compensation filter 135a uses the set filter coefficient #1 to perform dispersion pre-equalization on the GATE signal #1 output from the discovery function unit 141a. The dispersion compensation filter 135a outputs the GATE signal #1 that has been subjected to dispersion pre-equalization to the transmitter 121. The transmitter 121 converts the GATE signal #1 output from the dispersion compensation filter 135a into an optical signal and transmits it to the newly connected user device 200c-1 (step S302).

[0117] The receiver 222 of the user side device 200c-1 directly detects the optical signal (GATE signal #1) transmitted from the service provider side device 100c. If the filter coefficients used during dispersion pre-equalization performed on the GATE signal #1 are appropriate, the receiver 222 can receive the optical signal (GATE signal #1) transmitted from the service provider side device 100c. On the other hand, if the filter coefficients used during dispersion pre-equalization performed on the GATE signal #1 are inappropriate, the receiver 222 cannot receive the optical signal (GATE signal #1) transmitted from the service provider side device 100c. Here, it is assumed that the filter coefficients used during dispersion pre-equalization were inappropriate.

[0118] In this case, the receiver 222 cannot receive the signal (step S303). The discovery function unit 141a of the service provider device 100c waits for an ACK signal during the ACK signal reception period. Because the user device 200c-1 has not received the signal, the user device 200c-1 does not transmit an ACK signal. Therefore, the service provider device 100c does not receive the ACK signal.

[0119] If the discovery function unit 141a does not receive an ACK signal during the ACK signal reception period, the discovery function unit 141a outputs information indicating the second transmission distance to the filter coefficient calculation unit 133a. Furthermore, the discovery function unit 141a generates a GATE signal #2 and outputs the generated GATE signal #2 to the dispersion compensation filter 135a.

[0120] The filter coefficient calculation unit 133a calculates a filter coefficient #2 based on the information indicating the second transmission distance output from the discovery function unit 141a and the transmission path information obtained from the transmission path information acquisition unit 142. The filter coefficient calculation unit 133a outputs the calculated filter coefficient #2 to the dispersion compensation filter 135a. The dispersion compensation filter 135a sets the filter coefficient #2 output from the filter coefficient calculation unit 133a (step S304).

[0121] The dispersion compensation filter 135a uses the set filter coefficient #2 to perform dispersion pre-equalization on the GATE signal #2 output from the discovery function unit 141a. The dispersion compensation filter 135a outputs the GATE signal #2 that has been subjected to dispersion pre-equalization to the transmitter 121. The transmitter 121 converts the GATE signal #2 output from the dispersion compensation filter 135a into an optical signal and transmits it to the newly connected user device 200c-1 (step S305).

[0122] The receiver 222 of the user device 200c-1 directly detects the optical signal (GATE signal #2) transmitted from the service provider device 100c. If the filter coefficients used during dispersion pre-equalization performed on the GATE signal #2 are appropriate, the receiver 222 can receive the optical signal (GATE signal #2) transmitted from the service provider device 100c. On the other hand, if the filter coefficients used during dispersion pre-equalization performed on the GATE signal #2 are inappropriate, the receiver 222 cannot receive the optical signal (GATE signal #2) transmitted from the service provider device 100c. Here, it is assumed that the filter coefficients used during dispersion pre-equalization are appropriate.

[0123] In this case, the receiver 222 can receive the signal (step S306). The receiver 222 converts the received optical signal into an electrical signal and outputs it to the control unit 240c via the digital signal processing unit 230c. In response to receiving the received signal (GATE signal #2), the control unit 240c instructs the digital signal processing unit 230c to send an ACK signal.

[0124] The digital signal processing unit 230c outputs an ACK signal to the transmitter 221c in response to an instruction from the control unit 240c. The transmitter 221c waits until the timing to transmit the ACK signal (step S307). The service providing device 100c optimizes the wavelength dispersion filter of the receiver 122c (step S308). At the timing to transmit the ACK signal, the transmitter 221c intensity-modulates the ACK signal, converts it into an optical signal, and transmits it to the service providing device 100c (step S309).

[0125] The service provider device 100c receives the optical signal (ACK signal) transmitted from the user device 200c-1. The discovery function unit 141a of the service provider device 100c, having received the ACK signal during the reception period of the ACK signal, establishes communication between the service provider device 100c and the newly connected user device 200c-1 according to the same flow as conventional discovery (step S310).

[0126] Then, the discovery function unit 141a determines the filter coefficients to be used for communication with the newly connected user device 200c-1. For example, the discovery function unit 141a determines the filter coefficients #2 used during dispersion pre-equalization of the GATE signal #2 as the filter coefficients to be used for communication with the newly connected user device 200c-1. The filter coefficient calculation unit 133a associates the determined filter coefficients #2 with the identification information of the newly connected user device 200c-1 and stores them in the filter coefficient storage unit 134.

[0127] According to the communication system 1c configured as described above, the same effects as those of the first embodiment can be obtained even in a configuration in which a coherent receiver is provided as the receiver 122c of the service providing device 100c and an intensity modulator is provided as the transmitter 221c of the user device 200c.

[0128] (Variation of the Third Embodiment) The service provider device 100c may be configured to determine the coefficients of a filter used for dispersion pre-equalization based on the filter coefficients of a coherent receiver. This process will be described with reference to Fig. 12. Fig. 12 is a sequence diagram showing the flow of processes performed by a communication system 1c in a variation of the third embodiment. In Fig. 12, the same processes as those in Fig. 11 are assigned the same reference numerals as those in Fig. 11, and descriptions thereof will be omitted.

[0129] When the receiver 122c receives an ACK signal, the filter coefficient calculation unit 133a of the service provider device 100c calculates the coefficients of a filter to be used for dispersion pre-equalization based on the filter coefficients of the filter included in the coherent receiver 122c. If the calculated filter coefficients differ from the filter coefficients already obtained, the filter coefficient calculation unit 133a determines the filter coefficients obtained in response to the reception of the ACK signal as the filter coefficients to be used for communication with the newly connected user device 200c.

[0130] Some of the functional units of the service provider devices 100a, 100b, and 100c and the user devices 200a, 200b, and 200c 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.

[0131] 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).

[0132] 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.

[0133] The present invention can be applied to a communication system that performs chromatic dispersion compensation.

[0134] 1a, 1b, 1c... communication systems, 100a, 100b, 100c... service provider side devices, 200a, 200a-1 to 200a-N, 200b, 200b-1 to 200b-N, 200c, 200c-1 to 200c-N... user side devices, 120, 120c, 220, 220c... data communication transceivers, 121, 221, 221c... transmitters, 122, 122c, 222... receivers, 130a, 230a, 230c... digital signal processing units, 131, 232... dispersion compensation units, 132a, 233a, 233b... dispersion pre-equalization units, 133a, 234a... filter coefficient calculation units, 134, 235a... filter coefficient storage units Dispersion compensation filters 135a, 236a, control units 140a, 240a, 240b, 240c, discovery function units 141a, transmission path information acquisition units 142

Claims

1. A service providing device comprising: a dispersion pre-equalization unit that performs dispersion pre-equalization on a control frame using filters with different coefficients used for dispersion pre-equalization; and a transmission unit that transmits each control frame that has been dispersion pre-equalized by each filter in the dispersion pre-equalization unit to a newly connected identical communication device.

2. The service providing device according to claim 1, wherein the transmitting unit transmits each control frame including information indicating parameters used to calculate the coefficients of the filter to the newly connected same communication device.

3. The service providing device according to claim 1, wherein the transmitting unit transmits each control frame including information indicating the coefficient of the filter to the same newly connected communication device.

4. A service providing device as described in any one of claims 1 to 3, wherein the dispersion pre-equalization unit generates filters with different coefficients by switching the coefficients of the filters over time, and the transmission unit transmits each control frame dispersion pre-equalized by the dispersion pre-equalization unit to the newly connected identical communication device at different timings.

5. A service providing device as described in any one of claims 1 to 3, further comprising a receiving unit that receives a response signal transmitted from a user device, wherein the dispersion pre-equalization unit determines the coefficients of the filter used when the response signal was received as the coefficients of the filter to be used for dispersion pre-equalization of communication with a newly connected communication device.

6. A communications device comprising: a receiver that, when connecting to a system, receives a control frame that has been dispersion pre-equalized using a filter with appropriate coefficients for dispersion pre-equalization from among multiple control frames transmitted from a service provider device that provides a service; a dispersion pre-equalization unit that performs dispersion pre-equalization on a response signal to the control frame received by the receiver; and a transmitter that transmits the dispersion pre-equalized response signal to the service provider device.

7. A communications system comprising one or more user devices and a service providing device that provides services to the one or more user devices, wherein the service providing device comprises: a dispersion pre-equalization unit that performs dispersion pre-equalization on a control frame using filters with different coefficients used for dispersion pre-equalization; and a transmission unit that transmits each control frame that has been dispersion pre-equalized by each filter in the dispersion pre-equalization unit to a newly connected identical user device; and the one or more communications devices comprise: a reception unit that receives, from each control frame transmitted from the service providing device, a control frame that has been dispersion pre-equalized using a filter with an appropriate filter coefficient; a dispersion pre-equalization unit that performs dispersion pre-equalization on a response signal to the control frame received by the reception unit; and a transmission unit that transmits the dispersion pre-equalized response signal to the service providing device.

8. A communication method in which dispersion pre-equalization is performed on a control frame using filters with different coefficients used for dispersion pre-equalization, and each control frame that has been dispersion pre-equalized by each filter is transmitted to the same newly connected communication device.

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