Transmission control system

Abstract

A transmission control system according to one aspect of the present invention controls the transmission of an optical signal converted from an RF signal in a transmission system that transmits the optical signal, the transmission control system comprising: an amplifier that amplifies the optical signal; a branching device that causes the optical signal amplified by the amplifier to branch; and a control unit that executes an optical modulation degree measurement process for measuring the optical modulation degree of one optical signal branched by the branching device, and an amplification control process for controlling, on the basis of the measurement result of the optical modulation degree measurement process, the amplification degree of the optical signal amplified by the amplifier.

Description

Transmission Control System

[0001] The present invention relates to a transmission control system.

[0002] There are transmission systems that convert frequency division multiplexed (FDM) signals, which are multiplexed RF (Radio Frequency) signals such as video signals, into optical signals and transmit them. Such systems use three types of optical communication devices: an optical transmitter (Tx) that inputs RF signals, converts them into optical signals, and outputs them; an optical transmission device (V-OLT) that relays and branches the optical signals; and an optical receiving device (V-ONU) that receives the optical signals, demodulates them, and outputs the original RF signals.

[0003] Methods for converting signals to optical signals at the Tx include an optical intensity modulation method (see Non-Patent Document 1) and a method combining FM batch conversion and optical intensity modulation (see Non-Patent Document 2).

[0004] The V-OLT also includes an optical signal amplifier for outputting an optical signal at a predetermined level.

[0005] “Transmission equipment for multi-channel television signals over optical access networks by sub-carrier multiplexing (SCM)” ITU-T Rec. J. 186, 2008. “Transmission equipment for transferring multi-channel television signals over optical access networks by frequency modulation conversion” ITU-T Rec. J. 185, 2012.

[0006] The RF signal output from the V-ONU may be subject to quality regulations such as the signal's Carrier-to-Noise Ratio (CNR) and distortion (secondary D / U, tertiary D / U; desired signal / undesired signal). These can deteriorate during transmission due to factors such as the nonlinear optical effect of the optical signal and chromatic dispersion. Therefore, in signal transmission, one of the important technologies is to suppress the deterioration of the quality of the resulting RF signal.

[0007] In view of the above circumstances, an object of the present invention is to provide a technique for suppressing deterioration in the quality of an obtained RF signal.

[0008] One aspect of the present invention is a transmission control system that controls the transmission of an optical signal converted from an RF signal in a transmission system that transmits the optical signal, the transmission control system comprising: an amplifier that amplifies the optical signal; a branching unit that branches the optical signal amplified by the amplifier; and a control unit that executes an optical modulation index measurement process that measures the optical modulation index of one of the optical signals branched by the branching unit; and an amplification control process that controls the amplification index of the optical signal by the amplifier based on the measurement results of the optical modulation index measurement process.

[0009] According to the present invention, it is possible to suppress deterioration in the quality of the obtained RF signal.

[0010] The present invention relates to a transmission control system and a control device for controlling a transmission of a signal transmitted from a transmission source to a transmission target.

[0011] (Embodiment) Fig. 1 is an explanatory diagram illustrating a transmission system 100 according to an embodiment. The transmission system 100 is a system that converts an RF signal into an optical signal, transmits the signal to a destination, and converts the optical signal into an RF (Radio Frequency) signal at the destination. The transmission system 100 includes a transmitting device 1, a receiving device 2, and a transmission control system 10. The transmission control system 10 controls the transmission of the optical signal. That is, the transmission control system controls the transmission of the optical signal in the transmission system 100, which transmits the optical signal converted from the RF signal. The transmission control system 10 includes an amplifier 3, a splitter 4, and a control device 5.

[0012] The transmitter 1 converts the optical RF signal into an optical signal and outputs the resulting optical signal.

[0013] The receiving device 2 receives an optical signal, converts the received optical signal into an RF signal, and outputs the RF signal obtained by the conversion. Therefore, the receiving device 2 is an example of the above-mentioned transmission destination.

[0014] The amplifier 3 amplifies the optical signal output by the transmitter 1. The splitter 4 splits the optical signal amplified by the amplifier 3. The splitter 4 is, for example, an optical fiber coupler. The control device 5 receives one of the optical signals split by the splitter 4, and controls the amplification degree of the optical signal by the amplifier 3 based on the received optical signal. The processing performed by the control device 5 will be described in more detail below.

[0015] At least a portion of the other optical signal branched by the branching device 4 reaches the receiving device 2 .

[0016] In the transmission system 100 and the transmission control system 10, optical signals are transmitted via a transmission line 6. The transmission line 6 is a transmission line that transmits optical signals. The transmission line 6 is, for example, an optical fiber. The transmission line 6 is located at a position that connects devices. Therefore, the transmission line 6 connects, for example, a transmitting device 1 and an amplifier 3, and transmits light from the transmitting device 1 to the amplifier 3. The transmission line 6 connects, for example, an amplifier 3 and a splitter 4, and transmits light from the amplifier 3 to the splitter 4. The transmission line 6 connects, for example, the splitter 4 and a control device 5, and transmits light from the splitter 4 to the control device 5. The transmission line 6 connects, for example, the splitter 4 and a receiving device 2, and transmits light from the splitter 4 to the receiving device 2.

[0017] 1 shows examples of the transmission direction of optical signals with arrows L1, L2, L3, and L4. Arrow L1 indicates that an optical signal is transmitted from transmitting device 1 to amplifier 3. Arrow L2 indicates that an optical signal is transmitted from amplifier 3 to splitter 4. Arrow L3 indicates that an optical signal is transmitted from splitter 4 to receiving device 2. Arrow L4 indicates that an optical signal is transmitted from splitter 4 to control device 5. In the transmission of these optical signals, the optical signals are transmitted via transmission path 6.

[0018] <Details of Processing Executed by Control Device 5> The control device 5 executes an optical modulation index measurement process and an amplification control process. The optical modulation index measurement process is a process for measuring the optical modulation index of one of the received optical signals. The amplification control process is a process for controlling the amplification index of the optical signal by the amplifier 3 based on the measurement result of the optical modulation index measurement process.

[0019] Incidentally, the optical modulation index is described after the modified examples just to be sure, so please refer to it if necessary.

[0020] In the amplification control process, the amplification degree of the optical signal by the amplifier 3 is controlled based on the optical modulation index measured in the optical modulation index measurement process in accordance with a predetermined rule regarding control of the amplification degree (hereinafter referred to as the "amplification control rule"). The amplification control rule is, for example, a rule that controls the amplification degree of the optical signal by the amplifier 3 based on amplification correspondence information, which is information indicating the correspondence relationship between the optical modulation index and the amplification degree, to the amplification degree that corresponds to the optical modulation index measured in the optical modulation index measurement process and is indicated by the amplification correspondence information.

[0021] The correspondence relationship between the optical modulation index and the amplification index indicated by the amplification correspondence information is a correspondence relationship that is determined in advance based on knowledge obtained through, for example, simulations, experiments, or the like.

[0022] Other examples of the amplification control rule will be described later in the modified examples.

[0023] <Effects of Optical Modulation Index Measurement Processing and Amplification Control Processing> In fact, for an optical signal to have a predetermined quality, the optical modulation index must be within a certain range during the transmission of the optical signal. This certain range of the optical modulation index is determined in advance depending on the type of transmission, such as the type of transmission signal and the transmission distance limit.

[0024] However, the optical modulation index fluctuates due to the effects of nonlinear optical effects and chromatic dispersion that occur during the transmission of the optical signal. If the optical modulation index is too low, the carrier-to-noise ratio (CNR) decreases, and if it is too high, the distortion of the optical signal increases accordingly (see Reference 1 below). Thus, if the optical modulation index is too low or too high, the RF signal obtained by the receiver 2 will be degraded.

[0025] Reference 1: Japanese Patent Application Laid-Open No. 2012-009577

[0026] On the other hand, if the optical modulation index is within a predetermined range H, degradation of the RF signal obtained by the receiving device 2 is suppressed. Control of the amplifier 3 by the optical modulation index measurement process and the amplification control process is a technology that utilizes this phenomenon to suppress degradation of the RF signal obtained by the receiving device 2.

[0027] Specifically, the control device 5 measures the optical modulation index and, based on the measurement results, controls the amplification factor of the amplifier 3 so that the optical modulation index falls within a predetermined range H, thereby suppressing degradation of the RF signal obtained by the receiving device 2. The predetermined range H of the optical modulation index is a range that is determined in advance based on knowledge obtained through simulations, experiments, etc., so that the quality of the RF signal obtained by the receiving device 2 satisfies a predetermined standard.

[0028] The predetermined range H of the optical modulation degree has an upper limit of 33% in, for example, Non-Patent Document 1. The predetermined range H of the optical modulation degree has a lower limit of 70% and an upper limit of 95% in, for example, Non-Patent Document 2.

[0029] The transmission control system 10 configured as described above and including the amplifier 3, the splitter 4, and the control device 5 can suppress deterioration in the quality of the RF signal obtained by the receiving device 2.

[0030] <Other Effects of the Transmission Control System 10> Furthermore, the control device 5 does not operate only when the transmission system 100 is constructed, but can operate at a predetermined timing after the transmission system 100 has started to be used. Therefore, compared to the comparative technology, the transmission system 100 including the transmission control system 10 suppresses deterioration of the quality of the RF signal over the long term. The comparative technology is a different system from the transmission system 100 that transmits RF signals, and is a technology in which the quality of the RF signal is measured and controlled only during construction.

[0031] Furthermore, in the case of the compared technology, the quality of the RF signal may be evaluated by measuring values ​​using an external device that has the function of measuring CNR or distortion. The reason for using an external device is that measuring CNR or distortion requires the function of demodulating the optical signal back to the original RF signal, and if the compared technology had that function, the device would be complicated or large.

[0032] On the other hand, the transmission control system 10 suppresses degradation of the RF signal by controlling the optical modulation index through control of the amplification index of the amplifier 3. The transmission control system 10 does not use a technology that suppresses degradation of the RF signal by measuring CNR or distortion. Therefore, the transmission control system 10 does not need to convert the optical signal into an RF signal. As a result, the transmission control system 10 can suppress the complexity and size of the device.

[0033] 2 is a diagram showing an example of a more specific hardware configuration of the control device 5 in the embodiment. The control device 5 includes a control unit 51 including a processor 91 such as a CPU and a memory 92 connected by a bus, and executes a program. By executing the program, the control device 5 functions as a device including the control unit 51, an interface unit 52, a storage unit 53, and an optical receiver 54.

[0034] More specifically, the processor 91 reads out a program stored in the storage unit 53 and stores the read out program in the memory 92. The processor 91 executes the program stored in the memory 92, whereby the control device 5 functions as a device including the control unit 51, the interface unit 52, the storage unit 53, and the optical receiver 54.

[0035] The control unit 51 executes an optical modulation index measurement process and an amplification control process. The control unit 51 executes the optical modulation index measurement process to measure the optical modulation index of an optical signal received by the optical receiver 54. The control unit 51 controls the operation of each functional unit included in the control device 5. The control unit 51 controls, for example, the amplification index of the amplifier 3 via the interface unit 52.

[0036] The control unit 51 acquires, for example, information stored in the storage unit 53. Specifically, the process of acquiring information stored in the storage unit 53 is a read process.

[0037] The interface unit 52 includes a communication interface for connecting the control device 5 to an external device. The interface unit 52 communicates with the external device via wired or wireless communication. The external device is, for example, the amplifier 3. In such a case, the interface unit 52 controls the amplification degree of the amplifier 3 by communicating with the amplifier 3.

[0038] The interface unit 52 may be configured to include input devices such as a mouse, a keyboard, a touch panel, etc. The interface unit 52 may be configured as an interface that connects these input devices to the control device 5. In this way, the interface unit 52 accepts input of various information to the control device 5 via the input devices, either wired or wireless.

[0039] The interface unit 52 outputs, for example, various types of information. The interface unit 52 includes a display device such as a CRT (Cathode Ray Tube) display, a liquid crystal display, or an organic EL (Electro-Luminescence) display. The interface unit 52 may be configured as an interface that connects these display devices to the control device 5. The interface unit 52 outputs, for example, information input to the interface unit 52.

[0040] The storage unit 53 is configured using a computer-readable storage medium device (non-transitory computer-readable recording medium) such as a magnetic hard disk device or a semiconductor storage device. The storage unit 53 stores various information related to the control device 5. The storage unit 53 stores, for example, various information generated by the operation of the control unit 51. The storage unit 53 stores, for example, information acquired by the interface unit 52. The storage unit 53 stores, in advance, information used in the amplification control process, such as amplification support information.

[0041] The optical receiver 54 receives an optical signal. The optical receiver 54 receives one of the optical signals branched by the brancher 4, converts it into an electrical signal, and outputs it. The output destination is, for example, the control unit 51. The optical receiver 54 is, for example, a photoelectric conversion element.

[0042] 3 is a diagram showing an example of the flow of processing executed by the transmission control system 10 in the embodiment. The amplifier 3 amplifies the optical signal (step S101). Next, the branching device 4 branches the optical signal amplified by the amplifier 3 (step S102). Next, the optical receiver 54 receives one of the optical signals branched by the branching device 4 (step S103). That is, the control device 5 receives one of the optical signals branched by the branching device 4. After step S103, the control unit 51 executes an optical modulation index measurement process (step S104). Next, the control unit 51 executes an amplification control process (step S105).

[0043] The transmission control system 10 configured in this manner includes an amplifier 3, a splitter 4, and a control device 5. Therefore, as described above in <Effects of Optical Modulation Degree Measurement Processing and Amplification Control Processing>, it is possible to suppress deterioration in the quality of the RF signal obtained by the receiving device 2.

[0044] (Modification) The transmitting device 1 may be, for example, an optical transmitting device (Tx), and the receiving device 2 may be, for example, an optical receiving device (V-ONU).

[0045] The transmission control system 10 may be, for example, an optical transmission device (V-OLT).

[0046] The transmission system 100 does not necessarily have to include only one transmission control system 10, but may include multiple transmission control systems 10. In such a case, the other optical signal output from at least one of the multiple branching devices 4 is amplified by another amplifier 3 before entering the receiving device 2.

[0047] When the control unit 51 changes the amplification factor of the amplifier 3, it is not necessary for the control unit 51 to control the amplification factor of the amplifier 3 until the optical modulation factor falls outside the predetermined range H. This makes it possible to prevent a situation in which energy is consumed to control the operation of the amplifier 3 even though there is no change in the optical modulation factor.

[0048] <Another Example of Amplification Control Rule> Another example of the amplification control rule will be described. For example, if the method for converting an RF signal to an optical signal in the transmitting device 1 includes FM batch conversion, the amplification control rule may be a rule that controls the amplification degree of the amplified optical signal so that the CNR obtained by a CNR calculation formula in the FM batch conversion method satisfies a predetermined standard. The CNR calculation formula in the FM batch conversion method may be any well-known formula as long as it is a CNR calculation formula in the FM batch conversion method.

[0049] In addition, the control so that the CNR obtained by the CNR calculation formula in the FM batch conversion method in the amplified optical signal satisfies a predetermined standard may be controlled based on a predetermined relationship between the optical modulation index measured by the optical modulation index measurement process, the amplification degree, and the CNR. In such a case, the predetermined relationship between the optical modulation index measured by the optical modulation index measurement process, the amplification degree, and the CNR indicates a relationship between the optical modulation index, the amplification degree, and the CNR such that the CNR obtained by the CNR calculation formula in the FM batch conversion method in the amplified optical signal satisfies the predetermined standard.

[0050] In addition, the control so that the CNR obtained by the CNR calculation formula in the optical intensity modulation method in the amplified optical signal satisfies a predetermined standard may be controlled based on a predetermined relationship between the optical modulation index measured by the optical modulation index measurement process, the amplification degree, and the CNR. In such a case, the predetermined relationship between the optical modulation index measured by the optical modulation index measurement process, the amplification degree, and the CNR indicates a relationship between the optical modulation index, the amplification degree, and the CNR such that the CNR obtained by the CNR calculation formula in the optical intensity modulation method in the amplified optical signal satisfies the predetermined standard.

[0051] The control device 5 may be implemented using a plurality of information processing devices connected to each other via a network. In this case, the processes executed by the control unit 51 may be distributed among the plurality of information processing devices. Therefore, for example, the optical modulation index measurement process and the amplification control process may be executed by different information processing devices.

[0052] Note that all or part of the functions of the control device 5 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program may be transmitted via a telecommunications line.

[0053] 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.

[0054] <What is optical modulation index?> Optical modulation index will be explained using FIG. 4. FIG. 4 is an explanatory diagram illustrating optical modulation index in a modified example. More specifically, FIG. 4 shows an example of the waveform of an optical signal. The horizontal axis of FIG. 4 represents time, and the vertical axis represents optical output level. Note that optical output level refers to the intensity of the optical signal. Intensity is the square of the amplitude. Optical modulation index is the degree of level fluctuation A relative to the average value P of the optical output level of an optical signal over a certain period of time. Therefore, expressed mathematically, optical modulation index is R = A / P. Here, R represents optical modulation index. Note that the level fluctuation is half the value obtained by subtracting the minimum value from the maximum value of the optical output level.

[0055] Since the optical modulation index R is R=A / P, when the level fluctuation A is large, the optical modulation index may be larger than the lower limit of the predetermined range H. Since the optical modulation index R is R=A / P, when the level fluctuation A is small, the optical modulation index may be smaller than the upper limit of the predetermined range H.

[0056] Furthermore, since the optical modulation index R = A / P, even if the amplification index by the amplifier 3 changes, it is possible to control so that the optical modulation index R does not change as a result of changes in both the average value P and the level fluctuation A of the optical output level of the optical signal. However, according to the well-known CNR calculation formula, even if the optical modulation index R does not change, the CNR can change due to changes in the average value P and the level fluctuation A of the optical output level of the optical signal. Therefore, the control device 5 may, for example, perform control to improve the CNR while preventing the optical modulation index R from changing.

[0057] REFERENCE SIGNS LIST 100... transmission system, 10... transmission control system, 1... transmitting device, 2... receiving device, 3... amplifier, 4... branching device, 5... control device, 6... transmission path, 51... control unit, 52... interface unit, 53... storage unit, 54... optical receiver, 91... processor, 92... memory

Claims

1. A transmission control system that controls the transmission of an optical signal converted from an RF signal in a transmission system that transmits the optical signal, comprising: an amplifier that amplifies the optical signal; a splitter that splits the optical signal amplified by the amplifier; and a control unit that executes an optical modulation measurement process that measures the optical modulation degree of one of the optical signals split by the splitter, and an amplification control process that controls the amplification degree of the optical signal by the amplifier based on the measurement results of the optical modulation measurement process.

2. The transmission control system according to claim 1, wherein in the optical modulation degree measurement process, the amplification degree is controlled so that the optical modulation degree is within a predetermined range.

3. The transmission control system according to claim 1 or 2, wherein in the optical modulation degree measurement process, the amplification degree is controlled based on a predetermined correspondence relationship between the optical modulation degree and the amplification degree.

4. The transmission control system according to claim 1, wherein the amplifier, the splitter, and the control unit are provided in an optical transmission device (V-OLT).

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