Branching ratio calculation method, branching ratio calculation device, and optical fiber radio system

Abstract

To provide a branching ratio calculation method, a branching ratio calculation device, and an optical fiber radio system, capable of appropriately calculating a branching ratio of an optical signal in accordance with an environment to which the optical fiber radio system is adopted.SOLUTION: A branching ratio calculation device 100 comprises an optical loss acquisition part 111 that acquires first optical loss information and second optical loss information. Also, the branching ratio calculation device 100 comprises a band loss acquisition part 112 that acquires first band loss information and second band loss information. Also, the branching ratio calculation device 100 comprises a transport loss calculation part 113 that calculates a first free space transport loss and a second free space transport loss. The branching ratio calculation device 100 comprises a difference calculation part 114 that calculates a gain difference on the basis of the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space transport loss, and the second free space transport loss. In addition, the branching ratio calculation device 100 comprises a branching ratio calculation part 115 that calculates the branching ratio in a coupler on the basis of the gain difference.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a branching ratio calculation method, a branching ratio calculation device, and a radio-over-fiber system. [Background technology]

[0002] Conventionally, technologies have been proposed to deliver high-frequency radio waves to places where they cannot reach due to obstruction, etc., by branching or relaying them. Patent Document 1 discloses a radio-on-fiber system that enables long-distance transmission that takes into account optical energy efficiency. The radio-on-fiber system disclosed in Patent Document 1 enables long-distance transmission that takes into account optical energy efficiency by branching optical signals using an unequal branching optical splitter, thereby improving network reliability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-36068 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in environments where radio-over-fiber systems are used, it is difficult to branch signals appropriately due to various factors such as the distance from the base station, optical fiber loss, the size of the room where the radio waves are radiated, etc. Therefore, there is a demand for a system that can branch signals appropriately according to the environment in which the radio-over-fiber system is used and deliver radio waves to areas where radio waves cannot reach.

[0005] The present invention has been made in consideration of the problems inherent in the conventional techniques, and an object of the present invention is to provide an optimal radio wave environment by appropriately calculating the branching ratio of an optical signal according to the environment in which the radio-on-fiber system is applied. [Means for solving the problem]

[0006] A branching ratio calculation method according to an embodiment of the present invention is executed by a computer or the like, and calculates a branching ratio to be set in a coupler that relays an optical signal propagating through an optical fiber, and includes obtaining first optical loss information on optical fiber loss from the coupler to a first module used in a first room and second optical loss information on optical fiber loss from the coupler to a second module used in a second room, obtaining first band loss information which is loss due to the optical fiber band from the coupler to the first module and second band loss information which is loss due to the optical fiber band from the coupler to the second module, calculating a first free space propagation loss which is the free space propagation loss of radio waves from the first module in the first room and a second free space propagation loss which is the free space propagation loss of radio waves from the second module in the second room, calculating a gain difference between the first module and the second module based on the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss, and calculating a branching ratio in the coupler based on the gain difference.

[0007] A branching ratio calculation device according to another aspect of the present invention is a branching ratio calculation device that calculates a branching ratio to be set in a coupler that relays an optical signal propagating through an optical fiber, and includes an optical loss acquisition unit that acquires first optical loss information relating to optical fiber loss from the coupler to a first module used in a first room and second optical loss information relating to optical fiber loss from the coupler to a second module used in a second room, first band loss information which is loss due to the optical fiber band from the coupler to the first module, and second band loss information which is loss due to the optical fiber band from the coupler to the second module. the first module and the second module based on the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss; and a branching ratio calculation unit that calculates a branching ratio in the coupler based on the gain difference.

[0008] A radio-over-fiber system according to another aspect of the present invention includes a transceiver module that receives a signal transmitted from a base station, converts the received signal into an optical signal and transmits it to an optical fiber, and converts the optical signal received via the optical fiber into a radio signal and transmits it to the base station, and a coupler that branches the optical signal transmitted from the transceiver module, the coupler having a branching ratio calculated by the branching ratio calculation method or branching ratio calculation device described above. Effect of the Invention

[0009] According to the present invention, it is possible to provide an optimal radio wave environment by appropriately calculating the branching ratio of an optical signal according to the environment in which the radio-on-fiber system is applied. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a configuration of a branching ratio calculation device according to a first embodiment. [Diagram 2] 1 is a diagram illustrating a functional configuration of a branching ratio calculation device according to a first embodiment. [Diagram 3] 1 is a diagram for explaining a radio-on-fiber system to which a branching ratio calculated by a branching ratio calculating device according to a first embodiment is applied. FIG. [Figure 4] 4 is a diagram for explaining data used in the branching ratio calculation device according to the first embodiment. FIG. [Diagram 5] 5 is a flowchart showing an example of processing performed by the branching ratio calculation device according to the first embodiment. [Figure 6] FIG. 11 is a diagram illustrating a functional configuration of a branching ratio calculation device according to a second embodiment. [Figure 7] 11 is a diagram for explaining a radio-on-fiber system to which a branching ratio calculated by a branching ratio calculating device according to a second embodiment is applied. FIG. [Figure 8] 13 is a diagram for explaining data used in the branching ratio calculation device according to the second embodiment. FIG. [Figure 9] 10 is a flowchart showing an example of processing performed by the branching ratio calculation device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the branching ratio calculation method and branching ratio calculation device 100 according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios. In addition, in the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0012] (First embodiment) Fig. 1 is a diagram showing the configuration of a branching ratio calculation device 100 that uses a branching ratio calculation method according to a first embodiment. The device will be described together with the method. In this embodiment, the branching ratio calculation device 100 is a device that uses a method for calculating information (branching ratio) to be set in a coupler 200 (see Fig. 3) that branches a signal in a radio-on-fiber system 10 (see Fig. 3) that relays a radio signal transmitted from a base station 300 (see Fig. 3). Details of a system to which the branching ratio calculated by this branching ratio calculation device 100 is applied will be described later.

[0013] In this embodiment, the branching ratio calculation device 100 is configured by a general computer including a control unit 110, a storage unit 120, an input / output IF 130 (Interface), and a communication IF 140. The control unit 110 and the storage unit 120 will be described in detail later.

[0014] The input / output IF 130 is, for example, a component (interface) for a user to exchange data with the branching ratio calculation device 100. The input / output IF 130 includes, for example, an input IF and an output IF (not shown).

[0015] The input IF in the input / output IF 130 has an interface function for inputting various information by a user, and information is input from outside the branching ratio calculation device 100. Information is input to the input IF by a user via, for example, a keyboard, a mouse, a touch panel, a trackball, a voice recognition device, or the like, connected to the branching ratio calculation device 100. The input IF can also input information as a data input terminal for inputting data from an external storage device (not shown) or the like.

[0016] The output IF in the input / output IF 130 can display acquired information and branching ratio information (described later) on a display device (not shown) connected to the branching ratio calculation device 100. The display device is, for example, a display device, a projector device, or the like.

[0017] The communication IF 140 is an interface that enables communication between the branching ratio calculation device 100 and an external device. For example, a user may exchange data with the branching ratio calculation device 100 via the communication IF 140 instead of the input / output IF 130.

[0018] (Functional Configuration of Branching Ratio Calculation Device 100) Fig. 2 is a diagram showing a functional configuration of the branching ratio calculation device 100 according to the first embodiment. As shown in Fig. 2, the control unit 110 of the branching ratio calculation device 100 includes, as functions, an optical loss acquisition unit 111, a band loss acquisition unit 112, a propagation loss calculation unit 113, a difference calculation unit 114, and a branching ratio calculation unit 115. Each function of the control unit 110 will be described later.

[0019] Furthermore, the control unit 110 operates, for example, an operating system to control the entire branching ratio calculation device 100. Furthermore, the control unit 110 operates based on a program stored in the storage unit 120 to execute each of the above-mentioned functions. Note that the program is not limited to being stored in the storage unit 120, and may be stored, for example, in a ROM (Read Only Memory) or the like (not shown) within the branching ratio calculation device 100.

[0020] 2, the storage unit 120 stores information included in an acquired information DB 121 (DB: Database), a difference information DB 122, and a branching ratio information DB 123 as data. The storage unit 120 for storing these pieces of data may be one or more. For example, the storage unit 120 may be configured to store data in separate areas in a single storage unit 120. Alternatively, data may be distributed and stored in a plurality of storage devices installed in physically separate locations.

[0021] (Configuration of Radio on Fiber System 10) FIG. 3 is a diagram for explaining a radio-on-fiber system 10 to which a branching ratio calculated by the branching ratio calculation method or branching ratio calculation device 100 according to the first embodiment is applied. As shown in FIG. 3, a radio signal transmitted from a base station 300 is received by a transmitting / receiving module M0. The radio signal received by the transmitting / receiving module M0 is converted into an optical signal and sent to a coupler 200 for branching the signal via an optical fiber 400. The coupler 200 branches the signal to be transmitted to a first module M1, which is a communication module used in a first room R1, and a second module M2, which is a communication module used in a second room R2. That is, an optical signal is propagated from the transmitting / receiving module M0 to the first module M1 via a first path 401. Also, an optical signal is propagated from the transmitting / receiving module M0 to the second module M2 via a second path 402.

[0022] For example, when the first room R1 and the second room R2 are different in size, if the coupler 200 equally divides the signal to the first module M1 and the second module M2, the radio waves may not be able to cover a large room. Also, when the distance from the transceiver module M0 to the first module M1 and the second module M2 is different, the strength of the signals from the first module M1 and the second module M2 may decrease due to the influence of propagation loss, etc. The branching ratio calculation device 100 according to this embodiment is a device for appropriately calculating the branching ratio in the coupler 200 in order to appropriately relay signals to the first room R1 and the second room R2.

[0023] The optical loss acquisition unit 111 acquires the optical fiber optical loss L11 from the coupler 200 to the first module M1 used in the first room R1 and the optical fiber optical loss L12 to the second module M2 used in the second room R2. The optical loss acquisition unit 111 acquires the optical fiber optical losses L11 and L12 via the above-mentioned input / output IF 130 or the communication IF 140, and stores them in the acquired information DB 121. The optical fiber optical loss L11 corresponds to the first optical loss information. Moreover, the optical fiber optical loss L12 corresponds to the second optical loss information.

[0024] The optical loss acquisition unit 111 may be configured to acquire, from the acquired information DB 121, the optical fiber losses L11 and L12 that have been stored in advance in the acquired information DB 121 by a user via the input / output IF 130 or the communication IF 140.

[0025] FIG. 4 is a diagram for explaining data used in the branching ratio calculation device 100 according to the first embodiment. For example, the optical fiber losses L11 and L12 stored in the acquired information DB 121 correspond to the item "optical fiber loss from the coupler to the module in the room" shown in FIG. 4. In the example shown in FIG. 4, the optical fiber loss L11 (converted into the amount of change in the value of the electrical stage of the optical receiver) is 0.2 dB, and the optical fiber loss L12 (converted into the amount of change in the value of the electrical stage of the optical receiver) is 0.4 dB. In the example shown in FIG. 4, "room 1" corresponds to the first room R1. In the example shown in FIG. 4, "room 2" corresponds to the second room R2.

[0026] The band loss acquisition unit 112 acquires the optical fiber band loss L21 due to the optical fiber band from the coupler 200 to the first module M1 and the optical fiber band loss L22 due to the optical fiber band to the second module M2, and stores them in the acquired information DB 121. The band loss acquisition unit 112 acquires the optical fiber band losses L21, L22 via the above-mentioned input / output IF 130 or the communication IF 140, and stores them in the acquired information DB 121. The optical fiber band loss L21 corresponds to the first band loss information. Moreover, the optical fiber band loss L22 corresponds to the second band loss information.

[0027] The band loss acquisition unit 112 may be configured to acquire, from the acquired information DB 121, the optical fiber band losses L21 and L22 that have been stored in advance in the acquired information DB 121 by a user via the input / output IF 130 or the communication IF 140.

[0028] For example, the optical fiber band losses L21 and L22 stored in the acquired information DB 121 correspond to the item "loss due to optical fiber band" shown in Fig. 4. In the example shown in Fig. 4, the optical fiber band loss L21 is 0.2 dB and the optical fiber band loss L22 is 0.4 dB.

[0029] The propagation loss calculation unit 113 calculates free space propagation losses L31 and L32 of radio waves from the first module M1 and the second module M2 in the first room R1 and the second room R2. The free space propagation loss L31 corresponds to the first free space propagation loss. The free space propagation loss L32 corresponds to the second free space propagation loss.

[0030] Specifically, the propagation loss calculation unit 113 calculates the free space propagation loss L3x based on the following formula (1). Here, x is a value for distinguishing the first path 401 from the second path 402, and corresponds to, for example, the first digit of the first path 401 and the second path 402. Furthermore, r is the propagation distance from the first module M1 and the second module M2. For example, in the example shown in FIG. 3, it corresponds to the distance between the center of the ellipse shown in the first room R1 and the first module M1. f indicates the frequency of the radio waves emitted from the first module M1 and the second module M2. Furthermore, c indicates the speed of light. Free space propagation loss L3x=20log(4πrf / c) (1)

[0031] 4 shows an example in which the propagation distances (coverage areas) required for the first module M1 and the second module M2 in the first room R1 and the second room R2 are 5 m and 7.7 m, respectively. In addition, when the frequency of the radio waves emitted from the first module M1 and the second module M2 is 28 GHz, the free space propagation losses L31 and L32 are 75.4 dB and 79.1 dB, respectively.

[0032] The difference calculation unit 114 calculates the gain difference between the radio waves emitted from the first module M1 and the second module M2, and stores it in the difference information DB 122. For example, in the example shown in Fig. 4, the gain difference between the radio waves emitted from the first module M1 and the second module M2 is (L12+L22+L32)-(L11+L21+L31)=4.1 dB.

[0033] The branching ratio calculation unit 115 calculates a branching ratio to be applied to the coupler 200 based on the gain difference calculated by the difference calculation unit 114, and stores the calculated branching ratio in the branching ratio information DB 123. Specifically, the branching ratio calculation unit 115 calculates the branching ratio to be applied to the coupler 200 based on the following formula (2). Here, b1 and b2 are values ​​indicating the relationship between the branching ratios b1:b2 of the coupler 200 between the first path 401 and the second path 402. 20log(b2 / (b1+b2))-20log(b1 / (b1+b2))= (L12+L22+L32)-(L11+L21+L31) ··· (2)

[0034] For example, in the example shown in FIG. 4, in order to eliminate the gain difference ΔG of 4.1 dB calculated by the difference calculation unit 114, it is necessary to set the power difference ΔP of the optical signals by the coupler 200, ΔP=|P2-P1|, to 2.05 dB, which is half of 4 dB. If the dB units are converted to real numbers, the terms on the left side of the formula (2) are each 10 (P1 / 10) , 10 (P2 / 10) Taking these ratios and using P2-P1=2.05 dB, the branching ratio of second path 402:first path 401 is 1:0.62, as shown in the following formula (3). 10 (P1 / 10) :10 (P2 / 10) =10 ((P1-P2) / 10) :1 =1:10 (-2.05 / 10) =1:0.62 (3)

[0035] The user sets the branching ratio calculated by the branching ratio calculation unit 115 in the coupler 200. For example, in the example shown in Fig. 3 and Fig. 4, the user sets the coupler 200 so that the branching ratio for the first path 401 and the second path 402 is 0.62:1. This enables the branching ratio calculation device 100 to appropriately set the coupler 200 taking into consideration the size of the room and losses such as optical loss and bandwidth loss of the optical fiber 400.

[0036] (Outline of Processing Flow of Branching Ratio Calculation Device 100) Next, the flow of processing in the branching ratio calculation device 100 will be described using the flowchart shown in Fig. 5. A series of operations of the branching ratio calculation device 100 shown in the flowchart of Fig. 5 starts when the branching ratio calculation device 100 is started, and ends when the operation is completed. The processing in the flowchart shown in Fig. 5 also ends when the power is turned off or an interrupt is issued to end the processing. In the following description of the flowchart, the same contents as those described in the above description of the branching ratio calculation device 100 will be omitted or simplified.

[0037] In step S501, the optical loss acquisition unit 111 acquires the optical fiber optical loss L11 from the coupler 200 to the first module M1 used in the first room R1 and the optical fiber optical loss L12 to the second module M2 used in the second room R2. The optical loss acquisition unit 111 acquires the optical fiber optical losses L11 and L12 via the above-mentioned input / output IF 130 or communication IF 140, and stores them in the acquired information DB 121. After that, the process proceeds to step S502.

[0038] In step S502, the band loss acquisition unit 112 acquires the optical fiber band loss L21 due to the optical fiber band from the coupler 200 to the first module M1 and the optical fiber band loss L22 due to the optical fiber band from the coupler 200 to the second module M2. The band loss acquisition unit 112 also stores the acquired optical fiber band losses L21 and L22 in the acquired information DB 121. After that, the process proceeds to step S503.

[0039] In step S503, the propagation loss calculation unit 113 calculates free space propagation losses L31 and L32 of radio waves from the first module M1 and the second module M2 in the first room R1 and the second room R2. Specifically, the propagation loss calculation unit 113 calculates the free space propagation loss L3x based on the above formula (1). After that, the process proceeds to step S504.

[0040] In step S504, the difference calculation unit 114 calculates the gain difference between the radio waves emitted from the first module M1 and the second module M2, and stores it in the difference information DB 122. After that, the process proceeds to step S505.

[0041] In step S505, the branching ratio calculation unit 115 calculates a branching ratio to be applied to the coupler 200 based on the gain difference calculated by the difference calculation unit 114, and stores the calculated branching ratio in the branching ratio information DB 123. Specifically, the branching ratio calculation unit 115 calculates the branching ratio to be applied to the coupler 200 based on the above formula (2).

[0042] The user sets the branching ratio calculated by the branching ratio calculation device 100 and stored in the branching ratio information DB 123 in the coupler 200. This enables the radio-on-fiber system 10 to emit appropriate radio waves from the modules installed in each room.

[0043] As described above, the branching ratio calculation device 100 according to the first embodiment is a branching ratio calculation device 100 that calculates a branching ratio to be set in the coupler 200 that relays an optical signal propagating through the optical fiber 400. The branching ratio calculation device 100 includes an optical loss acquisition unit 111, a band loss acquisition unit 112, a propagation loss calculation unit 113, a difference calculation unit 114, and a branching ratio calculation unit 115. The optical loss acquisition unit 111 acquires first optical loss information related to optical fiber loss from the coupler 200 to the first module M1 used in the first room, and second optical loss information related to optical fiber loss from the coupler 200 to the second module M2 used in the second room. The band loss acquisition unit 112 acquires first band loss information that is loss due to the optical fiber band from the coupler 200 to the first module M1, and second band loss information that is loss due to the optical fiber band from the coupler 200 to the second module M2. The propagation loss calculation unit 113 calculates a first free space propagation loss, which is a free space propagation loss of radio waves from the first module M1 in the first room, and a second free space propagation loss, which is a free space propagation loss of radio waves from the second module M2 in the second room. The difference calculation unit 114 calculates a gain difference between the first module M1 and the second module M2 based on the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss. The branching ratio calculation unit 115 calculates a branching ratio in the coupler 200 based on the gain difference.

[0044] This enables the branching ratio calculating device 100 to properly calculate the branching ratio of an optical signal according to the environment in which the radio-on-fiber system 10 is applied. Furthermore, the radio-on-fiber system 10 includes a coupler 200 in which a branching ratio properly calculated by the branching ratio calculating device 100 is set, making it possible to realize an energy-efficient communication environment.

[0045] Second embodiment As described above, one specific embodiment has been described, but the above-mentioned embodiment is merely an example and does not limit the embodiments. For example, the above-mentioned embodiment has been described as an example of a case where a wave does not reach a room directly from the base station 300. Here, a branching ratio calculation method and a branching ratio calculation device 100 according to a second embodiment, which calculates a branching ratio to be set in the coupler 200 when a wave reaches a room directly, will be described with respect to a configuration different from that of the first embodiment.

[0046] 6 is a diagram showing a functional configuration of a branching ratio calculation device 100 according to a second embodiment. The branching ratio calculation device 100 according to the second embodiment differs from the branching ratio calculation device 100 according to the first embodiment in that it includes a direct wave information acquisition unit 116.

[0047] The direct wave information acquisition unit 116 acquires the power Pd of the direct wave from the base station 300, and stores it in the acquired information DB 121. Specifically, the direct wave information acquisition unit 116 acquires the power Pd of the direct wave via the input / output IF 130 or the communication IF 140, and stores it in the acquired information DB 121. The power Pd of the direct wave corresponds to direct wave information.

[0048] The direct wave information acquiring unit 116 may be configured to acquire the power Pd of the direct wave, which is stored in advance in the acquired information DB 121 by the user via the input / output IF 130 or the communication IF 140, from the acquired information DB 121.

[0049] Fig. 7 is a diagram for explaining a radio-on-fiber system 10 to which a branching ratio calculated by the branching ratio calculating device 100 according to the second embodiment is applied. Fig. 7 shows an example in which a direct wave from a base station 300 reaches a first room R1 through a window W.

[0050] Fig. 8 is a diagram for explaining data used in the branching ratio calculating device 100 according to the second embodiment. In the example shown in Fig. 8, the strength of a direct wave to the transmitting / receiving module M0, which is a base station side module, is -55 dBm, and the strength (Pd) of a direct wave to the room 1, which is the first room R1, is -70 dBm.

[0051] In the example shown in FIG. 8, the coverage area required for the module is 5 m in both rooms 1 and 2, and the free space propagation losses L31 and L32 are 75.4 dB.

[0052] The branching ratio calculation unit 115 in the second embodiment calculates the branching ratio of the coupler 200 based on the following expressions (3) and (4). P21=Pd+Pa ≦P1-2L11-L21-L31+G+20log (b1 / (b1+b2)) (3) P22≦P1-2L12-L22-L32+G+20log (b2 / (b1+b2)) (4)

[0053] Here, Pd indicates the power of the direct wave, and P21 indicates the minimum receiving power of a terminal communicating with first module M1 in room 1 when there is a direct wave. Pa indicates the power required for a terminal to receive almost no direct waves at a location where the intensity of the direct wave and re-radiated radio waves is the lowest within the range that needs to be covered by radio-on-fiber system 10, that is, generally in the direction in which the radio waves arrive in the room and at a location farthest from radio-on-fiber system 10, and indicates the additional power required in addition to the direct wave. Also, P1 indicates the input power to first module M1 used in room 1.

[0054] Moreover, P22 indicates the minimum reception power of the terminal in a room where no direct wave arrives (room 2). Moreover, b1 and b2 indicate the branching ratio (b1:b2) between the first path 401 and the second path 402. Note that in the second embodiment, it is assumed that there is a room (room 1) that is affected by the direct wave, and the relationship P21>P22 is established.

[0055] Moreover, G denotes the gain of the radio-over-fiber system excluding the losses in the coupler 200 and the optical fiber 400 from the coupler 200 to the first module M1 and the second module M2 in the rooms 1 and 2.

[0056] An example will be shown in which the frequency handled by the radio-on-fiber system 10 shown in Fig. 7 is 28 GHz. It is assumed that the gain G of the radio-on-fiber system, including the antenna gain excluding the characteristics of the coupler 200 and the optical fiber 400 from the coupler 200 to the modules in each room, is 71 dB, and the input radio power P1 to the first module M1 on the base station 300 side is -52.8 dBm.

[0057] The loss of the optical fiber 400 and the free space propagation loss are assumed to be the values ​​shown in Fig. 8. Furthermore, P22 of the terminal in room 2 (when there is no direct wave) is assumed to be -68 dBm. Furthermore, Pa of the terminal in room 1 (when there is a direct wave) is assumed to be 14 dB stronger than the direct wave.

[0058] In this case, the minimum receiving power P21 of the terminal placed in room 1 is -75+14=-61 dBm, which is calculated by Pd+Pa. The necessary power is determined by P22 and P21, and the branching ratio of coupler 200 is second path 402:first path 401=1:0.47, according to the above equations (3) and (4).

[0059] Fig. 9 is a flowchart showing an example of processing of the branching ratio calculating device 100 according to the second embodiment. Note that the same processing as in the flowchart showing an example of processing of the branching ratio calculating device 100 according to the first embodiment shown in Fig. 5 will not be described here.

[0060] In step S901, the direct wave information acquisition unit 116 acquires the power Pd of the direct wave from the base station 300, and stores it in the acquired information DB 121. After that, the process proceeds to step S902. The processes from step S902 to step S905 are the same as the processes from step S501 to step S504 shown in FIG. 5, and therefore description thereof will be omitted here.

[0061] In step S906, the branching ratio calculation unit 115 calculates the branching ratio to be set in the coupler 200. Specifically, the branching ratio calculation unit 115 calculates the branching ratio based on the above formulas (3) and (4).

[0062] As described above, the branching ratio calculating device 100 according to the second embodiment may further include a direct wave information acquiring unit 116 that acquires direct wave information related to the power of a direct wave of a signal transmitted from the base station 300. In addition, the branching ratio calculating unit 115 calculates the branching ratio in the coupler 200 based on the gain difference, the direct wave information, the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss.

[0063] This makes it possible for the branching ratio calculating device 100 to properly calculate the branching ratio of an optical signal even for a radio-on-fiber system 10 that has an area where a direct wave from the base station 300 arrives due to a window or the like.

[0064] (Other embodiments) Although the embodiments have been described in detail with reference to the drawings, the present embodiments are not limited to the contents described in the above embodiments. The components described above include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described above can be appropriately combined. Various omissions, substitutions, or modifications of the configurations can be made without departing from the spirit of the embodiments.

[0065] In the above embodiment, only the case of the downlink from the base station 300 to the terminal is shown, but the present invention may also be applied to the uplink, which is the flow of signals from the terminal to the base station 300.

[0066] In the above-described embodiment, the coupler 200 may be an optical fiber coupler obtained by melt-drawing the optical fiber 400, a free space type coupler, a waveguide type coupler, or the like.

[0067] Furthermore, the radio-over-fiber system 10 may be configured such that modes are mixed and homogenized in the optical fiber 400 between the transceiver module M0 and the coupler 200. This allows the modes to be mixed and homogenized by microbending or the like. This reduces fluctuations in the branching ratio in the coupler 200, making it possible to provide a more stable radio-over-fiber system 10.

[0068] Furthermore, a computer program (branching ratio calculation program) that causes a computer to execute the processing (branching ratio calculation method) in the above-described branching ratio calculation device 100, and a computer-readable recording medium on which the program is recorded, are included in the scope of this embodiment. Here, any type of computer-readable recording medium may be used. Furthermore, the computer program is not limited to one recorded on the above-described recording medium, and may be one transmitted via an electric communication line, a wireless or wired communication line, a network such as the Internet, or the like.

[0069] The features of the branching ratio calculation method, the branching ratio calculation device 100, and the radio-on-fiber system 10 will be described below.

[0070] The branching ratio calculation method according to the first aspect is executed by a computer or the like, and calculates a branching ratio to be set in a coupler 200 that relays an optical signal propagating through an optical fiber 400. The branching ratio calculation method acquires first optical loss information related to an optical fiber loss from the coupler 200 to a first module M1 used in a first room, and second optical loss information related to an optical fiber loss from the coupler 200 to a second module M2 used in a second room. The branching ratio calculation method also acquires first band loss information that is a loss due to an optical fiber band from the coupler 200 to the first module M1, and second band loss information that is a loss due to an optical fiber band from the coupler 200 to the second module M2. The branching ratio calculation method also calculates a first free space propagation loss that is a free space propagation loss of radio waves from the first module M1 in the first room, and a second free space propagation loss that is a free space propagation loss of radio waves from the second module M2 in the second room. The branching ratio calculation method calculates a gain difference between the first module M1 and the second module M2 based on the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss. The branching ratio calculation method further calculates a branching ratio in the coupler 200 based on the gain difference.

[0071] According to the above configuration, the branching ratio calculation method can appropriately calculate the branching ratio of the optical signal according to the environment in which the radio-on-fiber system 10 is applied, thereby making it possible to create an optimal radio wave environment.

[0072] The branching ratio calculation device 100 according to the second aspect is a branching ratio calculation device 100 that calculates a branching ratio to be set in a coupler 200 that relays an optical signal propagating through an optical fiber 400. The branching ratio calculation device 100 includes an optical loss acquisition unit 111, a band loss acquisition unit 112, a propagation loss calculation unit 113, a difference calculation unit 114, and a branching ratio calculation unit 115. The optical loss acquisition unit 111 acquires first optical loss information related to optical fiber loss from the coupler 200 to a first module M1 used in a first room, and second optical loss information related to optical fiber loss from the coupler 200 to a second module M2 used in a second room. The band loss acquisition unit 112 acquires first band loss information that is loss due to an optical fiber band from the coupler 200 to the first module M1, and second band loss information that is loss due to an optical fiber band from the coupler 200 to the second module M2. The propagation loss calculation unit 113 calculates a first free space propagation loss, which is a free space propagation loss of radio waves from the first module M1 in the first room, and a second free space propagation loss, which is a free space propagation loss of radio waves from the second module M2 in the second room. The difference calculation unit 114 calculates a gain difference between the first module M1 and the second module M2 based on the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss. The branching ratio calculation unit 115 calculates a branching ratio in the coupler 200 based on the gain difference.

[0073] According to the above configuration, it is possible to appropriately calculate the branching ratio of the optical signal depending on the environment in which the radio-on-fiber system 10 is applied, and to create an optimal radio wave environment.

[0074] The branching ratio calculating device 100 according to the third aspect may further include a direct wave information acquiring unit 116 that acquires direct wave information related to the power of a direct wave of a signal transmitted from the base station 300. The branching ratio calculating unit 115 may calculate the branching ratio in the coupler 200 based on the gain difference, the direct wave information, the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss.

[0075] According to the above configuration, the branching ratio calculating device 100 can appropriately calculate the branching ratio of an optical signal even for a radio-on-fiber system 10 that has an area where a direct wave from the base station 300 arrives due to a window or the like.

[0076] The radio-on-fiber system 10 according to the fourth aspect includes a transceiver module M0 and a coupler 200. The transceiver module M0 receives a signal transmitted from a base station 300, converts the received signal into an optical signal and transmits it to an optical fiber 400, and converts the optical signal received via the optical fiber 400 into a wireless signal and transmits it to the base station 300. The coupler 200 branches the optical signal transmitted from the transceiver module M0, and is a coupler 200 in which a branching ratio calculated by the branching ratio calculation method or branching ratio calculation device 100 described above is set.

[0077] According to the above configuration, the radio-on-fiber system 10 includes the coupler 200 in which a branching ratio is set that is appropriately calculated by the branching ratio calculation method or branching ratio calculation device 100, and it becomes possible to realize an energy-efficient communication environment.

[0078] The optical fiber 400 of the radio-on-fiber system 10 according to the fifth embodiment may have a configuration in which modes are mixed and homogenized.

[0079] According to the above configuration, in the radio-on-fiber system 10, modes are mixed and homogenized by microbending etc. This reduces fluctuations in the branching ratio in the coupler 200, making it possible to provide a more stable radio-on-fiber system 10. [Explanation of symbols]

[0080] 10 Radio on Fiber Systems 100 Branching ratio calculation device 110 Control section 111 Optical loss acquisition section 112 Bandwidth loss acquisition unit 113 Propagation loss calculation unit 114 Difference calculation part 115 Branching ratio calculation unit 116 Direct wave information acquisition section 120 Storage section 121 Acquisition information DB 122 Difference information DB 123 Branching ratio information DB 130 Input / Output Interface 140 Communication Interface 200 Coupler 300 base stations 400 Optical Fiber 401 Route 1 402 Route 2 M0 Transmit / Receive Module M1 First module M2 2nd module R1 First Room R2 Second Room

Claims

1. A method for calculating a branching ratio to be set in a coupler that relays an optical signal propagating through an optical fiber, comprising the steps of: obtaining first optical loss information relating to an optical fiber loss from the coupler to a first module used in a first room, and second optical loss information relating to an optical fiber loss from the coupler to a second module used in a second room; acquiring first band loss information, which is a loss due to an optical fiber band from the coupler to the first module, and second band loss information, which is a loss due to an optical fiber band from the coupler to the second module; Calculating a first free space propagation loss which is a free space propagation loss of radio waves from the first module in the first room and a second free space propagation loss which is a free space propagation loss of radio waves from the second module in the second room; calculating a gain difference between the first module and the second module based on the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss; A branching ratio calculation method, comprising: calculating a branching ratio in the coupler based on the gain difference.

2. A branching ratio calculation device for calculating a branching ratio to be set in a coupler that relays an optical signal propagating through an optical fiber, comprising: an optical loss acquisition unit that acquires first optical loss information regarding an optical fiber loss from the coupler to a first module used in a first room, and second optical loss information regarding an optical fiber loss from the coupler to a second module used in a second room; a band loss acquisition unit that acquires first band loss information, which is a loss due to an optical fiber band from the coupler to the first module, and second band loss information, which is a loss due to an optical fiber band from the coupler to the second module; a propagation loss calculation unit that calculates a first free space propagation loss that is a free space propagation loss of radio waves from the first module in the first room and a second free space propagation loss that is a free space propagation loss of radio waves from the second module in the second room; a difference calculation unit that calculates a gain difference between the first module and the second module based on the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss; a branching ratio calculation unit that calculates a branching ratio in the coupler based on the gain difference; A branching ratio calculation device comprising:

3. A direct wave information acquisition unit that acquires direct wave information related to the power of a direct wave of a signal transmitted from a base station, 3. The branching ratio calculation device according to claim 2, wherein the branching ratio calculation unit calculates a branching ratio in the coupler based on the gain difference, the direct wave information, the first optical loss information, the second optical loss information, the first band loss information, the second band loss information, the first free space propagation loss, and the second free space propagation loss.

4. a transceiver module that receives a signal transmitted from a base station, converts the received signal into an optical signal, transmits the optical signal to an optical fiber, converts the optical signal received via the optical fiber into a wireless signal, and transmits the wireless signal to the base station; a coupler that branches an optical signal transmitted from the transceiver module, the coupler having a branching ratio calculated by the branching ratio calculation method according to claim 1 or the branching ratio calculation device according to claim 2 or 3 set therein.

5. 5. The radio-on-fiber system according to claim 4, wherein the optical fiber has a configuration in which modes are mixed and homogenized.

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