Signal conversion device, optical fiber radio system, and signal conversion method

Abstract

To provide a signal conversion device, an optical fiber radio system, and a signal conversion method that are capable of reducing energy loss and suppressing deterioration of signal quality.SOLUTION: A signal conversion device and a signal conversion method relate to an amplifier that amplifies an electric signal from a receiving antenna that receives a radio signal to generate a first signal, an attenuator that attenuates the first signal to generate a second signal, a measuring instrument that measures the intensity of the second signal, a controller that controls the amplifier and the attenuator, and a conversion unit that converts the second signal into an optical signal to be transmitted through an optical fiber. The controller determines whether the gain of the amplifier is greater than a predetermined threshold when the intensity is greater than a specified value, and reduces the gain of the amplifier when it is determined that the gain of the amplifier is greater than the predetermined threshold, and reduces the gain of the attenuator when it is not determined that the gain of the amplifier is greater than the predetermined threshold.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a signal conversion device, a radio-on-fiber system, and a signal conversion method. [Background technology]

[0002] Patent Document 1 discloses a technique for controlling the amplification gain at a wireless relay device based on a propagation loss value when a wireless signal propagates from a base station to a wireless relay device and a system margin that reflects the number of communication terminal devices currently in communication within the coverage area of ​​the base station. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4971332 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the technology disclosed in Patent Document 1, in order to control the amplification gain in a wireless relay device, the signal output from a low-noise amplifier is attenuated by varying the attenuation rate in a variable attenuator. This causes problems such as the amplified signal being converted into heat, resulting in energy loss, and degradation of signal quality.

[0005] The present invention has been made in view of the problems inherent in the conventional techniques, and an object of the present invention is to provide a signal conversion device, a radio-over-fiber system, and a signal conversion method that are capable of reducing energy loss and suppressing deterioration of signal quality. [Means for solving the problem]

[0006] A signal conversion device according to an embodiment of the present invention includes an amplifier that amplifies an electric signal from a receiving antenna that receives a radio signal to generate a first signal, an attenuator that attenuates the first signal to generate a second signal, a measuring device that measures the intensity of the second signal, a controller that controls the amplifier and the attenuator, and a conversion unit that converts the second signal into an optical signal to be transmitted through an optical fiber. The controller determines whether the gain of the amplifier is greater than a predetermined threshold when the intensity is greater than a specified value, and reduces the gain of the amplifier when it is determined that the gain of the amplifier is greater than the predetermined threshold, and reduces the gain of the attenuator when it is not determined that the gain of the amplifier is greater than the predetermined threshold.

[0007] A radio-over-fiber system according to an aspect of the present invention includes the above-mentioned signal conversion device, a receiving antenna, and an optical fiber.

[0008] In a signal conversion method according to an embodiment of the present invention, an amplifier amplifies an electric signal from a receiving antenna that receives a radio signal to generate a first signal, an attenuator attenuates the first signal to generate a second signal, and a measuring device measures the intensity of the second signal. Then, a controller that controls the amplifier and the attenuator determines whether the gain of the amplifier is greater than a predetermined threshold when the intensity is greater than a specified value, and decreases the gain of the amplifier when it is determined that the gain of the amplifier is greater than the predetermined threshold, and decreases the gain of the attenuator when it is not determined that the gain of the amplifier is greater than the predetermined threshold, and a conversion unit converts the second signal into an optical signal to be transmitted via an optical fiber. Effect of the Invention

[0009] According to the present invention, it is possible to provide a signal conversion device, a radio-over-fiber system, and a signal conversion method that can reduce energy loss and suppress deterioration of signal quality. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a configuration of a radio-on-fiber system according to an embodiment of the present invention; [Diagram 2]1 is a block diagram showing a configuration of a signal conversion device according to an embodiment of the present invention. [Diagram 3] 4 is a flowchart showing a process of the signal conversion device according to the present embodiment. [Figure 4] FIG. 4 is a diagram showing a change in signal strength caused by a signal conversion device. [Diagram 5] FIG. 13 is a diagram showing changes in signal and noise intensity caused by a signal conversion device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The signal conversion device, radio-on-fiber system, and signal conversion method according to the present embodiment will be described in detail below 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] [Example of a radio-on-fiber system configuration] Fig. 1 is a block diagram showing the configuration of a radio-on-fiber system according to this embodiment. The radio-on-fiber system 1 includes antennas AN1 and AN2, optical fibers FB1 and FB2, signal conversion devices T1 and T2, and transmission devices R1 and R2. The radio-on-fiber system 1 may also include circulators CQ1 and CQ2.

[0013] The radio-on-fiber system 1 receives radio signals from a base station in a location with a good reception environment, transmits the signals over long distances using optical fibers FB1 and FB2, and re-radiates the signals in locations where the radio signals from the base station are difficult to reach. This makes it possible to eliminate blind zones where it is difficult to receive radio signals from the base station.

[0014] Antenna AN1 is placed in a location with a good reception environment when receiving a radio signal from a base station. Antenna AN1 receives the radio signal from the base station, converts the radio signal into an electrical signal, and transmits the electrical signal to signal conversion device T1. In this case, antenna AN1 functions as a receiving antenna. In addition, antenna AN1 converts an electrical signal from transmission device R1 into a radio signal and transmits the signal. In this case, antenna AN1 functions as a transmitting antenna.

[0015] The circulator CQ1 is disposed on the path of the electric signal between the antenna AN1 and the signal conversion device T1, and on the path of the electric signal between the antenna AN1 and the transmitting device R1. The circulator CQ1 introduces the electric signal from the antenna AN1 to the signal conversion device T1, and introduces the electric signal from the transmitting device R1 to the antenna AN1. In this way, the circulator CQ1 transmits the signal in a fixed direction and does not transmit the signal in the reverse direction.

[0016] The signal conversion device T1 converts the electrical signal received from the antenna AN1 into an optical signal and introduces it to one end of the optical fiber FB1, as will be described in detail later.

[0017] The optical fiber FB1 transmits an optical signal from the signal conversion device T1 to the transmission device R2. One end of the optical fiber FB1 is connected to the signal conversion device T1, and the other end of the optical fiber FB1 is connected to the transmission device R2.

[0018] The transmitter R2 converts the optical signal transmitted over the optical fiber FB1 into a radio signal, more specifically, the transmitter R2 converts the optical signal transmitted over the optical fiber FB1 into an electrical signal to be introduced into the antenna AN2.

[0019] The circulator CQ2 is disposed on the path of the electric signal between the antenna AN2 and the signal conversion device T2, and on the path of the electric signal between the antenna AN2 and the transmitting device R2. The circulator CQ2 introduces the electric signal from the antenna AN2 to the signal conversion device T2, and introduces the electric signal from the transmitting device R2 to the antenna AN2. In this way, the circulator CQ2 transmits the signal in a fixed direction and does not transmit the signal in the reverse direction.

[0020] Antenna AN2 is placed in a location where radio signals from the base station are difficult to reach. Antenna AN2 receives radio signals from terminals and the like, converts the radio signals, and transmits the resulting electrical signals to signal conversion device T2. In this case, antenna AN2 functions as a receiving antenna. In addition, antenna AN2 converts electrical signals from transmission device R2 into radio signals and transmits them. In this case, antenna AN2 functions as a transmitting antenna.

[0021] The signal conversion device T2 converts the electrical signal received from the antenna AN2 into an optical signal and introduces it to one end of the optical fiber FB2, as will be described in detail later.

[0022] The optical fiber FB2 transmits the optical signal from the signal conversion device T2 to the transmission device R1. One end of the optical fiber FB2 is connected to the signal conversion device T2, and the other end of the optical fiber FB2 is connected to the transmission device R1.

[0023] The transmitter R1 converts the optical signal transmitted over the optical fiber FB2 into a radio signal, more specifically, the transmitter R1 converts the optical signal transmitted over the optical fiber FB2 into an electrical signal to be introduced into the antenna AN1.

[0024] The radio-over-fiber system may not include a transmitter and a transmitting antenna. For example, the optical fibers FB1 and FB2 may be connected to an external device, and the signals transmitted through the optical fibers FB1 and FB2 may be transmitted to the external device as they are without being converted into radio signals.

[0025] [Example of signal conversion device configuration] 2 is a block diagram showing the configuration of a signal conversion device according to this embodiment. The signal conversion devices T1 and T2 include an amplifier 10, an attenuator 20, a measuring device 30, a controller CR, and a conversion unit 60. In addition, the signal conversion devices T1 and T2 may include a band-pass filter 40 and a bias tee 50.

[0026] The amplifier 10 amplifies an electrical signal from antennas AN1 and AN2 that receive a radio signal to generate a first signal. For example, the amplifier 10 is a low-noise amplifier with variable gain. The gain of the low-noise amplifier can be adjusted by adjusting the drain current. The drain current can also be adjusted by changing the gate voltage of the low-noise amplifier.

[0027] In a typical low-noise amplifier, the gain can be reduced by reducing the drain current. By reducing the drain current, the power consumption of the low-noise amplifier can be reduced. When multiple low-noise amplifiers are used in the signal conversion devices T1 and T2, the power consumption of each low-noise amplifier can be reduced.

[0028] Alternatively, the amplifier 10 may be a power amplifier or a field-effect transistor (FET).

[0029] The attenuator 20 attenuates the first signal to generate the second signal. For example, the attenuator 20 is an attenuator with variable gain.

[0030] The measuring device 30 measures the intensity of the second signal. For example, the measuring device 30 may be a detector with a coupler. The measuring device 30 may measure power as the intensity of the second signal.

[0031] The controller CR is a general-purpose computer equipped with a CPU (Central Processing Unit), memory, a storage device, an input / output unit, etc. A computer program for functioning as part of a signal conversion device is installed in the controller CR. The computer program may be stored in a recording medium that can be read and written by a computer. The controller CR does not have to be a general-purpose computer. For example, the controller CR may be configured by discrete components such as an operational amplifier (op-amp).

[0032] The controller CR controls the amplifier 10 and the attenuator 20. In particular, the controller CR performs control to adjust the gain of the amplifier 10 and the gain of the attenuator 20 based on the intensity of the second signal measured by the measuring device 30. The gain of the amplifier 10 indicates the ratio of the power intensity of the first signal to the power intensity of the electrical signal input to the amplifier 10. The gain of the attenuator 20 indicates the ratio of the power intensity of the second signal to the power intensity of the first signal.

[0033] The controller CR determines whether the strength of the second signal is greater than a specified value, and if the strength of the second signal is greater than the specified value, the controller CR determines whether the gain of the amplifier 10 is greater than a predetermined threshold value.

[0034] Here, the "prescribed value" is a preset value within a range of power intensity suitable for the operation of bandpass filter 40, bias Tee 50, and conversion unit 60, which will be described later. Also, the "prescribed threshold" may be the minimum gain of amplifier 10 (the lower limit of the gain of amplifier 10). In other words, the "prescribed threshold" is the minimum gain value within the range of gains that amplifier 10 can have.

[0035] The controller CR decreases the gain of the amplifier 10 when it is determined that the gain of the amplifier 10 is greater than the predetermined threshold. On the other hand, the controller CR decreases the gain of the attenuator 20 when it is not determined that the gain of the amplifier 10 is greater than the predetermined threshold. That is, the controller CR decreases the gain of the amplifier 10 so that the intensity of the second signal is equal to or less than the specified value. Then, when the gain of the amplifier 10 is at the lower limit and the intensity of the second signal is greater than the specified value, the controller CR decreases the gain of the attenuator 20.

[0036] The controller CR may maintain the gains of the amplifier 10 and the attenuator 20 when the intensity of the second signal is equal to or less than a specified value. Alternatively, the controller CR may increase the gain of the attenuator 20 when the intensity of the second signal is less than a specified value. Furthermore, the controller CR may increase the gain of the amplifier 10 when the gain of the attenuator 20 is at its upper limit and the intensity of the second signal is less than the specified value.

[0037] As described above, the controller CR adjusts the gain of the amplifier 10 prior to adjusting the gain of the attenuator 20, and adjusts the strength of the second signal to be equal to or lower than the specified value.

[0038] The controller CR may refer to a programmable table to compare the strength of the second signal with the specified value. The controller CR may also refer to a table that stores combinations of the gain of the amplifier 10 and the gain of the attenuator 20 associated with combinations of the strength of the second signal and the specified value.

[0039] In addition, since the gain of the amplifier 10 may change due to a change in temperature of the amplifier 10, the controller CR may adjust the gain of the amplifier 10 to compensate for the effect of the temperature change. Since the gain of the attenuator 20 may change due to a change in temperature of the attenuator 20, the controller CR may adjust the gain of the attenuator 20 to compensate for the effect of the temperature change. For this reason, the signal conversion devices T1 and T2 may include temperature sensors that measure the temperatures of the amplifier 10 and the attenuator 20, and the controller CR may be connected to the temperature sensors.

[0040] The bandpass filter 40 is a filter that transmits only a specific frequency and cuts off other frequencies. Since only the radio signals targeted by the radio-over-fiber system 1 are transmitted through the optical fibers FB1 and FB2, the bandpass filter 40 may transmit only the frequencies corresponding to the radio signals.

[0041] The bias-tee 50 superimposes a DC current from a DC power supply (not shown) on the second signal. The bias-tee 50 is used to supply a DC current from the DC power supply to a conversion unit 60 (described later).

[0042] In addition, the magnitude of the DC current superimposed by the bias Tee 50 may be adjusted as appropriate to adjust the output of the conversion unit 60 described below. For example, since the intensity of the optical signal output by the conversion unit 60 may change due to temperature changes, the magnitude of the DC current superimposed by the bias Tee 50 may be adjusted to compensate for the effect of temperature changes. In addition, the DC current superimposed by the bias Tee 50 may be cut during power saving. This makes it possible to reduce power consumption.

[0043] The conversion unit 60 converts the second signal into an optical signal to be transmitted through the optical fibers FB1 and FB2. When the signal conversion devices T1 and T2 include the bandpass filter 40 and the bias Tee 50, the conversion unit 60 may convert the second signal after passing through the bandpass filter 40 and the bias Tee 50 into an optical signal.

[0044] For example, the conversion unit 60 is an active element such as a light-emitting element. The light-emitting element is, for example, a VCSEL (Vertical Cavity Surface Emitting Laser). Note that the configuration of the light-emitting element is not limited to this embodiment. For example, the light-emitting element may be a distributed feedback (DFB) laser or an LED (Light Emitting Diode).

[0045] [Processing procedure of signal conversion device] 3 is a flow chart showing the process of the signal conversion device according to the present embodiment. The process of the signal conversion device shown in FIG.

[0046] In step S101, measurement device 30 measures the intensity (signal strength) of the second signal.

[0047] In step S103, the controller CR determines whether the signal strength is equal to a specified value.

[0048] If the signal strength is equal to the specified value (YES in step S103), the controller CR maintains the gains of the amplifier 10 and the attenuator 20 in step S105.

[0049] If the signal strength is not equal to the specified value (NO in step S103), in step S111, the controller CR determines whether or not the signal strength is greater than the specified value.

[0050] If the signal strength is greater than the specified value (YES in step S111), in step S113, the controller CR determines whether or not the gate voltage of the amplifier 10 is equal to the lower limit. Here, the "lower limit" to which the gate voltage is compared is a predetermined value determined in advance for the operation of the amplifier 10, and is the minimum value of the voltage that can be set as the gate voltage of the amplifier 10.

[0051] If the gate voltage is not equal to the lower limit value (NO in step S113), it is possible to reduce the gate voltage of the amplifier 10 to reduce the gain of the amplifier 10. Therefore, in step S115, the controller CR reduces the gate voltage of the amplifier 10. As a result, the gain of the amplifier 10 is reduced.

[0052] If the gate voltage is equal to the lower limit (YES in step S113), it is impossible to reduce the gain of the amplifier 10 by lowering the gate voltage of the amplifier 10. Therefore, in step S117, the controller CR increases the attenuation of the attenuator 20. That is, the gain of the attenuator 20 is decreased.

[0053] As is clear from the processes in steps S113, S115, and S117, when the signal strength is greater than the specified value, the controller CR performs control to bring the signal strength closer to the specified value by reducing the gain of the amplifier 10 in preference to the attenuator 20. As a result, an increase in the amount of attenuation in the amplifier 10 is suppressed, and the power consumption in the amplifier 10 can be reduced.

[0054] If the signal strength is smaller than the specified value (NO in step S111), in step S121, the controller CR determines whether or not there is attenuation by the attenuator 20. That is, it determines whether or not the attenuation by the attenuator 20 is functioning.

[0055] If there is attenuation by the attenuator 20 (YES in step S121), in step S127, the controller CR decreases the amount of attenuation by the attenuator 20. That is, the controller CR increases the gain of the attenuator 20.

[0056] If there is no attenuation by the attenuator 20 (NO in step S121), in step S123, the controller CR determines whether or not the gate voltage of the amplifier 10 is equal to an upper limit value. Here, the "upper limit value" to which the gate voltage is compared is a predetermined value determined in advance for the operation of the amplifier 10, and is the maximum voltage that can be set as the gate voltage of the amplifier 10.

[0057] If the gate voltage is not equal to the upper limit (NO in step S123), it is possible to increase the gate voltage of the amplifier 10 to increase the gain of the amplifier 10. Therefore, in step S125, the controller CR increases the gate voltage of the amplifier 10. As a result, the gain of the amplifier 10 is increased.

[0058] If the gate voltage is equal to the upper limit (YES in step S123), it is impossible to increase the gain of the amplifier 10 by increasing the gate voltage of the amplifier 10. Also, there is no attenuation in the attenuator 20. Therefore, the process ends without doing anything.

[0059] As is clear from the processes in steps S121, S123, S125, and S127, when the signal strength is smaller than the specified value, the controller CR increases the gain of the attenuator 20 in preference to the amplifier 10, thereby controlling the signal strength to approach the specified value. As a result, the amount of attenuation in the amplifier 10 can be reduced, and the power consumption in the amplifier 10 can be reduced.

[0060] [Effects of the embodiment] As described above in detail, the signal conversion devices T1 and T2 according to the present embodiment include an amplifier 10 that amplifies an electric signal from the receiving antennas AN1 and AN2 that receive a radio signal to generate a first signal, an attenuator 20 that attenuates the first signal to generate a second signal, a measuring device 30 that measures the intensity of the second signal, a controller CR that controls the amplifier 10 and the attenuator 20, and a conversion unit 60 that converts the second signal into an optical signal to be transmitted through the optical fibers FB1 and FB2. When the intensity is greater than a specified value, the controller CR determines whether the gain of the amplifier 10 is greater than a predetermined threshold. When it is determined that the gain of the amplifier 10 is greater than the predetermined threshold, the controller CR reduces the gain of the amplifier 10, and when it is not determined that the gain of the amplifier 10 is greater than the predetermined threshold, the controller CR reduces the gain of the attenuator 20.

[0061] This reduces energy loss and suppresses deterioration of signal quality. In particular, when there is room for reducing the gain in the amplifier 10, the gain adjustment of the amplifier 10 is prioritized over the adjustment of the gain of the attenuator 20. As a result, the energy used to amplify the electrical signal by the amplifier 10 is prevented from being lost as heat energy in the attenuator 20.

[0062] 4 is a diagram showing a change in signal intensity caused by the signal conversion device. The effect of reducing the gain of the amplifier 10 before the attenuator 20 will be described below assuming a case where amplifiers are connected in multiple stages after the attenuator 20 to increase the gain.

[0063] For example, in the graph GS1 of the change in signal strength, the gain of the amplifier 10 is indicated as ΔP1, and the gain of the attenuator 20 is indicated as ΔP3.

[0064] Therefore, in graph GS2 of signal intensity change, assume that the gain of amplifier 10 is reduced from the state of graph GS1, and the gain is reduced by ΔP2 from ΔP1. Also assume that the gain of attenuator 20 is adjusted to obtain the same output as graph GS1 of signal intensity change. In this case, even if the input and output intensities are the same as those in graph GS1, the gain of attenuator 20 can be changed from ΔP3 to ΔP4. As a result, the thermal energy in attenuator 20 can be suppressed.

[0065] Fig. 5 is a diagram showing changes in signal and noise intensity caused by the signal conversion device, in which graphs GN1 and GN2 of noise intensity changes are shown in addition to the graphs GS1 and GS2 of signal intensity changes shown in Fig. 4.

[0066] The graph GN1 of the noise intensity change and the graph GS1 of the signal intensity change share the same gain settings for the amplifier 10 and the attenuator 20. Similarly, the graph GN2 of the noise intensity change and the graph GS2 of the signal intensity change share the same gain settings for the amplifier 10 and the attenuator 20.

[0067] When the gain of the amplifier 10 is not changed preferentially and the gain of the attenuator 20 is changed, the signal quality SN1 deteriorates at the time of output from the attenuator 20 due to the influence of the noise floor GT caused by thermal noise. On the other hand, when the gain of the amplifier 10 is changed preferentially, the signal quality becomes SN2, which is higher than the signal quality SN1. In other words, by changing the gain of the amplifier 10 preferentially, deterioration of the signal quality can be suppressed.

[0068] Furthermore, in the signal conversion devices T1 and T2 according to the present embodiment, the predetermined threshold may be the minimum gain of the amplifier 10. This allows the adjustment of the gain of the amplifier 10 to be prioritized over the adjustment of the gain of the attenuator 20 within a range adjustable by the amplifier 10. It is possible to minimize the loss of energy used in amplifying the electrical signal by the amplifier 10 as thermal energy in the attenuator 20. In the same manner, it is possible to minimize the deterioration of signal quality.

[0069] Furthermore, in the signal conversion devices T1 and T2 according to the present embodiment, the controller CR may control the gain of the amplifier 10 by controlling the gate voltage of the amplifier 10. This allows the gain of the amplifier 10 to be controlled with high precision. Also, the power consumption of the amplifier 10 can be reduced.

[0070] The radio-on-fiber system 1 according to this embodiment includes the above-mentioned signal conversion devices T1 and T2, receiving antennas AN1 and AN2, and optical fibers FB1 and FB2. The radio-on-fiber system 1 may further include a transmitting device that converts an optical signal transmitted through the optical fiber into a radio signal, and a transmitting antenna that transmits the radio signal.

[0071] This reduces energy loss and suppresses deterioration of signal quality. In particular, when there is room for reducing the gain in the amplifier 10, the gain adjustment of the amplifier 10 is prioritized over the adjustment of the gain of the attenuator 20. As a result, the energy used to amplify the electrical signal by the amplifier 10 is prevented from being lost as heat energy in the attenuator 20.

[0072] Furthermore, in the signal conversion method according to the present embodiment, the amplifier 10 amplifies an electrical signal from the receiving antennas AN1 and AN2 that receive a wireless signal to generate a first signal, the attenuator 20 attenuates the first signal to generate a second signal, and the measuring device 30 measures the intensity of the second signal. Then, the controller CR that controls the amplifier 10 and the attenuator 20 determines whether the gain of the amplifier 10 is greater than a predetermined threshold value when the intensity is greater than a specified value. When it is determined that the gain of the amplifier 10 is greater than the predetermined threshold value, the controller CR reduces the gain of the amplifier 10, and when it is not determined that the gain of the amplifier 10 is greater than the predetermined threshold value, the controller CR reduces the gain of the attenuator 20, and the converter 60 converts the second signal into an optical signal to be transmitted via an optical fiber.

[0073] This reduces energy loss and suppresses deterioration of signal quality. In particular, when there is room for reducing the gain in the amplifier 10, the gain adjustment of the amplifier 10 is prioritized over the adjustment of the gain of the attenuator 20. As a result, the energy used to amplify the electrical signal by the amplifier 10 is prevented from being lost as heat energy in the attenuator 20.

[0074] Each of the functions described in the above embodiments may be implemented by one or more processing circuits, including a programmed processor, an electrical circuit, or a device such as an application specific integrated circuit (ASIC), or a circuit component arranged to perform the described functions.

[0075] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment. [Explanation of symbols]

[0076] 1 Radio-over-fiber systems 10 Amplifier 20 Attenuator 30 Measuring instruments 60 Conversion unit CR Controller AN1,AN2 Antenna FB1, FB2 optical fiber R1, R2 transmitter T1, T2 signal conversion equipment

Claims

1. an amplifier that amplifies an electrical signal from a receiving antenna that receives a radio signal to generate a first signal; an attenuator for attenuating the first signal to generate a second signal; a measuring device for measuring the strength of the second signal; a controller for controlling the amplifier and the attenuator; a conversion unit that converts the second signal into an optical signal to be transmitted through an optical fiber; Equipped with The controller: If the intensity is greater than a specified value, determining whether the gain of the amplifier is greater than a predetermined threshold; decreasing the gain of the amplifier when it is determined that the gain of the amplifier is greater than the predetermined threshold; The signal conversion device reduces the gain of the attenuator if the gain of the amplifier is not determined to be greater than the predetermined threshold.

2. 2. The signal conversion device of claim 1, wherein the predetermined threshold is a minimum gain of the amplifier.

3. The signal conversion device according to claim 1 , wherein the controller controls a gate voltage of the amplifier to thereby control a gain of the amplifier.

4. A signal conversion device according to any one of claims 1 to 3, The receiving antenna; The optical fiber; A radio-on-fiber system comprising:

5. an amplifier amplifies an electrical signal from a receiving antenna that receives a radio signal to generate a first signal; an attenuator attenuating the first signal to generate a second signal; a measuring device for measuring a strength of the second signal; a controller for controlling the amplifier and the attenuator, If the intensity is greater than a specified value, determining whether the gain of the amplifier is greater than a predetermined threshold; decreasing the gain of the amplifier when it is determined that the gain of the amplifier is greater than the predetermined threshold; decreasing the gain of the attenuator if the gain of the amplifier is not determined to be greater than the predetermined threshold; A signal conversion method, comprising: a conversion unit converting the second signal into an optical signal for transmission through an optical fiber.

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