Rof transceiver and optical fiber wireless system

Abstract

To provide a RoF transceiver capable of effectively saving power of a wireless system while keeping the function of a wireless communication system.SOLUTION: A RoF transceiver 100 is a RoF transceiver 100 for relay transmission of a reception signal on wireless communication between a base station and a terminal through an optical fiber transmission line 200. The RoF transceiver 100 includes a reception signal level detection part 121 for detecting reception power of the reception signal. The RoF transceiver 100 also includes a first comparator 122a for comparing the reception power and a determination level stored in a storage part 180 in advance. Furthermore, the RoF transceiver 100 includes a switch control part 123 for controlling a light emission part 130a for emitting a light signal to the optical fiber transmission line 200 based on the result compared by the first comparator 122a. The switch control part 123 controls a protection switch to changeover to the side of a termination resistor 133 if the reception power exceeds an upper limit of the determination level.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a RoF transceiver and an optical fiber wireless system.

Background Art

[0002] Conventionally, a technique has been proposed to eliminate dead zones by receiving radio waves from a base station at a location with a good reception environment, transmitting them over a long distance via an optical fiber, and re-radiating them at a location where the radio waves from the base station are difficult to reach. Patent Document 1 discloses an optical fiber wireless system including a RoF (Radio over Fiber) transceiver that relays a radio signal in wireless communication between a base station and a terminal via an optical fiber transmission line. The optical fiber wireless system disclosed in Patent Document 1 enables radio waves to reach a location (dead zone) where direct radio waves cannot reach by taking advantage of the characteristics of a low-loss and wide-band optical fiber.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional optical fiber wireless system, a function for amplifying a weak received signal power is implemented, and power is required for this amplification. Also, in a conventional optical fiber wireless system, in order to be able to receive a very weak signal power, it is always amplified with the maximum gain even when not receiving, consuming unnecessary power. Furthermore, in a conventional optical fiber wireless system, the received signal is converted into an optical signal for transmission via an optical fiber, but since it is always emitting light, it may consume unnecessary power. Therefore, power saving is required in an optical fiber wireless system.

[0005] The present invention has been made in view of the problems of such prior art. An object of the present invention is to provide a RoF transceiver capable of efficiently reducing the power consumption of a wireless system while maintaining the functions of a wireless communication system.

Means for Solving the Problems

[0006] A RoF transceiver according to an aspect of the present invention is a RoF (Radio over Fiber) transceiver for relaying and transmitting a received signal in wireless communication between a base station and a terminal via an optical fiber transmission line, including a first amplifier, a second amplifier, and a first variable attenuator, a first variable gain amplification unit for increasing and decreasing the received power of the received signal, a received signal level detection unit for detecting the received power of the received signal, a light emitting unit including a protection switch, a light emitting element, a light emitting element driving unit, and a termination resistor, a first comparator for comparing the received power with a determination level stored in a storage unit in advance, a second comparator for comparing the received power with a first reference level stored in the storage unit in advance, a switch control unit for controlling the light emitting unit that emits an optical signal to the optical fiber transmission line based on the result compared by the first comparator, and a first attenuator control unit for controlling the first variable gain amplification unit based on the comparison result of the second comparator, and the switch control unit controls to switch the protection switch to the termination resistor side when the received power exceeds the upper limit of the determination level, and the first attenuator control unit controls the first variable attenuator so that the received power becomes equal to or lower than the first reference level when the received power is equal to or higher than the first reference level, and the first attenuator control unit controls so as not to attenuate the received signal in the first variable attenuator when the received power is lower than the first reference level.

[0007] An optical fiber wireless system according to another aspect of the present invention is the above RoF transceiver, including a first transceiver that performs wireless communication with a base station and a second transceiver that performs wireless communication with a terminal, and the first transceiver and the second transceiver are connected via an optical fiber transmission line.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a RoF transceiver that can efficiently reduce the power consumption of a wireless system while maintaining the functions of the wireless communication system.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7

Figure 8A

Figure 8B

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the RoF transceiver 100 and the optical fiber wireless system 10 according to this embodiment will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] (Overview of the optical fiber wireless system 10) FIG. 1 is a diagram showing the configuration of the optical fiber wireless system 10 according to this embodiment. As shown in FIG. 1, the optical fiber wireless system 10 includes a first transceiver 100a that performs wireless communication with the base station 300, and a second transceiver 100b that performs wireless communication with the terminal 400. The first transceiver 100a and the second transceiver 100b are connected via an optical fiber transmission line 200.

[0012] In the optical fiber wireless system 10 shown in FIG. 1, the wireless signal transmitted by the base station 300 is received by the receiving antenna 140 of the first transceiver 100a, and in the first transceiver 100a, the wireless signal is converted into an optical signal. The optical signal converted by the first transceiver 100a is sent to the second transceiver 100b via the optical fiber transmission line 200.

[0013] In the optical fiber wireless system 10, the first transceiver 100a and the second transceiver 100b are installed at separate locations to enable remote communication. The second transceiver 100b converts the optical signal received via the optical fiber transmission line 200 into an electrical signal, and further transmits it as a wireless signal to a terminal 400 such as a mobile terminal.

[0014] Also, in the optical fiber wireless system 10, the wireless signal transmitted by the terminal 400 is received by the receiving antenna 140 of the second transceiver 100b, and in the second transceiver 100b, the wireless signal is converted into an optical signal. The optical signal converted by the second transceiver 100b is sent to the first transceiver 100a via the optical fiber transmission line 200. The first transceiver 100a converts the optical signal received via the optical fiber transmission line 200 into an electrical signal, and further transmits it as a wireless signal to the base station 300.

[0015] That is, the optical fiber wireless system 10 is a system for relaying and transmitting communication between the base station 300 and the terminal 400. Furthermore, the optical fiber wireless system 10 is a RoF (Radio over Fiber, or Radio on Fiber) system for sending a wireless signal (RF signal, Radio Frequency) over a long distance via the optical fiber transmission line 200. The optical fiber wireless system 10, which is a RoF system, enables long-distance transmission by riding a wireless high-frequency signal on an optical fiber. In addition, the optical fiber wireless system 10 can deliver radio waves to a place (dead zone) where direct radio waves cannot reach by taking advantage of the characteristics of a low-loss and wide-band optical fiber.

[0016] (Configuration of the RoF transceiver 100) Next, the RoF transceiver 100 according to this embodiment will be described. As shown in FIG. 1, the RoF transceiver 100 is applied to the first transceiver 100a on the base station 300 side and the second transceiver 100b on the terminal 400 side. In this embodiment, it is assumed that the first transceiver 100a and the second transceiver 100b have the same configuration. Hereinafter, when it is not necessary to distinguish between the first transceiver 100a and the second transceiver 100b, they will be referred to as the "RoF transceiver 100".

[0017] FIG. 2 is a block diagram for explaining the functions of the RoF transceiver 100 according to this embodiment. Note that the block diagram shown in FIG. 2 schematically shows the functions on the transmission side of the RoF transceiver 100. As shown in FIG. 2, the wireless signal received via the receiving antenna 140 is adjusted by an amplifier and an attenuator so as to have a desired power. For example, the amplifier is composed of an LNA (Low Noise Amplifier) that enables amplification with low noise. Also, the attenuator is composed of a general variable ATT (Attenuator).

[0018] The power-adjusted signal has its received power detected by a detector with a coupler. The control circuit controls the variable ATT based on the detected received power to adjust the received signal. Also, the control circuit controls the light emission from the light-emitting element (VCSEL) based on the detected received power.

[0019] FIG. 3 is a block diagram showing the functional configuration of the RoF transceiver 100 according to the present embodiment. As shown in FIG. 3, the RoF transceiver 100 is composed of a RoF_Tx110a corresponding to the transmission side for an optical signal and a RoF_Rx110b corresponding to the reception side for the optical signal.

[0020] RoF_Tx110a includes band-pass filters 111a, 111b, a first variable gain amplifier 112a, a light-emitting section 130a, and a received signal level detection section 121. Also, RoF_Tx110a includes a first comparator 122a, a second comparator 122b, and a third comparator 122c. Also, RoF_Tx110a includes a switch control section 123, a first attenuator control section 124a, and a second attenuator control section 124b.

[0021] The light-emitting section 130a includes a protection switch 131, a light-emitting element drive section 132, a termination resistor 133, and a light-emitting element 134. In the example shown in FIG. 3, an example where an LD (semiconductor laser LD: Laser Diode) is applied as the light-emitting element 134 is shown. Also, in the example shown in FIG. 3, an example where an LD driver is applied as the light-emitting element drive section 132 is shown. Note that the light-emitting element 134 is not limited to an LD, and a vertical cavity surface emitting laser (VCSEL) or a light-emitting diode (LED) may be applied.

[0022] RoF_Rx110b includes a light-receiving section 130b, a second variable gain amplifier 112b, and a band-pass filter 111c. Also, the light-receiving section 130b includes a light-receiving element 135 and a current-voltage conversion section 136. The light-receiving element is composed of, for example, a PD (photodiode).

[0023] The first variable gain amplifier 112a includes a first amplifier 113a, a second amplifier 113b, and a first variable attenuator 114a, and increases or decreases the reception power of a radio signal.

[0024] The received signal level detection unit 121 detects the reception power of a radio signal. Note that the received signal level detection unit 121 corresponds to a general detector. The received signal level detection unit 121 detects the level of the received signal branched using a coupler (not shown). The received signal level detection unit 121 may use a detection circuit using a diode. Further, the received signal level detection unit 121 is preferably inserted at a subsequent stage of the band-pass filter 111b. Thereby, the received signal level detection unit 121 can prevent detection of unnecessary out-of-band power.

[0025] The first comparator 122a compares the reception power of the received signal with a determination level stored in the storage unit 180 in advance. Note that in the present embodiment, an upper limit and a lower limit are provided for the determination level.

[0026] FIG. 4 is a diagram for explaining the received signal level detection unit 121 according to the present embodiment. In order to detect the received signal level, the received signal level detection unit 121 uses, for example, a detector having the characteristics of FIG. 4. Note that in the example shown in FIG. 4, insertion loss and path loss are not considered.

[0027] For example, in the example shown in FIG. 4, when the upper limit of the power to be input to the light-emitting element 134 is 10 dBm and the lower limit is -20 dBm, 2V and 0.1V corresponding thereto are output from the detector. In this way, the received signal level detection unit 121 detects an output voltage corresponding to the reception power (input power). Using this output voltage, the first comparator 122a, the second comparator 122b, and the third comparator 122c described below determine the reception power.

[0028] That is, in the example shown in FIG. 4, the upper limit of the determination level is 2V, and the lower limit of the determination level corresponds to 0.1V. Note that the upper and lower limits of the determination level are not limited to these values, and values different from 2V and 0.1V may be applied according to the characteristics of the light emitting element 134 and the like.

[0029] The second comparator 122b compares the received power of the received signal with the first reference level stored in the storage unit 180 in advance. Also, the third comparator 122c compares the received power with the second reference level stored in the storage unit 180 in advance.

[0030] The switch control unit 123 controls the light emitting unit 130a that emits an optical signal to the optical fiber transmission line 200 based on the result compared by the first comparator 122a. Specifically, when the received power exceeds the upper limit of the determination level, the switch control unit 123 controls to switch the protection switch 131 to the termination resistor side.

[0031] The first attenuator control unit 124a controls the first variable gain amplifier unit 112a based on the comparison result of the second comparator 122b. Specifically, when the received power is equal to or higher than the first reference level, the first attenuator control unit 124a controls the first variable attenuator 114a so that the received power becomes equal to or lower than the first reference level.

[0032] Also, when the received power is lower than the first reference level, the first attenuator control unit 124a controls the first variable attenuator 114a not to attenuate the received signal.

[0033] The light receiving unit 130b receives the optical signal received from the optical fiber transmission line 200 by the light receiving element 135 and converts it into an electrical signal. Also, the current-voltage conversion unit 136 performs current-voltage conversion of the electrical signal converted by the light receiving element 135.

[0034] The second variable gain amplifier section 112b includes a third amplifier 113c, a fourth amplifier 113d, and a second variable attenuator 114b, and increases or decreases the transmission power of the transmission signal. Also, the second attenuator control section 124b controls the second variable gain amplifier section 112b based on the comparison result of the third comparator 122c. Specifically, when the received power is equal to or less than the second reference level, the second attenuator control section 124b controls the second variable attenuator 114b so that the transmission power becomes equal to or less than the second reference level.

[0035] In the present embodiment, a value is previously provided as the second reference level such that it is the transmission power when the isolation between RoF_Tx110a and RoF_Rx110b is not exceeded. Thereby, the optical fiber radio system 10 according to the present embodiment can prevent crosstalk and unnecessary radio wave radiation between RoF_Tx110a and RoF_Rx110b, and can reduce power consumption.

[0036] (Control of the light emitting element 134) Next, the control of the light emitting element 134 will be described. FIG. 5A is a diagram for explaining the control of the protection switch 131 according to the present embodiment. For example, the RoF transceiver 100 constitutes the first comparator 122a using an OP amplifier and controls the protection switch 131. When the output of the received signal level detection section 121 exceeds 2V which is the upper limit of the determination level, the output of the OP amplifier (the first comparator 122a) becomes High level, and the protection switch 131 is operated (the output port changes from RFout1 to RFout2). Thereby, the output destination of the received signal is connected to the termination resistor 133, and the light emitting element 134 is protected. Although this control uses an OP amplifier as an example, a microcomputer or a computer may be used.

[0037] FIG. 5B is a diagram for explaining the bias current control circuit according to the present embodiment. In the example shown in FIG. 5B, a control example when the input power to the received signal level detection section 121 is weak is shown. In the example shown in FIG. 5B, the first comparator 122a is configured using an OP amplifier, and the constant current source IC provided in the light emitting element drive section 132 is controlled.

[0038] When the output voltage of the received signal level detector 121 drops below 0.1 V, the output of the operational amplifier becomes Low level, and by disabling the constant current source IC, current is no longer supplied to the light emitting element 134. That is, when the received power is below the lower limit of the determination level, the switch control unit 123 turns off the light emitting element drive unit 132 and controls so that no current is supplied to the light emitting element 134.

[0039] This control uses an operational amplifier as a simple method similar to the control of the protection switch 131 described above, but a microcomputer or a computer may also be used. Also, the constant current source IC can be configured (discrete) by combining individual devices, but since it is generally integrated (IC), it can be configured more simply by using this.

[0040] FIG. 6 is a diagram for explaining the characteristics of the light emitting element according to the present embodiment. FIG. 6 shows the LIV (light quantity, current, voltage) characteristics when a VCSEL with low power consumption is used for the light emitting element 134.

[0041] For example, the power consumption when driven at 7 mA (2.4 V) is 16.8 mW. When the bias current is reduced to the threshold current of 0.5 mA (1.5 V), the power consumption becomes 0.75 mW, and power reduction of 95% or more is possible.

[0042] Also, when an LD with a larger consumption current than the VCSEL is used for the light emitting element 134, further power consumption reduction becomes possible. Thereby, during the time period and timing when the RoF transceiver 100 is not in use, not only can the power consumption be reduced, but also the heat generation of the electronic device can be suppressed.

[0043] In a situation where no wireless signal is detected, when transmitting radio waves from the base station 300, instead of transmitting in all directions, a beam is formed and transmitted. Therefore, when communication through the RoF transceiver 100 does not occur, the received signal power becomes weak. Also, for example, when temporarily blocked by a shielding object such as a bird, the detected amount of radio waves is also extremely small even in a case where radio waves are blocked.

[0044] Furthermore, the antenna side (the second transceiver 100b) installed in the dead zone, when there is no mobile terminal (terminal 400), since no wireless signal is transmitted from the terminal 400, there is no power detection at the RoF transceiver 100. And since the passability of reception differs for each frequency band by the band-pass filter (see FIG. 3), power is not detected for frequencies other than those corresponding to the RoF transceiver 100.

[0045] FIG. 7 is a diagram for explaining the effect of power consumption reduction by the optical fiber wireless system 10 according to the present embodiment. FIG. 7 shows the result of calculating the power values of a configuration in which the power supplies of the light emitting element 134 and the RoF transceiver 100 are interlocked regarding the suppression of power consumption when the RoF transceiver 100 is not used. Also, FIG. 8A shows the values of voltage, current, and power when the optical fiber wireless system 10 according to the present embodiment is not applied. Also, FIG. 8B shows the values of voltage, current, and power when the optical fiber wireless system 10 according to the present embodiment is applied.

[0046] As shown in FIG. 7, as a whole system, a 74% reduction in power consumption can be achieved instantaneously compared to the case where the RoF transceiver 100 is not applied. Conventionally, a process of demodulating the received wireless signal once was necessary, and there were concerns about an increase in power consumption and an increase in delay time due to demodulation.

[0047] On the other hand, in the optical fiber wireless system 10 according to the present embodiment, it has a function of detecting power even without a function of demodulating. Further, the optical fiber wireless system 10 according to the present embodiment can realize an analog RoF with lower power consumption than conventional ones by controlling the power not only of amplifiers (the first variable gain amplifier unit 112a and the second variable gain amplifier unit 112b) but also of the light emitting element 134.

[0048] As described above, the RoF transceiver 100 according to the present embodiment is a RoF (Radio over Fiber) transceiver for relaying and transmitting a received signal in wireless communication between the base station 300 and the terminal 400 via the optical fiber transmission line 200. The RoF transceiver 100 includes a first amplifier 113a, a second amplifier 113b, and a first variable attenuator 114a, and is provided with a first variable gain amplification unit 112a for increasing or decreasing the received power of the received signal. Further, the RoF transceiver 100 is provided with a received signal level detection unit 121 for detecting the received power of the received signal. Further, the RoF transceiver 100 includes a protection switch 131, a light emitting element 134, a light emitting element driving unit 132, and a termination resistor 133, and is provided with a light emitting unit 130a. Further, the RoF transceiver 100 is provided with a first comparator 122a for comparing the received power with a determination level stored in the storage unit 180 in advance. Further, the RoF transceiver 100 is provided with a second comparator 122b for comparing the received power with a first reference level stored in the storage unit 180 in advance. Further, the RoF transceiver 100 is provided with a switch control unit 123 for controlling the light emitting unit 130a that emits an optical signal to the optical fiber transmission line 200 based on the result compared by the first comparator 122a. Further, the RoF transceiver 100 is provided with a first attenuator control unit 124a for controlling the first variable gain amplification unit 112a based on the comparison result of the second comparator 122b. The switch control unit 123 controls to switch the protection switch 131 to the termination resistor 133 side when the received power exceeds the upper limit of the determination level. The first attenuator control unit 124a controls the first variable attenuator 114a so that the received power becomes equal to or lower than the first reference level when the received power is equal to or higher than the first reference level. Further, the first attenuator control unit 124a controls so as not to attenuate the received signal in the first variable attenuator 114a when the received power is lower than the first reference level.

[0049] Thereby, the RoF transceiver 100 adjusts the level of the received power according to the received power of the received signal, and appropriately controls the light emission of the light emitting element 134. Therefore, the RoF transceiver 100 can efficiently save power in the wireless system while maintaining the functions of the wireless communication system.

[0050] Furthermore, the RoF transceiver 100 may further include a light receiving element 135 that receives an optical signal received from the optical fiber transmission line 200 and converts it into an electrical signal. Also, the RoF transceiver 100 may include a current-voltage conversion unit 136 that performs current-voltage conversion on the electrical signal converted by the light receiving element 135. Also, the RoF transceiver 100 may include a third amplifier 113c, a fourth amplifier 113d, and a second variable attenuator 114b, and may include a second variable gain amplification unit 112b that increases or decreases the transmission power of the electrical signal. Also, the RoF transceiver 100 may include a third comparator 122c that compares the received power with a second reference level stored in the storage unit 180 in advance. Also, the RoF transceiver 100 may include a second attenuator control unit 124b that controls the second variable gain amplification unit 112b based on the comparison result of the third comparator 122c. When the received power is equal to or lower than the second reference level, the second attenuator control unit 124b may control the second variable attenuator 114b so that the transmission power becomes equal to or lower than the second reference level.

[0051] Thereby, the RoF transceiver 100 can prevent crosstalk and unnecessary radio wave radiation between the RoF_Tx110a and the RoF_Rx110b provided in the RoF transceiver 100, and can reduce power consumption.

[0052] Also, when the received power falls below the lower limit of the determination level, the switch control unit 123 may turn off the light emitting element driving unit 132 and control so that no current is supplied to the light emitting element 134. Thereby, the RoF transceiver 100 can efficiently reduce the power consumption of the wireless system with a simple configuration while maintaining the function of the wireless communication system.

[0053] (Other Embodiments) Although the embodiments have been described in detail with reference to the drawings, the present embodiments are not limited by the contents described in the above embodiments. Also, the constituent elements described above include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the configurations described above can be combined as appropriate. Also, various omissions, substitutions, or changes in the configuration can be made without departing from the gist of the embodiments.

[0054] The switch control unit 123 may detect the temperature and control the light-emitting element driving unit 132 so that the light emission amount of the light-emitting element 134 decreases when the temperature is equal to or higher than a predetermined temperature. Further, the switch control unit 123 may control the light-emitting element driving unit 132 so that the light emission amount of the light-emitting element 134 increases when the temperature is equal to or lower than the predetermined temperature. Thereby, the RoF transceiver 100 can maintain an appropriate light emission amount even when the temperature changes.

[0055] The features of the RoF transceiver 100 and the optical fiber wireless system 10 will be described below.

[0056] The RoF transceiver 100 according to the first aspect is a RoF (Radio over Fiber) transceiver for relaying and transmitting a received signal in wireless communication between the base station 300 and the terminal 400 via the optical fiber transmission line 200. The RoF transceiver 100 includes a first amplifier 113a, a second amplifier 113b, and a first variable attenuator 114a, and is provided with a first variable gain amplification unit 112a for increasing or decreasing the received power of the received signal. Further, the RoF transceiver 100 is provided with a received signal level detection unit 121 for detecting the received power of the received signal. Further, the RoF transceiver 100 is provided with a light emitting unit 130a including a protection switch 131, a light emitting element 134, a light emitting element driving unit 132, and a termination resistor 133. Further, the RoF transceiver 100 is provided with a first comparator 122a for comparing the received power with a determination level stored in the storage unit 180 in advance. Further, the RoF transceiver 100 is provided with a second comparator 122b for comparing the received power with a first reference level stored in the storage unit 180 in advance. Further, the RoF transceiver 100 is provided with a switch control unit 123 for controlling the light emitting unit 130a that emits an optical signal to the optical fiber transmission line 200 based on the result compared by the first comparator 122a. Further, the RoF transceiver 100 is provided with a first attenuator control unit 124a for controlling the first variable gain amplification unit 112a based on the comparison result of the second comparator 122b. The switch control unit 123 controls to switch the protection switch 131 to the termination resistor 133 side when the received power exceeds the upper limit of the determination level. The first attenuator control unit 124a controls the first variable attenuator 114a so that the received power becomes equal to or lower than the first reference level when the received power is equal to or higher than the first reference level. Further, the first attenuator control unit 124a controls so as not to attenuate the received signal in the first variable attenuator 114a when the received power is lower than the first reference level.

[0057] According to the above configuration, the RoF transceiver 100 adjusts the level of the received power according to the received power of the received signal, and appropriately controls the light emission of the light emitting element 134. Therefore, the RoF transceiver 100 can efficiently save power in the wireless system while maintaining the functions of the wireless communication system.

[0058] The RoF transceiver 100 according to the second aspect may further include a light receiving element 135 that receives an optical signal received from the optical fiber transmission line 200 and converts it into an electrical signal. Further, the RoF transceiver 100 may include a current-voltage conversion unit 136 that performs current-voltage conversion on the electrical signal converted by the light receiving element 135. Further, the RoF transceiver 100 may include a third amplifier 113c, a fourth amplifier 113d, and a second variable attenuator 114b, and may include a second variable gain amplifier unit 112b that increases or decreases the transmission power of the electrical signal. Further, the RoF transceiver 100 may include a third comparator 122c that compares the received power with a second reference level stored in the storage unit 180 in advance. Further, the RoF transceiver 100 may include a second attenuator control unit 124b that controls the second variable gain amplifier unit 112b based on the comparison result of the third comparator 122c. When the received power is equal to or lower than the second reference level, the second attenuator control unit 124b may control the second variable attenuator 114b so that the transmission power becomes equal to or lower than the second reference level.

[0059] According to the above configuration, the RoF transceiver 100 can prevent crosstalk and unnecessary radio wave radiation between the RoF_Tx110a and the RoF_Rx110b provided in the RoF transceiver 100, and can reduce power consumption.

[0060] When the received power is lower than the lower limit of the determination level, the switch control unit 123 of the RoF transceiver 100 according to the third aspect may turn off the light emitting element driving unit 132 and control so that no current is supplied to the light emitting element 134.

[0061] According to the above configuration, the RoF transceiver 100 can efficiently reduce the power consumption of the wireless system with a simple configuration while maintaining the functions of the wireless communication system.

[0062] The switch control unit 123 of the RoF transceiver 100 according to the fourth aspect may detect temperature. Further, when the temperature is equal to or higher than a predetermined temperature, the switch control unit 123 may control the light emitting element driving unit 132 so that the light emission amount of the light emitting element 134 decreases. Further, when the temperature is equal to or lower than a predetermined temperature, the switch control unit 123 may control the light emitting element driving unit 132 so that the light emission amount of the light emitting element 134 increases.

[0063] According to the above configuration, the RoF transceiver 100 can maintain an appropriate light emission amount even when the temperature changes.

[0064] The optical fiber wireless system 10 according to the fifth aspect is the above RoF transceiver 100, and includes a first transceiver 100a that performs wireless communication with the base station 300 and a second transceiver 100b that performs wireless communication with the terminal 400. Further, the first transceiver 100a and the second transceiver 100b are connected via the optical fiber transmission line 200.

[0065] According to the above configuration, the optical fiber wireless system 10 adjusts the level of the received power according to the received power of the received signal and appropriately controls the light emission of the light emitting element 134. Thereby, the optical fiber wireless system 10 can efficiently save power of the wireless system while maintaining the function of the wireless communication system in relaying the wireless signal to the dead zone.

Explanation of Signs

[0066] 10 Optical fiber wireless system 100 RoF transceiver 100a First transceiver 100b Second transceiver 110a RoF_Tx 110b RoF_Rx 111a, 111b, 111c Band-pass filter 112a First variable gain amplifier 112b Second variable gain amplifier 113a First amplifier 113b Second amplifier 113c Third Amplifier 113d Fourth Amplifier 114a First Variable Attenuator 114b Second Variable Attenuator 121 Received Signal Level Detector 122a First Comparator 122b Second Comparator 122c Third Comparator 123 Switch Control Unit 124a First Attenuator Control Unit 124b Second Attenuator Control Unit 131 Protection Switch 132 Light Emitting Element Driver 133 Termination Resistor 134 Light Emitting Element 135 Light Receiving Element 136 Current-Voltage Conversion Unit 140 Receiving Antenna 150 Transmitting Antenna 180 Memory Unit 200 Optical Fiber Transmission Line 300 Base Station 400 Terminal

Claims

1. An RoF (Radio over Fiber) transceiver for relaying a received signal in wireless communication between a base station and a terminal via an optical fiber transmission line, comprising a first amplifier, a second amplifier, and a first variable attenuator, and a first variable gain amplification unit that increases or decreases the received power of the received signal; a received signal level detection unit that detects the received power of the received signal; a light emitting unit including a protection switch, a light emitting element, a light emitting element driving unit, and a termination resistor; a first comparator that compares the received power with a determination level stored in a storage unit in advance; a second comparator that compares the received power with a first reference level stored in the storage unit in advance; a switch control unit that controls the light emitting unit that emits an optical signal to the optical fiber transmission line based on the result compared by the first comparator; and a first attenuator control unit that controls the first variable gain amplification unit based on the comparison result of the second comparator, wherein the switch control unit controls to switch the protection switch to the termination resistor side when the received power exceeds the upper limit of the determination level, the first attenuator control unit controls the first variable attenuator so that the received power becomes equal to or lower than the first reference level when the received power is equal to or higher than the first reference level, and the first attenuator control unit controls the first variable attenuator so as not to attenuate the received signal when the received power is lower than the first reference level. An RoF transceiver.

2. a light receiving element that receives an optical signal received from the optical fiber transmission line and converts it into an electrical signal; a current-voltage conversion unit that performs current-voltage conversion of the electrical signal converted by the light receiving element; a second variable gain amplification unit including a third amplifier, a fourth amplifier, and a second variable attenuator, and increasing or decreasing the transmission power of the electrical signal; a third comparator that compares the received power with a second reference level stored in the storage unit in advance; and a second attenuator control unit that controls the second variable gain amplification unit based on the comparison result of the third comparator, wherein the second attenuator control unit controls the second variable attenuator so that the transmission power becomes equal to or lower than the second reference level when the received power is equal to or lower than the second reference level. The RoF transceiver according to Claim 1.

3. The RoF transceiver according to claim 1, wherein when the received power is lower than the lower limit of the determination level, the switch control unit turns off the light emitting element driving unit and controls so that no current is supplied to the light emitting element.

4. The RoF transceiver according to claim 1, wherein the switch control unit detects temperature, and when the temperature is equal to or higher than a predetermined temperature, controls the light emitting element driving unit so that the light emission amount of the light emitting element decreases, and when the temperature is lower than the predetermined temperature, controls the light emitting element driving unit so that the light emission amount of the light emitting element increases.

5. The RoF transceiver according to any one of claims 1 to 4, comprising: a first transceiver that performs wireless communication with the base station; and a second transceiver that performs wireless communication with the terminal. The first transceiver and the second transceiver are an optical fiber wireless system connected via the optical fiber transmission line.

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