Reception device

Abstract

This reception device comprises a photoelectric converter, a compensation unit, a measurement unit, and a calculation unit. The photoelectric converter receives an optical modulation signal resulting from modulation by an electro-optical converter of a transmission device by using a radio signal, and converts the received optical modulation signal into an electric signal. The compensation unit performs compensation of nonlinear distortion of the electric signal resulting from conversion in accordance with a compensation characteristic corresponding to the electro-optical converter. The control unit provides, to the transmission device, instruction regarding a bias voltage value for the electro-optical converter. The measurement unit measures the optical power of the optical modulation signal resulting from modulation by the electro-optical converter in which the bias voltage value provided as instruction is set. The calculation unit acquires an extinction curve characteristic of the electro-optical converter on the basis of a set of the bias voltage value and the optical power obtained for each of multiple types of bias voltage values, and sets, in the compensation unit, a compensation characteristic calculated by using the acquired extinction curve characteristic.

Description

Receiver

[0001] This invention relates to a receiving device.

[0002] By dividing the functions of a wireless base station into a central station (CS) and a remote radio unit (RRU), and simplifying the remote unit by applying analog RoF (Radio-over-Fiber), it is possible to deploy wireless areas flexibly and economically. In such wireless communication systems, in order to mitigate the narrowing of the uplink dynamic range due to the influence of nonlinear distortion in the E / O (electric-optical) converter, it is being considered to apply post-distortion in the electrical stage after passing through the RoF section (see, for example, Non-Patent Document 1).

[0003] Figure 7 shows an example of a conventional wireless communication system. The control station and the wireless base station are connected by an optical transmission path for transmitting downlink optical signals and an optical transmission path for transmitting uplink optical signals. The control station's wireless modulator generates the wireless signal to be transmitted, and a pre-distorter performs pre-distortion on the generated wireless signal to compensate for the nonlinear distortion expected to occur during electro-optical conversion. The EOM (External Optical Modulator) modulates the light output from the LD (Laser Diode) with the pre-distorted wireless signal to obtain an optically modulated signal, which is then output to the downlink optical transmission path. The wireless base station's PD (Photodiode) detects the light intensity of the received optically modulated signal to acquire the wireless signal. The PA (Power Amplifier) ​​amplifies the wireless signal, and the CR (Circler) / DP (Duplexer) wirelessly transmits the amplified wireless signal from the antenna.

[0004] Also, the CR / DP of the radio base station outputs the radio signal received by the antenna wirelessly to the LNA (Low Noise Amplifier). The EOM outputs the optical signal intensity-modulated by the radio signal amplified by the LNA to the upstream optical transmission line. The PD of the control station detects the optical intensity of the received optical modulation signal to obtain the radio signal, and the post-distorter performs post-distortion to compensate for the non-linear distortion during the E / O conversion in the radio base station for the radio signal. The radio demodulator demodulates the post-distorted radio signal. The EOM of the radio base station, the upstream optical transmission line, the PD of the control station, and the post-distorter indicated by symbol A are the sections where the prior art post-distortion is applied.

[0005] Figure 8 is a diagram for explaining a method of obtaining information used for post-distortion. In the prior art, the extinction curve characteristics of the E / O converter of the EOM of the radio base station are measured in advance in a laboratory environment or the like. Figure 8(a) is a diagram showing the extinction ratio characteristics obtained by measurement. These extinction ratio characteristics show the extinction ratio with respect to the input voltage of the electro-absorption modulator (EAM) used as the EOM. A part of the extinction ratio characteristics is linear, but both ends are non-linear. Figure 8(b) is a diagram showing the compensation characteristics derived based on the extinction ratio characteristics shown in Figure 8(a). The information of these compensation characteristics is input in advance to the post-distorter of the control station. Thereby, after passing through the RoF section, non-linear distortion can be compensated.

[0006] Miyashita, "Improvement Method for Transmission Quality of Optical and Radio Wave Fusion Communication by Digital Signal Processing (Part 2) - Demonstration of Non-Linear Distortion Compensation Function -", Report of the Central Research Institute of Electric Power Industry, Central Research Institute of Electric Power Industry, 2006

[0007] It is difficult to obtain the extinction curve characteristics of an E / O converter after it has been installed in a device. On the other hand, the extinction curve characteristics of an E / O converter may change due to temperature changes within the communication device, for example. In such cases, the post-distortor, which performs distortion compensation based on previously obtained extinction curve characteristics, may not be able to perform appropriate nonlinear distortion compensation, resulting in a deterioration of signal quality.

[0008] In view of the above circumstances, the present invention aims to provide a receiving device that can perform nonlinear distortion compensation in accordance with changes in the extinction curve characteristics of an electro-optic converter incorporated in a device that transmits optical signals.

[0009] One aspect of the present invention is a receiving device comprising: an optical-electric converter that receives an optically modulated signal modulated using a wireless signal by an electro-optic converter of a transmitting device and converts the received optically modulated signal into an electrical signal; a compensation unit that compensates for the nonlinear distortion of the electrical signal converted by the optical-electric converter according to a compensation characteristic corresponding to the electro-optic converter; a control unit that instructs the transmitting device on the bias voltage value of the electro-optic converter; a measurement unit that measures the optical power of the optically modulated signal modulated by the electro-optic converter for which the bias voltage value has been set; and a calculation unit that acquires the extinction curve characteristics of the electro-optic converter based on the pairs of the bias voltage value and the optical power obtained for each of a plurality of bias voltage values ​​instructed by the control unit, and sets the compensation characteristics calculated using the acquired extinction curve characteristics to the compensation unit.

[0010] The present invention makes it possible to perform nonlinear distortion compensation in accordance with changes in the extinction curve characteristics of an electro-optic converter incorporated into a device that transmits optical signals.

[0011] This figure shows an example of the configuration of a wireless communication system according to one embodiment of the present invention. This figure shows an example of signal distortion in uplink communication of the wireless communication system according to the embodiment. This figure shows an example of the configuration of a wireless communication system according to the first embodiment. This is a flowchart showing the processing of the wireless communication system according to the first embodiment. This is a diagram for explaining the processing of the wireless communication system according to the first embodiment. This figure shows an example of the configuration of a wireless communication system according to the second embodiment. This figure shows an example of the configuration of a wireless communication system according to the prior art. This figure shows an example of a method for acquiring compensation characteristics according to the prior art.

[0012] Embodiments of the present invention will be described below with reference to the drawings. The receiving device according to the embodiment of the present invention remotely sets the bias voltage of the E / O converter of the transmitting device. After setting the bias voltage, the receiving device measures the optical power of the optical signal received from the transmitting device. As a result, even after the E / O converter is incorporated into the transmitting device, the receiving device can acquire extinction curve characteristics based on the relationship between the bias voltage and optical power. Since the receiving device can perform nonlinear distortion compensation of the optical signal received from the transmitting device based on the acquired extinction curve characteristics, flexible operation is possible.

[0013] Figure 1 is a diagram showing the configuration of a wireless communication system 10 according to an embodiment of the present invention. In Figure 1, only the functional blocks related to this embodiment are extracted and shown. The wireless communication system 10 includes a first communication device 100 and a second communication device 200. The first communication device 100 is an example of a transmitting device, and the second communication device 200 is an example of a receiving device. The first communication device 100 is, for example, an RRU (Remote Radio Unit), and the second communication device 200 is, for example, a CS (Central Station). The second communication device 200 may be connected to a plurality of first communication devices 100.

[0014] The first communication device 100 and the second communication device 200 are connected by an optical fiber 600. The optical fiber 600 is an example of an optical transmission path. The first communication device 100 and the second communication device 200 may be further connected by a communication network 700. The communication network 700 is an example of a transmission path. The communication network 700 is, for example, an IP network, but any data communication network of any communication type can be used.

[0015] The first communication device 100 has a transmitting unit 101. The transmitting unit 101 has an LD (Laser Diode) 102, an E / O (Electric-Optical) conversion unit 103, and a control unit 104. The LD 102 outputs light. The E / O conversion unit 103 is an E / O converter. The E / O conversion unit 103 operates at a bias voltage value set by the control unit 104 and generates an optically modulated signal that shows the waveform information of the radio signal by modulating the intensity of the light output by the LD 102 using the input radio signal. The radio signal is an electrical signal that represents the waveform of a signal received by radio. The E / O conversion unit 103 outputs the generated optically modulated signal to the optical fiber 600. The control unit 104 sets the bias voltage value instructed by the second communication device 200 to the E / O conversion unit 103.

[0016] The second communication device 200 has a receiving unit 201. The receiving unit 201 has an O / E (optical-electrical) conversion unit 202, a nonlinear distortion compensation unit 203, a control unit 204, a monitor unit 205, and a calculation unit 206. When the second communication device 200 is connected to a plurality of first communication devices 100, the second communication device 200 has a receiving unit 201 corresponding to each first communication device 100.

[0017] The O / E conversion unit 202 is an O / E converter. The O / E conversion unit 202 detects the optical signal output by the first communication device 100 and transmitted through the optical fiber 600, converts it into a wireless signal, and outputs it to the nonlinear distortion compensation unit 203. The output wireless signal contains nonlinear distortion.

[0018] The nonlinear distortion compensation unit 203 nonlinearly compensates the nonlinear distortion of the radio signal received from the O / E conversion unit 202 based on the compensation characteristics received from the calculation unit 206, and outputs the compensated radio signal. The output radio signal is demodulated by a subsequent demodulator (not shown).

[0019] The control unit 204 instructs the control unit 104 to set a bias voltage value in the E / O conversion unit 103 of the first communication device 100. The control unit 204 may transmit the instruction for the bias voltage value via an optical fiber 600 using an optical signal, or via the communication network 700. The control unit 204 repeatedly instructs the control unit 104 while changing the bias voltage value. The control unit 204 also notifies the calculation unit 206 of the bias voltage value instructed to the control unit 104.

[0020] The monitor unit 205 measures the power of the light received by the O / E conversion unit 202. This allows the monitor unit 205 to measure the optical power of the optically modulated signal generated by the E / O conversion unit 103 of the first communication device 100 using the bias voltage value instructed by the control unit 204. There are several methods for measuring the optical power by the monitor unit 205. For example, the monitor unit 205 can branch off a portion of the light from the O / E conversion unit 202 and measure the power of the branched light. Alternatively, for example, the monitor unit 205 can measure the PD output current value of the signal converted by the O / E conversion unit 202 and calculate the optical power based on the measured output current value. In this case, the monitor unit 205 monitors a portion of the distorted wireless signal output from the O / E conversion unit 202. If Iph is the PD output current, R is the susceptibility of the PD, and Pin is the light-receiving power of the PD, then the logical expression Iph = R・Pin is satisfied. Therefore, the monitor unit 205 works backward from this logical formula and calculates the optical power using Pin = Iph / R, with the measured output current value Iph and the known value of R.

[0021] The calculation unit 206 acquires the correspondence between the bias voltage notified by the control unit 204 and the optical power measured by the monitor unit 205. Based on the correspondence between each different bias voltage value and the optical power, the calculation unit 206 acquires the extinction curve characteristics of the E / O conversion unit 103 of the first communication device 100. The calculation unit 206 calculates the compensation characteristics based on the acquired extinction curve characteristics. The calculation unit 206 sets the calculated compensation characteristics in the nonlinear distortion compensation unit 203.

[0022] For example, the transmitting unit 101 and the receiving unit 201 can be used in the section of code A to which conventional post-distortion is applied in the wireless communication system shown in Figure 7.

[0023] Furthermore, the second communication device 200 may further have a transmitting unit that transmits optical signals to the first communication device 100, and the first communication device 100 may further have a receiving unit that receives optical signals received from the second communication device 200. Also, when the control unit 104 of the first communication device 100 and the control unit 204 of the second communication device 200 communicate via the optical fiber 600, the first communication device 100 and the second communication device 200 do not need to be connected to the communication network 700.

[0024] With the above configuration, the control unit 204 of the second communication device 200 instructs the control unit 104 of the first communication device 100 to set a bias voltage value, and the control unit 104 sets the instructed bias voltage value to the E / O conversion unit 103. The O / E conversion unit 202 of the second communication device 200 receives the optical modulation signal output by the E / O conversion unit 103 of the first communication device 100. The monitor unit 205 can measure the optical power relative to the bias voltage value set by the control unit 204 to the E / O conversion unit 103 based on the optical modulation signal received by the O / E conversion unit 202. Based on this pair of bias voltage value and optical power, the calculation unit 206 of the second communication device 200 can indirectly obtain the extinction curve characteristics of the E / O conversion unit 103. The calculation unit 206 derives a compensation pattern based on the acquired extinction curve characteristics and inputs it to the nonlinear distortion compensation unit 203. As a result, the second communication device 200 can compensate for the radio signal distorted by the E / O conversion unit 103 of the first communication device 100 and output the compensated radio signal.

[0025] Figure 2 shows an example of signal distortion during uplink communication. For example, when user equipment (UE) 500 approaches the RRU 100a, which is the first communication device 100, the voltage Vb of the radio signal input to the E / O conversion unit 103 is high, reaching the nonlinear region B of the extinction curve. As a result, the optical radio signal output to the CS 200a, which is the second communication device 200, is distorted. By compensating for the nonlinear region and extending the linear region C of the extinction curve, the dynamic range of uplink communication can be expanded. In this embodiment, with the configuration shown in Figure 1, the second communication device 200 can acquire the extinction curve characteristics and compensate for the nonlinear distortion by post-distortion, thereby expanding the dynamic range, even after the E / O conversion unit 103 of the transmitting unit 101 has been incorporated into the first communication device 100.

[0026] Furthermore, even if the extinction curve characteristics of the E / O conversion unit 103 change due to temperature changes or other factors, the second communication device 200 can reacquire the extinction curve characteristics and apply post-distortion. Detailed embodiments will be described below.

[0027] (First Embodiment) Figure 3 is a diagram showing the configuration of the wireless communication system 11 according to the first embodiment. In Figure 3, only the functional blocks related to this embodiment are extracted and shown. The wireless communication system 11 has a first communication device 110 and a second communication device 210. The first communication device 110 is an example of a transmitting device, and the second communication device 210 is an example of a receiving device. The first communication device 110 is, for example, an RRU, and the second communication device 210 is, for example, a CS. The second communication device 210 may be connected to a plurality of first communication devices 110. The first communication device 110 and the second communication device 210 are connected by an optical fiber 600.

[0028] The first communication device 110 has a transmitting unit 111. The transmitting unit 111 has an E / O conversion unit 113, a control unit 114, an O / E conversion unit 115, and an optical multiplexing / demultiplexing unit 116. The first communication device 110 also has an LD 102, but it is not shown in Figure 3.

[0029] The E / O conversion unit 113 is an E / O converter. The E / O conversion unit 113 operates at a bias voltage value set by the control unit 114 and modulates the intensity of the light output from the LD 102 using the input radio signal. The E / O conversion unit 113 outputs the optically modulated signal obtained by intensity modulation to the optical multiplexer / demultiplexer unit 116.

[0030] The control unit 114 sets the bias voltage value in the E / O conversion unit 113 according to the control signal received from the second communication device 210.

[0031] The O / E conversion unit 115 is an O / E converter. The O / E conversion unit 115 receives the optically modulated signal output by the second communication device 210 from the optical multiplexer / demultiplexer unit 116. The O / E conversion unit 115 extracts an electrical control signal from the optically modulated signal by detecting the light intensity of the optically modulated signal using, for example, a PD (photodiode), and outputs it to the control unit 114.

[0032] The optical multiplexer / demultiplexer 116 is, for example, an optical multiplexer / demultiplexer. The optical multiplexer / demultiplexer 116 combines and demultiplexes optical signals of different wavelengths. The optical multiplexer / demultiplexer 116 outputs the optically modulated signal output by the E / O conversion unit 113 to the optical fiber 600 according to its wavelength. The optical multiplexer / demultiplexer 116 also receives the optically modulated signal output from the second communication device 210 and transmitted through the optical fiber 600, and outputs the received optically modulated signal to the O / E conversion unit 115 according to its wavelength. An optical circulator may be used instead of the optical multiplexer / demultiplexer 116.

[0033] The second communication device 210 has a receiving unit 211. The receiving unit 211 has an O / E conversion unit 212, a nonlinear distortion compensation unit 213, a control unit 214, a monitor unit 215, a calculation unit 216, an E / O conversion unit 218, and an optical multiplexing / demultiplexing unit 219. When the second communication device 210 is simultaneously connected to a plurality of first communication devices 110, the second communication device 210 has a receiving unit 211 corresponding to each of the first communication devices 110. In this case, the optical multiplexing / demultiplexing unit 219 of the plurality of receiving units 211 may be common.

[0034] The O / E conversion unit 212 is an O / E converter. The O / E conversion unit 212 receives the optically modulated signal output by the first communication device 110 and transmitted through the optical fiber 600 from the optical multiplexing / demultiplexing unit 219. For example, the O / E conversion unit 212 uses a PD to detect the received optically modulated signal to extract a wireless signal and outputs it to the nonlinear distortion compensation unit 213. The extracted wireless signal contains nonlinear distortion.

[0035] The nonlinear distortion compensation unit 213 nonlinearly compensates the nonlinear distortion of the wireless signal received from the O / E conversion unit 212 based on the compensation characteristics received from the calculation unit 216, and outputs the compensated wireless signal. The device used for compensation may be analog or digital.

[0036] The control unit 214 outputs a control signal to the E / O conversion unit 218 to control the bias voltage value to be set in the E / O conversion unit 113 of the first communication device 110. The control unit 214 repeatedly transmits the control signal to the control unit 114 while changing the bias voltage value to be instructed. Instead of outputting the control signal to the E / O conversion unit 218, the control unit 214 may also directly transmit it to the control unit 114 of the first communication device 110 via another route, such as the communication network 700. The control unit 214 notifies the calculation unit 216 of the bias voltage value instructed to the control unit 114.

[0037] The monitor unit 215 measures the power of the light received by the O / E conversion unit 212. The monitor unit 215 outputs the measured light power information to the calculation unit 216 along with the bias voltage value set by the control unit 214 to the control unit 114. The monitor unit 215 may be adjusted to satisfy the measurement sensitivity by having an optical amplifier inside. Alternatively, by providing the monitor unit 215 inside the O / E conversion unit 212, the O / E conversion unit 212 may directly output the light power information to the calculation unit 216. The monitor unit 215 can measure light power in the same way as the monitor unit 205 described above. For example, the monitor unit 215 can branch off a portion of the light from the O / E conversion unit 212 and measure the power of the branched light. Alternatively, the monitor unit 215 measures the PD output current value of the signal from the electrical stage converted by the O / E conversion unit 212, and uses the measured output current value Iph and the known susceptibility R of the PD to calculate the PD's light-receiving power Pin = Iph / R.

[0038] The calculation unit 216 acquires multiple sets of data representing bias voltage values ​​and optical power. The calculation unit 216 records these acquired data in a storage unit 217 provided within the calculation unit 216. The storage unit 217 may be located outside the calculation unit 216. Based on the data stored in the storage unit 217, the calculation unit 216 calculates the extinction curve characteristics of the E / O conversion unit 113, and calculates compensation characteristics based on the calculated extinction curve characteristics. The calculation unit 216 sets the calculated compensation characteristics in the nonlinear distortion compensation unit 213.

[0039] The E / O conversion unit 218 is an E / O converter. The E / O conversion unit 218 outputs an optically modulated signal generated using a control signal input from the control unit 214 to the optical multiplexing / demultiplexing unit 219. The control signal may include control information other than the bias voltage value, such as time division duplex (TDD) timing, CLK, etc. In addition to the control signal, the E / O conversion unit 218 may electrically frequency multiplex the downlink main signal and transmit it as a subcarrier multiplexed signal. The E / O conversion unit 218 may be connected to the O / E conversion unit 115 or optical multiplexing / demultiplexing unit 116 of the first communication device 110 by an optical fiber other than the optical fiber 600, without going through the optical multiplexing / demultiplexing unit 219.

[0040] The optical multiplexer / demultiplexer 219 is, for example, an optical multiplexer / demultiplexer. The optical multiplexer / demultiplexer 219 outputs the optically modulated signal output by the E / O conversion unit 218 to the optical fiber 600 according to its wavelength. The optical multiplexer / demultiplexer 219 also receives the optically modulated signal output from the first communication device 110 and transmitted through the optical fiber 600, and outputs the received optically modulated signal to the O / E conversion unit 212 according to its wavelength. An optical circulator may be used instead of the optical multiplexer / demultiplexer 219.

[0041] Figure 4 is a flowchart showing the operation of the wireless communication system 11. The wireless communication system 11 repeats the processes of steps S1 to S3 from the start to the end of data acquisition for calculating extinction curve characteristics. Specifically, the wireless communication system 11 repeats the processes of steps S1 to S3 as many times as there are types of bias voltage setting values.

[0042] In step S1, the wireless communication system 11 sets a bias voltage. That is, the bias voltage is set from the receiving unit 211 of the second communication device 210 to the E / O conversion unit 113 of the transmitting unit 111 of the first communication device 110 through the control unit 214 and the control unit 114.

[0043] Specifically, the control unit 214 of the second communication device 210 determines the bias voltage value to be set to the E / O conversion unit 113. For example, the control unit 214 selects an unselected bias voltage value from a predetermined set of bias voltage values. The control unit 214 outputs a control signal instructing the control unit 114 to set the determined bias voltage value to the E / O conversion unit 218. Further, the control unit 214 notifies the calculation unit 216 of the bias voltage value for which the setting has been instructed. The E / O conversion unit 218 outputs the optical modulation signal generated using the control signal received from the control unit 214 to the optical multiplexer / demultiplexer 219. The optical multiplexer / demultiplexer 219 outputs the optical modulation signal output by the E / O conversion unit 218 to the optical fiber 600.

[0044] The optical multiplexer / demultiplexer 116 of the first communication device 110 receives the optical modulation signal output from the second communication device 210 and transmitted through the optical fiber 600, and outputs it to the O / E conversion unit 115. The O / E conversion unit 115 extracts an electrical signal control signal from the received optical modulation signal and outputs it to the control unit 114. The control unit 114 sets the bias voltage value instructed by the control signal received from the second communication device 210 to the E / O conversion unit 113.

[0045] In step S2, the wireless communication system 11 measures the optical power. That is, the receiving unit 211 of the second communication device 210 measures the optical power from the E / O conversion unit 113 of the transmitting unit 111 of the first communication device 110.

[0046] Specifically, the E / O conversion unit 113 of the first communication device 110 operates at the bias voltage value set in step S1, and intensity-modulates the light output from the LD 102 using the input wireless signal. When obtaining the extinction curve characteristics of the E / O conversion unit 113, even if the light is modulated by the wireless signal, the influence on the optical power is small. The E / O conversion unit 113 outputs the optical modulation signal obtained by intensity modulation to the optical multiplexer / demultiplexer unit 116. The optical multiplexer / demultiplexer unit 116 outputs the optical modulation signal output by the E / O conversion unit 113 to the optical fiber 600 according to its wavelength.

[0047] The optical multiplexer / demultiplexer unit 219 of the second communication device 210 receives the optical modulation signal output from the first communication device 110 and transmitted through the optical fiber 600, and outputs it to the O / E conversion unit 212. The O / E conversion unit 212 demodulates the optical modulation signal received from the optical multiplexer / demultiplexer unit 219, converts it into a wireless signal, and outputs it to the non-linear distortion compensation unit 213. The monitor unit 215 measures the optical power of the optical modulation signal received by the O / E conversion unit 212. The monitor unit 215 notifies the calculated unit 216 of the measured optical power value in combination with the bias voltage value notified by the control unit 214 to the calculated unit 216 in step S1.

[0048] In step S3, the calculation unit 216 stores the pair of the bias voltage value notified from the control unit 214 in step S1 and the measured value of the optical power notified from the monitor unit 215 in step S2 in the storage unit 217.

[0049] When the acquisition of the data for calculating the extinction curve characteristics is completed, the second communication device 210 performs the processes of steps S4 to S7. The processes of steps S4 to S7 will be described using FIG. 5.

[0050] FIG. 5 is a diagram for explaining the processes of steps S4 to S7 in FIG. 4. In step S4, the calculation unit 216 obtains the extinction curve characteristics of the E / O conversion unit 113. Specifically, the calculation unit 216 reads out the pair of the measured value of the optical power and the bias voltage value from the storage unit 217. The calculation unit 216 obtains the extinction curve characteristics by plotting the relationship between the bias voltage value and the optical power measured value of each pair in a two-dimensional coordinate. FIG. 5(a) is a diagram showing the extinction curve characteristics L1.

[0051] In step S5, the calculation unit 216 derives compensation characteristics based on the extinction curve characteristics obtained in step S4. Figure 5(b) shows the compensation characteristics L3 obtained based on the extinction curve characteristics L1. The calculation unit 216 derives the tangent L2 at the bias voltage used in actual communication based on the extinction curve characteristics L1. The calculation unit 216 plots the compensation characteristics L3 which are axially symmetric with respect to the derived tangent L2.

[0052] In step S6, the calculation unit 216 converts the compensation characteristic derived in step S5 into a continuous function. Figure 5(c) shows the compensation characteristic L4 converted into a continuous function. The calculation unit 216 obtains the compensation characteristic L4, which is a post-detorsion characteristic obtained by converting the compensation characteristic L3 plotted in step S5 into a continuous function as an Nth-degree polynomial using polynomial approximation.

[0053] In step S7, the calculation unit 216 sets the compensation characteristic L4, which was converted into a continuous function in step S6, to the nonlinear distortion compensation unit 213. As a result, the nonlinear distortion compensation unit 213 applies the set compensation characteristic in analog or digital form to improve the nonlinear distortion of the waveform of the wireless signal output from the O / E conversion unit 212.

[0054] Specifically, the E / O conversion unit 113 of the first communication device 110 modulates the intensity of the input radio signal, and the E / O conversion unit 113 outputs the optically modulated signal obtained by intensity modulation to the optical multiplexer / demultiplexer unit 116. The optical multiplexer / demultiplexer unit 116 outputs the optically modulated signal output by the E / O conversion unit 113 to the optical fiber 600. The optical multiplexer / demultiplexer unit 219 of the second communication device 210 receives the optically modulated signal transmitted through the optical fiber 600, and the O / E conversion unit 212 detects the optically modulated signal, converts it into a radio signal, and outputs it to the nonlinear distortion compensation unit 213. The nonlinear distortion compensation unit 213 applies the compensation characteristics set by the calculation unit 216 to improve the nonlinear distortion of the radio signal waveform.

[0055] Figure 5(d) shows a nonlinearly compensated signal. "before" shows the input waveform L5 to the E / O conversion unit 113, "after" shows the output waveform L6 from the E / O conversion unit 113, and "compensation" shows the waveform L7 after nonlinear compensation by the nonlinear distortion compensation unit 213. From Figure 5(d), it can be seen that the nonlinear distortion has been improved.

[0056] (Second Embodiment) In the second embodiment, when the transmission unit of the first communication device is rerouted from the path to the second communication device to the path to the third communication device, the extinction curve characteristics acquired in the second communication device are set in the third communication device. The second embodiment will be described focusing on the differences from the first embodiment.

[0057] Figure 6 shows the configuration of the wireless communication system 12 according to the second embodiment. In Figure 6, the same reference numerals are used for parts that are the same as those in the device according to the first embodiment shown in Figure 3, and their descriptions are omitted. The difference between the wireless communication system 12 shown in Figure 6 and the wireless communication system 11 of the first embodiment shown in Figure 3 is that it further includes a third communication device 310 and a shared server 400. The third communication device 310 is an example of a receiving device. The shared server 400 is connected to one or more second communication devices 210 and one or more third communication devices 310.

[0058] The second communication device 210 operates in the same manner as in the first embodiment. However, the calculation unit 216 notifies the shared server 400 of the acquired extinction curve characteristics.

[0059] The third communication device 310 has a receiving unit 311. The receiving unit 311 has an O / E conversion unit 312, a nonlinear distortion compensation unit 313, a calculation unit 316, an E / O conversion unit 318, and an optical multiplexing / demultiplexing unit 319. When the third communication device 310 is simultaneously connected to a plurality of first communication devices 110, the third communication device 310 has a receiving unit 311 corresponding to each of the first communication devices 110. In this case, the optical multiplexing / demultiplexing unit 319 of the plurality of receiving units 311 may be common.

[0060] The O / E conversion unit 312, the nonlinear distortion compensation unit 313, the E / O conversion unit 318, and the optical multiplexing / demultiplexing unit 319 each have the same functions as the O / E conversion unit 212, the nonlinear distortion compensation unit 213, the E / O conversion unit 318, and the optical multiplexing / demultiplexing unit 319 of the second communication device 210. However, the E / O conversion unit 318 may generate an optical modulation signal using control information other than the bias voltage value setting instruction. Also, the E / O conversion unit 318 may output an optical modulation signal generated using the main signal, which is the downstream wireless signal, to the optical multiplexing / demultiplexing unit 319. The calculation unit 316 acquires the extinction curve characteristics recorded by the second communication device 210 on the shared server 400. Using the acquired extinction curve characteristics, the calculation unit 316 performs the same processing as the calculation unit 216 of the second communication device 210 to acquire compensation characteristics and sets them in the nonlinear distortion compensation unit 313.

[0061] The third communication device 310 may have the same configuration as the second communication device 210. In this case, the calculation unit 216 of the second communication device 210 operates in the same way as the calculation unit 316 of the third communication device 310.

[0062] The shared server 400 stores the extinction curve received from the second communication device 210. The shared server 400 notifies the third communication device 310 of the stored extinction curve.

[0063] The operation of the wireless communication system 12 will now be described. Initially, the first communication device 110 is connected to the second communication device 210 by an optical fiber 600. The first communication device 110 and the second communication device 210 perform the same processing as in the first embodiment shown in Figure 4. However, the calculation unit 316 of the second communication device 210 notifies the shared server 400 of the extinction curve characteristics of the E / O conversion unit 113 calculated in step S4. The shared server 400 stores the extinction curve characteristics notified by the second communication device 210.

[0064] Next, the location of the first communication device 110 is moved. At the new location, the first communication device 110 is connected to the third communication device 310 by an optical fiber 601. The calculation unit 316 of the third communication device 310 acquires the extinction curve characteristics of the E / O conversion unit 113 recorded by the second communication device 210 from the shared server 400. The first communication device 110 and the third communication device 310 perform the processing from step S5 onwards in Figure 4. As a result, the calculation unit 316 of the third communication device 310 sets the compensation characteristics to the nonlinear distortion compensation unit 313. The nonlinear distortion compensation unit 313 applies the set compensation characteristics to compensate for the nonlinear distortion of the waveform of the electrical signal output from the O / E conversion unit 312.

[0065] Specifically, in step S5, the calculation unit 316 of the third communication device 310 derives compensation characteristics based on the acquired extinction curve characteristics. In step S6, the calculation unit 316 converts the compensation characteristics derived in step S5 into a continuous function. In step S7, the calculation unit 316 sets the compensation characteristics converted into a continuous function in step S6 to the nonlinear distortion compensation unit 313. The E / O conversion unit 113 of the first communication device 110 generates an optically modulated signal using a radio signal, and the optical multiplexing / demultiplexing unit 116 outputs the optically modulated signal to the optical fiber 601. The optical multiplexing / demultiplexing unit 319 of the third communication device 310 receives the optically modulated signal transmitted through the optical fiber 601, and the O / E conversion unit 312 converts the optically modulated signal into a radio signal. The nonlinear distortion compensation unit 313 applies the compensation characteristics set by the calculation unit 316 to improve the nonlinear distortion of the radio signal waveform.

[0066] As described above, by connecting the calculation units of multiple communication devices, such as the calculation unit 216 of the receiving unit 211 and the calculation unit 316 of the receiving unit 311, to the shared server 400, the extinction curve characteristics can be shared. For example, data is shared from the calculation unit 216, which stores the extinction curve characteristic data of the transmitting unit 111, to the calculation unit 316. This allows the nonlinear characteristics to be immediately reflected even when the installation location of the first communication device 110 is moved and the transmitting unit 111 communicates via a different optical fiber.

[0067] Furthermore, if the extinction curve characteristics of the E / O conversion unit 113 of the transmitting unit 111 of each of the multiple first communication devices 110 can be considered to be substantially the same, the extinction curve characteristics obtained for the transmitting unit 111 of a particular first communication device 110 can be reused for the nonlinear compensation of the transmitting unit 111 of the other first communication devices 110.

[0068] In the above description, the calculation unit 216 of the second communication device 210 transmits extinction curve characteristic data to the shared server 400, and the calculation unit 316 of the third communication device 310 receives the extinction curve characteristic data from the shared server 400. However, the calculation unit 216 of the second communication device 210 may also directly transmit the extinction curve characteristic data to the calculation unit 316 of the third communication device 310.

[0069] Furthermore, the control unit 114, control unit 214, calculation unit 216, and calculation unit 316 may be configured using a processor such as a CPU (Central Processing Unit) and memory (main memory). The control unit 114, control unit 214, calculation unit 216, and calculation unit 316 function as described above when the processor executes a program. Note that all or part of the functions of the control unit 114, control unit 214, calculation unit 216, and calculation unit 316 may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, semiconductor memory devices (e.g., SSDs), and memory devices such as hard disks and semiconductor memory devices built into a computer system. The above program may be transmitted via a telecommunications line.

[0070] According to the embodiment described above, the receiving device includes an optical-electric converter, a compensation unit, a control unit, a measurement unit, and a calculation unit. For example, the receiving device corresponds to the second communication devices 200 and 210 of the embodiment, and the measurement unit corresponds to the monitor units 205 and 215 of the embodiment. The optical-electric converter receives the optically modulated signal modulated by the electro-optical converter of the transmitting device using a wireless signal, and converts the received optically modulated signal into an electrical signal. For example, the transmitting device corresponds to the first communication devices 100 and 110 of the embodiment. The compensation unit compensates for the nonlinear distortion of the electrical signal converted by the optical-electric converter according to the compensation characteristics corresponding to the electro-optical converter. The control unit instructs the transmitting device to set a bias voltage value for the electro-optical converter. The measurement unit measures the optical power of the optically modulated signal modulated by the electro-optical converter to which the instructed bias voltage value has been set. The calculation unit acquires the extinction curve characteristics of the electro-optical converter based on the pairs of bias voltage value and optical power obtained for each of the multiple types of bias voltage values ​​instructed by the control unit, and sets the compensation characteristics calculated using the acquired extinction curve characteristics to the compensation unit.

[0071] The control unit may transmit an instruction for the bias voltage value to the transmitting device via an optical transmission path that transmits the optical modulation signal, or via a transmission path different from the optical transmission path.

[0072] The calculation unit may output the acquired extinction curve characteristics to another receiving device or a device connected to the other receiving device. The other receiving device comprises an optical-electric converter, a compensation unit, and a compensation characteristic calculation unit. The compensation characteristic calculation unit acquires the extinction curve characteristics output by the calculation unit and sets the compensation characteristics calculated using the acquired extinction curve characteristics to the compensation unit of its own device.

[0073] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments and include designs and the like that do not depart from the spirit of this invention.

[0074] 10, 11, 12 Wireless Communication System 100, 110 First Communication Device 101, 111 Transmitter 102 LD 103, 113 E / O Conversion Unit 104, 114 Control Unit 115 O / E Conversion Unit 116 Optical Multiplexer / Demultiplexer Unit 200, 210 Second Communication Device 201, 211, 311 Receiving Unit 202, 212, 312 O / E Conversion Unit 203, 213, 313 Nonlinear Distortion Compensation Unit 204, 214 Control Unit 205, 215 Monitor Unit 206, 216, 316 Calculation Unit 217 Memory Unit 218, 318 E / O Conversion Unit 219, 319 Optical Multiplexer / Demultiplexer Unit 310 Third Communication Device 400 Shared Server 600, 601 Optical Fiber 700 Communication Networks

Claims

1. A receiving device comprising: an optical-electric converter that receives an optically modulated signal modulated by an electro-optic converter of a transmitting device using a wireless signal and converts the received optically modulated signal into an electrical signal; a compensation unit that compensates for the nonlinear distortion of the electrical signal converted by the optical-electric converter according to a compensation characteristic corresponding to the electro-optic converter; a control unit that instructs the transmitting device on the bias voltage value of the electro-optic converter; a measurement unit that measures the optical power of the optically modulated signal modulated by the electro-optic converter for which the bias voltage value has been set; and a calculation unit that acquires the extinction curve characteristics of the electro-optic converter based on the pairs of the bias voltage value and the optical power obtained for each of a plurality of types of bias voltage values ​​instructed by the control unit, and sets the compensation characteristics calculated using the acquired extinction curve characteristics to the compensation unit.

2. The receiving device according to claim 1, wherein the control unit transmits an instruction for the bias voltage value to the transmitting device via an optical transmission path that transmits the optical modulation signal, or via a transmission path different from the optical transmission path.

3. The receiving device according to claim 1, wherein the calculation unit outputs the acquired extinction curve characteristics to another receiving device or a device connected to the other receiving device, and the other receiving device comprises the photoelectric converter, the compensation unit, and a compensation characteristic calculation unit that acquires the extinction curve characteristics output by the calculation unit and sets the compensation characteristics calculated using the acquired extinction curve characteristics to the compensation unit of its own device.

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