WO2025013129A1 - Noise reduction apparatus, noise reduction method, and program - Google Patents

Abstract

This noise reduction apparatus comprises: a first switch that generates pulse signals by performing modulation processing on analog communication signals on the basis of a first pattern in which switching between on and off is repeated at a prescribed rate; a branching device that branches the pulse signals in which noise is generated by a noise source; a second switch that performs, on the basis of the first pattern, first demodulation processing on one of the branched pulse signals and noise; a third switch that extracts noise from the other branched pulse signals and noise by performing, on the basis of a second pattern in which the on and off of the first pattern are inverted, second demodulation processing on the other branched pulse signals and noise; a subtractor for restoring the pulse signals by subtracting the extracted noise from one of the branched pulse signals and noise; and a filter for restoring the analog communication signals on the basis of the restored pulse signals.

Description

Noise reduction device, noise reduction method and program

The present invention relates to a noise reduction device, a noise reduction method, and a program.

By applying analog Radio-over-Fiber (RoF) to a wireless communication system, the functions of a wireless base station that performs wireless communication with user terminals may be divided into an aggregation station and a base station. Non-Patent Document 1 discloses a Direct Optical Switching (DOS) Code Division Multiple Access (CDMA) RoF system as an example of a wireless communication system to which analog RoF is applied.

In the RoF system disclosed in Non-Patent Document 1, the optical transmitter performs high-speed switching processing for modulation on an analog communication signal based on a CDMA signal. This generates a pulse signal (pulsed analog communication signal). The optical transmitter transmits the generated pulse signal to an optical transmission path. The optical receiver receives the pulse signal transmitted from the optical transmitter via the optical transmission path. The optical receiver performs high-speed switching processing for demodulation on the received pulse signal. This reduces interference signals between user terminals in the wireless communication system.

Higashino, Tsukamoto and Komaki, "Experimental study of received signal performance in direct optical switching CDMA ROF system m," 2002 International Topical Meeting on Microwave Photonics, Awaji, Japan, 2002, pp. 233-236, doi: 10.1109/MWP.2002.1158906.

In wireless communication systems, upstream communication signals can suffer from ingress noise. For example, in wireless communication systems that use analog RoF, when analog communication signals are transmitted upstream from multiple base stations to a single central station, ingress noise occurs in the analog communication signals.

However, although Non-Patent Document 1 can reduce interference signals in the optical domain, it cannot reduce noise such as ingress noise. Thus, there is a problem in that it is not possible to reduce noise that occurs in analog communication signals.

In view of the above, the present invention aims to provide a noise reduction device, a noise reduction method, and a program that are capable of reducing noise that occurs in an analog communication signal.

One aspect of the present invention is a noise reduction device that includes a first switch that generates a pulse signal by performing a modulation process on an analog communication signal based on a first pattern in which on-off switching is repeated at a predetermined speed, a splitter that splits the pulse signal in which noise has been generated by a noise source, a second switch that performs a first demodulation process on one of the split pulse signals and the noise based on the first pattern, a third switch that extracts the noise from the other of the split pulse signals and the noise by performing a second demodulation process on the other of the split pulse signals and the noise based on a second pattern in which the on-off patterns of the first pattern are inverted, a subtractor that restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and the noise, and a filter that restores the analog communication signal based on the restored pulse signal.

One aspect of the present invention is a noise reduction method executed by the noise reduction device described above, which includes the steps of: generating a pulse signal by performing a modulation process on an analog communication signal based on a first pattern in which on-off switching is repeated at a predetermined speed; branching the pulse signal in which noise has been generated by a noise source; performing a first demodulation process on one of the branched pulse signals and the noise based on the first pattern; extracting the noise from the other branched pulse signal and the noise by performing a second demodulation process on the other branched pulse signal and the noise based on a second pattern in which the on-off of the first pattern is inverted; restoring the pulse signal by subtracting the extracted noise from the one branched pulse signal and the noise; and restoring the analog communication signal based on the restored pulse signal.

One aspect of the present invention is a program for causing a computer to execute the steps of: generating a pulse signal by performing a modulation process on an analog communication signal based on a first pattern in which on-off switching is repeated at a predetermined speed; branching the pulse signal in which noise has been generated by a noise source; performing a first demodulation process on one of the branched pulse signals and the noise based on the first pattern; extracting the noise from the other branched pulse signal and the noise by performing a second demodulation process on the other branched pulse signal and the noise based on a second pattern in which the on-off of the first pattern is inverted; restoring the pulse signal by subtracting the extracted noise from one of the branched pulse signals and the noise; and restoring the analog communication signal based on the restored pulse signal.

The present invention makes it possible to reduce noise that occurs in analog communication signals.

FIG. 1 is a diagram illustrating an example of the configuration of a communication system in a first embodiment. 5A to 5C are diagrams illustrating an example of noise reduction processing in the first embodiment. 4 is a flowchart showing an example of the operation of the noise reduction device in the first embodiment. FIG. 11 is a diagram illustrating an example of the configuration of a communication system in a second embodiment. FIG. 13 is a diagram illustrating an example of the configuration of a communication system in a third embodiment. FIG. 13 is a diagram illustrating an example of the configuration of a communication system in a fourth embodiment. FIG. 13 is a diagram illustrating an example of the configuration of a communication system in a fifth embodiment. FIG. 23 is a diagram illustrating an example of the configuration of a communication system in a sixth embodiment. FIG. 23 is a diagram illustrating an example of the configuration of a communication system in a seventh embodiment. FIG. 2 is a diagram illustrating an example of the hardware configuration of a control device of a noise reduction device in each embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.
First Embodiment
1 is a diagram showing an example of the configuration of a communication system 1a according to a first embodiment. The communication system 1a is a wireless communication system to which analog RoF is applied. The communication system 1a includes a noise reduction device 10.

The noise reduction device 10 is a device that reduces noise that occurs in an upstream analog communication signal. The noise reduction device 10 includes a first switch 11a, a noise source 12, a splitter 13, a second switch 14a, a third switch 15a, a subtractor 16, and a filter 17.

An upstream analog communication signal is input to the first switch 11a. The analog communication signal is, for example, an upstream RF (Radio Frequency) signal based on a radio signal transmitted from a user terminal (not shown). The first switch 11a modulates the input analog communication signal with a first pattern in which high-speed on-off switching is repeated. That is, the first switch 11a multiplies the analog communication signal by 1 or 0 at a switching interval "t". The switching interval "t" is a sufficiently short time interval. For example, the switching speed (the inverse of the switching interval) is at least twice the maximum frequency band of the analog communication signal in the communication system 1a. As a result, the first switch 11a generates a pulse signal (a pulsed analog communication signal). The first switch 11a outputs the generated pulse signal to the noise source 12.

In the noise source 12, noise such as thermal noise is generated in the pulse signal input from the first switch 11a. In other words, the noise source 12 adds noise to the input pulse signal. The noise source 12 transmits the pulse signal with the noise generated to the splitter 13.

The splitter 13 receives a noisy pulse signal (pulse signal and noise) from the noise source 12. The splitter 13 splits the noisy pulse signal (the input pulse signal and noise). The splitter 13 outputs one of the split pulse signals and noise to the second switch 14a. The splitter 13 outputs the other of the split pulse signals and noise to the third switch 15a.

The second switch 14a receives one of the branched pulse signals and noise from the brancher 13. The second switch 14a demodulates the one of the branched pulse signals and noise in a first pattern in which high-speed on-off switching is repeated. That is, the second switch 14a multiplies the one of the branched pulse signals and noise by 1 or 0 at switching intervals "t". In this way, the second switch 14a extracts the demodulated pulse signal and noise from the one of the branched pulse signals and noise. Here, the extracted noise is also pulsed. The second switch 14a outputs the extracted pulse signal and noise to the subtractor 16.

The other branched pulse signal and noise are input to the third switch 15a from the branching device 13. The third switch 15a demodulates the other branched pulse signal and noise in a second pattern in which high-speed switching of off and on is repeated. That is, the third switch 15a multiplies the other branched pulse signal and noise by 0 or 1 at a switching interval "t". Here, the timing when the high-speed switching of the third switch 15a turns off is the timing when the high-speed switching of the second switch 14a turns on. That is, the values (on and off) are inverted between the second pattern and the first pattern. As a result, the third switch 15a extracts noise from the other branched pulse signal and noise. Here, the extracted noise is also pulsed. The second switch 14a outputs the extracted noise to the subtractor 16.

The subtractor 16 is, for example, a differential detector (balanced detector). The subtractor 16 executes a process to reduce the noise in the pulse signal and noise output from the second switch 14a based on the difference between the pulse signal and noise output from the second switch 14a and the noise output from the third switch 15a. That is, the subtractor 16 subtracts the noise output from the third switch 15a from the pulse signal and noise output from the second switch 14a.

The subtractor 16 may include a delay (not shown) that delays the timing of a signal such as noise by the switching interval "t". For example, the subtractor 16 delays the noise output from the third switch 15a. Based on this delayed noise and the pulse signal output from the second switch 14a, the subtractor 16 may execute a process to reduce the noise in the pulse signal output from the second switch 14a and the noise. In other words, the subtractor 16 may subtract the delayed noise from the pulse signal and noise output from the second switch 14a.

Filter 17 is, for example, an anti-aliasing filter. Filter 17 performs anti-aliasing processing on the pulse signal input from subtractor 16, thereby converting the pulse signal back into an analog communication signal. Filter 17 may output the analog communication signal to a predetermined functional unit (not shown).

FIG. 2 is a diagram showing an example of noise reduction processing (noise estimation) in the first embodiment. The second switch output 100 is a pulse signal output from the second switch 14a at the on timing of the high-speed switching. At the on timing in the first pattern, one of the branched pulse signals and noise are multiplied by 1, so the second switch output 100 contains a pulse signal and noise.

As mentioned above, the timing when the high-speed switching of the second switch 14a turns on ("1") is the timing when the high-speed switching of the third switch 15a turns off ("0").

The third switch output 101 is a pulse signal output from the third switch 15a at the off timing of the high-speed switching. At the off timing in the second pattern (at the on timing in the first pattern), the other branched pulse signal and noise are multiplied by 0, so the third switch output 101 does not contain a pulse signal, but only noise.

In FIG. 2, the third switch output 101 is delayed by the switching interval "t" from the second switch output 100 by a delay device (not shown) provided in the subtractor 16.

When the switching interval "t" is sufficiently short (when switching is fast), there is a correlation between the noise contained in the second switch output 100 and the noise contained in the third switch output 101. Therefore, the subtractor 16 subtracts the noise contained in the second switch output 100 from the pulse signal and noise contained in the second switch output 100. As a result, the subtractor 16 outputs only the pulse signal, which is the subtraction result, to the filter 17. The splitter 13 may be provided with a filter that performs band narrowing. The splitter 13 may perform band narrowing of the pulse signal input from the noise source 12 by filter processing so that the correlation between the noise contained in the second switch output 100 and the noise contained in the third switch output 101 becomes high. The filter that performs band narrowing may be provided between the noise source 12 and the splitter 13.

Next, an example of the operation of the noise reduction device 10 will be described.
3 is a flowchart showing an example of the operation of the noise reduction device 10 in the first embodiment. The first switch 11a performs a modulation process on the analog communication signal based on the first pattern (step S101). The splitter 13 splits the pulse signal in which noise has been generated by the noise source 12 (step S102). The second switch 14a performs a first demodulation process on one of the split pulse signals and noise based on the first pattern (step S103).

The third switch 15a performs a second demodulation process on the other branched pulse signal and noise based on the second pattern (step S104). The subtractor 16 subtracts the extracted noise from one branched pulse signal and noise (step S105). The filter 17 restores the analog communication signal based on the restored pulse signal (step S106).

As described above, the first switch 11a generates a pulse signal by performing a modulation process on the analog communication signal based on the first pattern in which switching between on and off is repeated at a predetermined speed. The predetermined speed (frequency) is, for example, more than twice the maximum frequency band of the analog communication signal in the communication system 1a based on the sampling theorem. The noise source 12 adds noise to the pulse signal. The splitter 13 splits the pulse signal in which noise has been generated by the noise source 12 to the second switch 14a and the third switch 15a. The second switch 14a performs a first demodulation process on one of the split pulse signals and noise based on the first pattern. The second pattern is a pattern in which the on and off of the first pattern are inverted. The third switch 15a extracts noise from the other of the split pulse signals and noise by performing a second demodulation process on the other of the split pulse signals and noise based on the second pattern. The subtractor 16 restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and noise. Filter 17 restores the analog communication signal based on the restored pulse signal.

This makes it possible to reduce noise that occurs in analog communication signals. In particular, it makes it possible to reduce inflow noise at an aggregation station where upstream analog communication signals transmitted from multiple user terminals (not shown) are aggregated. It is possible to reduce noise not only in the optical domain (optical signal) but also in the electrical domain (electrical signal). Since there is no need to control the power level of the transmitted signal in a complex manner, and there is no need to ensure responsiveness in controlling the power level, it is possible to reduce noise with a simple configuration. It is also possible to improve communication quality.

Second Embodiment
The second embodiment is different from the first embodiment mainly in that noise generated in the pulse signal at the base station is reduced. The second embodiment will be described focusing on the differences from the first embodiment.

FIG. 4 is a diagram showing an example of the configuration of a communication system 1b in the second embodiment. The communication system 1b includes a base station 2b and a central station (not shown). The base station 2b includes an O/E converter 21, a transmission signal amplifier 22, an antenna 23, a communication unit 24, a first switch 11b, a reception signal amplifier 12b, a splitter 13, a second switch 14b, a third switch 15b, a subtractor 16, a filter 17, and an E/O converter 25.

The communication system 1b includes a first switch 11b, a received signal amplifier 12b, a splitter 13, a second switch 14b, a third switch 15b, a subtractor 16, and a filter 17 as noise reduction devices. The received signal amplifier 12b corresponds to the noise source 12 of the communication system 1a illustrated in the first embodiment. In FIG. 4, the combination of the first switch 11b and the second switch 14b and the third switch 15b is arranged to sandwich the received signal amplifier 12b (noise source).

The O/E converter 21 receives a downstream optical signal from a central station (not shown) via an optical transmission path (optical fiber). The O/E converter 21 converts the downstream optical signal into a downstream analog communication signal (electrical signal). The O/E converter 21 outputs the downstream analog communication signal to the transmission signal amplifier 22.

The transmission signal amplifier 22 amplifies the strength of the downstream analog communication signal. The transmission signal amplifier 22 outputs the downstream analog communication signal to the communication unit 24 as a transmission signal.

The antenna 23 receives upstream radio signals from one or more user terminals (not shown). The antenna 23 generates an upstream analog communication signal based on the received upstream radio signals. The antenna 23 outputs the upstream analog communication signal to the communication unit 24.

The antenna 23 receives a downstream analog communication signal (transmission signal) from the communication unit 24. The antenna 23 transmits a downstream wireless signal based on the downstream analog communication signal to a specified user terminal (not shown).

The communication unit 24 is a functional unit (T/R switch) that switches between transmitting and receiving analog communication signals. The communication unit 24 obtains a downstream analog communication signal (transmission signal) from the transmission signal amplifier 22. The communication unit 24 outputs the downstream analog communication signal to the antenna 23.

The communication unit 24 receives an upstream analog communication signal (received signal) from the antenna 23. The communication unit 24 outputs the upstream analog communication signal to the first switch 11b.

The first switch 11b is an electrical switch (switching device) that performs high-speed switching for modulation. The first switch 11b is, for example, a Micro Electro Mechanical Systems (MEMS) switch, a Positive Intrinsic Negative (PIN) diode, a Gallium Nitride (GaN) transistor, or a Complementary Metal Oxide Semiconductor (CMOS) switch.

An upstream analog communication signal is input to the first switch 11b. The first switch 11b modulates the input analog communication signal with a first pattern in which rapid on-off switching is repeated. That is, the first switch 11b multiplies the analog communication signal by 1 or 0 at switching intervals "t". In this way, the first switch 11b generates an upstream pulse signal (pulsed analog communication signal). The first switch 11b outputs the generated upstream pulse signal to the received signal amplifier 12b.

The received signal amplifier 12b amplifies the strength of the upstream pulse signal. In the received signal amplifier 12b, noise is generated in the pulse signal input from the first switch 11b. The received signal amplifier 12b outputs the upstream pulse signal with noise generated as a received signal to the splitter 13.

The upstream pulse signal containing noise is input to the splitter 13 from the received signal amplifier 12b. That is, the pulse signal and noise are input to the splitter 13 from the received signal amplifier 12b. The splitter 13 splits the input pulse signal and noise. The splitter 13 outputs one of the split pulse signals and noise to the second switch 14b. The splitter 13 outputs the other of the split pulse signals and noise to the third switch 15b.

The second switch 14b is an electrical switch for demodulation. The second switch 14b is, for example, a MEMS switch, a PIN diode, a gallium nitride transistor, or a complementary metal oxide semiconductor switch.

The second switch 14b receives one of the branched pulse signals and noise from the brancher 13. The second switch 14b demodulates the one of the branched pulse signals and noise in a first pattern in which high-speed on-off switching is repeated. In other words, the second switch 14b multiplies the one of the branched pulse signals and noise by 1 or 0 at switching intervals "t". In this way, the second switch 14b extracts the demodulated pulse signal and noise from the one of the branched pulse signals and noise. The second switch 14b outputs the extracted pulse signal and noise to the subtractor 16.

The third switch 15b is an electrical switch for demodulation. The third switch 15b is, for example, a MEMS switch, a PIN diode, a gallium nitride transistor, or a complementary metal oxide semiconductor switch.

The other branched pulse signal and noise are input to the third switch 15b from the splitter 13. The third switch 15b demodulates the other branched pulse signal and noise in a second pattern in which high-speed switching between off and on is repeated. That is, the third switch 15b multiplies the other branched pulse signal and noise by 0 or 1 at a switching interval "t". Here, the timing when the high-speed switching of the third switch 15b turns off is the timing when the high-speed switching of the second switch 14b turns on. That is, the values are inverted between the second pattern and the first pattern. As a result, the third switch 15b extracts noise from the other branched pulse signal and noise. The second switch 14b outputs the extracted noise to the subtractor 16.

The subtractor 16 subtracts the noise output from the third switch 15b from the pulse signal and noise output from the second switch 14b. The filter 17 performs anti-aliasing processing on the pulse signal input from the subtractor 16 to return the pulse signal to an analog communication signal. The filter 17 outputs the analog communication signal to the E/O converter 25.

The E/O converter 25 receives an upstream analog communication signal (electrical signal) from the filter 17. The E/O converter 25 converts the upstream analog communication signal into an upstream optical signal. The E/O converter 25 transmits the upstream analog communication signal to a central station (not shown) via an optical transmission path (optical fiber).

As described above, the first switch 11b generates a pulse signal by performing modulation processing on the analog communication signal based on the first pattern. The noise source 12 adds noise to the pulse signal. The splitter 13 splits the pulse signal in which noise has been generated by the received signal amplifier 12b to the second switch 14b and the third switch 15b. The second switch 14b performs a first demodulation processing on one of the split pulse signals and noise based on the first pattern. The third switch 15b extracts noise from the other of the split pulse signals and noise by performing a second demodulation processing on the other of the split pulse signals and noise based on the second pattern. The subtractor 16 restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and noise. The filter 17 restores the analog communication signal based on the restored pulse signal.

This makes it possible to reduce noise that occurs in the analog communication signal. In addition, since the noise reduction process is completed at the base station 2b, it is easy to synchronize the second switch 14b and the third switch 15b.

Third Embodiment
The third embodiment is mainly different from the second embodiment in that noise generated in a pulse signal in an optical transmission path (analog RoF section) between a base station and a central station is reduced. The third embodiment will be described focusing on the differences from the second embodiment.

FIG. 5 is a diagram showing an example of the configuration of a communication system 1c in the third embodiment. The communication system 1c includes a base station 2c and a central station 3c. The base station 2c includes an O/E converter 21, a transmission signal amplifier 22, an antenna 23, a communication unit 24, a reception signal amplifier 12c, an E/O converter 25, a first switch 11c, and an optical transmission path 26. The central station 3c includes an E/O converter 31, a splitter 13, a second switch 14c, a third switch 15c, a subtractor 16, and a filter 17.

The communication system 1c includes a first switch 11c, a splitter 13, a second switch 14c, a third switch 15c, a subtractor 16, a filter 17, and an optical transmission path 26 as a noise reduction device. The optical transmission path 26 corresponds to the noise source 12 of the communication system 1a illustrated in the first embodiment. In FIG. 5, the first switch 11c and the combination of the second switch 14c and the third switch 15c are arranged on either side of the optical transmission path 26 (noise source).

The communication unit 24 acquires a downstream analog communication signal (transmission signal) from the transmission signal amplifier 22. The communication unit 24 outputs the downstream analog communication signal to the antenna 23. The communication unit 24 acquires an upstream analog communication signal (reception signal) from the antenna 23. The communication unit 24 outputs the upstream analog communication signal to the reception signal amplifier 12c.

The received signal amplifier 12c amplifies the strength of the upstream analog communication signal. In the received signal amplifier 12c, noise is generated in the analog communication signal input from the communication unit 24. The received signal amplifier 12c outputs the upstream analog communication signal to the E/O converter 25 as a received signal.

The E/O converter 25 receives an upstream analog communication signal (electrical signal) from the received signal amplifier 12c. The E/O converter 25 converts the upstream analog communication signal into an upstream optical signal. The E/O converter 25 outputs the upstream analog communication signal to the first switch 11c.

The first switch 11c is an optical switch (switching device) that performs high-speed switching for modulation. An upstream analog communication signal is input to the first switch 11c. The first switch 11c modulates the input analog communication signal with a first pattern in which high-speed on-off switching is repeated. That is, the first switch 11c multiplies the analog communication signal by 1 or 0 at switching intervals "t". In this way, the first switch 11c generates an upstream pulse signal (pulsed analog communication signal). The first switch 11c transmits the generated upstream pulse signal to the optical transmission path 26. The optical transmission path 26 transmits the upstream pulse signal to the splitter 13.

The splitter 13 receives a pulse signal containing noise from the first switch 11c via the optical transmission path 26. That is, the pulse signal and noise are input to the splitter 13 from the first switch 11c. The splitter 13 splits the input pulse signal and noise. The splitter 13 outputs the other split pulse signal and noise to the second switch 14c. The splitter 13 outputs the other split pulse signal and noise to the third switch 15c.

The second switch 14c is an optical switch for demodulation. The second switch 14c may be, for example, an OEO (Optical-Electro-Optical) type optical switch, or an OOO (Optical-Optical-Optical) type optical switch. The OOO type may be, for example, any of a mechanical type, a MEMS type, a waveguide type thermo-optical type, and a waveguide type lead lanthanum zirconate titanate (PLZT: PbLaZrTiO3) type.

The second switch 14c receives one of the branched pulse signals and noise from the branching device 13. The second switch 14c demodulates the one of the branched pulse signals and noise in a first pattern in which high-speed on-off switching is repeated. That is, the second switch 14c multiplies the one of the branched pulse signals and noise by 1 or 0 at a switching interval "t". In this way, the second switch 14b extracts the demodulated pulse signal and noise from the one of the branched pulse signals and noise. The second switch 14c outputs the extracted pulse signal and noise to the subtractor 16.

The third switch 15c is an optical switch for demodulation. The third switch 15c may be, for example, an OEO type optical switch or an OOO type optical switch.

The other branched pulse signal and noise are input to the third switch 15c from the splitter 13. The third switch 15c demodulates the other branched pulse signal and noise in a second pattern in which high-speed switching between off and on is repeated. That is, the third switch 15c multiplies the other branched pulse signal and noise by 0 or 1 at a switching interval "t". Here, the timing when the high-speed switching of the third switch 15c turns off is the timing when the high-speed switching of the second switch 14c turns on. That is, the values are inverted between the second pattern and the first pattern. As a result, the third switch 15c extracts noise from the other branched pulse signal and noise. The second switch 14c outputs the extracted noise to the subtractor 16.

The subtractor 16 is, for example, a differential amplifier having a PIN photodiode. The subtractor 16 executes a process to reduce the noise in the pulse signal and noise output from the second switch 14a based on the difference between the pulse signal and noise output from the second switch 14a and the noise output from the third switch 15a. In other words, the subtractor 16 subtracts the noise output from the third switch 15a from the pulse signal and noise output from the second switch 14a. The subtractor 16 also converts the pulse signal (optical signal) into a pulse signal (electrical signal).

The filter 17 performs anti-aliasing processing on the pulse signal (electrical signal) input from the subtractor 16, thereby converting the pulse signal back into an analog communication signal.

As described above, the first switch 11c generates a pulse signal by performing a modulation process on the analog communication signal based on the first pattern. The noise source 12 adds noise to the pulse signal. The splitter 13 splits the pulse signal in which noise has been generated by a noise source such as the received signal amplifier 12c to the second switch 14c and the third switch 15c. The second switch 14c performs a first demodulation process on one of the split pulse signals and noise based on the first pattern. The third switch 15c extracts noise from the other of the split pulse signals and noise by performing a second demodulation process on the other of the split pulse signals and noise based on the second pattern. The subtractor 16 restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and noise. The filter 17 restores the analog communication signal based on the restored pulse signal.

This makes it possible to reduce noise in analog communication signals.

Fourth Embodiment
The fourth embodiment is different from the second embodiment in that noise generated in a transmission path including an analog RoF section is reduced. The fourth embodiment will be described focusing on the differences from the second embodiment.

FIG. 6 is a diagram showing an example of the configuration of a communication system 1d in the fourth embodiment. The communication system 1d includes a base station 2d and a central station 3d. The base station 2d includes an O/E converter 21, a transmission signal amplifier 22, an antenna 23, a communication unit 24, a first switch 11d, a reception signal amplifier 12d, an E/O converter 25, and an optical transmission path 26.

The aggregation station 3d includes an E/O converter 31, an O/E converter 32, a splitter 13, a second switch 14c, a third switch 15c, a subtractor 16, and a filter 17.

The received signal amplifier 12d, the E/O converter 25, the optical transmission path 26, and the O/E converter 32 correspond to the noise source 12 of the communication system 1a illustrated in the first embodiment. In FIG. 6, a combination of a first switch 11d, a second switch 14d, and a third switch 15d is arranged to sandwich the noise sources of the received signal amplifier 12d, the E/O converter 25, the optical transmission path 26, and the O/E converter 32.

An upstream analog communication signal is input to the first switch 11d. The first switch 11d modulates the input analog communication signal with a first pattern in which rapid on-off switching is repeated. That is, the first switch 11d multiplies the analog communication signal by 1 or 0 at switching intervals "t". In this way, the first switch 11d generates an upstream pulse signal (pulsed analog communication signal). The first switch 11d outputs the generated upstream pulse signal to the received signal amplifier 12d.

The received signal amplifier 12d amplifies the strength of the upstream pulse signal. In the received signal amplifier 12d, noise is generated in the pulse signal input from the first switch 11d. The received signal amplifier 12d outputs the upstream pulse signal with noise generated as a received signal to the E/O converter 25.

The E/O converter 25 receives an upstream pulse signal containing noise from the received signal amplifier 12d. That is, the E/O converter 25 receives a pulse signal and noise from the received signal amplifier 12d. The E/O converter 25 converts the upstream pulse signal containing noise into an upstream optical signal containing noise. The E/O converter 25 transmits the upstream optical signal containing noise to the O/E converter 32 via the optical transmission path 26. The optical transmission path 26 transmits the upstream optical signal containing noise to the O/E converter 32.

The O/E converter 32 receives an upstream optical signal from the E/O converter 25 via the optical transmission path 26. The O/E converter 32 converts the upstream optical signal into an upstream pulse signal (electrical signal). The O/E converter 32 outputs the upstream pulse signal to the splitter 13.

The upstream pulse signal containing noise is input to the splitter 13 from the O/E converter 32. That is, the pulse signal and noise are input to the splitter 13 from the O/E converter 32. The splitter 13 splits the input pulse signal and noise. The splitter 13 outputs one of the split pulse signals and noise to the second switch 14d. The splitter 13 outputs the other of the split pulse signals and noise to the third switch 15d.

The filter 17 performs anti-aliasing processing on the pulse signal input from the subtractor 16, thereby converting the pulse signal back into an analog communication signal.

As described above, the first switch 11d generates a pulse signal by performing a modulation process on the analog communication signal based on the first pattern. The noise source 12 adds noise to the pulse signal. The splitter 13 splits the pulse signal in which noise has been generated by a noise source such as the received signal amplifier 12d to the second switch 14d and the third switch 15d. The second switch 14d performs a first demodulation process on one of the split pulse signals and noise based on the first pattern. The third switch 15d extracts noise from the other of the split pulse signals and noise by performing a second demodulation process on the other of the split pulse signals and noise based on the second pattern. The subtractor 16 restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and noise. The filter 17 restores the analog communication signal based on the restored pulse signal.

This makes it possible to reduce noise that occurs in the analog communication signal. It also makes it possible to reduce noise that occurs in the upstream transmission section from the receiving signal amplifier 12d of the base station 2d to the O/E converter 32 of the aggregation station 3d.

Fifth Embodiment
The fifth embodiment is mainly different from the second embodiment in that the communication system includes a plurality of base stations. The fifth embodiment will be described focusing on the differences from the second embodiment.

FIG. 7 is a diagram showing an example of the configuration of a communication system 1e in the fifth embodiment. The communication system 1e includes multiple base stations 2e and a central station (not shown). In FIG. 7, the communication system 1e includes two base stations 2e as an example of multiple base stations 2e. The multiple base stations 2e and the central station (not shown) may form a single-frequency network (SFN: Single-Frequency-Network). The communication system 1e includes an O/E converter 32 for each base station 2e. The communication system 1e includes a multiplexer 33 and a BBU 34 (BBU: Baseband Unit). The O/E converter 32, the multiplexer 33, and the BBU 34 are provided, for example, in the central station (not shown).

The base station 2e includes an O/E converter 21, a transmission signal amplifier 22, an antenna 23, a communication unit 24, a first switch 11e, a reception signal amplifier 12e, a splitter 13, a second switch 14e, a third switch 15e, a subtractor 16, a filter 17, and an E/O converter 25.

The base station 2e includes a first switch 11e, a received signal amplifier 12e, a splitter 13, a second switch 14e, a third switch 15e, a subtractor 16, and a filter 17 as noise reduction devices. The received signal amplifier 12e corresponds to the noise source 12 of the communication system 1a illustrated in the first embodiment. In the fifth embodiment, since the noise reduction process is completed in the base station 2e, switching does not need to be synchronized between the base stations 2e.

The E/O converter 25 receives an upstream analog communication signal (electrical signal) from the filter 17. The E/O converter 25 converts the upstream analog communication signal into an upstream optical signal. The E/O converter 25 transmits the upstream analog communication signal to the O/E converter 32 via an optical transmission path (optical fiber).

The O/E converter 32 receives an upstream optical signal from the E/O converter 25 via the optical transmission path. The O/E converter 32 converts the upstream optical signal into an upstream analog communication signal (electrical signal). The O/E converter 32 outputs the upstream analog communication signal to the multiplexer 33.

The multiplexer 33 multiplexes the upstream analog communication signals transmitted from the multiple O/E converters 32. The multiplexer 33 outputs the multiplexed upstream analog communication signal to the BBU 34.

The BBU 34 is a baseband device. The BBU 34 performs a predetermined baseband processing on the combined upstream analog communication signal. The BBU 34 may also perform a predetermined baseband processing on the downstream analog communication signal.

As described above, the first switch 11e generates a pulse signal by performing a modulation process on the analog communication signal based on the first pattern. The noise source 12 adds noise to the pulse signal. The splitter 13 splits the pulse signal in which noise has been generated by a noise source such as the received signal amplifier 12e to the second switch 14e and the third switch 15e. The second switch 14e performs a first demodulation process on one of the split pulse signals and noise based on the first pattern. The third switch 15e extracts noise from the other of the split pulse signals and noise by performing a second demodulation process on the other of the split pulse signals and noise based on the second pattern. The subtractor 16 restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and noise. The filter 17 restores the analog communication signal based on the restored pulse signal.

This makes it possible to reduce noise in analog communication signals.

Sixth Embodiment
The sixth embodiment is mainly different from the fourth embodiment in that the communication system includes a plurality of base stations. Also, the sixth embodiment is mainly different from the fifth embodiment in that a first switch in the base station is synchronized with a second switch and a third switch corresponding to the first switch in the central station. The sixth embodiment will be described focusing on the differences from the fourth and fifth embodiments.

FIG. 8 is a diagram showing an example of the configuration of a communication system 1f in the sixth embodiment. The communication system 1f includes a plurality of base stations 2f, a central station 3f, and a BBU 34. In FIG. 8, the communication system 1f includes two base stations 2f as an example of a plurality of base stations 2f. The base station 2f includes an O/E converter 21, a transmission signal amplifier 22, an antenna 23, a communication unit 24, a first switch 11f, a reception signal amplifier 12f, an E/O converter 25, and an optical transmission path 26.

The aggregation station 3f includes an E/O converter 31, an O/E converter 32, a splitter 13, a second switch 14f, a third switch 15f, a subtractor 16, and a filter 17 for each of the base stations 2f. The aggregation station 3f includes a multiplexer 33.

The received signal amplifier 12f, the E/O converter 25, the optical transmission path 26, and the O/E converter 32 correspond to the noise source 12 of the communication system 1a illustrated in the first embodiment.

The filter 17 performs anti-aliasing processing on the pulse signal input from the subtractor 16, thereby converting the pulse signal back into an analog communication signal. The filter 17 outputs the upstream analog communication signal to the multiplexer 33. The multiplexer 33 multiplexes the upstream analog communication signals transmitted from multiple filters 17. The multiplexer 33 outputs the combined upstream analog communication signal to the BBU 34.

As described above, the first switch 11f generates a pulse signal by performing a modulation process on the analog communication signal based on the first pattern. The noise source 12 adds noise to the pulse signal. The splitter 13 splits the pulse signal in which noise has been generated by a noise source such as the received signal amplifier 12f to the second switch 14f and the third switch 15f. The second switch 14f performs a first demodulation process on one of the split pulse signals and noise based on the first pattern. The third switch 15f extracts noise from the other of the split pulse signals and noise by performing a second demodulation process on the other of the split pulse signals and noise based on the second pattern. The subtractor 16 restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and noise. The filter 17 restores the analog communication signal based on the restored pulse signal.

This makes it possible to reduce noise in analog communication signals.

Seventh Embodiment
In the seventh embodiment, one of the main differences from the sixth embodiment is that a single combination of the second switch and the third switch is provided in the central station for a plurality of base stations. In addition, in the sixth embodiment, one of the main differences from the sixth embodiment is that each of the first switches in the plurality of base stations is synchronized with the second switch and the third switch in the central station. In the seventh embodiment, the differences from the sixth embodiment will be mainly described.

FIG. 9 is a diagram showing an example of the configuration of a communication system 1g in the seventh embodiment. The communication system 1g includes a plurality of base stations 2g and a central station 3g. In FIG. 9, the communication system 1g includes two base stations 2g as an example of a plurality of base stations 2g. The base station 2g includes an O/E converter 21, a transmission signal amplifier 22, an antenna 23, a communication unit 24, a first switch 11g, a reception signal amplifier 12g, an E/O converter 25, and an optical transmission path 26.

The aggregation station 3g includes an E/O converter 31 and an O/E converter 32 for each base station 2g. The aggregation station 3g includes a multiplexer 33, a splitter 13, a second switch 14g, a third switch 15g, a subtractor 16, a filter 17, and a BBU 34.

The received signal amplifier 12g, the E/O converter 25, the optical transmission path 26, the O/E converter 32, and the multiplexer 33 correspond to the noise source 12 of the communication system 1a illustrated in the first embodiment.

The upstream optical signal is input to the O/E converter 32 from the E/O converter 25 via the optical transmission path 26. The O/E converter 32 converts the upstream optical signal into an upstream pulse signal (electrical signal). The O/E converter 32 outputs the upstream pulse signal to the multiplexer 33.

The multiplexer 33 multiplexes the upstream analog communication signals transmitted from the multiple O/E converters 32. The multiplexer 33 outputs the multiplexed upstream analog communication signal to the splitter 13.

The upstream pulse signal containing noise is input to the splitter 13 from the multiplexer 33. That is, the pulse signal and noise are input to the splitter 13 from the multiplexer 33. The splitter 13 splits the input pulse signal and noise. The splitter 13 outputs one of the split pulse signals and noise to the second switch 14g. The splitter 13 outputs the other of the split pulse signals and noise to the third switch 15g.

The second switch 14g is an electrical switch for demodulation. The second switch 14g is, for example, a MEMS switch, a PIN diode, a gallium nitride transistor, or a complementary metal oxide semiconductor switch.

The second switch 14g receives one of the branched pulse signals and noise from the brancher 13. The second switch 14g demodulates the one of the branched pulse signals and noise in a first pattern in which high-speed on-off switching is repeated. That is, the second switch 14g multiplies the one of the branched pulse signals and noise by 1 or 0 at a switching interval "t". In this way, the second switch 14g extracts the demodulated pulse signal and noise from the one of the branched pulse signals and noise. The second switch 14g outputs the extracted pulse signal and noise to the subtractor 16.

The third switch 15g is an electrical switch for demodulation. The third switch 15g is, for example, a MEMS switch, a PIN diode, a gallium nitride transistor, or a complementary metal oxide semiconductor switch.

The other branched pulse signal and noise are input to the third switch 15g from the splitter 13. The third switch 15g demodulates the other branched pulse signal and noise in a second pattern in which high-speed switching between off and on is repeated. That is, the third switch 15g multiplies the other branched pulse signal and noise by 0 or 1 at a switching interval "t". Here, the timing at which the high-speed switching of the third switch 15g turns off is the timing at which the high-speed switching of the second switch 14g turns on. That is, the values are inverted between the second pattern and the first pattern. As a result, the third switch 15g extracts noise from the other branched pulse signal and noise. The second switch 14g outputs the extracted noise to the subtractor 16.

The subtractor 16 subtracts the noise output from the third switch 15g from the pulse signal and noise output from the second switch 14g. The filter 17 performs anti-aliasing processing on the pulse signal input from the subtractor 16 to return the pulse signal to an analog communication signal. The filter 17 outputs the analog communication signal to the BBU 34.

As described above, the first switch 11g generates a pulse signal by performing a modulation process on the analog communication signal based on the first pattern. The noise source 12 adds noise to the pulse signal. The splitter 13 splits the pulse signal in which noise has been generated by a noise source such as the received signal amplifier 12g to the second switch 14g and the third switch 15g. The second switch 14g performs a first demodulation process on one of the split pulse signals and the noise based on the first pattern. The third switch 15g extracts noise from the other of the split pulse signals and the noise by performing a second demodulation process on the other of the split pulse signals and the noise based on the second pattern. The subtractor 16 restores the pulse signal by subtracting the extracted noise from one of the split pulse signals and the noise. The filter 17 restores the analog communication signal based on the restored pulse signal.

This makes it possible to reduce noise in analog communication signals.

(Hardware configuration)
FIG. 10 is a diagram showing an example of a hardware configuration of a control device 200 of a noise reduction device in each embodiment. The control device 200 is realized as software by a processor 201 such as a CPU (Central Processing Unit) executing a program stored in a storage device 203 having a non-volatile recording medium (non-transient recording medium) and a memory 202. The program may be recorded in a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), a CD-ROM (Compact Disc Read Only Memory), or a non-transient recording medium such as a storage device such as a hard disk or a solid state drive (SSD) built into a computer system. The communication unit 204 executes a predetermined communication process.

The control device 200 may be realized using hardware (accelerator) including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

　Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs that do not deviate from the gist of the present invention.

The present invention is applicable to wireless communication systems that use analog RoF.

1a, 1b, 1c, 1d, 1e, 1f, 1g...Communication system, 2b, 2c, 2d, 2e, 2f, 2g...Outgoing station, 3c, 3d, 3e, 3f, 3g...Aggregation station, 10...Noise reduction device , 11a, 11b, 11c, 11d, 11e, 1 1f, 11g...first switch, 12...noise source, 12b, 12c, 12d, 12e, 12f, 12g...received signal amplifier, 13...brancher, 14a, 14b, 14c, 14d, 14e, 14f, 14g...second switch, 15a, 15 b, 15c, 15d, 15e, 15f, 15g...third switch, 16...subtractor, 17...filter, 21...O/E converter, 22...transmission signal amplifier, 23...antenna, 24...communication unit, 25... E/O converter, 26...optical transmission line, 31...E/O converter, 32...O/E converter, 33...multiplexer, 34...BBU, 100...second switch output, 101...third switch Output, 200...control device, 201...processor, 202...memory, 203...storage device, 204...communication unit

Claims (4)

a first switch that generates a pulse signal by performing a modulation process on an analog communication signal based on a first pattern in which the first switch is repeatedly switched on and off at a predetermined speed;
a branching device for branching the pulse signal in which noise has been generated by a noise source;
a second switch that performs a first demodulation process on one of the branched pulse signals and the noise based on the first pattern;
a third switch that extracts the noise from the other of the branched pulse signals and the noise by executing a second demodulation process on the other of the branched pulse signals and the noise based on a second pattern that is an inverted on/off pattern of the first pattern;
a subtractor that restores the pulse signal by subtracting the extracted noise from one of the branched pulse signals and the noise;
a filter that restores the analog communication signal based on the restored pulse signal. The noise reduction device of claim 1, wherein the predetermined speed is at least twice the maximum frequency band of the analog communication signal. A noise reduction method performed by a noise reduction device, comprising:
performing a modulation process on an analog communication signal based on a first pattern of repeated on and off switching at a predetermined rate to generate a pulse signal;
branching said pulse signal noisy due to a noise source;
performing a first demodulation process on one of the branched pulse signals and the noise based on the first pattern;
extracting the noise from the other of the branched pulse signals and the noise by performing a second demodulation process on the other of the branched pulse signals and the noise based on a second pattern that is an inverted pattern of the first pattern;
restoring the pulse signal by subtracting the extracted noise from one of the branched pulse signals and the noise;
and restoring the analog communication signal based on the restored pulse signal. On the computer,
generating a pulse signal by performing a modulation process on an analog communication signal based on a first pattern in which the analog communication signal is repeatedly switched on and off at a predetermined rate;
branching said pulse signal noisy due to a noise source;
performing a first demodulation process on one of the branched pulse signals and the noise based on the first pattern;
extracting the noise from the other of the branched pulse signals and the noise by executing a second demodulation process on the other of the branched pulse signals and the noise based on a second pattern that is an inverted pattern of the first pattern;
A step of restoring the pulse signal by subtracting the extracted noise from one of the branched pulse signals and the noise;
and a procedure for restoring the analog communication signal based on the restored pulse signal.

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