JP2012217174A - Optical transmission system, master station device and slave station device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a master station device and improve CNR deterioration.SOLUTION: An uplink transmitter of a slave station device 50 comprises: a frequency converter 52 for down-converting a received RF signal; an A/D converter 54 for converting to a digital signal; a transmission digital signal processor 55 for converting a parallel digital signal to a serial digital signal; and an optical transmitter 56 for outputting converting the serial digital electrical signal to an optical signal and outputting the optical signal to an optical fiber Fb2. An uplink receiver of a master station device 1 comprises: optical receivers 3 which convert optical signals input from slave station devices and whose number is equal to slave station devices 50; a reception digital signal processor 4 for receiving plural digital signals whose number is smaller than the number of the optical receivers 3, converting each digital signal to a parallel digital signal and performing digital addition; a D/A converter 5 for converting the added digital signal to an analog signal; a compositor 6 for combining the analog signals; and a frequency converter 9 for up-converting to a transmission RF signal.

Description

  The present invention relates to an optical transmission system, a master station device, and a slave station device that are mainly used in a relay system for countermeasures against radio wave dead areas in a mobile communication system such as a mobile phone.

  In wireless communications such as mobile phones, a technology for modulating the intensity of optical signals with radio signals and transmitting them over optical fibers as a method for providing services to areas where base station radio waves are difficult to reach, such as in high-rise buildings, underground malls, and tunnels There is an optical repeater based on the RoF technology (Radio on Fiber or Radio over Fiber) (see Non-Patent Documents 1 and 2, for example).

  FIG. 6 is a schematic block diagram of an optical transmission system showing a conventional example of an optical repeater system. In FIG. 6, an RF signal input from the base station side to the master station device 100 passes through the multiplexer / demultiplexer 101 and the amplifier 102, and is then converted into an optical signal by the E / O converter 103. This optical signal is power-distributed in a number corresponding to the number of the plurality of slave station devices 150 by the optical distributor 105 and transmitted to the plurality of slave station devices 150 by the optical fiber 106 respectively.

  The optical signal input to the slave station device 150 is converted into an electric signal by the O / E converter 152. The RF signal that is the converted electric signal is amplified by the amplifier 153, further amplified by the amplifier 154, and then radiated and output through the multiplexer / demultiplexer 155 and the antenna 156.

  The RF signal input to the slave station device 150 via the antenna 156 is converted into an optical signal by the E / O converter 158 after passing through the multiplexer / demultiplexer 155 and the amplifier 157. This optical signal is transmitted to the master station device 100 through the optical fiber 159.

  The optical signal from each slave station device 150 input to the master station device 100 is converted into an RF signal which is an electrical signal by the O / E converter 107, and passes through the amplifier 108, the combiner 110, and the multiplexer / demultiplexer 101. Transmitted to the base station.

Kakinuma, et al. "Tunnel Booster for 1.5GHz Digital Mobile Communication", NTT DOCOMO Technical Journal, Vol.2, No.2, PP.20-23, 1994 Fukuya, et al. “Optical Transmission Booster”, NTT DOCOMO Technical Journal, Vol. 5, No. 1, PP. 29-32, 1997

  However, in the case of the conventional optical transmission systems as shown in Non-Patent Documents 1 and 2, with the increase in the number of connected slave station devices, the number of parts of the uplink portion to the master station device increases, Power consumption also increases. Specifically, the number of reception units 109 in the master station device 100 shown in FIG. 6 is required by the number of slave station devices, and the number of reception units 109 increases as the number of slave station devices 150 increases. .

ここで、m：光変調度、S：受光器の受光感度[A/W]、Pr：受光パワー[W]、Ｉth：等価熱雑音電流密度[A/√（Hz）]、q：電荷[C]、Ｉd：受光器の暗電流[A]、RIN：レーザの相対雑音強度、B：信号帯域幅[Hz]である。この式の分子は信号強度を表し、分母は雑音強度を表しており、分母の雑音は次のように分類することができる。すなわち、熱雑音（I^２th・B）、暗電流雑音（2qId・B）、受光器のショット雑音（２qSPr・B）、ＲＩＮ雑音（RIN(SPr)^２・Ｂ）である。よって、親局装置内では、これら全ての雑音成分と、増幅器等で付加される熱雑音とが、子局装置分合成され、親局装置へ伝送される。さらには信号の有無に関わらず、上記雑音成分は常に子局装置の数分、合成され、親局装置へ伝送される。 Further, since the RF signals from all the slave station devices are synthesized in the master station device, the noise component increases as the number of slave station devices increases. In general, in the case of the RoF transmission method, it is known that the CNR characteristic of a signal from the E / O converter to the O / E converter is expressed by the following equation.

Here, m: degree of light modulation, S: light receiving sensitivity of receiver (A / W), Pr: received light power [W], Ith: equivalent thermal noise current density [A / √ (Hz)], q: charge [ C], Id: dark current [A] of the light receiver, RIN: relative noise intensity of the laser, and B: signal bandwidth [Hz]. The numerator of this equation represents the signal strength, the denominator represents the noise strength, and the denominator noise can be classified as follows. That is, thermal noise (I ² th · B), dark current noise (2qId · B), receiver shot noise (2qSPr · B), and RIN noise (RIN (SPr) ² · B). Therefore, in the master station device, all these noise components and thermal noise added by an amplifier or the like are synthesized for the slave station device and transmitted to the master station device. Further, regardless of the presence or absence of a signal, the noise components are always combined by the number of slave station devices and transmitted to the master station device.

  The present invention has been made in view of the above, and an optical transmission system, a master station apparatus, and a slave station that can simplify the apparatus by reducing the number of parts of the master station apparatus and can improve CNR degradation. An object is to provide an apparatus.

  In order to solve the above-described problems and achieve the object, an optical transmission system according to the present invention is an optical transmission system in which a plurality of slave station devices are connected to one master station device by an optical fiber. The upstream transmission unit converts the received RF signal input to the slave station device into a received digital electrical signal, converts the received digital electrical signal into an optical signal, and outputs the optical signal to the optical fiber. And an upstream receiving unit of the master station device has the same number of light as the number of slave station devices that convert an optical signal input from the slave station device into a digital electrical signal via the optical fiber. A reception unit, and a single or a plurality of reception digital signal processing units that input a plurality of the digital electrical signals output from the optical reception unit and perform digital addition of the respective digital electrical signals, less than the number of the optical reception units; , Serial and single or plurality of D / A converter for converting the sum digital electrical signal output from each received digital signal processor to the adder an analog electrical signal, characterized by comprising a.

  The optical transmission system according to the present invention is the above invention, comprising a plurality of the D / A converters and a synthesizer for synthesizing the added analog electric signals output from the D / A converters. Features.

  In the optical transmission system according to the present invention, in the above invention, the A / D conversion unit down-converts the frequency of the received RF signal input to the slave station device and converts the frequency to the received digital electrical signal. A master station upstream frequency converter that includes an upstream frequency converter and upconverts the summed analog electrical signal output from each of the D / A converters or the electrical signal output from the synthesizer into a transmission RF signal and outputs the signal. It is further provided with a feature.

  In the optical transmission system according to the present invention, in the above invention, each of the D / A converters converts the added digital electric signal into an RF added analog electric signal and outputs the converted digital electric signal, and the combiner converts each of the D / A converters. The transmission RF signal is output by synthesizing the RF addition analog electric signal output from the unit.

  In the optical transmission system according to the present invention, in the above invention, the upstream reception unit of the master station device is provided with a switch on the output side of each D / A conversion unit, and the received digital signal processing unit is input The signal level of the digital electric signal is monitored, and when the signal level of all the digital electric signals is equal to or lower than the threshold value, the corresponding lower switch is opened.

  In the optical transmission system according to the present invention, in the above invention, the received digital signal processing unit monitors a signal level of the input digital electric signal, and the digital electric signal indicates when the signal level is equal to or less than a threshold value. The data value is processed as zero.

  In the optical transmission system according to the present invention, in the above invention, the upstream transmission unit of each slave station device determines whether the signal level of the received digital electrical signal is equal to or less than a threshold value after the A / D conversion unit. A transmission digital signal processing unit that adds additional information to be transmitted, and the upstream reception unit of the master station device is provided with a switch on the output side of each D / A conversion unit, and the reception digital signal processing unit is When the additional information of all the input digital electric signals indicates a threshold value or less, the corresponding lower switch is opened.

  In the optical transmission system according to the present invention, in the above invention, when the additional information of the input digital electric signal indicates a threshold value or less, the received digital signal processing unit processes the data value indicated by the digital electric signal as zero. It is characterized by doing.

  The master station device according to the present invention is a master station device of an optical transmission system in which a plurality of slave station devices are connected by an optical fiber, and an upstream receiving unit receives light input from the slave station device via the optical fiber. The same number of optical receivers as the number of slave station devices that convert signals into digital electrical signals, and the plurality of digital electrical signals output from the optical receivers, and the digital addition of each digital electrical signal One or a plurality of reception digital signal processing units smaller than the number of reception units, and a single or a plurality of D / A conversion units for converting the addition digital electric signal output from each reception digital signal processing unit into an addition analog electric signal And.

  In the above invention, the master station device according to the present invention comprises a plurality of the D / A converters and a synthesizer that synthesizes the added analog electric signals output from the D / A converters. Features.

  The master station apparatus according to the present invention is the master station device according to the above invention, wherein the master analog signal output from each of the D / A converters or the electrical signal output from the combiner is up-converted to a transmission RF signal and output. A station upstream frequency converter is further provided.

  In the master station device according to the present invention, in the above invention, each of the D / A converters converts the added digital electric signal into an RF added analog electric signal and outputs the converted digital electric signal, and the combiner converts the D / A conversion. The transmission RF signal is output by synthesizing the RF addition analog electric signal output from the unit.

  The slave station device according to the present invention is a slave station device of an optical transmission system that is connected to one master station device by an optical fiber, and the upstream transmission unit down-converts the frequency of the input received RF signal to receive digital An A / D converter that converts an electrical signal and an optical transmitter that converts the received digital electrical signal into an optical signal and outputs the optical signal to the optical fiber.

  In the slave station device according to the present invention, in the above invention, the A / D conversion unit downconverts the frequency of the received RF signal input to the slave station device and converts the frequency into a received digital electrical signal. A conversion unit is included.

  According to the present invention, it is possible to provide an optical transmission system, a master station device, and a slave station device that can simplify the device by reducing the number of parts of the master station device and can improve CNR degradation.

FIG. 1 is a schematic block diagram illustrating a configuration example of the optical transmission system according to the present embodiment. FIG. 2 is a block diagram showing a detailed configuration of the reception digital signal processing unit of the master station apparatus shown in FIG. FIG. 3 is a block diagram showing a detailed configuration of a transmission digital signal processing unit of a slave station apparatus in an optical transmission system that is a modification of the present embodiment. FIG. 4 is a block diagram showing a detailed configuration of the reception digital signal processing unit of the master station apparatus in the optical transmission system that is a modification of the present embodiment. FIG. 5 is a schematic block diagram illustrating a configuration example of an optical transmission system according to another embodiment. FIG. 6 is a schematic block diagram of an optical transmission system showing a conventional example of an optical repeater system.

  Embodiments of an optical transmission system, a master station device, and a slave station device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a schematic block diagram illustrating a configuration example of the optical transmission system according to the present embodiment. In the optical transmission system of the present embodiment, a plurality of slave station devices 50 (50-1 to 50-I) are connected to one master station device 1 via optical fibers Fb1 and Fb2. In FIG. 1, the number I of the slave station devices 50 connected to the master station device 1 is 16 as an example. The optical fiber Fb1 constitutes a downlink from the master station device 1 to the slave station device 50, and there are 16 optical fibers. Further, the optical fiber Fb2 forms an uplink from the slave station device 50 to the master station device 1, and there are 16 optical fibers Fb2. That is, the master station device 1 and the slave station device 50 are connected by 16 pairs of optical fibers Fb1 and Fb2.

  Here, the uplink transmission unit constituting the uplink in the slave station device 50 includes an amplifier 51, a frequency conversion unit 52 that down-converts the RF signal, a band limiting filter 53, and an A that converts the analog signal into a digital signal. / D conversion unit 54, transmission digital signal processing unit 55 that converts a parallel digital signal into a serial digital signal, and optical transmission unit 56 that converts a serial digital signal into an optical signal. The A / D converter 54 performs quantization with N bits. The transmission digital signal processing unit 55 is realized by an FPGA (Field-Programmable Gate Array).

  On the other hand, the upstream receiving unit constituting the upstream line in the master station device 1 includes the optical receiving unit 3 (3-1 to 3-16) that converts an optical signal into a serial digital signal, and the converted serial digital signal in parallel. A plurality of received digital signal processing units 4 (4-1 to 4-K) for converting into digital signals and adding a plurality of J (= 4) parallel digital signals, and a digital signal output from the received digital signal processing unit 4 Output from the D / A converter 5 (5-1 to 5-K) for converting the analog signal into the analog signal, the synthesizer 6 for synthesizing the converted analog signal, the band limiting filter 8, and the band limiting filter 8 A frequency converter 9 for up-converting an analog signal, and switches SW (SW-1 to SW-K) for switching between the D / A converter 5 and the synthesizer 6 are provided. Note that 16 optical receivers 3 are provided, and the number is the same as that of the slave station devices 50. Each received digital signal processing unit 4 processes signals from M (= 4) optical receiving units 3. M = 4 is an example, and for example, M = 8 may be used. M is a natural number satisfying 2 ≦ M ≦ I. Further, the number K of each of the received digital signal processing unit 4, the D / A conversion unit 5, and the switch SW is I = 16 and M = 4, so that K ≧ I / M becomes 4 (K is a natural number). ). Hereinafter, M = 4 and K = 4 will be described as an example. Therefore, a total of four received digital signal processing units 4 are provided. The D / A converter 5 and the switches SW are also provided in correspondence with the received digital signal processor 4, and there are four. That is, the reception digital signal processing unit 4, the D / A conversion unit 5, and the switch SW are provided for each of the four optical reception units 3. As a result, the number of received digital signal processing units 4 is smaller than the number 16 of slave station devices 50 to be connected. The reception digital signal processing unit 4 is realized by an FPGA.

  Here, the received digital signal processing unit 4 converts the four serial digital signals into parallel digital signals and performs digital addition. For this reason, in the D / A converter 5, the number of optical receivers 3 allocated to one received digital signal processor 4 is M with respect to the N-bit resolution of the A / D converter 54 on the slave station device 50 side. In this case, (N + logM / log2) bit resolution is provided. In FIG. 1, since M is 4, the D / A converter 5 has (N + 2) bit resolution. When eight optical receivers 3 (M = 8) are assigned to one received digital signal processor 4, the D / A converter 5 has (N + 3) bit resolution. In this case, the number of each of the received digital signal processing unit 4, the D / A conversion unit 5, and the switch SW is only four that is halved.

  Thus, the RF signal input via the antenna 71 (71-1 to 71-16) is input to the frequency conversion unit 52 via the multiplexer / demultiplexer 70 and the amplifier 51, and is down-converted to a predetermined frequency. The The down-converted analog signal is passed through the band limiting filter 53 to remove a predetermined unnecessary wave, and is input to the A / D converter 54 to be converted into a parallel digital signal. The converted parallel digital signal is converted into a serial digital signal by the transmission digital signal processing unit 55. The converted serial digital signal is converted into an optical signal by the optical transmitter 56 and transmitted to the master station device 1 side.

  The optical signal input to the master station device 1 is converted into a serial digital signal by each optical receiver 3 (3-1 to 3-16). The 16 serial digital signals thus converted are converted into parallel digital signals and digitally added by the received digital signal processing unit 4 for every four serial digital signals. The digitally added parallel digital signal is converted into an analog signal for each corresponding D / A converter 5. All (four) converted analog signals are synthesized by the synthesizer 6. The synthesized analog signal is converted into the frequency of the RF signal amplified by the frequency converter 9 after a predetermined unnecessary wave is removed through the band limiting filter 8. The converted analog signal is transmitted to the base station side via the multiplexer / demultiplexer 12.

  That is, in the present embodiment, the portion between the E / O conversion unit 158 of the slave station device 150 and the O / E conversion unit 107 of the parent station device 100 is digitized on the uplink in FIG. A digital signal is transmitted as an optical signal between the optical transmitter 56 and the optical receiver 3. Thereby, it is possible to simplify the apparatus by reducing the number of parts of the master station apparatus 1 for the uplink part.

  For the downlink, the RF signal input to the master station device 1 is down-converted to a predetermined frequency by the frequency converter 13 after passing through the multiplexer / demultiplexer 12. A predetermined unnecessary wave is removed through the band limiting filter 14 and then converted into a digital signal by the A / D converter 15. The A / D converter 15 is synchronized with the reference clock of the reference clock generator 16 together with the D / A converter 5, the received digital signal processor 4, the frequency converters 13 and 9, and the transmission digital signal processor 17. Works. The converted parallel digital signal is converted into a serial digital signal by a transmission digital signal processing unit 17 realized by an FPGA. The converted serial digital signal is input to the optical transmitter 18 and converted into an optical signal. At this time, the reference clock of the reference clock generator 16 is input to the optical transmitter 19 and converted into an optical signal. The WDM coupler 20 wavelength-multiplexes the optical signals input from the optical transmitter 18 and the optical transmitter 19 and outputs the optical signals to the optical distributor 21 as wavelength-multiplexed light obtained by wavelength-multiplexing the reference clock. The wavelength multiplexed light is distributed into 16 by the optical distributor 21 and transmitted to each of the 16 slave station devices 50-1 to 50-16 via the optical fiber Fb1.

  The clock wavelength multiplexed signal input to the slave station device 50 (50-1 to 50-16) is demultiplexed into an optical signal of a predetermined frequency and an optical signal of a reference clock by the WDM coupler 60. Each optical signal is converted into a digital signal by the optical receivers 61 and 62. The serial digital signal converted by the optical receiver 61 is converted into a parallel digital signal by a received digital signal processor 63 realized by an FPGA. The converted parallel digital signal is converted into a serial analog signal by the D / A converter 65. Then, after a predetermined unnecessary wave is removed by the band limiting filter 66, it is up-converted to the frequency of the RF signal by the frequency converter 67. Further, an RF signal is radiated from the antenna 71 via the band pass filter 68, the amplifier 69 and the multiplexer / demultiplexer 70. The reception digital signal processing unit 63, the D / A conversion unit 65, the frequency conversion units 67 and 52, the A / D conversion unit 54, and the transmission digital signal processing unit 55 are digital signals output from the optical reception unit 62. Operates in synchronization with the reference clock.

  By the way, the reception digital signal processing unit 4 (4-1 to 4-4) of the master station device 1 monitors the level of the digital signal (output of the optical reception unit 3) input from the slave station device 50 and is input. When the monitor values of the digital signal levels from all (four) slave station devices 50 are equal to or lower than the threshold level, the corresponding subsequent switches SW (SW-1 to SW-4) are opened. By opening the subsequent switches SW (SW-1 to SW-4), output of quantization noise and thermal noise from the D / A converter 4 is eliminated. This threshold level is preferably a signal level corresponding to the minimum reception sensitivity in the base station apparatus. As a result, the noise input to the combiner 6 in the master station device 1 can be reduced, and the CNR can be improved.

  Further, the received digital signal processing unit 4 (4-1 to 4-4) monitors the level of the input digital signal (output of the optical receiving unit 3), and the monitor value of the digital signal level is equal to or lower than the threshold level. In this case, the parallel digital data value of the digital signal may be output as zero (cut off). Thereby, noise reduction of the D / A converter 5 can be achieved.

  For example, as shown in FIG. 2, the reception digital signal processing unit 4-1 receives the digital signals input from the optical reception units 3-1 to 3-4 by the S / P conversion units 41-1 to 41-4, respectively. The digital signal converted into the parallel digital signal and added by the adder 42 is output to the D / A converter 5-1. Here, the level determination unit 43 monitors the level of the digital signal received by each of the S / P conversion units 41-1 to 41-4. If the level of all the digital signals is equal to or lower than the threshold level, the switch SW- 1 is opened so that the analog signal converted by the D / A converter 5-1 from the received digital signal processor 4-1 is not output to the synthesizer 6 side.

  The level determination unit 43 monitors the level of the digital signal received by each of the S / P conversion units 41-1 to 41-4. If there is a digital signal whose level is equal to or lower than the threshold level, an adder In 42, the parallel digital data value of this digital signal is set to zero and added. As a result, it is possible to reduce noise caused by a digital signal below the threshold level. When all the digital signals are below the threshold level, it is preferable to open the switch SW-1. This is because the noise caused by the D / A converter 5-1 can be reduced even if the parallel digital data values of all the digital signals are made zero.

  Further, as a modification, paying attention to the slave station device 50 side, the transmission digital signal processing unit 55 monitors the level of the digital signal input from the A / D conversion unit 54, and the monitor value of the digital signal level is equal to or less than the threshold level. In this case, it is transmitted to the master station device 1 side as a digital signal to which no-signal information (1 bit) is added. On the other hand, the received digital signal processing unit 4 of the master station device 1 monitors the presence / absence of information to be added (1 bit), and when the information is added, opens the switch SW or sets the parallel digital data value to zero. You may make it.

  For example, as shown in FIG. 3, the transmission digital signal processing unit 55 on the slave station device 50 side converts the digital signal from the A / D conversion unit 54 into a serial digital signal by the P / S conversion unit 81, and adds the addition unit. The digital signal to which the additional information is added is output to the optical transmitter 56 at 83. Here, when the monitor value of the digital signal level is equal to or lower than the threshold level, the level determination unit 82 sets and outputs the additional information (1 bit) indicating that the digital signal level is equal to or lower than the threshold level.

  On the other hand, as shown in FIG. 4, the reception digital signal processing unit 4-1 on the master station device 1 side has the same configuration as that in FIG. 2, but an addition determination unit 44 is provided instead of the level determination unit 43. The addition determination unit 44 monitors the additional information of the digital signal received by each of the S / P conversion units 41-1 to 41-4, and monitors whether or not all the additional information indicates a threshold level or less. If all the digital signals indicate a threshold level or less, the switch SW-1 is opened. Further, the addition determination unit 44 monitors the additional information of the digital signal received by each of the S / P conversion units 41-1 to 41-4, and if there is one that indicates a threshold level or less, parallel digital data of this digital signal The value is set to zero and added by the adder 42.

  Also in this modified example, quantization noise can be reduced, or noise in the D / A converter 5 can be reduced, and CNR can be improved. In addition, the load on the threshold level determination in the received digital signal processing unit 4 is reduced, and a quick determination process can be performed.

  The D / A conversion unit 5 has (N + logM / log2) bit resolution, but the D / A conversion processing can be performed at higher speed and higher resolution than the A / D conversion processing. Therefore, the transmission speed does not decrease.

  In the embodiment and the modification described above, the transmission digital signal processing unit 55 converts a parallel signal into a serial signal, and the reception digital signal processing unit 4 (4-1 to 4-4) converts the serial signal into a parallel signal. The conversion process is performed. However, if the A / D converter 54 corresponds to one output, it is not necessary to provide the transmission digital signal processor 55 only for the function of converting the parallel signal into the serial signal. Further, if the D / A conversion unit 5 corresponds to one input, the function of converting the serial signal into the parallel signal (S) among the functions of the reception digital signal processing unit 4 (4-1 to 4-4). / P parts 41-1 to 41-4) are not necessary.

  FIG. 5 is a schematic block diagram illustrating a configuration example of an optical transmission system according to another embodiment. The optical transmission system shown in FIG. 5 is different from the optical transmission system shown in FIG. 1 in that the master station device 1 and the slave station device 50 (50-1 to 50-I) are respectively connected to the master station device 1A and the slave station device 50A ( 50A-1 to 50A-I).

  The master station device 1A deletes the frequency converter 9 and the frequency converter 13 from the master station device 1, replaces the A / D converter 15 with the A / D converter 15A, and converts the D / A converter 5 (5- 1 to 5-K) is replaced with a D / A converter 5A (5A-1 to 5A-K). The slave station device 50A (50A-1 to 50A-I) deletes the frequency converters 52 and 67 and the band limiting filters 53 and 66 from the slave station device 50 (50-1 to 50-I), and performs A / D The conversion unit 54 is replaced with an A / D conversion unit 54A, and the D / A conversion unit 65 is replaced with a D / A conversion unit 65A.

  The A / D converters 15A and 54A and the D / A converters 5A (5A-1 to 5A-K) and 65A are both frequency converters by setting the sampling frequency to at least twice the bandwidth of the RF signal. Without analog conversion, an analog signal can be down-converted to a predetermined frequency or a digital signal can be up-converted to a predetermined RF frequency, so that the configuration can be simpler than that of the optical transmission system shown in FIG.

  In the above embodiment, the reception digital signal processing unit 4 includes a plurality of reception digital signal processing units 4-1 to 4 -K, and the D / A conversion unit 5 also includes a plurality of D / A conversion units 5. -1 to 5-K, the reception digital signal processing unit 4 is configured by one FPGA, and after parallel digital signal synthesis processing is performed inside this FPGA, one D / A conversion unit You may make it convert a digital signal into an analog signal. In this case, the synthesizer 6 may not be provided. In this case, only one switch SW may be provided on the output side of the D / A converter 5.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

1, 1A Master station device 3 (3-1 to 3-I) Optical receiving unit 4 (4-1 to 4-K) Reception digital signal processing unit 5, 5A D / A conversion unit 6 Synthesizer 8, 53 Band limitation Filter 9, 52 Frequency conversion unit 50 (50-1 to 50-I), 50A (50A-1 to 50A-I) Slave station device 41-1 to 41-4 S / P conversion unit 42 Addition unit 43, 82 levels Determination unit 44 Additional determination unit 54, 54A A / D conversion unit 55 Transmission digital signal processing unit 56 Optical transmission unit 81 P / S conversion unit 83 Additional unit SW (SW-1 to SW-K) switch

Claims (14)

In an optical transmission system in which a plurality of slave station devices are connected to one master station device by an optical fiber,
The upstream transmission unit of each slave station device
An A / D converter that converts a received RF signal input to the slave station device into a received digital electrical signal;
An optical transmitter that converts the received digital electrical signal into an optical signal and outputs the optical signal to the optical fiber;
With
The upstream receiving unit of the master station device is
The same number of optical receivers as the number of slave station devices that convert optical signals input from the slave station devices through the optical fiber into digital electrical signals;
A plurality of digital electrical signals output from the optical receiver, and a single or a plurality of received digital signal processors less than the number of the optical receivers for performing digital addition of each digital electrical signal; and
One or a plurality of D / A converters for converting the added digital electric signal output from each received digital signal processing unit into an added analog electric signal;
An optical transmission system comprising:   The optical transmission system according to claim 1, further comprising: a plurality of the D / A conversion units; and a combiner that combines the addition analog electric signals output from the D / A conversion units. The A / D converter includes a slave station upstream frequency converter that down-converts the frequency of the received RF signal input to the slave station device and converts the frequency into the received digital electrical signal,
And further comprising a master station upstream frequency converter for up-converting and outputting the addition analog electrical signal output from each D / A converter or the electrical signal output from the combiner to a transmission RF signal. The optical transmission system according to claim 1 or 2.   Each D / A converter converts the summed digital electrical signal into an RF summed analog electrical signal and outputs the result, and the combiner synthesizes the RF summed analog electrical signal output from each D / A converter. 3. The optical transmission system according to claim 2, wherein a transmission RF signal is output. The upstream receiving unit of the master station device is
A switch is provided on the output side of each D / A converter,
The received digital signal processor is
The signal level of the input digital electric signal is monitored, and when the level of all the digital electric signals is equal to or lower than a threshold value, the corresponding lower switch is opened. An optical transmission system according to any one of the above. The received digital signal processor is
The signal level of the input digital electric signal is monitored, and when the signal level is equal to or lower than a threshold value, the data value indicated by the digital electric signal is processed as zero. The optical transmission system described in 1. The upstream transmission unit of each slave station device
A transmission digital signal processing unit that adds and transmits additional information indicating whether or not the signal level of the received digital electrical signal is equal to or lower than a threshold value after the A / D conversion unit;
The upstream receiving unit of the master station device is
A switch is provided on the output side of each D / A converter,
The received digital signal processor is
5. The optical transmission system according to claim 1, wherein when the additional information of all the input digital electric signals indicates a threshold value or less, the corresponding lower switch is opened. . The received digital signal processor is
8. The optical transmission system according to claim 7, wherein when the additional information of the input digital electric signal indicates a threshold value or less, the data value indicated by the digital electric signal is processed as zero. In a master station device of an optical transmission system in which a plurality of slave station devices are connected by optical fibers,
The upstream receiver
The same number of optical receivers as the number of slave station devices that convert optical signals input from the slave station devices through the optical fiber into digital electrical signals;
A plurality of digital electrical signals output from the optical receiver, and a single or a plurality of received digital signal processors less than the number of the optical receivers for performing digital addition of each digital electrical signal; and
One or a plurality of D / A converters for converting the added digital electric signal output from each received digital signal processing unit into an added analog electric signal;
A master station apparatus comprising:   The master station apparatus according to claim 9, further comprising: a plurality of the D / A converters; and a synthesizer that synthesizes the added analog electric signals output from the D / A converters.   And further comprising a master station upstream frequency converter for up-converting and outputting the addition analog electrical signal output from each D / A converter or the electrical signal output from the combiner to a transmission RF signal. The master station device according to claim 9 or 10.   Each D / A converter converts the summed digital electrical signal into an RF summed analog electrical signal and outputs the result, and the combiner synthesizes the RF summed analog electrical signal output from each D / A converter. The master station apparatus according to claim 10, wherein a transmission RF signal is output. In a slave station device of an optical transmission system connected to one master station device by an optical fiber,
The upstream transmission unit
An A / D converter that down-converts the frequency of the input received RF signal and converts it to a received digital electrical signal;
An optical transmitter that converts the received digital electrical signal into an optical signal and outputs the optical signal to the optical fiber;
A slave station device comprising:   The A / D converter includes a slave station upstream frequency converter that down-converts the frequency of the received RF signal input to the slave station device and converts the frequency into a received digital electrical signal. The slave station device described.

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