JP2006304095A - Optical fiber radio apparatus, signal processing method thereof, and slave apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber radio apparatus capable of preventing transmission of spurious signals even when a transmission error occurs in a transmission signal, a signal processing method thereof, and a slave apparatus .
An ROF device (1) includes a parent device (2), a child device (3), and an optical fiber cable (4), and decodes a correction encoded digital signal received from the O / E unit (31) and the parent device into a digital encoded signal. An error processing unit 32, a D / A conversion unit 33, a frequency conversion unit 34 for outputting a transmission signal of a carrier frequency, a transmission amplifier 35, an antenna 36, a variable attenuator 38 inserted and connected to the input of the transmission amplifier 35, and an error processing unit A control unit 37 that controls to prevent spurious transmission when a transmission error occurs by receiving an alarm and outputting an output limiting signal for controlling the output of the transmission amplifier 35 to the variable attenuator 38 when error correction cannot be performed from the control unit 32; Is provided.
[Selection] Figure 1

Description

  The present invention relates to an optical fiber radio apparatus connected to a mobile phone base station and a signal processing method thereof.

  Many mobile phone base stations are installed with a cover area radius of 1 to 3 km, but as the number of terminals increases with the spread of mobile phones, the cover area is a small base station with a small output transmitter called a microcell Has been introduced. This small base station does not have an exchange function, traffic control, or the like, and is a head-end radio device installed in association with a normal mobile phone base station or a center device (for example, a patent) Literature 1.).

  Such a small base station that transmits and receives radio signals by transmitting and receiving radio signals to and from a mobile phone base station is called an optical fiber radio apparatus (hereinafter referred to as ROF apparatus), and the radio apparatus can be small. There are features. For this reason, it is installed in many places in downtown areas where buildings cannot communicate with the base station, or in busy areas where access frequently occurs, or the coverage area of mobile phone base stations is spot-like in rural villages far from the urban area. (For example, patent document 1).

  However, since this small base station modulates the optical intensity of the carrier signal of the transmission radio wave transmitted from the antenna as it is, there is a merit that it can be reduced in size, but there is a variation in attenuation etc. in the optical fiber cable that is the transmission path The transmission output varies according to the attenuation variation.

  In order to prevent the influence of fluctuations in the transmission path, the IF signal of the radio wave transmitted and received from the antenna is converted into a digitally encoded optical signal between the base station and the small base station and transmitted via an optical fiber cable. The method is adopted.

  FIG. 3 is a functional block diagram illustrating the configuration of the transmission system of the conventional ROF device 100. In FIG. 3, the transmission system of the conventional ROF device includes a master device 20, a slave device 30, and an optical fiber cable 70 installed in the mobile phone base station 10. The optical fiber cable 70 transmits an optical signal by connecting between an E / 0 unit 240 of the parent device 20 described later and an O / E unit 310 of the child device 30.

  The parent device 20 includes a frequency converter 210 that converts an IF signal (transmission signal) of a transmission radio wave output from the mobile phone base station 10 into a baseband signal, and A / D (analog-digital) conversion of the baseband signal. An A / D converter 220 that outputs a digitally encoded signal, a correction encoder 230 that receives the digitally encoded signal and performs error correction encoding, and an electro-optical conversion of the corrected encoded signal And an E / O unit 240 for outputting an optical signal.

  The slave device 30 demodulates the optical signal input from the optical fiber cable 70 into an optical-electrical signal and outputs it, and the digital signal based on the correction encoded digital signal input from the O / E unit 310. An error processing unit 320 that decodes an encoded signal, a D / A converter 330 that outputs a digitally encoded signal as a baseband signal, and a frequency converter 340 that receives the baseband signal and converts it into a transmission signal having a predetermined carrier frequency. And a transmission amplifier 350 that inputs a transmission signal and transmits it through the antenna 360.

In such an ROF device, the frequency of a transmission radio wave is high, and a digital encoded signal transmitted after being converted into an optical signal has a speed of several tens of Gbps or more. And since the optical fiber cable is resistant to EMI failure, transmission errors are less likely to occur, and the allowable size and device cost of a small base station are limited, error correction capability can be achieved even if correction coding is performed. It can be kept low. Therefore, when an electronic circuit part such as an A / D converter has an error in the upper bits of a digitally encoded signal due to power supply failure or induced noise due to noise, the radio wave at the time of high output becomes unexpectedly large. There is a problem that spurious noise exceeding an allowable level occurs.
Japanese Unexamined Patent Publication No. 2004-229180 (page 12, FIG. 1)

  The conventional ROF apparatus has a problem in that the transmission radio wave becomes a large output due to a transmission signal transmission error, and the spurious output exceeds an allowable level.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an ROF device and a signal processing method that prevent spurious signals from occurring even if a transmission error occurs in a transmission signal.

  In order to achieve the above object, an optical fiber radio apparatus of the present invention receives an IF signal of a transmission radio wave from a mobile phone base station, and converts the input IF signal into an optical signal of a correction encoded digital signal. An optical fiber radio apparatus comprising: a parent apparatus that transmits data via an optical fiber cable; and a slave apparatus that converts the optical signal received via the optical fiber cable into the transmission radio wave having a predetermined frequency and transmits the signal from an antenna. The slave device includes: an O / E unit that demodulates and outputs an optical signal received from the optical fiber cable into a correction encoded digital signal of an electrical signal; and a correction encoded digital input from the O / E unit An error processing unit for decoding a signal into a normal digital encoded signal, a D / A converter for outputting the digital encoded signal as a baseband signal, and the baseband A frequency converter that receives a signal and converts the signal into a transmission signal having a predetermined carrier frequency and outputs the transmission signal; a transmission amplifier that transmits the output transmission signal as a transmission radio wave having a predetermined output; The variable attenuator connected to the input or output, and the variable output limit signal for receiving the alarm output when the error processing unit detects an error and limiting the output of the transmission radio wave transmitted from the antenna And a controller for outputting to the attenuator.

  Also, the signal processing method of the optical fiber radio apparatus according to the present invention receives an IF signal of a transmission radio wave from a mobile phone base station, converts the input IF signal into an optical signal of a correction encoded digital signal, A signal of an optical fiber radio device comprising a parent device that transmits via a fiber cable and a slave device that converts the optical signal received via the optical fiber cable into the transmission radio wave of a predetermined frequency and transmits it from an antenna In the processing method, the slave device includes an O / E unit, an error processing unit, a D / A conversion unit, a frequency conversion unit, a transmission amplifier, a variable attenuator, and a control unit. The E unit demodulates and outputs the optical signal received from the optical fiber cable into a correction encoded digital signal of an electrical signal, and the error processing unit receives the correction encoded digital signal input from the O / E unit. Decodes into a normal digitally encoded signal and outputs it to the D / A converter, and outputs an alarm to the controller when an error is detected in the input corrected encoded digital signal, and the D / A converter The unit converts the input digitally encoded signal as a baseband signal and outputs the baseband signal to the frequency converter, and the frequency converter converts the baseband signal input from the D / A converter to a predetermined carrier. The transmission amplifier converts the signal into a frequency transmission signal and outputs it, and the transmission amplifier inputs the transmission signal via the variable attenuator and transmits it as a transmission wave of a required output from the antenna, or the frequency conversion unit The transmitting signal is transmitted from the antenna through the variable attenuator, and the control unit receives an alarm from the error processing unit. If, and outputs an output limit signal for limiting the output of the transmission radio wave transmitted from the antenna to the variable attenuator.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a case where a transmission error generate | occur | produces in a transmission signal, the optical fiber radio | wireless (ROF) apparatus which can prevent that a spurious is transmitted, and its signal processing method can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a functional configuration of an optical fiber radio apparatus (hereinafter referred to as ROF apparatus) according to an embodiment of the present invention.

  In FIG. 1, the transmission system (downlink) of the ROF device 1 according to the embodiment of the present invention includes a parent device 2, a child device 3, and an optical fiber cable 4 installed in a mobile phone base station 10.

  The optical fiber cable 4 transmits an optical signal by connecting between an E / 0 unit 24 of the parent device 2 described later and an O / E unit 310 of the child device 3.

  The parent device 2 includes a frequency conversion unit 21 that converts the IF signal of the transmission radio wave output from the mobile phone base station 1 into a baseband signal, and an A / D conversion unit that converts the baseband signal into a digital encoded signal and outputs it. 22. A digitally encoded signal is input, error correction encoding is performed, and an error correction code or a digital signal is output as a correction encoding unit 23; and an optical signal obtained by electro-optically converting the correction encoded digital signal is optical fiber And an E / O unit 24 that outputs to the cable 4.

  The correction encoding unit 23 uses, for example, an encoding method capable of self-error correction such as a Viterbi code, and the correction capability such as the number of error bits that can be corrected is paired with the error processing unit 32 of the child device 3. Is set.

  An O / E unit 31 that demodulates and outputs an optical signal input from the optical fiber cable 4 to a correction encoded digital signal of an electric signal, and error detection and correction of the correction encoded digital signal input from the O / E unit 31 , And an error processing unit 32 that performs processing for decoding into a normal digital encoded signal, a D / A conversion unit 33 that outputs the digital encoded signal as a baseband signal, and transmission of a predetermined carrier frequency when the baseband signal is input A frequency conversion unit 34 that converts the signal into a signal and outputs the signal and a transmission amplifier 35 that receives the transmission signal and transmits the signal via the antenna 36 are provided.

  In the slave device 3, in addition to the conventional ROF device, the variable attenuator 38 is inserted and connected to the input of the transmission amplifier 35, receives an alarm from the error processing unit 32, and controls the output of the transmission amplifier 35. A control unit 37 for outputting a signal to the variable attenuator 38 is added. Although not shown, the error processing unit 32 includes an error detection unit that outputs an alarm to the control unit 37 when an error is detected, and a decoding unit that corrects and decodes the error into a normal digital encoded signal.

  The above is the configuration of both devices related to the downlink, but for the uplink, the configuration in the downlink is the same in the reverse direction, so the details of the configuration and operation are easy to guess. Description is omitted.

FIG. 2 is a flowchart for explaining a downlink operation procedure in the child device 3 of the ROF device 1 according to the embodiment of the present invention.
Hereinafter, the operation procedure of the child device 3 will be described with reference to the flowcharts of FIGS. 1 and 2.
Here, it is assumed that correction coding is performed so that a discrete error of up to 3 bits can be detected and corrected. When the error processing unit 32 of the slave device 3 decodes the error correction encoded digital signal transmitted from the parent device 3 into a normal digital encoded signal, the error processing unit 32 detects an error in a predetermined processing procedure of correction encoding (step s1). If the detection error is an error of up to 3 bits or no error is detected (Yes in step s2), the correction code is removed and a digitally encoded signal with error correction is output (step s3).

  If an error of 3 bits or more occurs and the error can be detected but cannot be corrected (No in step s2), the error processing unit 32 outputs a digital encoded signal that is not corrected (step s4). At the same time, an alarm for notifying that there is an uncorrectable error in the output digital encoded signal is transmitted to the control unit 37 (step s5).

  In addition, some other criteria may be provided as the alarm output criteria. For example, an error is output to the control unit 37 every time an error is detected regardless of whether or not the error detection means of the error processing unit 32 can correct the error, and the control unit 37 generates an output restriction signal from the error occurrence pattern. Output. The control unit 37 that has received the alarm outputs an output limit signal to the variable attenuator 38 (step s6), and controls so that the transmission signal is not input to the transmission amplifier 35 or the output is suppressed by limiting the input level. To do.

  Error detection is performed on a frame-by-frame basis. For example, the alarm presence / absence is counted in blocks every 10 msec, and transmission output is stopped when there are two consecutive errors in the block. May be. With this method, burst errors that occur sporadically and generate a large amount of errors can be avoided by stopping transmission due to burst errors, compared to the case where transmission output control is simply performed based on the number of detected errors. As for the occurrence of an error with a low frequency such as burst noise due to, there is an effect that continuous transmission can be secured without stopping transmission.

  There are several methods for returning to normal operation after the alarm is not generated. For example, the control unit 37 monitors an alarm from the error processing unit 32 at a predetermined timing by referring to a timer (not shown). If the alarm signal is not input even after a predetermined time has elapsed (step s7 is Yes), the output restriction signal is canceled (step s8). Then, the transmission amplifier 35 starts again the operation of transmitting normal transmission radio waves from the antenna.

  The method of returning after the elapse of time can prevent frequent switching operation between transmission stop and transmission. For example, after switching to transmission stop due to an alarm, the error occurrence is counted at a block interval of 50 msec, and transmission is resumed if no alarm is generated twice or three times in succession. Alternatively, transmission is resumed if no alarm is generated four times at a block interval of 10 msec. In this method, for example, thunderclouds move away, frequent errors do not occur, the operation is stabilized, and transmission is resumed, so that stable communication can be ensured.

  With regard to the switching criteria related to transmission stop and transmission restart, the frequency of alarm occurrence (detection) is lower than when stopping transmission by increasing the block interval time or increasing the number of repetitions as described above. If transmission is resumed after that, a more stable switching operation is possible than when switching is performed under the same frequency condition.

  In addition, the output of the transmitter is limited so that the output level is suppressed to a low level instead of stopping (zeroing) the output when an error occurs, and compared to before stopping (or before suppressing), for example, −15 db , −10 db, −3 db, etc., may be used to restore the output level sequentially, and this method has an effect of preventing signal interruption and continuing communication.

  As another method, for example, when the error processing unit 32 detects, for example, a detected error number of 4 bits but an uncorrectable number of errors, a level 1 error is detected. Alarms are leveled and output as worse level 2, which cannot be corrected by continuous or burst errors. Then, the control unit 37 outputs the output limit signal to the variable attenuator 38 according to the level, thereby adjusting the input level of the transmission amplifier 35 and stopping the output of the transmission signal, or at a predetermined output level. It may be suppressed.

  With the above alarm processing method, even if there is a possibility that a transmission error occurs and spurious is generated, the transmission of the radio wave from the transmission amplifier 35 is stopped or the output level is suppressed after the error occurs. It is possible to fit in.

  In the above description, the variable attenuator 38 is inserted and connected to the input of the transmission amplifier 35. However, the variable attenuator 38 may be connected to the output side of the transmission amplifier 35. The variable attenuator 38 may be inserted between the D / A converter 33 and the frequency converter 34 to limit the output from the transmission amplifier 35. Alternatively, the output restriction signal may be input to an adjustment terminal (not shown) of the D / A converter 33 to adjust the output level of the D / A converter 33. Further, the output restriction signal may be input to an adjustment terminal (not shown) of the transmission amplifier 35 to adjust the transmission output level from the transmission amplifier 35 or to cut off the transmission.

  As described above, in the optical fiber radio (ROF) apparatus according to the present invention, even if a transmission error occurs in the transmission signal, the output of the transmission radio wave can be kept low, so that spurious transmission is prevented. Is possible.

The block diagram explaining the functional structure of the optical fiber radio | wireless apparatus concerning the Example of this invention. The flowchart explaining the operation | movement procedure of the subunit | mobile_unit of the optical fiber radio | wireless apparatus concerning the Example of this invention. The block diagram explaining the functional structure of the conventional optical fiber radio | wireless apparatus.

Explanation of symbols

1 Cellular phone base station 2 Master device 21 Frequency converter 22 A / D converter 23 Correction coding unit 24 E / O unit 3 Slave device 31 O / E unit 32 Error processing unit 33 D / A converter 34 Frequency converter 35 Transmitting Amplifier 36 Antenna 37 Control Unit 38 Variable Attenuator

Claims (16)

A parent device that receives an IF signal of a transmission radio wave from a mobile phone base station, converts the input IF signal into an optical signal of a correction encoded digital signal, and transmits the optical signal via an optical fiber cable; and the optical fiber cable In an optical fiber radio apparatus comprising a slave apparatus that converts the optical signal received via the antenna into the transmission radio wave of a predetermined frequency and transmits it from an antenna,
The child device is
An O / E unit that demodulates and outputs an optical signal received from the optical fiber cable into a correction-encoded digital signal of an electrical signal;
An error processing unit that detects an error in the correction-encoded digital signal input from the O / E unit and decodes the error into a normal digital-encoded signal;
A D / A converter that outputs the digitally encoded signal as a baseband signal;
A frequency converter that receives the baseband signal, converts it into a transmission signal having a predetermined carrier frequency, and outputs the transmission signal;
A transmission amplifier for transmitting the output transmission signal as a predetermined output transmission radio wave from an antenna;
A variable attenuator connected to the input or output of the transmission amplifier;
A control unit that receives an alarm that is output when the error processing unit detects an error and outputs an output limiting signal that limits an output of a transmission radio wave transmitted from the antenna to the variable attenuator. An optical fiber wireless device.   The optical fiber radio apparatus according to claim 1, wherein the alarm signal is leveled in accordance with the magnitude of the detected error.   2. The optical fiber radio apparatus according to claim 1, wherein when the control unit receives the alarm, the output control signal cuts the transmission output or reduces the output to a predetermined level. 3.   3. The control unit according to claim 2, wherein when the alarm is received, the output control signal cuts the transmission output or reduces the transmission output to a predetermined level in response to the level of the alarm. Fiber optic radio equipment. The output control signal is
2. The optical fiber radio according to claim 1, wherein instead of the variable attenuator, the optical fiber radio is input to an adjustment terminal included in the A / D conversion unit or the transmission amplifier, and the output of the transmission radio wave is limited. apparatus. The controller is
The alarm is monitored at a predetermined time interval, and when the alarm is received exceeding a predetermined frequency, the output control signal cuts off the transmission output or reduces it to a predetermined level. The optical fiber radio apparatus according to 1. The controller is
While the error is detected and the output of the transmission radio wave is limited, the alarm is monitored at a predetermined time interval, and when the alarm is received at a predetermined frequency or less, the output control signal performs the transmission. The optical fiber radio apparatus according to claim 1, wherein the optical fiber radio apparatus is resumed or returned to a predetermined level. The controller is
The alarm is monitored at a predetermined time interval, and when the alarm is received over a predetermined frequency, the output control signal cuts the transmission output or reduces it to a predetermined level,
The output is monitored when the alarm is monitored at a second predetermined time interval while the output of the transmission radio wave is limited and the alarm is received at a second frequency lower than the first frequency. The optical fiber radio apparatus according to claim 1, wherein the control signal restarts the transmission or returns the transmission to a predetermined level. A parent device that receives an IF signal of a transmission radio wave from a mobile phone base station, converts the input IF signal into an optical signal of a correction encoded digital signal, and transmits the optical signal via an optical fiber cable; and the optical fiber cable In a signal processing method of an optical fiber radio device comprising a slave device that converts the optical signal received via the antenna into the transmission radio wave of a predetermined frequency and transmits it from an antenna,
The slave device includes an O / E unit, an error processing unit, a D / A conversion unit, a frequency conversion unit, a transmission amplifier, a variable attenuator, and a control unit,
The O / E unit demodulates and outputs an optical signal received from the optical fiber cable into a correction-encoded digital signal of an electrical signal,
The error processing unit decodes the corrected encoded digital signal input from the O / E unit into a normal digital encoded signal, outputs the decoded digital signal to the D / A converter, and the input corrected encoded digital signal When an error is detected in the signal, an alarm is output to the control unit,
The D / A conversion unit converts the input digital encoded signal into a baseband signal and outputs the baseband signal to the frequency conversion unit,
The frequency conversion unit converts the baseband signal input from the D / A conversion unit into a transmission signal having a predetermined carrier frequency, and outputs the transmission signal.
The transmission amplifier inputs the transmission signal via the variable attenuator and transmits it from an antenna as a required output transmission radio wave, or inputs the transmission signal from the frequency converter and amplifies it Transmit the transmission radio wave to be output from the antenna via the variable attenuator,
When the control unit receives an alarm from the error processing unit, the control unit outputs to the variable attenuator an output limiting signal that limits an output of a transmission radio wave transmitted from the antenna. Signal processing method.   The signal processing method of the optical fiber radio apparatus according to claim 9, wherein the alarm signal is leveled corresponding to the magnitude of the detected error.   The signal processing of the optical fiber radio apparatus according to claim 9, wherein when the control unit receives the alarm, the output control signal cuts the transmission output or reduces the transmission output to a predetermined level. Method.   11. The control unit according to claim 10, wherein when the alarm is received, the output control signal cuts the transmission output or lowers the transmission output to a predetermined level corresponding to the level of the alarm. Signal processing method for optical fiber radio equipment. The output control signal is
10. The optical fiber radio according to claim 9, wherein instead of the variable attenuator, the optical fiber radio is input to an adjustment terminal included in the A / D conversion unit or the transmission amplifier, and the output of the transmission radio wave is limited. Device signal processing method. The controller is
The alarm is monitored at a predetermined time interval, and when the alarm is received exceeding a predetermined frequency, the output control signal cuts off the transmission output or reduces it to a predetermined level. The signal processing method of the optical fiber radio | wireless apparatus of Claim 9. The controller is
While the error is detected and the output of the transmission radio wave is limited, the alarm is monitored at a predetermined time interval, and when the alarm is received at a predetermined frequency or less, the output control signal performs the transmission. The signal processing method of the optical fiber radio apparatus according to claim 9, wherein the signal processing is resumed or returned to a predetermined level. The controller is
The alarm is monitored at a predetermined time interval, and when the alarm is received over a predetermined frequency, the output control signal cuts the transmission output or reduces it to a predetermined level,
The output is monitored when the alarm is monitored at a second predetermined time interval while the output of the transmission radio wave is limited and the alarm is received at a second frequency lower than the first frequency. The signal processing method of the optical fiber radio apparatus according to claim 9, wherein the control signal restarts the transmission or returns the transmission to a predetermined level.

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