JP2005057651A - Method for monitoring quality of optical digital transmission and radio base station apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly reliably monitor the quality of optical digital transmission in a radio base station apparatus. <P>SOLUTION: A radio base station apparatus in which an RRH part for performing at least radio amplification and a base station corresponding part for performing at least call processing and inputting/outputting a digital radio signal are constituted as different bodies and both parts are connected by digital optical transmission is provided with a format converting part for adding an inspection signal for measuring communication quality to the digital radio signal to perform a format conversion so as to be adapted for the digital optical transmission, an E/O converting part for applying an electro-optic conversion to an electrical signal being an output of the format converting and outputting the result signal to an optical transmission path, an O/E converting part for applying an optical-electric signal conversion to an output of the optical transmission path, a communication quality measuring means for measuring the communication quality of a signal outputted from the O/E converting part, and a control part for performing a report to a host monitoring device or interrupting an optical transmission system on the basis of the measurement result of the communication quality measuring means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an optical digital transmission quality monitoring method and a radio base station apparatus, and more particularly to an optical digital transmission quality monitoring method and a radio base station apparatus for separately configuring a radio amplifying unit and a call processing unit.

FIG. 5 is a configuration diagram of a general base station apparatus for digital mobile communication. As shown in FIG. 5, the base station apparatus normally incorporates a high-power amplifier (hereinafter referred to as PA) that amplifies a radio frequency signal for transmission in order to cover the entire area, and is configured integrally as a base station apparatus. . The PA and the antenna are connected by a coaxial cable. However, in consideration of maintainability, the base station apparatus may not be provided directly under the antenna, and the antenna and the PA may be separated by 50 m to 200 m. Loss and signal quality degradation become a problem.
In addition, since it is difficult to extend over 200 m, the base station apparatus is generally arranged for each accommodation area (cell), and there is a problem that base stations are distributed in various places, and maintenance and operation costs increase.

In order to solve these problems, the concepts of RRH (Remote Radio Head) and ROF (Radio On Fiber) were created. This is intended to solve the above problem by disconnecting a radio part close to an antenna from a base station and connecting both with an optical fiber or a coaxial cable that transmits a radio signal converted into an intermediate frequency (for example, a patent). Reference 1). In particular, when using existing equipment, the initial cost can be reduced and the operating cost can be reduced. It is not a large-scale base station but only a relatively small radio part that is distributed to various places. Therefore, it is a preferable form for maintenance.

Regarding the reliability when using optical fiber in the transmission line, a transmission level monitor can be installed in the optical fiber transceiver, and if the laser diode on the transmission side fails, it can be detected independently, and if it is It is also possible to construct a duplex system with a single optical fiber using wavelength multiplexing technology. Therefore, the reliability and economic efficiency of digital optical transmission itself in recent years have been improved.

Japanese Patent Laid-Open No. 2003-23396

However, since the above-described conventional technique is configured to monitor the transmitted and received light levels, there is a problem in that subtle deterioration in the optical transmission section cannot be detected. If the laser diode provided on the transmission side of the optical transmission does not go to the level where transmission is interrupted due to aging and temperature changes, or if a problem occurs in the optical fiber (for example, road construction) Etc., and the vibration itself deteriorates the optical transmission quality, or the gap between the optical fiber connectors increases due to the vibration, and the light level decreases). The detection accuracy was rough and could not be detected. In this case, in the worst case, an unnecessary radio wave that interferes with the radio wave law is emitted from the PA located at the last stage due to a signal error in the transmission path, which is a serious problem.

In view of the above problems, an object of the present invention is to disclose an optical digital transmission quality monitoring method and a radio base station apparatus capable of monitoring quality with high reliability.

An optical digital transmission quality used for at least a part of a section in which at least an RRH unit that performs radio amplification and at least a base station equivalent unit that performs call processing are configured separately, and the RRH unit and the base station equivalent unit are connected to each other A monitoring method is characterized in that the communication quality of a digital optical transmission section is monitored, and when the communication quality is lower than a predetermined quality, a report is made to a host device or the digital optical transmission is cut off. This is a quality monitoring method for optical digital transmission.

For the purpose of digital radio communication, at least an RRH unit that performs radio amplification and a base station equivalent unit that performs at least call processing and inputs and outputs digital radio signals are configured separately, and the RRH unit and the base station equivalent unit A radio base station apparatus that uses digital optical transmission in at least a part of a section to be connected, and adds a test signal for measuring communication quality to the digital radio signal and converts the format so as to be compatible with the digital optical transmission A format conversion unit that performs electrical-optical conversion of an electrical signal output from the format conversion unit and outputs the converted signal to an optical transmission line, and an O that performs optical-electrical signal conversion on the output of the optical transmission line. / E converter, communication quality measuring means for measuring communication quality for the signal output from the O / E converter, and based on the measurement result of the communication quality measuring means, Report of the apparatus, or a radio base station apparatus characterized by comprising a control unit for performing blocking of the optical transmission system.

Further, the communication quality measuring means detects a bit error rate by comparing the received check signal with a known signal or detects an error by comparing with a code generated by a cyclic redundancy check method. It is a radio base station apparatus.

According to the optical digital transmission quality monitoring method and the radio base station apparatus of the present invention, the optical digital transmission quality can be monitored with high reliability.

Hereinafter, the present invention will be described by way of examples. However, the following examples do not limit the claimed invention, and all combinations of features described in the examples serve as means for solving the invention. It is not always essential.

FIG. 1 is a configuration diagram of a radio base station apparatus according to the present embodiment. FIG. 1 shows a part of the present invention in a base station configuration when a single optical conversion unit is used (a) and when a redundant configuration or a diversity configuration is realized using a plurality of optical conversion units (b). Show. Reference numeral 11 denotes a base station equivalent device that performs call processing and the like, and corresponds to a base station device of FIG. 5 excluding the wireless unit and the PA. In this description, call processing includes all processing necessary for one base station apparatus to accommodate a slave station, and is representative processing of the base station apparatus. Reference numeral 12 denotes a digital optical I / F unit that exchanges radio signals to be transmitted and received with the base station equivalent device 11 in the form of digital radio signals (IQ signals) and converts between digital radio signals and optical signals. A single mode optical fiber 13 transmits an optical signal at 2.48832 Gbps. Reference numeral 14 denotes a digital optical I / F unit that converts an optical signal into a digital wireless signal, and has the same configuration as 12. 15 performs D / A conversion of the digital radio signal for each carrier on the downlink (base station to mobile station) line, performs conversion to radio frequency, band limitation, synthesis for each sector (antenna), amplification, etc. The uplink is a radio unit that performs reception amplification, band division for each carrier, band limitation, A / D conversion, quadrature detection, and the like. Reference numeral 16 denotes a PA that performs power amplification of a transmission signal. Reference numeral 17 denotes an optical demultiplexing unit for multiplexing and transmitting optical signals of different wavelengths on one optical fiber. In this embodiment, a baseband signal is assumed as the digital radio signal, but an intermediate frequency signal may be used. Further, 14, 15, 16 and, in some cases, including 17 are referred to as an RRH unit. The RRH section is installed near the antenna, for example, directly below or on the antenna tower.

FIG. 2 is a block diagram of the digital optical I / F unit 12 to which the present invention is applied. In FIG. 2, the left to right direction in the figure is assumed to be a downlink, and the right to left direction is assumed to be an uplink. This directionality does not determine the present invention. The format conversion unit 121 converts the digital radio signal (baseband signal) obtained from the base station equivalent apparatus 11 into a later-described optical transmission format for the downlink. At this time, an inspection signal capable of measuring transmission quality is supplied from the inspection signal generator 122. Transmission quality includes Bit-Error-Rate (bit error rate) and Frame-Error-Rate (error rate of a group of frames), and check signals include error detection codes and parity check bits (1,0). In order to equalize the occurrence probability of the signal, an intentionally inserted (1,0 signal) may be considered. Reference numeral 123 denotes an E / O unit that performs electrical / optical conversion, and is usually composed of a laser diode and a photodiode that monitors its optical output. An O / E unit 124 performs optical / electrical conversion. 123 and 124 may be integrally formed, and monitoring similar to the conventional case may be used in combination based on the monitored light output. Reference numeral 125 denotes a format converter that performs format conversion reverse to that of 121, and outputs a digital wireless signal and an inspection signal inserted on the optical transmission side.

FIG. 3 shows an optical transmission format. In FIG. 3, cdma2000 is taken as an example of digital mobile communication. In this description, a chip is a minimum unit of time interval spread by a spreading code in the CDMA system, and one chip is a reciprocal of 1.2288 MHz. In the format of FIG. 3, 20 msec is set as one cycle according to the radio frame, and a K28.7 code in 8B10B encoding is inserted as a frame recognition signal at the head of the one frame. Subsequent D1 and D2 are data of the first chip and the second chip, and each has 199 bytes. The following AGC (4 bytes) indicates a control signal for Automatic Gain Control necessary for transmission / reception of a radio signal. Used to control. The subsequent control (2 bytes) is a signal used for monitoring control of the apparatus. Such a two-chip section is thereafter repeated for one frame (for example, 24576 chips), but K28.5 is inserted as a chip alignment signal between the two-chip sections so as to divide the section. This format is 8B10B encoded when optically transmitted. This code assigns 8-bit data to a 10-bit code so that the DC component is reduced for serial communication. In addition to the 8-bit data, a special code such as K28.7 can be transmitted. And can be easily identified.

A baseband (IQ) signal (192 bytes) and a 7-byte inspection signal are inserted for each chip in the two-chip section divided by the K28.5 code. In the example of FIG. 3, a case is shown in which three sectors (in mobile communication, referred to as a sector when the area managed by the base station is divided) and 16 carrier signals are provided per sector. One data, for example, F1_I is 2 bytes (16 bits), but is used as a sampling rate of 1 chip and a signal width of 16 bits for the downlink, and as a sampling rate of 0.5 chips and a signal width of 8 bits for the uplink. The configuration is almost common between upstream and downstream.

The quality measuring unit 126 detects an error based on the frame timing by using, for example, a known fixed code between transmitters and receivers or a code having an error detection capability generated by a known method for the inspection signal. The result of the quality measuring means 126 is output to the control unit (not shown, but at least a part of the control unit is provided on the RRH unit side for evaluating the quality of the downlink), and is preset by the control unit. When a certain threshold value, for example, the error rate becomes worse than 10-12, it reports quality degradation to the host monitoring device, and when it is determined that the function as a base station device is affected, The optical transmission system is stopped. Thereby, wireless transmission from the base station apparatus is stopped. Alternatively, a control signal for stopping wireless transmission may be sent from the control unit to the wireless unit 15 or PA 16 without stopping the optical transmission system.
In addition, in the redundant configuration of FIG. 1B, it is possible to avoid the system down by mounting the blocked optical transmission data on another optical transmission device and dealing with the malfunction of the optical device. Is possible. When the optical fiber itself becomes NG, the system is simply stopped.

In the case of the prior art, the bit level error may not be detected because it depends on the light amount monitor of the optical transmission path. For example, when optical transmission of 10-12 is performed, for example, where a received light amount of -20 dBm is originally required, the level decreases by 4 dB due to aging of the laser diode on the transmitting side, temperature change, or external factors, and -24 dBm. Suppose that Since the light amount monitor generally monitors the light amount only with rough accuracy such as 3 dB and 5 dB, the 5 dB step light amount monitor sometimes cannot detect the level decrease.
The importance of error detection at this time will be discussed below.

Although there are several standards for optical digital transmission, generally, data transmission with a low error rate compared to wireless transmission, such as an error rate of 10-12 and 10-10, is the mainstream. FIG. 4 shows the error rate theoretical value versus required S / N of typical ASK (also referred to as Amplitude Shift Keying or On-Off Keying) in digital optical transmission. According to FIG. 4, S / N = 14 dB is required to achieve an error rate of 10-12. Now, suppose that the quality has been achieved, the light intensity has been reduced by 4 dB due to the malfunction of the transmitting laser diode, and the S / N has deteriorated by 4 dB. In the 5 dB step light intensity monitor, the light intensity is not considered to have changed. As shown in FIG. 4, when the level is lowered by 4 dB, the error rate deteriorates to 4 × 10 −6. Since 2.48832Gbps is assumed as the bit rate of the optical transmission section,
2.48832 × 109 × 4 × 10−6 = 9953.28
That is, an error of about 10,000 bits occurs per second. If 10,000 bits are evenly generated in one second, it corresponds to the error of one bit in about 100 μsec. Since the chip rate of cdma2000 is 1.2288 MHz, about 81.3 μsec corresponds to one chip. It is clear that the occurrence of an error once every 100 μsec has a serious influence on a wireless system that performs communication in units of 81.3 μsec, and naturally becomes a problem as a system. In the present invention, since the optical communication quality is constantly monitored with high accuracy, it can be avoided without falling into such a state.

In this embodiment, the error correction code (FEC) is not particularly mentioned. However, if BER is about 10-12, the influence on the baseband signals (D1, D2, etc.) can be almost ignored, and the AGC and the control signal are not affected. The reliability is improved by confirming majority processing or complete match on the transmission side by sending a plurality (for example, three) of the same data on the transmission side. In rare cases, when the frame recognition signal and the chip alignment signal cannot be detected due to a bit error, the data is discarded in units of frames or two chips. Frame retransmission control is not performed. Also, regarding the baseband signal, narrowband band limitation is appropriately performed after D / A conversion in the downlink, so that the out-of-band transmission level can be suppressed to the range of the Radio Law even if the BER is slightly deteriorated.

It is needless to say that the FEC and the present invention are independent technologies, and the present invention can be easily applied to a system equipped with the FEC, thereby further improving the reliability. When FEC is used together, almost error-free can be realized in a slight error rate environment, for example, BER = 10−4. However, since the error occurrence probability of the optical transmission line cannot be specified, it is not completely error-free. Considering the possibility that an unpredictable state may occur during operation assuming compliance with the Radio Law, all FEC The quality status monitoring as in the present invention is indispensable.

In this embodiment, the RRH unit is not limited to the digital optical I / F 14, the radio unit 15, and the PA 16, and the PA 16 and the radio unit 15 are partly separated from the antenna. It may be configured.

The present embodiment is different from the first embodiment in that the quality measuring unit 126 measures the optical transmission quality based on the bit error rate of the inspection signal. In this embodiment, as shown in FIG. 2, the inspection signal generation unit 122 outputs a known code that does not depend on the digital radio signal input to the digital optical I / F unit as the inspection signal. The quality measuring means 126 compares the known code with the received check signal and measures the bit error rate. In the case of the format of FIG. 3, the inspection signal insertion rate is 14 bytes / 405 bytes, that is, 3.45%. Therefore, in the 2.5Gbps optical transmission system,
2.48832 × 109 × 0.0345 = 8.6 × 107
Thus, 8.6 × 10 7 test signal bits are transmitted per second. In other words, if the error rate is 1.2 × 10 −8 (= 1 / 8.6 × 107), the measurement can be performed by measuring for 1 second. Naturally, if continuous measurement is performed for 10 seconds for the −9th power, 100 seconds for the −10th power, and 1000 seconds for the −11th power, it is possible to detect deterioration in communication quality in each order. Further, if the check bit insertion rate is increased, the error rate can be measured at high speed, but the existence rate of the signal that should be passed through decreases. These relationships are trade-offs and are the design items of the system builder.
According to the present embodiment, it is possible to measure at a high speed with the simplest configuration as compared with a method for detecting a frame error rate, a parity check, and the like.

The present embodiment is different from the first embodiment in that the optical transmission quality is measured based on CRC (Cyclic Redundancy Check). CRC is a method for detecting whether or not an error has occurred during transmission mainly in digital data transmission of a serial transfer system.
On the data transmission side, a cyclic algorithm (generation polynomial) is applied to each digital chip to transmit digital data to generate redundant data called CRC code, and this redundant data is transmitted as a check signal. On the receiving side of the optical transmission, the same algorithm as that on the transmitting side is applied to the data to calculate redundant data. If the CRC code calculated on the transmission side matches the CRC code calculated on the reception side, it can be confirmed that the data has been transmitted without error. Compared with the above-described parity check method, the detection accuracy of multi-bit errors is high.

In addition, the format shown in FIG. 3 may be slightly changed, and a CRC code may be added for each two-chip section or for each frame. If this is added for each frame, the frame error rate can be measured. What kind of check code is used as the CRC is a design matter of the system builder.
According to the present embodiment, in the second embodiment, it is possible to detect only errors that occur in the time zone of the inspection signal, whereas it is possible to detect bit errors that occur in all time zones. . Naturally, the present embodiment is slightly more complicated than the second embodiment, which is a trade-off between the complexity of the device configuration and the safety.

The present embodiment is different from the first embodiment in that the optical transmission quality is measured using the redundancy of the 8B / 10B code. In the 8B / 10B code, 256 codes out of 1024 are assigned to the 8-bit data, so that an error can be detected with a probability of about 75% when the error rate is low, and the BER can be estimated relatively accurately.

According to the best embodiment of the present invention described above, the use of digital optical transmission enables general-purpose digital light whose transmission quality can be accurately evaluated with an index such as BER as compared with analog optical transmission and whose quality is stable. Transmission lines can be used, and overall transmission quality can be easily maintained. In particular, when the transmission quality falls below a specified value, it is reported to the host device, so that it is possible to avoid a system down beforehand by responding to the equipment inspection, etc. When it is determined that the function is affected, the corresponding optical transmission system is cut off, so that the radio wave law can be reliably observed. As a result, if the reliability of base stations using digital optical transmission is improved and adopted, it will lead to reduction in installation and maintenance costs of mobile communication infrastructure.

Configuration diagram of base station apparatus in first to third embodiments Block diagram of digital optical I / F unit in Embodiments 1 and 2 The figure explaining the format for optical transmission in Examples 1-2 ASK error rate theoretical value vs. required S / N Configuration diagram of conventional radio base station apparatus

Explanation of symbols

11 base station equivalent device, 12 digital optical I / F unit, 13 optical fiber, 14 digital optical I / F unit, 15 radio unit, 16 PA

Claims (3)

An optical digital transmission quality used for at least a part of a section in which at least an RRH unit that performs radio amplification and at least a base station equivalent unit that performs call processing are configured separately, and the RRH unit and the base station equivalent unit are connected to each other A monitoring method,
Monitor the communication quality in the digital optical transmission section, and if the communication quality is lower than a predetermined quality, report to at least the host device or control to stop wireless transmission based on the digital optical transmission An optical digital transmission quality monitoring method characterized by the above. For the purpose of digital radio communication, at least an RRH unit that performs radio amplification and a base station equivalent unit that performs at least call processing and inputs and outputs digital radio signals are configured separately, and the RRH unit and the base station equivalent unit A radio base station apparatus that uses digital optical transmission for at least part of a section to be connected,
Adding a test signal for measuring communication quality to the digital radio signal, and a format converter for converting the format so as to be compatible with the digital optical transmission;
An E / O converter that converts an electrical signal output from the format converter to an optical transmission line after being subjected to electro-optical conversion;
An O / E converter that performs optical-electrical signal conversion on the output of the optical transmission line;
Communication quality measuring means for measuring communication quality for the signal output from the O / E converter;
Based on the measurement result of the communication quality measuring means, a control unit that performs at least one of reporting to a higher-level device or control for stopping radio transmission of the radio base station,
A radio base station apparatus comprising: The communication quality measuring means detects a bit error rate by comparing the received check signal with a known signal or detects an error by comparing with a code generated by a cyclic redundancy check method. 2. The radio base station apparatus according to 2.

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