KR20040100182A - Apparatus and a method for sensing oscillation of an rf repeater through signal demodulation, realized by detecting change characteristics of a qpsk modulation signal caused by oscillation generated because of failure of obtaining a sufficient isolation distance between a transmission antenna and a reception antenna - Google Patents

Abstract

PURPOSE: An apparatus and a method for sensing oscillation of an RF repeater through signal demodulation are provided to enable an actual mobile communication repeater having changing signal power to sense oscillation regardless of power control to discriminate whether there is an error. CONSTITUTION: A direct demodulator(100) is connected to an output of an RF repeater link and demodulates signals of the entire or a certain channel of the link. An amplifier(110) amplifies the demodulation signals(111) in the process of signal demodulation. A low pass filter(120) enhances the frequency selectivity of a sensor by removing high frequency noise generated due to a signal different from a local frequency(102) among the amplified signal(121). A comparator(130) compares the output signals(131) of the low pass filter(120) with a comparison level(132) controlled by a u-process and logic unit(140), and converts them(131) into a digital signal. A DAC(Digital Analog Converter)(150) generates the comparison level applied to the comparator(130). The number of times of asynchronization and pulse patterns of the pulse signals(141) successively outputted from the comparator(130) are detected and stored, and characteristics of the demodulation signals(111) stored according to each comparison level(132) are recognized.

Description

Oscillation Detection Device and Method of RF Repeater Using Signal Demodulation

The present invention relates to an oscillation detection apparatus and method of an RF repeater including mobile communication, and more particularly, to detect a change characteristic of a QPSK modulated signal that appears during an oscillation phenomenon due to insufficient isolation between a transmitting antenna and a receiving antenna in an RF repeater. This is to detect oscillation of RF repeater.

The mobile communication repeater receives the weak base station signal from the base station through the base station counter antenna 10 using an air line, amplifies the received signal through the forward path of the repeater, and transmits the signal to the mobile station through the mobile station counter antenna 20. It has a forward link and a reverse link that receives and amplifies a signal from a mobile station and transmits it to a base station. 1 illustrates a schematic configuration of a base station, a repeater, and a mobile station in a mobile communication system. In the mobile communication repeater, due to the lack of isolation between the base station counter antenna 10 and the mobile station counter antenna 20, signals transmitted from each link in the forward and reverse directions are fed back to the receiving end of the link. The input and amplification causes a decrease in the call quality due to the increase in the output of the repeater and signal distortion.

As a conventional technique of detecting an interference phenomenon (hereinafter referred to as oscillation) due to insufficient isolation between two antennas in the mobile communication repeater, it is common to measure oscillation by measuring the power of the RF signal output from the repeater's output. It was. However, in this method, it is impossible to distinguish between a power change of an instantaneous signal change and a power change generated by an oscillation phenomenon in a mobile communication system. Another conventional method is a method of detecting oscillation by processing a signal state of a signal at the time of oscillation by using a high speed signal processing technique, but it is costly to apply to a repeater system.

Oscillation caused by lack of isolation between two antennas in a mobile communication system is observed by using a spectrum analyzer. As the isolation becomes worse, CDMA RF signals become distorted, and continuous wave components of higher power than the CDMA signal level appear. . Figure 2a shows the shape of the CDMA signal in the repeater in normal operation, Figure 2b shows the shape of the CDMA RF signal distortion is caused by the oscillation phenomenon due to lack of isolation. For example, in the case of the forward link, when the CDMA signal is received through the support station counter antenna 10 and amplified by the repeater and then transmitted through the mobile station counter antenna 20, In the repeater which does not have sufficient isolation between the mobile station opposing antennas 20, the signal transmitted through the mobile station opposing antenna 20 is fed back to the base station opposing antenna 10, and the feedback loop and the repeater Continuous wave components generated at a plurality of resonant frequencies within an amplification band are generated differently depending on the characteristics of the feedback loop in the repeater system.

3 illustrates the amplification function of the feedback loop and the repeater in space caused by the lack of isolation between the two antennas described above. The input signal 51 is amplified by the repeater 50 having an amplification degree of A dB, where the output signal 52 is applied to the input through a feedback loop resulting from lack of isolation between the antennas, and the amount of the signal being returned is B dB is represented by the sum of the feedback rate 60 and the output signal 52. The feedback rate of B dB is used to mean isolation or loss, and it is equivalent to both the antenna gain and the loss in space. It is the equivalent value of the feedback path.

Since the signals returned in the feedback loop described above are subjected to constructive and destructive interference depending on the frequency, the positive feedback and the negative feedback are determined according to the frequency. Therefore, it can be said that oscillation phenomenon in the repeater in the mobile communication system is generated differently depending on the characteristics of the repeater, the feedback path, and the signal condition. As shown in Fig. 4b , when the oscillation occurs, it can be seen that power at specific frequencies in the signal band amplified by the repeater increases, which is generated by the frequencies of the above-mentioned constructive interference, that is, the positive feedback signal. It is explained by the distortion of the CDMA RF signal due to the continuous wave components, which causes a serious problem such as a reduction in the service area due to a drastic reduction in the call quality of the mobile communication system.

The present invention is applied to the function of the repeater shown in Figure 1 in order to solve the above problems, by applying the oscillation detection function of the present invention to overcome the inaccuracy of the determination of the oscillation using the power change, which was a problem in the prior art, In order to achieve the function of oscillation detection at a simple and low cost, it is simple by using the direct demodulator 100 used for receiving QPSK signals such as CDMA signals and the minimum necessary circuit, and maximizes the stability and reliability of the device. In addition, the function of Auto Gain Control detects the oscillation by detecting the state change characteristic of QPSK modulated signal that appears during oscillation of mobile communication repeater regardless of power change. When this oscillation occurs, the CDMA RF signal is processed by a unique technique in the circuit of the present invention. In the u-processor & Logic 140, asynchronous counts and pulse string level classifications, pulse patterns, and power of pressure signals are used. By collecting all the functions, it detects oscillation at the time of fine signal, oscillation at the time of repeater operation, and detects the inflow of external continuous wave.

The present invention has the following features.

-Stable mixer and demodulation of CDMA RF signal for oscillation detection using direct demodulator.

-Automatic gain adjustment enables detection of oscillations independent of signal power changes.

-The circuit is simpler and cheaper than the intermediate frequency method using the conventional saw filter by improving the frequency selectivity by appropriate combination of the amplifier 110, the low pass filter 120 and the comparator 130.

In the QPSK signal processing method, a high-speed ADC and a comparator 130 whose comparison criteria are controlled by a u-processor without excessive data processing are used, and the minimum data required for oscillation determination by asynchronous number of signal waveforms, etc. The configuration of the oscillation detection device is simplified by only processing.

-In addition to oscillation, it can detect continuous wave noise from outside during normal repeater operation.

-It is possible to monitor the signal in repeater band for each channel.

-To detect oscillation without generating random propagation and injecting into the amplification band of repeater or arbitrarily varying repeater gain for oscillation detection.

1 is a schematic configuration diagram of a mobile communication relay system according to the prior art.

2 is a waveform diagram of a signal generated in a conventional mobile communication repeater.

3 is a block diagram illustrating a path through which an RF signal is amplified and feedback in a conventional mobile communication repeater.

4 is a block diagram of an oscillation detection apparatus of a mobile communication relay station according to the present invention;

5 is a signal waveform diagram of the present invention.

6 is a display waveform diagram of the signal characteristics for each channel in the repeater band of the present invention.

In order to achieve the above object, the present invention takes a predetermined signal from the output of the repeater to detect the oscillation with a directional coupler and applies it to the oscillation detecting apparatus, wherein the applied CDMA RF signal 101 and PLL are applied. The QPSK signal 111 of the CDMA signal directly demodulated by the demodulator 100 by the local frequency 102 generated by the unit 160 passes through the amplifier 110 and the low pass filter 120. The signal 131, which is properly amplified by the amplifier 110 and passed through the low pass filter 120, is applied to the comparator 130 and the comparison level of the comparator 130 controlled by the u-Processor & Logic unit 140 ( 132) is converted into digital pulses of '0' and '1' (141), which is the same as the analog-to-digital converter (1bit ADC). As such, the reference level 132 of the comparator controlled by the u-Processor & Logic unit is a DAC (Digital-to-Analog) by the smoothing circuit of the PWM signal 151 output from the u-Processor & Logic unit 140. In this case, the generated pulses are sequentially compared to each of the plurality of feature levels by using the u-Processor & Logic unit 140. The pulse shaping method controlled by the u-Processor & Logic unit 140 converts a high speed QPSK signal into a simple digital pulse form that is relatively easy to process, thereby enabling the minimum processing required for oscillation determination. Also, the PLL unit 160 controlled by the u-Processor & Logic unit 140 generates a local frequency 102 that is the same as the frequency of the signal to be demodulated directly to the demodulator 100 for monitoring according to the frequency of the CDMA signal. Inject by In order to detect the oscillation, the PLL unit continuously changes or generates the local frequency by the u-Processor & Logic unit 140 in whole or in part of the band of the repeater. In the direct demodulation method, the local frequency 102 uses the same frequency as the input signal to be demodulated. When demodulating an arbitrary CDMA RF signal with a direct demodulator, the high frequency noise generated from the reaction of the local frequency of the PLL part with the CDMA RF signal of a different frequency passes through the low pass filter 120, that is, the frequency to be detected currently, that is, the local frequency 102 Except for the CDMA RF signal components, the magnitude of the waveform is significantly reduced. The reduced magnitude waveform 131 is compared by a comparison level 132 controlled through the DAC 150 by the u-Processor, where the number of pulses 141 produced is a frequency component different from the local frequency as described above. Since the number of pulses generated by the circuit is remarkably small, the frequency selectivity of the entire circuit can be improved. FIG. 5 shows the output signal 131 of the low pass filter 120 and the output pulse signal 141 of the comparator 130 when a signal of one channel is applied to the present invention using a CDMA signal generator. Shows the operation of frequency selection and operation of pulse signal generation by the comparator.

This is in contrast to the frequency selection function of the conventional frequency detection function of the mixer and the intermediate frequency detection circuit in which a signal down-converted by a local frequency having a difference frequency equal to that of the intermediate frequency is selected by a saw filter. Through the control of the comparison level 132 by the processor, the frequency selectivity of the RF signal is improved. However, the circuit operation can be performed by QPSK demodulation by constructing a circuit using a method of selecting a channel or a frequency by an intermediate frequency method using a saw filter rather than the direct demodulation method used in the present invention. It will be apparent to those skilled in the art of the present invention.

As described above, when the CDMA RF signal is distorted by the continuous wave components generated and increased by the positive feedback in the repeater amplification band, the number of pulse signals 141 is greater than the number of pulse signals 141 generated by the normal CDMA RF signal. It has a small value. The reason for this is that when QPSK demodulation of the continuous wave, the signal corresponding to the difference frequency with the local frequency is output 111. Ideally, when the input continuous wave and the local frequency exactly match each other without phase noise, No pulse will come out.

Therefore, as the oscillation phenomenon increases, the continuous wave component of the CDMA RF signal increases and the number of pulse signals 141 is reduced by breaking the pulse signal of the normal QPSK demodulation signal. It will be easy to see.

According to the oscillation detection function of the present invention, the isolation signal such as the gain of the normal signal and the repeater with 40 dB more isolation than the gain of the repeater in the mobile communication repeater for all 20 channels of the forward link among the CDMA RF signals taken from the actual outdoor antenna. 6A and 6B show the case of oscillation by operating with. This is a graph using a oscilloscope after changing the number of pulse signals 141 in 20 CDMA signal channels to an analog value through a DAC, and can be used for monitoring a simple repeater. The two bar graphs 200 and 202 are delimiters for triggering the screen of the oscilloscope, that is, for synchronously observing a signal in a time domain that is output periodically and continuously. Looking at the channels 204 of 4,5,6,7,8 of FIG. 6B , the bar representing the number of pulses 141 of the channel compared to the channels 201 of 4,5,6,7,8 of FIG. 6A. It can be seen that the heights of the graphs are generally small. This is because oscillation occurs and the number of pulse signals 141 decreases. This phenomenon becomes small and this phenomenon occurs when demodulating a channel having a continuous wave. When the number of pulse signals 141 is severely reduced, the channel center frequency generated in the PLL unit 160 and the frequency of the continuous wave generated in the CDMA channel are close to each other in order to demodulate the channel. Can be observed. The reduction of the number of pulse signals 141 is stored and processed by a program embedded in the u-processor & logic unit 140 to determine oscillation. As shown here, the oscillation detection function through signal demodulation according to the present invention determines the oscillation by recognizing the signs of oscillation before the point where the output signal changes, which is a conventional oscillation determination method, that is, a point equal to the gain of the repeater. Make it possible.

The reference value of the oscillation determination is a constant by applying a normal signal output without a feedback loop of the signal by initially connecting the terminal instead of the antenna to the output terminal of the repeater when installing the repeater to which the present invention is applied. The reference value required for oscillation determination is generated during the time and stored in the SRAM of the u-processor & logic unit 140. After inputting the reference value of the oscillation determination through the above method in the present invention, the terminal is connected to the antenna after the termination (Termination) installed in the output terminal for the operation of the repeater to operate the repeater. When generating the reference value of the oscillation determination is not easy by the above method, the SRAM of the u-processor & logic unit 140 as an experimental value for the pulse signal 141 generated by the present invention by processing the CDMA RF signal The above method can be replaced by resetting the data to the data of the signal input during actual operation.

Meanwhile, the voltage signal 142 transmitted from the direct demodulator 100 to the u-processor & logic unit 140 is a voltage signal for the power level of the RF input signal 101 applied to the direct demodulator. The u-processor & logic unit 140 detects the power level of the RF input signal 101 by means of a built-in analog to digital converter (ADC), so that the current input signal has a size that is suitable for oscillation detection, that is, an appropriate input signal. It determines whether or not to fall within the range of the present invention accordingly informs the operating state of the oscillation detection device of the present invention, the information on the power level signal 142 and the pulse signal 141 of the RF input signal 101 u-processor & Detects self oscillation (also called 'fine signal oscillation') by its own thermal noise even when there is no input signal from mobile communication repeater by collecting and judging by program built in logic unit 140 It is also possible.

In the present invention, if the pass characteristics of the local frequency and the low pass filter are adjusted, not only the CDMA signal of 1.2288 Mchips / s but also the oscillation detection in the WCDMA having a higher chip rate, the u-processor & logic unit 140 It is easy for those skilled in the art of the present invention to detect more detailed oscillation when adding the function of analyzing the pattern of the pulse signal string to the above-described number processing function of the pulse signal 141 using a high speed device. You will know.

As described above, the present invention can detect oscillation phenomena regardless of power control in the actual mobile communication repeater in which the signal power is changed, and can determine whether there is an abnormality of the repeater, and the oscillation determination operation based on the signal demodulation. Compared to the deterioration of RF signal quality, which is a problem during the actual oscillation phenomenon, the oscillation can be accurately detected. In addition, the present invention can be applied to all RF repeaters having a transmitting and receiving antenna.

Claims (3)

An oscillation detection circuit of an RF repeater including mobile communication for transmitting and receiving a signal between a base station and a mobile station, comprising: an apparatus (100) connected to an output of an RF repeater link to demodulate a signal of an entire link or a predetermined channel; An apparatus (110) for amplifying the demodulation signal (111) of the signal demodulation step; A low pass filter 120 that removes high frequency noise generated by a signal different from the local frequency 102 among the signals of the amplified signal 121 to improve frequency selectivity of the present sensing device; A comparator 130 for comparing the output signal 131 of the low pass filter 120 by a comparison level 132 controlled by a u-processor & logic unit 140 and converting the digital signal into a digital signal; a DAC unit 150 controlled by the u-processor & logic unit 140 to generate a comparison level 132 applied to the comparator 130; A method for recognizing and storing the characteristics of the demodulated signal stored for each comparison level (132) by recognizing and storing the asynchronous number and pulse pattern of pulse signals continuously output from the long comparator (130). A conversion circuit for monitoring the oscillation state and the repeater operation by using an oscilloscope by outputting the number of pulse signals stored for each channel for oscillation detection. The step of determining oscillation of the pulse signal 141 output from the comparator 130 by the u-processor & logic unit 140 is that oscillation does not occur in the present invention during the initial installation of the repeater to which the oscillation detection apparatus is applied. A method of determining whether the repeater oscillation and the normal operation are performed by applying and storing the output signal of the repeater as a reference of oscillation determination during repeater operation after installation; When it is not easy to use as a reference of oscillation determination through the above method, the oscillation determination data is stored in advance in the SRAM embedded in the u-processor & logic unit 140, and then the output signal of the repeater is applied to the present invention. A method of determining the oscillation determination and normal operation of the repeater by correcting the oscillation determination data by a program embedded in the u-processor & logic unit 140 and using the reference of the oscillation determination;