JP2006067047A - Input electric field intensity display method and circuit thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an input electric field intensity display method by which a more reliable digital radio transmission system can be realized even when the input electric field intensity of radio electric waves has a level sufficient to obtain a detection output or is a low level, and to provide a circuit therefor. <P>SOLUTION: In the input electric field intensity display method for a digital receiver, which receives a radio electric wave from a transmission side and demodulates a signal transmitted from a frequency converter 3 through an AGC amplifier 4 by a demodulator 5, whether or not a reception level in the post-stage of an AGC amplifier 4 is a predetermined critical value is determined to output a switching control signal. When the reception level exceeds the predetermined critical value, the level detection output of the AGC amplifier 4 is used as input electric field intensity, and when the reception level is not more than the predetermined critical value, an estimated value by a preliminarily decided conversion value is outputted and displayed as an input electric field intensity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an input electric field strength display method and circuit for displaying an input electric field strength or an estimated input electric field strength in a digital receiver, and more particularly to an antenna direction adjustment in a wireless transmission system and the like. The present invention relates to an input electric field strength display method and circuit for detecting an input electric field strength by receiving a video signal or the like or estimating and displaying an input electric field strength when the signal level is low.

  In general, in live broadcasts such as sports, transmission technology is used to transmit video from a relay site to a relay vehicle using a microwave by using an FPU (Field Pick-up Unit) device for signals captured by a TV camera. . A conventional FPU transmitter modulates a video signal or an audio signal, further performs frequency conversion, and transmits it as a radio wave. The FPU receiver adjusts the direction of the antenna so that the reception level becomes the maximum value while confirming the input electric field strength of the received radio wave with a level meter or the like, and demodulates a good image.

  In conventional analog FPU transmitters, video signals are frequency-modulated and transmitted. However, along with recent advances in digital technology, QPSK (Quadrature Phase Modulation), QAM (Quadrature Modulation), OFDM (Orthogonal Frequency Division Multiplexing) ) And other digital FPU receivers using digital modulation techniques. Digital FPU receivers differ from analog FPU receivers in theory because the input field strength that can be demodulated is much lower than analog FPU receivers, that is, the input signal is identified even if the signal level is lower than the noise level. It can be demodulated. (For example, see Patent Document 1)

Japanese Patent Laid-Open No. 2001-36506 (the whole specification and drawings)

  In the conventional analog FPU receiver, the received electric field strength of the input signal is detected from the AGC voltage (automatic gain control voltage) that is a detection output in the intermediate frequency amplifier in the IF (Intermediate Frequency) band, and the signal component is more Since it cannot be demodulated unless it is always sufficiently larger than the noise component, the input electric field strength is detected on the assumption that the SN ratio (CN ratio: voltage ratio of carrier wave to noise) is always positive. In the wireless transmission system, the antenna direction is adjusted by measuring the input electric field strength using the AGC voltage and driving the reception electric field strength meter. However, if the signal component is substantially equal to the noise component, I can not cope. In such a conventional circuit, it is difficult to adjust the direction of the antenna unless the SN ratio (CN ratio) is large to some extent (for example, 10 dB), and in the conventional input field strength measurement circuit, the reception field strength meter cannot be used. Had a point.

  By the way, the digital FPU receiver can identify and demodulate the received signal even if the signal component has a level substantially equal to the noise component. In the digital FPU receiver, the signal level in this area cannot be obtained even if the input field strength measuring circuit of the conventional analog FPU receiver as described above is used, and a new circuit is required. It was.

  In order to solve the above-mentioned problems, the present applicant has proposed an input electric field strength estimation circuit that can cope with an input electric field strength of a low level in Japanese Patent Application No. 2004-183534. This circuit is effective when the input electric field strength is low, but in a digital FPU receiver used for mobile relay, the SN ratio (CN ratio) may fluctuate greatly due to changes in environmental conditions. When the analog FPU receiver has sufficient input electric field strength to receive, the input electric field strength estimation circuit cannot reach the measurement limit and accurately display the input electric field strength. When the input electric field strength is sufficient, even the digital FPU receiver can use the input electric field strength measurement circuit used in the conventional analog FPU receiver.

  The present invention has been made in view of the above problems, and is more reliable even when the input electric field strength of a radio wave has a level sufficient to obtain a detection output or a low level. It is an object of the present invention to provide an input electric field intensity display method and its circuit which can be used as a high digital wireless transmission system.

The present invention achieves the above-mentioned problems, and the invention according to claim 1 is a digital receiver that receives a radio wave from the transmission side and demodulates the signal from the frequency conversion means through the variable amplification means by the demodulation means. An input electric field strength display method in
It is determined whether or not the reception level at the subsequent stage of the variable amplification means is a predetermined limit value, and a switching control signal is output. If the reception level exceeds the predetermined limit value, the level detection output of the variable amplification means Is an input electric field strength, and when the reception level is below a predetermined limit value, an estimated value based on a predetermined conversion value is output and displayed as the input electric field strength.

  The invention according to claim 2 is the input electric field strength display method according to claim 1, wherein the predetermined limit value is a value in which the levels of the signal component and the noise component are substantially equal.

The invention of claim 3 is an input electric field strength display circuit that receives a radio wave from the transmission side and displays the input electric field strength of the received radio wave,
A frequency converting means for amplifying the received radio wave and performing frequency conversion;
Variable amplification means for amplifying the output of the frequency conversion means to a constant level;
Gain control means for controlling the variable amplification means;
Calculating means for calculating received electric field strength from the gain control means;
Limit value determining means for detecting whether or not the output of the calculating means is a predetermined limit value;
Orthogonal demodulation means for orthogonally demodulating the output of the variable amplification means;
Correlation calculating means for calculating the correlation of the outputs of the orthogonal demodulating means;
Estimating means for estimating the input electric field intensity from the output of the correlation calculating means;
Switching means for selectively outputting either the output of the calculation means or the output of the estimation means based on the limit value determination means;
An input electric field intensity display circuit comprising:

  According to a fourth aspect of the present invention, there is provided the input electric field strength display circuit according to the third aspect, wherein the estimating means estimates the input electric field strength by conversion from a conversion data table estimated in advance.

The invention of claim 1 is an input electric field strength display method in a digital receiver that receives a radio wave from a transmission side and demodulates a signal from a frequency conversion unit through a variable amplification unit by a demodulation unit,
It is determined whether or not the reception level at the subsequent stage of the variable amplification means is a predetermined limit value, and a switching control signal is output. If the reception level exceeds the predetermined limit value, the level detection output of the variable amplification means Is an input electric field strength, and when the reception level is equal to or less than a predetermined limit value, an estimated value based on a predetermined conversion value is output and displayed as the input electric field strength. Even if the levels of the signal component and noise component are approximately equal, there is an advantage that the input electric field strength can be displayed from the reception level, and the input electric field strength can be displayed according to the demodulation performance in the digital receiver. When there is a sufficient level to obtain a detection output against the noise voltage, the switching control means automatically switches to the detection output in the variable amplification means and outputs it. Can be displayed, there is an advantage that it is possible to correspond to the input electric field intensity level of the wide range.

  Further, in the invention of claim 2, the predetermined limit value is the input electric field strength display method according to claim 1, characterized in that the level of the signal component and the noise component is substantially equal. At the reception level that can be detected by the detection circuit, the detection output of the variable amplification means is output. At the reception level that cannot be detected by the detection circuit, it is determined that the signal component and noise component levels have shifted to an approximately equal area, and the demodulator The input electric field strength can be estimated from the signal level of the video signal. In the digital receiver, the signal component and the noise component are shifted to a region where the level is substantially equal, and even if the signal level is lower than the noise level, the video signal can be recognized and demodulated. There is an advantage that it can correspond to the reception performance of the machine.

The invention of claim 3 is an input electric field strength display circuit that receives a radio wave from the transmission side and displays the input electric field strength of the received radio wave,
A frequency converting means for amplifying the received radio wave and performing frequency conversion;
Variable amplification means for amplifying the output of the frequency conversion means to a constant level;
Gain control means for controlling the variable amplification means;
Calculating means for calculating received electric field strength from the gain control means;
Limit value determining means for detecting whether or not the output of the calculating means is a predetermined limit value;
Orthogonal demodulation means for orthogonally demodulating the output of the variable amplification means;
Correlation calculating means for calculating the correlation of the outputs of the orthogonal demodulating means;
Estimating means for estimating the input electric field intensity from the output of the correlation calculating means;
Switching means for selectively outputting either the output of the calculation means or the output of the estimation means based on the limit value determination means;
In the case of a normal input field strength, the received field strength obtained from variable amplification means (AGC voltage) which is an intermediate frequency amplification stage in the IF band is input. In the case of low-level input field strength, the estimated input field strength can be obtained from the output (estimated value) of the estimation means for estimating the input field strength based on the output from the correlation calculation means. This has the effect that the receiving meter can be used without depending on the level. In addition, by providing the input field strength display circuit in the digital FPU receiver, it is possible to always drive the received field strength meter regardless of fluctuations in the input field strength, and to adjust the direction of the antenna in the microwave relay. Since it can be done reliably, it has the effect of improving the reliability of radio transmission in mobile relay.

  According to a fourth aspect of the present invention, in the input electric field strength display circuit according to the third aspect, the estimating means estimates the input electric field strength by converting from a conversion data table estimated in advance. By estimating from the conversion table, the circuit can be configured in a compact manner.

  Embodiments of an input electric field intensity display method and its circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a digital receiver including the input electric field strength display circuit of the present embodiment, and FIG. 2 is a diagram for explaining the operation of the present embodiment with a time chart.

  1 is a low noise amplifier (LNA) 2 that amplifies a received radio wave of a receiving antenna 1 that receives a radio wave transmitted from a transmitting side, and converts a signal of the low noise amplifier 2 into an intermediate frequency (IF). A frequency converter (D / C: down-converter) 3 that performs, and an AGC (Automatic Gain Control) amplifier 4 that applies negative feedback by a gain control signal so as to make the output level of the intermediate frequency signal from the frequency converter 3 constant. The demodulator 5 demodulates the output signal of the AGC amplifier 4, and the demodulated video signal is output from the output terminal 6. The gain control signal is generally a detection output obtained by level detection of the intermediate frequency signal, and this detection output is output as a control voltage. The intermediate frequency signal may be either the output stage of the AGC amplifier 4 or the input stage of the demodulator 5.

  The input electric field strength display circuit of this embodiment is provided in the digital receiver and will be described with reference to FIG. The input electric field strength display circuit determines whether or not the level of the input electric field strength is a predetermined limit value by the reception level detection means A, the reception level estimation means B, and the reception level detection means A and the reception level estimation means B. A limit value determination unit (limit value determination means) 9 that outputs a switching signal for selecting one of the outputs, and a switch 14 that selects one of the outputs of the reception level detection means A and the reception level estimation means B It consists of. The switching device 14 is controlled to be switched by a switching control signal from the limit value determination unit 9, and the output from the switching device 14 is converted into a digital value by the D / A converter 15, and is sent to a reception level meter (reception field strength meter) 16. Entered.

  The reception level detection means A includes a reception field strength calculation unit 7 that calculates an input field strength from a gain control voltage (gain control signal) obtained by detecting the output distributed from the input stage of the demodulator 5, and a reception field strength calculation. The A / D converter 8 converts the received voltage of the unit 7 into a digital value. The output of the A / D converter 8 is input to the switch 14 and also to the limit value determination unit 9. The reception level estimation means B includes a quadrature demodulator 10 that demodulates the output of the AGC amplifier, a correlation calculator 11 that calculates a correlation value in the quadrature demodulated IQ signal (output signal) of the quadrature demodulator 10, and a correlation calculation The maximum value detection unit 12 that outputs the average of the maximum values for each predetermined period of the result and the reception level estimation unit 13 that estimates the reception level from the correlation maximum value, the output of the reception level estimation unit 13 is sent to the switch 14. Entered.

  The reception level estimation unit 13 estimates the input electric field strength according to the reception level from the calculation data table measured before the result of the maximum value detection unit 12. In addition, the limit value of the received electric field strength in the analog FPU is generally −90 dBm. Therefore, if the limit value determination unit (limit value determination unit) 9 determines that the reception level is −90 dBm or less, the output of the reception level estimation unit B, that is, the estimated value by the reception level estimation unit 13 is switched by the switch 14. Is output from. If the limit value determination unit (limit value determination means) 9 determines that the reception level is −90 dBm or more, the output of the reception level detection means A is output through the switch 14. Note that the limit value of the received electric field intensity may be set to a limit value at which a detection output in the frequency converter 3 can be obtained.

  Further, the operation of this embodiment will be described with reference to FIGS. The received radio wave is amplified by the low noise amplifier 2, and the signal amplified by the low noise amplifier 2 is frequency-converted to an intermediate frequency signal by the frequency converter 3, and is amplified by the AGC amplifier 4 so as to be a constant level. The output of the AGC amplifier 4 is input to the demodulator 5 and demodulated, and the output distributed from the input stage of the demodulator 5 is input to the reception level detection means A. On the other hand, the output distributed from the AGC amplifier 4 is input to the reception level estimation means B.

  The output (digital value) of the reception level detection means A is an output corresponding to the reception electric field strength and is input to the limit value determination unit 9. The limit value determination unit 9 determines whether or not the gain control voltage of the AGC amplifier 4 is a predetermined limit value (−90 dBm). Alternatively, the limit value determination unit 9 determines whether or not the output of the reception level detection means A is greater than or equal to a predetermined limit value (whether it is less than or equal to). When the received electric field strength is greater than the predetermined limit value, the limit value determination unit 9 switches the switch 14 with a switch control signal and outputs the output of the reception level estimation means A from the switch 14. When the received electric field strength is smaller than the predetermined limit value, limit value determination unit 9 controls switching device 14 with a switching control signal, and outputs the output of reception level estimation unit 13 from switching device 14. The gain control voltage of the AGC amplifier 4 uses the detection output of the AGC amplifier 4 or the detection output of the output distributed from the input stage of the demodulator 5, and the limit value determination unit 9 controls the control voltage converted into a digital value. And a predetermined limit value are compared.

  Subsequently, the correlation calculation in the reception level estimation means B will be described with reference to the time charts of FIGS. FIG. 2 is a diagram for explaining the operation in this embodiment. The case where the output of the frequency converter 3 of the digital FPU receiver is an OFDM signal (orthogonal frequency division multiplexed signal) will be described.

  As shown in FIGS. 2A and 2B, one OFDM signal for one symbol includes a guard inverter part (guard period) and an effective symbol part (effective symbol period). As shown in FIG. 2 (c), the guard interval portion represents the same data as indicated by an arrow. Normally, the guard interval portion of the OFDM signal copies a predetermined portion (second half portion) of an effective symbol. To the top of each symbol. FIG. 2D is a delayed signal obtained by delaying FIG. 2C by one effective symbol period.

  FIG. 2 (e) shows the calculation results by the correlation calculation unit 11 and the maximum value detection unit 12, and the guard interval part (predetermined part of the effective symbol) in FIG. This is a result of correlation calculation with a predetermined portion of the same effective symbol. In FIG. 2E, since the guard interval portion is a copy of an effective symbol, the correlation level is increased. The correlation calculation result is large when the noise level of the input signal is small, and the value of the calculation result (signal level) is small when the noise level is large. Therefore, the noise level of the input signal is converted from the calculation result, and the power of the input signal is converted. Levels L1, L2, and L3 in FIG. 2 (e) are correlation calculation results, and the maximum value detection unit 12 detects the maximum power (level L1) from the correlation calculation result. When the level L1, the input power is the maximum power. Become. The reception level estimation circuit 13 outputs an estimated value obtained by converting the input electric field strength with the maximum power.

  For this conversion, the curve curve of FIG. 3 is used, the horizontal axis of the figure indicates the maximum correlation value (8-bit digital value), the vertical axis indicates the input electric field strength (dB), and the input from the maximum correlation value. Convert the electric field strength (estimated value). Each data constituting the curve curve is written in a memory to form a conversion data table, and based on this conversion data table, the input electric field strength (estimated value) can be converted from the maximum correlation value. Of course, the input electric field strength may be converted from the maximum correlation value using the curve curve of FIG. 3 as a function.

  In the above-described embodiment, the OFDM signal is illustrated as an input to the quadrature demodulator. However, as disclosed in Japanese Patent Application No. 2004-183534 filed by the applicant of the present application, a signal such as QAM is also used as a signal. When the level is equal to the noise level or the signal level is lower than the noise level, the input electric field strength can be displayed by regarding the signal level of the QAM signal as the input electric field strength.

  As an application example of the present invention, it is useful for antenna direction control of a digital receiver in an FPU device, can be used as a reception level display device, and is effective as a switching console (switcher) in a digital wireless transmission system, For example, it is possible to receive video signals and the like from a plurality of mobile relay stations and provide information such as antenna direction control and reception status effective for editing work for producing a program at a switching console.

It is a block diagram which shows one Embodiment of the input electric field strength display circuit of this invention. It is explanatory drawing for demonstrating the operation | movement of this embodiment, (a) is a time chart which shows the symbol signal area of an OFDM wave, (b) is a time chart which shows the rough structure, (c) Indicates a guard interval portion, (d) indicates a delayed signal, and (e) indicates a correlation calculation result. It is a figure which shows the curve data of a correlation maximum value and input electric field strength.

Explanation of symbols

1 Antenna 2 Low noise amplifier (LNA)
3 Down converter (D / C) (frequency conversion means)
4 AGC amplifier (variable amplification means)
5 Demodulator (demodulation means)
6 Output terminal 7 Received electric field strength calculation section 8 A / D converter (A / D)
9 Limit value judgment part (limit value judgment means)
10 Orthogonal demodulation unit (orthogonal demodulation means)
11 Correlation calculation unit (correlation calculation means)
12 Maximum value detection unit 13 Reception level estimation unit (estimation means)
14 Changer (switching means)
15 A / D converter (A / D)
16 Reception level meter A Reception level detection means B Reception level estimation means

Claims (4)

An input electric field strength display method in a digital receiver that receives a radio wave from a transmission side and demodulates a signal from a frequency conversion unit through a variable amplification unit by a demodulation unit,
It is determined whether or not the reception level at the subsequent stage of the variable amplification means is a predetermined limit value, and a switching control signal is output. If the reception level exceeds the predetermined limit value, the level detection output of the variable amplification means Is an input electric field strength, and when the reception level is equal to or lower than a predetermined limit value, an estimated value based on a predetermined conversion value is output and displayed as the input electric field strength.   2. The input electric field intensity display method according to claim 1, wherein the predetermined limit value is a value in which the levels of the signal component and the noise component are substantially equal. An input electric field strength display circuit that receives radio waves from the transmission side and displays the input electric field strength of the received radio waves
A frequency converting means for amplifying the received radio wave and performing frequency conversion;
Variable amplification means for amplifying the output of the frequency conversion means to a constant level;
Gain control means for controlling the variable amplification means;
Calculating means for calculating received electric field strength from the gain control means;
Limit value determining means for detecting whether or not the output of the calculating means is a predetermined limit value;
Orthogonal demodulation means for orthogonally demodulating the output of the variable amplification means;
Correlation calculating means for calculating the correlation of the outputs of the orthogonal demodulating means;
Estimating means for estimating the input electric field intensity from the output of the correlation calculating means;
Switching means for selectively outputting either the output of the calculation means or the output of the estimation means based on the limit value determination means;
An input electric field strength display circuit comprising:   4. The input electric field strength display circuit according to claim 3, wherein the estimating means estimates the input electric field strength by converting from a conversion data table estimated in advance.

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