JP4932623B2 - Determination circuit, squelch device, and determination method - Google Patents

Description

  The present invention relates to a determination circuit, a squelch device, and a determination method for a received signal, and more particularly to a determination circuit for determining whether a received signal is an OFDM signal, a squelch device having the determination circuit, and a determination method.

  A so-called digital transmission wave (radio wave) that has been digitally modulated has been used for a long time, and multiplexing techniques and techniques for preventing propagation deterioration have been introduced. Currently, television broadcast waves are also being digitized, and in Japan, a full transition from analog broadcasting to digital broadcasting is planned. In addition, in a relay apparatus from outside a television broadcast station, a digital modulation technique has already been introduced in many broadcast stations, and an analog method and a digital method are appropriately selected and used according to a transmission environment.

  As such a digital system, there is an OFDM (Orthogonal Frequency Division Multiplex) system in which a plurality of digital modulation waves are multiplexed to improve frequency use efficiency. By this method, it is possible to transmit relatively large capacity data with high quality.

By the way, there is a technique using guard correlation as a squelch technique for an OFDM transmission wave (hereinafter also simply referred to as “OFDM signal”). In the OFDM signal, a guard interval is provided in order to reduce the influence of reflection wave superposition. This guard interval uses part of the data in the effective symbol period, and even when the reflected wave is superimposed and the transmitted wave is distorted, the guard interval becomes a buffer and the influence of the reflected wave Can be reduced. In addition, since the signal of the guard interval is the same signal as a part of the signal in the effective symbol period, the correlation between the received OFDM signal and the signal delayed from the OFDM signal by the effective symbol period is used to obtain the guard interval signal. The correlation value increases only during the period. Therefore, there is a technique for taking a guard correlation in the same way for the received transmission wave and operating the squelch circuit by determining that the OFDM signal has not been received when a period in which the correlation value is high does not appear (for example, Patent Documents). 1).
JP 2004-242236 A

  However, the above technique cannot be applied to a transmission wave that does not include a guard interval. Further, the above-described technique tends to increase the circuit scale and complexity. Generally, when the circuit scale is large and complicated, the power consumption by the circuit increases. For example, in a relay device or the like, the available power may be limited. Further, in order to improve the portability of the relay device, it is highly desired to reduce the size of the device. If the squelch circuit can be simplified, mounting on the relay device is promoted, and therefore there is a high demand for a technique for simplifying the squelch circuit. Of course, the same applies to the demand in a reception-only device.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for simply determining whether or not an OFDM digital wave is received.

The apparatus according to the present invention relates to a determination circuit. The determination circuit determines whether or not the received signal is an OFDM signal based on a correlation between the received signal and an odd-order distortion signal of the third or higher order generated from the received signal.
Another device according to the present invention relates to a squelch device. The squelch device includes a determination circuit that determines whether or not the received signal is an OFDM signal based on a correlation between the received signal and a third-order or higher-order distortion signal generated from the received signal. A signal blocking unit that blocks signal output when the determination circuit determines that the signal is not an OFDM signal.
The method according to the present invention relates to a method for determining an OFDM signal. In this method, a third-order distortion signal is generated from the received signal, the third-order distortion signal and a complex conjugate signal of the received signal are subjected to complex multiplication, and when the result of the complex multiplication is 0, the received signal Is an OFDM signal.

  According to the present invention, a third-order distortion waveform is extracted from the received signal, and the correlation between the third-order distortion waveform and the received waveform is determined, and therefore the presence / absence of reception of an OFDM digital wave is simply determined. be able to.

  Next, the best mode for carrying out the present invention (hereinafter simply referred to as “embodiment”) will be specifically described with reference to the drawings. In the embodiment described below, in a relay device that relays the radio wave of the OFDM signal, when a radio wave that is not an OFDM signal is received, the squelch circuit is activated so that it is not output. First, the principle of determining whether or not the received radio wave is an OFDM signal will be described, and then a relay apparatus having a squelch circuit using the principle will be described.

  It is known that the amplitude probability density distribution of an OFDM signal exhibits a Rayleigh distribution. Therefore, in the present embodiment, it is determined whether the signal is an OFDM signal using the characteristics of the Rayleigh distribution.

  The static characteristics of the power amplifier 15 in the description of FIG. 1 to be described later are expressed as the following expression (1), where Vin is an input signal, Vout is an output signal, and Vout is expressed by a high-order polynomial. Here, up to the fifth term is shown.

In order to facilitate understanding now, a two-wave model in which the input signal Vin is represented by the following equation (2) will be considered.

When the expression (2) is substituted into the expression (1), for example, the first to fourth terms of the expression (1) become as the following expression (3).

Focusing on the fourth term of Vout, that is, “a3 · Vin ³ ” in the equation (1), this term includes cos (w1) + cos (w2) as a basic component and cos (3 · 3 as a third harmonic component). w1) + cos (3 · w2) at the same time. Although explanation is omitted, it is easily required that the Vout sixth term, that is, “a5 · Vin ⁵ ” includes the fundamental component, the third harmonic component, and the fifth harmonic component.

Therefore, an OFDM signal whose input signal is Vin is expressed as the following equation (4) as a function of the amplitude A (t) and the phase θ. Hereinafter, the amplitude “A (t)” is also simply expressed as “A” as appropriate.

Further, it is known that the probability density variable (pdf) of the equation (4) is the following equation (5) when the standard deviation is σ and the probability density variable is an OFDM signal indicating a Rayleigh distribution. .

また、σ＝１のときの振幅Ａの平均値は、以下の（７）式となる。

For the sake of simplicity, assuming that σ = 1 (mean square deviation rms = 1), the probability density function of the amplitude A (t) is expressed by the following equation (6).

Further, the average value of the amplitude A when σ = 1 is expressed by the following equation (7).

The average values of A ⁿ (n = 1 to 10, 12, 14) calculated in the same manner are collectively shown in Table 1 below.

  As described above, the terms related to the third harmonic and the fifth harmonic in the equation (1) are the third and fifth power terms. However, these terms include fundamental wave components and other harmonic components as shown in the two-wave model. Therefore, by subtracting the fundamental component from the third power term and the third harmonic component and the fundamental component from the fifth power term, a signal including only an independent third harmonic component or fifth harmonic component is obtained. The same applies to odd-order harmonic components after the seventh order.

Therefore, in order to know the magnitude of the fundamental wave component included in the cube term in the OFDM signal, the cross-correlation coefficient η31 is obtained by the following equation (8).

また、（９）式のｒｍｓ値は、次の（１０）式の通りである。

したがって、σ＝１（ｒｍｓ値＝１）の３次歪信号（３次高調波）ＩＭ３は、（１０）式で正規化すると、以下の（１１）式となる。

From this equation (8), it can be seen that the cubic term includes a basic component of size 2. The signal im3 including only the third-order distortion is obtained by subtracting the fundamental wave component, and can be expressed by the following equation (9).

Further, the rms value of the equation (9) is as the following equation (10).

Therefore, the third-order distortion signal (third-order harmonic) IM3 with σ = 1 (rms value = 1) becomes the following expression (11) when normalized by expression (10).

つまり、入力信号ＶｉｎがＯＦＤＭ信号である場合、後述する積分回路で入力信号Ｖｉｎと３次歪信号ＩＭ３の共役複素数とを複素乗算すると、出力がゼロとなる。一方、入力信号ＶｉｎがＯＦＤＭ信号でない場合、振幅の確率密度変数はレイレー分布とならないため、積分回路の出力はゼロにならない。 Here, when the conjugate complex number of the input signal Vin, which is an OFDM signal, and the third-order distortion signal IM3 is complex multiplied, the following equation (12) is obtained.

That is, when the input signal Vin is an OFDM signal, the output becomes zero when the input signal Vin is complex-multiplied with the conjugate complex number of the third-order distortion signal IM3 by an integration circuit described later. On the other hand, when the input signal Vin is not an OFDM signal, the probability density variable of amplitude does not have a Rayleigh distribution, so the output of the integrating circuit does not become zero.

  Although not described in detail here, even when a fifth-order distortion signal or a seventh-order distortion signal is used, if the input signal Vin is an OFDM signal based on the same principle, the output of the integration circuit becomes zero.

  In this way, it is possible to determine whether the signal is an OFDM signal by generating a third-order distortion signal from the input signal and performing complex multiplication of the input signal Vin, which is an OFDM signal, and the third-order distortion signal IM3 by an integration circuit. . Therefore, an OFDM signal squelch circuit can be realized by using this principle.

  Next, a relay device including the squelch circuit using the above principle will be described with reference to a functional block diagram of the relay device shown in FIG. 1 and a functional block diagram of the squelch circuit shown in FIG. Here, the squelch circuit is applied to the relay device, but the present invention is not limited to the relay device and can be applied to devices that receive OFDM signals.

  As shown in FIG. 1, the relay apparatus 10 according to the present embodiment includes a reception BPF (Band Pass Filter) 12, a reception converter 13, a squelch circuit 20, a transmission converter 14, a power amplifier 15, and a transmission. BFP16.

  The reception BPF 12 extracts only a signal in a predetermined frequency band, for example, 470 MHz to 770 MHz, from the digital broadcast wave received by the reception antenna 11 and outputs it to the reception converter 13.

  The reception converter 13 converts the signal extracted by the reception BPF 12 into an IF (Intermediate Frequency) band signal (hereinafter referred to as “IF signal”) of a predetermined frequency, for example, an IF signal having a center frequency of 37.15 MHz. .

  Then, the squelch circuit 20 determines whether this IF signal is an OFDM signal. That is, it is determined whether the digital broadcast wave received by the receiving antenna 11 is an OFDM signal. Here, it is determined whether or not it is an OFDM signal by using the above-described determination method using the third-order distortion signal. Further, when the squelch circuit 20 determines that the received digital signal wave is an OFDM signal, the squelch circuit 20 outputs a signal to the transmission converter 14. If the squelch circuit 20 determines that the received digital signal wave is not an OFDM signal, the squelch circuit 20 cuts off the output to the transmission converter 14. That is, a signal whose signal level is zero is output.

  The transmission converter 14 converts the signal output from the squelch circuit 20 into an RF (Radio Frequency) signal in a predetermined frequency band. Then, the power amplifier 15 amplifies the signal converted into the RF signal so as to have a predetermined power, and retransmits it from the transmission antenna 17.

  As shown in FIG. 2, the squelch circuit 20 includes an A / D converter 21, an AGC controller 27, a quadrature demodulator 23, an output cutoff circuit 24, a quadrature modulator 25, and a D / A converter 26. OFDM determination circuit 50.

  The A / D converter 21 converts the analog signal converted into the IF signal by the reception converter 13 into a digital signal. The digitally converted signal is feedback-controlled so as to have a predetermined output level by an AGC multiplier 22 included in an AGC controller 27 described later, and is output to the quadrature demodulator 23.

  The orthogonal demodulator 23 orthogonally demodulates the IF signal output from the AGC multiplier 22 into a baseband signal. Further, the quadrature demodulator 23 converts the baseband signal from the time domain signal to a frequency domain signal expressed by a real part and an imaginary part, outputs the real part to the real signal line RL1, and converts the imaginary part to an imaginary signal. Output to line IL1.

  Each signal output from the real signal line RL1 and the imaginary signal line IL1 is branched into a plurality of signals and input to the AGC controller 27, the OFDM determination circuit 50, and the output cutoff circuit 24.

  The real part signal and the imaginary part signal input to the AGC controller 27 are squared by the real number multiplier 31a and the imaginary number multiplier 31b, respectively, and the two squared signals are added by the first AGC adder 32. . Subsequently, the second AGC adder 33 subtracts the signal added by the first AGC adder 32 from the target value set in the AGC target value unit 36 and outputs the result to the AGC integration circuit 34.

  The AGC integration circuit 34 smoothes the signal output from the second AGC adder 33 and outputs the smoothed signal to the third AGC adder 35. The third AGC adder 35 adds the signal output from the AGC integration circuit 34 and the target value set in the AGC target value unit 36 and outputs the result to the AGC multiplier 22. Then, as described above, the AGC multiplier 22 multiplies the signal converted by the A / D converter 21 by the output of the third AGC adder 35, thereby converting the signal input to the quadrature demodulator 23 to a signal of a predetermined level ( rms signal).

  Further, the OFDM determination circuit 50 determines whether or not the signal output from the quadrature demodulator 23 is an OFDM signal with a configuration described later. When it is determined that the acquired signal is an OFDM signal, the OFDM determination circuit 50 determines the determination signal “1” as a determination result, and when it is determined that the acquired signal is not an OFDM signal, the OFDM determination circuit 50 Outputs a determination signal “0” to the output cutoff circuit 24 as a determination result.

  The output cutoff circuit 24 orthogonally demodulates the above-mentioned “1” or “0” determination signal in the real cutoff multiplier 24a provided on the real signal line RL1 and the imaginary cutoff multiplier 24b on the imaginary signal line IL1. The signal output from the multiplier 23 is multiplied and output to the quadrature modulator 25. Therefore, when the signal output from the quadrature demodulator 23 is an OFDM signal, the signal as it is is output to the quadrature modulator 25. If the signal output from the quadrature demodulator 23 is not an OFDM signal, the output signal level is “0”, and so-called squelch operation is performed in which the output signal is blocked.

  The quadrature modulator 25 has a function of executing processing that is almost the reverse of the processing in the quadrature demodulator 23, and performs quadrature modulation on the baseband signal output from the output cutoff circuit 24 so as to become an OFDM signal. To the D / A converter 26. The D / A converter 26 digitally converts the signal modulated into the OFDM signal and outputs the signal to the transmission converter 14.

  Next, the configuration of the above-described OFDM determination circuit 50 will be described with reference to the circuit diagram shown in FIG.

  The OFDM determination circuit 50 includes a conjugate signal generation unit 51, a conjugate signal multiplier 52, a determination integration circuit 53, and a cutoff signal output unit 54.

  The conjugate signal generation unit 51 generates conj (IM3) of the above-described equation (12). More specifically, the conjugate signal generation unit 51 converts the real part signal obtained from the real signal line RL1 and the imaginary part signal obtained from the imaginary signal line IL1 into the first determination multiplier 61 and the second multiplier, respectively. The signal is squared by the decision multiplier 62, and the decision adder 55 adds the two squared signals, and outputs the result to the decision subtracter 56.

Subsequently, the determination subtracter 56 subtracts “2” from the signal output from the determination adder 55 and outputs the result to the third determination multiplier 63. The third determination multiplier 63 multiplies the signal output from the determination subtracter 56 by “2 ^−0.5 ” and outputs the result to the fourth determination multiplier 64 and the fifth determination multiplier 65. .

  The fourth determination multiplier 64 multiplies the output of the third determination multiplier 63 by the signal of the real part branched and input from the real signal line RL1, and the conjugate signal multiplier 52 through the real signal line RL2. Output to.

  The fifth determination multiplier 65 multiplies the imaginary part signal that is branched and input from the imaginary signal line IL1 by the output of the third determination multiplier 63 and outputs the result to the sixth determination multiplier 66. To do.

  At this time, the set of signals output from the fourth determination multiplier 64 and the fifth determination multiplier 65 is the third-order distortion signal represented by the above-described equation (11).

  Further, the sixth determination multiplier 66 multiplies the output of the second determination multiplier 62 by “−1” in order to generate a conjugate complex number of the imaginary part signal of the imaginary number signal line IL1, and generates an imaginary number signal. The signal is output to the conjugate signal multiplier 52 through the line IL2.

  As a result, a set of signals output from the fourth determination multiplier 64 and the sixth determination multiplier 66 is a conjugate complex signal (conjugate complex number) of the third-order distortion signal of the above-described equation (12).

  The conjugate signal multiplier 52 multiplies the original signal (input signal) represented by a pair of signals of the real signal line RL1 and the imaginary signal line IL1 and the conjugate complex signal of the third-order distortion signal generated from the original signal. And output to the determination integrating circuit 53.

  The determination integration circuit 53 smoothes the multiplication result of the conjugate signal multiplier 52. Then, when the smoothing result is “0”, the cutoff signal output unit 54 determines that the original signal is an OFDM signal based on the above-described principle, and outputs “1” as the determination signal shown in FIG. Output to the circuit 24. When the smoothing result is other than “0”, the cutoff signal output unit 54 outputs the determination result “0” to the output cutoff circuit 24 in order to cut off the output. As a result, the squelch operation in the output cutoff circuit 24 described above is performed.

  As described above, according to the present embodiment, when the digital broadcast wave signal is an OFDM signal, the squelch operation can be realized by using the characteristic that the amplitude density distribution of the OFDM signal becomes a Rayleigh distribution. More specifically, when the third-order distortion signal generated from the original signal is converted into a frequency domain expressed by a real number and an imaginary number, and a conjugate complex number of the converted signal is generated and multiplied by the original signal, When the signal is an OFDM signal, a squelch circuit for the OFDM signal can be realized by using the characteristic that the smoothed value of the multiplication result is “0”.

  In this embodiment, since so-called guard correlation is not used, a squelch operation can be executed even for an OFDM signal having no guard interval. In addition, since guard correlation is not used, it is possible to determine whether or not the signal is an OFDM signal with a relatively simple circuit configuration as described above. Further, since the circuit configuration is simple, power consumption can be reduced.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of these components, and such modifications are also within the scope of the present invention. For example, as described above, the above determination can be performed not only for the third-order distortion signal but also for the fifth-order, seventh-order,..., (2N + 1) -order distortion signal (odd-order distortion signal).

  Further, the result of the first AGC adder 32 of the OFDM determination circuit 50 may be used as the result of the determination adder 55 in the OFDM determination circuit 50.

It is a functional block diagram which shows the outline | summary of the relay system provided with a squelch circuit of embodiment by this invention. It is a circuit block diagram of the squelch circuit of embodiment by this invention. It is a circuit block diagram of the determination circuit of embodiment by this invention.

Explanation of symbols

10 relay device 11 receiving antenna 12 receiving BPF
13 Reception converter 14 Transmission converter 15 Power amplifier 16 Transmission BFP
17 transmitting antenna 20 squelch circuit 21 A / D converter 22 AGC multiplier 23 orthogonal demodulator 24 output cutoff circuit 24a real cutoff multiplier 24b imaginary cutoff multiplier 25 orthogonal modulator 26 D / A converter 27 AGC controller 31a real multiplication Unit 31b Imaginary multiplier 32 First AGC adder 33 Second AGC adder 34 AGC integration circuit 35 Third AGC adder 36 AGC target value unit 50 OFDM determination circuit 51 Conjugate signal generation unit 52 Conjugate signal multiplier 53 Determination integration circuit 54 Blocking Signal output unit 55 Judgment adder 56 Judgment subtracter 61 First decision multiplier 62 Second decision multiplier 63 Third decision multiplier 64 Fourth decision multiplier 65 Fifth decision multiplier 66 6 decision multiplier

Claims (3)

  A determination comprising: a means for determining whether or not the received signal is an OFDM signal based on a correlation between the received signal and an odd-order or higher-order distortion signal generated from the received signal. circuit. A determination circuit for determining whether or not the received signal is an OFDM signal based on a correlation between the received signal and an odd-order distortion signal of third or higher order generated from the received signal;
A signal blocking unit that blocks the output of the signal when the determination circuit determines that the signal is not an OFDM signal;
A squelch device comprising:   A third-order distortion signal is generated from the received signal, the third-order distortion signal and the complex conjugate signal of the received signal are subjected to complex multiplication, and when the result of the complex multiplication is 0, the received signal is an OFDM signal. An OFDM signal determination method, characterized by determining that there is an OFDM signal.

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