JP5249720B2 - Broadcast signal relay device - Google Patents

Description

  The present invention relates to a broadcast signal relay apparatus that receives broadcast radio waves of a predetermined channel, amplifies the received signal, and retransmits the broadcast signal as a broadcast signal having the same frequency as the reception channel.

  Conventionally, a technique called SFN (Single Frequency Network) is sometimes used in terrestrial digital broadcasting of television.

  The SFN constitutes a relay station network using the same channel as the transmission radio wave from the upper station, and the relay station receives the transmission radio wave from the upper station, amplifies it to a predetermined power, and sends the amplified signal. Retransmit at the same frequency (same channel) as the received wave.

  By the way, in this relay station, transmission radio waves may be mixed into the receiver input of the local station due to reflection of transmission radio waves generated in surrounding buildings, trees, topography, etc., or due to radio wave coupling between devices. .

  Even if the transmission radio wave is mixed in the receiver input in this way, if the degree of mixing is small, the transmission wave transmitted from the relay station can be regarded as almost equivalent to the reception waveform (that is, the radio wave of the upper station), As the degree of mixing increases, the transmission waveform differs from the reception wave. In the worst case, an oscillation state occurs.

  Therefore, in order to prevent such problems, conventionally, not only devising the mounting position of the reception antenna and the transmission antenna so that the wrapping of the transmission radio wave to the reception side is reduced, It has been proposed to control the gain of the device so that it does not fall into abnormal operation such as oscillation.

Specifically, the peak level of the transmission signal output to the transmission antenna is detected, and the gain of the device is set so that the detected value (or the integrated value of the detected value) does not exceed a preset threshold value. Control (for example, refer to Patent Documents 1 and 2, etc.) or detect the average power (average value) of the received broadcast signal so that the average value does not exceed a preset threshold value It is proposed to control the gain (see, for example, Patent Document 3).
JP 2004-2448078 A JP-A-9-98130 JP 2004-186829 A

  However, in the proposed technique, the oscillation due to the wrapping of the transmission radio wave to the receiving side is determined depending on whether the peak value or average value of the broadcast signal to be retransmitted exceeds the threshold value, so that the oscillation does not occur. Since the gain is controlled, there is no guarantee that it will not oscillate, and there is a problem that the possibility of oscillation due to changes in environmental conditions cannot be denied.

  This problem was discovered by the inventor of the present application through experiments (detailed simulation) described later.

  The present invention has been made in view of such problems, and in a broadcast signal relay apparatus that receives and amplifies broadcast radio waves of a predetermined channel, and retransmits the amplified reception signal without converting the frequency. It is an object to prevent the quality of broadcast radio waves to be retransmitted from being deteriorated due to problems such as oscillation caused by signal wrapping.

In order to achieve this object, the invention according to claim 1 receives a broadcast radio wave of a predetermined channel, amplifies the received signal, and converts the amplified received signal into a broadcast signal having the same frequency as that of the received channel. As a broadcast signal relay device for wireless transmission,
Average amplitude detection means for detecting the average amplitude (A) of a broadcast signal to be transmitted wirelessly;
Peak value detecting means for detecting the peak value (P) of the amplitude of the broadcast signal to be transmitted wirelessly;
The ratio (P / A) between the peak value (P) detected by the peak value detection means and the average amplitude (A) detected by the average amplitude detection means exceeds a preset threshold value. Control means for controlling the gain of the broadcast signal relay device,
It is provided with.

  In the broadcast signal relay device according to claim 1, the peak value (P) or the ratio (P / A) exceeds a set value for abnormality determination in the broadcast signal relay device according to claim 1, or When the average amplitude (A) is lower than a set value for abnormality determination, an alarm means for notifying the operation abnormality of the relay device is provided.

  Further, the invention according to claim 3 is the broadcast signal relay device according to claim 1, comprising power detection means for detecting transmission power (W) of the broadcast signal instead of the average amplitude detection means, The control means is configured such that a ratio (P / W) between the peak value (P) detected by the peak value detection means and the transmission power (W) detected by the power detection means is a preset threshold value. The gain of the broadcast signal relay device is controlled so as not to exceed.

  According to the broadcast signal relay apparatus according to claim 1, the average amplitude detecting means and the peak value detecting means detect the average amplitude (A) and the peak value (P) of the broadcast signal transmitted by radio, respectively, and the control means However, the gain of the broadcast signal relay apparatus is controlled so that the ratio (P / A) of the detected peak value (P) and average amplitude (A) does not exceed a preset threshold value.

  This is because, as in the conventional apparatus described above, when the peak value (P) or average value (average amplitude A) of the broadcast signal exceeds a threshold, oscillation is detected and the gain of the apparatus is reduced. This is because oscillation cannot be reliably prevented and the quality of the transmission signal may be degraded.

  Hereinafter, this point will be described in detail.

  First, assuming that the path through which the transmission radio wave wraps around the reception side is a feedback path, the equivalent circuit of the broadcast signal relay device of the present invention can be described as the feedback circuit shown in FIG.

  In FIG. 1, R is a received signal, X is an input signal to a relay device internal circuit (amplifier circuit, etc.), Y is an output signal from the transmitting antenna, and Z (ω) is a feedback path from the transmitting antenna to the receiving antenna. Which is a function of the frequency ω. G (ω) is a frequency characteristic of an internal circuit of the relay device such as an amplifier circuit.

  The response of this feedback circuit is expressed by the following equation (1).

Here, G (ω) can be regarded as a flat frequency characteristic within the transmission frequency band (there is a delay).

  Now, assuming that the characteristic of the feedback path is a simple delay characteristic, the expression (1) can be written as the following expression (2).

FIG. 2 shows an example of the response characteristic of the above equation (2), that is, the Y / R amplitude characteristic. Here, the product of G (ω) and Z (ω) is defined as a “wrapping amount”, and in FIG. 2A, this is graphed as a parameter.

  As shown in FIG. 2A, the peak appearing in the frequency characteristic of the output increases as the amount of wrap-around approaches 0 dB, and at 0 dB, the output signal has an infinite amplitude, that is, an oscillation state at a specific frequency. .

  FIG. 2B shows the average amplitude of the output signal, the ratio of the maximum peak amplitude (peak value) to the average amplitude, and the output power plotted against the amount of wraparound (that is, the detection value vs. the number of times). ). In FIG. 2B, the average amplitude and the output power are expressed with reference to a value (0 dB) when there is no wraparound.

  Then, as shown in FIG. 2B, by detecting the ratio between the peak value and the average amplitude in the output signal (peak value / average amplitude: hereinafter referred to as PA ratio), how much the amount of wrapping is You can know if it is.

  Next, FIGS. 3A and 3B show output frequency characteristics and detected value vs. wrap-around amount characteristics when there are two feedback paths, corresponding to FIGS. 2A and 2B. It is. Each path has a different delay and attenuation.

  The amount of wraparound in this case is defined by the sum of the power of the feedback signal component, that is, the sum of the feedback power of path 1 and the power of path 2. As shown in FIG. 3, when there are two feedback paths, a larger peak occurs in the output frequency characteristics than in the case of the single feedback path shown in FIG. 2, and the PA ratio increases. In addition, the characteristics of the average amplitude and the output power are different from those in the case of a single path in a region where the amount of entrainment is large (around −3 dB).

  In general, when there are a plurality of feedback paths, the output response of the feedback circuit exhibits different characteristics depending on the delay amount of each path and the mutual amplitude relationship. This suggests that attention must be paid when abnormal operation avoidance (oscillation prevention) is performed using information on output power and average amplitude. Actually, since the delay and attenuation amount of the feedback path are various for each relay station, it is impossible to obtain appropriate information for all conditions.

  FIGS. 4A and 4B show detection values obtained by plotting the average amplitude, PA ratio, and output power by randomly generating various delays and attenuations when the number of feedback paths is 2 and 10. FIG. The VS entrainment amount characteristic is shown. The solid line in the figure connects the average values of the plots for each wrap-around amount, and can be said to be an expected value for random conditions.

  Among these three, only the PA ratio is a monotonically increasing function with respect to the amount of entrainment, and the other two have a range that becomes a decrementing function in a region where the amount of entrainment is large. Since it exists (see, for example, FIG. 3), it can be said that it is not suitable for use as control information.

  From the above, in order to avoid abnormal operation such as oscillation by controlling the gain, the PA ratio, which is the ratio of these, is used rather than using the average amplitude (A) and the peak value (P) as in the prior art. It turns out that it is appropriate to use.

  In the broadcast signal relay apparatus of the present invention, the apparatus gain is controlled (reduced) when the peak value (P) or the average value (average amplitude A) of the broadcast signal exceeds the threshold value as in the prior art. Instead, based on the ratio (PA ratio: P / A) of these parameters (peak value P, average amplitude A), the gain of the apparatus is controlled so that the PA ratio does not exceed the threshold value. In the relay device, it is possible to prevent an abnormal operation such as oscillation from occurring and deterioration of the quality of the broadcast signal wirelessly transmitted from the transmission antenna.

  In addition, according to the broadcast signal relay device of the present invention, not only can abnormal operations such as oscillation be prevented, but also broadcast radio waves transmitted from the relay device can be kept within a predetermined frequency characteristic deviation. , It is possible to prevent the quality of the broadcast signal from being degraded.

  That is, in the case of a plurality of feedback paths, when Z (ω) in the above equation (1) is expressed by the following equation (3), the ratio of the maximum peak to the minimum peak (PP deviation) of the output signal is as follows: Is calculated.

Substituting this into the equation (1) or (2) to find the maximum and minimum values,

It becomes.

  As a result, PP deviation (PP) is

Then, by deleting Σ | Ak | from the equations (4) and (5), the following equation (6) is obtained.

In the region where the amount of entrainment is small, the average amplitude is a substantially constant value (see FIG. 4), so the value (= GR) when there is no feedback path can be used as the average amplitude value. In this case, the PA ratio is

Thus, the value of the PA ratio to be set in order to keep the PP deviation within a predetermined value is obtained.

  Next, since simulation was performed to support the above effect, the simulation result will be described.

  In this simulation, the PA ratio is 6 dB (doubled), the delay amount of the feedback path is randomly generated in 100 ways, and the gain G of the amplifier circuit that amplifies the received signal so that the maximum value at that time does not exceed the PA ratio. Controlled. The results are shown in FIGS.

  FIG. 5 shows a simulation result when the number of feedback paths is two, and FIG. 6 shows a simulation result when the number of feedback paths is ten. In these figures, (a) represents characteristics with respect to each random delay amount, and (b) represents characteristics obtained by averaging the characteristics shown in (a). Therefore, (b) can be regarded as a typical characteristic (expected value) with respect to the number of feedback paths. Further, the wraparound amount FB in the case of such multiple feedback paths is defined by the power sum of the following equation (8).

As is apparent from FIGS. 5 and 6, as in the present invention, if the gain (G) of the device is controlled so that the PA ratio does not exceed the threshold value, the average amplitude of the output signal when the amount of wrap-around increases. And power can be reduced.

  That is, regardless of whether the number of feedback paths is 2 or 10, the control starts to operate when the wrap-around amount is about −10 dB, and the output power starts to decrease. Therefore, in such a relay device that avoids abnormal operation by gain control, an antenna or the like may be installed so that the amount of wrap-around becomes -10 dB or less.

  Note that the output power is slightly increased in the region where the PA ratio is close to the specified value (in this example, the wrap-around amount is in the vicinity of −10 dB), but the amount is about 0.5 dB, and there is no practical problem.

  On the other hand, FIGS. 7 and 8 show simulation results when the gain G is controlled so that the average amplitude of the output signal is constant, and FIGS. 9 and 10 control the gain G so that the output power is constant. The simulation result is shown.

  7, 8, 9, and 10 show the simulation results corresponding to FIGS. 5 and 6, respectively. FIGS. 7 and 9 show the case where the number of feedback paths is two. 8 and 10 show simulation results when the number of feedback paths is ten. In these figures, (a) represents characteristics with respect to each random delay amount, and (b) represents characteristics obtained by averaging the characteristics shown in (a).

  In these cases, the average amplitude and output power to be controlled are controlled to be substantially constant, but as is clear from the maximum / average (ie PA ratio) shown in (a) of each figure, the maximum value of the output signal ( (Peak value) may be very large.

  For this reason, when the gain is adjusted based on the average amplitude and output power of the output signal, even if the oscillation phenomenon can be avoided, the large amplitude component is clipped by the amplifier circuit, etc., and the amplitude proportional noise increases significantly. As a result, the receiving device that receives the transmission radio wave from the relay device cannot receive normally. The amplitude proportional noise is described in detail in the technical data (ARIB TR-B14 9th deviation) of the Radio Industries Association and the description thereof is omitted here.

  For example, in FIG. 8, although the average amplitude is controlled to be a constant value, the value decreases when the wrap-around amount is around 0 dB. This is because when the average amplitude is controlled to a specified value (in this case, 0 dB), the control loop may fall into the oscillation state, and in the simulation, the gain G is kept in the state immediately before the oscillation. As described above, when there are a plurality of feedback paths, the average amplitude value with respect to the amount of entrainment may be a decreasing function. In this case, if the control loop is operated carelessly, oscillation will occur. That is, it can be said that there is no guarantee that oscillation can be reliably avoided in the case of average value control or output power control.

  Therefore, from the simulation results shown in FIGS. 5 to 10, in order to avoid abnormal operation such as oscillation of the relay device by controlling the gain of the broadcast signal relay device, the average amplitude ( It can be seen that it is appropriate to use the PA ratio, which is the ratio of these, rather than using A) or the peak value (P).

  By the way, in the broadcast signal relay device of the present invention, by controlling the gain so that the PA ratio does not exceed the threshold value, abnormal operation such as oscillation of the broadcast signal relay device is prevented. May be lower than a specified value and may not function normally as a broadcast signal relay device.

  Therefore, in the broadcast signal relay device of the present invention, as described in claim 2, the peak value (P) or the PA ratio (P / A) exceeds the set value for abnormality determination, or the average amplitude ( When A) falls below the set value for abnormality determination, alarm means for notifying the operation abnormality of the relay device may be provided.

  In this way, when the gain (G) is reduced to prevent abnormal operations such as oscillation, the transmission power of the broadcast signal is likely to be lower than the specified value or likely to be lower than the specified value. When this happens, it is possible to notify the administrator of the relay device or the like and prompt the repair / inspection of the relay device.

  As is apparent from FIGS. 2 to 6, the average amplitude (A) of the output signal (broadcast signal) to be retransmitted and the output power (transmission power) of the output signal (broadcast signal) Although the change ratio with respect to the increase is different, the change characteristics (in other words, the change tendency) are substantially the same. Therefore, when the abnormal operation such as oscillation of the broadcast signal relay apparatus is prevented, the PA ratio (P / A) is not necessarily required. As described in claim 3, the ratio (P / W) between the peak value (P) and the transmission power (W) may be used.

  That is, the broadcast signal relay device according to claim 3 is provided with power detection means for detecting the transmission power (W) of the broadcast signal instead of the average amplitude detection means, and the control means is provided with the peak value detection means. The broadcast signal relay device so that the ratio (P / W) between the peak value (P) detected in this way and the transmission power (W) detected by the power detection means does not exceed a preset threshold value. However, even if the broadcast signal relay device is configured in this way, the same effect as the broadcast signal relay device according to claim 1 can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
[Configuration of the embodiment]
FIG. 11 is a block diagram showing the configuration of the entire broadcast signal relay apparatus according to the embodiment to which the present invention is applied.

  As shown in FIG. 11, the broadcast signal relay device of this embodiment includes a receiving antenna 2 that receives a broadcast wave of terrestrial digital broadcasting transmitted from the broadcasting station, and a received signal from the receiving antenna 2. The input amplifier circuit 4 that selectively amplifies the broadcast signal of a specific channel to be retransmitted, and the gain for the broadcast signal of the relay device is increased by attenuating the broadcast signal amplified by the input amplifier circuit 4 A gain adjusting circuit 6 for adjusting, a power amplifying circuit 8 for amplifying a broadcast signal that has passed through the gain adjusting circuit 6 into a transmission signal, and a transmission signal output from the power amplifying circuit 8 are transmitted from a higher-level broadcasting station. And a transmission antenna 10 for retransmitting to a region where radio waves do not reach, and a broadcast signal of a predetermined channel received by the reception antenna 2 is sequentially amplified by the input amplification circuit 4 and the power amplification circuit 8 Te, and it is configured to re-transmitted from the transmitting antenna 10 in the broadcast signal received at the same frequency (co-channel in other words).

  Further, in the broadcast signal relay device of this embodiment, a part of the transmission signal (broadcast signal) output from the power amplifier circuit 8 to the transmission antenna 10 is taken in via the coupler 12, and the average amplitude of the broadcast signal is acquired. By adjusting the attenuation amount of the gain adjustment circuit 6 based on (A) and the peak value (P), the control circuit 20 that controls the gain of the relay device, and the average amplitude of the broadcast signal detected by the control circuit 20 ( A) calculating the ratio between the peak value (P) and the peak value (P) (PA ratio: P / A), and determining the abnormality of the relay device based on the output from the arithmetic circuit 30 to the administrator And an alarm device 32 for reporting an abnormality.

  Next, the control circuit 20 includes diodes D1 and D2 that detect broadcast signals received via the coupler 12, and a peak detection circuit 21 that detects a peak value (P) of the broadcast signal detected by the diode D1. And an average value detection circuit 22 for detecting the average amplitude (A) of the broadcast signal detected by the diode D2.

  The peak detection circuit 21 has an inverting input terminal and an output terminal connected to each other, and is composed mainly of an operational amplifier A1 in which a broadcast signal is input from a diode D1 to a non-inverting input terminal. And a capacitor R1 provided between the output terminal and the ground line, and a variable resistor VR1 provided between the output terminal and the ground line.

  As a result, in the peak detection circuit 21, the broadcast signal is peak-held by the capacitor C1, and the peak hold value is discharged through the resistor R1 with a constant time constant, and the peak hold value (that is, broadcast) is output from the operational amplifier A1. The peak value P) of the signal is output (see the waveform of peak detection in FIG. 12A).

  The average value detection circuit 22 has an inverting input terminal and an output terminal connected to each other, and is composed mainly of an operational amplifier A1 in which a broadcast signal is input from a diode D2 to a non-inverting input terminal via a resistor R22. A resistor R21 provided between the connection point of D2 and the resistor R22 and the ground line, and a capacitor C2 provided between the connection point of the resistor R22 and the non-inverting input terminal of the operational amplifier A1 and the ground line. Prepare.

  As a result, in the average value detection circuit 22, the broadcast signal is integrated with the resistor R22 and the capacitor C2 with a predetermined time constant, and the integrated value is output as an average value (average amplitude A) from the operational amplifier A2. .

  The time constant (R1 · C1) of the peak detection circuit 21 is set to a value (for example, 3 ms) suitable for detecting the peak value (P) of the broadcast signal, and the time constant of the average value detection circuit 22 ( R22 · C2) is set to a value (for example, 1 sec) suitable for detecting the broadcast signal average amplitude (A).

  Further, the variable resistor VR1 provided at the output stage of the peak detection circuit 21 divides the output from the operational amplifier A1, so that the ratio of the peak value P to the output from the average value detection circuit 22 is an upper limit value (that is, a threshold value). For example, if the voltage division ratio of the variable resistor VR1 is “1/2”, the peak value (P) of the broadcast signal is When the ratio (PA ratio) to the average amplitude (A) exceeds the value 2 (= threshold), the output from the peak detection circuit 21 becomes larger than the output from the average value detection circuit.

  Next, the outputs from the peak detection circuit 21 and the average value detection circuit 22 are respectively input to the abnormality determination circuit 23. The abnormality determination circuit 23 compares these inputs so that the ratio (PA ratio: P / A) between the peak value (P) of the broadcast signal amplitude and the average amplitude (A) is divided by the variable resistor VR1. This is for determining whether or not a threshold determined by the value has been exceeded, and is composed mainly of the operational amplifier A3.

  That is, the abnormality determination circuit 23 takes in the peak value divided by the threshold value from the sliding contact of the variable resistor VR1 of the peak detection circuit 21, and inputs the resistance R31 input to the inverting input terminal of the operational amplifier A3 and the inversion of the operational amplifier A3. A diode D3 and a resistor R32 are provided between the input terminal and the output terminal, respectively, and the output from the average value detection circuit 22 is input to the non-inverting input terminal of the operational amplifier A3.

  The diode D3 has an anode connected to the output terminal of the operational amplifier A3 and a cathode connected to the inverting input terminal of the operational amplifier A3.

  As a result, if the PA ratio of the broadcast signal does not exceed the threshold determined by the divided voltage value of the variable resistor VR1, the output from the abnormality determination circuit 23 is the same level as the output of the average value detection circuit 22, and the PA of the broadcast signal When the ratio exceeds a threshold value determined by the divided voltage value of the variable resistor VR1, the output from the abnormality determination circuit 23 becomes a negative voltage that indicates an abnormality caused by the broadcast signal wraparound.

  That is, the operational amplifier A3 that constitutes the abnormality determination circuit 23 operates as a rectifier circuit, and generates a large negative polarity pulse when the level-adjusted peak value (P) detection signal exceeds the average amplitude (A) detection signal. When the detection signal of the peak value (P) does not exceed the detection signal of the average amplitude (A), the detection signal of the average amplitude (A) is output (see the waveform of the A3 output shown in FIG. 12B). ).

  The output from the abnormality determination circuit 23 is input to the smoothing circuit 24 together with the output from the average value detection circuit 22.

  In the smoothing circuit 24, the output from the abnormality determination circuit 23 is input to the inverting input terminal via the resistor R41, the output from the average value detection circuit 22 is input to the non-inverting input terminal, and between the inverting input terminal and the output terminal. The operational amplifier A4 is provided with a smoothing capacitor C4 and a resistor R42.

  Therefore, the smoothing circuit 24 adds the output (negative voltage) from the abnormality determination circuit 23 to the output (average amplitude A) from the average value detection circuit 22, and smoothes it with a predetermined time constant (C4 / resistance R42). The signal (see A3 output smoothing waveform shown in FIG. 12B) is output.

The output from the smoothing circuit 24 is compared with the reference voltage Eo by the output circuit 25 including the operational amplifier A5, and is converted into a control signal for gain adjustment corresponding to the difference from the reference voltage Eo. It is output to the circuit 6.
[Effect of the embodiment]
Therefore, when the PA ratio (P / A) of the broadcast signal output to the transmission antenna 10 does not exceed a predetermined threshold, the control circuit 20 of the present embodiment controls the average for controlling the average amplitude of the broadcast signal to the target value. It operates as an amplitude control circuit, and when the PA ratio exceeds a predetermined threshold, it operates as a control circuit that suppresses the peak value (P) of the broadcast signal and controls the PA ratio below the threshold.

  Thus, according to the broadcast signal relay device of this embodiment, the gain of the relay device is adjusted so that the PA ratio of the broadcast signal transmitted from the transmission antenna 10 does not exceed a preset threshold value. As a result, the oscillation of the relay device can be prevented more reliably than the conventional device that performs gain adjustment using only the average amplitude (A) and peak value (P) of the broadcast signal as parameters, and the transmission antenna 10 It is possible to prevent the quality of the broadcast signal (radio wave) transmitted from being deteriorated.

  In the broadcast signal relay device of this embodiment, an arithmetic circuit that calculates the ratio (PA ratio: P / A) between the average amplitude (A) and the peak value (P) of the broadcast signal detected by the control circuit 20. 30 and an alarm device 32 that determines an abnormality of the relay device based on the output from the arithmetic circuit 30 and reports the abnormality to the administrator. When the transmission power of the broadcast signal is lower than the specified value or is likely to decrease, the alarm device 32 can detect that fact and notify the administrator. Therefore, the administrator can quickly detect such an abnormality and promptly repair and check the broadcast signal relay device.

In the present embodiment, the average value detection circuit 22 corresponds to the average amplitude detection means of the present invention, the peak detection circuit 21 corresponds to the peak value detection means of the present invention, the abnormality determination circuit 23, and the smoothing circuit 24. The output circuit 25 and the gain adjustment circuit 6 correspond to the control means of the present invention, and the arithmetic circuit 30 and the alarm device 32 correspond to the alarm means of the present invention.
[Consideration of peak value detection]
Here, the broadcast signal relay device of the above embodiment has been described as retransmitting a television broadcast signal of digital terrestrial broadcasting. However, this broadcast signal is an OFDM (Orthogonal Frequency Division Multiplex) wave, and is generated from a large number of carriers. It is configured.

  For this reason, a signal whose ratio (P / A) of the peak value (P) and the average amplitude (A) exceeds the threshold is detected from the broadcast signal (OFDM wave), and the gain of the broadcast signal relay device is increased. In order to control, it is necessary to appropriately set the time constant (R1 · C1) of the peak detection circuit 21 so that the peak value where the PA ratio exceeds the threshold value can be supplemented.

  Further, if the time constant (R1 · C1) of the peak detection circuit 21 is too large, the peak value exceeding the threshold is detected and the value is held. The constant (R1 · C1) needs to be set so that the detected peak value (P) can be updated at an appropriate frequency.

  Therefore, next, the setting of the time constant (R1 · C1) of the peak detection circuit 21 in the broadcast signal relay device of the above embodiment will be considered.

  First, since the OFDM wave is composed of a large number of carrier waves, the amplitude distribution can be approximated by a normal distribution (the law of large numbers). In this case, it is considered whether the amplitude exceeding the specified value can be supplemented by observing the signal over how long (number of samples).

  Now, let N be the number of samples of the peak value (P) observed during the observation period, and the probability Perr that all of these samples are equal to or less than the specified value can be described as the following equation (9).

However, in the above equation (9), Err (x) is the probability that the sample exceeds the specified value, and is a well-known normal distribution complementary function.

Next, FIG. 13 shows the number of observation samples necessary to make the non-detection probability equal to or less than a predetermined value, calculated using equation (9). For example, when trying to capture samples exceeding 3 × σ, in order to make the non-detection probability 10 ⁻⁶ or less, 10,000 or more observation samples are required.

  Since the number of independent information in one OFDM frame period is equal to the number of OFDM carriers, the number of statistically independent samples observed in one OFDM frame period is also equal to the number of carriers. The terrestrial digital broadcast wave is usually operated in a mode using about 5600 OFDM carriers. In this case, in order to obtain 10,000 independent samples, it is necessary to observe over about 2 · OFDM frame period. There is.

  Here, the peak detection time constant (R1 · C1) is appropriately determined so as to perform the following operation. That is, the detected peak value is held for a predetermined period (in this example, 2 · OFDM frame) to obtain the peak value in the period. When this time constant is extremely shorter than the predetermined period, the peak value is updated every short period, so that the peak value in the predetermined period cannot be detected.

  On the other hand, if the peak detection time constant is set too long, once a large peak value is detected for some reason, it will be retained forever, so the detected peak value is updated at an appropriate frequency. You must select a time constant. A suitable time constant value is approximately 10 times the predetermined period.

  Further, since the peak value detected by the peak detection circuit 21 is different every time it is detected, if the gain is controlled based on the detected peak value, the output power of the broadcast signal frequently changes. Therefore, the peak value detected by the peak detection circuit 21 needs to be smoothed with an appropriate time constant by the smoothing circuit 24 as in the above embodiment.

  FIG. 14 shows a simulation of the relationship between the number of OFDM carrier samples and the average value of peak values exceeding a specified value. For example, when more than 3 × σ is detected, the detection value is averaged over a period of tens of thousands of samples or more, and the value is almost constant. Therefore, the time constant (C4 · R42) of the smoothing circuit 24 in FIG.

  Next, “Table 1” shown in FIG. 15 is a simulation result in which the level exceeding the specified value is detected using the number of smoothed samples as a parameter. In this simulation, the operation of averaging the detected sample values with the section length of the number of smoothed samples was performed 1000 times.

  In the table, “not detected” indicates the number of times that the specified value level was not detected after 1000 trials, “μ” indicates the average value exceeding the specified value level, and “σ” indicates the standard deviation above the specified value level. ing.

  16 and 17 are plots of detected values for each trial during this simulation.

  The examination so far relates to detection of the peak value of the OFDM wave, but in the present invention, when there is a return path of the broadcast wave transmitted from the transmission antenna 10, the peak value when the OFDM signal is passed through that path. It is important to seek

  If there is a feedback path, a peak appears at a specific frequency as shown in FIGS. 2 and 3, so that the peak value of the time waveform can also be regarded as generated by these frequency neighboring components. .

  That is, the peak value of the time waveform can be approximated by a value obtained by observing only the OFDM carrier in the vicinity of the frequency at which the peak of the frequency characteristic is observed. The number of carriers in the vicinity of the peak depends on the PA ratio after control and the delay time, but in the case of a normally assumed PA ratio of about 6 dB, this number is about 1/10 to 1/100 of the total number of carriers ( This is called the peak number ratio). Further, the number of samples that substantially contribute to the detection of the peak value can be regarded as the peak number ratio of all the observed samples.

  Therefore, in order to obtain sufficient accuracy as control information detected after smoothing, it is necessary to multiply the number of observation samples by the peak number ratio. If the peak number ratio is 1/100, the “number of smoothed samples” in Table 1 is 100 times the value described. Assuming that the response speed of the entire control is 1 second, about 5.6 million samples are observed during this period, but the number of samples contributing to peak value detection is 1/100 to 50000.

  In this case, if the PA ratio is not set to 3 × σ or less, the probability that the peak value is not observed within the observation period increases, and the control is not performed correctly.

  From the above examination, when the control response speed is about 1 second, the PA ratio is 3 × σ, and when it is about 0.1 second, the PA ratio is 2 × σ.

As shown in “Table 1” in FIG. 15, the detected value of the average amplitude is about 0.8 times the input power σ, and this needs to be taken into consideration when setting the PA ratio.
[Modification of Embodiment]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.

  For example, in the above embodiment, when the broadcast signal transmission power becomes equal to or less than a specified value due to the gain adjustment based on the PA ratio, and the broadcast signal relay device does not function normally, this is detected and the alarm device 32 is detected. In order to generate an alarm, the calculation circuit 30 for calculating the PA ratio from the output of the peak detection circuit 21 and the output of the average value detection circuit 22 has been described. However, for example, as shown by a dotted line in FIG. Instead of the arithmetic circuit 30, the output (average amplitude A of the broadcast signal) from the average value detection circuit 22 is compared with the reference voltage Ee for abnormality determination, and the average amplitude (A) is lower than the reference voltage Ee. Then, a comparator 34 that outputs a drive signal to the alarm device 32 to generate an alarm may be provided.

  Further, instead of the arithmetic circuit 30, an output from the peak detection circuit 21 (broadcast signal peak value P) is compared with a reference voltage for abnormality determination, and if the peak value (P) exceeds the reference voltage, an alarm device is provided. A comparator that outputs a drive signal to 32 to generate an alarm may be provided.

  In this case, in any case, it is possible to detect (or estimate) a decrease in the transmission power of the broadcast signal from the transmission antenna 10 and notify the administrator to that effect. The same effect can be obtained.

  Next, in the above-described embodiment, in the control circuit 20, the retransmitted broadcast signal received via the coupler 12 is directly used as the peak detection circuit 21 and the average value detection circuit via the detection diodes D1 and D2. 18, for example, as shown in FIG. 18, the broadcast signal from the coupler 12 to the peak detection circuit 21 and the average value detection circuit 22 that takes in the broadcast signal via the diodes D <b> 1 and D <b> 2. The high frequency signal output from the sweep oscillator 27 and the broadcast signal are mixed in the input path, and only the broadcast signal (specifically, the OFDM carrier) corresponding to the high frequency signal is frequency-converted to the intermediate frequency band, and the frequency The converted broadcast signal may be input to the peak detection circuit 21 and the average value detection circuit 22 via the band pass filter 29. .

  In this way, the peak detection circuit 21 and the average value detection circuit 22 can detect the peak value and the average amplitude for each OFDM carrier corresponding to the high frequency signal output from the sweep oscillator 27. As in the above embodiment, it is possible to easily determine whether or not the PA ratio exceeds the threshold for each OFDM carrier without finely adjusting the time constant (C1 · R1) of the peak detection circuit 21. .

  Furthermore, in the above embodiment, the abnormality determination circuit 23 of the control circuit 20 has a ratio (PA ratio: P / A) between the peak value (P) of the broadcast signal captured via the coupler 12 and the average amplitude (A). ) Exceeds the threshold, a negative signal indicating that is generated. However, for example, as shown in FIG. 19, the transmission power of the broadcast signal is detected instead of the average value detection circuit 22. The abnormality determination circuit 23 is provided with a ratio (P) between the transmission power (W) detected by the transmission power detection circuit and the peak value (P) detected by the peak detection circuit 21 (P When / W) exceeds a threshold value, a negative signal indicating that may be generated.

  In this way, the gain of the broadcast signal relay apparatus is controlled by the control circuit 20 so that the ratio (P / W) between the peak value (P) and the transmission power (W) does not exceed the threshold value. At the same time, when the ratio (P / W) between the peak value (P) and the transmission power (W) is equal to or less than the threshold value, the transmission power (W) is controlled to be a predetermined target value. Similar to the embodiment, it is possible to prevent the quality of the transmission signal from being lowered while preventing the oscillation caused by the wrapping of the transmission radio wave in the broadcast signal relay device.

It is explanatory drawing showing the equivalent circuit (feedback circuit) of a broadcast signal relay apparatus. FIG. 2 is an explanatory diagram illustrating an output frequency characteristic and a detected value vs. wraparound amount characteristic in the feedback circuit illustrated in FIG. 1. It is explanatory drawing showing the frequency characteristic of an output in case two feedback paths exist, and a detected value vs wraparound amount characteristic. It is explanatory drawing showing the detection value vs wrap-around amount characteristic obtained when a delay and attenuation are generated at random when there are a plurality of feedback paths. It is explanatory drawing showing the simulation result at the time of controlling a gain so that PA ratio may become below a threshold value when two feedback paths exist. It is explanatory drawing showing the simulation result at the time of controlling a gain so that PA ratio may become below a threshold value when there are ten feedback paths. It is explanatory drawing showing the simulation result at the time of controlling a gain so that an average amplitude becomes a constant value when two feedback paths exist. It is explanatory drawing showing the simulation result at the time of controlling a gain so that an average amplitude becomes a constant value when ten feedback paths exist. It is explanatory drawing showing the simulation result at the time of controlling a gain so that output electric power may become a constant value when two feedback paths exist. It is explanatory drawing showing the simulation result at the time of controlling a gain so that output electric power may become a constant value when ten feedback paths exist. It is a block diagram showing the structure of the whole broadcast signal relay apparatus of embodiment. 12 is a time chart showing the operation in the control circuit 20 shown in FIG. It is explanatory drawing showing the calculation result of the number of samples required to make a non-detection probability below a predetermined value. It is explanatory drawing showing the relationship between the number of samples of an OFDM carrier, and the average value of the peak value exceeding the designated value. It is explanatory drawing (table | surface) showing the simulation result which performed the specified value super-level detection using the number of smoothing samples as a parameter. It is explanatory drawing showing the detected value for every trial at the time of the simulation shown in FIG. It is explanatory drawing showing the detected value for every trial at the time of the simulation shown in FIG. It is a block diagram showing the structure of the broadcast signal relay apparatus which provided the sweep oscillator in the control circuit. It is a block diagram showing the structure of the broadcast signal relay apparatus which provided the transmission power detection circuit in the control circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Reception antenna, 4 ... Input amplification circuit, 6 ... Gain adjustment circuit, 8 ... Power amplification circuit, 10 ... Transmission antenna, 12 ... Coupler, 20 ... Control circuit, 21 ... Peak detection circuit, 22 ... Average value detection circuit , 23: Abnormality determination circuit, 24: Smoothing circuit, 25 ... Output circuit, 27 ... Sweep oscillator, 29 ... Bandpass filter, 30 ... Arithmetic circuit, 32 ... Alarm device, 34 ... Comparator, 40 ... Transmission power detection circuit, A1 ~ A5 ... operational amplifier.

Claims (3)

In a broadcast signal relay device that receives a broadcast radio wave of a predetermined channel at a receiving antenna, amplifies the received signal, and retransmits the amplified received signal from the transmitting antenna as a broadcast signal of the same frequency as at the time of reception,
Average amplitude detection means for detecting the average amplitude (A) of the broadcast signal to be retransmitted;
Peak value detection means for detecting the peak value (P) of the amplitude of the broadcast signal to be retransmitted;
The ratio (P / A) between the peak value (P) detected by the peak value detection means and the average amplitude (A) detected by the average amplitude detection means exceeds a preset threshold value. Control means for controlling the gain of the broadcast signal relay device,
A broadcast signal relay device comprising:   When the peak value (P) or the ratio (P / A) exceeds the set value for abnormality determination, or the average amplitude (A) falls below the set value for abnormality determination, the relay device malfunctions. The broadcast signal relay apparatus according to claim 1, further comprising alarm means for informing the user.   In place of the average amplitude detection means, a power detection means for detecting the transmission power (W) of the broadcast signal is provided, and the control means includes the peak value (P) detected by the peak value detection means and the power. The gain of the broadcast signal relay apparatus is controlled so that the ratio (P / W) to the transmission power (W) detected by the detecting means does not exceed a preset threshold value. Item 2. The broadcast signal relay device according to Item 1.