JP2006013602A - Digital terrestrial broadcast retransmission equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To regulate the output level of each channel through a simple arrangement. <P>SOLUTION: A digital terrestrial broadcast signal, i.e. an RF input, comprising a plurality of OFDM channels is amplified at a first RF amplifying section 20 and fed to a BPF 21. High frequency signal of a channel for regulating the level is extracted by the BPF 21 and fed to a second RF amplifying section 22. A channel regulated to a specific level at the second RF amplifying section 22 is mixed with other channel subjected to level regulation by means of a mixer before being outputted. Even if the pass band of the BPF 21 extends into the frequency band of a channel adjacent to a passing channel, occurrence of ghost is prevented through action of guard interval in OFDM. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a terrestrial digital broadcast retransmission apparatus that retransmits a terrestrial digital broadcast in CATV, joint reception, or the like.

  The terrestrial digital broadcast re-transmission device consists of a terrestrial digital signal processor, terrestrial digital channel proper amplifier (reference Japan CATV Technology Association JCTEA STD-011), etc. It is a device to do. Digital terrestrial broadcast waves have different signal qualities such as the signal level that can be received depending on the position of the reception point, and change depending on time and season. For this reason, the terrestrial digital broadcast retransmitting device includes circuits having various functions such as an auto gain control circuit (AGC), an output level adjustment circuit, and a frequency conversion circuit. Also, the signal processing of the terrestrial digital broadcast retransmitting device is generally performed by converting the signal to an intermediate frequency using a local oscillation signal from a local oscillator, and after the signal processing, the same channel as the input channel is used. When outputting, up-conversion is performed using the same local signal. Further, when output is performed on a channel different from the input channel, it is up-converted using a local signal from another local oscillator and is output as a terrestrial digital broadcast signal of a different channel.

  Terrestrial digital broadcasting employs OFDM (Orthogonal Frequency Division Multiplexing). In general, an OFDM signal is composed of a large number of carriers having a narrow bandwidth, and has a rectangular spectrum. As the time waveform, in order to make it less susceptible to multipath, the rear part of the effective symbol is copied and pasted in front of the effective symbol as a guard interval. Thereby, it becomes difficult to receive the influence of the interference by the multipath of the delay time below a guard interval. Note that OFDM has a longer symbol length and a longer guard interval than single carrier modulation, and thus has a higher resistance to multipath interference. However, since a large number of carriers are used, mutual interference between carriers due to nonlinearities in the transmission path, etc. It is characterized by being easily affected by nonlinear distortion that generates modulation distortion.

FIG. 10 shows a configuration of a conventional terrestrial digital signal processor as an example of such a terrestrial digital broadcast retransmission apparatus that retransmits terrestrial digital broadcasts.
The terrestrial digital signal processor 100 shown in FIG. 10 is supplied with a terrestrial digital broadcast signal as an RF input. The RF input is applied to the RF amplification unit 110 and amplified at a high frequency, and then applied to the first mixer (MIXa). A local oscillation signal from the first local oscillator (OSC1) 111 is supplied to MIX1, and a frequency of a predetermined channel in the RF input is frequency-converted by this local oscillation signal, and an intermediate frequency signal is output from MIX1. . The intermediate frequency signal is subjected to signal processing in the IF signal processing unit 112 and controlled so that the output level of the output intermediate frequency signal becomes a level defined by the AGC circuit 114. The AGC circuit 114 detects the level of the intermediate frequency signal output from the IF signal processing unit 112 and controls the amplification degree of the RF amplification unit 110 and the amplification degree of the IF signal processing unit 112 according to the detected level. is doing.

  The intermediate frequency signal output from the IF signal processing unit 112 is up-converted by a local oscillation signal applied and supplied to the second mixer (MIX2), and is converted into a terrestrial digital broadcast signal of a predetermined channel to adjust the RF level. Supplied to the unit 116. The MIX2 is supplied with a local oscillation signal via the switch SW, and when the output is performed on the same channel as the input channel, the contact a of the switch SW is switched to the contact b on the first local oscillator 111 side. When output is performed on a channel different from the selected channel, the contact a of the switch SW is switched to the contact c to the second local oscillator (OSC2) 117 side. The RF level adjustment unit 116 adjusts the level of the terrestrial digital broadcast signal, which is the RF output, to a predetermined output level, and outputs the terrestrial digital broadcast signal retransmitted from the terrestrial digital signal processor 100.

  In the terrestrial digital signal processor 100, the output level of the RF output is set to a predetermined output level. Since the terrestrial digital signal processor 100 shown in FIG. 10 is for one channel, and terrestrial digital broadcasting is generally composed of a plurality of channels, the level of the predetermined channel shown in FIG. By doing so, a configuration for outputting at a predetermined output level is provided for the number of terrestrial digital broadcast channels. As a result, the level of each channel of the terrestrial digital broadcast is output by being aligned by the terrestrial digital signal processor 100.

  In this way, the level of each channel is aligned in the terrestrial digital signal processor 100 for the following reason. Television broadcast waves such as terrestrial digital broadcasting differ in signal quality such as the signal level that can be received depending on the position of the reception point, and change depending on time and season. In this case, there may be a level difference between the channels. When this level difference is large, it is likely to be affected by nonlinear distortion, and particularly in a reception system using an amplifier. For this reason, a device capable of level adjustment for each channel, that is, the terrestrial digital signal processor 100 is required.

Since this terrestrial digital signal processor 100 converts and adjusts the output level of each channel of terrestrial digital broadcasting into an intermediate frequency signal, it is shown in FIG. It is necessary to have the configuration shown in FIG. The terrestrial digital signal processor 100 has various functions such as AGC, output level adjustment, frequency conversion, etc., and performs signal processing by converting to an intermediate frequency as shown in FIG. Thus, by converting to an intermediate frequency, a steep band pass filter (BPF) can be easily realized, and an intermediate frequency signal of only a target channel can be extracted. However, conversion to an intermediate frequency increases the circuit scale and requires a high-performance local oscillator, resulting in a very expensive product.
Therefore, it is desired to simplify the configuration of the terrestrial digital signal processor 100 in order to reduce the size and to make it inexpensive. In order to simplify the configuration of the terrestrial digital signal processor 100, instead of down-converting to an intermediate frequency and adjusting the level as shown in FIG. 10, the high-frequency signal is directly converted without converting the high-frequency signal of each channel into the intermediate frequency. It is possible to adjust the level. In order to directly adjust the level of the high-frequency signal, it is necessary to extract the signal of each channel in a high-frequency band such as UHF by a band pass filter (BPF).

  By the way, in the case of conventional terrestrial analog broadcasting, at least every other channel among the channels arranged on the frequency axis is assigned to a broadcasting station and transmitted. For this reason, since there is no adjacent channel component when the high-frequency signal of each channel is extracted by the BPF, it is not necessary to make the BPF passband characteristic a steep frequency characteristic, and the BPF can be configured with a relatively simple configuration. it can.

  However, in the case of terrestrial digital broadcasting, an adjacent channel is often assigned to another broadcasting station and transmitted from the viewpoint of effective use of a frequency band. For this reason, the BPF that extracts the high-frequency signal of each channel requires a steep frequency characteristic that blocks the components of adjacent channels. For example, when terrestrial digital broadcasting is composed of 8 channels from 20 channels to 27 channels, the frequency band is a UHF frequency band of 512 to 560 MHz, the bandwidth of each channel is 6 MHz, and the guard bands on both sides are The bandwidth is about 430 kHz, and the passband characteristics of the BPF that allows each channel to pass are defined as follows. Attenuation is 0 dB in the band of ± 2.79 MHz from the center frequency, −20 dB or less in the band of ± 2.86 MHz from the center frequency, and −27 dB or less in the band of ± 3 MHz from the center frequency. The attenuation is -50 dB or less in the band of ± 4.95 MHz from the center frequency, and the attenuation is -50 dB or less in the band of ± 9 MHz from the center frequency. A BPF having such a passband characteristic requires a steep attenuation characteristic of a cutoff characteristic, which increases the complexity and size of the BPF, making it expensive, and providing a terrestrial digital signal processor at a small size and at a low cost. There was a problem that could not be done.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a digital terrestrial broadcast retransmission apparatus that can adjust the output level of each channel in digital terrestrial broadcasting with a simple configuration.

  In order to achieve the above object, the digital terrestrial broadcast retransmission apparatus according to the present invention provides an attenuation gradient of a cutoff characteristic of a bandpass filter unit that extracts a high-frequency signal of a channel whose level should be adjusted from a terrestrial digital broadcast signal composed of a plurality of channels. The main feature is that the component of the channel adjacent to the channel is also passed.

  According to the present invention, the attenuation slope of the cutoff characteristic of the band-pass filter unit that extracts the high-frequency signal of the channel whose level is to be adjusted from the terrestrial digital broadcasting signal composed of a plurality of channels is moderated, and the channel adjacent to the channel is Since the components also pass, the configuration of the bandpass filter can be simplified, and the configuration of the terrestrial digital broadcast retransmission apparatus can be simplified. For this reason, it becomes possible to reduce the size of the terrestrial digital broadcast retransmitting device and to reduce the cost. Even if the pass band of the band pass filter section extends over the frequency band of the channel adjacent to the channel, adverse effects can be prevented by the action of the guard interval in OFDM.

  For the purpose of providing a terrestrial digital broadcast retransmission device that can adjust the output level of each channel in terrestrial digital broadcasting with a simple configuration, the high-frequency signal of the channel whose level should be adjusted from the terrestrial digital broadcast signal consisting of multiple channels This is realized by making the attenuation slope of the cutoff characteristic of the band-pass filter part for extracting the signal moderate and passing the component of the channel adjacent to the channel.

FIG. 1 is a circuit block diagram showing the configuration of a terrestrial digital signal processor which is a terrestrial digital broadcast retransmission apparatus according to the present invention. However, the terrestrial digital signal processor 1 shown in FIG. 1 is configured to support terrestrial digital broadcasting composed of up to eight channels.
As shown in FIG. 1, the terrestrial digital signal processor 1 according to the first embodiment of the present invention is supplied with a terrestrial digital broadcast signal composed of a plurality of channels as an RF input. This RF input is divided into, for example, eight by the distributor 11 and each distribution output has eight RF level adjustment units a, RF level adjustment units b, RF level adjustment units c, RF level adjustment units d, and RF level adjustment units e. , RF level adjustment unit f, RF level adjustment unit g, and RF level adjustment unit h.
The RF level adjustment unit a to the RF level adjustment unit h adjust the high-frequency level of each channel constituting the terrestrial digital broadcast for each channel and output it at a predetermined output level. The high-frequency signals of the respective channels having the predetermined output levels output from the RF level adjustment unit a to the RF level adjustment unit h are mixed by the mixer 12 so that the level of each channel is adjusted from the terrestrial digital signal processor 1. Is output as the RF output.

The RF level adjustment unit a to the RF level adjustment unit h have the same configuration, and a circuit block diagram showing a first configuration example is shown in FIG.
The RF level adjustment unit 10 shown in FIG. 2 includes a first RF amplification unit 20, a band pass filter (BPF) 21, and a second RF amplification unit 22. The first RF amplification unit 20 is supplied with a terrestrial digital broadcast signal as an RF input. The first RF amplification unit 20 amplifies the RF input by a predetermined level and outputs the amplified signal to the BPF 21. In this case, the RF amplification unit 20 is an RF amplifier with a fixed amplification degree. The BPF 21 is a filter that extracts a high-frequency signal of a channel assigned to the RF level adjustment unit 10, and has a pass band in which the attenuation slope of the cutoff characteristic on both sides is moderate with the frequency band of the channel as a center. ing.

  In this way, the high-frequency signal of the channel extracted including the component of the adjacent channel from the BPF 21 is supplied to the second RF amplification unit 22. The second RF amplifying unit 22 is a variable amplifier, and adjusts the level of the supplied high-frequency signal to automatically amplify and adjust the output level so that the RF output level becomes a predetermined level. Further, a squelch is provided to turn off the output from the RF level adjustment unit 10 when the channel is not broadcast (when there is no input). The passband of the BPF 21 is a passband corresponding to the channel assigned to the RF level adjustment unit 10, and the passband has a gentle attenuation slope of the cutoff characteristics on both sides centering on the frequency band of the channel. Therefore, the configuration of the BPF 21 can be simplified.

Next, FIG. 3 shows a circuit block diagram showing a second configuration example of the RF level adjustment unit a to the RF level adjustment unit h.
The RF level adjustment unit 10 ′ shown in FIG. 3 includes a first RF amplification unit 20 ′, a bandpass filter (BPF) 21 ′, a second RF amplification unit 22 ′, and a control unit (AGC circuit) 23. The first RF amplification unit 20 ′ is supplied with a digital terrestrial broadcast signal as an RF input. The first RF amplification unit 20 amplifies the RF input by a predetermined level and outputs the amplified signal to the BPF 21 ′. In this case, the RF amplification unit 20 ′ is a variable amplifier whose amplification degree is controlled by the control unit 23. The BPF 21 ′ is a filter that extracts a high-frequency signal of a channel assigned to the RF level adjustment unit 10 ′. A BPF 21 ′ has a passband in which the attenuation slope of the cutoff characteristic on both sides is moderate with respect to the frequency band of the channel. Have.

  In this way, the high-frequency signal of the channel extracted including the component of the adjacent channel from the BPF 21 ′ is supplied to the second RF amplification unit 22 ′ that is a variable amplifier and is also supplied to the control unit 23. The control unit 23 controls the degree of amplification of the first RF amplification unit 20 'and the second RF amplification unit 22' so that the level of the high-frequency signal supplied from the BPF 21 'becomes a predetermined level. As a result, the level of the RF output output from the second RF amplifying unit 22 'becomes a predetermined level. Further, the second RF amplification unit 22 'includes a squelch that cuts off the output from the RF level adjustment unit 10' when the channel is not broadcast (when there is no input). Note that the pass band of the BPF 21 ′ is changed according to the channel assigned to the RF level adjustment unit 10 ′, and the pass band in which the attenuation slope of the cutoff characteristic on both sides is moderate with the frequency band of the channel as the center. Therefore, the configuration of the BPF 21 ′ can be simplified.

Next, an example of the passband characteristics of the BPFs 21 and 21 ′ in the RF level adjustment units 10 and 10 ′ will be described with reference to FIG.
FIG. 4A shows an RF input input to the terrestrial digital signal processor 1 and is composed of high-frequency signals of a plurality of channels for terrestrial digital broadcasting. In the illustrated example, terrestrial digital broadcasting is composed of eight channels a (CHa) to channel h (CHh), and the level of each channel has a level difference as illustrated. FIG. 4B is a diagram illustrating the passband characteristics of the BPFa and the signal components of the passed channel in the RF level adjustment unit a to which the channel a is assigned. As shown in the figure, the pass band of BPFa is such that the attenuation slope of the cutoff characteristic on both sides with respect to channel a is moderate, so that in addition to the signal component a1 of channel a, some signal components of adjacent channel b b1 is also output from BPFa.

FIG. 4C is a diagram showing the passband characteristics of the BPFb and the signal components of the passed channels in the RF level adjustment unit b to which the channel b is assigned. As shown in the figure, the pass band of the BPFb has a moderate attenuation slope of the cutoff characteristic on both sides centering on the channel b. Therefore, in addition to the signal component b2 of the channel b, some signal components of the adjacent channel a The signal component c2 of a2 and the channel c is also output from the BPFb.
Further, FIG. 4D is a diagram showing the BPFc passband characteristics and the signal components of the passed channels in the RF level adjustment unit c to which the channel c is assigned. As shown in the figure, the pass band of BPFc has a moderate attenuation slope of the cutoff characteristic on both sides centering on channel c, so that in addition to the signal component c3 of channel c, some signal components of adjacent channel b The signal component d3 of b3 and channel d is also output from BPFc.

FIG. 4 (e) is a diagram showing the passband characteristics of BPFd and the signal components of the passed channels in the RF level adjustment unit d to which the channel d is assigned. As shown in the figure, the pass band of the BPFd has a moderate attenuation slope of the cutoff characteristic on both sides centering on the channel d, so that in addition to the signal component d4 of the channel d, some signal components of the adjacent channel c The signal component e4 of c4 and channel e is also output from BPFd.
Furthermore, FIG. 4F is a diagram showing the passband characteristics of BPFe and the signal components of the passed channel in the RF level adjustment unit e to which the channel e is assigned. As shown in the figure, since the passband of BPFe has a moderate attenuation characteristic of the cutoff characteristic on both sides centering on the channel e, in addition to the signal component e5 of the channel e, some signal components of the adjacent channel d The signal component f5 of d5 and channel f is also output from BPFe.
The RF level adjustment units f to h to which the channels f to h are assigned operate in the same manner, but are omitted in FIG.

The high-frequency signals that have passed through these BPFa to BPFh are each adjusted in level to a prescribed level and mixed by the mixer 12. As a result, the RF output of the terrestrial digital broadcast shown in FIG. 4 (g) consisting of the channels a to h having the same level is output from the mixer 12.
Here, paying attention to the channel b, the component of the channel b is composed of the main signal component b2 output from the BPFb and the signal component b1 output from the partially passed BPFa and the signal component b3 output from the BPFc. Will be output. Here, since the delay times of the signals of the RF level adjustment unit a, the RF level adjustment unit b, and the RF level adjustment unit c are not normally matched, the components of the output channels b1, b2, and b3 are also shifted from each other. It comes to be. In this case, in the case of analog broadcasting, a ghost is generated when three components whose delay times are shifted are combined. However, since terrestrial digital broadcasting is an orthogonal frequency division multiplexing (OFDM) system having a guard interval, no ghost is generated even if three components having different delay times are combined. Become. This will be described with reference to FIGS.

FIG. 7 is a diagram showing an outline of the OFDM signal, and FIGS. 8 and 9 are diagrams showing the operation of the guard interval (GI).
An OFDM signal is composed of a number of carriers that are orthogonal to each other. For example, as shown in FIG. 7, an OFDM signal is formed by adding (k + 1) carriers 0, carrier 1,..., Carrier k that are orthogonal to each other. The (k + 1) carriers are modulated with different transmission data. The waveform shown on the left side of FIG. 7 is a spectrum of an OFDM signal obtained by adding each spectrum of carrier 0, carrier 1,..., Carrier k and (k + 1) carriers, and the horizontal axis is the frequency. The waveform shown on the right side of FIG. 7 is a waveform of an OFDM signal obtained by adding the waveforms of carrier 0, carrier 1,..., Carrier k and (k + 1) carriers, and the horizontal axis represents time. .

  In such an OFDM signal, a guard interval (GI: Guard Intarval) of the period Tg is added before the symbol period Ts. In the GI period Tg, the waveform of the end period Tg ′ in the symbol period Ts is copied. As a result, the phases of the GI waveform and the symbol waveform become continuous, and the orthogonality of the waveform can be maintained even when the GI is added. Thus, in OFDM, an information data sequence is transmitted using a number of subcarriers orthogonal to each other. In this case, since the symbol period Ts can be lengthened, ghost interference can be reduced. Furthermore, providing a guard interval makes it more resistant to frequency selective fading. Moreover, the spectrum of each subcarrier can be densely arranged, and the frequency utilization efficiency can be increased. Furthermore, since information to each subcarrier can be arbitrarily assigned, it is possible to perform flexible information transmission such as not using subcarriers that are expected to interfere.

Next, the operation of the guard interval will be described. FIG. 8 shows a case where multipath propagation occurs in OFDM without a guard interval.
In this case, when multipath propagation occurs, the main wave and the delayed wave obtained by delaying the main wave arrive at the receiving side, and the combined wave is received. Here, the delayed wave is delayed from the main wave by a delay time td. Then, in the symbol period Ts1 in the composite wave, the delay wave includes a part of the symbol period of the immediately preceding symbol Sn-1, so that the orthogonality of the composite wave is disturbed within the delay time td. For this reason, the symbol Sn in the symbol period Ts1 cannot be demodulated. The same applies to the symbol Sn + 1, and the orthogonality of the combined wave is disturbed by the symbol period of the previous symbol Sn within the delay time td, and the symbol Sn + 1 in the symbol period Ts2 cannot be demodulated.

FIG. 9 shows a case where multipath propagation occurs in OFDM with a guard interval.
In this case, when multipath propagation occurs, the main wave and the delayed wave obtained by delaying the main wave arrive at the receiving side, and the combined wave is received. Here, the delayed wave is delayed from the main wave by a delay time td. However, the delay time td is a time within the guard interval (GI). Then, in the symbol period Ts1 in the composite wave, the delay wave includes a part of the guard interval period of the symbol Sn, so that the orthogonality of the composite wave is not disturbed even within the delay time td. For this reason, the symbol Sn in the symbol period Ts1 can be demodulated without being affected by the delay wave. The same applies to the symbol Sn + 1, and the orthogonality of the combined wave is not disturbed by the guard interval period of the symbol Sn + 1 within the delay time td, and the symbol Sn + 1 in the symbol period Ts2 can be demodulated. In this way, when the delayed wave is delayed by a delay time smaller than the guard interval period, even if multipath propagation occurs, orthogonality between subcarriers in OFDM is maintained, and deterioration of transmission characteristics is prevented. be able to.

  Returning to FIG. 4 and focusing on channel b, the component of channel b is composed of the main signal component b2 output from BPFb and the signal component b1 output from BPFa and the signal component b3 output from BPFc. Will be output. Since the delay times of the signals of the RF level adjustment unit a, the RF level adjustment unit b, and the RF level adjustment unit c are not normally coincident, the components of the output channels b1, b2, and b3 are also shifted from each other. Become like that. However, since terrestrial digital broadcasting is OFDM and has a guard interval, even if components b1, b2, and b3 having different delay times are combined by the action of the guard interval described in FIG. Orthogonality between subcarriers is maintained, and ghosts are not generated. On the contrary, the level of the channel is increased by combining the components b1, b2, and b3. The same applies to channels other than channel b.

In addition, since the two components to be combined for the channel a and the channel h at both ends become slightly lower than the other channels when combined, the RF level adjustment unit a and the RF level adjustment unit h It is preferable to slightly increase the output level.
In this way, even if the attenuation slope of the cutoff characteristics of the BPFs 21 and 21 ′ included in the RF level adjustment units 10 and 10 ′ is moderate, the levels of the respective channels of digital terrestrial broadcasting can be made uniform without generating a ghost. Become. Therefore, the BPF 21 and BPF 21 ′ having a simple configuration can be employed, and the terrestrial digital signal processor 1 can be reduced in size and cost.

The passband characteristics of the BPFs 21 and 21 ′ included in the RF level adjustment unit 10 are not limited to the passband characteristics shown in FIG. 4, and may be passband characteristics in which the attenuation slope of the cutoff characteristics shown in FIG.
FIGS. 5 (a) to 5 (g) correspond to FIGS. 4 (a) to 4 (g), respectively, and the RF input shown in FIG. 5 (a) corresponds to the RF level adjustment unit a to RF level adjustment. A high frequency signal of each channel is extracted by BPFa ′ to BPFh ′ having the passband characteristics shown in FIG. 5B to FIG. In this case, as shown in FIGS. 5 (b) to 5 (f), the passband characteristics of BPFa ′ to BPFh ′ have a more gentle attenuation slope of the cutoff characteristics on both sides than the passband characteristics shown in FIG. It is considered to be a passband characteristic. As a result, as shown in the figure, the components of adjacent channels located on both sides are passed more. The high-frequency signals that have passed through these BPFa ′ to BPFh ′ are adjusted in level to prescribed levels and mixed by the mixer 12. As a result, the RF output of the terrestrial digital broadcast shown in FIG. 5 (g) consisting of the channels a to h having the same level is output from the mixer 12.

  Here, focusing on channel b, the components of channel b are the main signal component b2 ′ output from BPFb ′, the signal component b1 ′ output from BPFa ′, and the signal component b3 ′ output from BPFc ′. Are combined and output. Here, since the delay times of the signals of the RF level adjustment unit a, the RF level adjustment unit b, and the RF level adjustment unit c do not normally coincide with each other, the output channel b components also appear to be offset from each other. become. However, since digital terrestrial broadcasting is set to OFDM and has a guard interval, components b1 ′, b2 ′, and b3 ′ having different delay times are synthesized by the action of the guard interval described in FIG. However, orthogonality between subcarriers in OFDM is maintained, and ghosts are not generated. On the contrary, the level of the channel is increased by combining the components b1 ', b2', b3 '. The same applies to channels other than channel b.

As described above, even if the attenuation slope of the cutoff characteristics of the BPFs 21 and 21 ′ included in the RF level adjustment units 10 and 10 ′ is made gentler as shown in FIG. 5, the level of each channel of the terrestrial digital broadcasting without causing ghosts. Can be aligned. Therefore, the BPF 21 and BPF 21 ′ having a simple configuration can be employed, and the terrestrial digital signal processor 1 can be reduced in size and cost.
In addition, since the two components to be combined for the channel a and the channel h at both ends become slightly lower than the other channels when combined, the RF level adjustment unit a and the RF level adjustment unit h It is preferable to slightly increase the output level.

A specific example of the passband characteristics will be described. In the passband characteristics of the BPFs 21 and 21 ′ included in the RF level adjustment unit 10 shown in FIG. 4, the attenuation is 0 dB in the ± 2.8 MHz band from the center frequency. In the band of ± 3.2 MHz, the attenuation is a gentle attenuation gradient with an attenuation of −20 dB or less. And it is considered as a passband characteristic in which the attenuation amount increases as the band increases. Further, in the passband characteristics of the BPFs 21 and 21 ′ included in the RF level adjustment unit 10 shown in FIG. 5, the passband is slightly widened, and the attenuation slope of the cutoff characteristic is a gentle attenuation that attenuates by -20 dB or more in the bandwidth of 400 kHz. It is assumed to be a slope. And it is considered as a passband characteristic in which the attenuation amount increases as the band increases.
Note that the attenuation gradient defined in the prior art is a steep attenuation gradient in which the attenuation gradient of the cutoff characteristic attenuates by -20 dB or more in the bandwidth of 130 kHz as described above.

The passband characteristics of the BPFs 21 and 21 ′ included in the RF level adjusting unit 10 may be further changed to passband characteristics in which the attenuation amount of the stopband with respect to the passband is reduced as shown in FIG.
6 (a) to 6 (g) correspond to FIGS. 4 (a) to 4 (g), respectively, and the RF input shown in FIG. 6 (a) corresponds to the RF level adjustment unit a to RF level adjustment. The high frequency signal of each channel is extracted by BPFa ″ to BPFh ″ having the passband characteristics shown in FIGS. 6B to 5F, which are input to the unit h. In this case, as shown in FIGS. 6B to 6F, the passband characteristics of BPFa ″ to BPFh ″ are smaller in the stopband attenuation with respect to the passband than the passband characteristics shown in FIG. It is considered to be a passband characteristic. As a result, the components of channels other than the channel to be passed are also passed as shown in the figure. The high-frequency signals that have passed through these BPFa ″ to BPFh ″ are adjusted in level to prescribed levels and mixed by the mixer 12. As a result, the RF output of the terrestrial digital broadcast shown in FIG. 6 (g) consisting of the channels a to h having the same level is output from the mixer 12.

  Here, focusing on channel b, the component of channel b is the main signal component b2 ″ output from BPFb ″, the signal component b1 ″ output from BPFa ″, and the signal component b3 ″ output from BPFc ″. A signal component b4 "output from BPFd", a signal component b5 "output from BPFfe", a signal component b6 "output from BPFf" (not shown), and a signal component b7 "output from BPFg" And the signal component b8 ″ output from BPFh ″ are combined and output. Here, since the delay times of the signals of the RF level adjustment unit a to the RF level adjustment unit h usually do not coincide with each other, each of the channels b output from the RF level adjustment unit a to the RF level adjustment unit h. The components also appear to be shifted in delay time. However, since digital terrestrial broadcasting is set to OFDM and has a guard interval, components b1 ", b2", b3 ", and b4" having different delay times due to the action of the guard interval described in FIG. , Component b5 ″, component b6 ″, component b7 ″, and component b8 ″ are combined so that orthogonality between subcarriers in OFDM is maintained, and no ghost is generated. On the contrary, the level of the channel is increased by synthesizing the components b1 "to b8". The same applies to channels other than channel b.

As described above, even if the attenuation amount of the stop band with respect to the pass band of the BPFs 21 and 21 ′ included in the RF level adjustment units 10 and 10 ′ is small as shown in FIG. Channel levels can be adjusted. Therefore, the BPF 21 and BPF 21 ′ having a simple configuration can be employed, and the terrestrial digital signal processor 1 can be reduced in size and cost. A specific example of the passband characteristics of the BPFs 21 and 21 ′ included in the RF level adjustment units 10 and 10 ′ in this case is 0 dB in the band of ± 2.8 MHz from the center frequency and ± 3. In the 2 MHz band, the attenuation is a gradual attenuation gradient with an attenuation of -20 dB or less. And even if a zone | band increases, it is set as the passband characteristic which does not increase attenuation amount but maintains -20 dB or less.
The BPFs 21 and 21 ′ included in the RF level adjustment units 10 and 10 ′ according to the present invention described above can be configured by a helical filter, a surface acoustic wave (SAW) filter, or a dielectric filter.

  In the above description, the terrestrial digital broadcast retransmission apparatus is used. However, the present invention is not limited to this, and can be applied to a communication apparatus having a plurality of OFDM channels.

It is a circuit block diagram which shows the structure of the terrestrial digital signal processor which is a terrestrial digital broadcast re-transmission apparatus of this invention. It is a circuit block diagram which shows the 1st structural example of the RF level adjustment unit in the terrestrial digital signal processor concerning this invention. It is a circuit block diagram which shows the 2nd structural example of the RF level adjustment unit in the terrestrial digital signal processor concerning this invention. It is a figure which shows an example of the passband characteristic of BPF of the RF level adjustment unit in the terrestrial digital signal processor concerning this invention. It is a figure which shows the other example of the passband characteristic of BPF of the RF level adjustment unit in the terrestrial digital signal processor concerning this invention. It is a figure which shows the further another example of the passband characteristic of BPF of the RF level adjustment unit in the terrestrial digital signal processor concerning this invention. It is a figure which shows the outline | summary of an OFDM signal. It is a figure which shows the case where multipath propagation arises in OFDM which does not provide a guard interval. It is a figure which shows the case where multipath propagation arises in OFDM which provided the guard interval. It is a circuit block diagram which shows the structure of the conventional terrestrial digital signal processor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Terrestrial digital signal processor 10, 10 'Level adjustment unit 11 Divider 12 Mixer 20, 20' 1st RF amplification part 21, 21 'BPF
22, 22 '2nd RF amplification part 23 Control part (AGC circuit)
100 Terrestrial digital signal processor 110 RF amplification unit 111 First local oscillator 112 Signal processing unit 114 AGC circuit 116 Level adjustment unit 117 Second local oscillator SW switch

Claims (4)

A digital terrestrial broadcast retransmission apparatus that outputs the terrestrial digital broadcast signal composed of a plurality of channels in an orthogonal frequency division multiplex communication system (OFDM) with the same level of each channel,
A high-frequency level adjustment unit provided for each channel that adjusts the level of the input high-frequency signal to a predetermined level;
A mixing unit that mixes and outputs the high-frequency signal of each channel output from the high-frequency level adjustment unit,
The high-frequency level adjusting unit is configured to extract a high-frequency signal of a channel whose level is to be adjusted from an input terrestrial digital broadcast signal including a plurality of channels, and a level of the high-frequency signal output from the band-pass filter unit A high-frequency level adjusting unit that adjusts the frequency to a predetermined level, wherein the attenuation characteristic of the cutoff characteristic of the band-pass filter unit is moderate, and a component of a channel adjacent to the channel also passes. A terrestrial digital broadcast retransmission device. A digital terrestrial broadcast retransmission apparatus that outputs the terrestrial digital broadcast signal composed of a plurality of channels in an orthogonal frequency division multiplex communication system (OFDM) with the same level of each channel,
A high-frequency level adjustment unit provided for each channel that adjusts the level of the input high-frequency signal to a predetermined level;
A mixing unit that mixes and outputs the high-frequency signal of each channel output from the high-frequency level adjustment unit,
The high-frequency level adjusting unit is configured to extract a high-frequency signal of a channel whose level is to be adjusted from an input terrestrial digital broadcast signal including a plurality of channels, and a level of the high-frequency signal output from the band-pass filter unit A high-frequency level adjustment unit that adjusts so that a predetermined level is obtained, and the attenuation amount of the stop band with respect to the pass band of the band-pass filter unit is reduced, and components of channels other than the channel are also passed. A terrestrial digital broadcast retransmitting device.   The high-frequency level adjusting unit includes a high-frequency amplifier that amplifies an input terrestrial digital broadcast signal, and the band-pass filter unit that extracts a high-frequency signal of a channel whose level is to be adjusted from the terrestrial digital broadcast signal amplified by the high-frequency amplifier. 3. A terrestrial digital broadcast re-transmission according to claim 1, wherein the high-frequency variable amplifier adjusts the level of the high-frequency signal output from the band-pass filter unit to a predetermined level. apparatus. The high-frequency level adjusting unit extracts a high-frequency signal of a channel whose level is to be adjusted from a first high-frequency variable amplifier that amplifies an input terrestrial digital broadcast signal and the terrestrial digital broadcast signal amplified by the high-frequency variable amplifier. A band-pass filter unit; a second high-frequency variable amplifier that amplifies the high-frequency signal output from the band-pass filter unit; and the first high-frequency signal output from the second high-frequency variable amplifier to have a predetermined level. 3. The terrestrial digital broadcast retransmission apparatus according to claim 1, further comprising a high frequency variable amplifier and a control unit that automatically controls the second high frequency variable amplifier.

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