WO2011115208A1 - Wraparound canceller and relay device - Google Patents

Abstract

Disclosed is a wraparound canceller that—in a relay device that receives the OFDM signals of multiple channels using a reception antenna and retransmits said received signal from a transmission antenna—eliminates a wraparound signal that is superimposed on the aforementioned received signal by means of the radio waves transmitted from the aforementioned transmission antenna wrapping around the aforementioned reception antenna. Said wraparound canceller is provided with a signal extraction means, a single lag profile calculation means, an elimination signal generating means, a wraparound elimination means, a frequency conversion means, a mixing means, and a level adjustment means.

Description

Wraparound canceller and relay device Cross-reference of related applications

This international application includes Japanese Patent Application No. 2010-60740 filed with the Japan Patent Office on March 17, 2010 and Japanese Patent Application No. 2010-60740 filed with the Japan Patent Office on October 29, 2010. The contents of Japanese Patent Application No. 2010-60740 and Japanese Patent Application No. 2010-244448 are incorporated herein by reference in their entirety.

The present invention relates to a wraparound canceller used in a relay device that relays an OFDM signal used in terrestrial digital television broadcasting or the like. Specifically, the present invention relates to a sneak canceller for removing a sneak signal superimposed on a received signal when a transmission radio wave from a transmission antenna sneaks around to a reception antenna. The present invention also relates to a relay device provided with this wraparound canceller.

The SFN relay device is provided with a wraparound canceller. The sneak canceller prevents the transmission radio wave from the transmission antenna from sneaking to the reception antenna and retransmitting the sneak signal. The SFN relay device is a device that relays OFDM signals used in digital terrestrial television broadcasting or the like without frequency conversion (in other words, channel conversion).

This sneak canceller measures the delay profile (complex impulse response) of the sneak signal and removes the sneak signal component from the received signal according to the measured delay profile.

As a method for measuring a delay profile, for example, various methods such as the following (a) to (c) are known (see, for example, Patent Document 1).
(A) A transfer function of a transmission path is estimated using a reference signal such as an SP signal (Scattered Pilot Signal) inserted as an amplitude phase reference at the time of synchronous demodulation in an OFDM signal, and the reciprocal of the estimated transfer function of the transmission path A method for measuring a delay profile by performing inverse discrete Fourier transform.
(B) A method of extracting a spectrum within a reception band by performing a discrete Fourier transform on the received OFDM signal, averaging each spectrum in terms of time, and performing an inverse discrete Fourier transform on the reciprocal thereof (for details, refer to Patent Document 2). reference).
(C) Similar to (b) above, each spectrum on the frequency axis of the OFDM signal is averaged over time, the amplitude characteristic of each spectrum is obtained from the time average value, and the transmission path of the transmission line is determined using the minimum phase condition or the like A method of measuring a delay profile by estimating a transfer function and performing an inverse discrete Fourier transform on an inverse of the estimated transfer function of the transmission path.

In addition, in a relay device for terrestrial digital television broadcasting or the like, there is a device configured not to retransmit an OFDM signal for one channel but to retransmit all multi-channel OFDM signals received by a receiving antenna. is there.

In this type of relay apparatus, the following methods 1 and 2 are known as methods for removing the sneak signal component from the OFDM signal of each channel (see, for example, Patent Documents 2 and 3). Method 1 is a method in which a delay profile is measured for each OFDM signal of each channel, and a wraparound signal component is removed for each channel. Method 2 is a method in which the delay profile is collectively measured within the frequency band of all channels, and the sneak signal component is removed collectively for all channels.

JP 2004-080668 A JP 2008-017236 A JP 2009-100067 A

However, if the delay profile is measured for each channel in order to remove the sneak signal from the multi-channel OFDM signal as in method 1, the calculation processing for one OFDM signal wave is executed in parallel for a plurality of channels. Must. Therefore, in this case, it is necessary to increase the number of arithmetic processing circuits in accordance with the number of channels, which causes a problem of increasing the cost of the wraparound canceller.

Further, when the delay profile is measured collectively in the frequency band of all channels in order to remove the sneak signal from the multi-channel OFDM signal as in the method 2, the frequency band to be calculated is calculated. Increases with the number of channels. Therefore, in order to measure a delay profile with the same accuracy as one wave of an OFDM signal, it is necessary to increase the sampling frequency of the received signal and execute arithmetic processing at high speed.

For this reason, even if the delay profile of the multi-channel OFMD signal is calculated for all channels at the same time, there is a problem that the cost of the wraparound canceller is increased as in the case of calculating for each channel.

On the other hand, in view of such problems, the present inventors have proposed a method for removing a sneak signal from a multi-channel OFDM signal. The method consists of the following steps.
A preset one-channel OFDM signal is extracted from a plurality of channels of OFDM signals received by the receiving antenna.

A delay profile of the extracted OFDM signal is calculated.
From the delay profile, a wraparound removal signal is generated for the OFDM signals of all channels received by the receiving antenna.

Since the SFN relay device is normally used as a fixed station, it is considered that frequency errors are hardly generated in transmission / reception signals, and the delay profiles of OFDM signals of each channel are considered to be substantially the same.

In the above technique proposed by the present inventors, the OFDM signal of a specific channel is extracted from the received OFDM signals of all channels. Then, the delay profile of the OFDM signal is measured. Next, based on the delay profile, a wraparound removal signal is generated for the received OFDM signals of all channels, and the wraparound signal is removed from the OFDM signals of each channel.

Therefore, according to this technique proposed by the present inventors, it is necessary to calculate a delay profile for each OFDM of each channel or to calculate a delay profile for all channels at once as in the prior art. Absent. Since the sneak signal of each channel can be removed using the delay profile for one OFDM signal channel, a multi-channel sneak canceller can be realized at low cost.

However, in the above technique proposed by the present inventors, there is a level difference in the OFDM signal for each channel received by the receiving antenna, causing a problem. Specifically, when a signal is re-transmitted after aligning the signal level with an amplifier with an AGC circuit for each of a plurality of channels, there is an OFDM level difference between the OFDM signal of a specific channel whose delay profile is measured. There was a problem that the signal was overcompensated or undercompensated due to the level difference. That is, there is a problem that the sneak signal cannot be satisfactorily reduced from the OFDM signals of all channels.

Specifically, in a channel whose reception level is lower than the OFDM signal of the specific channel, the amplification factor of the OFDM signal by the amplifier with the AGC circuit is larger than the amplification factor of the specific channel. For this reason, the signal level of the sneak removal signal added to the OFDM signal for sneak signal removal becomes larger than an appropriate value, resulting in overcompensation.

Conversely, in a channel having a higher reception level than the OFDM signal of the specific channel, the amplification factor of the OFDM signal by the amplifier with the AGC circuit is smaller than the amplification factor of the specific channel. For this reason, the signal level of the sneak removal signal added to the OFDM signal for sneak signal removal becomes smaller than an appropriate value, resulting in insufficient compensation.

In the above technique proposed by the present inventors, it is assumed that the wraparound characteristic of the transmitted OFDM signal of each channel is substantially the same in each channel, so that the wraparound characteristic of each channel is different. In such a case, there is also a problem that the sneak signal cannot be reduced satisfactorily.

According to the present invention, a sneak canceller used in an SFN-type repeater that relays multi-channel OFDM signals without frequency conversion, using a common delay profile measurement means for each channel, and appropriate for each channel. It is desirable to provide a sneak canceller that can generate a sneak removal signal. Further, it is desirable that the sneak signal is appropriately removed without increasing the cost of the sneak canceller.

The invention of the first aspect of the present application made in order to achieve such an object,
In a relay apparatus that receives a multi-channel OFDM signal at a receiving antenna and retransmits the received signal from a transmitting antenna, a wraparound that is superimposed on the received signal when a transmission radio wave from the transmitting antenna wraps around the receiving antenna A wraparound canceller that removes the signal,
A plurality of signal extraction means for frequency-converting the OFDM signal of each channel received by the receiving antenna to a specific frequency common to all channels, and extracting the OFDM signal of the specific frequency after the frequency conversion;
One delay profile that sequentially captures OFDM signals of each channel extracted by the plurality of signal extraction means in a time division manner and calculates a delay profile of the OFDM signal transmitted from the transmission antenna for each of the captured channels. A calculation means;
A plurality of removal signal generation means each for generating a wraparound removal signal for the OFDM signal of each channel received by the reception antenna based on the delay profile calculated for each channel by the delay profile calculation means;
A plurality of wraparound removal means for removing a wraparound signal from the OFDM signals of each channel extracted by the plurality of signal extraction means, using the wraparound removal signals of each channel generated by the plurality of removal signal generation means; ,
A plurality of frequency conversion means for frequency-converting the OFDM signal from which the sneak signal has been removed by the plurality of wraparound removal means to the original frequency before being frequency-converted by the signal extraction means;
Mixing means for mixing the OFDM signals of the respective channels frequency-converted by the plurality of frequency converting means and outputting them to the transmitting antenna side;
The signal levels of the OFDM signal from which the sneak signal has been removed by the plurality of sneak removal means or the OFDM signal that has been frequency-converted by the plurality of frequency conversion means and input to the mixing means are respectively transmitted in a predetermined manner. A plurality of level adjusting means for adjusting to the level;
It is provided with.

The invention described in the second aspect of the present application is the wraparound canceller described in the first aspect.
The delay profile calculation means includes:
A discrete Fourier transform unit for extracting a spectrum on the frequency axis of the OFDM signal by performing a discrete Fourier transform on the OFDM signal extracted by each of the signal extraction units;
A transfer function calculating unit that calculates a transfer function of a transmission path from the transmitting antenna to the receiving antenna based on the spectrum extracted by the discrete Fourier transform unit;
An inverse calculation unit for calculating the inverse of the transfer function calculated by the transfer function calculation unit;
An inverse discrete Fourier transform unit that derives the delay profile by performing an inverse discrete Fourier transform on an output from the inverse number calculation unit;
It is provided with.

The invention described in the third aspect of the present application is the wraparound canceller described in the first aspect or the second aspect.
An input means for externally designating a target channel from which a wraparound signal is to be removed;
The signal extraction means, the removal signal generation means, the wraparound removal means, the frequency conversion means, and the level adjustment means are designated via the input means among a plurality of signal processing means configured for each channel. The signal processing unit corresponding to the target channel is selectively operated, the operation of the signal processing unit corresponding to the channel other than the target channel is stopped, and the delay profile calculation unit sequentially captures the delay profile in time division. Control means for limiting the OFDM signal to be calculated to the OFDM signal of the target channel designated via the input means;
It is provided with.

The invention described in the fourth aspect of the present application is a relay apparatus that receives a multi-channel OFDM signal at a receiving antenna and retransmits the received signal from the transmitting antenna. A sneak canceller according to any one of the first to third aspects is provided as a sneak canceller that removes a sneak signal superimposed on the received signal by sneaking around an antenna.

In the wraparound canceller described in the first aspect of the present application, the OFDM signal of each channel received by the receiving antenna is frequency-converted to a specific frequency common to all channels, and the OFDM of the specific frequency after the frequency conversion is performed. A plurality of signal extraction means for extracting a signal are provided.

Then, one delay profile calculation unit common to all channels sequentially captures the OFDM signal of each channel extracted by each signal extraction unit in a time division manner, and the OFDM signal transmitted from the transmission antenna for each of the captured channels. The delay profile is calculated.

In other words, in the wraparound canceller of the present invention, the OFDM signal of each channel is converted by the plurality of signal extraction means so that the delay profile of the OFDM signal of each channel can be calculated by time division by one delay profile calculation means. Frequency conversion to a specific frequency common to all channels. Then, the delay profile calculating means calculates the delay profile of each channel from the frequency-converted OFDM signal of each channel.

In addition, the delay profile calculated for each channel by the delay profile calculation unit is input to a plurality of removal signal generation units.
The plurality of removal signal generation means are means for generating a wraparound removal signal for the OFDM signal of the channel corresponding to the delay profile, using the delay profile of one channel calculated by the delay profile calculation means. At least one removal signal generating means is provided for each channel received by the receiving antenna, like the signal extracting means.

Then, the sneak removal signal of each channel generated by each of these removal signal generation means is input to the sneak removal means of the corresponding channel, respectively, and from the OFDM signal of each channel extracted by the plurality of signal extraction means. Used to remove sneak signals.

Further, the OFDM signal of each channel from which the sneak signal is removed by each sneak removal unit is the original frequency before being frequency-converted by each signal extraction unit by a plurality of frequency conversion units provided for each channel. After the frequency conversion, the signal is mixed by the mixing means and output to the transmitting antenna side.

In addition, the OFDM signal from which the sneak signal is removed by each sneak removal unit, or the OFDM signal that is frequency-converted by each frequency conversion unit and input to the mixing unit has a signal level of a predetermined transmission level. The level is adjusted by level adjusting means provided for each channel.

As described above, in the wraparound canceller of the present invention, a delay profile is calculated by extracting an OFDM signal of a specific channel from OFDM signals of a plurality of channels received by a receiving antenna, and all received signals are obtained from the delay profile. Instead of generating a wraparound removal signal for the OFDM signal of the channel, a delay profile is calculated for each channel using the OFDM signal of each channel, and a wraparound removal signal for the OFDM signal of each channel is generated.

Therefore, according to the present invention, even when there is a variation in the signal level of the OFDM signal of each channel received by the receiving antenna, the wraparound removal is performed when the wrap signal is removed from the OFDM signal of each channel. The signal will not deviate from the proper value and will not be overcompensated or undercompensated. Therefore, the sneak signal can be satisfactorily removed from the OFDM signal of each channel.

The wraparound canceller of the present invention includes one delay profile calculation means common to all channels. The OFDM signal of each channel is input to this delay profile calculation means in a time division manner, and the frequency of the input OFDM signal is set to a specific frequency common to all channels.

For this reason, according to the present invention, in the conventional apparatus for calculating the delay profile for each channel, only one delay profile calculation means similar to the delay profile calculation means provided for each channel may be provided. Therefore, the cost can be sufficiently reduced as compared with the conventional apparatus.

By the way, as this delay profile calculation means, a delay profile is calculated using various conventionally known calculation methods such as the methods (a) to (c) mentioned in the section of “Background Art”. Can be configured. On the other hand, for example, if configured as follows, a delay profile to be measured can be accurately calculated.

Specifically, the delay profile calculation unit first extracts a spectrum on the frequency axis of the OFDM signal by performing a discrete Fourier transform on the OFDM signal extracted by the signal extraction unit in the discrete Fourier transform unit. . Then, the transfer function calculation unit calculates the transfer function of the transmission path from the transmission antenna to the reception antenna based on the spectrum extracted by the discrete Fourier transform unit. Then, the reciprocal number calculation unit calculates the reciprocal number of the transfer function calculated by the transfer function calculation unit. Further, the inverse discrete Fourier transform unit performs an inverse discrete Fourier transform on the output from the reciprocal number calculation unit. Thereby, the delay profile calculating means derives the delay profile.

If the delay profile calculating means is configured in this way, the delay profile of the OFDM signal can be derived based on the transfer function of the transmission path, so that the delay profile can be calculated with high accuracy, and thus each channel. It is possible to satisfactorily remove the sneak signal from the OFDM signal.

On the other hand, in the sneak canceller of the present invention, the signal extraction unit, the removal signal generation unit, the sneak removal unit, the frequency conversion unit, and the level adjustment unit are provided for each channel received by the reception antenna. The number of OFDM signal channels that should be removed from the sneak signal may vary depending on the installation location of the relay device in which the sneak canceller is installed, the broadcast situation from the broadcast station, and the like.

For this reason, when the signal processing means constituted by the signal extraction means, the removal signal generation means, the sneak removal means, the frequency conversion means, and the level adjustment means is operated for all channels provided in the sneak canceller. The signal processing means corresponding to the channel that does not need to remove the sneak signal (in other words, the channel of the OFDM signal that does not actually exist) generates a sneak removal signal that is unnecessary for the removal of the sneak signal. become. Then, there is a possibility that the unnecessary wraparound removal signal becomes noise and adversely affects the OFDM signals of other channels.

Therefore, the sneak canceller of the present invention may further include an input unit for externally specifying a target channel from which a sneak signal is to be removed, and a control unit.
That is, in the sneak canceller of the present invention, the control means includes a signal extraction means, a removal signal generation means, a sneak removal means, a frequency conversion means, and a plurality of signal processing means configured for each channel by the level adjustment means. The signal processing means corresponding to the target channel designated via the input means is selectively operated, the operation of the signal processing means corresponding to the channel other than the target channel is stopped, and the delay profile calculation means is time-divisionally divided. The OFDM signal for calculating the sequential capture delay profile is limited to the OFDM signal of the target channel designated via the input means.

According to the sneak canceller of the present invention as described above, the signal extraction unit, the removal signal generation unit, the sneak removal unit, the frequency conversion unit, and the level adjustment unit, among the plurality of signal processing units configured for each channel, are input. Only the signal processing means corresponding to the target channel designated via the means operates, and the signal processing means corresponding to a channel other than the target channel designated via the input means stops operating.

Therefore, according to the sneak canceller of the present invention, only the signal processing unit corresponding to the target channel from which the sneak signal should be removed is selectively operated among the plurality of signal processing units, and the signal processing unit does not correspond to the target channel. By stopping the operation, power consumption by the wraparound canceller can be reduced.

Further, by stopping the operation of the signal processing means that does not correspond to the target channel, it is possible to suppress the generation of unnecessary noise and improve the signal quality of the transmission signal transmitted from the transmission antenna.

Further, according to the wraparound canceller of the present invention, the control means is not only to selectively operate the signal processing means corresponding to the target channel, but also to the OFDM signal that the delay profile calculation means sequentially takes in time division. The OFDM signal for which the delay profile is calculated is limited to the OFDM signal of the target channel designated via the input means. According to this, the calculation cycle of the delay profile corresponding to the target channel, that is, the calculation cycle of the wraparound removal signal can be shortened to the minimum necessary.

Therefore, according to the sneak canceller of the present invention, it is possible to increase the update frequency of the sneak removal signal and improve the sneak signal removal accuracy.
Further, according to the relay device of the present invention, since the wraparound canceler of the present invention described above is provided, even if the transmission radio wave from the transmission antenna wraps around the reception antenna and the wraparound signal is superimposed on the reception signal, The sneak canceller can remove the sneak signal from the received signal.

And the sneak canceller of the present invention can not only effectively remove the sneak signal, but also can reduce the manufacturing cost as compared with the conventional one. For this reason, according to the relay apparatus of the present invention, a relay apparatus that can suppress the occurrence of problems such as oscillation due to the sneak signal can be realized at low cost.

It is a block diagram showing the structure of the relay apparatus of embodiment. It is a block diagram showing the structure of the calculating part shown in FIG. FIG. 2 is an explanatory diagram of received signals in the respective units (a) to (e) shown in FIG. It is a block diagram showing the structure of the relay apparatus of the modification of embodiment.

2 ... receiving antenna, 4 ... transmitting antenna, 6 ... A / D converter, 7 ... receiving frequency converter, 8 ... D / A converter, 9 ... transmission frequency converter , 10 ... Channel signal processing part, 12 ... Local oscillation part, 14 ... Mixer part, 16 ... LPF, 18 ... Downsampling part, 20 ... FIR filter, 22 ... Adder 24 ... LPF 26 ... delay element 28 ... amplifier 30 ... upsampling 32 ... LPF 34 ... mixer 40 ... Mixing unit, 42 ... input selection unit, 44 ... output selection unit, 46 ... timing control unit, 50 ... calculation unit, 52 ... discrete Fourier transform unit, 54 ... transfer function calculation , 56... Reciprocal calculation unit, 58... Inverse discrete Fourier transform unit, 60. Number calculating unit, 62 ... target channel selection switch, 64 ... target channel setting unit.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the entire relay apparatus to which the present invention is applied.
The relay apparatus according to the present embodiment is an apparatus that receives a broadcast wave of terrestrial digital television broadcasting with a reception antenna 2 and retransmits the received signal from the transmission antenna 4 toward an area where the broadcast wave does not reach directly.

The relay apparatus according to the present embodiment includes an A / D conversion unit 6, a reception frequency conversion unit 7, a channel signal processing unit 10, a mixing unit 40, a D / A conversion unit 8, and a transmission frequency conversion unit 9 as a wraparound canceller. , An input selection unit 42, an output selection unit 44, a timing control unit 46, and a calculation unit 50 are provided. The wraparound canceller is provided in the relay apparatus in order to remove the wraparound signal superimposed on the reception signal when the transmission radio wave from the transmission antenna 4 wraps around the reception antenna 2 in the relay apparatus.

The channel signal processing unit 10 determines the number of channels (n) of the broadcast signal (OFDM signal) to be retransmitted, as is clear from the reference numerals 10-1, 10-2,. A corresponding number is provided.

Here, first, the reception frequency conversion unit 7 determines that the OFDM signal to be relayed among the reception signals from the reception antenna 2 is a fixed interval for each channel near the baseband (in this embodiment, as shown in FIG. 3A). The received signals are frequency-converted for each channel (all four channels in FIG. 3A) so that they are arranged at intervals of 6 MHz.

Then, the A / D conversion unit 6 converts the reception signals of all channels arranged by the reception frequency conversion unit 7 into digital data.
3A and 3B represent image components generated by sampling the received signal at the sampling frequency Fs by the A / D conversion unit 6.

Next, baseband OFDM signals (see FIG. 3A) converted into digital data by the A / D conversion unit 6 are respectively supplied to n channel signal processing units 10 (10-1, 10-2,.・ ・ 10-n)

Each channel signal processing unit 10 (10-1, 10-2,... 10-n) removes a wraparound signal for each OFDM signal of a channel to be processed assigned to each channel signal processing unit 10. A sneak removal signal (hereinafter referred to as a cancel signal) necessary for the above is generated, and the generated cancel signal is added to the OFDM signal to remove the sneak signal from the OFDM signal.

Then, the OFDM signal of each channel from which the sneak signal is removed by each channel signal processing unit 10 (10-1, 10-2,... 10-n) is mixed (added) by the mixing unit 40. Thereafter, the data is output to the D / A converter 8. The D / A converter 8 converts the input signal (multi-channel OFMD signal) from the mixing unit 40 into an analog signal.

The analog signal converted by the D / A converter 8 is input to the transmission frequency converter 9. The analog signal is frequency-converted by the transmission frequency conversion unit 9 to the original frequency before being frequency-converted by the reception frequency conversion unit 7 for each channel, and then transmitted to the transmission antenna 4 as a transmission signal for retransmission. Is output.

Next, the configuration of the channel signal processing unit 10 (10-1, 10-2,... 10-n), and the operations of the input selection unit 42, the output selection unit 44, the timing control unit 46, and the calculation unit 50, Will be described.

All of these units are configured by digital circuits that process digital data. Each channel signal processing unit 10 is also composed of an ASIC composed of various digital circuits (logic gates and the like). In FIG. 1, the configuration of each channel signal processing unit 10 is represented by functional blocks in order to easily explain the function of each channel signal processing unit 10.

As shown in FIG. 1, each channel signal processing unit 10 is provided with a frequency conversion unit (input-side frequency conversion unit). The frequency conversion unit mixes the reception signal input via the A / D conversion unit 6 and the local oscillation signal generated by the local oscillation unit 12 in the mixer unit 14, so that the specific channel to be processed is mixed. The received signal is frequency-converted so that the center frequency of the OFDM signal becomes a reference frequency (for example, 0 MHz).

Each channel signal processing unit 10 (10-1, 10-2,... 10-n) is a processing target as illustrated in FIG. 3B, although the channel of the OFDM signal to be processed is different. The received signal is frequency-converted so that the center frequency of the OFDM signal is a reference frequency common to each channel (for example, 0 MHz).

Therefore, in each channel signal processing unit 10 (10-1, 10-2,... 10-n), the frequency of the local oscillation signal generated by the local oscillation unit 12 is a processing target of the received signal. The frequency is set to be a frequency corresponding to the center frequency of the OFDM signal (6 MHz, 12 MHz, 18 MHz, 24 MHz when the OFDM signal of each channel is the frequency array shown in FIG. 3).

The frequency-converted reception signal is passed through a low-pass filter (LPF: digital filter) 16 that selectively passes only the OFDM signal (frequency band: reference frequency ± 2.8 MHz) to be processed. Input to the downsampling unit 18.

The downsampling unit 18 downsamples the OFDM signal output from the LPF 16 so that the number of data of the OFDM signal is a predetermined number (m).
Then, the downsampled OFDM signal (see FIG. 3C) is input to the adder 22, and is added to the wraparound removal signal generated by the FIR filter 20 in the adder 22. As a result, the sneak signal is removed from the OFDM signal.

Further, the OFDM signal (see FIG. 3D) after the wraparound signal removal is passed to a low-pass filter (LPF: digital filter) 24 that selectively passes only the OFDM signal (frequency band: reference frequency ± 2.8 MHz) to be processed. After being input, noise components outside the band are removed (see FIG. 3E), and then input to the amplifying unit 28.

The amplifying unit 28 is an amplifying unit with a so-called AGC circuit. The OFDM signal is amplified so that its output level becomes a constant level, and then input to the upsampling unit 30.

Then, in the upsampling unit 30, the number of data of the OFDM signal is upsampled by a predetermined number (m) times so that the number of data of the OFDM signal becomes the number of data before being downsampled by the downsampling unit 18. .

The OFDM signal up-sampled by the up-sampling unit 30 performs a filter process similar to that of the LPF 16 to selectively pass only the OFDM signal (frequency band: reference frequency ± 2.8 MHz) ( The signal is input to the mixer unit 34 via an LPF (digital filter) 32. The upsampled OFDM signal is mixed with the local oscillation signal generated by the local oscillation unit 12 in the mixer unit 34, so that the original frequency band before being frequency-converted by the frequency conversion unit on the input side is mixed. After being converted to an OFDM signal, it is output to the mixing unit 40.

Next, the FIR filter 20 takes in the OFDM signal filtered by the LPF 24 through the delay element unit 26 and filters the taken-in OFDM signal based on the filter coefficient input through the output selection unit 44. By processing, a cancel signal for removing the sneak signal from the OFDM signal input via the downsampling unit 18 is generated.

The delay element unit 26 is input to the FIR filter 20 in order to match the phase of the OFDM signal input to the adder unit 22 via the downsampling unit 18 and the cancel signal generated by the FIR filter 20. The delay amount Z- ^X is set in advance.

Next, the filter coefficient of the FIR filter 20 is calculated by the calculation unit 50. As shown in FIG. 2, the calculation unit 50 includes a discrete Fourier transform unit 52, a transfer function calculation unit 54, an inverse number calculation unit 56, an inverse discrete Fourier transform unit 58, and a coefficient calculation unit 60.

In the arithmetic unit 50, one of the OFDM signals respectively filtered by the LPF 24 in the plurality (n) of channel signal processing units 10 (10-1, 10-2,... 10-n) is stored. Are selectively input via the input selection unit 42. The arithmetic unit 50 performs arithmetic processing on the input OFDM signal.

That is, first, the discrete Fourier transform unit 52 extracts a spectrum on the frequency axis of the OFDM signal by performing a discrete Fourier transform on the OFDM signal input via the input selection unit 42. Then, the extracted spectrum is input to the transfer function calculation unit 54.

Next, based on the spectrum extracted by the discrete Fourier transform unit 52, the transfer function calculation unit 54 calculates the transfer function of the transmission path of the wraparound signal from the transmission antenna 4 to the reception antenna 2. The reciprocal calculator 56 calculates the reciprocal of the transfer function calculated by the transfer function calculator 54. The inverse discrete Fourier transform unit 58 performs an inverse discrete Fourier transform on the output from the inverse number calculation unit 56. Thereby, a delay profile is derived.

Note that the procedure for calculating the transfer function and calculating the delay profile from the reciprocal thereof is described in the above-mentioned Patent Document 1 and the like, and has been heretofore known, so detailed description thereof is omitted here.

The delay profile calculated by the inverse discrete Fourier transform unit 58 is input to the coefficient calculation unit 60. The coefficient calculation unit 60 calculates a filter coefficient required to generate a cancel signal for removing the sneak signal in the FIR filter 20 based on the delay profile of the input OFDM signal, and the calculated filter coefficient is The data is output to the output selection unit 44.

The output selection unit 44 outputs the filter coefficient output from the calculation unit 50 to the channel signal processing unit 10 corresponding to the OFDM signal selected by the input selection unit 42. As a result, the output selection unit 44 updates the filter coefficient of the FIR filter 20 in the channel signal processing unit 10 to the filter coefficient calculated by the calculation unit 50. More specifically, the output selection unit 44 performs selection of the filter signal update target channel signal processing unit 10 and update of the filter coefficient in synchronization with the switching timing signal output from the timing control unit 46. .

The input selection unit 42 selects the channel signal processing unit 10 that inputs the OFDM signal to the calculation unit 50 in synchronization with the switching timing signal output from the timing control unit 46. The arithmetic unit 50 also starts a series of processes from the discrete Fourier transform unit 52 to the coefficient calculation unit 60 in synchronization with the switching timing signal output from the timing control unit 46.

That is, in the present embodiment, the timing control unit 46 is configured to periodically output the switching timing signal at a constant interval that is slightly longer than the time required for the calculation unit 50 to execute a series of calculation processes. Yes.

Then, the input selection unit 42 sequentially switches the channel signal processing unit 10 that inputs the OFDM signal to the calculation unit between the channel signal processing units 10-1 to 10-n in synchronization with the switching timing signal. Next, the calculation unit 50 sequentially calculates filter coefficients corresponding to each channel signal processing unit 10 based on the switched OFDM signal from the channel signal processing unit 10. Then, the output selection unit 44 outputs the calculated filter coefficient to the channel signal processing unit 10 corresponding to the filter coefficient, thereby updating the filter coefficient of the FIR filter 20 in the channel signal processing unit 10. .

As described above, according to the relay apparatus of this embodiment (in other words, the wraparound canceller), the channel signal processing unit 10 generates a cancellation signal for wraparound signal removal for each OFDM signal of the channel to be relayed. Thus, the sneak signal is removed from the OFDM signal.

A cancel signal for removing the sneak signal is generated by the FIR filter 20 dedicated to each channel provided in each channel signal processing unit 10, and the filter coefficient of the FIR filter 20 is sent to the calculation unit 50. And calculated based on the OFDM signal of the corresponding channel.

Therefore, according to the relay device of this embodiment (in other words, the wraparound canceller), even if the signal level of the OFDM signal of each channel received by the receiving antenna 2 varies, the cancel signal is transmitted in a certain channel. Does not deviate from the proper value and the quality compensation for the OFDM signal of that channel is not overcompensated or undercompensated, and the wraparound signal can be satisfactorily removed from the OFDM signal of each channel.

In addition, according to the relay device of this embodiment (in other words, the wraparound canceller), an appropriate cancel signal can be generated for each channel, but the filter coefficient (in other words, the delay profile) used for the generation is common to all channels. Therefore, it is not necessary to provide the calculation unit 50 for each channel, and the cost of the wraparound canceller can be reduced.

Hereinafter, the correspondence between words will be described.
The local oscillating unit 12, the mixer unit 14, and the LPF 16 in each channel signal processing unit 10 correspond to an example of a signal extraction unit, and the delay element unit 26 and the FIR filter 20 correspond to an example of a removal signal generation unit, and are added. The unit 22 and the LPF 24 correspond to an example of a sneak removal unit, the local oscillation unit 12 and the mixer unit 34 correspond to an example of a frequency conversion unit, and the amplification unit 28 corresponds to an example of a level adjustment unit. The channel signal processing means 10-1, 10-2,..., 10-n configured in the above correspond to an example of the signal processing means. The mixing unit 40 corresponds to an example of a mixing unit, and the calculation unit 50 corresponds to an example of a delay profile calculation unit.

Here, in the present embodiment, the downsampling unit 18 downsamples the number of data of the OFDM signal that has passed through the LPF 16 to be a predetermined number (m), and the amplification unit 28 further reduces the data to a certain level. The upsampling unit 30 multiplies the number of data of the amplified OFDM signal by a predetermined number (m), thereby returning the number of data to the original number of data. The reason is as follows.

First, when sampling Japanese terrestrial digital broadcasting signals (TV broadcasting signals using OFDM signals), the “basic sampling number” per wave necessary to accurately perform the sampling is at least “2 ¹³ ”. It is necessary to.

If the sampling number per wave when sampling the received signal of the terrestrial digital broadcast signal is M ′, the total sampling number M required to accurately sample the multi-wave received signal is given by the following formula (1 ), The number of samplings M ′ per wave is obtained by multiplying by a predetermined value j consisting of “power value of 2” determined according to the wave number to be received.

Total sampling number M = sampling number per wave M ′ × j (1)
Here, the sampling number M ′ per wave is expressed by the following equation (2).
Sampling number M ′ = 2 ¹³ × 2 ^k (2)
(However, k = 0, 1, 2, 3 ...)
The predetermined value j is j = wave number (for example, when wave number = 4: j = 2 ² , and when wave number = 8: j = 2 ³ ) when the wave number is 2 or more and “power value of 2”. It becomes. Further, when the wave number is 2 or more and is not “a power of 2”, the predetermined value j is j = a power value of “2” that is the most recent value greater than the wave number (for example, when wave number = 3: j = 2 ² and wave number = 5, 6 and 7: j = 2 ³ ).

Note that k is a correction value for determining the sampling number M ′ per wave, and is used when the sampling number per wave is increased from the basic sampling number: 2 ^{13 in} order to increase the sampling accuracy.

In other words, the minimum value of the total sampling number M is the number of samplings M '= 2 ¹³ × 2 ⁰ per one wave when the k = 0, becomes a value obtained by multiplying a predetermined value j determined according to the wave number, sampling and In order to increase the accuracy of the calculation, “2 ¹ ” (k = 1), “2 ² ” (k = 2), “2 ¹³ ” which is the “basic sampling number” required per wave,. The number of samplings M ′ per wave may be increased by multiplying by.

In the present embodiment, for example, the sampling number M ^{'= 2 13} × ^{2 0} per one wave, as 8-wave maximum wavenumber of the received signal, the received signal by the A / D converter 6 (8 waves of the OFDM signal ) Is A / D-converted, the sampling number M is 65536 as shown in the following equation (3).

M = “2 ¹³ × 2 ⁰ ” × “2 ³ ” (3)
= 8192 × 8
= 65536
In the present embodiment, the LPF 12 extracts one OFDM signal from the OFDM signal (multi-wave) A / D converted (sampled) by the A / D converter 6, and the extracted OFDM signal Based on the above, a delay profile (and hence a cancel signal) is calculated.

For calculating the delay profile, it is not necessary to use all data (65536) of one wave of the OFDM signal filtered by the LPF 16, and even if the output data from the LPF 16 is down-sampled, Can be calculated.

Therefore, in the present embodiment, a downsampling unit 18 is provided between the LPF 16 and the adding unit 22 to downsample the data for one channel of the received signal output from the LPF 16, thereby delay profile (and thus canceling). The number of data of the OFDM signal used for the calculation of the signal) is reduced to a predetermined number (m) of the sampling number in the A / D converter 6 to reduce the calculation load on the channel signal processing unit 10 and the calculation unit 50. After that, the upsampling unit 30 upsamples the number of samplings of the OFDM signal by a predetermined number (m), so that the mixer unit 34 restores the OFDM signal having the same number of data as the original OFDM signal. I am doing so.

Further, in this way, when the data of the total sampling number M output from the LPF 16 is down-sampled to a predetermined number (m), the sampling number M ″ after the down-sampling is “ or basic sampling number "= same as" 2 ¹³ ", or" 2 ¹³ larger than "may be determined so as not to exceed the total sampling number M becomes" power of two values ".

Specifically, in the case of three-wave reception, since M ′ = (2 ¹³ × 2 ^k ) and j = 2 ² , the total sampling number M = (2 ¹³ × 2 ^k ) × 2 ² , and during downsampling The predetermined number (m) of k is 0: 2 ⁰ , 2 ¹ , 2 ² , and k = 1: 2 ⁰ , 2 ¹ , 2 ² , 2 ³ .

In the case of 8-wave reception, since M ′ = (2 ¹³ × 2 ^k ) and j = 2 ³ , the total sampling number M = (2 ¹³ × 2 ^k ) × 2 ³ , which is a predetermined number at the time of downsampling (M) is any of 2 ⁰ , 2 ¹ , 2 ² , 2 ³ when k = ⁰ , and 2 ⁰ , 2 ¹ when k = ^1.
, 2 ² , 2 ³ , 2 ⁴ .

That is, the predetermined number (m) for determining the size of downsampling may be any one of “power-of-two values” within the following range.
1 ≤ predetermined number (m)
Predetermined number (m) ≤ total sampling number M / "basic sampling number"
In this embodiment, the predetermined value (m) when down-sampling by the down-sampling unit 18 is set to the value 8 (= 2 ³ ), so that data for one wave of the OFDM signal output from the LPF 16 (sampling number) M: 65536) is down-sampled to 1/8, and the data after the down-sampling (sampling number: 8192) is output to the arithmetic unit 50, thereby calculating a delay profile (and thus a filter coefficient). Further, the upsampling unit 30 multiplies the OFDM signal (sampling number: 8192) output from the amplifying unit 28 by 8 so that the OFDM signal becomes the number of data before being down-pulled.

To summarize the above description, when configuring the relay device of the present embodiment, the following settings may be made.
The total sampling number M, the sampling number M ′ per wave, the downsampling size, the upsampling size, etc. are all “power-of-two values”.

A predetermined value j consisting of “a power of 2” corresponding to the received wave number is determined.
The total sampling number M for receiving a plurality of channels is equal to the sampling number M ′ (2 ¹³ × 2 ^k ) per wave obtained from the “basic sampling number” (for example, 2 ¹³ ). It is determined by multiplying a predetermined value j determined accordingly.

-The predetermined number (m) for determining the size of downsampling is the "number of samplings M" after downsampling obtained by dividing the calculated total sampling number M by the predetermined number (m). 2 is determined to be “a power of 2” that is equal to ¹³ or does not exceed the total sampling number M.

Upsampling is expanded with the same size as a predetermined number (m) of downsampling.
However, the “basic sampling number” does not necessarily need to be “2 ¹³ ” or more, and may be set as appropriate according to a relay signal (OFDM signal) by the relay apparatus to which the present invention is applied.

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, the channel signal processing units 10-1, 10-2,... 10-n as signal processing means always operate, and the input selection unit 42 periodically outputs from the timing control unit 46. In synchronization with the switching timing signal, the input source of the OFDM signal to the calculation unit 50 is sequentially switched to one of the channel signal processing units 10-1 to 10-n. In synchronization with the switching, the output selection unit 44 switches the channel signal processing units 10-1 to 10-n that update the filter coefficients of the FIR filter 20 to the filter coefficients calculated by the calculation unit 50.

However, in this case, the number of OFDM signal channels to be retransmitted is smaller than the number of channels from which the sneak signal can be removed by the channel signal processing units 10-1 to 10-n, and the sneak signal removal operation is unnecessary. In the case where the correct channel signal processing unit 10 exists, the unnecessary channel signal processing unit 10 generates a sneak removal signal that is unnecessary for the removal of the sneak signal.

For this reason, as shown in FIG. 4, the wraparound canceller of the above embodiment may further include a target channel selection switch 62 and a target channel setting unit 64. The target channel selection switch 62 is a switch for manually specifying a target channel from which a wraparound signal is to be removed by an external operation. The target channel setting unit 64 sets the operations of the channel signal processing units 10-1 to 10-n, the input selection unit 42, and the output selection unit 44 according to the target channel designated by the target channel selection switch 62. .

The target channel setting unit 64 corresponds to an example of a control unit. The target channel setting unit 64 selectively operates the channel signal processing unit 10 corresponding to the target channel according to the target channel specified via the target channel selection switch 62 as an example of the input unit, Then, the operation of the channel signal processing unit 10 corresponding to a channel other than the target channel is stopped. In addition, the target channel setting unit 64 sets the channel signal processing unit 10 that is the source from which the input selection unit 42 receives the OFDM signal and the output selection unit 44 outputs the filter coefficient to the channel corresponding to the target channel. The signal processing unit 10 is limited.

As a result, according to the wraparound canceller shown in FIG. 4, only the channel signal processing unit 10 corresponding to the target channel specified via the target channel selection switch 62 operates. In this case, the operation of the channel signal processing unit 10 that does not correspond to the target channel is stopped and the power consumption is reduced. As a result, the wraparound canceller can save energy.

Further, by stopping the operation of the channel signal processing unit 10 that does not correspond to the target channel, generation of unnecessary noise from the channel signal processing unit 10 that has stopped the operation is suppressed, and transmission transmitted from the transmission antenna 4 is performed. The signal quality of the signal can be improved.

Further, the target channel setting unit 70 not only selectively operates the channel signal processing unit 10 corresponding to the target channel, but also applies the OFDM signal input to the calculation unit 50 via the input selection unit 42 as a target. Restrict to channel OFDM signal. Therefore, the calculation cycle of the delay profile corresponding to the target channel by the calculation unit 50, that is, the calculation cycle of the wraparound removal signal in the channel signal processing unit 10 in operation can be shortened to the minimum necessary.

For this reason, according to the sneak canceller shown in FIG. 4, the update frequency of the sneak removal signal can be increased to improve the sneak signal removal accuracy.
Note that the target channel setting unit 64 has a function of switching each channel signal processing unit 10 to an operating state or a stopped state. For example, whether or not to supply an operation clock to each channel signal processing unit 10 You may make it carry out by switching. Alternatively, conduction / cutoff of the power supply line to each channel signal processing unit 10 may be switched. Further, for example, the gain (gain) of the amplifier 28 constituting each channel signal processing unit 10 may be switched between a normal gain adjusted gain and zero.

On the other hand, for example, in the embodiment described above, the downsampling unit 18 and the upsampling unit 30 are provided in order to reduce the calculation load in each channel signal processing unit 10 and the calculation unit 50. The upsampling unit 30 is not necessarily provided.

Further, for example, in the above-described embodiment, in order to calculate the delay profile from the OFDM signal of each channel by the calculation unit 50 common to each channel, each calculation unit 50 includes a discrete Fourier transform unit 52, a transfer function calculation unit. 54, the reciprocal number calculation unit 56 and the inverse discrete Fourier transform unit 58 have been described. However, since various methods are conventionally known as delay profile calculation methods, the delay profile calculation unit uses those methods. You may select suitably and may comprise.

In the above-described embodiment, each channel signal processing unit 10 has been described as including an amplification unit 28 that amplifies the OFDM signal after removal of the sneak signal that has passed through the LPF 24 to a certain level. It may be provided between the mixer unit 34 and the mixing unit 40 so as to amplify the OFDM signal frequency-converted by the unit 34.

Furthermore, in the above embodiment, the cancellation signal is generated and the delay profile and the filter coefficient are calculated by inputting the OFDM signal after removal of the sneak signal that has passed through the LPF 24 to the FIR filter 20 and the calculation unit 50. As described above, for example, even if the OFDM signal that has passed through the LPF 16 and is down-sampled by the down-sampling unit 18 is input to the FIR filter 20 and the calculation unit 50, the generation of the cancellation signal, the delay profile, and the filter Coefficients can be calculated.

Claims (6)

1. In a relay apparatus that receives a multi-channel OFDM signal at a receiving antenna and retransmits the received signal from a transmitting antenna, a wraparound that is superimposed on the received signal when a transmission radio wave from the transmitting antenna wraps around the receiving antenna A wraparound canceller that removes the signal,
   A plurality of signal extraction means for frequency-converting the OFDM signal of each channel received by the receiving antenna to a specific frequency common to all channels, and extracting the OFDM signal of the specific frequency after the frequency conversion;
   One delay profile that sequentially captures OFDM signals of each channel extracted by the plurality of signal extraction means in a time division manner and calculates a delay profile of the OFDM signal transmitted from the transmission antenna for each of the captured channels. A calculation means;
   A plurality of removal signal generation means each for generating a wraparound removal signal for the OFDM signal of each channel received by the reception antenna based on the delay profile calculated for each channel by the delay profile calculation means;
   A plurality of wraparound removal means for removing a wraparound signal from the OFDM signals of each channel extracted by the plurality of signal extraction means, using the wraparound removal signals of each channel generated by the plurality of removal signal generation means; ,
   A plurality of frequency conversion means for frequency-converting the OFDM signal from which the sneak signal has been removed by the plurality of wraparound removal means to the original frequency before being frequency-converted by the signal extraction means;
   Mixing means for mixing the OFDM signals of the respective channels frequency-converted by the plurality of frequency converting means and outputting them to the transmitting antenna side;
   The signal levels of the OFDM signal from which the sneak signal has been removed by the plurality of sneak removal means or the OFDM signal that has been frequency-converted by the plurality of frequency conversion means and input to the mixing means are respectively transmitted in a predetermined manner. A plurality of level adjusting means for adjusting to the level;
   A wraparound canceller characterized by comprising:
2. The delay profile calculation means includes:
   A discrete Fourier transform unit for extracting a spectrum on the frequency axis of the OFDM signal by performing a discrete Fourier transform on the OFDM signal extracted by each of the signal extraction units;
   A transfer function calculating unit that calculates a transfer function of a transmission path from the transmitting antenna to the receiving antenna based on the spectrum extracted by the discrete Fourier transform unit;
   An inverse calculation unit for calculating the inverse of the transfer function calculated by the transfer function calculation unit;
   An inverse discrete Fourier transform unit that derives the delay profile by performing an inverse discrete Fourier transform on an output from the inverse number calculation unit;
   The wraparound canceller according to claim 1, comprising:
3. An input means for externally designating a target channel from which a wraparound signal is to be removed;
   The signal extraction means, the removal signal generation means, the wraparound removal means, the frequency conversion means, and the level adjustment means are designated via the input means among a plurality of signal processing means configured for each channel. The signal processing unit corresponding to the target channel is selectively operated, the operation of the signal processing unit corresponding to the channel other than the target channel is stopped, and the delay profile calculation unit sequentially captures the delay profile in time division. Control means for limiting the OFDM signal to be calculated to the OFDM signal of the target channel designated via the input means;
   The wraparound canceller according to claim 1, comprising:
4. In a relay apparatus that receives a multi-channel OFDM signal at a receiving antenna and retransmits the received signal from a transmitting antenna
   As a sneak canceller that removes a sneak signal superimposed on the received signal by sneaking a transmission radio wave from the transmitting antenna to the receiving antenna,
   A plurality of signal extraction means for frequency-converting the OFDM signal of each channel received by the receiving antenna to a specific frequency common to all channels, and extracting the OFDM signal of the specific frequency after the frequency conversion;
   One delay profile that sequentially captures OFDM signals of each channel extracted by the plurality of signal extraction means in a time division manner and calculates a delay profile of the OFDM signal transmitted from the transmission antenna for each of the captured channels. A calculation means;
   A plurality of removal signal generation means each for generating a wraparound removal signal for the OFDM signal of each channel received by the reception antenna based on the delay profile calculated for each channel by the delay profile calculation means;
   Using the wraparound removal signal of each channel generated by the plurality of removal signal generation means,
   A plurality of wraparound removing means for removing a wraparound signal from the OFDM signal of each channel extracted by the plurality of signal extracting means;
   A plurality of frequency conversion means for frequency-converting the OFDM signal from which the sneak signal has been removed by the plurality of wraparound removal means to the original frequency before being frequency-converted by the signal extraction means;
   Mixing means for mixing the OFDM signals of the respective channels frequency-converted by the plurality of frequency converting means and outputting them to the transmitting antenna side;
   The signal levels of the OFDM signal from which the sneak signal has been removed by the plurality of sneak removal means or the OFDM signal that has been frequency-converted by the plurality of frequency conversion means and input to the mixing means are respectively transmitted in a predetermined manner. A relay apparatus comprising a wraparound canceller comprising a plurality of level adjusting means for adjusting to a level.
5. The delay profile calculation means includes:
   A discrete Fourier transform unit for extracting a spectrum on the frequency axis of the OFDM signal by performing a discrete Fourier transform on the OFDM signal extracted by each of the signal extraction units;
   A transfer function calculating unit that calculates a transfer function of a transmission path from the transmitting antenna to the receiving antenna based on the spectrum extracted by the discrete Fourier transform unit;
   An inverse calculation unit for calculating the inverse of the transfer function calculated by the transfer function calculation unit;
   An inverse discrete Fourier transform unit that derives the delay profile by performing an inverse discrete Fourier transform on an output from the inverse number calculation unit;
   The relay apparatus according to claim 4, further comprising:
6. The wraparound canceller is
   An input means for externally designating a target channel from which a wraparound signal is to be removed;
   The signal extraction means, the removal signal generation means, the wraparound removal means, the frequency conversion means, and the level adjustment means are designated via the input means among a plurality of signal processing means configured for each channel. The signal processing unit corresponding to the target channel is selectively operated, the operation of the signal processing unit corresponding to the channel other than the target channel is stopped, and the delay profile calculation unit sequentially captures the delay profile in time division. The relay apparatus according to claim 4, further comprising: a control unit that limits an OFDM signal to be calculated to an OFDM signal of a target channel designated through the input unit.

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