JP2006222789A - Device and method for canceling sneak - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continue a stable operation for a long period of time regardless of large changes in transmission line environment due to seasonal variances, wind, etc. in broadcast wave relay using a device for canceling sneak. <P>SOLUTION: A sneak canceling device includes a level control part 116 for controlling an output level of a digital filter part 115 and threshold setting parts 101 and 114 for setting thresholds of mask processing parts 109 and 112 in accordance with an output from an oscillation detection part 106. According as an oscillation level detected by the oscillation detection part 106 gets higher, a relay signal output level is made lower by a level control part 117 and an output value of a digital filter 115 for cancellation is made smaller by the level control part 116, and a threshold for masking coefficient values smaller than a prescribed value, with zero in preprocessing of reflecting an estimation result of a sneak transmission line on the digital filter 115 for cancellation is made larger in accordance with rise of the detected oscillation level. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wraparound canceling apparatus that suppresses a wraparound phenomenon that becomes a problem when a radio signal transmitted by an orthogonal frequency division multiplexing (OFDM) system or the like is relayed at the same frequency without being demodulated, and It relates to a wraparound cancellation method.

  In digital broadcast (or digital transmission) using an OFDM signal, when a broadcast wave is relayed by retransmission at the same frequency at a relay station constituting an SFN (Single Frequency Network), the transmission antenna relays to the reception antenna. The signal wraps around and degrades the quality of the relay signal. A technique for canceling this sneak wave by digital signal processing is known (see, for example, Patent Document 1).

  Furthermore, as a method for updating the coefficient of the digital filter to be adaptively changed, it is configured to update the error from the previously updated coefficient, thereby reducing the performance required by the automatic frequency control unit and automatic gain control unit. The technique of doing is also well-known (for example, refer patent document 2). A technique for stably operating even in a transmission path environment in which the sneak wave power is larger than the received wave power from the master station is also known (see, for example, Patent Document 3).

  In addition, a technique for performing control at the time of starting abnormal oscillation or relay signal transmission is also known (see, for example, Patent Document 4). Conventionally, when an oscillation symptom is confirmed by the oscillation detection means, a technique has been used in which a digital filter coefficient for feedback is reset to zero and at the same time a relay signal is not output. In addition, a technique for performing control so as to reduce the level of the relay output when an omen of oscillation is confirmed is also known. FIG. 4 is a block diagram showing a schematic configuration of a broadcast repeater including such a conventional wraparound canceling apparatus.

The conventional broadcast repeater shown in FIG. 4 includes a reception antenna 101, a reception conversion unit 102, an analog / digital conversion unit 103, a subtraction unit 104, a Fourier transform unit 105, an oscillation detection unit 106, and a frequency characteristic estimation. Unit 107, inverse Fourier transform unit 108, mask processing units 109 and 112, threshold setting units 110 and 114, coefficient update unit 111, delay unit 113, digital filter unit 115, level control unit 117, transmission A conversion unit 118 and a transmission antenna 119 are provided. Each unit other than the reception antenna 101, the reception conversion unit 102, the analog / digital conversion unit 103, the transmission conversion unit 118, and the transmission antenna 119 constitutes a wraparound cancel device. This conventional wraparound canceling device for a broadcast repeater resets the digital filter coefficient for feedback to zero when the oscillation detection unit 106 confirms a sign of oscillation, and at the same time prevents the relay signal from being output to the level control unit 117. To control.
JP-A-11-355160 JP 2000-341238 A JP 2000-341242 A JP 2001-160794 A

  By the way, when the sneak cancel device is used for broadcast wave relay, it is required to operate stably over a long period of several years. However, since the transmission path environment greatly fluctuates due to seasonal fluctuations and winds, it is difficult to continue stable operation over the long term.

  Also, in a wireless transmission environment where a relay station is installed, various levels of sneak waves exist at various delay times, and the received wave power (D) from the master station and the signal transmitted from the own station are transmitted to the receiving antenna. It has been confirmed that even in a transmission path environment in which the ratio D / U of the encircling wave power (U) is less than 1 and the encircling cancellation operation is relatively easy, the oscillation suddenly occurs.

  The reason for sudden oscillation even in the transmission path environment where the wraparound cancellation is relatively easy as described above is that the coefficient of the feedback digital filter falls into a combination of coefficients that causes oscillation, and the wireless transmission path It is presumed that abnormal oscillation has occurred in the signal processing unit inside the apparatus, not abnormal oscillation due to the sneak wave from.

  The present invention has been made in view of such a point, and suppresses a wraparound phenomenon that becomes a problem when a radio signal transmitted by an orthogonal frequency division multiplexing (OFDM) system or the like is relayed at the same frequency without being demodulated. An object of the present invention is to provide a sneak cancel device and a sneak cancel method that can be stably operated in the long term even if the transmission path environment varies greatly due to seasonal fluctuations or wind.

(1) A wraparound cancellation apparatus according to the present invention is a wraparound cancellation apparatus that cancels a wraparound wave in which a relay signal wraps around from a transmission antenna to a reception antenna when relaying by retransmission at the same frequency. A filter coefficient generation circuit for generating a filter coefficient, a signal processing means for generating a copy of the sneak signal included in the received signal, and a copy of the replica generated by the signal processing means from the actual sneak signal included in the received signal Subtracting means for subtracting the sneak signal, oscillation level detecting means for detecting the oscillation level of the loop formed by the subtracting means and the transversal filter, and the magnitude of the loop oscillation level detected by the oscillation level detecting means Accordingly, the relay signal level after the sneak wave cancellation process At the same time controlling the Le employs a configuration having a, a level control means for controlling the level of the output signal of the transversal filter.

  According to the above configuration, as the loop oscillation level increases, the level of the relay signal after the sneak wave canceling process can be lowered, and at the same time the level of the output signal of the transversal filter can be lowered. Accordingly, it is possible to appropriately cope with fluctuations in the level of the sneak wave that changes in response to the above, and even if the transmission path environment fluctuates greatly due to seasonal fluctuations or winds, stable operation can be continued for a long time.

(2) The wraparound canceling apparatus according to the present invention is the wraparound canceling apparatus according to (1), wherein the signal processing means has an amplitude value for a signal corresponding to a cancellation error that becomes a filter coefficient of the filter coefficient generation circuit. A mask processing means for replacing with zero when the value is smaller than a predetermined threshold, and the predetermined threshold used by the mask processing means is set according to the magnitude of the loop oscillation level detected by the oscillation level detecting means And a threshold setting means.

  According to the above configuration, since the threshold value in the mask processing means can be increased as the loop oscillation level increases, the ratio of masking to zero before falling into a situation where the oscillation phenomenon cannot be suppressed can be increased. It becomes possible to avoid the phenomenon, and further stable operation can be continued.

(3) The broadcast repeater of the present invention employs a configuration including the wraparound cancel device described in (1) or (2) above.

  According to the above configuration, it is possible to provide a broadcast repeater capable of continuing stable operation over a long period of time even if the transmission path environment varies greatly due to seasonal fluctuations or wind.

(4) The wraparound cancellation method of the present invention is a wraparound cancellation method for canceling a wraparound wave in which a relay signal wraps around from a transmission antenna to a reception antenna during relay by the same frequency retransmission. A copy of the sneak signal included in the received signal is generated using a filter coefficient generation circuit that generates a filter coefficient, and the generated sneak signal is applied to the subtracting unit to cancel the actual sneak signal included in the received signal; The oscillation level of the loop formed by the transversal filter and the subtracting unit is detected, and the level of the relay signal after the sneak wave cancellation processing is controlled according to the level, and at the same time, the output of the transversal filter Control the level of the signal.

  According to the above method, the level of the output signal of the transversal filter can be lowered at the same time as the level of the relay signal after the sneak wave canceling process is lowered as the loop oscillation level increases. Accordingly, it is possible to appropriately cope with fluctuations in the level of the sneak wave that changes in response to the above, and even if the transmission path environment fluctuates greatly due to seasonal fluctuations or winds, stable operation can be continued for a long time.

(5) The wraparound canceling method of the present invention is the wraparound canceling method according to (4) described above, wherein the wraparound transmission path is estimated, and the result of the preceding process for reflecting the result on the transversal filter is greater than a predetermined value. A threshold value for masking a small coefficient value to zero is controlled according to the detected oscillation level.

  According to the above method, since the threshold value in the mask process can be increased as the loop oscillation level increases, the ratio of masking to zero before falling into a situation where the oscillation phenomenon cannot be suppressed can be increased. Can be avoided, and more stable operation can be continued.

  According to the present invention, it is possible to provide a sneak cancel device and a sneak cancel method capable of continuing a stable operation in the long term even if the transmission path environment largely fluctuates due to seasonal fluctuations or winds.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a broadcast repeater according to an embodiment of the present invention. In this figure, the same reference numerals are given to the portions common to the broadcast repeater of FIG. 4 described above. Also, the broadcast repeater of the present embodiment is used for terrestrial digital broadcasting.

  In FIG. 1, the broadcast repeater of the present embodiment includes a receiving antenna 101, a receiving conversion unit 102, an analog / digital conversion unit 103, a subtraction unit 104, a Fourier transformation unit 105, an oscillation detection unit 106, Frequency characteristic estimation unit 107, inverse Fourier transform unit 108, mask processing units 109 and 112, threshold setting units 110 and 114, coefficient update unit 111, delay unit 113, digital filter unit 115, and level control unit 116 and 117, a transmission conversion unit 118, and a transmission antenna 119.

  Note that each unit other than the reception antenna 101, the reception conversion unit 102, the analog / digital conversion unit 103, the transmission conversion unit 118, and the transmission antenna 119 constitutes a wraparound cancel device. In addition, the Fourier transform unit 105, the frequency characteristic estimation unit 107, the inverse Fourier transform unit 108, the mask processing units 109 and 112, the threshold setting units 110 and 114, the coefficient update unit 111, and the delay unit 113 constitute a signal processing unit. The subtraction unit 104 corresponds to subtraction means, and the digital filter unit 115 corresponds to a transversal filter. The mask processing units 109 and 112 constitute a mask processing unit, and the threshold setting units 110 and 114 constitute a threshold setting unit. The oscillation detection unit 106 corresponds to an oscillation level detection unit. The level controllers 116 and 117 constitute level control means.

  The sneaking cancel device of the present embodiment has a level control unit 116 that controls the output level of the digital filter unit 115 in addition to the same configuration as the conventional sneaking cancel device, while the output from the oscillation detection unit 106 is a threshold value. The threshold values of the setting units 110 and 114 can be changed.

  Only a desired channel signal is extracted from the radio signal received by the receiving antenna 101 by the reception conversion unit 102, and frequency-converted to an intermediate frequency band (IF band). The signal frequency-converted to the IF band is subjected to analog / digital conversion by the analog / digital conversion unit 103, and then the subtraction unit 104 obtains a difference from the signal fed back as a sneak wave replica in the wireless transmission path. The wraparound component is canceled. The output signal of the subtraction unit 104 is branched, one is input to the level control unit 117, and the other is input to the Fourier transform unit 105 and the digital filter unit 115.

  In the level control unit 117, when the oscillation detection unit 106 detects a warning of oscillation, the level control unit 117 is controlled to lower the level or completely stop the output. The output of the level control unit 117 is input to the transmission conversion unit 118, frequency-converted to a radio frequency band, power amplified, and radiated from the transmission antenna 119 into the air.

  On the other hand, in the Fourier transform unit 105, the signal in the time axis domain is Fourier transformed into the signal in the frequency axis domain, and the frequency characteristic estimation unit 107 estimates the frequency characteristic corresponding to the cancellation error. It is preferable that the frequency characteristic estimation unit 107 calculates the transmission line characteristic using a known signal inserted in the symbol as in the prior art, and obtains the frequency characteristic of the wraparound transmission line.

  The estimated frequency characteristic is returned again to the signal on the time axis region by the inverse Fourier transform unit 108, and a value smaller than a predetermined threshold is changed to zero by the mask processing unit 109. The predetermined threshold is preferably set as a ratio with respect to the maximum absolute value amplitude as in the prior art. By performing the masking process, an effect of extrapolating the frequency characteristic estimated from the limited band is produced, and wraparound outside the band can be compensated, and a stable canceling operation is possible.

  The signal subjected to the mask processing by the mask processing unit 109 is input to the coefficient updating unit 111 and is added to the coefficient updated at the previous coefficient update, thereby obtaining a coefficient that minimizes the cancellation error. Then, the output of the coefficient updating unit 111 is input to the mask processing unit 112 so that the mask processing is performed again. As a mask process for the updated coefficient, as in the prior art, a method may be used in which the ratio to the level of the master station wave (main wave) is equal to or less than zero, but for more stable operation. In addition, it is also preferable to set the value to zero when the value itself output regardless of the master station wave level is below a certain value. The output of the mask processing unit 112 is branched. One of the outputs is input to the delay unit 113 and the value is held until the next coefficient update. The held value is input to the coefficient update unit 111. The other is set as a filter coefficient of the digital filter unit 115. The digital filter unit 115 receives the output from the subtraction unit 104 and performs a convolution operation according to the set filter coefficient.

  Here, the difference from the conventional sneak cancel device shown in FIG. 4 will be described. In the conventional sneak cancel device shown in FIG. 4, the output of the digital filter unit 115 is directly input to the subtractor 104, but in the sneak cancel device of the present embodiment, the oscillation detection unit 106 responds to the oscillation state caused by the sneak current. A level control unit 116 is provided to control the level. In this case, if the level control units 116 and 117 are configured to operate in synchronization, it is possible to appropriately cope with the level fluctuation of the sneak wave that changes corresponding to the level of the relay output signal, which is preferable.

  Also, only when the conventional situation where the oscillation phenomenon cannot be suppressed, all the values output from the mask processing unit 112 connected to the coefficient updating unit 111 are reset to zero, and the relay signal transmission is also stopped. However, before the oscillation phenomenon can not be suppressed in this embodiment, the threshold value in the mask processing units 109 and 112 is controlled, and the oscillation phenomenon is reduced by increasing the masking ratio to zero. I try to avoid it. By controlling in this way, it is possible to prevent a situation in which a combination of coefficients of the digital filter unit 115 that easily induces oscillation occurs.

  For the oscillation detection unit 106, a conventional technique may be used in which the level of each carrier output from the Fourier transform unit 105 is observed and it is determined that larger oscillation is generated as the maximum value is larger.

  As the maximum value increases, the threshold setting units 110 and 114 are increased in threshold value, and the masking ratio is increased so that the output level in the level control units 116 and 117 is controlled to decrease. Can be reduced, which is preferable. Here, when the level is controlled by the level control unit 117, the level of the signal itself from the relay station changes and, strictly speaking, the range of the area where the radio wave reaches changes, but falls into an uncontrollable oscillation state. Can be avoided, and relaying can be continued, which has a great advantage for users who receive radio waves.

  As described above, according to the broadcast repeater of the present embodiment, in the wraparound canceling apparatus, the relay signal output level is lowered as the oscillation level detected by the oscillation detection unit 106 increases, and at the same time, the cancellation digital filter 115, the threshold value when the coefficient value smaller than a predetermined value is masked to zero is detected as a pre-process for reducing the output value of 115 and reflecting the estimation result of the sneak path to the cancellation digital filter 115. Since the level is increased as the level increases, stable operation can be continued in the long term even if the transmission path environment changes greatly due to seasonal fluctuations or wind.

  It should be noted that even if not all of the above-described configurations are used as an embodiment, the use of only a part can also suppress the oscillation, and for example, the configurations of FIGS. 2 and 3 are conceivable. The sneak cancel device shown in FIG. 2 has only a function of controlling the level of the relay signal after the sneak wave cancellation process according to the magnitude of the oscillation level and at the same time controlling the level of the output signal of the cancellation digital filter 115. In addition, the sneak cancel device shown in FIG. 3 has only a function of controlling the threshold according to the magnitude of the oscillation level.

  According to the present invention, a sneak canceller suppresses a sneak phenomenon which becomes a problem when relaying at the same frequency without demodulation in relaying a radio signal by an OFDM transmission method or the like, and to stably operate a sneak canceller for a long time. It is useful as a broadcast relay field or a wireless relay field.

The block diagram which shows schematic structure of the broadcast repeater which concerns on one embodiment of this invention. The block diagram which shows schematic structure of the application example of the broadcast repeater which concerns on one embodiment of this invention The block diagram which shows schematic structure of the application example of the broadcast repeater which concerns on one embodiment of this invention Block diagram showing the schematic configuration of a conventional broadcast repeater

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Reception antenna 102 Reception conversion part 103 Analog / digital conversion part 104 Subtraction part 105 Fourier transform part 106 Oscillation detection part 107 Frequency characteristic estimation part 108 Inverse Fourier transform part 109, 112 Mask processing part 110, 114 Threshold setting part 111 Coefficient update part 113 delay unit 115 digital filter unit 116, 117 level control unit 118 transmission conversion unit 119 transmission antenna

Claims (5)

In the sneak cancel device for canceling the sneak wave in which the relay signal sneaks from the transmitting antenna to the receiving antenna when relaying by the same frequency retransmission
A signal processing unit that includes a transversal filter and a filter coefficient generation circuit that generates a filter coefficient of the transversal filter, and that generates a copy of a wraparound signal included in the received signal;
Subtracting means for subtracting a duplicate sneak signal generated by the signal processing means from an actual sneak signal included in the received signal;
An oscillation level detection means for detecting an oscillation level of a loop formed by the subtraction means and the transversal filter;
Level control means for controlling the level of the output signal of the transversal filter at the same time as controlling the level of the relay signal after the sneak wave cancellation process according to the magnitude of the loop oscillation level detected by the oscillation level detection means. A wraparound cancel device provided. The signal processing means includes
A mask processing means for replacing a signal corresponding to a cancellation error serving as a filter coefficient of the filter coefficient generation circuit with zero when the amplitude value is smaller than a predetermined threshold;
Threshold setting means for setting the predetermined threshold used by the mask processing means according to the magnitude of the loop oscillation level detected by the oscillation level detection means;
The wraparound cancel device according to claim 1, comprising:   A broadcast repeater comprising the wraparound cancel device according to claim 1. In the wraparound cancellation method for canceling the sneak wave in which the relay signal wraps around from the transmission antenna to the reception antenna when relaying by the same frequency retransmission,
Using a transversal filter and a filter coefficient generation circuit for generating a filter coefficient of the transversal filter, a duplicate of the sneak signal included in the received signal is generated, and the generated sneak signal is supplied to the subtracting means and included in the received signal. The actual sneak signal is canceled, the oscillation level of the loop formed by the transversal filter and the subtracting means is detected, and the level of the relay signal after the sneak wave cancellation process is determined according to the magnitude of the level. A wraparound canceling method for simultaneously controlling the level of the output signal of the transversal filter.   A threshold for masking a coefficient value smaller than a predetermined value to zero is controlled in accordance with a detected oscillation level as a pre-stage process for estimating a sneak path and reflecting the result in the transversal filter. Item 5. The wraparound canceling method according to Item 4.

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