JPH0691628B2 - Method for transmitting and receiving reference signal for ghost removal - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ghost-removing reference signal transmitting / receiving method for removing group delay distortion, amplitude characteristic distortion, ghost, etc., which occur during transmission of a television signal. Is.

2. Description of the Related Art Conventionally, as a most effective means for removing a ghost generated during transmission of a television signal, there is a ghost removing device using a transversal filter as shown in FIG. This is a thing which considers the transmission system which produces | generates a ghost as one filter, produces | generates the filter characteristic used as the reverse characteristic by the said transversal filter, and removes a ghost.

The most important point in the ghost elimination device using this transversal filter is the reference signal for estimating the filter characteristic of the transmission system. As the reference signal, the differential signal at the leading edge of the vertical synchronizing signal as shown in FIG. 4 is used.

(Reference: Onishi et al., Automatic ghost removal of TV images,
(Showa 53.5 NHK STRL Monthly Report) This differential signal represents an approximate value of the impulse response of the transmission system.

Further, the Japan Broadcasting Corporation has proposed a ghost elimination reference signal (GCR) as shown in FIG. (Reference: Ohara et al., Examination of Reference Waveform for Ghost Removal TV Technical Report, RE81-6, Showa 56.2) This signal consists of pulse signal and bar signal. The pulse signal is used to infer the impulse response of the transmission system. The bar signal is used to detect the occurrence of sag by the transversal filter.

Problems to be Solved by the Invention A problem in using a vertical synchronizing signal as a reference signal for ghost elimination is that the signal quality of a synchronizing signal of a television signal is not as guaranteed as that of a video signal. Further, the synchronizing signal portion of the modulated television signal has the largest signal power and is easily subject to nonlinear distortion. Therefore, there is no complete correlation between the waveforms of the video signal and the sync signal, and it is difficult to sufficiently remove the ghost when the leading edge of the vertical sync signal is used as a reference signal for ghost removal.

Also in the ghost removing reference signal proposed by the Japan Broadcasting Corporation, the pulse signal is required to have a pulse equivalent to 1.5 T pulse (half-value width 187.5 nsec) in order to sufficiently remove the ghost. (Reference: Ohara et al., System study of adapter type ghost canceller.
However, in the case of such a pulse signal, it is difficult to obtain information for proximity ghosts, group delay distortion, and correction of frequency-amplitude characteristics, which are problems in teletext broadcasting. Because such an impulse response is expressed as a set of many pulses in the vicinity of the original pulse.
Therefore, it is difficult to separate the latter pulse and the original pulse.

Also, since it is a single pulse, its signal power is small and it is easily affected by noise and the like.

Further, even in the time range in which the ghost can be removed, in the method in which the leading edge of the vertical synchronizing signal is used as the reference signal, the delayed signal is not due to the reference signal with respect to the ghost which is 1/2 horizontal period or more. Therefore, it is impossible to determine whether the signal is delayed or another signal is delayed. Therefore, the ghost elimination range of the ghost elimination device using the leading edge of the vertical synchronization signal as a reference signal is only 1/2 horizontal synchronization at maximum. Further, in the ghost elimination reference signal proposed by the Japan Broadcasting Corporation,
Due to the signal format, a ghost having a delay time of 16.8 μsec or more cannot be removed for the same reason as above.

Means for Solving the Problems In order to solve the above problems, the present invention provides a digital signal train generating means, a means for superimposing the digital signal train in a vertical blanking period of a television signal, and the digital signal train. Transmission means for transmitting the television signal superimposed with, the group delay distortion generated in the transmission means to the television signal transmitted from the transmission means, amplitude characteristic distortion,
It is a thing comprising ghost removing means for removing ghosts and the like.

Operation The present invention uses the above-mentioned means to superimpose a digital signal train on the television signal and use it as a reference signal for ghost elimination, so that the signal has a power larger than that of a single pulse signal and a half horizontal period. The present invention provides a reference signal for removing a ghost, which is capable of removing the above-mentioned delayed ghost and is transmitted under exactly the same conditions as other video signals.

Embodiment 1 FIG. 1 is a circuit configuration diagram of a ghost removing reference signal transmitting / receiving method of the present invention. In the figure, 1 is a digital signal train generation circuit, 2 is a signal superposition circuit, 3 is a signal transmission system, and 4 is a ghost elimination device.

The operation will be described below. The output signal of the digital signal sequence generating circuit 1 is superimposed by the signal superimposing circuit 2 in the vertical retrace period of the television. The ghost removing device 4 removes the group delay distortion, the amplitude characteristic distortion, the ghost, etc. generated in the transmission system 3 by using the superimposed digital signal sequence as a reference signal.

Here, the transmission system 3 is one that modulates a television signal into an RF signal and transmits the signal in a wireless system or a wired system, or records or reproduces the signal in any recording medium like a video tape recorder. Means signal transmission.

FIG. 2 is a waveform diagram showing an example of a ghost eliminating reference signal superimposed during the vertical blanking period. In this example, the signal train is superposed as a binary NRZ signal in the signal train superimposing period shown in FIG. 2 other than the vertical synchronizing signal and the vertical equalizing pulse period in the vertical blanking period.

Next, how to use the superimposed digital signal sequence as a reference signal for ghost removal will be described.

FIG. 3 is a circuit configuration diagram showing a ghost removing device using a transversal filter as an example of the ghost removing device. In the figure, a television signal including a ghost has a transversal filter 20 having characteristics reverse to those of the transmission system 3 that generates group delay distortion, amplitude characteristic distortion, ghost, and the like.
Thus, the group delay distortion, the amplitude characteristic distortion, the ghost, etc. are removed. From this output signal, in the error signal string generation circuit 22,
An error signal sequence corresponding to waveform distortion due to the group delay distortion, amplitude characteristic distortion, ghost, etc. is generated. How to determine the error signal sequence is transmitted, and from the television signal in which the group delay distortion, the amplitude characteristic distortion, the ghost, etc. are removed by the transversal filter 20, the digital signal sequence that is the reference signal is selected, and the error signal is selected. In the column generation circuit 22. Alternatively, it is determined as a difference from the expected signal sequence corresponding to the selected digital signal sequence calculated in the error signal sequence generation circuit 22. This error signal string and the input signal of the transversal filter 20 cause the control circuit 21
Then, the transversal filter 20 is controlled so that the error signal sequence is minimized, that is, the group delay distortion, the amplitude characteristic distortion, and the ghost are eliminated.

The power of the digital signal train is larger than that of a single pulse. Therefore, when the digital signal train is used as the reference signal, the influence of noise is less than that of the conventional single pulse.

Furthermore, by using the least squares error method or the like as the control method of the transversal filter 20, by calculating the correction amount of the tap weight by correlating the error signal sequence with the input signal sequence, etc. Even if an error due to a signal other than the reference signal is included in, the effect can be removed. Therefore, it is possible to remove the delayed ghost of 1/2 horizontal period or more.

EFFECTS OF THE INVENTION As described above, according to the present invention, by superimposing a digital signal sequence on a television signal and using it as a ghost elimination reference signal, a signal having a larger power than a single pulse signal, / 2 It is possible to obtain a reference signal for removing ghosts that is transmitted under the same conditions as other video signals, and can also remove delayed ghosts that exceed the horizontal period.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a configuration of an apparatus to which the present invention is applied, FIG. 2 is a waveform diagram showing a reference signal for ghost removal, FIG. 3 is a circuit configuration diagram showing a ghost removal apparatus, and FIG.
FIG. 5 is a waveform diagram showing a conventional ghost eliminating reference signal. 1 ... Digital signal train generation circuit, 2 ... Signal superposition circuit,
3 ... Transmission system, 4 ... Ghost elimination device, 20 ... Transversal filter, 21 ... Control circuit, 22 ... Error signal string generation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Furubo 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-56-166674 (JP, A)

Claims (1)

[Claims] 1. A means for generating a digital signal sequence, a means for superimposing the digital signal sequence on a vertical blanking period of a television signal, and a transmitting means for transmitting the television signal on which the digital signal sequence is superimposed. A ghost removing means for removing group delay distortion, amplitude characteristic distortion, ghost, etc. generated in the transmitting means with respect to the television signal transmitted by the transmitting means, and the ghost removing means is superimposed on the television signal. A method for transmitting and receiving a reference signal for ghost removal, characterized in that the digital signal sequence thus generated is used as a reference signal.