JPH0557778B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an information signal transmission method for transmitting information signals such as image signals via a transmission path, and in particular,
The information signal, which is originally in the form of an analog signal, is transmitted in its original form without deteriorating performance such as the signal-to-noise ratio, and the overall transmission characteristics can be digitally equalized and compensated.

(Summary of the invention) An information signal such as a high-quality image signal that is still in the form of a main line analog signal provided with a delay means for timing adjustment is converted into a digital signal and passed through a transversal filter, and then a pilot signal is generated. The same information signals of the inserted branch paths are added with the required polarity and sent out to the transmission path, and the characteristics of the transversal filter are adjusted by successive approximation so that the pilot signal being transmitted has an ideal characteristic waveform.
An information signal transmission method that equalizes the overall transmission characteristics without impairing the S/N of the main information signal.

(Prior Art) For example, in a high-definition television broadcasting system using a broadcasting satellite, imperfections in a transmission path are compensated for by an equalizer provided in an encoder on the transmitting side.
However, although such a transmission path equalization method is effective for the satellite broadcasting system itself, it is necessary to receive high-definition television signals from satellite broadcasting and continue to use CATV.
When transmitting high-definition television signals using a CATV system, it is not possible to compensate for the transmission path characteristics of the CATV system.

(Problem to be Solved by the Invention) Compensation for the CATV system transmission line characteristics in the above case needs to be performed independently using an additional equalization method, separately from the compensation for the characteristics of the satellite broadcasting system transmission line. be.

However, as an equalization method that compensates for the characteristics of this type of information transmission path, there is a ghost canceller method used in television signal transmission systems. This method detects ghost waveforms and adds similar waveforms in reverse phase to cancel and remove them, and is difficult to apply to digital information transmission lines such as satellite broadcasting systems that perform subsample transmission of high-definition television signals.

On the other hand, to compensate for the characteristics of a high-definition television signal sub-sampled transmission path, conventionally a pilot signal such as a unit impulse is inserted into the vertical retrace period of the television signal to compensate for the transmission distortion of the pilot signal waveform. An equalization method is adopted that controls a variable coefficient transversal filter inserted at the output end, but in this equalization method,
Since all the transmitted information signals into which the pilot signal has been inserted pass through a digital filter, the transmitted information signals must be A/D converted once, passed through the filter, and then D/A converted again. become. Therefore, the information signal repeats A/D conversion and D/A conversion each time it passes through the equalizer, and a problem arises in that the S/N deteriorates each time.

Furthermore, when digitally transmitting high-definition television signals, for example, an analog-to-digital converter with a sampling clock rate of 32.4 MS/S and a resolution of 10 bits is required to maintain high-definition image quality. However, at present, it is difficult to obtain a converter that can exhibit such performance with at least sufficient accuracy, and even if it were available, there are problems in that it would be extremely expensive and its operation would tend to be unstable.

Therefore, in order to transmit information signals such as high-definition television signals while maintaining their high quality, it is necessary to digitally equalize the transmission path characteristics. The problem was that transmission was difficult to implement.

(Means for Solving the Problems) An object of the present invention is to solve the above-mentioned conventional problems, and to transmit the information signal itself in an analog manner.
The object of the present invention is to provide an information signal transmission system that can digitally equalize transmission path characteristics.

Another object of the present invention is to provide an information signal transmission system in which equalization of transmission characteristics can be completed independently for each transmission path when different types of transmission paths are continuously connected.

That is, the information signal transmission system of the present invention allows the timing of an information signal in the form of an analog signal passed through a delay means and the information signal in the form of a digital signal passed through a transversal filter to be aligned by the delay means and at a required ratio. and each coefficient and the clock of the digital signal, which are added with the required polarity and sent out to the transmission path, and the transmission characteristics of the sent out information signals are multiplied by the sequentially delayed information signals that are combined with each other in the transversal filter. The present invention is characterized in that by controlling at least one of the phases, each transmission path is independently completed and equalized to the transmission characteristics of the transmission path.

(Function) Therefore, in the information signal transmission system of the present invention, even if an analog-to-digital converter with low precision is used, the quality of the information signal is not degraded, and transmission path characteristics with sufficiently high precision can be achieved. Equalization can be completed and completed independently for each transmission path.

(Example) The present invention will be described in detail below with reference to the drawings.

First, an example of the configuration of an information signal transmission system according to the present invention is shown in FIG. In the illustrated transmission system, an analog information signal from an input terminal 1 is guided to a differential amplifier 4 via an amplifier 2 and an analog delay element 3, and is also guided to a differential amplifier 4 via an amplifier 6 and a low-pass filter 7.・The signal is guided to a digital converter 8, and after being converted into a digital signal, it is led to a variable tap transversal filter 9, and after adjusting the phase characteristics of the digitized information signal, it is led to a digital-to-analog converter 10, which converts it into an analog signal. and low pass filter 1
1 to a differential amplifier 4 and subtracted from the input analog signal introduced via an analog delay element 3 at an appropriate ratio. Therefore, in a state where the variable tap transversal filter is set to the center tap and the phase deviation is zero, the analog information signal in the same state as it was input from the differential amplifier 4 can be obtained at an appropriate signal level. The signal is sent from the input end 5 to the transmission line 12.

Therefore, in the transmission system of the present invention, an impulse waveform signal of an appropriate form is generated from the impulse generator 17 at the center tap of the variable tap transversal filter 9 for the transmitted information signal in such a state. Insert as a pilot signal. As the pilot signal, for example, an impulse waveform signal having a configuration as shown in FIG. The phase distortion of the received conversion output waveform due to the distortion of the transmission characteristics can be detected by comparison with the ideal waveform.

Therefore, the received output information signal is extracted from the output end 13 of the transmission line 12 and converted into a digital signal by the analog-to-digital converter 14, and the pilot signal inserted in the digital information signal is extracted by the test signal extraction circuit 15. The coefficient data required to correct the phase distortion of the received converted output waveform as shown in FIG. By changing the coefficients that are supplied to each coefficient unit connected to the tap and multiplying the sequentially delayed signals that are combined with each other according to the coefficient data, or by changing the coefficients that are supplied to each coefficient unit connected to the tap, or by changing the coefficients that are multiplied by the sequential delay signals connected to By modulating the phase of the clock pulses that drive 8 and 10, for example, the clock pulse that drives the digital-to-analog converter 10 as shown in the figure, transmission distortion occurring not only in the transmission path but also in the entire transmission system can be corrected. to equalize the overall transmission characteristics.

Therefore, in the main line system of the illustrated configuration according to the transmission method of the present invention, the information signal is transmitted only by analog processing, but it is necessary to adjust the signal timing with the digital correction system at the input of the differential amplifier 4. Since the analog delay element 2 for this purpose has a considerable amount of delay, sometimes reaching several microseconds, it is often difficult to make the transmission characteristics of this delay element 3 completely flat. However, since the transmission characteristics of the entire transmission system, including imperfections in the transmission characteristics of the analog main line system, are comprehensively corrected based on the reception conversion output waveform of the inserted pilot signal as described above, the analog delay element The characteristics of 2 itself do not require strictness.

On the other hand, the low-pass filter 7 in the digital correction system is used to prevent the generation of aliasing distortion components in the subsequent sampling at a frequency of 32.4 Ms/s, and a cutoff frequency of about 13 to 14 MHz is desirable, and the phase characteristics are as described above. Although this is not strictly necessary, it is necessary to use a video filter with a certain degree of phase compensation.

Further, the analog-to-digital converter 8 only needs to have a clock frequency of 32.4 Ms/s and a resolution of about 8 bits, and a commercially available product can be used.

Further, a monitor decoder or the like can be used as the test signal extraction circuit 15, but any monitor device that can extract a pilot signal inserted into the vertical retrace period of a television signal is sufficient, for example.

Now, the variable tap transversal filter 9, which is the main element of the digital correction system, has a random access memory or the like stored in advance in the memory with output values corresponding to all input values in the coefficient unit of the transversal filter.
Use a transversal filter that can access the actual input value and immediately output the required output value, effectively functioning as a coefficient unit. Preferably, two filters with the same configuration are used. While the coefficient data from the arithmetic processing unit 16 is being loaded into the coefficient unit of one filter as described above, the other filter, which is in the state before loading, is connected to the digital correction system and the rotator is They are used alternately so that the main line system is not affected by the main line system. In addition, if two filters with the same configuration cannot be installed in parallel, set the data output to zero at the filter output stage and temporarily operate only on the main line system while loading coefficient data to the coefficient unit of the filter. Try to get it. Note that it is sufficient that the resolution of the filter 9 is about 10 bits, and a commercially available digital-to-analog converter 10 that processes digital signals with this resolution can also be used.

In the illustrated transmission system according to the present invention, the analog main line system and the digital correction system are connected in parallel. By changing the equalization delay amount of the digital correction system depending on the contents of By changing the phase of the clock pulse that drives the converter 10 and resamples the converted output analog signal, it is possible to easily achieve approximate phase alignment. It is more practical to perform rough phase matching and attempt to easily bring the distortion of the transmission characteristics within acceptable limits.

The algorithm for automatic equalization of transmission path characteristics using the transmission system of the illustrated configuration according to the transmission system of the present invention is as follows.

(1) Detect the impulse response when all coefficient correction data supplied from the arithmetic processing unit 16 to each coefficient unit of the variable tap transversal filter 9 is set to zero, and set it to H(0).

(2) At the position considered to be the center tap of the variable tap transversal filter 9, an impulse with a signal waveform as shown in FIG. Against - (1/10)
For example, insert the signal into a specific line period in the vertical retrace period of a television signal, detect the impulse response as shown in Figure 3, and convert the impulse response at that time to H (1). In addition,
Such an impulse response can be detected without disturbing information signal transmission in the main line system by switching between two filters or by setting the filter output to zero only during the impulse insertion period as described above. be able to.

(3) Assuming that the delay characteristics of the analog delay element 3 are relatively good, especially the group delay characteristics are not bad, and the entire transmission system has linear characteristics, H(0)-H(1) (1 ) can be used to estimate the internal characteristics of the modified equalization form. In particular, when determining the phase difference between the above-mentioned impulse responses H(0) and H(1), the phase difference between the main line system and the equalization correction system is obtained, so so that the phase difference becomes zero, First, for example, the phase of the clock pulse that drives the digital-to-analog converter 10 is regulated.

(4) To regulate the clock phase, gradual iterative correction is performed in the same way as normal characteristic equalization, and the above-mentioned phase difference detection and the above-mentioned gradual correction are repeated. During the implementation, the iteration flag is raised as usual to notify the subsequent transmission system.

(5) If characteristic equalization within the permissible limits cannot be obtained by regulating the clock phase, each coefficient unit of the variable tap transversal filter 9 is Correct the coefficient of.

(6) If more precise equalization of transmission characteristics is required, clock phase regulation and filter coefficient correction are iteratively repeated.

Note that it is necessary to determine the phase characteristics of the equalization correction system itself in advance and give the opposite characteristics to the pilot signal inserted into the information signal to detect and equalize the phase characteristics of only the transmission path. In some cases, it is preferable to adopt one of the following methods.

(a) As shown by the dotted line in FIG. 1, the impulse waveform signal from the impulse generator 17 is converted into a digital-to-analog converter at a period corresponding to the vertical retrace period of a television signal, regardless of the input information signal. 10 input side and send it out, and find the impulse response in that case.

(b) As shown by the dotted lines in FIG. The signal is guided to the test signal extraction circuit 15 via the analog-to-digital converter 14, and the impulse response at that time is compared with the impulse response after passing through the transmission line 12 described in detail above.
Detect its own transmission characteristics.

Generally, unless the characteristics of the transmission path itself have deteriorated significantly, it is not necessary to separately detect the transmission characteristics of the equalization correction system and the transmission path as described above, and it is not necessary to detect the transmission characteristics of the equalization correction system and the transmission path separately. It is enough if you do it properly.

In addition, since the above-mentioned equalization correction of the transmission system characteristics is performed iteratively and gradually, the phase shift between the main line system and the equalization correction system is reduced as described above. As mentioned above, once the characteristics are roughly matched to the main line system, the rest is equalized and corrected by comprehensive automatic equalization.

As mentioned at the beginning, the automatic equalization of transmission characteristics of the method of the present invention can be applied to individual transmission systems, such as CATV transmission systems connected to a satellite broadcast receiving end, or when different types of transmission systems are cascaded. However, the above-mentioned automatic specialization of transmission characteristics is suitable for use when the transmission characteristics of selected disparate transmission systems, such as satellite broadcasting receiving systems, are not being equalized and the commonly used iteration flag is turned off. It goes without saying that during characteristic equalization of a self-transmission system, the commonly used iteration flag should be turned on to inform subsequent dissimilar transmission systems.

(Effects of the Invention) As is clear from the above description, according to the present invention, equalization correction of information signal transmission path characteristics can be performed by digital processing while the information signal itself remains in an analog transmission state. Moreover, it is possible to additionally perform sufficiently high-precision transmission line characteristic equalization even with a less accurate analog-to-digital converter, and the main line system that performs analog transmission can be Regardless of the status, the data is always transmitted normally and there is no intermediate
Furthermore, it is not necessary to pay special consideration to the phase shift caused by the components between the main line system and the equalization correction system, and the remarkable effect is that the characteristics of the entire transmission system can be equalized in a comprehensive manner. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the configuration of an information signal transmission system according to the present invention, FIG. 2 is a waveform diagram showing an example of a test signal transmission waveform used for equalizing transmission characteristics in the present invention, and FIG. is a waveform diagram showing an example of the test signal reception waveform. 1...Input terminal, 2, 6...Amplifier, 3...Analog delay element, 4...Differential amplifier, 5...Input terminal, 7, 11...Low pass filter, 8, 14...
...analog-digital converter, 9...variable tap transversal filter, 10...digital-analog converter, 12...transmission line, 13...
...Output end, 15...Test signal extraction circuit, 16...
... Arithmetic processing unit, 17... Impulse generator.

[Claims]

1. In order to remove echoes leaking from the transmitting circuit to the receiving circuit on the 4-wire side of the 2-wire/4-wire conversion circuit, an echo replica is generated based on the transmitted signal using an adaptive filter, and the reception obtained by the receiving circuit is The echo replica is subtracted from a mixed signal in which a signal and the echo are mixed, the sign of the difference signal is multiplied by the sign of the echo replica, and then averaged to output a value according to the degree of correlation. Forcibly return the output to a positive value and supply it to the signal conversion means,
In an echo canceller device that operates to adaptively change the magnitude of the tap correction amount of the adaptive filter in accordance with the magnitude of the output of the signal conversion means, when the adaptive operation of the echo canceller converges, An echo canceller device characterized in that the input/output characteristic of the signal converting means is such that the rate of change in the output of the signal converting means is smaller than the rate of change in the input of the signal converting means. 2. The echo canceller device according to claim 1, wherein the signal converting means is constituted by input/output converting means having hysteresis characteristics. 3. The echo canceller device according to claim 1, wherein the signal converting means is constituted by input/output converting means having nonlinear characteristics.

Claims (1)

4. The information signal transmission method according to claim 1, wherein the phase characteristics of the information signal transmission are changed and equalized by adjusting the information signal. 5. During the operation of equalizing the characteristics of the information signal transmission by the transversal filter, an identification code indicating that the equalization operation is in progress is added to the information signal and transmitted to the transmission path, and the information signal is transmitted to the transmission path. When the incoming information signal has been added with another identification code that is the same as the identification code indicating that the characteristic equalization operation of the information signal transmission in the other transmission path is in progress, the transversal filter 5. The information signal transmission method according to claim 1, wherein an operation of equalizing characteristics of the transmission path is not performed.