MXPA97009204A - Detection of interference of channels shared in televis digital signals - Google Patents

Abstract

The present invention relates to a receiver for receiving an advanced digitally coded television (ATV) signal comprising a plurality of multilevel symbols and having recurring field synchronization signals in an interference area of shared channels and another, the receiver is characterized because it includes a means for combining corresponding portions of the field synchronization signals to develop a subtraction signal, a means for processing the subtraction signal to reduce the interference of shared channels, a comparison means for comparing the subtraction signal with the processed subtraction signal, and means for selectively processing the ATV signal to reduce the interference of shared channels sensitive to the comparison medium

Description

DETECTION OF INTERFERENCE OF SHARED CHANNELS IN DIGITAL TELEVISION SIGNALS Background of the Invention and Previous Technique This invention relates in general to advanced digitally encoded television (ATV) that includes high definition television (HDTV) and in particular to ATV receivers that are operated in an area where there is interference from signals from shared channels of NTSC and others. In the North American Patent No. 5,260,793; A television receiver receives a digitally compressed ATV signal having a predetermined field synchronization code that is compared to a reference frame code to determine which of the two routes should be used to process the signal. One of the processing routes submits the received ATV signal, which is precoded in advance of the interference of NTSC shared channels, to a comb filter to reduce the interference of shared NTSC channels. The other route derives the comb filter. If the comb filter field's synchronization code produces fewer errors (ie, it is REF: 26036 characterized by less interference or a high ratio of S / N) when compared to a reference frame code than the derivative or direct route signal, the received ATV signal is subjected to comb filtration reduction of interference of NTSC shared channels. If the comparison of combed field reference and synchronization codes does not produce significantly fewer errors than the comparison for the direct signal path, comb filtering is not used since the comb filter introduces a 3 dB increase in the comb filter. White noise. Most ATV receivers will also include adaptive channel equalizers to aid in adjusting the receiver response to optimize the reception of the entire signal in response to the known (command) compensation signal. It is often very difficult to differentiate between the interference of shared channels and other types of interference. This makes it very difficult to decide whether to submit the received ATV signal to the NTSC shared channel interference rejection comb filter. For example, certain recurring interference such as light DC deviations and other types of static linear distortion, can easily fool the responsible circuitry to determine the mode of the comb filter. Also, it is hardly associated with intersymbol interference in the ATV multi-level signal which results in a signal-to-noise degradation even without the interference of shared channels. Other interference such as "ghost" is added to the difficulty of determining the filtering mode of NTSC shared channels. With the present invention, more accurate systems are provided to determine the correct mode of operation for the NTSC shared channel interference reduction system.

Objects of the Invention A principal object of the invention is to provide an improved ATV receiver. Another object of the invention is to provide an ATV receiver that can more accurately determine the optimal processing with respect to the interference of shared channels of STC and another.

A further object of the invention is to provide a new method for determining the optimal signal processing path for an ATV receiver in an interference environment of shared NTSC channels.

Brief Description of the Drawings These and other objects and advantages of the invention will be apparent upon reading the following description in conjunction with the drawings, in which: Figure 1 is a partial block diagram of a receiver constructed in accordance with the present invention; Y Figure 2 is a representation of the ATV signal according to the invention.

Description of the Preferred Modality With reference to Figure 1 of the drawings, a tuner 10 receives a digitally encoded HDTV signal similar to that described in US Patent No. 5., 216,793 identified above and passes it to a SA filter 12. In the preferred embodiment of the invention, the received signal is encoded using a trellis-coded modulation scheme and comprises a plurality of multiple bit values that represent the amplitudes of the symbols comprising the received ATV signal. The signal is formatted, as shown in Figure 2, into repetitive data segments of 832 symbols each. Each data frame has a first field segment followed by 312 data segments. Each data segment consists of a data synchronization of 4 level 2 symbols followed by 828 data symbols and FEC (Advance Error Correction). The field synchronization segments are characterized by a sequence of 511 pseudo-random number symbols, followed by three sequences of 63 pseudo-random number symbols, with the average sequence of 63 pseudo-random, which is of inverted polarity in alternating fields. The rest of the field synchronization segments have an identification of the VSB mode of 24 symbols, a block 92 of inverted symbols and a precode of 12 symbols for the trellis coding. The SAW filter 12 is coupled to a block 14, which identifies a demodulator of the IF amplifier and the A / D converter, the output of which is coupled to an A terminal of a switch 19 by an interference reduction comb filter. of STNC shared channels, indicated by a block 16 of broken lines and a terminal B of the switch 19 by a straight connection 16A. The comb filter 16, the operation of which is described in more detail in U.S. Patent No. 5,087,975, consists of a delay 18 of 12 symbols and an addition 20. The signal from block 14 is supplied to the positive input of the adder 20 and through the delay 18 to the negative input of the adder 20. The output terminal C of the switch 19 is coupled to an adaptive equalizer 22, the output of which is coupled to a phase tracker 24 (see US Patent No. 5,406,587) . The output of the phase tracker 24 is coupled in turn to a trellis decoder 26 comprising a first processing path that includes a module decoder complementary to the precoder used to encode the received signal (see US Patent No. 5,087,975) and a second processing path that does not include the module decoder (nor the processing path that is shown). The switch 19, the adaptive equalizer 22, the phase tracker 24 and the trellis decoder 26 are all operated in response to an output signal from a comparator 36. The signal demodulated from the block 14 is also applied to a circuit 30 of filter comb (indicated by the broken line block) and a synchronization circuit 44. The synchronization circuit 44 is coupled to the comparator 36 and controls its operation. In particular, the synchronization circuit 44 generates an output signal to allow the comparator 36 during a selected portion of the field synchronization segment. In a preferred embodiment, this portion comprises the second half of the sequence of 511 pseudorandom number symbols, shown in Figure 2, the symbols on either side of which (i.e., the first half of the 511 sequence and the first half). sequence of 63 pseudorandom numbers) are invariant from field to field. The field comb 34 may comprise a field delay circuit 32 and an adder 34. The signal from the demodulator 14 is applied additively to the adder 34 and, through the field delay 32 is applied subtractively to the adder 34. The result is that the pairs of successive fields of the demodulated signal are subtracted, at the output of the field comb 30. The output of the field comb 30 is applied to an input of the controller 36 and also to a NTSC shared channel rejection comb filter circuit 38 (indicated by the block of dashed lines) similar to the filter 16 and comprising a delay 40 of 12 symbols and an adder 42. The output of the comb filter 38 is applied to a second input of the comparator 36. In a preferred embodiment of the invention, the delay element 32 of the field comb 30 is responsive to a signal from the synchronization circuit 44 and comprises only enough memory to store the symbols in the second half of the sequence of 511 symbols of the field synchronization segment. The timing circuit 44 also regulates the adder 34 only during this portion of the field that corresponds in time to the period during which the comparator 36 is enabled. Thus, not only are the effects of the ghosts static symbols and the intersymbol interference which is carried from one segment to the other minimized, but a substantive recession in the required memory capacity of the frame comb 30 is achieved. It will be appreciated that the signal that is transmitted to the television receiver and that is received and processed by the tuner 10 is precoded in advance that the ATV receiver will be operated in the area of an NTSC shared channels signal. The precoding of the ATV signal allows filtering the appropriate comb in the ATV receiver (eg, by filter 16) to substantially remove the interference effects of the NTSC shared channel while still allowing the ATV data to recover properly. However, the use of the comb filter 16 reduces the signal-to-noise ratio (S / N) of the received ATV signal, which is to be avoided whenever possible. Accordingly, it is desirable to derive the comb filter 16 when the received signal is processed unless there is substantial interference of comparative channels. The field comb 30 is provided to essentially subtract the successive field synchronization signals (the second half of the sequence of 511 successive frame symbols in the preferred embodiment) which is identical in each field, to develop an error signal. Under ideal conditions, without interference from shared channels and without any other interference, the subtraction signal will represent a zero output from the field comb. It will be appreciated that interference other than static interference, for example interference that repeats every 1 field, it will not be affected by field comb 30. White noise, for example, is not uniform and will not be canceled. Similarly, the phase noise will not be canceled and of course the noise of shared channels will not be canceled. On the other hand, intersimbolo interference, static ghosts, and DC deviations will be canceled. In this way, the subtraction signal substantially represents only the interference of shared channels, the phase noise, the white noise and the mobile ghosts. The subtraction signal is then applied to the comparator 36 and compared to the subtraction signal that has been filtered by the filter 38 to remove the interference of shared NTSC channels. If there is very little difference between the two compared channels, it can be deduced that there is very little interference from shared channels. This information is used to determine the mode of the switch 19 for inserting the comb filter 16 into the processing path of the received ATV signal and to control the operation of the adaptive equalizer 22, the phase tracker 24 and the trellis decoder 26. . More specifically, the level 2 field synchronization symbols are converted to level 3 symbols by the comb filter 16. The operation of the adaptive equalizer 22 of the phase tracker 24 must therefore be controlled appropriately depending on whether the switch 29 is operated to apply the direct output of the demodulator 14 (level 2 synchronization). Also, the trellis decoder 26 must be operated to select the route that includes the complementary module decoder, if the switch 19 is operated to apply directly to the output of the demodulator 14. In order to facilitate the above it is necessary to deviate in a precise manner the frequency of the ATV carrier relative to the NTSC image carrier such that the NTSC signal produced in this way falls at or near a maximum value of the transfer function of the field comb. This ensures that the phase of the NTSC bearer alternates during the successive ATV field synchronization segments, so that the NTSC shared channels signal in successive fields will increase at the output of the field comb 30. Therefore, the comparator 36 is provided with the increased NTSC shared channel signal, substantially free of any of the ATV components. What has been described is a new HDTV receiver for discrimination against the interference of NTSC shared channels. It is recognized that numerous changes in the described embodiment of the invention will be apparent to those skilled in the art, without departing from their true spirit and scope. The invention should be limited only as defined in the claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the present invention is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property:

Claims (14)

1. A receiver for receiving a digitally encoded advanced television (ATV) signal comprising a plurality of multilevel symbols and having recurring field synchronization signals in a shared channel interference area and another, the receiver is characterized in that it includes a medium to combine corresponding portions of the field synchronization signals to develop a subtraction signal, a means to process the subtraction signal to reduce the interference of shared channels, a comparison means for comparing the subtraction signal with the processed subtraction signal , and a means for selectively processing the ATV signal to reduce the interference of shared channels sensitive to the comparison medium.

2. The receiver according to claim 1, characterized in that the combining means comprises a field comb.

3. The receiver according to claim 1 or 2, characterized in that the interference of shared channels is the signal from the related National Television Systems (NTSC) committee, the receiver including a comb filter selectively operated in response to the comparison means to process the received ATV signal.

4. The receiver according to claim 3, characterized in that the ATV signal has a carrier that is offset with respect to the image carrier of the NTSC signal, this deviation causing increased interference of shared channels of NTSC at the output of comb filter.

5. The receiver according to claim 1 or 2, characterized in that the comparing means compares corresponding portions of the processed subtraction and subtraction signals.

6. The receiver according to any of claims 1 or 2, characterized in that the comparison means compares corresponding portions of the field synchronization signals that are isolated by invariant symbols from symbols that can vary from field to field.

7. The receiver according to claim 6, characterized in that the field synchronization signal includes a sequence of 511 symbols followed by at least a shorter sequence of symbols and wherein the corresponding portions of the field synchronization signals comprise a series of symbols near the end of the sequence of 511 symbols.

8. The receiver according to claim 6, characterized in that the field synchronization signals include a relatively long first symbol sequence followed by at least a relatively short symbol sequence, and wherein the corresponding portions of the field synchronization symbols comprise a series of symbols near the end of the relatively long sequence of symbols.

9. A method for receiving a digitally encoded advanced television (ATV) signal, comprising a plurality of multilevel symbols, having recurring field synchronization signals, in an area of shared channel interference and another, the method is characterized in that it includes the steps of combining corresponding portions of successive field synchronization signals of the field synchronization signals, to develop a subtraction signal, to process the subtraction signal to reduce the interference of shared channels, which compares the subtraction signal with the processed subtraction signal, and process the received ATV signal to reduce the interference of shared channels based on the comparison.

10. The method according to claim 9, characterized in that the combination of the field synchronization signals comprises the step of combining the field the ATV signals to develop the subtraction signal.

11. The method according to claim 9 or 10, characterized in that the interference of shared channels is the signal of the related National Television Systems (NTSC) committee and wherein the processing of the received ATV signal comprises the step of filtering the filter of comb on the ATV signal.

12. The method according to claim 9 or 10, characterized in that the carrier of the ATV signal deviates with respect to the signal carrier of the shared NTSC channel to increase the shared channel interference of NTSC.

13. The method according to claim 9 or 10, characterized in that the comparison step is confined to corresponding portions of the field synchronization signals that are isolated by invariant symbols from symbols that vary from field to field.

14. The method according to claim 13, characterized in that the field synchronization signals include a sequence of 511 symbols, and wherein the corresponding portions comprise a series of symbols near the end of the sequence of 511 symbols, preferably, the second half of the symbols of the sequence of 511 symbols.