JP4806170B2 - Apparatus and method for detecting and selectively filtering co-channel interference - Google Patents

Description

  The present invention relates to co-channel interference filtering in digital TV signals, and more particularly, to an apparatus and method for detecting the presence of co-channel interference in order to selectively apply a co-channel cancellation filter.

  Strictly speaking, a general broadcast TV signal is analog in nature. Such TV signals generally belong to any one of three broadcast formats. That is, there is the NTSC (National Television System Committee) format applied in Korea, the United States and some countries, and the PAL (Phase Alternation By Line) format and SECAM (System Electron Couleur) that are applied in most other countries. Ave Memoire) format.

  The HDTV (High-Definition Television), or more generally, the DTV (Digital Television) format uses a digitally encoded signal and is different from a general analog TV signal format. Since most video signals have unnecessarily redundant signals, such uncompressed video sequences can be digitally compressed in a way that is not visually perceived. Thus, such a DTV signal can carry more information than when transmitted by the same analog signal having the same bandwidth. Currently, according to the HDTV format implemented in the United States, the HDTV bandwidth is set to have almost the same bandwidth as the analog NTSC broadcast, and is set to use the same channel as the channel assigned to the NTSC channel. ing.

  From a long-term perspective, the NTSC channel will disappear, but at present most TV users do not yet have HDTV receivers, and the transition to the HDTV era is gradually expanding. In the current transition period, a TV broadcasting station that broadcasts an HDTV signal assigns an HDTV signal to be replaced in the future and a relatively strong but gradually disappearing NTSC signal to the same channel for a user having an HDTV receiver. Under such circumstances, NTSC and HDTV signals interfere with each other, which is called so-called co-channel interference.

  Referring to FIG. 1, a frequency spectrum 100 of an NTSC signal is shown. When the DTV signal is assigned to the same channel as the NTSC signal, the DTV information transmitted in the NTSC signal channel is the envelope 110 of FIG. Video carrier V, which is 1.25 MHz away from the lower edge of the assigned frequency spectrum, is used for demodulation of the luminance component of the NTSC signal. Color subcarrier C, which is 3.58 MHz away from video carrier V, is used for NTSC quadrature color difference signal demodulation in a color TV receiver. An audio carrier A 4.5 MHz away from the video carrier V is used for demodulation of an NTSC FM (Frequency Modulation) audio signal transmitted from a relatively small frequency band.

  When the HDTV signal is assigned to the same channel as the NTSC signal, the NTSC signal may cause strong interference. Thus, to prefilter the received HDTV signal, an NTSC removal filter is used that removes the expected components for the NTSC signal, ie video, color and audio carriers. In general, a comb filter is used as an NTSC removal filter. As shown in FIG. 1, the comb filter 120 has empty information at a location separated by 57 fH Hz. Here, fH is the horizontal scanning frequency of the analog video signal (NTSC video 15.734 kHz). One of the comb filter vacancy information is aligned with the video carrier V, the other comb filter vacancy information is aligned with the color subcarrier C, and the other comb filter vacancy information is aligned with the audio carrier A.

  In FIG. 1, the comb filter may have other free information in the HDTV channel space. In such a case, co-channel interference cannot be improved. In effect, the NTSC removal filter distorts the SNR (Signal-to-Noise Ratio) of the HDTV signal of about 3 dB when the NTSC signal is not included. Therefore, if the NTSC co-channel interference is 3 dB or less, it is better not to use the NTSC cancellation filter. Therefore, when there is no NTSC signal, the NTSC removal filter does not operate and it is necessary to directly process the HDTV signal.

  There are several ways to determine if an NTSC signal is present on the HDTV channel. Patent Document 1 introduces a method of calculating a noise energy estimation value with a received signal for each of the cases where the NTSC removal filter is present and not. If the difference between these two noise energies is greater than a predetermined critical value, an NTSC signal is detected. If an NTSC signal is detected, an NTSC removal filter is used in the HDTV processing process.

Patent Document 2 introduces another method for determining whether or not co-channel interference exists. An error detection / correction circuit provided in the HDTV receiver outputs an error rate of the received digital signal. Such error rates are compared for each condition with and without the NTSC rejection filter. Among these, the configuration corresponding to the lowest error rate is selected as the HDTV signal processing path.
US Pat. No. 6,201,576 US Pat. No. 6,421,077

  A technical problem to be solved by the present invention is a DTV receiver that uses a cochannel removal filter only when an analog broadcast signal exists in a cochannel in which an analog broadcast signal and a DTV broadcast signal are assigned to the same channel, and A DTV signal processing method is provided.

  To achieve the above object, a TV receiver for receiving a DTV signal according to an aspect of the present invention includes a processing path of the received DTV signal, an analog TV signal removal filter, a sink signal detector, and a switching circuit. And The analog TV signal removal filter filters one or more spectral components from the frequency spectrum of the received signal. The sync signal detector detects the presence of an analog TV signal synchronization pulse within the frequency spectrum of the received signal. The switching circuit includes the analog TV signal removal filter in the processing path of the received DTV signal when the sync signal detector detects the presence of an analog TV signal synchronization pulse in the received signal. .

  To achieve the above object, a TV receiver for receiving a DTV signal according to another aspect of the present invention includes a tuner, a demodulator, a sync separator, a signal controller, an analog TV signal removal filter, and a multiplexer. To do. The tuner selects a TV signal and outputs a channel signal. The demodulator receives the channel signal and outputs a demodulated channel signal. The sync separator receives the channel signal, detects an analog TV signal synchronization pulse in the channel signal, and outputs a synchronization pulse signal. The signal controller receives the synchronization pulse signal from the sync separator and generates a control signal indicating whether an analog TV signal is present in the channel signal. The analog TV signal removal filter filters one or more spectral components from the frequency spectrum of the demodulated channel signal and outputs a filtered demodulated channel signal. The multiplexer selects one of the demodulated channel signal and the filtered demodulated channel signal using the control signal.

  According to still another aspect of the present invention for achieving the above object, a TV receiver for receiving a DTV signal includes a demodulator, a signal controller, an analog TV signal removal filter, and a multiplexer. The demodulator receives a channel signal and outputs a demodulated channel signal. The signal controller receives an analog TV signal synchronization pulse signal from a channel signal sync separator, and generates a control signal indicating the presence or absence of the analog TV signal in the channel signal. The analog TV signal removal filter filters one or more spectral components from the frequency spectrum of the demodulated channel signal and outputs a filtered demodulated channel signal. The multiplexer selects one of the demodulated channel signal and the filtered demodulated channel signal using the control signal.

  According to another aspect of the present invention, there is provided a DTV signal processing method according to an aspect of the present invention, wherein when an analog TV synchronization signal can be detected within a frequency band of a DTV signal, the analog TV synchronization is performed within the frequency band of the DTV signal. Detecting an analog signal, determining from the detected analog TV synchronization signal whether an analog TV signal is within the frequency band of the DTV signal, and determining that an analog TV signal is present, Filtering the DTV signal through an analog TV signal removal filter before decoding the DTV signal.

  In accordance with the present invention, many different synchronization signal analysis techniques can be used, for example, to determine whether to use an NTSC or PAL rejection filter. As the simplest example, whether there is a horizontal sync pulse train having a repetition rate close to the predicted repetition rate can be used to determine whether to use the filter. Alternatively, the presence of a vertical pulse train may be used. Alternatively, the signal controller may require both horizontal and vertical pulses to increase accuracy. As another example, the signal controller enables counting of horizontal pulses detected between successive vertical sync pulses.

  More precise methods can also be used. For example, an automatic gain controller function at the sync separator can adjust the relative level of the sync pulse in relation to the tuner output. The output level of the automatic gain controller can be provided to the signal controller for additional other calculations. When the output level of the automatic gain controller represents a relatively weak NTSC or PAL signal, the signal controller does not select a rejection filter, even if a weak or intermittent sync pulse is detected.

  The sync separator may operate using digital samples generated within the HDTV demodulator. For example, the sink separator can low-pass filter the analog-to-digital converter output, and then low-pass filtered form (eg, fast Fourier transform) for frequency components that correspond to the horizontal line rate and vertical field rate of the analog TV signal. Can be analyzed). The relative strength of such a signal can be analyzed by a signal controller to determine if the insertion of a removal filter is appropriate.

  A system that can be programmed to detect co-channel interference from any one of a variety of analog TV formats (eg, NTSC, NTSC variants, PAL, SECAM, etc.) using any such technique. Can be realized. If various forms of rejection filters are inserted into a system, the system can be designed to detect interference from multiple analog TV formats and insert appropriate cancellation filters.

  For a full understanding of the invention, its operational advantages, and the objectives achieved by the practice of the invention, reference should be made to the accompanying drawings that illustrate preferred embodiments of the invention and the contents described in the drawings. There must be.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings represent the same members.

  In the present invention, an embodiment is disclosed that determines whether an interfering NTSC (or other analog) TV signal occupies the same channel as a DTV signal by detecting certain properties of the analog TV signal. The For example, an NTSC signal includes a vertical synchronization pulse repeated at a 59.94 Hz field rate and a horizontal synchronization pulse repeated at a 15.734 kHz line rate. The PAL signal includes a vertical synchronization pulse repeated at a 50 Hz field rate and a horizontal synchronization pulse repeated at a 15.625 kHz line rate. Such sync characteristics are used in embodiments of the present invention to determine whether a given analog TV signal is present in the currently tuned HDTV frequency space.

  Referring to FIG. 2, a TV receiver according to a first embodiment of the present invention is shown. The DTV processing path 210 includes a tuner 220, a demodulator 230, a MUX 260, and other known DTV processing functional blocks (not shown) that are not a major part of the present invention. Alternatively, the filter 240 may be inserted into the DTV processing path 210 when matched to the analog TV signal removal filter 240 and an analog TV signal is detected.

  The tuner 220 receives the input signal IN and selects one channel. The selected channel is input to the demodulator 230, so that the demodulator 230 performs signal timing and synchronization and performs other filtering operations. The output of the demodulator 230 is supplied to the first input of the MUX 260 and also to the input of the analog TV signal removal filter 240. The output of the analog TV signal removal filter 240 is supplied to the second input of the MUX 260. The selection signal SELECT is used for switching so that one of the first and second inputs of the MUX 260 is selectively output from the MUX 260. The output of MUX 260 is used for DTV processing in subsequent blocks.

  Outside the DTV processing path 210, the sync signal detector 250 receives the output from the tuner 220 and attempts to detect one or more analog TV sync signals in the tuned channel. If a sync signal is present, the sync signal detector 250 switches the MUX 260 to insert the analog TV signal removal filter 240 into the DTV processing path 210 according to the selection signal SELECT. Further, the sync signal detector 250 switches the MUX 260 so that the output of the demodulator 230 is passed through the DTV processing path 210 by the selection signal SELECT. As an option, the “ENABLE” output of the sink signal detector 250 may turn off the analog TV signal removal filter 240, if desired.

  FIG. 3 shows a general method 300 for processing a DTV signal at the receiver 200 of FIG. 2, for example. The method 300 attempts to detect one or more analog TV sync signals (step 302). If no sync signal is detected (step 304), the DTV signal is not filtered (step 312). If a sync signal is detected (step 304), the sync pulse repetition rate is measured (step 306) and compared to the predicted pulse repetition rate (step 308). If the sync pulse repetition rate is different from the predicted pulse repetition rate, an analog TV signal may be present, but is not in a form that can be filtered by the removal filter 240. Eventually, if the measured sync pulse repetition rate matches the predicted pulse repetition rate, the DTV signal is filtered with a removal filter 240 (step 310).

  FIG. 4 is a block diagram showing a TV receiver 400 according to the second embodiment of the present invention. TV receiver 400 includes a tuner 420 having an output shared by DTV receiver 410 and analog TV receiver 470. Each of DTV receiver 410 and analog TV receiver 470 provides a video output signal. The DTV receiver 410 includes a demodulator 430, an analog TV signal removal filter 440, and a MUX 460. Here, the same elements as those in the receiver 200 of FIG. 2 operate in the same manner as in FIG. In addition, the signal controller 450 provides the selection signal SELECT to the MUX 460.

  Analog TV receiver 470 is part of normal processing and includes a sync separator that detects vertical and horizontal synchronization pulses present in the analog TV signal when an analog TV signal is present. In FIG. 4, the sync separator of the analog TV receiver 470 is enabled when at least the video output of the DTV receiver 400 is selected to be output from the receiver 400. Therefore, the sync pulse detected by the analog TV receiver 470 is input to the signal controller 450 inside the DTV receiver 410. The signal controller 450 uses the sync pulse signal from the analog TV receiver 470 to determine the output state of the selection signal SELECT. For example, the analog and digital TV receivers 410 and 470 can be built in a common integrated circuit. As another example, a separate general analog TV receiver may be used.

  FIG. 5 is an example illustrating a DTV receiver 500 applicable to NTSC co-channel interference. DTV receiver 500 includes a tuner 520, a demodulator 530, an NTSC removal filter 540, and a MUX 560. Here, the same elements as those in the receiver 200 of FIG. 2 operate in the same manner as in FIG. The other elements for normal DTV processing, namely equalizer 570 and forward error correction (FEC) circuit 580, represent the successor of MUX 560 for DTV signal processing.

  Demodulator 530 includes several sub-blocks. The output of the tuner 520 is connected to the analog-to-digital converter 532, and the digital samples that are the output of the analog-to-digital converter 532 are input to the clock recovery and synchronization timing recovery block 534. Matched filter 536 uses the digital samples to detect a properly filtered binary stream. Such a binary stream is input to MUX 560 and NTSC removal filter 540.

  The output of the tuner 520 is also input to the sync separator 552. Sink separator 552 attempts to detect NTSC vertical and / or horizontal synchronization pulses from the tuned signal. If a synchronization pulse is detected, the pulse is transmitted to the signal controller 554. The signal controller 554 determines whether to select the output of the NTSC removal filter 540 as the output of the MUX 560 using the detection of the sync pulse and the repetition rate of the sync pulse.

  FIG. 6 is an example illustrating a DTV receiver 600 applicable to PAL co-channel interference. The DTV receiver 600 includes a tuner 620, a demodulator 630, a PAL removal filter 640, and a MUX 660. Here, the same elements as those in the receiver 200 of FIG. 2 operate in the same manner as in FIG. FEC circuit 680 represents the successor of MUX 560 for DTV signal processing.

  Demodulator 630 includes several sub-blocks. The output of the tuner 620 is connected to the analog-to-digital converter 632, and the digital samples that are the output of the analog-to-digital converter 532 are input to the clock recovery and synchronization timing recovery block 634. Fast Fourier transform 636 and equalizer / mapper 638 provide a binary stream in the frequency domain. Such a frequency domain signal is input to the MUX 660 and the PAL removal filter 640.

  The output of the tuner 620 is also input to the sync separator 652. Sink separator 652 attempts to detect PAL vertical and / or horizontal synchronization pulses from the tuned signal. If a synchronization pulse is detected, the pulse is transmitted to the signal controller 654. The signal controller 654 determines whether or not to select the output of the PAL removal filter 640 as the MUX 660 output using the detection of the sync pulse and the repetition rate of the sync pulse.

  Although comb filters have been described in the above embodiments, other filtering techniques can be used to remove one or more spectral components in the interfering analog TV signal. Those skilled in the art will appreciate that various modifications and other equivalent embodiments are possible from this. Therefore, the true technical protection scope of the present invention must be determined by the technical idea of the claims. In addition, as described above, specific terms are used in the preferred embodiments disclosed in the drawings and the specification, but these are used only for the purpose of describing the present invention, and are limited in meaning. And is not intended to limit the scope of the invention as set forth in the claims.

  The digital TV receiver and the digital TV signal processing method according to the present invention can be used for a digital TV and a set-up box for the TV.

It is a figure explaining the frequency spectrum which the NTSC and DTV signal which occupies the same channel cause interference, and how the spectrum is aligned with the comb filter used for NTSC signal removal. 1 is a block diagram illustrating a TV receiver according to an embodiment of the present invention. FIG. 3 is a flowchart showing a process of determining whether to use a filter in FIG. FIG. 2 is a block diagram illustrating a TV receiver having a configuration of a DTV and an analog TV receiver that determines whether a filter is used. FIG. 2 is a block diagram representing a DTV receiver when an NTSC signal is present. FIG. 2 is a block diagram illustrating a DTV receiver when a PAL signal is present.

Explanation of symbols

200 Receiver 210 DTV Processing Path 220 Tuner 230 Demodulator 240 Analog TV Signal Removal Filter 250 Sink Signal Detector 260 MUX

Claims (20)

A processing path of the received DTV signal;
An analog TV signal removal filter for removing an analog TV signal included in the DTV signal from the frequency spectrum of the received signal ;
A sink signal detector for detecting the presence of analog TV signal synchronization pulses in the frequency spectrum of the received signal;
When the SYNC signal detector detects the presence of the analog TV signal synchronization pulses in the received signal,
The repetition rate of the analog TV signal synchronization pulse is measured, and if the measured repetition rate matches the predicted pulse repetition rate, the analog TV signal removal filter is included in the processing path of the received DTV signal. A switching circuit that is driven not to include if they do not match ,
A TV receiver for receiving a DTV signal. The switching circuit is
The TV receiver for receiving a DTV signal according to claim 1, further comprising a signal controller circuit for sensing a pulse repetition rate of the analog TV signal synchronization pulse. The predicted pulse repetition rate is
The TV receiver for receiving a DTV signal according to claim 1 , wherein the TV receiver is programmed with any one of an NTSC format pulse repetition rate and a PAL format pulse repetition rate.   The TV receiver for receiving a DTV signal according to claim 1, wherein the detected analog TV signal synchronization pulse includes vertical, horizontal, or vertical and horizontal synchronization pulses. The analog TV signal removal filter is:
2. The TV receiver for receiving a DTV signal according to claim 1, wherein the TV receiver is an NTSC cancellation filter, and the sync signal detector is an NTSC synchronization pulse. The analog TV signal removal filter is:
2. The TV receiver for receiving a DTV signal according to claim 1, wherein the TV receiver is a PAL removal filter, and the sync signal detector is a PAL synchronization pulse. The switching circuit is
First input data inserted into a processing path of the received DTV signal and connected to an output of the analog TV signal removal filter, second input data bypassing the analog TV signal removal filter, and a multiplexer output A multiplexer having a selection input for selecting any one of the data;
Has output coupled to the multiplexer select input, if the measured repetition rate and said predicted pulse repetition rate is matched, a signal controller which outputs a signal for selecting the first input data of said multiplexer,
A TV receiver for receiving a DTV signal according to claim 1. The TV receiver
Further comprising an analog TV signal processing path for receiving an analog TV signal,
The TV receiver for receiving a DTV signal according to claim 1, wherein the sync signal detector is part of a processing path of the analog TV signal. The sync signal detector is
Detecting the relative strength of the analog TV signal synchronization pulse within the frequency spectrum of the received signal, and the switching circuit before including the analog TV signal removal filter in the processing path of the received DTV signal; The TV receiver for receiving a DTV signal according to claim 1, wherein the detected analog TV signal synchronization pulse is required to have at least a minimum relative intensity. A tuner that selects a TV signal and outputs a channel signal;
A demodulator that receives the channel signal and outputs a demodulated channel signal;
A sync separator that receives the channel signal, detects an analog TV signal synchronization pulse in the channel signal, and outputs a synchronization pulse signal;
A signal controller that receives the synchronization pulse signal from the sync separator and generates a control signal indicating whether an analog TV signal is present in the channel signal;
An analog TV signal removal filter for filtering an analog TV signal from the frequency spectrum of the demodulated channel signal and outputting a filtered demodulated channel signal;
A multiplexer that selects one of the demodulated channel signal or the filtered demodulated channel signal using the control signal;
Equipped with a,
The multiplexer measures the repetition rate of the analog TV signal synchronization pulse when the control signal indicates the presence of the analog TV signal in the channel signal, and the measured repetition rate matches the predicted pulse repetition rate. A TV receiver for receiving a DTV signal, wherein the TV receiver selects the filtered demodulated channel signal, and if not, selects the demodulated channel signal . A demodulator that receives the channel signal and outputs a demodulated channel signal;
A signal controller for receiving an analog TV signal synchronization pulse signal from a channel signal sync separator and generating a control signal indicating the presence or absence of the analog TV signal in the channel signal;
An analog TV signal removal filter for filtering an analog TV signal from the frequency spectrum of the demodulated channel signal and outputting a filtered demodulated channel signal;
A multiplexer that selects one of the demodulated channel signal or the filtered demodulated channel signal using the control signal , and
The multiplexer measures the repetition rate of the analog TV signal synchronization pulse when the control signal indicates the presence of the analog TV signal in the channel signal, and the measured repetition rate matches the predicted pulse repetition rate. A TV receiver for receiving a DTV signal, wherein the TV receiver selects the filtered demodulated channel signal, and if not, selects the demodulated channel signal . The TV receiver
The TV receiver for receiving a DTV signal according to claim 11 , further comprising the channel signal sync separator. The TV receiver
Further comprising an analog TV signal processing path for receiving an analog TV signal,
The TV receiver for receiving a DTV signal according to claim 12 , wherein the channel sync signal separator is a part of a processing path of the analog TV signal. When an analog TV signal synchronization pulse is detected within the frequency band of the DTV signal by the sync signal detector, the repetition rate of the analog TV signal synchronization pulse is measured, and the measured repetition rate and a predetermined analog TV signal format are measured. Determining that an analog TV signal is present in the frequency band of the DTV signal if the predicted pulse repetition rate for the analog TV signal synchronization pulse matches ,
Filtering the DTV signal through an analog TV signal removal filter before decoding the DTV signal when it is determined that the analog TV signal is present;
A DTV signal processing method comprising: The method of claim 14 , wherein the detected analog TV signal synchronization pulse comprises a vertical synchronization signal, and the predicted pulse repetition rate is the predicted vertical sync rate corresponding to the predetermined analog TV format. DTV signal processing method. The DTV of claim 14 , wherein the detected analog TV signal synchronization pulse comprises a horizontal synchronization signal, and the predicted pulse repetition rate is the predicted horizontal sync rate of the predetermined analog TV format. Signal processing method. The detected analog TV signal synchronization pulse further comprises a vertical synchronization signal, and the predicted pulse repetition rate further comprises the predicted vertical sync rate of the predetermined analog TV format;
Measuring the pulse repetition rate of the detected analog TV signal synchronization pulse comprises measuring a vertical sync rate and a horizontal sync rate;
The comparison between the predicted pulse repetition rate and the measured pulse repetition rate is a comparison between the predicted vertical sync rate and the measured vertical sync rate, and a comparison between the predicted horizontal sync rate and the measured horizontal sync rate. Including
Presence declaration of the analog TV signal, when said measured vertical sync rate is substantially the predicted vertical sync rate matching, the measured horizontal sync rate is substantially the predicted horizontal sync rate matching The DTV signal processing method according to claim 16 , wherein the DTV signal processing method is performed. The predicted pulse repetition rate is
The method of claim 14 , wherein the DTV signal is selected between at least two rates of the analog TV signal format. The extraction of the analog TV signal is as follows:
The method of claim 14 , wherein the relative signal energy present at a frequency corresponding to the synchronization signal pulse repetition rate is measured. The presence determination of the analog TV signal is as follows:
Requesting that the relative signal energy present at the frequency corresponding to the synchronization signal pulse repetition rate has at least a minimum relative strength before it is determined that an analog TV signal is present. The DTV signal processing method according to claim 19 .

Images