MXPA98005806A - Digital television receiver with adapter filter circuits to remove the n deco-channel interference - Google Patents
Digital television receiver with adapter filter circuits to remove the n deco-channel interferenceInfo
- Publication number
- MXPA98005806A MXPA98005806A MXPA/A/1998/005806A MX9805806A MXPA98005806A MX PA98005806 A MXPA98005806 A MX PA98005806A MX 9805806 A MX9805806 A MX 9805806A MX PA98005806 A MXPA98005806 A MX PA98005806A
- Authority
- MX
- Mexico
- Prior art keywords
- symbols
- symbol
- level
- signal
- results
- Prior art date
Links
- 230000003111 delayed Effects 0.000 claims abstract description 40
- 230000001629 suppression Effects 0.000 claims abstract description 33
- 230000004044 response Effects 0.000 claims description 108
- 239000000203 mixture Substances 0.000 claims description 60
- 239000000969 carrier Substances 0.000 claims description 58
- 238000000034 method Methods 0.000 claims description 44
- 238000001914 filtration Methods 0.000 claims description 22
- 241001442055 Vipera berus Species 0.000 claims description 19
- 230000001143 conditioned Effects 0.000 claims description 19
- 238000001514 detection method Methods 0.000 claims description 17
- 230000000051 modifying Effects 0.000 claims description 13
- 230000000996 additive Effects 0.000 claims description 11
- 239000000654 additive Substances 0.000 claims description 11
- 238000006243 chemical reaction Methods 0.000 claims description 9
- 230000001360 synchronised Effects 0.000 claims description 7
- 230000005236 sound signal Effects 0.000 claims description 6
- 239000003607 modifier Substances 0.000 claims description 3
- 230000001172 regenerating Effects 0.000 claims description 2
- 230000000979 retarding Effects 0.000 claims description 2
- 230000011664 signaling Effects 0.000 claims description 2
- 238000010586 diagram Methods 0.000 description 22
- 230000015654 memory Effects 0.000 description 22
- 230000005540 biological transmission Effects 0.000 description 16
- 230000001702 transmitter Effects 0.000 description 15
- UIIMBOGNXHQVGW-UHFFFAOYSA-M buffer Substances [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 11
- 230000002829 reduced Effects 0.000 description 10
- 230000000694 effects Effects 0.000 description 9
- 238000010897 surface acoustic wave method Methods 0.000 description 9
- 238000009825 accumulation Methods 0.000 description 7
- 241000894007 species Species 0.000 description 7
- 230000001934 delay Effects 0.000 description 6
- 230000004075 alteration Effects 0.000 description 4
- 238000003379 elimination reaction Methods 0.000 description 3
- 230000001747 exhibiting Effects 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000006011 modification reaction Methods 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 230000001131 transforming Effects 0.000 description 3
- 230000003321 amplification Effects 0.000 description 2
- 230000000295 complement Effects 0.000 description 2
- 230000000875 corresponding Effects 0.000 description 2
- 230000002950 deficient Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- 230000036961 partial Effects 0.000 description 2
- 238000011002 quantification Methods 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 206010001534 Air-borne transmission Diseases 0.000 description 1
- 230000003044 adaptive Effects 0.000 description 1
- 230000005557 airborne transmission Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000003750 conditioning Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000001186 cumulative Effects 0.000 description 1
- 230000001066 destructive Effects 0.000 description 1
- 230000004069 differentiation Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000002452 interceptive Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000004091 panning Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 230000002035 prolonged Effects 0.000 description 1
- 230000000644 propagated Effects 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 230000003595 spectral Effects 0.000 description 1
Abstract
The present invention relates to the co-channel interference that accompanies multi-level symbols in a digital receiver, such as a digital television receiver, which is suppressed by using a first comb characteristic filter to reduce the energy of a digital receiver. the co-channel interference before the data sectioning. The first comb characteristic filter incidentally pre-encodes the decoding results of symbols generated by the data sectioning. A second comb characteristic filter post-encodes decoding results of pre-encoded symbols from data sectioning to generate corrected symbol decoding results. The pre-coding of symbols of the input symbol stream results from the differential delay and the first linear combination of the differentially delayed terms. The post-coding of the symbol stream recovered by the data sectioning results from the second linear combination of the symbol stream with the delayed result of the second linear combination and is carried out according to a modular arithmetic. One of the first and second linear combinations is subtraction and the other is addition. The results of the second linear combination are the results of decoding of corregid symbols
Description
DIGITAL TELEVISION RECEIVER WITH ADAPTER FILTER CIRCUITS TO SUPPRESS NTSC CO-CHANNEL INTERFERENCE Description of the invention The present invention relates to digital television systems, such as the digital high-definition television (HDTV) system , used for terrestrial broadcast in the United States of America, according to the standard of the Television Sub-Committee
Advanced (ATSC) and more particularly with digital television receivers with adaptive filter circuits to suppress co-channel interference of analog television signals, such as those that conform to the National Television Systems Committee standard
(NTSC).
BACKGROUND OF THE INVENTION A Digital Television Standard, published on September 16, 1995 by the Advanced Television Subcommittee (ATSC) specifies residual sideband (VSB) signals to transmit digital television (DTV) signals on television channels. of 6 MHz bandwidth, such as those used in the air broadcast of analog television signals of the National Television Subcommittee (NTSC) in the United States of America. The VSB DTV signal is designed in such a way that it is
REF: 27947 its spectrum is interspersed with the spectrum of a NTSC analog television signal of co-channel interference. This is done by positioning the pilot carrier and the sideband frequencies of the main amplitude modulation of the DTV signal in odd multiples (nones) of a quarter of the horizontal scan line (or scan) speed of the signal of NTSC analog television falling between the even multiples of a quarter of the horizontal scanning line speed of the signal of
NTSC analog television, in which even multiples the majority of the energy of the luminance and chrominance components of a NTSC analog television signal of co-channel interference will fall. The video carrier of a NTSC analog television signal is shifted
1.25 MHz of the lower frequency limit of the channel
^? TV. The carrier of the DTV signal is shifted from such a video carrier by 59.75 times the horizontal scanning line speed of the analog NTSC television signal to place the carrier of the DTV signal
to approximately 309,877.6 KHz of the lower limit frequency of the television channel. Thus, the carrier of the DTV signal is approximately 2.690122.4 Hz of the average frequency of the television channel. The exact symbol speed in the Standard of
Digital Television is (684/286) times the 4.5 MHz sound carrier shifted from the video carrier to a NTSC analog television signal. The number of symbols per horizontal scanning line in a NTSC analog television signal is 684 and 286 is the factor by which the 5 speed of the horizontal scan line in an analog television signal of NTSC is multiplied to obtain the carrier of the 4.5 MHz sound shifted from the video carrier to an analog television signal of NTSC. The speed or proportion of symbols is 10.762238
megsymbols per second, which may be contained in a VSB signal extending 5.381119 MHz from the DTV signal carrier. That is, the VSB signal may be limited to a band that extends 5.690997 MHz from the lower limit frequency of the television channel. 15 The ATSC standard for terrestrial broadcasting of digital HDTV signals in the United States of America is capable of transmitting in either of two high definition television (HDTV) formats with an aspect ratio of 16: 9. An HDTV screen format uses 1920
samples per scan or scan line and 1080 active scan or horizontal scan lines per 30 Hz frame with 2: 1 field interleaving. The other HDTV screen format uses 1280 luminance samples per scan line and 720 scan lines scanned
progressively from television image to 60 Hz frame.
The ATSC standard also accommodates the transmission of different DTV screen formats to HDTV screen formats, such as the parallel transmission of four television signals having normal definition compared to a NTSC analog television signal. The DTV transmitted by amplitude modulation (7AM) of residual lateral band (VSB) during terrestrial diffusion in the United States of North America comprises a succession of consecutive data fields in time that each contain 313 consecutive data segments in time. The data fields can be considered consecutively numbered from module-2, with each data field numbered odd and the data field with successive even number forming a frame or data frame. The proportion of frames is 20.66 frames per second. Each data segment is 77.3 microseconds in duration. In this way, with the proportion of symbols that is 10.76 MHz there are 832 symbols per data segment. Each data segment begins with a line synchronization code group of four symbols that have successive values of + S, -S, -S, and + S. The value + S is at a level below the maximum positive data excursion and the value of -S is above a level of the maximum negative data excursion. The initial line of each data field includes a field synchronization code group that encodes an instruction signal for channel equalization or compensation and multi-path cancellation procedures. The instruction signal is a pseudo noise sequence of 511 samples (or "PN sequence") followed by three PN sequences of 63 samples. This instruction signal is transmitted according to a first logical convention on the first line of each odd number data field and according to a second logical convention on the first line of each even number data field, the first and second ones Logical conventions are respectively complementary to each other. The data within the data lines are encoded by trellis coding using twelve interleaved trellis codes / each of a 2/3 speed trellis code with an uncoded bit. Interleaved trellis codes are subject to Reed-Solomon's send error correction coding, which provides error correction of the chromatic sync signal that arises from noise sources such as the ignition system of an unshielded car close, The results of Reed-Solomon coding are transmitted as coding of constellation symbols of an 8-level dimension (3 bits / symbol) for airborne transmission, which transmissions are performed without separate symbol pre-coding of the '- ^ * trellis coding procedure. The results of the Reed-Solomon coding are transmitted as one-dimensional constellation symbol coding of 16 levels (4 bits / symbol) for the cable transmission, which transmissions are performed without pre-coding. The VSB signals have their natural carrier wave, which would vary in amplitude depending on the modulation percentage suppressed. # The natural carrier wave is replaced by a
pilot wave of fixed amplitude, which amplitude corresponds to the prescribed modulation percentage. This fixed amplitude pilot carrier wave is generated by introducing a displacement of the direct component to the modulation voltage applied to the balanced modulator that generates the
lateral bands of modulated amplitude that are supplied to the filter that provides the VSB signal as its response. If the eight levels of 4-bit symbol coding have normalized values of -7, -5, -3, -1, +1, +3, +5 and +7 in the carrier modulation signal, the carrier
pilot has a normalized value of 1.25. The normalized value of + S is +5 and the normalized value of -S is -5. In the initial development of the DTV technique it was contemplated that the DTV transmitter could decide whether or not to use a pre-encoder of symbols in the
Transmitter, which symbol precoder would follow the symbol generation circuits and provide the precoded filtering of the symbols. This decision by the transmitter would have depended on whether or not interference from an NTSC co-channel broadcast station was expected or not. The symbol pre-encoder would complement the post-coding of symbols introduced incidentally in each DTV receiver by means of a characteristic filter in jj. comb used before the data disconnector in the symbol decoder circuit to reject the
artifacts of the NTSC co-channel interference signal The symbol pre-coding would not be used for the data line synchronization code groups or during the data lines in which the data synchronization data is transmitted. data field, 15 Co-channel interference is reduced to greater distances from the NTSC broadcast station and is more likely to occur when certain ionospheric conditions are obtained, the summer months during the years of high solar activity that are notorious for the probability of
co-channel interference. Of course, such interference would not occur if there were no co-channel NTSC broadcast stations. If there was a probability of NTSC interference in this broadcast coverage area, it is assumed that the HDTV broadcaster would use the symbol pre-encoder
to facilitate that the HDTV signal would be more easily separated from the NTSC interference and thus, a comb characteristic filter would be used as a symbol postcode in the DTV receiver to complete the matching filtering. If there was no possibility of interference of 5 NTSC or there would be an insubstantial probability of it, in order that the flat spectrum noise would be less likely to cause erroneous decisions regarding the
»Symbol values in the trellis decoder, it is assumed that the DTV transmitter would no longer use the pre-symbol encoder; and thus, the post-encoder of symbols would then be disabled in each DTV receiver. Without the transmitter being aware of the condition, the actual co-channel NTSC interference may be substantial for portions of the receiving area for a
diffusion, due to monstrous omission conditions, due to leakage from cable transmission or broadcasting, due to inadequate intermediate frequency image suppression in NTSC receivers, due to the magnetic tape used to record digital television that has
previous analog television recording remaining or due to some other unusual condition. The current ATSC DTV standard does not authorize the transmitter to use the symbol pre-encoder. It is assumed that the suppression of the analog television signal of
The co-channel interference is carried out in the trellis decoding process, after the data sectioning procedures, associated with the decoding of symbols. This procedure avoids the problem of determining whether pre-coding is done on the transmitter. However, the analog co-channel interference television signal undesirably introduces errors in the data sectioning processes, which places more burden on error correction decoding procedures, trellis decoding and decoding
of Reed-Solomon. These errors would reduce the area of transmission coverage, which may cause loss of revenue for the commercial DTV transmitter. Thus, the provision for suppression of a co-channel analog television signal before data sectioning
is still desirable, despite the pre-coding of symbols in the DTV transmitter that is not authorized by the current ATSC DTV standard. The term "linear combination" refers here in general to addition and subtraction, either
carried out according to conventional arithmetic or modular arithmetic. The term "modular combination" refers to the linear combination carried out according to a modular arithmetic. That type of coding that re-encodes a stream of digital symbols by means of
The differential delay and linear combination of the differentially delayed terms, exemplified by the symbol post-coding used in the HDTV receivers of the prior art, is defined as "recoding of symbols of the first type" in this specification. That encoding type 5 that re-encodes a digital symbol stream by means of its modular combination with the delayed result of the modular combination, exemplified by the Pt pre-coding symbols used in the HDTV transmitters of the prior art, it is defined as "re encoding symbols of the second type" in this specification. The problem of co-channel interference of analog television signals can be visualized from the point of view of a problem of alterations in the
receiver, to be solved by the filter circuit
B adapter in the receiver. As long as the dynamic range of the system channel is not exceeded, such that 'co-channel interference can capture the system channel by destroying the signal transmission capacity
for DTV modulation, the performance of the system can be visualized as a problem of superposition of signals. The filter circuit in the receiver is adapted to select the digital signal of the co-channel interference caused by the analog television signals, which
depend on the pronounced correlation and anti-correlation properties of analog television signals to reduce their energy sufficiently to capture the system channel from them. Since the co-channel interference of the analog television signals is involved, it enters the system channel after the DTV transmitter and before the DTV receiver. The use or non-use of symbol pre-coding in the DTV transmitter has no effect on the co-channel interference of the analog television signals. In the DTV receiver, as long as the co-channel interference is not so great as to overload the front end of the receiver and capture the channel of the system, it is advantageous to precede the data sectioning circuit with a comb characteristic filter for reduce the energy of the higher energy spectral components of the co-channel interference, in order to reduce the errors that occur during the data sectioning. The DTV transmitter must adjust its carrier frequency, which is nominally 310 KHz above the lower limit frequency of the television channel assignment, in such a way that its carrier frequency is optimally shifted in frequency of the video carrier of a co-channel NTSC analog television signal that is likely to cause interference. This optimal offset at the carrier frequency is exactly 59.75 times the horizontal sweep line frequency fjj of the analog television signal of NTSC.
Then, the artifacts of the co-channel interference in the demodulated DTV signal will include oscillations at 59.75 times the horizontal sweep line frequency fu_ of the NTSC analog television signal, generated by the heterodyne mix between the digital HDTV carrier and the video carrier of the analog television signal of co-channel interference and oscillations at 287.25 times fjj, generated by the heterodyne mixture between the digital HDTV carrier and the chrominance subcarrier of the analog television signal of co-channel interference. -channel, which oscillations are quite close in frequency to the fifth harmonic of the oscillations at 59.75 times fjj. The artifacts will also include oscillations at approximately 345.75 times fu_, generated by the heterodyne mixture between the digital HDTV carrier and the audio carrier of the analog co-channel interference television signal, which oscillations are quite close in frequency to the sixth harmonic of the oscillations at 59.75 times fu_. The almost harmonic relationship of these oscillations allows them to be suppressed by a single comb characteristic filter, appropriately designed, which incorporates only a few epochs of differential delay symbols. The use of a NTSC reject comb characteristic filter prior to data sectioning in the DTV receiver incidentally carries out the recoding of symbols of the first type, to modify the symbols obtained by the data sectioning. The data sectioning operation following this re-encoding of symbols of the first type in the DTV receiver is a quantization process that is not destructive of the symbols resulting from the recoding of symbols of the first type, since the data transmission, since data quantization levels are designed to match symbol levels. Quantification discriminates remnants of analog television signal from co-channel interference that persist after filtering, associated with the recoding of symbols of the first type and which are, however, appreciably smaller than the stages between the levels of code of symbols. This is a kind of capture phenomenon in which a stronger signal phenomenon gains at the expense of a weaker one, in a quantification process. Since data transmission is involved, the stream of digital data symbols flows through the full length of the system channel. When the recoding of symbols of the second type is done as the pre-coding of symbols in the DTV transmitter, the additive combination of the differentially delayed data symbol streams is done in a modular basis that does not reinforce the transmitter power or increases the average intersymbol distance, to further assist in overcoming the disturbing analog television signal. Instead, the main mechanism for overcoming the disturbing analog television signal is its attenuation to the DTV signal, as stipulated by the comb characteristic filtering in the DTV receiver, to cause the signal to Analogue television remaining in the comb filter characteristic response is suppressed by the quantization effects in the data disconnector that immediately follow the comb characteristic filter. The order to carry out the re-coding procedures of symbols of the first and second types has no appreciable effect on the signal transmission by means of the system channel under such circumstances, since no coding scheme destroys the transmission capacity of signal for the stream of symbols. The order to carry out the recoding procedures of symbols of the first and second types has no appreciable effect on the ability of the digital receiver to suppress the analog television signal of co-channel interference, since the recoding of symbols of the second type does not stand between the recoding of symbols of the first type and the subsequent data sectioning. These characteristics 5 provide the general basis on which the invention is based. The co-channel interference that accompanies multilevel symbols in a digital receiver, such as a digital television receiver, is suppressed by using a
first comb characteristic filter to reduce the energy of the co-channel interference before data sectioning. The first comb characteristic filter is fed with a stream of 2N level symbols, each having a time of symbols of one
specified length in time, which stream of 2N level symbols is susceptible to be accompanied by analog television signal artifacts of co-channel interference and provides a response in which those artifacts of the analog television signal of
co-channel interference are suppressed if they are obtained. The first comb characteristic filter incidentally carries out a symbol recoding procedure of the first type that introduces error to the decoding results of symbols generated by the
data sectioning. Assume that the first comb characteristic # filter delays the current of 2N level symbols by a prescribed number of symbol epochs to generate a 2N level symbol delay current, then linearly combines the level current of 2N symbols and the delayed current of level 2N symbols to generate first linear combination results as the response of the first comb characteristic filter. This response, which has level symbols (4N-1), is supplied to a first data disconnector. In the context of the invention, this method of recoding symbols of the first type carried out before the data sectioning by the first data disconnector is displayed as a pre-coding procedure. A second characteristic filter in
comb, performs a method of re-encoding symbols of the second type after data sectioning, implements a post-coding procedure to compensate the symbol recoding procedure of the first type and generate decoding results of
corrected symbols. The method of recoding of symbols of the first type re-encodes a stream of input symbols by means of differential delay and first linear combination of the differentially delayed terms. The recoding procedure of
symbols of the second type re-encodes the results of • f decoding of filtered symbols partially recovered by the first data disconnector. This method of symbol recoding of the second type uses a second linear combination of the symbol decoding results partially filtered with the delayed result of the second linear combination and is carried out according to a modular arithmetic. One of the first and second linear combinations is fugitive and the other is additive. The results of the
The second linear combination is the results of decoding of post-encoded symbols. The post-coding performed subsequent to feature filtering in comb and data sectioning has a basic problem that must be solved with
so that post-coding works properly. One aspect of this problem is that once the error occurs in the decoding results of partially filtered symbols, the error is fed back with delay, which tends to propagate the error during the
generation of decoding results of post-encoded symbols. Other aspects of this problem are concerned with how to initialize or adjust to initial values the conditions in the delayed feedback circuits and how to readjust to
initial values the conditions in the delayed feedback circuits once the propagation of the error occurs. This problem arises when the re-coding of the second type is used for post-coding because the feedback used in such recoding is cumulative and provides an integration class over time. When the recoding of the second type is carried out during the pre-coding and the recoding of the first type is carried out during the post-coding, the recoding of the first type provides a kind of differentiation with the passage of time that quickly suppresses the response to the initial conditions of the recoding of the second type. There is no concern about the initial conditions of accumulation or integration. When the recoding of the first type is carried out during the pre-coding and the recoding of the second type is carried out during the post-coding, the error caused by the incorrect initial conditions of the accumulation or integration in the recoding of the second type propagates itself same during post-coding. The resulting operation error in the final decoding results in a systematic error, instead of a random error, so generally speaking, the operation error will not have the possibility of self-correcting by probability.
BRIEF DESCRIPTION OF THE INVENTION One aspect of the invention is a method of symbol decoding of a stream of 2N level symbols, each having an epoch of symbols of a specified length in time, which stream of level symbols. 2N is likely to be accompanied by analog television signal artifacts of co-channel interference, N is a positive integer. The method generates symbol decoding results selected by stages in which a feature filtering stage is included in 2N level symbol current comb to generate a comb characteristic filter response with pre-encoded level symbols (4N -1) of which the artifacts of the analog co-channel interference television signal, if any, are suppressed. This comb characteristic filtering step includes the sub-steps of retarding the stream of 2N level symbols by a prescribed number of symbol epochs, to generate a delayed current of 2N level symbols and to linearly combine the symbol level current of symbols. 2N and the delayed current of 2N level symbols, according to one of the addition and subtraction procedures, to generate first linear combination results as the response of the comb characteristic filter with pre-encoded level symbols (4N-1 ). There is a step of data sectioning of the response of the comb characteristic filter with the pre-encoded level symbols (4N-1) to generate decoding results of pre-encoded symbols. There are stages of delay of symbol decoding results selected by the prescribed number of symbol epochs, to generate decoding results of selected delayed symbols and to linearly combine the decoded results of pre-encoded symbols with the decoded results of selected symbols delayed to generate second linear combination results. The linear combination performed to generate the second linear combination results is performed according to the opposite procedures of the addition and subtraction procedures of those used in the linear combination sub-step performed to generate the first linear combination results and is carried out according to a modular arithmetic. There are steps of determining when the symbol coding descriptive of the synchronization data is presented in the 2N level symbol stream, of regenerating the synchronization data without error when the symbol coding descriptive of the synchronization data is presented in the level 2N symbol current, and generation of the selected symbol decoding results, in such a way as to correspond to the synchronization data without error, when the symbol coding descriptive of the synchronization data is presented in the current of 2N level symbols and in such a manner as to correspond to the second linear combination results, at least during selected times when the symbol coding is presented which is not descriptive of the synchronization data in the 2N level symbol stream. One aspect of the invention consists of a combination of circuits, as described in this paragraph, which circuits are included within a digital television receiver. The combination includes digital television signal detection devices for supplying a stream of 2N level symbols, each having a time of symbols of a specified length in time, which current is likely to be accompanied by television signal artifacts. analogous co-channel interference. The combination includes first and second delay devices, each exhibiting a delay of a first prescribed number of symbol epochs. The combination includes first and second linear combiners, one of which is an adder or adder and the other of which is a subtracter, the second linear combiner works in a 2N module arithmetic. The first delay device is connected to respond to the current of 2N level symbols with a first delayed current of 2N level symbols, thereby generating a first pair of delayed currents 5 differentially of the 2N level symbols. The first linear combiner is connected to linearly combine the first pair of differentially delayed currents of the 2N level symbols, which are received as the first and second respective input signals of the
first linear combiner. In response to these input signals, the first linear combiner generates a first level symbol current (4N-1) as its input signal. A first data disconnector is included in the combination to generate first results of
decoding of pre-encoded symbols by decoding the first level symbol stream
(4N-1) supplied as a respective output signal of the first linear combiner. The second linear combiner, to linearly combine the first and second signals of
The respective input, received therefrom to supply a respective output signal thereof, is switched on to receive the first decoding results of pre-encoded symbols as a respective first input signal thereof. The second
The delay device is connected to delay a respective input signal thereof to generate the second input signal of the second linear combiner. The combination further includes data synchronization circuits to determine when symbols used for data synchronization appear in the stream of 2N level symbols and circuits to generate ideal symbol decoding results when it is determined that the symbols used for the synchronization of data appear in the stream of 2N level symbols. The combination further includes a first multiplexer of multiple inputs for supplying a respective output signal thereof to the second delay device as the respective input signal thereto, to receive the decoding results of ideal symbols as a first of its signaling signals. input and to receive the output signal of the second linear combiner as another of its input signals. The first multiplexer is conditioned to reproduce as its output signal the first of its input signals when and only when it is determined that the symbols used for data synchronization appear in the 2N level symbol stream. Otherwise, the first multiplexer is conditioned, at least at selected times, to reproduce the output signal of the second linear combiner as the first decoded results of post-encoded symbols.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic block diagram of a digital television signal receiver utilizing a NTSC reject comb characteristic filter prior to symbol decoding and a post comb feature filter. coding after the decoding of symbols, according to the invention and using a co-channel interference detector that compares the energies of the baseband. Figure 2 is a schematic block diagram of an NTSC co-channel interference detector for use in the digital television signal receiver of Figure 1. Figure 3 is a schematic block diagram of a portion of a digital television signal receiver using a NTSC reject comb characteristic filter before symbol decoding and a post-coding comb characteristic filter after decoding symbols, according to the invention and using a co-channel interference detector of a type described by the inventor in U.S. Patent Application No. (Case of Attorney 1500-1) filed on March 21, 1997. Figure 4 is a schematic block diagram of a portion of a digital television signal receiver that uses a feature filter on the NTSC reject comb before symbol decoding and a feature filter in post-coding comb after the decoding of symbols according to the invention and using a co-channel interference detector of a type described by the inventor in the US patent application Serial No. (Case of the lawyer 1501 -1) filed on March 21, 1997. Figure 5 is a schematic block diagram showing the details of a portion of the digital television signal receiver of Figure 1., 3 or 4 concerning the selection of the final symbol decoding results, selected from the symbol decoding results prescribed during the data synchronization intervals and selected at other times from the response of the data disconnector to the symbol codes received baseband or from the response of the post-encoded data disconnector to the response of the comb characteristic filter to the received baseband symbol codes, depending on whether the received baseband symbol codes are substantially or not free of NTSC co-channel interference. Figure 6 is a schematic block diagram of alternative circuits to those in Figure 5. Figure 7 is a schematic block diagram of other alternative circuits to those in Figure 5. Figure 8 is a schematic block diagram showing the details of a portion of the digital television signal receiver of Figure 1, 3 or 4, to generate prescribed symbol decoding results during data synchronization intervals. Fig. 9 is a schematic block diagram showing the details of a portion of the digital television signal receiver of Fig. 1, 3 or 4 when the NTSC reject characteristic comb filter employs a delay of 12 symbols. Fig. 10 is a schematic block diagram showing the details of a portion of the digital television signal receiver of Fig. 1, 3 'or 4 when the NTSC reject characteristic comb filter employs a delay of 6 symbols . Figure 11 is a schematic block diagram showing the details of a digital television signal receiver portion of Figure 1, 3 or 4 when the NTSC reject comb characteristic filter employs a delay of 2 video lines . Figure 12 is a schematic block diagram showing the details of a portion of the television signal receiver of Figure 1, 3 or 4, when the NTSC reject comb feature filter uses a delay of 262 video lines . Figure 13 is a schematic block diagram showing details of a portion of the digital television signal receiver of Figure 1, 3 or 4 when the NTSC reject comb feature filter uses a delay of 2 video frames . Fig. 14 is a schematic block diagram showing a digital television signal receiver using a plurality of NTSC reject comb feature filters to perform a parallel symbol decoding. Figure 15 is a mounting diagram showing how figures 15a and 15b can be coupled together to form a single figure referred to as figure 15 in the following, which figure 15 shows the details of symbol code selection circuits which can be used in a digital television signal receiver of the type shown in Figure 14.
Figure 15A is a schematic block diagram showing the details of the circuits in the digital television signal receiver of Figure 14 to generate prescribed symbol decoding results during data synchronization intervals. Fig. 15B is a schematic block diagram showing the details of the circuits in the digital television signal receiver of Fig. 14 for selecting between symbol decoding results during periods of time between data synchronization intervals.
DETAILED DESCRIPTION At various points in the circuits shown in the figures of the drawings, adjustment delays have been inserted, in order that the operation sequence is correct, as will be understood by those experienced in the design of electronic components. Unless there is something out of the ordinary about a particular adjustment delay requirement, there will be no explicit reference to it in the specification that follows. Figure 1 shows a digital television signal receiver used to recover fault-corrected data, which data is suitable for recording by a digital video cassette recorder or for MPEG-2 decoding and display on a television set. The DTV signal receiver of Figure 1 is shown as a receiver of television broadcast signals of a receiving antenna 8, but it can receive the signals instead of a cable network. The television broadcast signals are fed as an input signal to the "input" electronic components. The "input" electronic components 10 generally include a radio frequency amplifier and a first detector for
converting the radiofrequency television signals into intermediate frequency television signals, supplied as an input signal to an intermediate frequency amplifier chain (or chain of amplifiers) (I-F) for sideband DTV signal
residual. The DTV receiver preferably consists of a plural type of conversion with the IF amplifier chain 12 which includes an intermediate frequency amplifier for amplifying the DTV signals, such as they are converted to an ultra high frequency (UHF) band by the first
detector, a second detector for converting the amplified DTV signals to a very high frequency (VHF) band and an additional intermediate frequency amplifier for amplifying the DTV signals, as they are converted to the VHF band. If the demodulation is carried out to the band
Based on the digital regime, the chain 12 of IF amplifiers will also include a third detector, to convert the amplified DTV signals to a final intermediate frequency band closer to the baseband. • Preferably, a surface acoustic wave (SAW) filter is used in the IF amplifier for the UHF band, to form the channel selection response and reject the adjacent channels. This SAW filter cuts rapidly just beyond 5.38 MHz separated from the suppressed carrier frequency of the DTV signal of the VSB frequency and the pilot carrier, which is of similar frequency and of fixed amplitude. Thus, this SAW filter rejects much of the frequency-modulated sound carrier of any analog co-channel interference television signal. The elimination of the FM sound carrier from any analog television signal of co-channel interference in the chain 12 of IF amplifiers prevents the artifacts of that carrier from being generated when the final IF signal is detected to recover the symbols of baseband and prevents such artifacts from interfering with the data sectioning of those baseband symbols during symbol decoding. The prevention of such artifacts that interfere with the data sectioning of those baseband symbols during symbol decoding is best accomplished by relying on feature filtering in a comb prior to data sectioning. The final I-F output signals of the chain 12 of the IF amplifier are supplied to a complex demodulator 14., which demodulates the DTV signal of residual sideband amplitude modulation in the final intermediate frequency band to recover a real baseband signal and an imaginary baseband signal. The demodulation can be done in the digital regime after the analog-to-digital conversion of a final intermediate frequency band in the range of a few megacycles as described for example by CB Patel et al in U.S. Patent No. 5,479,449, issued on December 26, 1995 and titled "DIGITAL VSB DETECTOR WITH PHASE TRACKER, AS FOR INCLUSION IN AN HDTV RECEIVER". Alternatively, the demodulation can be performed in the analogous regime, in which case, the results are usually subjected to analogous to digital conversion to facilitate further processing. The complex demodulation is preferably carried out by phase synchronized demodulation (I) and phase quadrature (Q) synchronized demodulation. The digital results of the above demodulation procedures conventionally have an accuracy of 8 bits or more and describe 2N level symbols, which encode N data bits. Currently, 2N is eight in the case where the DTV signal receiver of Figure 1 receives a broadcast in the air via antenna 12 and is sixteen in the case where the DTV signal receiver of Figure 1 receives transmission by cable. The invention is concerned with the reception of airborne, terrestrial transmissions and Figure 1 does not show the portions of the DTV receiver that provide decoding of symbols and error correction decoding for received cable transmissions. Synchronizer and symbol compensator circuits 16 receive at least the real samples transformed to the digital language of the baseband signal (channel I) in phase, of the complex demodulator 14; in the DTV receiver of figure 1, it is also shown that the circuits 16 receive the imaginary samples transformed into the digital language of the quadrature-phase baseband signal (channel Q). Circuits 16 include a digital filter with adjustable weighting coefficients that compensate for ghosts and skew distortion in the received signal. The symbol synchronizer and compensator circuit 16 provides symbol synchronization or "de-rotation" also as amplitude equalization and phantom elimination. Synchronizer and symbol compensator circuits in which symbol synchronization is performed before amplitude compensation is known from U.S. Patent No. 5,479,449. In such designs, the demodulator 14 will provide real and imaginary baseband signals containing oversampled demodulator responses to the synchronizer and compensator circuitry 16. After symbol synchronization, the oversampled data is transformed to decimals to extract the baseband I channel signal at the normal symbol rate, to reduce the sampling rate by means of digital filtering used for the amplitude compensation and the ghost elimination. The synchronizer and compensator circuitry in which the compensation or amplitude equalization precedes symbol synchronization, "de-rotation", or "phase tracking" is also known to those skilled in the art of receiver design. digital signal. Each sample of the output signal of circuit 16 is resolved to ten or more bits and is in effect a digital description of an analogous symbol that exhibits one of (2N = 8) levels. The output signal of the circuit 16 is carefully controlled in gain by any of several known methods, such that the ideal stage levels for the symbols are known. A preferred gain control method, because the response speed of such gain control is exceptionally fast, regulates the direct component of the actual baseband signal, supplied from the complex demodulator 14 to a normalized level of + 1.25. . This gain control method is generally described in U.S. Patent No. 5,479,449 and is more specifically described by CB Patel et al in the co-assigned US Patent Application, Serial No. 5,573,454 filed on December 15, 1995, entitled " AUTOMATIC GAIN CONTROL OF RADIO RECEIVER FO RECEIVING DIGITAL HIGH-DEFINITION TELEVISION SIGNALS ", and incorporated herein by reference. The output signal of the circuit 16 is supplied as an input signal to the data synchronization detection circuit 18, which retrieves the data field synchronization information F and the synchronization information S of the data segment of the signal of the data signal. channel I compensated baseband. Alternatively, the input signal to the data synchronization detection circuit 18 may be obtained before compensation or equalization. The signal samples of channel I, compensated, at normal symbol rate, supplied as output signal of circuit 16, are applied as the input signal to a NTSC reject comb characteristic filter 20. The comb feature filter 20 includes a first delay device 201 for generating a differential pair differentially delayed from the 2N level symbols and a first linear combiner 202 for linearly combining the differentially delayed symbol currents to generate the filter response. of characteristic in comb. As described in U.S. Patent No. 5,260,793, the first delay device 201 can provide a delay equal to the period of twelve level 2N symbols and the first linear combiner 202 can be a subtracter. Each sample of the output signal of the comb characteristic filter 20 is resolved to ten or more bits and is in effect a digital description of an analogous symbol that exhibits one of (4N-1) = 15 levels. It is assumed that the synchronizer and symbol compensator circuit 16 is designed to suppress the direct bias component of its input signal (as expressed in digital samples), which direct bias component has a normalized level of +1.25 and appears in the actual baseband signal fed from the complex demodulator 14 due to the detection of the pilot carrier. Thus, each sample of the output signal of the circuit 16 applied as the input signal of the comb characteristic filter 20 is, in effect, a digital description of an analogous symbol exhibiting one of the following normalized levels: -7, - 5, • -3, -1, +1, +3, +5 and +7. These symbol levels are referred to as "odd" or "odd" symbol levels and are detected by an odd-level data disconnector 32 to generate intermediate symbol decoding results of 000, 001, 010, 011, 100, 101 , 110 and 111, respectively. Each sample of the output signal of the comb characteristic filter 20 is in effect a digital description of an analogous symbol exhibiting one of the
following normalized levels: -14, -12, -10, -8, -6, -4, -2, 0, +2, +4, +6, +8, +10, +12 and +14. These symbol levels are referred to as "even" symbol levels and are detected by an even-level data disconnector 24 to generate symbol decoding results
pre-coded of 001, 010, 011, 100, 101, 110, 111, 000, 001, 010, 011, 100, 101, 110 and 111, respectively. The data disconnectors 22 and 24 can be of the so-called "physical decision" type, as assumed at this point in the description or they can be of the so-called type of
"programming decision" used in the implementation of a Viterbi decoding scheme. Arrangements are possible in which the odd-level data disconnector 22 and the even-level data disconnector 24 are replaced by a single data disconnector, which uses
multiplexer connections to shift its phase in the circuit and to provide polarization to modify its sectioning ranges, but these arrangements are not preferred, due to the complexity of operation. It is assumed that the synchronizer and symbol compensator circuitry 16, in the above description, is designed to suppress the direct bias component of its input signal (as expressed in digital samples), which direct bias component it has a normalized level of +1.25 and appears in the actual baseband signal supplied from the complex demodulator 14 due to the detection of the pilot carrier. Alternatively, the synchro and compensator circuitry 16 is designed to preserve the direct bias component of its input signal *, which simplifies the design of the compensation filter (or equalization) in circuit 16 in some way. In such a case, the data sectioning levels in the odd level data switch 22 are shifted to take into account the direct bias component that accompanies the data stages in its input signal. Provided that the first linear combiner 202 is a subtracter, if the circuit 16 is designed to suppress or preserve the direct bias component of its input signal, it has no consequence with respect to the data sectioning levels in the disconnector of data 24 of • even level. However, if the differential delay provided by the first delay device 201 is chosen such that the first linear combiner 202 is an adder, the data sectioning levels in the even level data switch 24 must be shifted to Take into account the duplicated direct bias component that accompanies the data stages in your input signal. A comb feature filter 26 is used
after the data disconnectors 22 and 24 to generate a response of the post-coding filter to the response * of the pre-coding filter of the comb characteristic filter 20. The comb feature filter 26 includes a multiplexer 261 with three inputs, a
second linear combiner 262 and a second delay device 263 with delay equal to that of the first delay device 201 in the comb characteristic filter 20. The second linear combiner 262 is a modifier 8 if the first linear combiner 202 is a subtracter and is
a module subtractor 8 if the first linear combiner 202 is an adder. The first linear combiner 202 and the second linear combiner 262 can be constructed as respective read-only memory (ROM) to accelerate the linear combination operations sufficiently to
support the sampling rates involved. The output signal of the multiplexer 261 provides the response of the feature filter 26 in the post-encoding comb and is delayed by the second delay device 263. The second linear combiner 262 combines the decoding results of the pre-encoded symbols of the data disconnector 24. of even level with the output signal of the second delay device 263. The output signal of the multiplexer 261 reproduces one of the three input signals applied to the multiplexer 261, as selected in response to first, second and third states of a multiplexer control signal, fed to multiplexer 261 from a controller 28. The first input gate of multiplexer 261 receives the ideal symbol decoding results, fed from the memory that is inside the controller 28, during the time when the data field synchronization information F and the synchronization information S of the data segment of the compensated baseband channel I signal are recovered by the circuit 18 of data synchronization detection. The controller 28 supplies the first state of the multiplexer control signal to the multiplexer 261 during this time, to condition the multiplexer 261 to provide, as the final coding results which are its input signal, the ideal symbol decoding results. supplied from the memory inside the controller 28. The odd-level data disconnector 22 supplies decoding results of intermediate symbols as its output signal to the second input gate of the multiplexer 261. The multiplexer 261 is conditioned by the second state of the multiplexer control signal to reproduce decoding results of the intermediate symbol, as the final encoding results the
which are your output signal. The second linear combiner 262 supplies the decoding results of the post-encoded symbols as its output signal to the third input gate of the multiplexer 261. The multiplexer 261 is conditioned by the third signal state of the signal.
control of the multiplexer to reproduce the decoding results of post-encoded symbols, such as the final coding results which are its output signal. Operating errors in the results of
The decoding of post-coding symbols of the feature filter 26 in the post-coding comb is reduced by feedback of the decoding results of the ideal symbols supplied from the memory inside the controller 28 during the time when
the data synchronization detecting circuit 18 retrieves data field synchronization information F and the data segment synchronization information S. This is an important aspect of the invention, which will be described in further detail in this specification. The output signal of the multiplexer 261 in the post-coding comb characteristic filter 26 comprises the decoding results of final symbols in groups of 3 parallel bits, assembled by f a data assembler 30 for the application to a
data interleaver 32. The data interleaver 32 switches the assembled data into parallel data streams for application to the trellis decoder circuit 34. The trellis decoder circuit 34 conventionally uses 12 trellis decoders. The
The trellis decoding results are supplied from the trellis decoder circuit 34 to the data deinterleaver circuit 36 for switching off. The byte parser circuit 38 converts the output signal of the data interleaver 36 into coding bits by
Reed-Solomon error correction for application to the Reed-Solomon decoding circuit 40, which performs the decoding of Reed-Solomon to generate a stream of corrected bytes by error supplied to a data descrambler 42. The descrambler 42 of
data supplies the reproduced data to the rest of the receiver (not shown). The rest of a complete DTV receiver will include a packet classifier, an audio decoder, an MPEG-2 decoder and so on. The rest of a DTV receiver incorporated in a digital tape recorder / player will include circuits to convert the data to a form for recording or recording. An NTSC co-channel interference detector 44 supplies or feeds the controller 28 with an indication of whether the NTSC co-channel interference is of sufficient intensity to cause an incorrigible error in the data sectioning carried out by the disconnector 24 of data. If the detector 44 indicates that the NTSC co-channel interference is not of such intensity, the controller 28 will supply the second state of the multiplexer control signal to the multiplexer 261, at different times than those times when the synchronization information F of the data field and the synchronization information S of the data segment are recovered by the data synchronization detection circuit 18. This conditions the multiplexer 261 to reproduce, as its output signal, the decoding results of intermediate symbols fed from the odd-level data disconnector 22. If the detector 44 indicates that the NTSC co-channel interference is of sufficient intensity to cause incorrigible error in the data sectioning carried out by the data disconnect 22, the controller 28 will supply the third state of the control signal of the multiplexer to the multiplexer 261 at different times than those times when the synchronization information F The data field and the data sronization information S of the data segment are recovered by the data sronization detection circuit 18. This conditions the multiplexer 261 to reproduce as its output signal the post-encoded symbol decoding results provided as the second linear combination results of the second linear combiner 262. FIG. 2 shows a form that the co-channel interference detector 44. NTSC channel can take, it is believed that such form is new in the art. A subtracter 441 differentially combines the decoding results of intermediate symbols supplied from the odd-level data disconnector 22 and the decoded results of the post-encoded symbols provided as the second linear combination results of the second linear combiner 262. If the interference amount of NTSC co-channel is negligible and if the random noise in the baseband I channel signal is negligible, these decoding results of intermediate and post-coded symbols should be similar, such that the difference output signal of the subtracter 441 should be low. However, if the amount of NTSC co-channel interference is appreciable, the difference output signal of the subtracter 441 will not be generally low, but rather will be frequently high. A measure of the energy in the difference output signal of the subtracter 441 is developed by squaring the difference output signal with a quadrant circuit 442 and by determining the average of the squared response over a prescribed short time interval with an averaging circuit 443. The quadrant circuit 442 can be implemented using read-only memory (ROM). The averaging circuit 443 can be implemented using a delay line memory for storing several successive digital samples and an adder to sum the digital samples currently stored in the delay line memory. The short-term average of the energy in the output signal difference of the subtracter 441, as determined by the averaging circuit 443, is supplied to a connected digital comparator to provide a threshold detector 444. The threshold in the detector 444 is high enough not to be exceeded by the short-term average of the differences in random noise that accompanies the intermediate symbol decoding results and the decoded results of post-encoded symbols applied to the subtracter 441. The The threshold is exceeded if the NTSC co-channel interference is of sufficient intensity to cause an incorrigible error in the data sectioning carried out by the data disconnector 22. The threshold detector 444 supplies the controller 28 with an indication of whether the threshold is exceeded or not. Figure 3 shows a digital television receiver different from that of Figure 1, in which the circuit to determine if the NTSC co-channel interference is of sufficient intensity or not to cause an incorrigible error in the data sectioning carried out finished
by means of the data disconnector 22 and is of the type described by the inventor in the US patent application Serial No. (Case of the lawyer 1500-1) filed on March 21, 1997 and entitled "USING VIDEO SIGNALS FROM AUXILIARY ANALOG TV RECEIVERS FOR DETECTING NTSC
INTERFERENCE IN DIGITAL TV RECEIVERS. "The DTV signal, as it is converted to IF by the" input "electronic components 10, is supplied to an IF amplifier chain 46 for the NTSC signals. IF for NTSC signals differs from the
chain of IF amplifiers used in conventional NTSC signal receivers. Since medium band gain characteristics are involved, the amplifier stages in the IF amplifier chain 46 for the NTSC signals correspond to the amplifier stages in the IF amplifier chain 12 for the DTV signals, which have gains substantially linear and having the same automatic gain control as the corresponding amplifier stages in the chain 12 of IF amplifiers. The residual sideband of the NTSC signal is not suppressed in the IF amplifier chain 46. The entire sideband portion of the NTSC signal that is from a single sideband in character is preferably suppressed in the chain 46 of the IF amplifier to reduce the energy of the co-channel DTV signal. This reduces the dynamic range of the response of the 46 string of IF amplifiers to facilitate further amplification of the video carrier to fix the phase of a local video carrier oscillator, used in the complex 48 demodulator. Filtering procedures to establish the bandwidth of the IF amplifier chain 46 can be carried out by SAW filtering in a 'UHF IF amplifier if the circuits of the plural conversion receiver are used. The amplified IF response of the string 46 of the IF amplifier is supplied to a complex demodulator 48 for the NTSC video signal either directly or after some further amplification. The complex demodulator 48 provides a phase I channel response composed of several NTSC signal samples and the actual component of the 5 accompanying DTV artifacts. The complex demodulator 48 also provides a phase quadrature Q-channel response composed of samples of the imaginary component of the accompanying DTV artifacts, which samples are applied to a Hilbert transformation filter 50. The
The response of the Hilbert transformation filter 50 is supplied to a linear combiner 52. The linear combiner 52 combines the response of the Hilbert transformation filter 50 with the phase I response in phase, appropriately delayed, to recover the signal samples from
NTSC substantially free of accompanying DTV artifacts. The linear combiner 52 is an adder or subtractor, depending on the phase of the relative video carrier during the synchronized demodulation procedures used in the complex demodulator 48 for
generate the channel I and Q channel responses. The substantially free NTSC signal from the accompanying DTV artifacts supplied from the linear combiner 52 is applied to a low pass filter 54 with a cutoff frequency of 750 KHz or less. A value
The estimate of the luminance signal energy in the NTSC signal of co-channel interference is generated by squaring the response of the low pass filter 54 with a square circuit 56 and determining the average of the square circuit response over a prescribed short time interval with an averaging circuit 58. This estimated value is supplied to a threshold detector 58. The threshold in the threshold detector 58 is exceeded if the interference of the NTSC co-channel is of sufficient intensity to cause an incorrigible error in the data sectioning carried out by the data disconnector 22. The threshold detector 58 supplies to the controller 28 an indication of whether the threshold is exceeded or not. Figure 4 shows a digital television receiver different from the receivers of Figures 1 and 3 in that the circuit to determine if the NTSC co-channel interference is or is not of sufficient intensity to cause the incorrigible error in the data sectioning carried out by means of the data disconnect 22 is of the type described by the inventor in the US patent application Serial No. (case of proxy 1501-1) filed on March 21, 1997 and entitled "USING INTERCARRIER SIGNALS FOR DETECTING NTSC INTERFERENCE IN DIGITAL TV RECEIVERS ". The DTV signal, as it is converted to IF (intermediate frequency) by the electronic "input" components 10, is supplied to an IF amplifier chain 62 of the near parallel type for the NTSC sound signals. The amplifier stages in the IF amplifier chain 62 for the NTSC sound signals correspond to the similar amplifier stages in the IF amplifier chain 12 for the DTV signals, which have substantially linear gains and which have the same control of automatic gain as the corresponding amplifier stages
in the chain 12 IF amplifier. The frequency selectivity of the IF amplifier chain 62 is such as to emphasize the response within ± 250 KHz of the audio carrier and within ± 250 KHz or so on successively of the NTSC video carrier. The procedures of
Filtering to establish the frequency selectivity of the IF chain 62 of IF amplifiers can be carried out by SAW filtering in a UHF IF amplifier if a plural conversion receiver circuit is used. The response of the 62 chain of IF amplifiers is
supplied to an intercarrier detector 64, which uses the modulated NTSC video carrier as an increased carrier to heterodyne the NTSC audio carrier to generate an intercarrier sound intermediate frequency signal with a frequency of
4.5 MHz carrier. This intercarrier sound IF (intermediate frequency) signal is amplified by an intercarrier sound intermediate frequency amplifier 66, which 4.5 MHz IF amplifier 66 supplies the amplified intercarrier sound IF signal. to a detector 68 of intercarrier amplitude. The response of the amplitude detector 68 is averaged over a short time interval prescribed with an averaging circuit 70 and the resulting average is supplied to a threshold detector 72. The threshold in the threshold detector 72 is exceeded if the interference -NTSC channel is of sufficient intensity to cause an incorrigible error in the data sectioning carried out by the data disconnector 22. The threshold detector 72 supplies to the controller 28 an indication of whether the threshold is exceeded or not. Figure 5 shows a preferred way in which the multiplexer 261 is implemented in the post-coding comb characteristic filter 26. Multiplexer 261 with 3 inputs comprises two multiplexers 2611 and 2612 with 2 inputs. The controller 28 applies the output signal from the NTSC co-channel interference detector (e.g.
44) as a control signal to the 2-input multiplexer 2611. If the NTSC co-channel interference is of sufficient intensity to cause an incorrigible error in the data sectioning carried out by the data disconnector 22, the output signal UNO resulting from the co-channel interference detector NTSC conditions the multiplexer 2611 for reproducing, for application to the second input gate of the multiplexer 2612, the decoded results of the post-encoded symbols that the second linear combiner 262 supplies to the first input gate of the multiplexer 2611. If the interference of co- NTSC channel is of insufficient intensity to cause incorrigible error in the data sectioning carried out by the data disconnector 22, the output signal ZERO resulting from the NTSC co-channel interference detector conditions the multiplexer 2611 to reproduce the results of decoding intermediate symbols that the data disconnecting 22 supplies to the second comp input gate of multiplexer 2611. These reproduced intermediate symbol decoding results are applied to the second input gate of multiplexer 2612. Figures 5, 6 and 7 show a gate 0 281 that is included in controller 28. gate O 281 provides a response that is ONE, when the field segment synchronization detector 181 provides a ONE to it in response to the presence of a field synchronization segment that is detected and when the data segment synchronization detector 182 it provides a UNO to it in response to the presence of a data synchronization code that is detected. At all other times, gate 0 281 supplies a 5 response that is ZERO. In figure 5, the response of the gate 0 281 is applied as a control signal to the multiplexer 2621. The response of the gate 281 0, being ZERO, conditions the multiplexer 2612 to reproduce, as a result of the
Final symbol decoding, for application to the data assembler 30, the output signal of the multiplexer 2611 supplied to the second input gate of the multiplexer 2612, as the best estimated value of the symbol decoding result. The response of gate 0
281, as UNO conditions the multiplexer 2612 to reproduce, as a result of final symbol decoding, for application to the data assembler, ideal decoding results extracted from the memory in the controller 28 as will be described in further detail in
this specification with reference to Figure 8 of the drawings. Figure 6 shows an alternative construction 260 of the postcode coding characteristic filter 26. The multiplexer 261 of three inputs comprises
two multiplexers 2611 and 2612 of 2 inputs, replaced by a multiplexer 2610 of 3 inputs comprising 3 multiplexers of 2 inputs 26101, 26102, and 26103. Figure 7 shows a modification 2600 of the feature filter 26 in post-coding comb , wherein the three-input multiplexer 261 comprising two 2-input multiplexers 2611 and 2612 is replaced by a 3-input multiplexer 26100 comprising 2 multiplexers of two inputs 2610001 and 261002 which receive their respective control signals from gate O 281 and the NTSC co-channel interference detector. The post-coding comb characteristic filter 2600 provides a somewhat different operation result from the post-coding comb feature filters 26 and 260. The multiplexer 261001 replaces the post-encoded symbol decoding results with the decoding results of ideal symbols when the response of gate 0 281 is ONE. When the NTSC co-channel interference detector provides a UNO, an indicator that the NTSC co-channel interference is of sufficient intensity to cause an incorrigible error in the data sectioning carried out by the data disconnector 22, a multiplexer 261002 selects the resulting modified decoded symbol decoding results as final symbol decoding results for application to the data assembler fl ^ 7. When the NTSC co-channel interference detector supplies a ZERO indicator that the NTSC co-channel interference is of insufficient intensity to cause an incorrigible error in the
data sectioning carried out by the data disconnector 22, the multiplexer 261002 selects the decoding results of intermediate symbols of the data disconnector 22 as the results of decoding of final symbols for its application to the
data assembler 30, without any replacement of those intermediate symbol decoding results by decoding results of ideal symbols. Figure 8 shows multiplexer 2612 of Figure 5 in greater detail, together with the circuits for
generate the decoding results of ideal symbols applied to the multiplexer 2612. The multiplexer 2612 comprises the intermediate output registers of the read-only memory (ROM) 74, 76, 78 to selectively read an output distribution line 80 of 3. bits wide
of the multiplexer 2612. The multiplexer 2612 further comprises a three-state buffer 82 for selectively sending the 3-bit-wide output of the multiplexer 2611 to the main output line 80. The circuits for generating the results of
Decoding of ideal symbols applied to multiplexer 2612 comprises ROMs 74, 76, 78; a synchronization generator 84 or symbol clock; an address counter 86 for addressing ROMs 74, 76, 78; a circuit 88 for resetting the alteration, for resetting the counter 86; the address decoders 94, 96, 98 for generating read enable signals for the ROM 74, 76, 78; and an NI gate 92 for controlling the three-state buffer 82. The address counter 86 counts the input pulses received at the symbol decoding rate of the symbol clock generator 84, thereby generating successive descriptive addresses respectively of the symbols in a data box. Appropriate portions of these addresses apply to ROMs 74, 76, 78 as their entry addresses. The reset circuit 88 of the alteration resets the counter 86 to the appropriate counts responsive to the data field synchronization information F and the synchronization information S of the data segment retrieved by the data synchronization detection circuit 18 of the Figure 1, 3 6 4. It is preferable to configure the counter 86 in such a way that a group of more significant bits counts the number of data segments per data frame and thus a group of less significant bits count the number of symbols per segment of data. data. This simplifies the design of the circuit 88 for resetting the alteration; reduces the bit widths of the input signal to the address decoders 94, 96, 98; and it makes it easier for the ROMs 74, 76, 78 to be addressed by the partial addresses of the counter 86, to reduce the bit widths of the ROM address. The ROM 74 stores the decoding results of ideal symbols for an odd-field synchronization segment and is selectively enabled for reading upon receipt of a UNO from the address decoder 94. The ROM 74 is addressed by the group of least significant bits of the counter output 86, which counts the number of symbols per group of data segments and the address decoder 94 responds to the most significant group of bits counting the number of segments of data by data box. The address decoder 94 generates an ON when and only when the data segment portion of the address provided by the address counter 86 corresponds to the address of an odd field synchronization segment. The ROM 76 stores the decoding results of ideal symbols for an even field synchronization segment and is selectively enabled for reading upon receipt of a UNO from the address decoder 96. The ROM 76 is addressed by the group of least significant bits of the output of the counter 86 that counts the number of symbols per group of data segments; and the address decoder 96 responds to the most significant group of bits, which counts the data segment number per data frame. The address decoder 96 generates an ON when and only when the portion of the data segment of the address supplied by the address counter 86 corresponds to the direction of an even field synchronization segment. The ROM 78 stores the decoding results of ideal symbols for the initial encoding group at the beginning of each synchronization segment and is selectively enabled for reading upon receiving an ONU of the address decoder 98. The ROM 78 responds to the two least significant bits of the output of the counter 86; and the address decoder 98 responds to the group of least significant bits of the output of the counter 86 that counts the number of symbols per data segment group. The address decoder 98 generates an ONE when and only when the data symbol per count portion in the address data segment supplied by the address counter 86 corresponds to the partial address of a start code group.
The gate 92 receives the rnses from the address decoders 94, 96 and 98 in a rctive connection of its three input connections. When the ideal symbol decoding results are available, one of the address decoders 94, 96, and 98 supplies a UNO as its output signal, to condition the NI 92 output gate to provide a ZERO rnse to the buffer 82 data from three states. This conditions the three-state data memory 82 to display a high-impedance source to the main data distribution line 80, such that the signal sent from the multiplexer 2611 will not be secured on the main data line 80. width bits of the multiplexer 2612. During those portions of the data segments for which the decoding results of ideal symbols are not predictable, none of the address decoders 94, 96 and 98 supplies a UNO as their output signal, for conditioning the NI gate 92 to provide a ONE rnse to the three-state data memory 82. This conditions the three-state data memory 82 to display a low source impedance to the main data line 80, such that the signal sent from the multiplexer 2611 will be asserted on the main data line 80 of 3 bit wide. of multiplexer 2612.
The circuits of Figure 8 for generating the ideal symbol decoding results applied to the multiplexer 2612 are readily adapted by those skilled in the art of digital circuit design for use in the configurations shown in Figures 6 and 7. Figure 9 is a schematic block diagram showing the details of a portion of the digital television signal receiver of Fig. 1, 3 or 4 using a species 120 of the NTSC reject comb characteristic filter 20 and a species 126 of the filter 26 of characteristic in comb of post-coding. A subtractor 1202 - serves as the first linear combiner in the NTSC reject comb feature 120 filter and a modifier additive 1262 serves as the second linear combiner in the postcode coding characteristic filter 126. The NTSC reject comb feature filter 120 utilizes a first delay device 1201 that exhibits a delay of twelve symbol epochs and the post combustion feature filter 126 utilizes a second delay device 1263 that also exhibits a delay of 12. delay of twelve epochs of symbols. The delay of 12 symbols displayed by each of the delay devices 1201 and 1263 is close to the delay of one cycle of the television video carrier artifact analogous to 59.75 times the analogue panning frequency of the analog television fjj. The delay of 12 symbols is close to five cycles of the television chrominance subcarrier artifact analogous to 287.25 times fu_. He
delay of 12 symbols is close to six cycles of the television sound carrier artifact analogous to 345.75 times fu_. This is the reason why the differentially combined rnse of the subtractor 1202 to the audio carrier, to the video carrier and to the
frequencies close to the chrominance subcarrier differentially delayed by the first delay device 1201 tend to have reduced co-channel interference. However, in the portions of a video signal in which the edges cross a sweep line
horizontally, the amount of correlation in the television video signal k analogous to such distances in the horizontal spatial direction is quite low. A kind 1261 of the multiplexer 261 is controlled by the control signal of the multiplexer that is
finds in its second state most of the time when it is determined that there is insufficient NTSC co-channel interference to cause an incorrigible error in the output signal of the data disconnector 22 and that it is in its third state in the largest part of the time when it
determines that there is sufficient NTSC co-channel interference to cause an incorrigible error in the output signal of the data disconnector 22. The multiplexer 1261 is conditioned by its control signal to be in its third state to feedback the results of sum of the module 8 of the adder 1262, as twelve symbol epochs are delayed by the delay device 1263, to the adder 1262 as a summand. This is a modular accumulation procedure in which a single error propagates as an operation error, with the error recurring every twelve symbol epochs. The operation errors in the decoding results of post-code symbols of the feature filter 126 in the post-coding comb are reduced by the multiplexer 1261 by being placed in its first state for four symbol epochs at the beginning of each data segment, also as for the entirety of each data segment that contains field synchronization. When this control signal is in its first state, the multiplexer 1261 reproduces as its output signal decoding results of ideal symbols supplied from the memory in the controller 28. The introduction of the decoding results of ideal symbols to the signal of output of multiplexer 1261 stops an operation error. Since there are 4 + 69 (12) symbols per data segment, the decoding results of the ideal symbol slide back four times of symbol in phase each data segment, so that no operation error can persist for more than three segments of data. Fig. 10 is a schematic block diagram 5 showing the details of a portion of the digital television signal receiver of Fig. 1, 3 or 4, which uses a sort 220 of the NTSC reject comb characteristic filter 20 and a kind 226 of the filter 26 of
F characteristic in post-coding comb. The filter 220
The NTSC reject comb feature feature uses a first delay device 2201 that exhibits a delay of six times of symbols, and the feature filter 226 in a post-encoding comb uses a second delay device 2263 that also exhibits a delay. of six epochs
of symbols. The delay of 6 symbols exhibited by each of the delay devices 2201 and 2263 is close to a
F 0.5-cycle delay of analog television video carrier artifact to 59.75 times the analog TV horizontal sweep frequency fjj, close to 2.5 cycles
of the television chrominance subcarrier artifact analogous to 287.25 times fu_, and close to 3 cycles of any - television audio carrier artifact analogous to 345.75 times fu_- An addon 2202 serves as the first linear combiner in the filter 220 of 25 feature in NTSC rejection comb and a subtractor 2262 of module 8 serves as the second linear combiner in feature filter in post-encoding comb. Since the delay exhibited by the delay devices 2201 and 2263 is shorter than the delay exhibited by the delay devices 1201 and 1263, although the almost null frequencies converted from the analog television carrier frequencies are narrower band, there is more likely to be a good anti-correlation in the combined signals additively
through the additive 2202, that the probability of there being a good correlation in the signals differentially combined by the subtracter 1202. The deletion of the sound carrier is more deficient in the response of the NTSC reject comb filter 220 that
in the response of the filter 120 of feature in NTSC rejection comb. However, if the sound carrier of f an analog co-channel interference television signal has been suppressed by SAW filtering or a sound trap in the IF amplifier chain 12, the rejection of P.
deficient filter 220 sound of comb combing is not a problem. The responses to the synchronization tips are reduced in duration by using the NTSC reject comb feature filter 220 of FIG. 10, instead of the feature filter 120
The NTSC reject comb of FIG. 9 is such that there is a substantially reduced tendency to overcome the error correction in trellis decoding and Reed-Solomon coding. A 2261 sort of multiplexer 261 is controlled by a control signal from the multiplexer that is in its second state most of the time when it is determined that there is insufficient NTSC co-channel interference to cause an incorrigible error in the signal of output of the data disconnector 22 and that
finds in its third state most of the time when it is determined that there is sufficient NTSC co-channel interference to cause an incorrigible error in the output signal of the data disconnector 22. The multiplexer 2261 is conditioned by its control signal to be
in its third state to feedback the results of the sum of modulo 8 of the adder 2262, as delayed by six symbol epochs by the delay device 2263 to the adder 2262 as a summand. This is a modular accumulation procedure in which only one
error propagates as an operation error, with recurring error every six symbol epochs. The operation errors in the decoding results of post-encoded symbols of the feature filter in the post-coding comb 226 are reduced by the multiplexer 2261
when placed in its first state by four times of symbol at the beginning of each data segment, as well as during the entirety of each data segment containing the field synchronization. When this control signal is in its first state, the multiplexer 2261 reproduces
as its output signal the decoding results of ideal symbols supplied from the memory in the controller 28. The input of the decoding results of ideal symbols to the output signal of the multiplexer 2261 stops an operation error. Since
there are 4 + 138 (6) symbols per data segment, the decoding results of ideal symbols are backward to four symbol times in phase for each data segment, so that no operation error can persist for more than two data segments.
The probability of a prolonged period of operating error in the post-coding comb characteristic filter 226 is substantially less than in the post-coding comb characteristic filter 216, although the operation error recurred more frequently and affected
twice to both of the twelve trellis codes interspersed. Figure 11 is a schematic block diagram showing the details of a portion of the digital television signal receiver of Figure 1, 3 or 4 that
uses a sort 320 of the NTSC reject comb characteristic filter 20 and a species 326 of the post-coding comb characteristic filter 26. The NTSC Reject Comb Filter 320 uses a first delay device 3201 that exhibits a delay of 5 1368 symbol times, which delay is substantially equal to the time of two horizontal scan lines of a analog television signal and the feature 326 filter in post-coding comb uses a
* second delay device 3263 which also exhibits such
delay. The first linear combiner in the NTSC rejection comb feature filter 320 is an additive 3202, and the second linear combiner in the post-coding comb feature filter 326 is a subtractor 3262 of module 8. 15 A sort 3261 of the multiplexer 261 is controlled by a control signal of the multiplexer which is in its second state most of the time when it is determined that there is insufficient co-channel interference of NTSC to cause an incorrigible error in the
output signal of the data disconnector 22 and which is in its third state most of the time when it is determined that there is sufficient NTSC co-channel interference to cause an incorrigible error in the output signal of the data disconnector 22 The receiver of
DTV preferably contains circuits for detecting the change between alternative scan lines in the NTSC co-channel interference, such that the controller 28 can stop feeding the first state of the control signal of the multiplexer 3261 under such conditions. terms. The multiplexer 3261 is conditioned by its control signal to be in its third state to feedback the results of the sum of the module 8 to the adder 3262, as it is delayed 1368 times of symbol
by the delay device 3263, to the adder 3262 as a summand. This is a modular accumulation procedure in which a single error propagates as an operation error, with the error recurring every 1368 times of the symbol. This spacing of symbol code is more
that the spacing for a single block of the Reed-Solomon code in such a way that a single operation error is corrected quickly during the decoding of Reed-Solomon. Operating errors in decoding results of post-encoded 326 filter symbols
of feature in post-coding comb are reduced by multiplexer 3261 to be placed in its first state for the entirety of each data segment containing field synchronization, as well as for four times of symbols at the beginning of each segment of
data. When this control signal is in its first state, the multiplexer 3261 reproduces as its output signal the decoding results of ideal symbols supplied from the memory in the controller 28. The introduction of the decoding results of 5 ideal symbols to the output signal of multiplexer 3261 stops an operation error. The duration of 16.67 milliseconds of an NTSC video field exhibits a phase shift versus the duration of 24.19 milliseconds of a DTV data field, such that the segments
DTV data containing field synchronization eventually sweep the entire frame of the NTSC frame. The 525 lines in the NTSC frame plot each contain 684 times of ~ symbols, for a total of 359, 100 times of symbols. Since this is somewhat less than 432 times
832 times of symbols in a DTV data segment containing field synchronization, it can be assumed with reasonable confidence that operation errors of duration greater than 432 data fields will be expulsed by multiplexer 3261 reproducing decoding results
of ideal symbols during the DTV data segments containing field synchronization. There is also a phase shift between the data segments for the start code groups from which the decoding results of ideal symbols are available and
NTSC video scan lines. You can estimate 359,100 symbol epochs, which are 89,775 times the four symbol epochs in a code start group, are scanned during 89,775 consecutive data segments. Since there are 313 data segments per 5 DTV data field, it can be assumed with reasonable confidence that lifetime operation errors greater than 287 data fields will be expulsed by multiplexer 3261 that reproduces ideal symbol decoding results during the Start groups of the code. The two sources of
suppression of operation errors are reasonably independent of each other, such that operation errors of duration greater than two hundred or so such that the data fields are quite improbable. Also, if the NTSC co-channel interference decreases at one time
when the operation error is again presented to condition the multiplexer 3261 to reproduce the response of the data disconnector 22, as an output signal, the error can be corrected sooner than would be corrected in the other case. The comb-like filter 320 of the NTSC reject of FIG. 11 is good enough to suppress the demodulation artifacts generated in response to horizontal analog television synchronization pulses, as well as to suppress many of the
demodulation artifacts generated in response to the vertical synchronization pulses of analog television and compensation pulses. These artifacts are the co-channel interference with the highest energy. Except where there is a change from scan line to scan line 5 in the video content of the analog television signal during the period of two scan lines, the NTSC reject comb feature filter 320 provides reasonably good suppression of that content in the video regardless of its color. The suppression of
FM audio carrier of the analog television signal is reasonably good, in the case that it has not been suppressed by a tracking reject filter in the symbols sync and compensation circuit 16. The artifacts of most of the over-amplifications
Sudden or analog TV color synchronization pulses are suppressed in the response 320 of the NTSC reject comb feature filter as well. In addition, the filtering provided by the NTSC reject comb feature filter 320 is "orthogonal" to the
NTSC interference rejection integrated in trellis decoding procedures. Figure 12 is a schematic block diagram showing the details of a portion of the digital television signal receiver of Figure 1, 3 or 4, which
uses a type 420 of feature filter 20 on the NTSC reject comb and a species 426 of the post-coding comb characteristic filter 26. The NTSC reject comb feature filter 420 utilizes a first delay device 4201 that exhibits a delay of 5 179,208 symbol times, which delay is substantially equal to the period of 262 horizontal scan lines of an analog television signal and the post-coding comb feature filter 426 uses a second delay device 4261 which also exhibits
such delay. An additive 4202 serves as the first linear combiner in the NTSC reject comb feature filter 420 and a subtractor 4262 of module 8 serves as the second linear combiner in the post-coding comb characteristic filter 426. 15 A species 4261 of multiplexer 261 is controlled by a multiplexer control signal that is in its second state most of the time when it is determined that there is insufficient NTSC co-channel interference to cause an incorrigible error in the
output signal of the data disconnector 22 and which is in its third state most of the time when it is determined that there is sufficient co-channel interference of NTSC, to cause an incorrigible error in the output signal of the data disconnector 22. The receiver of
DTV preferably contains circuits to detect the A field-to-field change in the NTSC co-channel interference, such that the controller 28 can stop the supply of the third state of the control signal of the multiplexer 4261 under such conditions . The multiplexer 4261 is conditioned by its control signal to be in its third state to feed back the results of the sum of the module 8 of the adder 4262 as they are delayed 179,208 epochs of
# symbol through the delay device 4263 to
adder 4262 as a summand. This is a modular accumulation procedure in which a single error is propagated as an operation error, with each error recurring every 179,208 symbol epochs. This spacing of the symbol code is greater than the spacing for a single block
of Reed-Solomon code, such that a single operation error is easily corrected during the decoding of Reed-Solomon. The operation errors in decoding results of post-code symbols of feature filter 426 on comb
Post-coding is reduced by multiplexer 4261 when placed in its first state for the entirety of each data segment containing field synchronization, as well as for four symbol epochs at the beginning of each data segment. When this control signal is
finds in its first state, the multiplexer 4261 reproduces as its output signal the decoding results of ideal symbols supplied from the memory in the controller 28. The introduction of the ideal symbol decoding results to the output signal of the multiplexer 4261 stops an operation error. The maximum number of data fields required to expire the operation error in the output signal of the multiplexer 4261 is substantially the same as is required to overcome the operation error in the output signal of the multiplexer.
3261. However, the number of times the error occurs again in that period is smaller by a factor of 131. The NTSC reject comb feature filter 420 of FIG. 12 suppresses most artifacts from demodulation generated in response to the
vertical sync pulses of analog television and compensation pulses, as well as suppresses all demodulation artifacts generated in response to analog sync pulses. These artifacts are the co-channel interference
with the highest energy. Also, the NTSC reject comb feature filter 420 removes artifacts arising from the video content of the analog television signal that do not change from field to field or line to line, to override the configurations
stationary regardless of their horizontal spatial frequency or color. The artifacts of most abrupt analog TV color overshoots are suppressed in the NTSC reject comb feature filter response 420 as well. Figure 13 is a schematic block diagram showing the details of a portion of the television signal receiver of Figure 1, 3 or 4, which uses a species 520 of the NTSC reject comb characteristic filter 20 and a species 526 of the characteristic 26 filter in post-coding comb. The NTSC reject comb feature filter 520 uses a first delay device 5201 that exhibits a delay of 718,200 times of symbols, which delay is substantially equal to the period of two frames of an analog television signal and the filter 526 of post-coding comb feature uses a second delay device 5261 which also exhibits such a delay. A subtractor 5202 serves as the first linear combiner in the reject comb characteristic filter NTSC 520 and a module addiver 5262 serves as the second linear combiner in the postcode encoding characteristic filter 526. A 5261 sort of multiplexer 261 is controlled by a multiplexer control signal that is in its second state most of the time when it is determined that there is insufficient NTSC co-channel interference to cause an incorrigible error in the output signal of the data disconnector 22 and which is in its third state most of the time 5 when it is determined that there is sufficient co-channel interference of NTSC, to cause an incorrigible error in the output signal of the data disconnect 22. The DTV receiver preferably contains circuits for detecting the change between alternative frames in the NTSC channel interference, such that the controller 28 can stop supplying the third state of the multiplexer control signal 5261 under such conditions. . The multiplexer 5261 is conditioned by its control signal to be in its third state for
feedback the summation results of the module 8 of the adder 5262 as 718,200 symbol times are delayed by the delay device 5263 to the adder 5262 as an addend. This is a modular accumulation procedure in which a single error propagates
as an operation error, with the recurring error every 718,200 times of symbol. This spacing of symbol code is greater than the spacing for a single block of Reed-Solomon code, such that a single operation error is easily corrected during the
decoding of Reed-Solomon. The operation errors in the post-encoded symbol decoding results of the post-coding comb characteristic filter 526 are reduced by the multiplexer 5261 when placed in its first state for the entirety of each data segment it contains. field synchronization, also as for four symbol epochs at the beginning of each data segment. When this control signal is in its first state, multiplexer 5261 reproduces
# as its output signal the decoding results of
ideal symbols supplied from the memory in the controller 28. The input of the decoding results of ideal symbols to the output signal of the multiplexer 5261 stops an operation error. The maximum number of data fields required to expire the error
of operation in the output signal the multiplexer 5261 is substantially the same as is required to expire the operating error in the output signal of the multiplexer 3261. However, the number of times the error occurs again in that period it is smaller by a factor of 525.
The NTSC reject comb feature filter 520 of FIG. 13 suppresses all demodulation artifacts generated in response to vertical analog television sync pulses and compensation pulses, as well as suppresses all artifacts.
of demodulation generated in response to analog horizontal television synchronization pulses. These artifacts are the co-channel interference with the highest energy. Also, the NTSC rejection comb feature filter 520 removes artifacts arising from the video content of the analog television signal that do not change during two frames, to cancel such very stationary configurations regardless of their spatial frequency or color. The artifacts of all abrupt overshoots or analog television color sync pulse are suppressed in the NTSC reject comb feature filter response 520 as well. Those experienced in the television system design technique will be able to discern other correlation and anti-correlation properties in analog television signals that can be exploited in the design of NTSC rejection filters of yet other types than those shown in the figures. 9-13. The use of NTSC reject filters that cascade two NTSC rejection filters of the types already described increase the 2N levels of the baseband signals to data levels (8N-1). Such filters may be required to overcome particularly bad co-channel interference problems despite their disadvantage in reducing the signal to noise for random noise interference with symbol decoding. Figure 14 shows a modification of a digital television signal receiver as heretofore described, constructed in accordance with a further aspect of the invention, to put into operation in parallel a plurality of symbol decoders using f respective disconnectors of level data for each preceded by a different type of characteristic filter
in NTSC reject comb and each followed by a respective post-coding comb characteristic filter to compensate for the precoding introduced by the preceding NTSC reject comb characteristic filter. An even-level data switch A24 converts the response
of an NTSC reject filter A20 of a first type to first decoding results of pre-encoded symbols for application to a post-coding comb characteristic filter A26 of a first type. An even-level B24 data switch converts the response
of a NTSC rejection filter B20 from a second type to second pre-encoded symbol decoding results for application to a post-coding characteristic B26 filter of a second type. An even-level data switch C24 converts the
The response of an NTSC reject filter C20 of a third type to third results and decoding of pre-encoded symbols for application to a post-coding C26 comb filter of a third type. The data splitter 22 of the even level 5 supplies the decoding results of intermediate symbols to the post-coding comb feature filters A26, B26 and C26. The prefixes a, B and C in the identification numbers for the elements of figure 14 f are different integers which will correspond to
the respective integers 1, 2, 3, 4, and 5 when the receiver portions are used as shown in Figures 9-13. The symbol decoding selection circuit 90 in Figure 14 formulates a best estimated value of
decoding of corrected symbols for application to the trellis decoding circuit 34 to select from the decoding results of intermediate symbols received from the data disconnector 22 and the various symbol coding results
postcodes received from the post-coding comb feature filters A26, B26, and C26. The best estimated value of the symbol decoding results are used to correct the summation procedures in the post-25 characteristic coding filters A26, B26 and C26.
Figure 15, which comprises Figures 15A and 15B illustrates in greater detail a currently preferred way to implement the symbol decoding selection circuit 90. Figure 15A shows the details of the circuits for generating the symbol decoding results prescribed for application, during data synchronization intervals, to the main line 800 of output data of 3 bits in width, of the circuits 90 for selection of decoding of symbols. The circuit 15A operates similarly to the circuits described above with reference to FIG. 8. FIG. 15B illustrates in more detail the circuits within the symbol decoding selection circuits 90 to select between the decoding results of intermediate symbols and the various symbols. Decoding results of post-encoded symbols to generate the decoding results of final symbols during periods of time between the data synchronization intervals. The efficiencies of the NTSC reject filters A20, B20 and C20 to separate the NTSC co-channel interference from the DTV signal are determined by observing how well-connected the NTSC A100, B100 and C100 reject filters reduce energy. of the NTSC co-channel interference translated to the baseband and separated from the DTV signal artifacts. The separation of the NTSC co-channel interference from the DTV signal proceeds as previously described with reference to Figure 3. The response of the low pass filter 54, to the baseband video that has been detected in a synchronized manner of the NSTC co-channel interference is supplied as an input signal to the NTSC A100, B100 and C100 rejection filters. The NTSC A100 reject filter differs from the NTSC reject filter A20 of the first type in that the linear combiner type is used, the linear combiner in one of the filters A20 and A100 consists of one adder and the linear combiner in the other of filters A20 and A100 is a subtracter. This is because the A100 filter is powered with baseband video, but the artifact of the NTSC video carrier in the DTV signal supplied to the A20 filter is not in the baseband for the video carrier. For similar reasons, the NTSC reject filter B100 differs from the NTSC rejection filter B20 of the second type since the linear combiner type is used and the NTSC reject filter C100 differs from the NTSC reject filter C20 of the third type since the type of linear combiner is used. The response of the NTSC reject filters A100, B100 and C100 are raised to -quated by quad circuits Al02, B102 and C102 respectively, to determine the energies of these responses. The response of the low pass filter 54 is squared by a quadrant circuit 104 to determine its energy. Figure 15B shows the circuits of Figure 8 modified to replace the multiplexer 2611 and the three-state data buffer 82 with four three-state data buffers 082, A82, B82 and C82. The three-state data buffer 082 is used to selectively assert the decoding results of intermediate symbols of the data disconnector 22 on the main data line 800 of output 3 bits wide of the symbol decoding selection circuit 90. The three three-state data buffers A82, B82 and C82 are used to selectively assert the decoding results of post-encoded symbols of the post-coding comb characteristic filters A26, B26 and C26 respectively, on the main line data 800. It will be determined if any of the response of the NTSC reject filters A100, B100 and C100 has substantially less energy than the response of the low pass filter 54 to determine that one of the three intermediate data memories of three states A82, B82 and C82, instead of the three-state data buffer -JD82, will be conditioned to provide a source of low impedance when the response of gate NI 92 is ONE. If such a determination is made, it will be additionally determined which of the responses of the NTSC reject filters A100, B100 and C100 has the minimum energy remaining in them, to determine which of the three three data buffers of three states 082, A82, B82 and C82 will be conditioned to provide the source of low impedance, when the response of gate NI 92 is ONE. Towards these objectives, the responses of the quadrilateral circuits 104 and A102 are compared by means of a
comparator 106; the responses of the square circuits 104 and B102 are compared by a comparator 108; the responses of the square circuits 104 and C102 are compared by a comparator 110; The responses of the square circuits Al02 and B102 are compared by a
comparator 112; the responses of the square circuits A102 and C102 are compared by a comparator 114; and the responses of the quadrilateral circuits B102 and C102 are compared by a comparator 112. A NI gate with 3 inputs 118 responds to
none of the comparators 106, 108 and 110, indicating that the response of the quadrant circuit 104 exceeds any of the responses of the quadrant circuits A102, B102 and C102 to provide an ONE as an output signal; otherwise, the output signal of the gate
NI 118 is a ZERO. A two-input Y gate 120 • provides a response of ONE that conditions the three three-state data buffers 082 to provide a source of low impedance when and only when the response of the NI 92 gate is UNO 5 at the same time the response of the NI 118 gate is a UNO. A gate Y of 3 inputs, 122 provide an output signal of ONE sensitive to the output of the
* comparator 106 which is a UNO, which indicates that the answer
of the quadrant circuit A102 has lower energy than the response of the quadrant circuit 102 at the same time that the complemented outputs of the comparators 112 and 114 are ONE, indicating that the response of the quadrant circuit 104 has no more power than the responses of the circuits
squares B102 and C102; otherwise, the output signal from gate Y 122 is a ZERO. A gate Y of two inputs 124, provide an ONE response that conditions the three data memories of three states A82 to provide a low impedance source
when and only when gate NI 92 is ONE at the same time that the response of gate Y 122 is a ONE. A 3-input Y gate 126 provides an output signal of ONE responsive to the complemented output of the comparator 116 which is a UNO, which indicates that the
quadrature circuit response B102 does not have more power than the response of the C102 quadrant circuit, while the outputs of comparators 108 and 112 are ONE, indicating that the response of the B102 quadrant circuit has less energy than LOS responses. circuits 5 quadrants 104 and A102; otherwise, the output signal from gate Y 126 is a ZERO. A 2-input Y gate 128 provides an ONE response that conditions the three three-state data buffers B82 to provide a low impedance source when and
only when the response of gate NI 92 is ONE at the same time as the response of gate Y 126 is a ONE. A 3-input Y gate 130 provides an output signal ONE when the outputs of the comparators
, 110, 114 and 116 are all ONE, indicating that the response of the quadrant circuit C102 has lower energy than the responses of the quadrant circuits 104, A102 and B102; otherwise, the gate Y output signal 130 is a ZERO. One Y gate with two inputs 132
provides a response of UNO which conditions the three data memories of three states C82 to provide a source of low impedance when and only when the response of gate NI 92 is ONE at the same time as the response of gate Y 130 is a
ONE.
Referring again to Figure 14, the NTSC reject comb characteristic filter A20 and the post-coding comb feature filter circuits A26 are advantageously chosen in such a way that they are of the filter-like types 520 of feature in NTSC rejection comb and the circuits of the feature filter in post-coding comb 526 of FIG. 13. This is so despite a considerable cost in memory, since 718, 200 symbols
must be stored in each of the delays of 2 video frames 5201 and 5263. (However, storage at the 5201 delay of 2 video frames provides the storage required for the co-channel interference detector A44. Figure 15. In addition, the
The same memory can be used to perform the shorter delays 4201, 3201, 2201, 1201 and the shorter delays in the other co-channel interference detectors of FIG. 15. Also, storage in the 5263 delay of 2 frames of video provides the storage required
for the shorter delays 4263, 3263, 2263, 1263). High-energy demodulation artifacts, generated in response to analog television synchronization pulses, compensating pulses and color color-synchronizing pulses are all
suppressed when the NTSC reject comb characteristic filter A20 combines additive video frames in an additive manner. Also, artifacts that arise from the video content of the analog television signal that do not change during two frames are suppressed, to cancel the stationary settings regardless of their spatial frequency or color. When the NTSC reject comb characteristic filter A20 alternately combines the video frames, the NTSC reject comb characteristic filter A100 differentially combines those alternative video frames and in conjunction with the Al02 quadrant circuit provides a detector for the change between alternative frames in NTSC co-channel interference. The remaining problem of suppressing the demodulation artifacts is concerned mainly with the suppression of those demodulation artifacts that arise from the difference of frame a. box in certain pixel sites within the analog television signal frame. "§gjKu- These demodulation artifacts can be suppressed by intra-frame filtering techniques.The B20 feature filter on NTSC reject comb and the characteristic B26 filter traces on post-coding comb can be chosen to suppress artifacts. The remaining demodulation signals depend on the correlation in the horizontal direction and the characteristic C20 filter on the NTSC rejection comb and the C26 circuits on the post-coding feature filter can be chosen to suppress the remaining demodulation artifacts by relying on the 5 Correlation in the vertical direction Consider how much design decision can be further implemented If the sound carrier of an analog co-channel interference television signal is not suppressed by SAW filtering or a sound trap
in the IF amplifier chain 12, the NTSC reject comb characteristic filter B20 and the post-coding comb characteristic filter B26 circuits are advantageously chosen such that they are of the type similar to the characteristic filter 120
NTSC reject comb and the circuits of the post-coding characteristic feature filter 126 of FIG. 9. If the sound carrier of a co-channel analog interference television signal is suppressed by SAW filtering or a trap of sound on the chain 12 amplifier
of IF 12, the characteristic B20 filter in NTSC rejection comb and the characteristic filter circuits B26 in post-coding comb are advantageously chosen in such a way that they are types similar to the comb characteristic filter 220 of rejection of NTSC and
the circuits of the post-coding comb feature filter 226 of FIG. 10. This is because the anti-correlation between the video components of only six times of symbols with each other is usually better than the correlation between the components of the video. video of twelve eras of 5 symbols separated from each other. The optimal choice of the characteristic comb filter C20 of the NTSC rejection and the L circuits of the characteristic C26 filter in the post-coding comb is less direct, due to the choice to be made (in consideration of the field lattice in the analog interference television signal) of whether to choose the temporarily closest sweep line in the same field or the spatially closest line in the preceding field to be combined with the current sweep line 15 in the NTSC reject comb characteristic filter C20. By choosing the closest sweep line temporarily in the same field, it is generally the best choice, since the jump cuts between the fields are less likely to destroy the NTSC reject by the comb characteristic filter C20. With such a choice, the NTSC reject comb characteristic filter C20 and the post-coding comb characteristic filter C26 circuits are types similar to the NSTC reject comb filter 320 and the 25 filter circuits 326 of the post-coding comb feature of Figure 11. When the NTSC reject comb characteristic filter C20 addively combines the alternative video scan lines, the NTSC reject comb characteristic filter C100 5 it differentially combines those alternative video scan lines and together with the C102 quadrant circuit provides a detector for switching between alternative scan lines in the NTSC co-channel interference. 10 With the other choice, instead of this, the filter
Feature C20 on NTSC rejection comb and C26 filter circuits for post-coding comb are of types such as NTSC reject comb feature filter 420 and circuits
of the post-coding comb characteristic filter 426 of FIG. 12. The NTSC reject comb characteristic filter C100 and the C102 quadrant circuit together provide a detector for switching between the fields in the interference
NTSC co-channel. In Figure 14, the digital receiver apparatus is modified in still other embodiments of the invention to use additional parallel data sectioning operations, each carried out by means of a connection
in cascade of a respective NTSC reject filter followed by a respective even level level data switch followed by a respective post-coding comb characteristic filter. While two additional parallel data sectioning operations are shown in Figure 14, modifications to use additional parallel data sectioning operations may provide ability to refine the best estimate value of the symbol decoding result still further corrected. The circuits 34 of the trellis decoder can be replicated and the relative success of various symbol decoding decisions can be compared to refine the best estimate value of the symbol decoding result in addition. However, this involves considerably more digital physical elements. In certain embodiments of the invention alternatives to those previously described, the symbol decoding selection circuits 90 include voting circuits for scrutinizing the symbol codes supplied from the odd-level data switch 22, the characteristic filter A26 in the post-coding comb of the first type, the characteristic B26 filter in the post-coding comb of the second type and the characteristic C26 filter in the post-coding comb of the third type. If all four of the symbol decoding results concur, the symbol decoding result to be concurred will be supplied to the data assembler 30. If the 5 symbol decoding results supplied from the odd level data disconnector 22, the characteristic filter A26 in post-coding comb of the first type, characteristic filter B26 in post-coding comb of the second type and filter C26 of
The post-coding comb characteristic of the third type does not concur and a simple voting procedure is carried out by the voting circuits to select that the least likely decoding result is an error. A more accurate symbol decoding will be
obtained if the time of a weighted voting procedure is followed in the voting circuit. The weights of the votes can be modified to take into account the variances of the decoding results, to reduce the weight according to a decoding result in the
The method of voting if it deviates from a decoding result concurred by a majority of the other symbol decoding circuits. By using circuits similar to some of the circuits shown in Figure 15B and some additional circuits, the
weightings of the votes can also be determined in # inverse relations to the energy measurements generated by the quadrillion circuit 104, by means of the filter Al00 of rejection comb NTSC and the quadrilateral circuit A102 by means of the filter B100 of characteristic in 5 comb of NTSC rejection and the B102 square circuit and by the NTSC reject comb characteristic C100 filter and the C102 square circuit. Co-channel interference by analog television signals from standards other than
NTSC, as in the PAL standard, may arise from digital television systems adapted from the digital television system used for terrestrial transmission in the United States of America. The invention is easily modified as a single question of
design paxa accommodate to such csg-channel interference. Those skilled in the art of designing the digital communications receiver and familiar with the above specification and drawings will have the ability to design many embodiments of the invention other than those specifically preferred and described. This should be borne in mind when interpreting the scope of the appended claims. In the claims that follow, the word "said" is used whenever reference is made to an antecedent, and the word "he or she" is used for grammatical purposes different from that referred to in an antecedent. It is noted that, with regard to this date, the best method known to the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following •
Claims (28)
- # Claims 1. A method of symbol decoding of a stream of 2N level symbols, each having a time of symbols of a specified duration of time, the symbol current of level 2N is capable of being accompanied by signal artifacts of analog co-channel interference television, N is a positive integer, the method generates decoding results of selected symbols, and is characterized in that it comprises the 10 stages of: filtering by a comb characteristic filter, the symbol current of level 2N to generate a comb characteristic filter response with pre-coded level symbols (4N-1) from which any of the artifacts of the analog co-channel interference television signal are suppressed, the filtering stage in comb characteristic filter includes the sub-stages of: retarding the current of 2N level symbols by 20 a num The prescribed time of symbol times to generate a 2N level symbol current and linearly combine current xle 2N level symbols and delayed current of 2N symbol symbols, according to one of the additive procedures and 25 subtraction, to generate first linear combination results as the responses of the comb characteristic filter with pre-coded level symbols (4N-1); sectioning the response data of the comb characteristic filter with the pre-coded symbols of the 5 level (4N-1) to generate the pre-encoded symbol decoding results; delay the decoding results of selected symbols by the prescribed number of symbol epochs to generate the results of 10 decoding of selected delayed symbols; linearly combining the decoding results of pre-encoded symbols with the results - of decoding of selected delayed symbols to generate second results of combinations 15 linear; the step of linearly combining the decoding results of pre-encoded symbols with the decoding results of selected delayed symbols is carried out in accordance with procedures 20 opposed to the addition and subtraction procedures of the addition and subtraction procedures used in the sub-step of linearly combining the current of 2N level symbols and the delayed current of 2N level symbols to generate the first linear combination results, 25 the procedures opposite to the procedures of addition # and subtraction are carried out according to a modular arithmetic; determining when the symbol coding descriptive of the synchronization data is presented in the symbol stream of level 2N; regenerating the synchronization data without error when the symbol coding descriptive of the synchronization data is presented in the current of the 2N level symbols; and 10 generating the decoding results of selected symbols to correspond with the synchronization data without error when the symbol coding descriptive of the synchronization data is presented in the stream of 2N level symbols and to correspond to 15 the second linear combination results for at least selected time when the symbol coding which is not descriptive of the synchronization data is presented in the 2N level symbol stream.
- 2. The symbol decoding method according to claim 1, characterized in that it is included in a symbol decoding method of the symbol stream of level 2N, to generate results of decoding of final symbols, in which 25 analog channel signal artifacts of co-channel #interference are automatically suppressed during decoding of symbols, the method for generating the decoding results of final symbols is characterized in that it further includes the steps 5 of: sectioning the data of the 2N level symbol stream to generate intermediate symbol decoding results; determine if the symbol current level 2N 10 is accompanied or not by signal artifacts of analogous co-channel interference selection that are of sufficient intensity to cause substantial error in the intermediate symbol decoding results; including the decoding results of intermediate symbols in the final symbol decoding results, sensitive to the determination that the 2N level symbol stream is not accompanied by co-channel analog television signal artifacts that are sufficient intensity to cause substantial error in the intermediate symbol decoding results; and in response to the determination that the 2N level symbol stream is accompanied by analog interference signal television signal artifact. 25 co-channel which are of sufficient intensity to cause a substantial error in the decoding results of intermediate symbols which cause the final symbol coding results to correspond to the decoding results of selected symbols.
- 3. The method for generating decoding results of final symbols according to claim 2, characterized in that in response to a determination that the 2N level symbol stream is not accompanied by television signal artifacts. 10 analog co-channel interference which are of sufficient intensity to cause substantial error in the intermediate symbol decoding results, the intermediate symbol decoding results are included in the final symbol decoding results 15 only during the selected times when the symbol coding is presented which is not descriptive of the synchronization data in the 2N level symbol stream; and where an additional step of: causing the decoding results of 20 end symbols correspond to the synchronization data without error, when the symbol coding is presented which is descriptive of the synchronization data in the 2N level symbol stream.
- 4. The method to generate the results of Decoding of final symbols according to claim 3, characterized in that the step of determining whether or not the 2N level symbol stream is accompanied by co-channel interference analog television signal artifacts. sufficient intensity to cause substantial error in the decoding results of intermediate symbols, which comprise the steps of sub-steps of: differentially combining the decoding results of intermediate-symbols and the second ones 10 linear combination results to generate a difference signal; determine the energy of the difference signal; and detect when the energy of the difference signal exceeds a prescribed threshold value, to 15 thereby determining, that the 2N level symbol stream is accompanied by analog co-channel interference television signal artifacts that are of sufficient intensity to cause substantial error in the intermediate symbol decoding results; and detect when the energy of the difference signal does not exceed the prescribed threshold value, thereby determining that the symbol current level .2N is not accompanied by co-channel analog television signal artifacts that are of sufficient intensity to cause substantial error in the decoding results of intermediate symbols.
- 5. The method for generating decoding results of final symbols according to claim 3, characterized in that the step of determining whether or not the symbol current level 2N is accompanied by analog interference signal television artifacts channels that are of sufficient intensity to cause substantial error in the results of intermediate symbol decoding, which comprises the sub-steps of: differentially combining the intermediate symbol decoding results and the second linear combination results to generate a difference signal; squaring the difference signal to generate a squared difference signal; generate an average of the difference signal squared; 20 detecting when the average exceeds a prescribed threshold value, thereby determining that the 2N level symbol stream is accompanied by co-channel analog television signal artifacts that are of sufficient intensity to cause substantial error in the decoding results of intermediate symbols; and detecting when the rectified low pass filtering response does not exceed the prescribed threshold value, 5 to thereby determine that the 2N level symbol stream is not accompanied by co-channel interference analog television signal artifacts. are of sufficient intensity to cause substantial error in the * decoding results of intermediate symbols.
- 6. The method for generating final symbol decoding results according to claim 2, characterized in that it is used with a digital television receiver that generates the 2N level symbol current by means of demodulation of digital signals. 15 intermediate amplified frequencies, which intermediate frequency signals are generated by frequency conversion of digital television signals, where the stage of determining whether the current of 2N level symbols is accompanied by analog television signal artifacts 20 of co-channel interference that are of sufficient intensity to cause substantial error in the intermediate symbol decoding results, comprising the sub-steps of: * generating intermediate frequency signals by frequency conversion of the digital television signals; amplifying the intermediate frequency signals 5 to supply amplified intermediate frequency signals; detecting in a synchronized manner the amplified intermediate frequency signals at a video carrier frequency of the analog television signal of co-channel interference, in a complex demodulation process to generate synchronized video detection responses in phase and in phase quadrature; separating a video component from the analog television signal of co-channel interference from the synchronized video responses in phase and quadrature phase; determining the energy of the video component separated from the analog television signal of co-channel interference; 20 detecting when the energy of the video component separated from the analog co-channel interference television signal exceeds a prescribed threshold value, thereby determining that the 2N level symbol stream is accompanied by signal artifacts of 25 analogous co-channel interference television which are of sufficient intensity to cause substantial error in the intermediate symbol decoding results; and detecting when the rectified low pass filtering response does not exceed the prescribed threshold value, 5 to thereby determine that the 2N level symbol stream is not accompanied by co-channel interference analog television signal artifacts. they are of sufficient intensity to cause substantial error in the decoding results of intermediate symbols.
- 7. The method for generating decoding results of final symbols according to claim 2, characterized in that it is used with a digital television receiver that generates the 2N level symbol current by means of demodulation of digital signals. 15 intermediate frequencies, which signals of intermediate frequency are generated by frequency conversion of digital television signals, where the stage of determining whether or not the current of symbols of level 2N is accompanied by television signal artifacts Analogous co-channel interference which are of sufficient intensity to cause substantial error in the intermediate symbol decoding results, comprising the sub-steps of: '' generating intermediate frequency signals by frequency conversion of the digital television signals; amplify intermediate frequency signals 5 for supplying amplified intermediate frequency signals including the modulated audio and video carriers of the analog co-channel interference television signal; detect an intercarrier sound signal 10 sensitive to the heterodyne mixture between the modulated audio and video carriers of the analog co-channel interference television signal included in the amplified intermediate frequency signals, determine the energy of the intercarrier sound signal 15; detecting when the intercarrier sound signal energy exceeds a prescribed threshold value, thereby determining that the 2N level symbol stream is accompanied by co-channel analog signal television signal artifacts that are of intensity sufficient to cause substantial error in the intermediate symbol decoding results; and detect when the energy of the intercarrier sound signal does not exceed the prescribed threshold value, for 25 thereby determining that the 2N level symbol stream is not accompanied by co-channel analog television signal artifacts that are of sufficient intensity to cause substantial error in the decoding results of intermediate symbols.
- 8. The symbol decoding method according to claim 1, characterized in that the sub-step of linearly combining the 2N level symbol current and the 2N level symbol delay current in the comb filter characteristic filter step is a subtractor method, and wherein the step of linearly combining the decoding results of pre-encoded symbols with the decoding results of selected delayed symbols is an additive procedure carried out in a 2N module arithmetic.
- 9. The symbol decoding method according to claim 8, characterized in that the prescribed number of symbol epochs is twelve.
- The symbol decoding method according to claim 1, characterized in that the sub-step of linearly combining the 2N level symbol current and the 2N level symbol delay current in the comb filter characteristic filter step is an additive method, and wherein the step of linearly combining the decoding results of pre-encoded symbols * with the decoding results of selected delayed symbols is a subtraction procedure carried out in a 2N module arithmetic.
- 11. The symbol decoding method according to claim 10, characterized in that the prescribed number of symbol epochs is six.
- The symbol decoding method according to claim 10, characterized in that the prescribed number of symbol epochs is substantially 10 equal to the duration of two horizontal scan lines of the analog television signal of co-channel interference.
- The method of decoding symbols according to claim 10, characterized in that the prescribed number of symbol epochs is substantially 15 equal to the duration of two hundred and sixty-two horizontal scan lines of the analog television signal of co-channel interference.
- 14. The symbol decoding method according to claim 10, characterized in that 20 the prescribed number of times of symbols is substantially equal to the duration of two video frames of the analog television signal of co-channel interference.
- 15. In combination: a digital television signal detection apparatus 25 for supplying a stream of 2N level symbols having each, a symbol time of a specified time duration, which current is likely to be accompanied by artifacts Analog television signal of co-channel interference; 5 a first delay device for displaying a delay of the first prescribed number of symbol times, connected to respond to the symbol current of level 2N with a first delay current of 2N level symbols, to thereby generate a first pair of streams 10 differentially delayed from 2N level symbols; a first linear combiner which linearly combines the first pair of differentially delayed currents of the 2N level symbols susceptible to being accompanied by artifacts of a television signal Analogous co-channel interference received as first and second respective input signals of the first linear combiner, to generate a first current of level symbols (4N-1) as an output signal of the first linear combiner, the first current of symbols of 20 level (4N-1) provides a first response of the filter in comb characteristic, in which the artifacts of the analog co-channel interference television signal are suppressed; a first data disconnector that decodes the The first level symbol stream (4N-1) supplied * as a respective output signal of the first linear combiner, for generating first decoding results of pre-encoded symbols; a second linear combiner which combines linearly first and second respective input signals received, to thereby provide a respective output signal thereof, the second linear combiner is connected to receive the first decoding results of pre-encoded symbols As the first respective input signal thereof, one of the first and second linear combiners consists of one adder and the other of the first and second linear combiners consists of a subtracter; a second delay device connected to recharge a respective input signal thereof, the first prescribed number of symbol epochs to generate the second input signal of the second linear combiner; data synchronization circuits for determining when the symbols used for data synchronization appear in the 2N level symbol stream; circuits for generating ideal symbol decoding results when it is determined that the symbols used for data synchronization appear in the 2N level symbol stream; a first multiplexer of several inputs joined to supply a respective output signal thereof to the second delay device as the second input signal thereto, to receive the results of decoding of ideal symbols as a first of its input signals and to receive the output signal of the second linear combiner as another of its input signals, the first multiplexer is conditioned to reproduce as its output signal the first of its signals 10, when and only when it is determined that the symbols used for data synchronization appear in the 2N level symbol stream and otherwise is conditioned at least at selected times to reproduce the output signal of the second linear combiner 15 as the first results of decoding of post-encoded symbols.
- 16. The combination according to claim 15, characterized in that it further comprises: a second data disconnector that decodes the 20 symbol level 2N current to generate the decoding results of intermediate symbols supplied to the first multiplexer as a second input signal thereof, the output signal of the second linear combiner is supplied to the first multiplexer as 25 a third input signal thereof; and * an NTSC co-channel interference detection circuit to determine whether or not the 2N level symbol current is accompanied by co-channel analog television signal artifacts that will cause an incorrigible error in the results. of decoding intermediate symbols generated by the second data disconnector, the first multiplexer is conditioned to reproduce the second of its signals of | input when the interference detection circuit of The NTSC co-channel determines that the 2N level symbol stream is not accompanied by analog television signal artifact of co-channel interference that will cause an incorrigible error in the intermediate symbol decoding results, and the first multiplexer is conditioned to reproduce the third of its input signals when the NTSC co-channel interference detection circuits determine that the 2N level symbol stream is accompanied by analog signal television signal artifacts. 20 co-channel interference that will cause an incorrigible error in the decoding results of intermediate symbols.
- The combination according to claim 16, characterized in that it further comprises: a third delay device for displaying a delay of a second prescribed number of symbol times, connected to respond to the current of 2N level symbols with a second current delay of symbols of 5 level 2N, to thereby generate a first pair of differentially delayed currents of the level 2N symbols; a third linear combiner which linearly combines the second pair of delayed currents 10 differentially of the level 2N symbols susceptible to being accompanied by artifacts of a co-channel analog interference television signal, received as the first and second respective input signals of the third linear combiner, to generate a second current 15 of level symbols (4N-1) as an output signal of the third linear combiner, the second level symbol stream (4N-1) provides a second filter response in comb characteristic, in which the artifacts of the Analog television signal of co-channel interference are suppressed; a fourth linear combiner which linearly combines the respective first and second input signals received, to thereby supply a respective output signal thereof, to the first multiplexer as 25 an additional input signal thereof, one of the * third and fourth linear combiners consists of one additioner and the other of the first and second linear combiners consists of a subtracter; a third data switch that decodes the second stream of level symbols (4N-1) supplied as a respective output signal of the third linear combiner, to generate second decoding results of pre-encoded symbols applied to the fourth linear combiner as the first respective input signal of the 10 same; and a fourth delay device connected to delay the output signal of the first multiplexer, the second prescribed number of symbol epochs to generate the input signal of the fourth linear combiner.
- 18. The combination according to claim 15, characterized in that the first multiplexer is a two-input multiplexer conditioned to reproduce the other of its input signals as its output signal when it is not conditioned to reproduce 20 the first of its input signals as its output signal, the combination further comprises: a second data switch that decodes the 2N level symbol stream to generate the decoding results of intermediate symbols 25 supplied to the first multiplexer as a second input signal thereof, the output signal of the second linear combiner is supplied to the first multiplexer as a third input signal thereof; and NTSC co-channel interference detection circuits to determine whether or not the 2N level symbol current is accompanied by analog co-channel interference television signal artifacts that will cause an incorrigible error in the decoding results. of intermediate symbols generated by 10 the second data disconnector; a second multi-input multiplexer, connected to supply a respective output signal thereof which reproduces a respective input signal thereof as a result of decoding of final symbols 15 to receive the decoding results of intermediate symbols as a first input signal thereof and to receive the output signal of the first multiplexer as another input signal thereof, the multiplexer is conditioned to reproduce the first of its signaling signals. 20 when and only when the NTSC co-channel interference detection circuit determines that the 2N level symbol stream is not accompanied by co-channel analog television signal artifacts which will cause an incorrigible error in the 25 decoding results of - intermediate symbols and the second multiplexer is conditioned to reproduce the other input signal thereof when the NTSC co-channel interference detection circuit determines that the 2N level symbol stream is accompanied by 5 artifacts of analog television signal of co-channel interference that will cause an incorrigible error in the decoding results of intermediate symbols.
- 19. The combination according to claim 15, characterized in that the first combiner 10 linear is a subtracter and the second linear combiner is a 2N modifier.
- 20. The combination according to claim 19, characterized in that the first prescribed number of symbol epochs is twelve.
- 21. The combination according to claim 15, characterized in that the first linear combiner is an adder and the second linear combiner is a subtractor of module 2N.
- 22. The combination according to claim 21, characterized in that the first prescribed number of symbol epochs is six.
- 23. The combination according to claim 21, characterized in that the first prescribed number of times of symbol is substantially equal to 25 number of symbol times in two horizontal scan lines * of the analog co-channel interference television signal.
- 24. The combination according to claim 21, characterized in that the first number 5 prescribed symbol times is one thousand three hundred and sixty-eight.
- 25. The combination according to claim 21, characterized in that the first prescribed number of times of symbol is substantially equal to 10 number of symbol times in two hundred and sixty-two horizontal scan lines of the analog co-channel interference television signal.
- 26. The combination according to claim 21, characterized in that the first number 15 prescribed of times of symbol is one hundred and seventy-nine thousand two hundred and eight.
- 27. The combination according to claim 21, characterized in that the first prescribed number of times of symbols is substantially equal to 20 number of times of symbols in two video frames d the analog television signal of co-channel interference.
- 28. The combination according to claim 21, characterized in that the first prescribed number of times of symbols is seven hundred and eighteen thousand 25 two hundred. # Summary of the Invention The co-channel interference accompanying multi-level symbols in a digital receiver, such as a digital television receiver, is described which is suppressed by using a first comb characteristic filter to reduce the energy of co-channel interference before data sectioning. The first comb characteristic filter • incidentally pre-encodes decoding results for symbols generated by 10 the data sectioning. A second comb characteristic filter post-encodes decoding results of pre-encoded symbols from data sectioning to generate corrected symbol decoding results. The pre-coding 15 of symbols of the input symbol stream results from the differential delay and the first linear combination of the differentially delayed terms. The postcoding of the symbol stream recovered by the data sectioning results from the second combination Linear of the symbol stream with the delayed result of the second linear combination and is carried out according to a modular arithmetic. One of the first and second linear combinations is subtraction and the other is addition. The results of the second linear combination are the results of decoding of corrected symbols.
Publications (1)
| Publication Number | Publication Date |
|---|---|
| MXPA98005806A true MXPA98005806A (en) | 2000-01-01 |
Family
ID=
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US7038732B1 (en) | DTV signal with GCR components in plural-data-segment frame headers and receiver apparatus for such signal | |
| US5748226A (en) | Digital television receiver with adaptive filter circuitry for suppressing NTSC co-channel interference | |
| US6057877A (en) | NTSC interference detectors using pairs of comb filters with zero-frequency responses, as for DTV receivers | |
| US5835131A (en) | Digital television receiver with adaptive filter circuitry for suppressing NTSC co-channel interference | |
| JPH10276375A (en) | Design method for ntsc elimination filter with unchanged level number and receiver adopting it | |
| US5995135A (en) | Digital television receiver with adaptive filter circuitry for suppressing NTSC Co-channel interference | |
| US5801759A (en) | Digital TV receiver circuitry for detecting and suppressing NTSC co-channel interference | |
| US6480233B1 (en) | NTSC co-channel interference detectors responsive to received Q-channel signals in digital TV signal receivers | |
| KR100246767B1 (en) | A digital tv signal using special ntsc receiver to detect when co-channel interfering ntsc signal from auxiliary analog tv receivers for detecting ntsc interference in digital tv receivers | |
| KR100557122B1 (en) | A receiver for dtv signals subject to co-channel ntsc interference and method of operating therefor | |
| KR100392681B1 (en) | Method of formatting signal for dtv with gcr components in plural-data-segment frame headers and receiver apparatus for such signal | |
| US6023306A (en) | NTSC interference detectors using comb filters that suppress digital TV pilot carrier for NTSC extraction | |
| US6201564B1 (en) | Method of operating the channel equalizer in a receiver for DTV signals subject to co-channel NTSC interference | |
| US6400393B1 (en) | DTV receiver with filter in I-F circuitry to suppress FM sound carrier of NTSC Co-channel interfering signal | |
| US6188441B1 (en) | Detection of PN sequences accompanying VSB signal to control operating mode of QAM/VSB DTV signal receiver | |
| JP3755990B2 (en) | Digital TV receiver with adaptive filter circuit for suppressing NTSC co-channel interference | |
| KR100260422B1 (en) | Digital television signal receiver | |
| MXPA98005806A (en) | Digital television receiver with adapter filter circuits to remove the n deco-channel interference | |
| CA2267679C (en) | Ntsc co-channel interference detectors responsive to received q-channel signals in digital tv signal receivers | |
| CA2241590C (en) | Digital tv receiver circuitry for detecting and suppressing ntsc co-channel interference | |
| CA2241067C (en) | Digital television receiver with adaptive filter circuitry for suppressing ntsc co-channel interference | |
| AU702137B1 (en) | Digital television receiver with adaptive filter circuitry for suppressing NTSC co-channel interference | |
| KR100288290B1 (en) | Dtv receiver with adaptive filter circuit for rejecting ntsc co-channel interference and symbol decoding method thereof | |
| KR100246916B1 (en) | Dtv receiver with filter in i-f circuitry to suppress fm sound carrier of ntsc co-channel interfering signal | |
| KR100273762B1 (en) | An image signal receiver taking vsb modulation mode and method for choiceing level mode in the receiver |