I Umted States Patent [19]
`Wei
`
`US005243629A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,243,629
`Sep. 7, 1993
`
`[54] MULTI-SUBCARRIER MODULATION FOR
`HDTV TRANSMISSION
`_
`[75] Inventor: Lee-Fang Wei, Lmcroft, NJ.
`.
`[73] Asslgnee: AT&T Bell Laboratories, Murray
`Hm, N_J_
`
`[211 App]. 190.: 753,491
`[22] Filed:
`sep. 3’ 1991
`
`[5
`
`Cl-S ................... ..
`
`H04L 27/20
`[52] U.S. Cl. ...................................... .. 375/59; 375/38;
`375/ 100; 375/ 102; 371/ 371; 371/ 43
`[58] Field of Search ................... .. 375/27, 38, 40, 100,
`375/102, 58, 59; 370/691, 71, 73; 371/43, 37.1;
`455/8
`
`[561
`
`_
`Refarences Cited
`U.S. PATENT DOCUMENTS
`
`3,988,679 10/1976 Clarkeet a1. ...................... .. 375/ 102
`4’613’975 9/1986 APYagI et a1‘
`"" " 375/102
`4,622,680 11/1986 Zmser . . . . . . . . . . .
`. . . . . .. 375/38
`4,715,048 12/1987 Masamura ................. .. 375/100
`4,831,636 5/1989 Taniguchi et a1. .......... .. 375/27
`4,868,851 9/1989 Trinidad et a]. ..
`375/40
`4,890,283 12/1989 Tsinberg et a1. ................ .. 375/27
`
`4,903,126 2/1990 Kassatly ........................... .. 370/69.1
`4,935,940 6/1990 Reindl ............................... .. 375/100
`4,980,897 12/1990 Decker et a1. ...................... .. 375/38
`
`OTHER PUBLICATIONS
`_
`_
`3
`Co-pendmg applicanon V. B. Lawrence et a1, Ser. No.
`07/611,225 ?led Nov. 7, 1990,_ entitled “Coding for
`Digital Transmission”.
`Co-pending application L. -.F. Wei, Ser. No.
`07/611,200 ?led Nov. 7, 1990, entitled “Coded Modula
`Error Protection”_
`Co-pending application J. D. Johnston et a1, Ser. No.
`07/625349 ?led Dec_ 11, 1990, entitled "A High Ddmi
`tion Television Coding Arrangement with Graceful
`Degmdationq
`_
`_
`_
`Primary Examiner-Curtis Kuntz
`Assistant Examiner-Don N. V0
`Attorney, Agent, or Firm-Henry T. Brendzel
`[57]
`ABSTRACI‘
`
`A high de?nition television (HDTV) Signal is transmit_
`ted by a multi-subcarrier transmission scheme in which
`h b
`.
`.
`d t
`d.ff
`1
`f
`ea° “Farmer .15 “Se
`° carry a ‘ “em “55 0
`HDTV mfc’matm
`
`24 Claims, 4 Drawing Sheets
`
`TRANSMITTER m
`
`LESS IMPORTANT DATA
`
`MORE IMPORTANT DATA
`
`O I‘
`
`I2
`
`I3
`
`a I
`f8
`In
`
`fol“ )
`1
`
`101
`2
`
`“M0 .6.
`516m
`SOURCE
`SOURCE
`ENCODER
`
`F131- ---------- ’‘1 ‘51X
`1
`N
`“I w
`1
`105
`1.535559%’, 3‘
`\ r" , I
`CHANNEL '“1"'1 consnumou I
`I1
`I11I 'L_E_NCODER
`__!APPER J
`=
`---=---------=---
`LESS
`IMPORTANT
`f 123'\
`I43'\
`1, WBQSEBAND
`DATA
`,
`1
`CHANNEL
`cousnumon +_,“°DULmR
`L
`(
`m’; I
`ENCODER
`MAPPER
`I3
`i
`ms'i‘rs
`13
`I
`L-------_ _____ ---|
`-
`‘BAND
`"-__:"'T1-_+F___":___"
`I.
`“ODUWOR
`:
`CHANNEL
`'
`' CONSTELLATION '
`mi I
`ENCOOER w“ {i
`“——-.--—-—————.—-—J
`=
`————- -—-———'——— I68
`i 128\
`H8“
`1
`B‘SEBAND
`1
`CHANNEL
`CONSTELLATION WWW“
`I
`I
`ENCODER
`MAPPER
`1
`I
`mai’l'a
`I
`L---.---------.---J
`
`MORE
`IMPORTANT
`0111
`1118
`
`1
`
`IT?” “HR-“'1 “21351110
`
`CHANNEL
`l
`CONSTELLATION
`m
`I mom
`MAPPER H'?owmoR
`1 k=12|
`m H
`1
`'12
`L _____ -LLLZ ____ ___|
`22
`
`‘2
`
`195
`
`r
`,
`555
`MODULATOR
`
`2
`
`‘75
`
`\
`,5
`
`2;’
`
`8mm“ -
`911mm
`
`Page 1 of 10
`
`

`
`U.S. Patent
`
`Sep. 7, 1993
`
`Sheet 1 of 4
`
`5,243,629
`
`35.
`
`3
`
`m.N.__9
`
`
`
`E3=§o.=._:2.
`
`53250.3.as
`
`asstanza:x65%
`
`SN
`
`massN5s<a._
`
`am
`
`§:a§.
`
`Page 2 of 10
`
`Page 2 of 10
`
`

`
`U.S. Patent
`
`Sep.7,1993
`
`Sheet 2 of 4
`
`5,243,629
`
`5522...
`
`szzsa
`
`.
`
`
`
`5:...$552:
`
`325222
`
`am5::§.a§_
`
`._
`
`*
`
`5::W
`2.32;
`
`__
`
`
`
`E5:mms_e§_
`
`am$>_§¢
`
`N65%
`
`._z§£_
`
`53322
`
`ozémg
`
`mesaofi.
`
`ozéua
`
`~_oS_§§_
`
`.332.
`
`§s=8a__
`
`ez<$§
`
`$3222
`
`Sm
`
`Eu
`
`2%..
`
`Page 3 0f10
`
`Page 3 of 10
`
`
`
`
`
`
`
`
`
`

`
`US. Patent
`
`Sep.7,1993
`
`Sheet 3 of 4
`
`5,243,629
`
`Q
`
`l - - - _
`
`i. \ E a.‘ a: c
`
`a; <55 22>
`a; a;
`E55 :8 555
`
`>32.
`
`m. .Qhm
`
`
`
`
`
`<23 256%: mm:
`
`Page 4 of 10
`
`

`
`US. Patent
`
`Sep. 7, 1993
`
`Sheet 4 of 4
`
`5,243,629
`
`FIG. 5
`
`FIG. 6
`
`4 DAN SIGNAL GONSTEUATION
`
`I2 QAN SIGNAL CONSTELLATION
`
`I I6 OAN SIGNAL CONSTELLATION
`
`Page 5 of 10
`
`

`
`1
`
`MULTI-SUBCARRIER MODULATION FOR HDTV
`TRANSMISSION
`
`5
`
`O
`
`20
`
`BACKGROUND OF THE INVENTION
`The present invention relates to the transmission of
`digital data, particularly the transmission of digital data
`that represents video signals.
`It is generally acknowledged that some form of digi
`tal transmission will be required for the next generation
`of television (TV) technology, conventionally referred
`to as high de?nition television, or HDTV. This require
`ment is due mostly to the fact that much more powerful
`video compression schemes can be implemented with
`digital signal processing than with analog signal pro
`cessing. However, in any HDTV digital transmission
`system, there are three major areas of concern that have
`to be addressed: graceful degradation, NTSC (National
`Television System Committee) co-channel interference
`and ghost cancellation.
`A number of co-pending, commonly assigned United
`States patent applications disclose various techniques
`that provide graceful degradation in the reception qual
`ity at a TV set location. There are: V. B. Lawrence et
`al. entitled “Coding for Digital Transmission,” Ser. No.
`07/6ll,225, ?led on Nov. 7, 1990; L.-F. Wei entitled
`“Coded Modulation with Unequal Error Protection,”
`Ser. No. 07/6ll,200, ?led on Nov. 7, 1990; J. D. John
`ston et al. entitled “A High De?nition Television Cod
`ing Arrangement with Graceful Degradation,” Ser. No.
`07/625,349, ?led on Dec. 11, 1990; and H. Y. Chung et
`al. entitled “Multiplexed Coded Modulation with Un
`equal Error Protection,” Ser. No. 07/627,156, ?led on
`Dec. 13, 1990. The Lawrence et al. patent application,
`for example, teaches the notion of characterizing the
`HDTV signal into classes of “more important” and
`“less important” information, which will then use a
`constellation of non-uniformly spaced signal points.
`This approach provides unequal error protection, i.e.,
`more error protection for the more important informa
`tion, and allows a graceful degradation in reception
`quality at the TV set location because, as the bit-error
`rate at the receiver begins to increase with increasing
`distance from the broadcast transmitter, it will be the
`bits that represent proportionately less of the TV signal
`information that will be the ?rst affected.
`However, although the above-mentioned patent ap
`plications teach advantageous techniques for providing
`unequal error protection to different classes of informa
`tion, these approaches primarily address the problem of
`50
`providing graceful degradation for an HDTV signal in
`a single carrier transmission environment and do not
`address the problems of NTSC co-channel interference
`and ghost cancellation.
`NTSC co-channel interference is a result of the fact
`that any HDTV transmission scheme will co-exist with
`existing NTSC TV transmission schemes and will use
`the available NTSC frequency spectrum, or channel
`assignments. For example, in the New York City geo
`60
`graphical area an HDTV television station may be as
`signed to broadcast on channel 3. However, there may
`also be an NTSC television station assigned to channel
`3 in a neighboring geographical area such as Philadel
`phia. As a result, there will be parts of New Jersey that
`receive both the HDTV and NTSC television signals
`assigned to channel 3. This results in a geographical
`region of overlap of the NTSC and HDTV transmission
`signals in which the -NTSC and HDTV signals interfere
`
`5,243,629
`2
`with each other. To reduce the interference from the
`HDTV signal to the existing NTSC signal, the transmit
`ted power of the HDTV signal should be set at a value
`at least 10 dB below that of the NTSC signal so that the
`HDTV signal does not interfere with the NTSC signal.
`As a result, the HDTV signal is even more susceptible
`to interference from the NTSC signal. This NTSC in
`terference must be reduced in order to ensure that the
`coverage area of the HDTV signal is large enough.
`Finally, there is the problem of ghost cancellation. In
`any TV transmission scheme, re?ection of the transmit
`ted signal may occur that results in ghosting, which
`generally manifests itself in the form of double images.
`However, the problem of ghosting is compounded in an
`HDTV transmission scheme because of the use of com
`pression algorithms to squeeze it full-bandwidth HDTV
`signal, e.g., 800M bits/sec, into an NTSC 6 MHz chan
`nel. This necessitates the use of a complex equalizer to
`cancel the ghost images in an HDTV transmission
`scheme.
`Before proceeding with a description of an illustra
`tive embodiment, it should be noted that the various
`digital signaling concepts described herein-with the
`exception, of course, of the inventive concept itsel
`f-—are all well known in, for example, the digital radio
`and voiceband data transmission (modern) arts and thus
`need notbe described in detail herein. These include
`such concepts as multidimensional signaling using 2N
`dimensional channel symbol constellations, where N is
`some integer; trellis coding; fractional coding; scram
`bling; passband shaping; equalization; Viterbi, or max
`imum-likelihood, decoding; etc.
`SUMMARY OF THE INVENTION
`In accordance with the invention, a signal is divided
`into a plurality of classes of information which are en
`coded for different error protection levels. Each class of
`information is then modulated into a subchannel of the
`channel assigned to the signal. To further enhance sig
`nal reception, the subchannel assignments are based on
`noise and interference considerations.
`The signal is separated into a plurality of classes of
`information such that at least one class of information is
`“more important” and is provided with more error
`protection than the remaining classes of information.
`The plurality of classes of information are then fre
`quency division multiplexed such that each class of
`information is modulated by a subcarrier into a subchan
`nel within a frequency band.
`In accordance with a feature of the invention, the
`effect of the NTSC co-channel interference is reduced
`by assigning the subchannel that carries the more im
`portant information to a frequency spectrum portion
`that is not subject to substantial NTSC interference. As
`a result, the more important data of the HDTV signal
`can still be recovered even in a fringe area where sub
`stantial NTSC co-channel interference is present.
`In accordance with another feature of the invention,
`the use of multiple subcarriers results in longer symbol
`intervals and a ?atter frequency response in each of the
`subchannels. As a result, a simpler equalizer can be used
`in the HDTV receiver to mitigate the effects of “ghost
`111%
`BRIEF DESCRIPTION OF THE DRAWING
`FIG. 1 is a block diagram of a transmitter embodying
`the principles of the invention;
`
`4-0
`
`45
`
`65
`
`Page 6 of 10
`
`

`
`15
`
`20
`
`35
`
`5,243,629
`4
`3
`FIG. 2 is a block diagram of a receiver embodying
`tion scheme that provides error protection to the more
`important class of information. The various coded mod
`the principles of the invention;
`ulation schemes that are implemented by the plurality of
`FIG. 3 is the frequency spectrum for an NTSC signal;
`FIG. 4 is the frequency spectrum for an HDTV sig
`channel encoders, e.g., 121, 123, 128, 132, etc., and
`respective constellation mappers, 141, 143, 148, 152,
`nal embodying the principles of the invention; and
`FIGS. 5-8 are illustrative 4, 8, l2 and 16 QAM signal
`etc., are chosen to provide unequal error protection to
`constellations, respectively.
`the plurality of classes of information such that the
`more important information is provided with more
`DETAILED DESCRIPTION
`error protection. Unequal error protection can be im
`In accordance with the principles of my invention, all
`plemented in a number of ways, such as different chan
`nel encoders, different constellations sizes and/or dif
`three of the above-mentioned areas of concern in
`ferent symbol rates for the various channel encoders
`HDTV transmission are addressed. The signal is di
`and constellation mappers. For example, referring to
`vided into a plurality of classes of information and each
`FIG. 1, all of the channel encoders can be identical. The
`class of information is encoded to a different level of
`signal constellation of constellation mapper 148 has,
`error protection. Each class of information is then mod
`however, the smallest size compared to those of the
`ulated into a subchannel of the channel assigned to the
`signal.
`other constellation mappers. For example, the constella
`Turning to FIG. 1, video signal source 101 generates
`tion used by constellation mapper 148 is the 4~QAM of
`an HDTV analog video signal representing picture
`FIG. 5, while the B-QAM, l2-QAM and 16-QAM of
`information. As taught in the Lawrence et al. patent,
`FIGS. 6-8 can be used by the other constellation map
`this HDTV analog video signal is passed on to source
`pers. This assumes that the transmitted power for each
`encoder 105, which generates a digital signal compris
`subcarrier is the same, with the result that there is more
`separation between the signal points of the 4-QAM
`ing a plurality of “classes of information” in which at
`constellation of FIG. 5 (i.e., the spacing between the
`least one class of information is more important, i.e.,
`signal points), than in the constellations of FIGS. 6-8.
`contains “more important data,” than the remainder of
`25
`the classes of information that, therefore, contain “less
`Consequently, there is more error protection for the
`important data.” For example, the more important data
`more important data, i.e., this provides unequal error
`protection for, and allows graceful degradation of, the
`represents that information which is more important for
`HDTV signal.
`reception of the information signal. In an HDTV signal,
`Before proceeding, reference should be made to FIG.
`it is that information, which, if properly received, will
`form a rough picture, e.g., audio information, framing
`3, which is a representative frequency spectrum for an
`illustrative NTSC analog TV baseband transmission
`information, etc., and the less important data represents
`the information that comprises the remainder of the
`signal that has a bandwidth of 6 MHz. (Although refer
`HDTV signal. As represented herein, source encoder
`ence is made to the baseband signal, the actual transmit
`ted signal is modulated to the respective frequency
`105 illustratively provides k: 12 classes of information
`with the class of information on lead 18 being “more
`spectrum for a particular assigned channel. For exam
`ple, channel 3 is transmitted in the frequency spectrum
`important” than the other classes of “less important”
`information on the remaining leads, e.g., leads 11, 13
`of 60 to 66 MHz.) In accordance with the invention, this
`and 22. Illustratively, each class of information com
`6 MHz NTSC bandwidth is divided into a number of
`prises a plurality of data bits, with an average of m,- bits,
`subchannels, each subchannel assigned to one of a num
`léié 12, being generated on each lead for each signal
`ber of classes of information, which represent the
`ing interval, which is of duration T seconds.
`HDTV signal. For the purpose of illustration, as shown
`in FIG. 4, the NTSC bandwidth is divided into 12 sub
`From FIG. 1 it can be seen that each class of informa
`tion, which is represented by m; bits, is processed by. a
`channels, with each subchannel having a bandwidth
`equal to 500 Khz, i.e., the NTSC bandwidth divided by
`channel encoder, a constellation mapper and a baseband
`modulator. For simplicity, the operation of transmitter
`the number of subchannels. Referring now back to FIG.
`1, the HDTV signal is similarly divided into 12 classes
`100 will be described, for the moment, in the context of
`of information. The output from each of the constella
`the more important information on lead 18. A similar
`description would apply to the processing of each of the
`tion mappers, e.g., 141, 143, 148, 152, etc. is provided to
`respective baseband modulators 161, 163, 168, 172, etc.
`other classes of information. The more important infor
`The latter frequency modulates each of the encoded
`mation, which is represented by mg bits on lead 18, is
`input to channel encoder‘128. The latter operates in
`classes of information to a respective subcarrier, f,
`accordance with known encoding techniques, such as
`(where léié 12), such that each class of information is
`trellis coding, and provides mg+rg data bits as output,
`now provided in a respective subchannel. The outputs
`where r3 represents the average number of redundant
`of the baseband modulators, e. g., 161, 163, 168, 172, etc.,
`bits introduced by channel encoder 128 in each signal
`are summed, or frequency division multiplexed, by
`ing interval. (It should be noted that error correcting
`adder 175. The output of adder 175 is transmitted by
`single sideband (SSB) modulator 195. The latter is rep
`codes, such as a Reed-Solomon code, can also be used in
`resentative of conventional SSB modulation circuitry,
`place of, or in conjunction with, a coded modulation
`scheme.) The encoded output of channel encoder 128 is
`e.g., oscillator, antenna, etc., and provides a broadcast
`mapped, by constellation mapper 148, to a signal point,
`HDTV signal to broadcast channel 200.
`taken from a signal point constellation, in each signaling
`From FIG. 3, it can be seen that the energy of the
`interval. It is assumed that the signal point constellation
`NTSC transmission signal is generally concentrated in
`is representative of well-known uniformly-spaced
`those frequency regions that contain the visual, chroma
`QAM constellations such as is shown in FIGS. 5 to 8 for
`and aural carriers, at 1.25 MHz, 4.83 MHz and 5.75
`4, 8, l2 and 16 signal point constellations.
`MHz, respectively. As a result, any co-existing HDTV
`transmission signal in these frequency regions is subject
`Channel encoder 128 and constellation mapper 148,
`taken together, implement a particular coded modula
`to substantial interference. Therefore, and in accor
`
`40
`
`45
`
`55
`
`65
`
`Page 7 of 10
`
`

`
`5,243,629
`
`25
`
`5
`dance with a feature of the invention, the effect of
`NTSC co~channel interference can be reduced by as
`signing the more important information to a subchannel
`that is different from the subchannels that are subject to
`substantial interference from the NTSC visual, chroma
`and aural carriers. This is shown in FIG. 1, where the
`more important information is transmitted on subcarrier
`f3, thereby avoiding the subchannels that are subject to
`substantial interference from the visual, chroma and
`aural carriers of the NTSC transmission signal, e.g., the
`subchannels associated with subcarriers f3, fro, flz, etc.
`By avoiding those parts of the frequency spectrum of
`the NTSC transmission signal from which substantial
`interference is expected, the more important informa
`tion is provided with more error protection than those
`classes of information that are assigned to those sub
`channels that overlap with the visual, chroma and aural
`carriers of the NTSC transmission signal. This addi
`tional error protection occurs even if all of the classes of
`information have the same encoding schemes. In addi
`20
`tion, if an error occurs in those subchannels to which
`the less important information has been assigned, that
`information can simply be ignored by an HDTV re
`ceiver. For example, from FIG. 1, the less important
`information is assigned to subcarrier f3, which is
`strongly interfered with by the visual carrier of the
`NTSC transmission signal. As a result, when an error
`occurs on this subchannel the less important informa
`tion is ignored by the receiver. It should also be noted
`that those subchannels that experience substantial inter
`ference from the visual, chroma and aural carriers of the
`NTSC transmission signal can be intentionally left un
`used.
`In accordance with another feature of the invention,
`the use of multiple subcarriers results in longer symbol
`intervals and a flatter frequency response in each of the
`subchannels. As a result, a simpler equalizer can be used
`in the HDTV receiver to mitigate the effects of ghost
`ing. Further, a larger symbol interval provides more
`protection against noise spikes of short duration since
`fewer symbols would be effected.
`Turning to the HDTV receiver of FIG. 2, the broad
`cast HDTV signal is received from broadcast channel
`200 by receiver 300. The broadcast HDTV signal is
`received by SSB demodulator 395, which is representa
`tive of conventional reception and demodulation cir
`cuitry, e.g., the antenna, local oscillator, mixer, etc. SSB
`demodulator 350 provides a frequency multiplexed
`signal to each one of the plurality of bandpass ?lters,
`e.g., 341, 343, 348, 352, etc. For example, bandpass filter
`50
`348 ?lters out subcarrier fg, which contains the more
`important information. This subcarrier is applied to
`equalizer 388 to compensate for intersymbol interfer
`ence. The output of equalizer 388 is then provided to
`baseband demodulator 368, which provides a digital
`signal representing the received coded output to chan
`nel decoder 328. The latter decodes the received coded
`output to provide the more important data, on lead 68,
`to source decoder 305. Similarly, each of the other
`classes of information is decoded by receiver 300
`through the respective demodulation and decoding
`circuitry. Source decoder 305 provides the inverse
`function of source encoder 105, of transmitter 100. Spe
`ci?cally, source decoder 305 takes into account the
`subchannel that each class of information is assigned to
`in a predetermined manner. For example, in order to
`recreate the analog HDTV signal, source decoder 305
`knows a priori that the more important information is
`
`45
`
`6
`received on lead 68. As a result, source decoder 305
`combines the various classes of information to provide
`the received analog HDTV signal to CRT display 301.
`The foregoing merely illustrates the principles of the
`invention and it will thus be appreciated that those
`skilled in the art will be able to devise various alterna
`tive arrangements, which, although not explicitly de
`scribed herein, embody the principles of the invention
`and are within its spirit and scope.
`For example, as described hereinabove, all of the
`coded modulation schemes could be the same. Different
`symbol rates, or subchannels with different frequency
`bandwidths, could be used for the various classes of
`information. The use of a smaller symbol rate for the
`more important information would further mitigate the
`effects of ghosting, and hence provide more error pro
`tection for the more important data.‘
`Also, it should be observed that one subchannel can
`be used to carry other information in addition to the
`plurality of classes of information of the HDTV signal.
`For example, a subchannel with a ?xed coding and
`modulation format, which carries the more important
`information, can be used to transmit information as to
`the coding and modulation formats used on the other
`subchannels so that, illustratively, a variable bit rate can
`be used for each of class of information.
`In addition, more than one class of information may
`be carried by each subchannel and a nonuniformly
`spaced signal point constellation can also be used. Alter
`natively, more than one constellation may be used by
`each subchannel, each constellation being for one class
`of information and this constellation being time-divi
`sion-multiplexed.
`It may also be noted that the number of subcarriers
`used is not restricted to twelve but can be any number
`greater than one. Further, the implementation of the
`frequency division multiplexed scheme can include
`overlapping of the spectra of different subcarriers and
`/or different modulation schemes. Also, other commu
`nications system components can be used as well, such
`as an interleaver to protect against bursty noise. In
`addition, although the invention is illustrated herein as
`being implemented with discrete functional building
`blocks, e.g., trellis encoders, constellation mappers, etc.,
`the functions of any one or more of those building
`blocks can be carried out using one or more appropriate
`programmed processors, digital signal processing
`(DSP) chips, etc.
`I claim:
`1. A method for processing an information signal
`comprising the steps of
`separating the information signal into a plurality of
`classes of information such that at least one of the
`plurality of classes of information is more impor
`tant for reception of the information signal than the
`other ones of the plurality of classes of information,
`encoding the plurality of classes of information to
`provide a plurality of encoded symbols such that
`the more important information has more error
`protection than the remaining ones of the plurality
`of classes of information, and
`modulating the plurality of encoded symbols into a
`plurality of subchannels within a frequency band,
`each subchannel occupying a different frequency
`spectrum.
`2. The method of claim 1 wherein the frequency band
`is assigned to a different signal.
`
`55
`
`60
`
`65
`
`Page 8 of 10
`
`

`
`5
`
`20
`
`25
`
`35
`
`5,243,629
`7
`8
`3. The method of claim 2 wherein the modulating
`classes of information is more important than the
`step place the more important information into a sub
`other ones of the plurality of classes of information
`for reception of the information signal, and
`channel that does not contain a carrier of the different
`signal.
`assigning the more important information to a sub
`4. The method of claim 1 wherein the encoding step
`channel that does not contain a carrier of the sec
`includes the steps of
`ond signal.
`channel encoding each one of the plurality of classes
`15. The method of claim 14 wherein the ?rst signal is
`of information to provide a plurality of encoded
`a High De?nition Television signal, the second signal is
`outputs, and
`a National Television System Committee signal, and the
`mapping each one of the plurality of encoded outputs
`more important information is assigned to a subchannel
`to signal constellation to provide the plurality of
`that is different from those subchannels that contain the
`encoded symbols.
`visual, chroma or aural carriers of the signal.
`5. The method of claim 4 wherein the channel encod
`16. A method for processing a signal, the signal being
`ing step for the more important information is different
`comprised of a plurality of subchannels, each subchan
`from the channel encoding step of at least one other of
`nel carrying a class of information, with one subchannel
`the plurality of classes of information.
`carrying the more important information, said plurality
`6. The method of claim 5 wherein the channel encod
`of subchannels occupying a frequency band that is as
`ing step operates in accordance with an error correcting
`signed to a different signal, with the subchannel that is
`code.
`carrying the more important information being different
`7. The method of claim 5 wherein the channel encod
`from those subchannels that are subject to substantial
`ing step operates in accordance with coded modulation.
`interference from the different signal, the method com
`8. The method of claim 5 wherein the channel encod
`prising the steps of
`ing step operates in accordance with coded modulation
`receiving the signal,
`and an error correcting code.
`.
`?ltering the received signal to provide the plurality of
`9. The method of claim 4 wherein the mapping step
`subchannels,
`for the more important information uses a signal point
`demodulating each one of the received plurality of
`constellation that is different from at least one other of
`subchannels to provide a plurality of received en
`the signal point constellations used for the other plural
`coded symbols,
`ity of classes of information.
`decoding each one of the plurality of received en
`10. The method of claim 1 wherein the encoding step
`coded symbols to provide the plurality of classes of
`uses a symbol rate for the more important class of infor
`information, and
`mation that is different from the symbol rate of a least
`combining each one of the plurality of classes of
`one other class of information.
`information in a predetermined manner, which
`11. A method for transmitting a first signal in a fre
`takes into account which subchannel carried the
`quency band allocated to a second signal comprising the
`more important information, to recreate the infor
`step of
`mation signal.
`dividing the frequency band into a number of sub
`17. Apparatus for processing an information signal
`channels,
`comprising
`separating the ?rst signal into a plurality of classes of
`means for separating the information signal into a
`information such that at least one of the plurality of
`40
`plurality of classes of information such that at least
`classes of information in more important for recep
`one of the plurality of classes of information is
`tion of the information signal than the other ones of
`more important than the other ones of the plurality
`the plurality of classes of information, and
`of classes of information for reception of the infor
`assigning the more important information to a sub
`mation signal,
`channel that is different from those subchannels
`means for providing unequal levels of error protec
`that are subject to substantial interference from the
`tion to the plurality of classes of information to
`second signal.
`provide a plurality of encoded symbols for each
`12. The method of claim 11 wherein the assigning
`one of the plurality of classes of information such
`step includes the steps of
`that the more important information has more
`encoding each one of plurality of classes of informa
`error protection than the remaining ones of the
`tion, and
`plurality of classes of information, and
`frequency modulating the encoded plurality of I
`means for modulating the plurality of encoded sym
`classes of information to the respective subchannel.
`bols for each one of the plurality of classes of infor
`13. The method of claim 11 wherein the ?rst signal is
`a High De?nition Television signal, the second signal is
`' mation to a plurality of subchannels within a fre
`quency band, each subchannel occupying a differ
`a National Television System Committee signal, and the
`ent frequency spectrum.
`more important information is assigned to a subchannel
`18. The apparatus of claim 17 wherein the frequency
`that is different from those subchannels that are subject
`band is assigned to a different signal.
`to substantial interference from the visual, chroma or
`19. The apparatus of claim 18 wherein the means for
`aural carriers of the National Television System Com
`mittee signal.
`modulating places the more important information into
`14. A method for transmitting a ?rst signal in a fre
`a subchannel that does not contain a carrier of the dif
`ferent signal.
`quency band allocated to a second signal comprising the
`steps of
`20. The apparatus of claim 17 wherein the means for
`providing unequal error protection further comprises
`dividing the frequency band into a number of sub
`channels,
`channel encoding means for each one of the plurality
`separating the ?rst signal into a plurality of classes of
`of classes of information to provide a plurality of
`encoded outputs, and
`information such that at least one of the plurality of
`
`60
`
`45
`
`55
`
`65
`
`Page 9 of 10
`
`

`
`5,243,629
`10
`9
`of subchannels occupying a frequency band that is as
`means for mapping each one of the plurality of en
`signed to a different signal, with the subchannel that is
`coded outputs to a signal constellation to provide
`carrying the more important information being different
`the plurality of encoded symbols.
`from those subchannels that are subject to substantial
`21. The apparatus of claim 20 wherein the channel
`interference from the different signal, the apparatus
`encoding means for the more important information is
`comprising
`different from the channel encoding means of at least
`means for receiving the signal,
`one other of the plurality of classes of information,
`means for ?ltering the received signal to provide the
`22. The apparatus of claim 20 wherein the means for
`mapping the more important information uses a signal
`plurality of subchannels,
`-
`means for demodulating each one of the received
`point constellation that is different from at least one
`plurality of subchannels to provide a plurality of
`other of the signal point constellations used for the
`received encoded symbols,
`other plurality of classes of information.
`means for decoding each one of the plurality of re
`23. The apparatus of claim 17 wherein the mean