WO2007040572A1

WO2007040572A1 - Transmission of information on an auxiliary channel

Info

Publication number: WO2007040572A1
Application number: PCT/US2005/045170
Authority: WO
Inventors: Maxim Borisovich Belotserkovsky; Ivonete Markman; Gabriel Alfred Edde
Original assignee: Thomson Licensing
Priority date: 2005-09-28
Filing date: 2005-12-13
Publication date: 2007-04-12

Abstract

A transmitter comprises an ATSC (Advanced Television Systems Committee) modulator and an auxiliary channel (AC) discrete multitone (DMT) modulator. The ATSC modulator provides an ATSC signal for broadcast in a channel for communicating a high definition television (HDTV) service. The DMT modulator receives auxiliary data for the HDTV service and modulates this auxiliary data to provide an AC signal for broadcast in the same channel, i.e., the AC signal is a co-channel interfering signal to the broadcast ATSC signal. In particular, the DMT modulator modulates the auxiliary data such that the AC signal imitates one, or more, spectral properties of an NTSC (National Television Systems Committee) broadcast signal. In a complementary fashion, a receiver comprises an ATSC demodulator, for recovery of a high definition television (HDTV) signal, and a discrete multitone (DMT) demodulator, for recovery of the auxiliary data.

Description

TRANSMISSION OF INFORMATION ON AN AUXILIARY CHANNEL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 60/721,427, filed September 28, 2005.

BACKGROUND OF THE INVENTION

[0002] The present invention generally relates to communications systems and, more particularly, to wireless systems, e.g., terrestrial broadcast, cellular, Wireless-Fidelity (Wi- Fi), satellite, etc. [0003] In March of 2000, the Advanced Television Systems Committee (ATSC) organization formed an RF (radio frequency) Task Force to explore Digital Television (DTV) broadcaster requirements and evolution of the ATSC DTV Standard <e.g., see, United States Advanced Television Systems Committee, "ATSC Digital Television Standard", Document A/53, September 16, 1995 and "Guide to the Use of the ATSC Digital Television Standard", Document A/54, October 4, 1995). Of particular interest at the time was the idea of adding enhancements to the standard that improved the fixed terrestrial reception and also allowed for portable, pedestrian and mobile reception. Subsequently, an RF Transmission Specialist Group (T3/S9) was created and requested proposals for RF enhancements to the ATSC DTV Standard in January of 2001. In response, the proposals presented were either compatible or non-compatible with the ATSC DTV original standard. Compatible proposals were viewed as those RF enhancements that were still capable of reception by existing (legacy) ATSC receivers albeit with a possible loss in performance so that customers, if they desired, would not have to replace their ATSC receiver (e.g., their TV set). [0004] The majority of the non-compatible proposals to the original ATSC DTV standards proposed the addition of some form of training to the ATSC-DTV signal to aid the equalization of channels with strong (static or dynamic) multipath interference, which is one of the main issues associated with the terrestrial broadcast reception. However, in the end, the T3/S9 body rejected any non-compatible proposals because of the existence of thousands of legacy ATSC receivers throughout the country. [0005] With respect to the compatible proposals, there were, generally-speaking, three suggested RF enhancements. The first proposal, Enhanced- Vestigial SideBand (E-VSB), proposed an outer FEC (forward error correction) coding enhancement to the ATSC bit stream that trades payload bit rate for improved white noise performance (Threshold of Visibility, TOV) when properly equipped receivers are utilized. The E-VSB stream is transmitted in association with null-packets of the ATSC stream, which are discarded by the transport layer decoder of the receiver. As a result, a legacy ATSC receiver is unaffected. The E-VSB proposal was approved by the ATSC organization as an optional feature of the ATSC standard.

[0006] The second proposal also described a technique for transmission of a modified ATSC bit stream that added Reed-Solomon (RS) coding, a robust symbol mapping consisting of 2- VSB, 4- VSB or an additional mode called hierarchical (H)-VSB. An ATSC receiver modified to receive this added data will have a lower TOV compared to reception of an original ATSC bit stream. Like the first proposal, the added data is transmitted in association with null-packets of the ATSC stream without affecting legacy ATSC receivers; [0007] The third proposal traded off payload with an additional training sequence to improve overall equalizer performance at the cost of a 0.2 dB increase in the TOV. Specifically, 414 8-VSB symbols are replaced by extra training symbols once in every field. The removal of the data and replacement with training symbols is performed after the RS encoder and before the trellis encoder. The impact of removing the payload data is the reduction of the error correction capability of the RS code, therefore increasing the JOV. Although attempting to address the very important issue of equalization, this proposal was withdrawn from final consideration by the T3/S9 body.

[0008] Unfortunately, none of the above-described compatible proposals adequately addressed the problem of equalization in a mobile receiver environment. In particular, while the E-VSB proposal (approved by the ATSC) and the above-noted second proposal both help reception in channels with low signal-to-noise ratio (SNR), both of these proposals failed the pedestrian and mobile ATSC field tests. Further, while the above-noted third proposal addressed equalization without compromising the payload, this proposal did not seem to add enough training to represent a substantial improvement in equalizer performance. [0009] Despite the fact that the issue of mobility was not addressed in the above-noted proposals, the convergence of terrestrial broadcast and advanced mobile wireless multimedia services is a subject of increased interest. Particularly, in July of 2005, the Telecommunications Industry Association (TIA), a leading trade association and developer of standards for the communications and information technology industry, announced the formation of a new engineering committee, "Terrestrial Mobile Multimedia Multicast" (TM3), to address the standardization of critical aspects of the technologies driving this convergence of services. [0010] In view of the above, there are currently no reliable backward-compatible systems that adequately address mobile (or portable) reception of DTV.

SUMMARY OF THE INVENTION

[0011] It is known that an ATSC receiver is designed to co-exist in an NTSC (National

Television Systems Committee) environment during the transition from NTSC broadcasts to ATSC broadcasts. As such, an ATSC receiver is generally not substantially affected by a co- channel interfering NTSC signal. Indeed, the ATSC receiver does not even use the eo- channel interfering NTSC signal and may have filters specifically designed to remove the co- channel interfering NTSC signal. Thus, as the transition from NTSC broadcasts to ATSC broadcasts is completed, the co-channel interfering NTSC signal will disappear without affecting ATSC receivers. However, we have realized that such an event means it is now possible to broadcast an additional, or auxiliary, signal that will not effect legacy ATSC equipment if this auxiliary signal looks like an NTSC signal. This auxiliary signal can be used to convey auxiliary data for one, or more, features or services, like multipath equalization or low resolution video transmission. In other words, it is possible to offer an RF enhancement to the ATSC standard that addresses the equalization problem under strong (static and dynamic) multipath environments, improves the fixed terrestrial reception, as well as allows for portable, pedestrian and mobile reception — without compromising the original ATSC payload, i.e., the auxiliary signal is backward compatible with legacy ATSC receivers. [0012] Therefore, and in accordance with the principles of the invention, a transmitter transmits a first signal in a channel, wherein the first signal conveys data, or information, associated with a service; and transmits a second signal in the same channel, wherein the second signal is a co-channel interferer to the first signal and the second signal conveys auxiliary data for the service. [0013] In an embodiment of the invention, a transmitter comprises an ATSC modulator and an auxiliary channel (AC) discrete multitone (DMT) modulator. The ATSC modulator provides an ATSC signal for broadcast in a channel for communicating a high definition television (HDTV) service. The DMT modulator receives auxiliary data for the HDTV service and modulates this auxiliary data to provide an AC signal for broadcast in the same channel, i.e., the AC signal is a co-channel interfering signal to the broadcast ATSC signal. In particular, the DMT modulator modulates the auxiliary data such that the AC signal imitates one, or more, spectral properties of a co-channel interfering NTSC broadcast signal. [0014] In another embodiment of the invention, a receiver comprises an ATSC demodulator and an auxiliary channel (AC) discrete multitone (DMT) demodulator. The ATSC demodulator is for receiving an ATSC service as represented by a broadcast ATSC signal for a particular channel, and for recovering therefrom ATSC information, such as, but not limited to, one, or more, of the following: an HDTV signal, program and system information (PSIP), etc. The DMT demodulator is for receiving a broadcast AC signal in the same channel as the received ATSC signal, i.e., the received AC signal is a co-channel interfering signal to the received ATSC signal. In particular, the received AC signal imitates one, or more, spectral properties of an NTSC broadcast signal. The DMT demodulator demodulates the received AC signal for recovering therefrom auxiliary data associated with the ASTC service.

[0015] In accordance with a feature of the invention, the auxiliary data is for use by the ATSC demodulator for acquiring the broadcast ATSC signal. [0016] In another embodiment of the invention, a receiver comprises an input for use in receiving from an antenna (a) a broadcast ATSC signal in a channel, wherein the broadcast ATSC signal conveys information associated with an ATSC service, and wherein the information may include, but is not limited to, one, or more, of the following: an HDTV signal, program and system information (PSIP), etc. and (b) a second signal in the same channel, wherein the second signal is a co-channel interferer to the broadcast ATSC signal; and wherein the receiver includes a demodulator for demodulating the received second signal for recovering therefrom auxiliary data associated with the ATSC service. [0017] In view of the above, and as will be apparent from reading the detailed description, other embodiments and features are also possible and fall within the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGs. 1-3 illustrate prior art NTSC transmission; [0019] FIG. 4 shows an illustrative embodiment of an ATSC-DTV system in accordance with the principles of the invention;

[0020] FIG. 5 shows an illustrative embodiment of a transmitter for use in the system of

FIG. 4 in accordance with the principles of the invention; [0021] FIGs. 6 and 7 show an illustrative DMT transmission in accordance with the principles of the invention;

[0022] FIG. 8 shows an illustrative flow chart for use in a transmitter in accordance with the principles of the invention;

[0023] FIG. 9 shows another illustrative embodiment of a transmitter for use in the system of FIG. 4 in accordance with the principles of the invention;

[0024] FIG. 10 shows an illustrative embodiment of a device for receiving an auxiliary channel in accordance with the principles of the invention;

[0025] FIG. 11 shows an illustrative embodiment of a receiver in accordance with the principles of the invention; [0026] FIG. 12 shows an illustrative flow chart for use in a receiver in accordance with the principles of the invention; and

[0027] FIG. 13 shows another illustrative embodiment of a receiver in accordance with the principles of the invention.

DETAILED DESCRIPTION [0028] Other than the inventive concept, the elements shown in the figures are well known and will not be described in detail. Also, familiarity with television broadcasting, receivers and video encoding is assumed and is not described in detail herein. For example, other than the inventive concept, familiarity with current and proposed recommendations for TV standards such as NTSC (National Television Systems Committee), PAL (Phase Alternation Lines), SECAM (SEquential Couleur Avec Memoire) and ATSC (Advanced Television Systems Committee) (ATSC) is assumed. Likewise, other than the inventive concept, transmission concepts such as eight-level vestigial sideband (8- VSB), Quadrature Amplitude Modulation (QAM), orthogonal frequency division multiplexing <OFDM) or coded OFDM (COFDM)), and receiver components such as a radio-frequency (RF) front- end, or receiver section, such as a low noise block, tuners, and demodulators, correlators, leak integrators and squarers is assumed. Similarly, other than the inventive concept, formatting and encoding methods (such as Moving Picture Expert Group (MPEG)-2 Systems Standard (ISO/DEC 13818-1)) for generating transport bit streams are well-known and not described herein. It should also be noted that the inventive concept may be implemented using conventional programming techniques, which, as such, will not be described herein. Finally, like-numbers on the figures represent similar elements. [0029] Before describing the inventive concept, some brief background information on a legacy ATSC receiver and, in particular, on an NTSC system is described and shown in FIGs. 1-3. FIG. 1 shows a sample time domain (TD) representation of an NTSC signal as known in the art. A corresponding frequency spectrum of an NTSC signal transmission is shown in FIG. 2. Of particular note is that the bulk of the NTSC energy is located in specific areas of the spectrum, i.e., around the picture carrier (video 10), the sound carrier (audio 12) and the chroma carrier (chroma 11). Currently, an ATSC legacy receiver is inherently capable of rejecting an NTSC transmission (of limited power) located in-band of the desired ATSC channel (the so-called NTSC co-channel). In many ATSC legacy receivers currently on the market this rejection is facilitated by either the use of the so-called comb filter or by the main channel equalizer, hi both of these cases, the ATSC legacy receiver is relying on the fact that the bulk of the energy of the NTSC co-channel is concentrated in the above- noted specific areas rather than being spread evenly across the band. As such, and as known in the art, it is relatively easy to remove this energy with a comb filter, hi particular, the comb filter will actually remove this energy in 12 evenly-spaced locations in the full spectrum (roughly 10.76 MHz (millions of hertz)). However, in a single sideband 8-VSB signal only half of the spectrum, 5.38 MHz, is available. As such, the number of nulls is 7, of which one coincides with the ATSC pilot signal. The operation of the comb filter is shown in FIG. 3, which illustrates three of the comb filter nulls as indicated by arrows 15, 16 and 17, which correspond to the video 10, audio 12 and chroma 11 carriers, respectively. [0030] hi accordance with the principles of the invention, a co-channel information- bearing transmission — from now on referred to as the Auxiliary Channel (AC) — is designed in such a way as to mimic one, or more, spectral Frequency Domain (FD) properties of a true NTSC co-channel transmission, thus allowing legacy ATSC receivers to effectively reject it. As a result, the AC enables additional information to be sent to an ATSC receiver — yet legacy ATSC receivers will not be significantly affected, i.e., the system is backward-compatible. The use of the AC channel described herein facilitates a number of services. For example, an ATSC broadcaster can use the AC to transmit an AC stream inside the broadcaster's own licensed ATSC band to, e.g., facilitate mobile reception of the ATSC transmission, provide a lower resolution video signal, etc. As used herein, this additional information is referred to as auxiliary data that supports one, or more, services provided via the ATSC signal. The auxiliary data can represent, e.g., training information, content (video and/or audio), setup information, system information, program information, etc

[0031] In addition, and in accordance with a feature of the invention, since legacy ATSC receivers may rely on specific TD portions of an NSTC co-channel interferer to recognize the interferer as such (e.g., the NTSC horizontal and vertical blanking intervals and syncs, etc.), the proposed AC signal can advantageously imitate those as well. It should be noted that these TD portions of the signal, such as "dummy" syncs, are not entirely wasteful but can actually be used by a receiver that embodies the principles of the invention for synchronization purposes, etc. However, the inventive concept is not so limited, and it is not required that the AC signal provide, e.g., these "dummy" syncs or that the receiver use them even if these "dummy" syncs are provided.

[0032] Turning now to FIG. 4, an illustrative embodiment of an ATSC-DTV system 100 in accordance with the principles of the invention is shown. ATSC DTV system 100 comprises an ATSC DTV transmitter 105 and at least one ATSC DTV receiver. The latter is represented in FIG. 4 by mobile DTV 150 and a DTV 155. Mobile DTV 150 is a small, portable, DTV, e.g., hand-held, and DTV 155 is representative of a more conventionally- sized DTVs for use, e.g., in a home. ATSC DTV transmitter 105 broadcasts an ATSC signal 111 as known in the art and represented in dotted-line form in FIG. 4. ATSC signal 111 is a data-bearing signal in the form of a packetized data stream and is modulated in an 8-VSB format. This is also known in the art as a "physical transmission channel" (PTC). The PTC has a center frequency (carrier frequency) and bandwidth. The PTC offers about 19 Mbits/sec (millions of bits per second) for transmission of an MPEG2-compressed HDTV (high definition TV) signal (MPEG2 refers to Moving Picture Expert Group (MPEG)-2 Systems Standard (ISO/IEC 13818-1)). As such, around four to six standard definition TV channels can be safely supported in a single PTC without congestion. [0033] In addition, and in accordance with the principles of the invention, ATSC DTV transmitter 105 also broadcasts an AC signal 116, represented in dashed-line form in FIG. 4. As noted above, and described further below, AC signal 116 looks like a co-channel NTSC signal but, in fact, conveys auxiliary data for use by an ATSC receiver, such as mobile DTV 150 and/or DTV 155. This auxiliary data enables the provisioning of additional services to ATSC receivers — yet does not affect a legacy ATSC receiver.

[0034] An illustrative embodiment of transmitter 105 in accordance with the principles of the invention is shown in FIG. 5. Transmitter 105 comprises an 8-VSB modulator 110 and an AC modulator 115. In addition, transmitter 105 is a processor-based system and includes one, or more, processors and associated memory as represented by processor 190 and memory 195 shown in the form of dashed boxes in FIG. 5. hi this context, computer programs, or software, are stored in memory 195 for execution by processor 190. The latter is representative of one, or more, stored-program control processors and these do not have to be dedicated to the transmitter function, e.g., processor 190 may also control other functions of transmitter 105. Memory 195 is representative of any storage device, e.g., random-access memory (RAM), read-only memory (ROM), etc.; may be internal and/or external to transmitter 105; and is volatile and/or non- volatile as necessary. The 8-VSB modulator 110 receives signal 109, which is representative of a data-bearing signal for conveying DTV program and system information, and modulates this data-bearing signal to provide ATSC signal 111 for broadcast on a particular PTC. In accordance with the principles of the invention, the AC modulator 115 receives signal 114, which is representative of a data- bearing signal for conveying auxiliary data, and modulates this data-bearing signal to provide AC signal 116 for broadcast on the same PTC as was used for ATSC signal 111.

[0035] As noted above, the AC imitates, or mimics, an NTSC co-channel, hi order to achieve the desired spectral properties (i.e., energy concentrated one, or more, specific areas of the spectrum), the preferred modulation method is to use a variant of a discrete (orthogonal) multitone (DMT) signal to carry the AC information. As such, in this example, AC modulator 115 is a DMT modulator. Other than the inventive concept, those familiar with DMT (also referred to as OFDM or COFDM) principles will recognize why such a transmission can be designed to have the desired spectral properties and will also appreciate other advantages of using DMT-based transmission, especially in terms of the ease of equalization of such a signal. However, the inventive concept is not so limited and other transmission techniques may be used.

[0036] Referring now to FIG. 6, operation of AC modulator 115 is shown in the context of using DMT modulation for producing AC signal 116 with one, or more, of the desired spectral properties of an NTSC signal. In particular, FIG. 6 shows an illustrative portion of an AC signal imitating a single NTSC line, which is the basic building block for the AC co- channel waveform. It should be noted that the portion corresponding to an NTSC horizontal blanking period is drawn in a simplified way only to signify the fact that the corresponding portion of the AC signal does not carry a payload. As shown in FIG. 6, the A C information content is advantageously transmitted during a time interval 31 that corresponds to the active video interval (21) of the NTSC line shown in FIG. 1. Other than the inventive concept, the AC information can be encoded as magnitude and/or phase of a section of a complex/real sine-wave as known in the art. The single sine-wave shown in FIG. 6 is drawn for illustration purposes only. The frequencies of the sine- waves should be selected to place the energy of the AC transmission in at least one of the areas where a co-channel interfering NTSC picture carrier, NTSC sound carrier and/or NTSC chroma carrier would be expected as shown in FIG. 2. In the context of a DMT transmission, it should be noted that only a portion of interval 31 contains the AC payload waveform. In particular, and in accordance with DMT transmission, portions of the interval 31 are allocated to cyclic extensions (or cyclic prefixes (CPs)) of the Payload to help cope with multipath. These are shown in FIG. 6 as CPland CP2, which are allocated as shown to portions 32 and 33, respectively. As a result, the AC payload is allocated to portion 34 of interval 31. It should be noted that since AC signal 116 is a co-channel interferer to the ATSC signal 111, it may be preferable that the power level of AC signal 116 be set so that the ratio of the power of AC signal 116 to the power level of ATSC signal 111 be comparable to what is generally expected of an actual NTSC co-channel interferer. Indeed, since a broadcaster may control both ATSC signal 111 and AC signal 116, this power ratio (analogous to the desired-to-undesired (DfO) ratio in ATSC broadcast) may be adjusted in a static and/or a dynamic fashion via one, or more, signals as represented by signal 106, which is shown in dashed-line form in FIG. 5.

[0037] In FIG. 6, exemplary numerical values have been assigned to the respective portions of interval 31. For example, portion 34 is allocated to 22.3 μsec (microsecond). As such, the inverse of the payload length is exactly 1/120-th of the ATSC signal bandwidth of 5.38 MHz, which allows for 6 orthogonal AC subcarriers to be placed within an ATSC spectrum 5.38 MHz/6 = 897 kHz (thousands of hertz) apart (as noted above, one of the 7 nulls is associated with the ATSC pilot signal). This is further illustrated in FIG. 7, which shows an illustrative power spectral density for AC signal 116 having N subcarriers, where (f_k-f_k-i) = 897 kHz. In accordance with the principles of the invention, the specific /* values are selected to match one, or more, of the 6 frequency locations notched-out by the comb filter of an ATSC receiver as illustrated earlier in FIG. 3.

[0038] In view of the above, an illustrative flow chart for use in transmitter 105 in accordance with the principles of the invention is shown in FIG. 8. In step 160, transmitter 105 receives auxiliary data for the AC. The auxiliary data supports one, or more, services provided via an ATSC signal. In step 165, transmitter 105 forms a co-channel interfering signal to the ATSC signal in accordance with the principles of the invention. In this example, transmitter 105 transmits AC signal 116 as a DMT signal that imitates at least one spectral property of an NTSC broadcast signal.

[0039] As noted above, the inventive concept allows a broadcaster to provide one, or more, services via the AC that supports one, or, more services provided via the ATSC signal. As one example, the AC is a support channel to facilitate reception of ATSC signal 111 (e.g., to allow the ATSC signal to be received in a mobile environment as represented by mobile DTV 150 of FIG. 4). In this scenario, the broadcaster's advance knowledge, of the information to be transmitted on the main ATSC channel (ATSC signal 111) is used to transmit support information on the AC channel, which is synchronized with the main ATSC channel. For example, assume an information stream relating to a program is scheduled to be transmitted, via ATSC signal 111, at a scheduled time Ts- Additional information, or a subset of the information stream to be transmitted via ATSC signal 111, is sent as auxiliary data, via AC signal 116, ahead of time at a time T_E. This auxiliary data is used by mobile DTV 150 to facilitate reception of ATSC signal 111. The value for TE is chosen such that the resulting time interval TS-TE provides mobile DTV 150 enough time to process the auxiliary data before the arrival of the scheduled information stream via ATSC signal 111 at time Ts. Thus, mobile DTV 150 can receive information on the AC channel to help receive the main ATSC channel. Illustratively, an especially advantageous way to use the AC channel for training is. to send, as auxiliary data, data that is used for training (training data) and may also include data representing the location of the training data in ATSC signal 111.

Thus, reception of the AC by mobile DTV 150 then enables mobile DTV 150 to further identify the training data and its location in the received version of ATSC signal 111. This variation of transmitter 105 is shown in FIG. 9 by dashed line 109-1, where a subset of data provided in ATSC signal 111 (e.g., training data) is also sent via AC modulator 116. [0040] As another example, the AC is an independent data or video channel that supports one, or more, services provided via the ATSC signal. For example, in a mobile environment, the ATSC broadcaster can transmit, via the AC, a lower resolution video as compared to the resolution of video conveyed via the ATSC signal. This lower resolution video can represent a program also conveyed via the ATSC signal or a completely different program that is simply at a lower resolution than video conveyed in the ATSC signal. [0041] Similarly, the AC can be used for non-real-time transmissions of file-based information to pedestrian and mobile receivers that can store the information for later use. [0042] As another example, the AC is a robust/fallback audio channel. An attribute of analog television transmission is that the sound will usually continue to work when the picture suffers momentary interference. Viewers will tolerate momentary freeze or loss of picture, but loss of sound is more objectionable. As such, another application of the AC is to provide an audio service that would be less likely to be affected by momentary reduction of a received signal level in an ATSC receiver. [0043] As yet another example, the AC is an antenna pointing/diagnostic information provider for use in reception of the ATSC signal. Use of the AC to improve consumer "ease of use" would be helpful. As an example, diagnostic information could be displayed to help consumers with antenna pointing or, in conjunction with CEA Antenna Control Interface Standard (CEA-909), facilitate automatic antenna pointing. [0044] Thus, as described above, and in accordance with the principles of the invention, the AC conveys data associated with at least one service conveyed by the co-channel ATSC signal (main ATSC channel). In this context, the term "service" relates to one, or more of the following, singly or in combination: the type of information conveyed to a user, e.g., the AC may convey additional programming (news, entertainment, etc.) that is independent of, or related to, programming (news, entertainment, etc.) conveyed to the user by the main ATSC channel; the type of content conveyed in the main ATSC channel, e.g., the AC may convey additional news, audio and/or video etc., in a content format that is different from that conveyed in the main channel (e.g., the above-noted lower resolution video); the operation of the ATSC receiver, e.g., the AC may convey training information, setup information and/or diagnostic information, etc., in support of receiving the main ATSC channel. . . [0045] Referring now to FIG. 10, an illustrative embodiment of a device 200 in accordance with the principles of the invention is shown. Device 200 is representative of any processor-based platform, e.g., a PC, a server, a set-top box, a personal digital assistant (PDA), a cellular telephone, mobile DTV 150, DTV 155, etc. In this regard, device 200 includes one, or more, processors with associated memory (not shown) and also comprises receiver 210. The latter receives ATSC signal 111 and AC signal 116 via an antenna (not shown)). Receiver 210 processes received ATSC signal 111 to recover therefrom an HDTV signal 211 for application to a display 220, which may, or may not, be a part of device 200 as represented in dashed-line form, m addition, receiver 210 processes received AC signal 116 to recover therefrom auxiliary data 216. Depending on the particular service, the auxiliary data 216 may be used by receiver 210 itself (e.g., in the case of training data, described above), or the auxiliary data 216 can be provided to another portion of device 200, or external to device 200. One example is shown in FIG 10, where auxiliary data 216 (in dotted line form) represents low resolution video content. In this case, display 220 can use the low resolution video content of auxiliary data 216 instead of the high resolution video content of HDTV signal 211. Or, device 200 can select between HDTV signal 211 and the low resolution video of auxiliary data 216 as the video source for display 220. This selection can be performed in any number of ways, e.g., as a function of a comparison by receiver 210 between the corresponding signal-to-noise ratios (SNRs) for received ATSC signal 111 and received AC signal 116, where the signal with the highest SNR is selected.

[0046] An illustrative embodiment of a receiver 210 in accordance with the principles of the invention is shown in FIG. 11. Receiver 210 comprises an ATSC demodulator 240, an AC detector 235 and an AC demodulator 230. In addition, receiver 210 is a processor-based system and includes one, or more, processors and associated memory as represented by processor 390 and memory 395 shown in the form of dashed boxes in FIG. 11. In this context, computer programs, or software, are stored in memory 395 for execution by processor 390. The latter is representative of one, or more, stored-program control processors and these do not have to be dedicated to the receiver function, e.g., processor 390 may also control other functions of receiver 210. For example, if receiver 210 is a part of a larger device, processor 390 may control other functions of this device. Memory 195 is representative of any storage device, e.g., random-access memory (RAM), read-only memory (ROM), etc.; may be internal and/or external to transmitter 105; and is volatile and/or non-volatile as necessary.

[0047] Antenna 301 of FIG. 11 receives one, or more, broadcast signals and provides them to receiver 210 via input 299. In this example, antenna 301 provides ATSC signal 111 and also the co-channel interfering signal AC signal 116. It is assumed that receiver 210 is tuned to a particular channel for receiving, e.g., ATSC signal 111. ATSC demodulator 240 receives ATSC signal 111 and provides the above-mentioned HDTV signal 211. In this example, it is assumed that ATSC demodulator 240 also includes any required decoding functions. AC detector 235 monitors the currently tuned channel for AC signal 116. Since, in accordance with the principles of the invention, AC signal 116 looks like an NTSC co- channel signal, AC detector 235 may be constructed in a fashion similar to current NTSC signal detectors. Upon detection of the presence of AC signal 116, AC detector provides one, or more, signals as represented by any one of signals 236, 237 and 238 in dashed-line form. With respect to signal 237, this signal is provided to ATSC demodulator 240. The latter, in response to detection of the presence of AC signal 116, enables comb filters (not shown) of ATSC demodulator 240 to remove the interfering signal as it would for a co- channel interfering NTSC signal. With respect to signal 238, this signal is provided to AC demodulator 230. Upon detection of AC signal 116, AC demodulator 230 is activated to demodulate AC signal 116 to recover therefrom auxiliary data 216. Depending on the modulation and coding scheme used to encode the auxiliary data for transmission, AC demodulator 230 may also include any required decoding functions. In this example, AC demodulator 230 is a DMT demodulator. With respect to signal 236, this signal may be provided to alert other portions of device 200, or another device, that an AC signal has been detected. Finally, it should be noted that the earlier-noted TD portions of the signal, such as 'dummy' horizontal syncs of AC signal 116, can also be used by receiver 210 to help its reception by making it easier to locate the OFDM symbols in the AC stream. [0048] In view of the above, an illustrative flow chart for use in receiver 210 in accordance with the principles of the invention is shown in FIG. 12. In step 405, receiver 210 receives a broadcast AC signal 116 that conveys auxiliary data as a co-channel interfering signal to an ATSC transmission. In step 410, receiver 210 demodulates the received AC signal to provide the auxiliary data. In this example, receiver 210 demodulates AC signal 116 using a DMT demodulator, where received AC signal 116 imitates at least one spectral property of an NTSC signal.

[0049] As described above and in accordance with the principles of the invention, the AC conveys data associated with at least one service conveyed by a co-channel ATSC signal (main ATSC channel). However, in addition to the illustrative embodiments shown above, another illustrative embodiment of a receiver in accordance with the principles of the invention is shown in FIG. 13. Receiver 210' is similar to receiver 210 of FIG. 11, except that there is no demodulator for the main ATSC channel. Instead, the AC is used to support services found in the main ATSC channel by providing these services to a user via the AC. For example, programming (news, entertainment) found in the main ATSC channel is provided to the user via the AC; and/or the type of content conveyed in the main ATSC channel is provided via the AC in a format different from that conveyed in the main channel (e.g., the above-noted lower resolution video); and/or the AC conveys auxiliary data related to the operation of receiver 201', e.g., the AC may convey training information, setup information and/or diagnostic information, etc.

[0050] As described above, and in accordance with the principles of the invention, an independent data channel can non-destructively co-exist with some other wide-band (or other) transmission located in the same frequency band. It should be noted. that although the inventive concept was described in the context of a United States (US) terrestrial digital TV (ATSC) system, the inventive concept is not so limited and is applicable to other communications systems. Further, although particular uses of the AC were described above, the inventive concept is not so limited and other uses can also be envisioned in accordance with the principle of the invention. In addition, other variations in accordance with the inventive concept are possible. For example, although the inventive concept was illustrated by a receiver having a comb filter, the invention is not so limited and the illustrative embodiment described above can be readily modified for the case when the comb filter is not used. Further, although the inventive concept was illustrated in the context of a broadcaster transmitting both the ATSC signal and the AC signal, the invention is not so limited. For example, the ATSC signal conveys services, e.g., news and information. In this regard, the AC channel could be used to convey auxiliary data for the news service. For example, the AC channel could be used to provide periodic emergency notification information that is periodically tuned to by the ATSC receiver. As such, this AC channel could be broadcast by other providers and from other locations. In this regard, it is not required that the ATSC transmitter and the AC transmitter be co-located, even if these signals are provided by the same service provider.

[0051] In view of the above, 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 numerous alternative arrangements which, although not explicitly described herein, embody the principles of the invention and are within its spirit and scope. For example, although illustrated in the context of separate functional elements, these functional elements may be embodied in one, or more, integrated circuits (ICs). Similarly, although shown as separate elements, any or all of the elements may be implemented in a stored-program-controlled processor, e.g., a digital signal processor, which executes associated software, e.g., corresponding to one, or more, of the steps shown in, e.g., FIGs. 8 and/or 12, etc. Further, the principles of the invention are applicable to other types of communications systems, e.g., satellite, Wireless-Fidelity (Wi-Fi), cellular, etc. Indeed, the inventive concept is also applicable to stationary or mobile receivers. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A method for use in a transmitter, the method comprising: transmitting a first signal in a channel, wherein the first signal conveys data associated with a service; and transmitting a second signal in the same channel, wherein the second signal is a co- channel interferer to the first signal and the second signal conveys auxiliary data for the service.

2. The method of claim 1, wherein the first signal is an ATSC DTV (Advanced Television Systems Committee-Digital Television) signal for conveying data representing a high definition television (HDTV) service.

3. The method of claim 2, wherein the transmitting a first signal step uses a vestigial sideband modulation, and the transmitting a second signal step uses a discrete multitone (DMT) modulation.

4. The method of claim 3, wherein a frequency of at least one carrier of the second signal corresponds to an ATSC (Advanced Television Systems Committee) comb filter null location.

5. The method of claim 2, wherein the second signal imitates at least one spectral property of an NTSC (National Television Systems Committee) broadcast signal.

6. The method of claim 2, wherein the auxiliary data is video data having a lower resolution than video data conveyed in the ATSC DTV signal.

7. The method of claim 1, wherein the auxiliary data conveys training information for use by a receiver for receiving the first signal.

8. A method comprising the steps of: providing an ATSC (Advanced Television Systems Committee) signal for broadcast in a channel for communicating a high definition television (HDTV) service; and providing an auxiliary channel (AC) signal for broadcast in the same channel as the ATSC signal; wherein the AC signal conveys auxiliary data for the HDTV service, and the providing step provides the AC signal such that the AC signal imitates at least one spectral property of an NTSC broadcast signal.

9. A method for use in a receiver, the method comprising: receiving a first signal in a channel, wherein the first signal conveys data associated with a service; and receiving a second signal in the same channel, wherein the second signal is a co- channel interferer to the first signal and the second signal conveys auxiliary data for the service.

10. The method of claim 9, wherein the first signal is an ATSC DTV (Advanced Television Systems Committee-Digital Television) signal for conveying data representing a high definition television (HDTV) service.

11. The method of claim 10, wherein the first signal is a vestigial sideband modulated signal and the second signal is discrete multitone (DMT) modulated signal.

12. The method of claim 11, wherein a frequency of at least one carrier of the second signal corresponds to an ATSC (Advanced Television Systems Committee) comb filter null location.

13. The method of claim 10, wherein the second signal imitates at least one spectral property of an NTSC (National Television Systems Committee) broadcast signal.

14. The method of claim 10, wherein the auxiliary data is video data having a lower resolution than video data conveyed in the ATSC DTV signal and further comprising using the auxiliary data as a source of video provided to a user.

15. The method of claim 9, wherein the auxiliary data conveys training information for use in the receiving a first signal step.

16. A method for use in a receiver, the method comprising: receiving a broadcast ATSC (Advanced Television Systems Committee) signal for a particular channel; recovering an HDTV signal from the received broadcast ATSC signal; receiving a broadcast auxiliary channel (AC) signal in the same channel as the received ATSC signal; and recovering auxiliary data associated with the HDTV signal from the received broadcast AC signal; wherein the received AC signal is a co-channel interfering signal to the received ATSC signal and the received AC signal imitates at least one spectral property of an NTSC (National Television Systems Committee) broadcast signal.

17. The method of claim 16, comprising: recovering an HDTV signal from the received broadcast ATSC signal.

18. Apparatus comprising: a first modulator for transmitting a first signal in a channel, wherein the first signal conveys data associated with a service; and a second modulator for transmitting a second signal in the same channel, wherein the second signal is a co-channel interferer to the first signal and the second signal conveys auxiliary data for the service.

19. The apparatus of claim 18,. wherein the first signal is an ATSC DTV (Advanced Television Systems Committee-Digital Television) signal for conveying data representing a high definition television (HDTV) service.

20. The apparatus of claim 19, wherein the first modulator uses a vestigial sideband modulation and the second modulator uses a discrete multitone (DMT) modulation.

21. The apparatus of claim 20, wherein a frequency of at least one carrier of the second signal corresponds to an ATSC (Advanced Television Systems Committee) comb filter null location.

22. The apparatus of claim 19, wherein the second signal imitates at least one spectral property of an NTSC (National Television Systems Committee) broadcast signal.

23. The apparatus of claim 19, wherein the auxiliary data is video data having a lower resolution than video data conveyed in the ATSC DTV signal.

24. The apparatus of claim 18, wherein the auxiliary data conveys training information for use by a receiver for receiving the first signal.

25. Apparatus comprising: an ATSC (Advanced Television Systems Committee) modulator for providing an

ATSC signal for broadcast in a channel for communicating a high definition television

(HDTV) service; and a discrete multitone (DMT) modulator for modulating auxiliary data to provide an auxiliary channel (AC) signal for broadcast in the same channel as the ATSC signal; wherein the auxiliary data is associated with the HDTV service and the DMT modulator modulates the auxiliary data such that the AC signal imitates at least one spectral property of an NTSC broadcast signal.

26. Apparatus comprising: an input for use in receiving from an antenna (a) a first signal in a channel, wherein the first signal conveys information associated with a service, and <b) a second signal in the same channel, wherein the second signal is a co-channel interferer to the first signal; and a demodulator for demodulating the received second signal for recovering therefrom auxiliary data associated with the service. .

27. The apparatus of claim 26, wherein the first signal is an ATSC DTV (Advanced Television Systems Committee-Digital Television) signal for conveying data associated with a high definition television (HDTV) service.

28. The apparatus of claim 27, wherein the first signal is a vestigial sideband modulated signal and the second signal is discrete multitone (DMT) modulated signal.

29. The apparatus of claim 28, wherein a frequency of at least one carrier of the second signal corresponds to an ATSC (Advanced Television Systems Committee) comb filter null location.

30. The apparatus of claim 27, wherein the second signal imitates at least one spectral property of an NTSC (National Television Systems Committee) broadcast signal.

31. The apparatus of claim 27, wherein the auxiliary data is video data having. a lower resolution than video data conveyed in the ATSC DTV signal.

32. The apparatus of claim 26, wherein the apparatus comprises a demodulator for processing the received first signal to recover the information associated with the service.

33. The apparatus of claim 32, wherein the auxiliary data conveys training information for use by the demodulator for processing the received first signal.

34. Apparatus comprising: an input for use in receiving from an antenna (a) a broadcast ATSC (Advanced

Television Systems Committee) for conveying a high-definition television (HDTV) service on a channel; and (b) a broadcast auxiliary channel (AC) signal in the same channel as the broadcast ATSC signal; and a discrete multitone (DMT) demodulator for demodulating the broadcast AC signal to provide auxiliary data associated with the HDTV service; wherein the broadcast AC signal is a co-channel interfering signal to the broadcast ATSC signal and the broadcast AC signal imitates at least one spectral property of an NTSC (National Television Systems Committee) broadcast signal.

35. The apparatus of claim 34, further comprising: an ATSC demodulator for demodulating the broadcast ATSC signal for recovering therefrom an HDTV signal.

36. The apparatus of claim 35, wherein the auxiliary data conveys training information for use by the ATSC demodulator for demodulating the broadcast ATSC signal.