KR20090012224A - Discrete multitone(dmt) communications without using a cyclic prefix - Google Patents

Abstract

A Discrete Multitone (DMT) modulator modulates symbols with subcarriers for providing DMT symbols, wherein the subcarriers are divided into a number of subcarrier subsets such that adjacent DMT symbols formed from different subcarrier subsets.

Description

DISCRETE MULTITONE (DMT) COMMUNICATIONS WITHOUT USING A CYCLIC PREFIX}

TECHNICAL FIELD The present invention relates to a communication system, and more particularly to a wireless system such as terrestrial broadcasting, cellular, Wi-Fi, satellite, and the like.

In discrete multitone (DMT) transmission systems, it is also common to transmit a so-called Cyclic Prefix (CP) with each DMT symbol to help mitigate multipath effects. Unfortunately, the use of CP increases the DMT symbol duration for the same payload, thereby reducing the information throughput of the system.

However, if such mitigation is not taken, the presence of multiple paths results in Inter Symbol Interference (ISI), which requires a much more complex receiver and can cause irreducible signal distortion at the output of the DMT receiver. There is a possibility. For example, if no CP is used at all, or if a CP that is much shorter than the expected multipath delay is used, ISI inevitably occurs when the multipath length exceeds the length of the CP. To reduce the impact of ISI in such a system, a DMT receiver typically adds a time domain (TD) equalizer instead of a frequency domain (FD) equalizer or instead of a frequency domain (FD) equalizer commonly used in DMT receivers. Also includes. Unfortunately, this method is very expensive to implement in a DMT receiver, not only in terms of the required hardware size but also in terms of the processing time necessary to perform TD equalization, and this feature is usually repetitive in nature for such a system.

The inventors have found that in some discrete multitone (DMT) systems it is possible to eliminate the need for cyclic prefixes without increasing the complexity or cost of the DMT receiver as described above. In particular, in accordance with the principles of the present invention, a DMT modulator modulates a symbol with a subcarrier to provide a DMT symbol, in which case the subcarrier is arranged such that multiple subcarrier subs are formed such that adjacent DMT symbols are formed from different subcarrier subsets. Are divided into sets. Therefore, in some DMT systems, greater information throughput can be achieved by not using a cyclic prefix without causing a significant increase in receiver complexity.

In one embodiment of the invention, the transmitter comprises a DMT modulator for providing a sequence of DMT symbols, in which case the DMT symbol (X _k) any of the sub-carrier (S _i) with previous and next DMT symbol (X with respect to the _{k -l} , X _{k + l} ) do not contain identically numbered subcarriers. For example, the DMT modulator uses six sets of subcarriers (S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , S ₆ ) to make DMT symbols. This set of subcarriers is divided into two subsets of subcarriers, the first subset comprising subcarriers (S ₁ , S ₃ , S ₅ ) and the second subset containing subcarriers (S ₂ , S ₄₎ , S ₆ ). The first subset and the second subset are separate. The DMT modulator uses the first subset to provide one DMT symbol and then uses the second subset to provide the next DMT symbol. In other words, the first subset is used for transmission of even DMT symbols and the second subset is used for transmission of odd DMT symbols (or vice versa).

Other embodiments and features are also possible and within the principles of the invention, as will be apparent from consideration of the above and reading the detailed description.

1-3 illustrate prior art NTSC transmissions.

4 illustrates an exemplary embodiment of an ATSC-DTV system in accordance with the principles of the present invention.

FIG. 5 illustrates an exemplary embodiment of a transmitter for use in the system of FIG. 4 in accordance with the principles of the present invention. FIG.

6-9 illustrate exemplary DMT transmissions.

10-15 illustrate exemplary DMT transmissions in accordance with the principles of the present invention.

FIG. 16 illustrates another exemplary embodiment of a transmitter for use in the system of FIG. 4 in accordance with the principles of the present invention. FIG.

FIG. 17 illustrates an exemplary embodiment of a device for receiving an auxiliary channel in accordance with the principles of the present invention. FIG.

18 illustrates an exemplary embodiment of a receiver in accordance with the principles of the invention.

19 is an exemplary flow chart for use in a receiver in accordance with the principles of the present invention.

20 illustrates another exemplary embodiment of a receiver in accordance with the principles of the invention.

In addition to the concept of the present invention, the elements shown in the figures are known and will not be described in detail. For example, the present invention, in addition to the concept, is familiar with discrete multitone (DMT) transmissions (or also called orthogonal frequency division multiplexing (OFDM) or coded orthogonal frequency division multiplexing (COFDM)). This is assumed and not described herein. Familiarity with television broadcasts, receivers and video encodings is also assumed and is not described in detail herein. For example, apart from the concept of the present invention, the present and proposed proposals regarding TV standards such as National Television Systems Committee (NTSC), Phase Alternation Lines (PAL), SECURE Couleur Avec Memoire (SECAM), and Advanced Television Systems Committee (ATSC) Familiarity with the recommendations is assumed. Likewise, in addition to the concepts of the present invention, other transmission concepts such as 8-level residual sideband (8-VSB), quadrature amplitude modulation (QAM), and radio-frequency (RF) front-ends, Receiver components or receiver sections such as low noise blocks, tuners, demodulators, correlators, leak integrators, and squarers are assumed. Similarly, in addition to the concepts of the present invention, formatting and encoding methods (such as the MPEG-2 System Standard (ISO / IEC 13818-1)) are known and not described herein for generating a transport bit stream. It should also be noted that the concept of the present invention can be implemented using conventional programming techniques as such will not be described herein. Finally, like numerals in the figures represent like elements.

The concept of the present invention is described in the context of an ATSC auxiliary channel. However, the concept of the present invention is not limited thereto and can be applied to any DMT based system. Before explaining the concepts of the present invention, some brief background information for legacy ATSC receivers, in particular background information for NTSC systems, is described and shown in FIGS. 1 shows a sample time domain (TD) representation of an NTSC signal as known in the art. The corresponding frequency spectrum of the NTSC signal transmission is shown in FIG. Of particular note is that most of the NTSC energy is located around a specific area of the spectrum: the picture carrier (video 10), the sound carrier (audio 12), and the chroma carrier (chroma 11). Currently, ATSC legacy receivers can reject NTSC transmissions (of limited power) that are located essentially within the band of the desired ATSC channel (so-called NTSC co-channel). In many ATSC legacy receivers on the market, this rejection is facilitated by the use of so-called comb filters or by the main channel equalizer. In both of these cases, ATSC legacy receivers rely on the fact that the energy of most NTSC identical channels is concentrated in the specific area noted above, rather than spreading evenly across the band. As such and as known in the art, it is relatively easy to remove this energy with a comb filter. In particular, the comb filter actually removes this energy at 12 equally spaced positions in the full spectrum (approximately 10.76 MHz). However, for a single sideband 8-VSB signal, only 5.38 MHz, half of the spectrum, is available. As such, the number of nulls is seven, one of which matches 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, 17, which are respectively video 10 and audio 12. And a chroma 11 carrier.

However, as described in co-owned international patent application PCT / US2005 / 045170, filed December 13, 2005, there is one information-bearing transmission on the same channel-hereafter referred to as an auxiliary channel (AC). It is designed in such a way as to mimic the spectral frequency domain (FD) characteristics of the actual NTSC co-channel transmission. As a result, the AC allows additional information to be sent to the ATSC receiver but the legacy ATSC receiver is not significantly affected, i.e. the system can be backward compatible. The use of AC channels described herein allows for a number of services. For example, an ATSC broadcaster may use AC to transmit an AC stream within the licensed ATSC band of the broadcaster itself to facilitate mobile reception of ATSC transmissions, to provide lower resolution video signals, and the like. As used herein, this additional information is called auxiliary data supporting one or more services provided by ATSC signals. This assistance data may represent such things as training information, content (video and / or audio), setup information, system information, program information, and the like.

In addition, because legacy ATSC receivers may rely on specific TD portions of NTSC co-channel interferers to recognize such interferers (eg, NTSC horizontal and vertical blanking intervals and syncs). Etc. The proposed AC signals can advantageously mimic them too. It should be noted that the TD portions of the signal, such as a "dummy" sink, are not entirely consumable but can actually be used by the receiver for synchronization purposes and the like. However, it is not required that an AC signal provide these "dummy" sinks or use the receiver even if these "dummy" sinks are provided.

Referring now to FIG. 4, one exemplary embodiment of an ATSC-DTV system 100 in accordance with the principles of the present invention is shown. The ATSC-DTV system 100 includes an ATSC-DTV transmitter 105 and at least one ATSC-DTV receiver. The ATSC-DTV receiver is represented in FIG. 4 by the mobile DTV 150 and the DTV 155. Mobile DTV 150 is a small, portable DTV, such as a hand-held, and DTV 155 represents a more general sized DTV for use at home, for example. The ATSC-DTV transmitter 105 broadcasts an ATSC signal as known in the art and is shown in tangential form in FIG. 4. The ATSC signal 111 is a data related signal in the form of a packetized data stream and is modulated in an 8-VSB format. It is also known in the art as "Physical transmission channel". This PTC has a center frequency (carrier frequency) and bandwidth. PTC provides approximately 19 Mbits / sec for transmission of MPEG2-compressed HDTV (high definition TV) signals (MPEG2 refers to the Moving Picture Expert Group-2 system standard (ISO / IEC 13818-1)). As such, four to six standard definition TV channels can be safely supported in a single PTC without congestion.

In addition, in accordance with the principles of the present invention, the ATSC DTV transmitter 105 also broadcasts the AC signal 116 shown in dashed form in FIG. As noted above and described further below, the AC signal 116 looks like a co-channel NTSC signal, but is actually auxiliary data for use by an ATSC receiver such as a mobile DTV 150 and / or a DTV 155. To carry. This auxiliary data makes it possible to provide additional services to ATSC receivers but does not affect legacy ATSC receivers.

One exemplary embodiment of the transmitter 105 is shown in FIG. 5. The transmitter 105 includes an 8-VSB modulator 110 and a DMT modulator 115 in accordance with the principles of the present invention, and provides an auxiliary channel. As noted above, AC mimics or mimics NTSC co-channels. To achieve the desired spectral characteristics (ie, one or more specific regions of the energy-intensive spectrum), a preferred modulation method is to use one variant of a discrete (orthogonal) multitone (DMT) signal to carry AC information. In addition to the concept of the present invention, those familiar with the principle of DMT (also known as OFDM or COFDM) will realize why such a transmission can be designed to have the desired spectral characteristics, and in particular in terms of ease of such signal equalization, DMT-based You will see other advantages of using the transmission of. Transmitter 105 is also a processor-based system and includes memory associated with one or more processors, such as processor 190 and memory 195 shown in dotted box form in FIG. 5. In this situation, computer programs or software are stored in the memory 195 for execution by the processor 190. This processor 190 represents one or more stored program control processors, which need not be dedicated to the transmitter function, for example, the processor 190 may control other functions of the transmitter 105. Memory 195 represents any storage device, such as random access memory (RAM), read-only memory (ROM), etc., may be internal and / or external to transmitter 105, and may be volatile and / or as desired. It is nonvolatile. The 8-VSB modulator 110 receives a signal 109 representing a data related signal for carrying DTV program and system information and modulates this data related signal to provide an ATSC signal 111 for broadcasting on a particular PTC. do. In accordance with the principles of the present invention, the DMT modulator 115 receives a signal 114 representing a data related signal for carrying ancillary data and modulates the data related signal as described below, thereby providing an ATSC signal 111. An AC signal 116 is provided for broadcasting on the same PTC as used for.

Referring now to FIG. 6, operation of the DMT modulator 115 is shown in the context of using DMT modulation to produce an AC signal 116 having one or more desired spectral characteristics of the NTSC signal. In particular, FIG. 6 shows an exemplary portion of an AC signal that mimics a single NTSC line, which is the basic building block for an AC co-channel waveform. Note that the part corresponding to the NTSC horizontal blanking period is drawn in a simplified manner only to indicate that the corresponding part of the AC signal does not carry a payload. As shown in FIG. 6, the AC information content is advantageously transmitted during the time interval 31 corresponding to the active video interval 21 of the NTSC line shown in FIG. 1. In addition to the concept of the present invention, AC information may be coded as the magnitude and / or phase of a section of complex / real sine wave as known in the art. The single sine wave shown in FIG. 6 is drawn for illustrative purposes only. The frequency of the sine waves should be chosen to place the AC transmission energy in at least one of the areas where the co-channel interfering NTSC picture carrier, NTSC sound carrier and / or NTSC chroma carrier are expected as shown in FIG. In the context of DMT transmission, it should be noted that only a portion of the interval 31 contains the AC payload waveform. In particular, and according to the DMT transmission, portions of the interval 31 are assigned to a cyclic extension (or cyclic prefix or guardband) to help cope with multiple paths. These are shown in FIG. 6 as CP1 and CP2, which are assigned as shown in parts 32 and 33, respectively. As a result, the AC payload is assigned to the portion 34 of the interval 31. Since the AC signal 116 is a co-channel interferer for the ATSC signal 111, the power level of the AC signal 116 is the ratio of the power of the AC signal 116 to the power level of the ATSC signal 111. Note that it may be desirable to be set to match the generally expected of the co-channel interferer. Indeed, since the broadcaster can control both the ATSC signal 111 and the AC signal 116, this power ratio (similar to the ratio of desirable-to-desirable (D / U) in ATSC broadcasting) One or more such as represented by signal 106 may be adjusted in a static and / or dynamic manner by the signals, which are shown in phantom in FIG. 5.

In FIG. 6, exemplary numerical values are assigned to each portion of the interval 31. For example, portion 34 is assigned to 22.3 ms. As such, the inverse of the payload length is 1 / 120-th of the ATSC signal bandwidth of exactly 5.38 MHz, which allows six orthogonal AC subcarriers to lie within the ATSC spectrum by 5.38 MHz / 6 = 897 kHz. (As noted above, one of the seven nulls is associated with the ATSC pilot signal). It is also shown in FIG. 7, which shows an exemplary power spectral density for an AC signal 116 with (f _k -f _{k -l} ) = 897 kHz and six subcarriers. Specific f _k The value is selected to match one or more of the six frequency positions notched-out by the comb filter of the ATSC receiver as illustrated earlier in FIG. 3. In the time domain TD, each DMT (OFDM) symbol is made up of the sum of the subcarriers, each of which has an appropriate phase and size windowed to the desired length. By way of example, the length of the time domain window in this example is taken to be a large multiple of the minimum orthogonal spacing of the subcarriers. This is illustrated in FIG. 7 by the inner envelope 41 as compared to using the minimum-length 12 TD window as shown by the outer dashed line 42 around S ₁ . This is done to concentrate the signal energy in a very narrow area around the desired spectral position, which is dictated by the constraints imposed on the auxiliary channel transmission. (It should be noted that this multiple is usually equal to '1' in conventional DMT systems.)

Returning briefly to FIG. 6, it can be observed that the use of CP reduces the information throughput of the system. For example, the payload portion 34 is only 22.3 ms out of the allowable 52.6 ms. However, the inventors have found that if each TD symbol duration is chosen to be substantially longer than the minimum orthogonal spacing of the six subcarriers-in the absence of CP-the multipath will affect this transmission in a somewhat special manner. In particular, with regard to any multipath delay (ie, with respect to any duration overlapping between adjacent symbols), each subcarrier within a given symbol is most likely to be equally numbered subcarriers of the adjacent symbol. Will be affected.

This point is further clarified by referring to Fig. 7, regarding the subcarriers designated S ₁ and S ₆ again. The frequency of S ₁ is 20/240 = 1/12 (the frequencies are given as fractions of the selected sampling rate (Fs), where Fs is equal to 2 * 5.38MHz = 10.76MHz). The frequencies of the remaining five subcarriers are integer multiples of the frequency of S ₁ , as shown in FIG. 7. Since the subcarrier frequencies are all integer multiples of 1/12 * Fs, the minimum time interval at which these frequencies are orthogonal to each other is 12 * 1 / Fs = 12 * Ts (where Ts is the TD sampling interval). As such, if this is a conventional DMT-based system, the required TD window length is 12 * Ts. However, and noted above, in this example the TD symbol duration is chosen to be substantially longer than the minimum orthogonal spacing of the six subcarriers to allow the energy of the subcarriers to be concentrated in a much narrower frequency region. For example, assume that the TD window duration (W) is a value of W = 240 or 20 times the orthogonal interval. An exemplary TD plot of a single DMT symbol for the value of W = 240 is shown in FIG. 8 (single subcarrier S ₁ is shown for illustrative purposes only). With this idea in mind now and with attention to FIG. 9, FIG. 9 illustrates a sequence of time domains for three transmitted DMT symbols (X _{k −1} , X _k , X _{k +1} ). It is assumed that the upper part 61 represents the main path and the lower part 62 represents the 'ghost', where 'ghost' is the main path symbol stream which is delayed by d samples and then added to the main path ( Ie multipath). As can be seen from FIG. 9, the symbol X _k overlaps a portion of itself (length Wd) and a portion of the preceding symbol X _{k −1} (length d). If, for example, such a time domain sequence is seen from the subcarrier S _l point of view, all of these overlapping portions are projected onto the subcarrier S _l to create a two-fold effect. First, the phase and magnitude of the subcarrier S _l in each symbol in the main path sequence will be changed by some fixed complex factor that depends on the magnitude of the ghost and the delay d. Second, a contribution such as noise is added to the subcarrier S _l of each symbol in the main path sequence. The first effect is due to the contribution of the delayed version of S _l of the symbol (X _k ) itself and can easily be overridden through the use of a simple 1-tap equalizer, while the second effect is X _k and X _{k. -1} all of subcarriers (S ₂ to S _6), the contribution due to the contribution of the well will not only S _l of the symbol (X _{k -1)} is much more difficult to cancel (even if that is possible).

With the contribution from the remaining sub-carriers, the observation of the contribution from the sub-carrier of the X _{k -1} (S _l) can also be made. In particular, the contribution from the subcarrier S _l of X _{k -1} grows linearly as a function of d and X _k when d = W It potentially reaches the same value as its desired contribution of S ₁ . In the case of contributions from the rest of the subcarriers, contributions from S ₂ to S ₆ of both X _k and X _{k -1} grow only as a function of d modulo12, and (12) of the power of the desired contribution to S _l . / 240) never exceeds ² = 1/400. Therefore, these latter contributions can be neglected, especially if it is substantially smaller than the contribution expected from other interference sources at the receiver. In the example shown in FIG. 4, this situation applies because the AC power is well below the main ATSC channel power.

In view of the above observations, the inventors have realized that it is possible to eliminate the need for cyclic prefixes and still cope with multiple paths without increasing the complexity or cost of the DMT receiver. Therefore, as can be observed from FIG. 10, since the payload portion 34 ′ is now increased to 52.6 ms, the CP can be eliminated and larger information throughput can be achieved. In particular, and in accordance with the principles of the present invention, a DMT modulator modulates symbols into subcarriers for providing a DMT symbol, in which case the subcarriers use multiple subcarrier subs such that adjacent DMT symbols use different subcarrier subsets. Are divided into sets. In other words, the symbol (X _{k -1,} X _{k +1)} according to any of the subcarriers (S _i) of the symbol (X _k) does not include the sub-carriers are equally numbered.

11 illustrates one exemplary embodiment of a DMT modulator 115 in accordance with the principles of the present invention. FIG. 11 shows a subset of K carriers (K> 1, K> 1, from 117-1 to 117-K, such that DMT modulation uses different subcarrier subsets of adjacent DMT symbols provided by DMT modulator 115). It is similar to FIG. 5 except that the placement of the DMT modulator 115 is clarified to show what is being done using. For example, continuing with the example described above of a set of six subcarriers from S ₁ to S ₆ , an exemplary division into subcarrier subsets for use by the DMT modulator 115 is K. A value of = 2, ie two subsets of carriers, is shown in FIGS. In particular, as shown in FIG. 12, subset 1 includes subcarriers S ₁ , S ₃ , and S ₅ , and as shown in FIG. 13, subset 2 includes subcarriers S ₂ , S ₄ , and S _6. ). The DMT modulator 115 uses the first subset to provide one DMT symbol and then uses the second subset to provide the next DMT symbol. In other words, the first subset is used for transmission of odd DMT symbols, and the second subset is used for transmission of even DMT symbols (or vice versa).

In view of the above, an exemplary flow diagram for use in transmitter 105 in accordance with the principles of the present invention is shown in FIG. 14. In step 160, the transmitter 105 receives auxiliary data regarding AC. Ancillary data supports one or more services provided via ATSC signals. In step 165, the transmitter 105 forms a co-channel interference signal into an ATSC signal in accordance with the principles of the present invention. In this example, transmitter 105 transmits AC signal 116 as a DMT signal that mimics at least one spectral characteristic of an NTSC broadcast signal using DMT-based transmission. Further, the set of available subcarriers is divided into K subcarrier subsets, and the DMT modulator 115 uses different carrier subsets to form adjacent DMT symbols.

It should be noted that additional steps may also be performed when transmitting the AC signal to ensure "link budget" conservation compared to legacy systems. For example, when there are two subcarrier subsets each having the same number of subcarriers, the following two additional steps are also proposed when transmitting an AC signal. The first is that the power of each subcarrier in the subcarrier subset must be increased by a factor of two (by increasing the magnitude by a factor of √2). In this way the total average signal power (and hence signal-to-noise ratio (SNR) at the receiver) remains the same. Second, the TD duration of the new symbol pair (eg, each of the two symbols in the pair includes one of two non-overlapping subcarrier subsets) equals the single symbol duration of the older system. In order to do this, the TD window length should be reduced by a factor of two. In this way (in conjunction with the power adjustment suggested above), for each received subcarrier, the ratio of the magnitude of the projection of the signal component and the standard deviation of the projection of the noise component are kept the same as in the original system. Preserve your budget. This is also illustrated in FIG. 15, which shows the subcarrier S ₁ with respect to the sequence of transmitted DMT symbols X _{k -2} , X _{k -1} , X _k , X _{k +1} , X _{k +2} . Shows a sample time domain sequence as " seen " by a receiver tuned to " (now W = 120 = 240/2). It can also be observed from FIG. 15 that the adjacent DMT symbols are done back and forth between using subcarrier subset 1 and using subcarrier subset 2. FIG.

As noted above, the inventive concept allows broadcasters to provide one or more services via AC that support one or more services provided by ATSC signals. As one example, AC is a support channel (e.g., to allow ATSC signal to be received in a mobile environment as represented by mobile DTV 150 of FIG. 4) to facilitate reception of ATSC signal 111. . In this scenario, the broadcaster's prior knowledge (ATSC signal 111) of the information to be transmitted on the main ATSC channel is used to transmit support information for the AC channel. For example, assume that an information stream relating to a program is to be transmitted at a predetermined time T _S by the ATSC signal 111. The additional information, ie a subset of the information stream to be transmitted by the ATSC signal 111, is sent as auxiliary data by the AC signal 116 in advance at time T _E. This assistance data is used by the mobile DTV 150 to facilitate the reception of the ATSC signal 111. The value of T _E indicates that the resulting time interval T _S -T _E has sufficient time to process auxiliary data prior to the arrival of the information stream scheduled by the ATSC signal 111 at time T _S. Picked to provide. Therefore, mobile DTV 150 may receive information about the AC channel to help receive the main ATSC channel. By way of example, a particularly advantageous way of using an AC channel for training is to send data (training data) used for training as auxiliary data, which is also data indicating the position of the training data in the ATSC signal 111. It may include. Therefore, reception of AC by mobile DTV 150 then allows mobile DTV 150 to further identify training data and its location in the received version of ATSC signal 111. A variation of this transmitter 105 is shown by dashed line 109-1 in FIG. 16, in which case a subset of the data provided in the ATSC signal 111 (eg, training data) is also via the DMT modulator 115. Is sent.

As another example, an AC is an independent data or video channel that supports one or more services provided by ATSC signals. For example, in a mobile environment, an ATSC broadcaster may transmit a lower resolution video over the AC as compared to the resolution of the video carried by the ATSC signal. This lower resolution video may represent a program also carried by the ATSC signal or simply a completely different program at a lower resolution than the video carried in the ATSC signal.

Similarly, AC can be used for non-real-time transmission of file-based information to pedestrians and mobile receivers that can store information for later use.

As another example, AC is a robust / fallback audio channel. The nature of analog television transmission is that sound usually continues to work even when the picture experiences momentary interference. The viewer endures the momentary freeze or loss of the picture, but the loss of sound is more unpleasant. As such, another application of AC is to provide an audio service that is less affected by the instantaneous decrease in signal level received at an ATSC receiver.

As another example, AC is an antenna pointing / diagnostic information provider for use in receiving ATSC signals. It may be helpful for the consumer to use AC to enhance the "ease of use". As an example, the diagnostic information may be displayed to facilitate the automatic antenna indication by assisting the user with respect to antenna pointing or the CEA antenna control interface standard (CEA-909).

Therefore, as described above and in accordance with the principles of the present invention, the AC carries data associated with at least one service carried by the co-channel ATSC signal (main ATSC channel). In this context, the term "service" refers to the following, i.e., AC may carry additional programming (news, entertainment, etc.) that is independent of or related to programming carried on the user by the main ATSC channel (news, entertainment, etc.). The type of information carried to the user as can be, for example, the type of content carried in the main ATSC channel, such as the AC can carry additional news, audio and / or video, etc. in a different content format than that carried in the main channel. For example, it relates to one or more of the operations of an ATSC receiver, or to a combination thereof, such as for example to support AC receiving the main ATSC channel to carry training information, setup information and / or diagnostic information, and the like.

Referring now to FIG. 17, one exemplary embodiment of a device 200 in accordance with the principles of the present invention is shown. Device 200 represents any processor-based platform such as, for example, a PC, server, set-top box, personal digital assistant, cellular telephone, mobile DTV 150, DTV 155, and the like. In this regard, device 200 includes one or more processors with associated memory (not shown) and also includes receiver 210. The receiver 210 receives the ATSC signal 111 and the AC signal 116 by an antenna (not shown). The receiver 210 processes the received ATSC signal 111 to recover the HDTV signal 211 for application to the display 220, and the display 220 is part of the device 200 as shown in dotted line form or It may not be part of it. Receiver 210 also processes the received AC signal 116 to recover auxiliary data 216. Depending on the particular service, assistance data 216 may be used by receiver 210 itself (eg, in the case of the training data described above), or assistance data 216 may be another portion of device 200 or device ( 200 may be provided outside. An example is shown in FIG. 17, in which auxiliary data 216 (in the form of dashed lines) represents low resolution video content. In this case, the display 220 may use the low resolution video content of the auxiliary data 216 instead of the high resolution video content of the HDTV signal 211. Alternatively, the device 200 may select between the HDTV signal 211 and the low resolution video of the auxiliary data 216 as a video source for the display 220. This selection may be performed in any manner, for example as a function of the comparison by the receiver 210 between the received ATSC signal 111 and the corresponding signal to noise ratios (SNRs) for the received AC signal 116. In this case, the signal with the highest SNR is selected.

18 illustrates one exemplary embodiment of a receiver 210 in accordance with the principles of the present invention. The receiver 210 includes an ATSC demodulator 240, an AC detector 235, and a DMT demodulator 230. Receiver 210 is also a processor-based system and includes memory associated with one or more processors, such as represented by processor 390 and memory 395, shown in dotted box form in FIG. 18. In this situation, a computer program or software is stored in the memory 395 for execution by the processor 390. This processor 390 represents one or more stored program control processors, which need not be dedicated to the receiver function, for example, the processor 390 can also control other functions of the receiver 210. For example, if receiver 210 is part of a larger device, processor 390 may control other functions of this device. Memory 195 represents any storage device, such as random access memory (RAM), read-only memory (ROM), and the like, and may be internal and / or external to transmitter 105, and may be volatile or nonvolatile as needed.

The antenna 301 of FIG. 18 receives one or more broadcast signals and provides them to the receiver 210 via an input 299. In this example, antenna 301 provides ATSC signal 111 and also provides AC signal 116, which is a co-channel interference signal. It is assumed that receiver 210 is tuned to a particular channel to receive something such as ATSC signal 111. ATSC demodulator 240 receives ATSC signal 111 and provides the HDTV signal 211 mentioned above. In this example, it is assumed that ATSC demodulator 240 also includes any desired decoding functionality. AC detector 235 monitors the currently tuned channel with respect to AC signal 116. According to the principles of the present invention, since the AC signal 116 looks like an NTSC co-channel signal, the AC detector 235 can be configured in a manner similar to current NTSC signal detectors. Upon detecting the presence of the AC signal 116, the AC detector provides one or more signals, such as represented by any one of the signals 236, 237, 238 in the form of dashed lines. For signal 237, this signal is provided to ATSC demodulator 240. The ATSC demodulator 240, in response to detecting the presence of the AC signal 116, may remove the interfering signal as a comb filter (not shown) of the ATSC demodulator 240 does for the co-channel interfering NTSC signal. To be able. As for the signal 238, this signal is provided to the DMT demodulator 230. Upon detection of AC signal 116, DMT demodulator 230 is activated to demodulate AC signal 116 to recover auxiliary data 216. Regarding 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, earlier noted TD portions of the signal, such as the 'dummy' horizontal sync of the AC signal 116 can also be used by the receiver 210 to receive it by making it easier to locate OFDM symbols in the AC stream. To help.

As mentioned above, and in accordance with the principles of the present invention, a DMT-based transmitter uses different subcarrier subsets in forming DMT symbols. As a result, the corresponding receiver must be synchronized with the transmission pattern, i. E. The sequence of subcarrier subsets used by the DMT-based transmitter. In the situation of the above example, for two subcarrier subsets, the transmission pattern can be seen as an "odd / even" pattern. For example, for a first received DMT symbol, a first subcarrier subset is used for demodulation, whereas for a second received DMT symbol, a second subcarrier subset is used for demodulation. By way of example, such synchronization may be performed in any of several ways. For example, the transmitter 105 transmits a predefined training sequence of DMT symbols as part of the AC signal 116. Upon detection of an AC signal received by the AC detector 235 of the receiver 210, the DMT demodulator 230 is locked to the received training sequence, and between subcarrier subsets to demodulate the received DMT symbol data. It starts to come and go. For example, the DMT demodulator 230 uses the first subcarrier subset to demodulate the first received DMT symbol, then continues in the same way for each received " odd " DMT symbol, and the second received Use a second subset of subcarriers to demodulate the DMT symbols, and then do the same for each received " even " DMT symbol (or vice versa). Alternatively, different types of training sequences may be predefined in the system to represent different types of patterns of the subcarrier subset, so that once the DMT demodulator 210 has identified a particular training sequence, the subcarrier subs to use. Special patterns of the set were also identified by the DMT demodulator 230. In addition, such particular pattern of information may be carried over an out-of-band channel, such as a portion of system information carried in a received ATSC signal 111, as known in the art.

In view of the above, FIG. 19 shows an exemplary flow diagram for use in receiver 210 in accordance with the principles of the present invention. In step 405, the receiver 210 receives a broadcast AC signal 116 carrying auxiliary data as co-channel interference signals for ATSC transmission. In step 410, the DMT demodulator determines a subcarrier subset pattern to use to demodulate received DMT symbols, such as by locking with a training signal. In step 415, receiver 210 demodulates the received AC signal to provide assistance data.

In addition to the exemplary embodiment shown above, another exemplary embodiment of a receiver in accordance with the principles of the present invention is shown in FIG. 20. Receiver 210 'is similar to receiver 210 of FIG. 18 except that there is no demodulator for the primary ATSC channel. Instead, AC is used to support the services found on the main ATSC channel, which is done by providing these services to the user via AC. For example, programming (news, entertainment) found in the main ATSC channel is provided to the user via AC and / or the type of content carried in the main ATSC channel is carried in the main channel (e.g., the lower noted above). AC is associated with the operation of the receiver 201 'such as provided via AC in a format different from video of a resolution) and / or the AC may carry training information, setup information and / or diagnostic information, and the like. Carrying data is done.

As mentioned above, and in accordance with the principles of the present invention, it is possible to eliminate the need for a cyclic prefix (or also referred to as a cyclic extension or guardband), so that a larger without causing a significant increase in receiver complexity. Provide information throughput. As such, although the concept of the present invention has been described in the context of an auxiliary channel in an ATSC transmission system, the present invention is not limited thereto and is applicable to any DMT-based communication system. Further, although the concept of the present invention has been described in the context of an "odd / even" pattern, the concept of the present invention is not limited thereto and can be applied to any pattern of K subcarrier subsets. Further, although the concept of the present invention has been described in the context of dividing the set of subcarriers into K subcarrier subsets (each subcarrier subset having the same number of subcarriers), the present invention is not limited thereto, but The above subcarrier subset may have a different number of subcarriers than the remaining subcarrier subset.

In view of the above, the foregoing is merely illustrative of the principles of the present invention, and therefore those skilled in the art, although not expressly described herein, many alternatives that implement the principles of the present invention and are within the spirit and scope of the present invention. It turns out that you can devise a logical layout. For example, although illustrated in the context of separate functional elements, these functional elements may be implemented in one or more integrated circuits (ICs). Similarly, although shown as independent elements, any or all of these elements may be implemented in a stored program control processor such as a digital signal processor, such digital signal processor as shown, for example, in FIGS. Run associated software, such as corresponding to one or more steps. In addition, the principles of the present invention are applicable to other types of communication systems such as satellites, Wi-Fi, cellular, and the like. Indeed, the concepts of the present invention may apply to stationary or mobile receivers. Therefore, it should be understood that numerous modifications may be made to the exemplary embodiments, and that other arrangements may be devised without departing from the spirit and scope of the invention as defined by the appended claims.

As described above, the present invention can be used in the field of wireless systems such as terrestrial broadcasting, cellular, Wi-Fi, satellite, and the like.

Claims (30)

As a device, A discrete multi-tone (DMT) modulator for modulating the symbol on the subcarrier to transmit the DMT symbol, And the subcarrier is divided into a plurality of subcarrier subsets such that adjacent DMT symbols are formed from different subcarrier subsets. The apparatus of claim 1, wherein the subcarriers are divided into K subcarrier subsets such that each subcarrier subset is separated from the remaining subcarrier subsets. 3. The apparatus of claim 2, wherein each subcarrier subset has the same number of subcarriers as the remaining subcarrier subset. 3. The apparatus of claim 2, wherein K is equal to 2 and the DMT modulator moves back and forth between subcarrier subsets when forming DMT symbols. 5. The apparatus of claim 4, wherein the number of subcarriers is six. 2. The system of claim 1, further comprising an ATSC Advanced Television Systems Committee-Digital Television (ATTV) modulator for carrying data indicative of a high definition television (HDTV) service, Wherein the DMT symbols represent auxiliary channel data for an HDTV service. 7. The apparatus of claim 6, wherein the DMT modulator forms an auxiliary channel such that the auxiliary channel mimics at least one spectral characteristic of the NTSC broadcast signal. An apparatus, comprising: a discrete multi-tone (DMT) demodulator for demodulating received DMT symbols to provide recovered data, For each received DMT symbol, the DMT demodulator uses a subset of subcarriers for demodulating the received DMT symbols, and the DMT demodulator uses a different subset of subcarriers to demodulate adjacent received DMT symbols. , Device. 9. The apparatus of claim 8, wherein the subcarriers are divided into K subcarrier subsets such that each subcarrier subset is separated from the remaining subcarrier subsets. 10. The apparatus of claim 9, wherein each subcarrier subset has the same number of subcarriers as the remaining subcarrier subset. 10. The apparatus of claim 9, wherein K is equal to 2 and the DMT demodulator cycles back and forth between subcarrier subsets when demodulating received DMT symbols. The apparatus of claim 11, wherein the number of subcarriers is six. 9. The apparatus of claim 8, further comprising an ATSC DTV demodulator for recovering the HDTV signal, wherein the recovered data provided by the DMT demodulator represents auxiliary data associated with the HDTV signal. 14. The apparatus of claim 13, further comprising a detector for enabling a DMT demodulator by detecting the presence of a signal indicative of a received DMT symbol, wherein the detector comprises at least one of a National Television Systems Committee (NTSC) broadcast signal in the signal. And detecting its presence by detecting spectral characteristics. As a method for use in a transmitter, Receiving data for transmission; Modulating the received data using discrete multi-tone (DMT) based modulation to provide a sequence of DMT symbols for transmission, And the DMT subcarrier is divided into a plurality of subcarrier subsets such that adjacent DMT symbols are formed from different subcarrier subsets. 16. The method of claim 15, wherein the subcarriers are divided into K subcarrier subsets such that each subcarrier subset is separated from the remaining subcarrier subsets. 17. The method of claim 16, wherein each subcarrier subset has the same number of subcarriers as the remaining subcarrier subsets. 17. The method of claim 16, wherein K is equal to 2 and the modulating step is to switch back and forth between subcarrier subsets in the formation of a DMT symbol. 19. The method of claim 18, wherein the number of subcarriers is six. 16. The method of claim 15, further comprising modulating the data to provide an ATSC DTV signal to carry data indicative of high definition television (HDTV) services. The DMT symbol represents auxiliary channel data for the HDTV service. 21. The method of claim 20, wherein the DMT modulation step forms the auxiliary channel such that the auxiliary channel mimics at least one spectral characteristic of an NTSC broadcast signal. As a method for use in a receiver, Receiving DMT symbols; Demodulating each received DMT symbol to provide recovered data using the subcarrier subset, A different subset of subcarriers is used to demodulate adjacent received DMT symbols. 23. The method of claim 22, wherein the subcarrier is divided into K subcarrier subsets such that each subcarrier subset is separated from the remaining subcarrier subsets. 24. The method of claim 23, wherein each subcarrier subset has the same number of subcarriers as the remaining subcarrier subset. 24. The method of claim 23, wherein K is equal to 2 and the demodulation step is to step back and forth between the subcarrier subsets when demodulating the received DMT symbol. 27. The method of claim 25, wherein the number of subcarriers is six. 23. The method of claim 22, further comprising demodulating the received ATSC DTV signal to recover the HDTV signal, The recovered data provided by the DMT demodulation step represents ancillary data associated with the HDTV signal. 28. The method of claim 27, further comprising: detecting the presence of a signal indicative of a received DMT symbol, detecting the presence of a signal that detects the presence by detecting at least one spectral characteristic of the NTSC broadcast signal in the signal; If there is a signal indicative of the received DMT symbol, further comprising performing a DMT demodulation step. 23. The method of claim 22, wherein demodulating comprises determining a subcarrier subset pattern for use in demodulating each received DMT symbol having a particular subcarrier subset. 30. The method of claim 29, wherein determining the subcarrier subset pattern comprises detecting a training sequence associated with the subcarrier subset pattern.

Images