Abstract:
A transport stream for conveying a program for a particular channel includes an auxiliary channel, which conveys multiple lower resolution programs associated with other channels. When a receiver has difficulty receiving a particular channel due to the geographical location of the receiver, the receiver tunes to a stronger signal associated with another channel and recovers a lower resolution version of the desired program from the auxiliary channel conveyed therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/666,077, filed Mar. 29, 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 many wireless communications systems, the key problem is that a receiver may be able to receive the transmission of some of the channels (or signals) but not all of them. For example, in a terrestrial broadcast television (TV) system in the United States, a city may typically have 5 to 15 terrestrial transmitters that are geographically separated, each terrestrial transmitter broadcasting content on a particular channel (or channels). However, a TV set may only be able to receive a subset of the channels being broadcast in a given geographical area because of the geographical location of the TV set. Indeed, for a modern digital communication system like the ATSC-DTV (Advanced Television Systems Committee-Digital Television) system (e.g., see, United States Advanced Television Systems Committee, “ATSC Digital Television Standard”, Document A/53, Sep. 16, 1995 and “Guide to the Use of the ATSC Digital Television Standard”, Document A/54, Oct. 4, 1995), it is well known that the coverage for a given area varies depending on the location of the TV set. This is further illustrated in  FIG. 1 . A geographical area includes terrestrial ATSC-DTV transmission towers T 1 , T 2 , T 3  and T 4 , for broadcasting content associated with channels 1, 2, 3 and 4, respectively. (For the purposes of this example, it is assumed that each transmission tower only broadcasts programming for a single channel.) In this geographical area, two TV sets, TV set  10  and TV set  20 , are located. As illustrated in  FIG. 1  by the dotted lines arrows, TV set  10  is only able to receive a subset of the available channels, i.e., channels 2, 3 and 4. Likewise, the dashed line arrows of  FIG. 1  illustrate that TV set  20  is only able to receive channels 1, 2 and 4. 
         [0004]    There is no solution today that can mitigate this problem. 
       SUMMARY OF THE INVENTION 
       [0005]    At present, an ATSC-DTV system 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 physical transmission channel (PTC) without congestion. Additionally, enough bandwidth remains within this transport stream to provide several additional low-bandwidth non-conventional services such as weather reports, stock indices, headline news, home shopping, etc. In fact, due to improvements in both MPEG2 encoding and the introduction of advanced codec (coder/decoder) technology (such as H.264 or VC1), even more additional spare capacity is becoming available in a PTC. 
         [0006]    I have observed that this spare capacity can be put to use to provide a method and apparatus for providing robust reception in a wireless communications system. In particular, and in accordance with the principles of the invention, a transport stream for conveying a program for a particular channel includes an auxiliary channel, which conveys multiple lower resolution programs associated with other channels. Thus, if a receiver has difficulty receiving a particular channel due to the location of the receiver, the receiver can tune to a stronger signal associated with another channel and recover a lower resolution version of the desired program from the auxiliary channel conveyed therein. 
         [0007]    In an embodiment of the invention, an ATSC-DTV transmitter for a TV provider transmits a digital multiplex that includes a primary channel and an auxiliary channel. The primary channel includes one or more high definition TV (HDTV) channels offered by the TV provider; while the auxiliary channel rebroadcasts multiple lower resolution programs associated with channels broadcast by other ATSC-DTV transmitters. 
         [0008]    In another embodiment of the invention, an ATSC-DTV receiver performs a method that provides for a more robust reception of terrestrial video signals. Illustratively, the ATSC-DTV receiver initially tunes to the PTC associated with the desired channel. If the ATSC-DTV receiver determines that no signal is available (e.g., an associated received signal strength indicator (RSSI) is below a predetermined value), then the ATSC-DTV receiver tunes to another PTC and, upon detection, recovers the desired program from the auxiliary channel conveyed therein. 
         [0009]    In another embodiment of the invention, program content is embodied in a data-bearing signal comprising at least one carrier wave, the data bearing signal representing a plurality of packets for conveying program content for at least one primary channel and an auxiliary channel, wherein the auxiliary channel rebroadcasts lower resolution program content from other channels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  illustrates reception problems in a terrestrial television broadcast areas; 
           [0011]      FIG. 2  illustrates terrestrial broadcast in accordance with the principles of the invention; 
           [0012]      FIG. 3  shows an illustrative block diagram of a transmitter embodying the principles of the invention; 
           [0013]      FIG. 4  shows an illustrative flow chart in accordance with the principles of the invention for use in the transmitter of  FIG. 3 ; 
           [0014]      FIG. 5  shows a portion of an illustrative signal format in accordance with the principles of the invention; 
           [0015]      FIG. 6  shows an illustration of a primary channel and an auxiliary channel in the context of the terrestrial broadcast arrangement illustrated in  FIG. 2 ; 
           [0016]      FIG. 7  shows an illustrative high-level block diagram of a receiver embodying the principles of the invention; 
           [0017]      FIG. 8  show illustrative portions of a receiver embodying the principles of the invention; and 
           [0018]      FIG. 9  shows an illustrative flow chart for use in a receiver in accordance with the principles of the invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0019]    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 and receivers 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), and receiver components such as a radio-frequency (RF) front-end, or receiver section, such as a low noise block, tuners, demodulators, correlators, leak integrators and squarers is assumed. Similarly, formatting and encoding methods (such as Moving Picture Expert Group (MPEG)-2 Systems Standard (ISO/IEC 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. 
         [0020]    An illustrative arrangement for ATSC-DTV terrestrial broadcast in accordance with the principles of the invention is shown in  FIG. 2 . This figure is similar to  FIG. 1  except that one, or more, of the transmission towers shown in  FIG. 2  transmits a signal in accordance with the principles of the invention (described below). In this example, a transmitter  100  is associated with transmission tower T 2  for transmitting a signal  111  in accordance with the principles of the invention. The other transmission towers, T 1 , T 3  and T 4  may, or may not, have similar transmitters in accordance with the principles of the invention. Similarly, receivers, as represented by TV sets  200  and  205 , are adapted, in accordance with the principles of the invention, to take advantage of the transmitted signal to provide for robust reception. As can be observed from the dotted arrows of  FIG. 2 , TV set  200  is only able to receive a subset of the available channels, i.e., channels 2, 3 and 4. Reception for channel 1 is either too poor or nonexistent. Likewise, the dashed line arrows of  FIG. 2  illustrate that TV set  205  is only able to receive channels 1, 2 and 4 for effective viewing of the content therein. TV set  205  is similar to TV set  200  (described below) and is not described further herein. For the purposes of this example, each transmission tower is illustratively associated with a particular TV provider, which transmits programming on a single channel. For example, transmission tower T 1  broadcasts programming for channel 1.1, transmission tower T 2  broadcasts programming for channel 2.1, transmission tower T 3  broadcasts programming for channel 3.1 and transmission tower T 4  broadcasts programming for channel 4.1, where each channel number uses the ATSC major-minor channel number format as known in the art. However, the invention is not so limited. For example, transmission tower T 1  may broadcast programming for more than one channel, e.g., channels 1.1, 1.2, etc. Similarly, a transmission tower may not be associated with a particular TV provider. 
         [0021]    Turning now to  FIG. 3 , an illustrative embodiment of transmitter  100  is shown. Other than the inventive concept, transmitter  100  forms an ATSC-DTV signal  111  for transmission via transmission tower T 2  of  FIG. 2  as known in the art. Transmitter  100  comprises a modulator  110 , a low resolution encoder  115 , a memory  120  and a processor  105 . The latter is representative of one or more microprocessors and/or digital signal processors (DSPs) and may include additional memory (not shown) for executing programs and storing data. In this regard, memory  120  is representative of memory in transmitter  100  and includes, e.g., any memory of processor  105  and/or modulator  110  and/or low resolution encoder  115 . Reference at this time should also be made to  FIG. 4 , which shows an illustrative flowchart in accordance with the principles of the invention for use in transmitter  100 . 
         [0022]    In accordance with the principles of the invention, transmitter  100  forms an auxiliary channel in step  160 . In particular, transmitter  100  receives programming content for each of the other channels, via signal  114 , and encodes this program data at a lower resolution, via lower resolution encoder  115 . The latter provides auxiliary channel data  116 , which represents a statistically multiplexed data stream of lower resolution programs associated with other channels. In this example, programs for channels 1, 2, 3 and 4 of  FIG. 2  are provided via auxiliary channel data  116 , albeit at a lower resolution. It should be noted that lower resolution encoder  115  is representative of one, or more, encoders for providing lower resolution programming content. As such, other variations are possible. For example, transmitter  100  can comprise an array of lower resolution encoders, where each lower resolution encoder receives program content from one provider. In addition, each lower resolution encoder can use a different encoding or compression format. Alternatively, the auxiliary channel may be formed elsewhere and provided directly to transmitter  100  for rebroadcast as part of the PTC, etc. In step  165 , processor  105  receives data related to each of the PTCs, PTC(0) through PTC(K−1), where K&gt;0, via signal  104 , and forms a “Master Program Guide” (MPG or G)  123  for storage in memory  120 . Other than the inventive concept, processor  105  forms the MPG as known in the art (e.g., see “ATSC Standard: Program and System Information Protocol for Terrestrial Broadcast and Cable (Revision B),” Doc. A/65B, Advance Television Systems Committee, which, as such, is not described herein). As can be observed from  FIG. 3 , the MPG includes data, or information, for each of the PTCs as illustrated by the MPG data associated with PTC (K−1). The data associated with each PTC includes modulation format, etc., and data related to each of the M programs channels that are a part of a particular PTC. In addition, and in accordance with the principles of the invention, the MPG includes auxiliary program channel information  121 , which includes program data and PID data similar to that found for each of the M program channels except that these relate to packets conveying lower resolution data and have different PIDs as formed in step  160 . It should be noted that the value of M may be different for each PTC. It should also be noted that the MPG can be formed in other ways, e.g., data representing an MPG can be received by processor  105  from an external source such that transmitter  100  does not have to form the MPG. 
         [0023]    Finally, in step  170 , transmitter  100  forms a transport stream comprising a primary channel and the auxiliary channel. In particular, modulator  110  receives signals  109 ,  114  and  106  and forms a transport stream (or digital multiplex) as represented by PTC  111  of  FIG. 3  for transmission via transmission tower T 2  of  FIG. 2 . Signal  109  represents a data stream for conveying one or more high definition TV (HDTV) channels offered by the TV provider associated with transmission tower T 2  as known in the art; signal  116  is the above-described auxiliary channel and signal  106  represents MPG  123 . Modulator  110  provides PTC  111  at the appropriate carrier frequency, where, and in accordance with the principles of the invention, the transport stream includes a primary channel and an auxiliary channel. 
         [0024]    Turning now to  FIG. 5 , an illustrative format for a PTC in accordance with the principles of the invention is shown. PTC  111  represents a data-bearing signal comprising at least one carrier wave (not shown), the data bearing signal representing a plurality of packets for conveying program content for at least one primary channel and an auxiliary channel, wherein the auxiliary channel conveys lower resolution program content from other channels. In particular, PTC  111  represents a stream of packets  70 . The stream of packets includes at least one MPG (G) packet  75 , at least one content (C) packet  80  and at least one auxiliary packet (A) packet  90 . Each content packet  80  comprises a packet identifier (PID) and content (video, audio and/or data). For example, the content could relate to video and/or audio for a particular program channel, or even data representing an executable program being downloaded to receiver  300 . In accordance with the principles of the invention, an auxiliary packet  90  represents lower resolution data for conveying programs at a lower resolution, where at least some of these programs are associated with channels transmitted by other ATSC-DTV transmitters. Illustratively, the content packets  80  convey HDTV signals. 
         [0025]    Referring now to  FIG. 6 , this figure shows an illustration of a primary channel and an auxiliary channel in the context of the terrestrial broadcast arrangement illustrated in  FIG. 2 . As can be seen in  FIG. 6 , the primary channel for PTC  111  includes programming for a major-minor channel number 2.1; while the auxiliary channel includes programming for major-minor channel numbers 1.1, 2.1, 3.1 and 4.1. As noted earlier, the inventive concept is not so limited and, e.g., the primary channel can include other programming, e.g., for channels 2.1, 2.2, etc. Further, the auxiliary channel does not have to include a reduced resolution form of the primary channel for that transmitter (in this example, the auxiliary channel does not have to include 2.1). 
         [0026]    In view of the above, a wireless system can provide improved coverage for a geographical area. If one assumes that there are N transmitters in a city, it is likely that (N−k; k&gt;0), are reliably received by over 90% of the receivers in the field. If the providers agree to share any spare capacity on a PTC, then this spare capacity is allocated to the above-described auxiliary channel. As such, the auxiliary channel can convey one or more channels to improve coverage albeit at a reduced resolution. For example, it may be that only the providers associated with transmission towers T 1  and T 2  agree to share capacity. In this case, the above-described auxiliary channel transmitted by T 2  may only include the reduced resolution programming for T 1 . For the example described above, if 3 Mbits/sec of spare capacity is available on a PTC, a station may choose to share 1 Mbit/sec (whether this is a constant bit rate or variable bit rate with 1 Mbit/sec being the average is up to the individual channels) on a reciprocal basis with three other stations (T 1 , T 2  and T 3 ) to be carried within the auxiliary channel. In this case the remaining 2 Mbit/sec of spare capacity can be used to offer other services. It should be noted that spare capacity in a PTC can be created by restricting transmission of primary channels, e.g., selecting the number of primary channels such that the requisite amount of spare capacity is created in the PTC. An extreme example is the transmission of only one primary channel as represented in  FIG. 6 . Alternatively, advantage can be taken of improvements in both MPEG2 encoding and the introduction of advanced codec (coder/decoder) technology (such as H.264, which is also known as AVC (Advanced Video Coding) or MPEG-4 Part 10 or VC1) to create spare capacity in a PTC. 
         [0027]    A high-level block diagram of an illustrative TV set  200  in accordance with the principles of the invention is shown in  FIG. 7 . TV set  200  includes a receiver  300  and a display  220 . Illustratively, receiver  300  is an ATSC-compatible receiver. It should be noted that receiver  300  may also be NTSC (National Television Systems Committee)-compatible, i.e., have an NTSC mode of operation and an ATSC mode of operation such that TV set  200  is capable of displaying video content from an NTSC broadcast or an ATSC broadcast. For simplicity in describing the inventive concept, only the ATSC mode of operation is described herein. Receiver  300  receives a broadcast signal  111  (e.g., via an antenna (not shown)) for processing to recover therefrom, e.g., an HDTV (high definition TV) video signal for application to display  220  for viewing video content thereon. 
         [0028]    In accordance with the principles of the invention, receiver  300  is also able to recover a low resolution signal for viewing if the reception for a selected channel is either too poor or non-existent. Turning now to receiver  300 , an illustrative portion of receiver  300  in accordance with the principles of the invention is shown in  FIG. 8 . Receiver  300  includes front-end filter  305 , analog-to-digital (A/D) converter  310 , demodulator  390 , forward error correction (FEC) decoder  395 , transport processor  350 , controller  355  and memory  360 . Both transport processor  350  and controller  355  are each representative of one or more microprocessors and/or digital signal processors (DSPs) and may include memory for executing programs and storing data. In this regard, memory  360  is representative of memory in receiver  300  and includes, e.g., any memory of transport processor  350  and/or controller  355 . An illustrative bidirectional data and control bus  301  couples various ones of the elements of  FIG. 8  together as shown. Control bus  301  is merely representative, e.g., individual signals (in a parallel and/or serial form) may be used, etc., for conveying data and control signaling between the elements of  FIG. 8 . Front end filter  305  down-converts and filters received signal  111  to provide a near base-band signal to A/D converter  310 , which samples the down converted signal to convert the signal to the digital domain and provide a sequence of samples  311  to demodulator  390 . The latter performs demodulation of signal  311  and provides a demodulated signal  391 , e.g., a sequence of signal points, to FEC decoder  395 . The latter examines the inphase (I) and quadrature (Q) components of each of the signal points of demodulated signal  391  at the symbol rate, 1/T, and decodes the signal into a probable set of transmitted bits as represented by decoded signal  396 . Decoded signal  396  is provided to transport processor  350 , which distributes video, audio and data bits as represented by content signal  351  to appropriate subsequent circuitry (not shown). It should be noted that transport processor  350  illustratively includes a high resolution decoder (H)  370  and a low resolution decoder (L)  380 . In this regard, receiver  300  may additionally process the content before application to display  220  and/or directly provide the content to display  220 , via signal  331 . It should be noted that location of the high resolution and low resolution decoders in transport processor  350  is not required. It should also be noted that receiver  300  may receive commands, e.g., program selection, via a remote control (not shown). 
         [0029]    To get an appreciation of the benefits of the inventive concept, attention should now be directed to  FIG. 9 , which shows an illustrative flow chart for providing for a more robust reception of wireless signals in a receiver. For the purposes of this example, it is assumed that receiver  300  has already received a form of the above-described MPG. Other than the inventive concept, use of an MPG by a receiver to tune to channels therein is known in the art. For example, see U.S. Pat. No. 6,366,326 issued Apr. 2, 2002 to Ozkan et al. and/or U.S. Pat. No. 5,946,052 issued Aug. 31, 1999 issued to Ozkan et al. As such, searching for, and acquisition of, an MPG is not described herein. 
         [0030]    In step  505 , receiver  300  (e.g., controller  355 ) receives a channel selection from a user (not shown), e.g., via the above-mentioned remote control. In step  510 , receiver  300  (e.g., controller  355 ) uses information from the acquired MPG (via memory  360 ) to tune to the PTC associated with that channel. In particular, front end filter  305  is tuned to the PTC via control bus  301 . In step  515 , receiver  300  (e.g., controller  355 ) checks the received signal strength indicator (RSSI) via signal  356  of  FIG. 8 . If the RSSI value is equal to, or above, a predetermined value, e.g., −75 dBm (decibels referenced to one milliwatt), then reception should be good and receiver  300  selects packets from the primary channel of the PTC in accordance with the PID information from the acquired MPG in step  520  (e.g., via controller  355 , transport processor  350  and high resolution decoder  370 ). Video content from the selected packets are then provided to display  220  (this step is not shown in  FIG. 9 ). However, if the RSSI value is below the predetermined value, then reception is determined to be bad. In this case, receiver  300  (e.g., controller  355 ) in accordance with the principles of the invention, attempts to locate an auxiliary channel for recovery of the content for the selected channel. In particular, receiver  300  tunes to another PTC in step  525  and again checks the RSSI value in step  530 . If reception is bad, receiver  300  continues to check available PTCs as indicated in the acquired MPG. If no PTC is eventually acquired, an error message is generated (not shown in  FIG. 9 ). However, once a PTC is found with good reception, execution proceeds to step  535 . In this step receiver  300  selects packets from the auxiliary channel of the acquired PTC in accordance with the PID information from the acquired MPG in step  520  for the selected channel (e.g., via controller  355 , transport processor  350  and low resolution decoder  380 ). Video content from the selected packets are then provided to display  220  (this step is not shown in  FIG. 9 ) so that the user can view the desired program, albeit in a lower resolution. 
         [0031]    A described above, and in accordance with the inventive concept, a robust transmission and reception method is described for a system having multiple originating sources and multiple destinations (receivers or sinks). Indeed, the above-described inventive concept can be described as a form of spatial diversity. For example, in the illustrative embodiment above, the ATSC-DTV system of  FIG. 2  incorporated spatial diversity in accordance with the principles of the invention. 
         [0032]    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 on one or more integrated circuits (ICs). Similarly, although shown as separate elements, any or all of the elements of 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. 4  and/or  9 , etc. Further, although shown as elements bundled within TV set  200 , the elements therein may be distributed in different units in any combination thereof. For example, receiver  300  of  FIG. 7  may be a part of a device, or box, such as a set-top box that is physically separate from the device, or box, incorporating display  220 , etc. Also, it should be noted that although described in the context of terrestrial broadcast (e.g., ATSC-DTV), the principles of the invention are applicable to other types of communications systems, e.g., satellite, Wi-Fi, cellular, etc. Indeed, even though the inventive concept was illustrated in the context of stationary receivers, the inventive concept is also applicable to 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.