Abstract:
Transmission of a digital television signal conveys data parameters along with the encoder data that are utilized by the receiver in equalization and in decoding the encoded data. Leveraging the existing digital television standard data formatting, parameters are split between the two fields of a frame of the interlaced signal. Spread spectrum techniques are employed to robustly convey the parameters in encoded form to the receiver.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention claims the benefit of commonly-owned, U.S. Provisional Patent Application Ser. No. 60/408,956 filed Sep. 6, 2002, U.S. Provisional Patent Application Serial No. 60/466,038 filed Apr. 28, 2003 and is related to U.S. Patent Publication Nos. 2002/0194570, 2002/0191712, 2002/0181581, filed on Apr. 22, 2002, Apr. 9, 2002, Feb. 19, 2002, respectively, and to the commonly-assigned patent application entitled “PACKET INSERTION MECHANISM FOR AN IMPROVED ATSC DTV SYSTEM,” U.S. Provisional Patent Application Ser. No. 60/462,776 filed on Apr. 14, 2003, the entire contents and disclosure of each of which are incorporated by reference as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a digital signal transmission system and particularly to the transmission of a signal representative of encoded digital data. 
     DISCUSSION OF THE PRIOR ART 
     The ATSC standard for high-definition television (HDTV) transmission over terrestrial broadcast channels uses a signal that comprises a sequence of twelve (12) independent time-multiplexed trellis-coded data streams modulated as an eight (8) level vestigial sideband (VSB) symbol stream with a rate of 10.76 MHz. This signal is converted to a six (6) MHz frequency band that corresponds to a standard VHF or UHF terrestrial television channel, over which the signal is broadcast at a data rate of 19.39 million bits per second (Mbps). Details regarding the (ATSC) Digital Television Standard and the latest revision A/53 are available at http://www.atsc.org/. 
     While the existing ATSC 8-VSB A/53 digital television standard is sufficiently capable of transmitting signals that overcome numerous channel impairments such as ghosts, noise bursts, signal fades and interferences in a terrestrial setting, receiving antennas have increasingly been placed indoors, adding to the challenge of delivering a clear signal. There accordingly exists a need for flexibility in the ATSC standard so that streams of varying priority and data rates may be accommodated. 
     To address these concerns, the present inventors have disclosed enhancements to the A/53 transmitter in U.S. patent Publication Nos. 2002/0194570 (hereinafter “the &#39;570 application”), 2002/0191712 (hereinafter “the 712” application”), 2002/0181581 (hereinafter “the 581 application”) and “PACKET INSERTION MECHANISM FOR AN IMPROVED ATSC DTV SYSTEM” (hereinafter “the Packet Insertion application”) whose disclosures have been incorporated by reference herein. 
     The present invention is directed to further improvements relating to signal transmission quality and to efficient leverage of existing A/53 infrastructure. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention concerns the encoding of parameters to be embodied within a television broadcast signal for transmission. 
     In another aspect, the present invention relates to techniques for encoding into a signal parameters to be transmitted and which are needed by a wireless receiver both to correctly ascertain the transmitted signal and to decode data accompanying the parameters in the signal. 
     In yet another aspect, the present invention concerns leveraging data structures in a standard television protocol to accommodate enhancements to the standard that retain compatibility with existing receivers. 
     In accordance with preferred embodiments of the invention, there is provided wireless communication of a leading bit string comprising a header and a body, and a trailing bit string comprising a header and a body. For example, a bit string of length N may have a header X 0 , X 1 , . . . X K  and a body X K+1 , X K+2 , . . . X N−1 . Data is encoded to form the body of the leading bit string. The header of the trailing bit string is formed to include at least one bit of a parameter to be used by a receiver in decoding the encoded data. A wireless signal representing at the receiver the leading bit string and then the trailing bit string is transmitted to the receiver. 
     The encoding techniques preferably include applying a fixed code to encode bits of a bit-stream, one-by-one, to create an encoded bit-stream. The encoded bit-stream is modulated to produce a signal whose frequency range at any given time is predetermined independently of the code. The signal, thus modulated, is transmitted within the frequency range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Details of the invention disclosed herein shall be described below, with the aid of the figures listed below: 
         FIG. 1  illustrates a block diagram of an exemplary television communication system according with the present invention; 
         FIG. 2  is a diagram of a circuit used for encoding parameters in the system portrayed in  FIG. 1 ; and 
         FIG. 3  is an exemplary flow diagram representative of processing that data for transmission undergoes in the system of  FIG. 1  prior to transmission and after reception. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  depicts an exemplary embodiment of television communication system  100  in accordance with the invention. The communication system  100  includes an encoder  104 , a transmitter  108 , a receiver  112  and a data decoder  116 . The encoder  104  includes a data encoder  120 , which receives a parameter bit-stream  124  and a data bit-stream  128 , and a parameter encoder  132 . The transmitter  108  is communicatively connected to the encoder  104  and has a modulator  136  and an antenna  140 . The receiver  100  an  112  has an antenna  144  configured for wireless reception of signaling from the antenna  140 . The receiver  112  further includes a demodulator  148 , a parameter decoder  152  and an equalizer  156 , and is communicatively connected with the data decoder  116 . 
       FIG. 2  illustrates an example of a sequence generator  200  utilized for bit encoding in accordance with the present invention. The sequence generator  200  includes a four element shift register  204 , which has four delay elements such as D flip-flops  208 ,  212 ,  216 ,  220 . An exclusive-OR gate tap  224  is disposed between the third element  216  and the fourth element  220 . The fourth element  220  has an output terminal  228  which feeds back to an input terminal  232  of the first element  208  and to the tap  224 . 
     As shown in  FIG. 2 , each of the flip-flops  208 - 220  has a pre-loaded bit value and is connected to a common clock (not shown). With the first clock pulse, for example, the output “0” on the fourth flip-flop  220  feeds back to first flip-flop  208 . On that same pulse, the value “1” of the first flip-flop  208  shifts forward to the second flip-flop  212 . Likewise, the value “0” on the second flip-flop  212  shifts forward to the third flip-flop  216 . Again, on that same pulse, the value “0” of the third flip-flop  216  is exclusively-ORed with the output “0” to shift the result, “0”, to the fourth flip  220 . Accordingly, after the first clock pulse, the register contents have changed from “1000” to “0100”. Each subsequent clock pulse changes the register contents, and the sequence starts to repeat after 15 clock pulses. The pre-load followed by 14 clock pulses generates at the output  228  the sequence “000111101011001” which repeats for each subsequent 15 clock pulses. This sequence is a linear recursive sequence, i.e., a periodic sequence of bits generated by shift register with feedback. The above sequence is used in the present invention as a fixed code. In particular, the fixed code is applied to each bit of data to be encoded to produce the same 15-bit fixed code if the bit is zero, or the opposite of the code, i.e., with zeroes becoming ones and ones becoming zeroes, if the bit is one. This can be implemented by, for example, connecting the output  228  and the bit to be encoded to an XOR gate, and the resulting output and the bit value “1” to another XOR gate. Advantageously, the sequence “000111101011001” can be reliably detected at the receiver, because it minimally correlates with a shifted version of itself. In an alternative implementation, the sequence generator  200  can include an additional XOR gate tap between the first element  208  and the second element  212  that is fed by the output  228 . Also, pre-load values other than “1000” can be used. Nor is a sequence generator in accordance with the invention limited to four delay elements. It is further within the intended scope of the invention for the sequence generator  200  to be implemented with an XOR gate or gates in the feedback path rather than embedded within register  204 . 
       FIG. 3  is an exemplary flow diagram which shows one example of the processing of the parameter and data bit-streams  124 ,  128  in the digital television communication system  100 . A frequency range of the signal for transmission is determined ( 304 ) and may, alternatively, be determined at any point before modulation of the signal for transmission. The frequency range of the signal may also be changed or varied, for example in accordance with the type of data being processed, although it is predetermined independently of the fixed code. In step  308 , a fixed code is determined, although it can be determined any time before encoding. 
     If there is no data for transmission ( 312 ), processing waits. 
     Otherwise, if the parameter bit-stream  124  is ready for reception by the data encoder  120 , it is received ( 316 ). The parameter bit-stream  124  is time-synchronized with the data bit-stream  128 , and may therefore not be ready for reception if the data bit-stream is not ready. In addition, no parameters may be ready for reception if parameters have not changed, since parameters for the system  100  do not necessarily change in any particular time period. If the parameter bit-stream  124  is received, its bits are encoded bit-by-bit, one bit at a time, by the parameter encoder  132  using the fixed code ( 320 ). A predetermined number of encoded bits are used in forming the headers of two bit strings before a new bit string pair is utilized, each bit string consisting of two parts, a header and a body. One of the two bit strings is a leading bit string and the other one is a trailing bit string. Specific ones of the encoded parameters are allotted the leading bit string header and the other parameters are allotted to the trailing bit string header ( 324 ). 
     Meanwhile, if the data bit-stream  128  is ready for input, it is received ( 328 ) and encoded ( 332 ). Although the parameter bit-stream  124  is preferably encoded bit-by-bit, one bit at a time, encoding of the data bit-stream would not typically be subject to such restrictions. The data bit-stream  128  is a video interlaced signal, and, as such, represents a frame which divides into two fields, an even field and an odd field. Encoded data from one of the fields is used in forming the body of a leading bit string. Similarly, encoded data from the other field is used in filling the body of a trailing bit string ( 336 ). Processing of the data and parameter bit-streams  124 ,  128  is synchronized so that each of the two types of bit strings receives its respective encoded data and encoded parameters that correspond to that data. In one embodiment, although the encoded parameters for a frame are divided into two groups for forming their respective field headers, the encoded parameters apply to the encoded data of the entire frame. 
     A carrier signal is then modulated by the modulator  136  using the encoded bit string pair for wireless transmission of a signal representing at the receiver the leading bit string and then the trailing bit string ( 340 ). 
     The received signal is demodulated by the demodulator  148  ( 344 ), and parameters are decoded by the parameter decoder  152  ( 348 ). 
     The parameters define the number of discrete levels in the digital wireless signal conveying the bit-streams  124 ,  128 , and are therefore used by the equalizer  156  in resolving multipath or otherwise converging the signal ( 352 ). The decoded parameters are also utilized in decoding the data bit-stream  128  ( 356 ). 
     The inventive television communication system  100  can be implemented to enhance an A/53 system proposed by the current inventors and described in the Packet Insertion application. 
     The Packet Insertion application discusses the use of the following parameters in a parameter bit-stream. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Parameter Definitions 
               
             
          
           
               
                 Parameter 
                   
                 Number 
               
               
                 Name 
                 Definition 
                 of bits 
               
               
                   
               
               
                 MODE 
                 Modulation type (2-VSB, E-VSB etc) 
                 2 
               
               
                 NRS 
                 Presence of Backward Compatible Parity Byte 
                 1 
               
               
                   
                 Generator (BCPBG) 
                   
               
               
                 NRP 
                 Number of robust packets before encoding 
                 4 
               
               
                 TR 
                 Coding Rate 
                 1 
               
               
                   
               
             
          
         
       
     
     The parameters convey the number of levels in the transmitted signal, and since this information is used by the equalizer, the parameters must be decoded before equalization. Therefore, robust methods that can survive severe channel conditions are needed. The present invention expands on the &#39;570 techniques of transmitting these parameters to the receiver in a reliable manner. 
     In accordance with the A/53 standard, the header of each field contains an 832-bit “data field sync” of specific format. The format includes a 92-bit reserved area (corresponding to symbol numbers 729-820) which the standard recommends be filled with repeated information for extra redundancy. 
     As shown above in TABLE 1, 8 parameter bits need to be transmitted. Encoding by the sequence generator of  FIG. 2  yields 8×15=120 bits, a total which exceeds the 92 bits of reserved space. The inventive technique splits the encoded bits between the two fields of a frame, e.g. 4 bits allocated per field. An extra parity bit is added to each group of 4 bits for an additional level of error detection, bringing the total to 5 bits, or 5×15=75 encoded bits, per field. TABLE 2 below defines the symbols 729-820 for odd and even fields. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Symbol definitions in Field sync 
               
             
          
           
               
                 Symbol Number 
                 Even (odd) field sync 
                 Odd (even) field sync 
               
               
                   
               
               
                 729-743 
                 LSB of MODE 
                 bit0 (LSB) of NRP 
               
               
                 744-758 
                 MSB of MODE 
                 bit1 of NRP 
               
               
                 759-773 
                 NRS 
                 bit2 of NRP 
               
               
                 774-788 
                 TR 
                 bit3 (MSB) of NRP 
               
               
                 789-803 
                 Parity bit 
                 Parity bit 
               
               
                 804-820 
                 Reserved 
                 Reserved 
               
               
                   
               
             
          
         
       
     
     As set forth more fully in the Packet Insertion application, if MODE=0, the rest of the parameters are not utilized. Receivers adapted for the enhancements by the current inventors can decode the MODE parameter to identify whether the received signal embodies the enhanced bit-stream formats, and, if so, can decode the other parameters. 
     While there have been shown and described what are considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.