Abstract:
An apparatus comprising a first circuit and a second circuit. The first circuit may be configured to generate an MPEG packet data stream. The second circuit may be configured to (i) scramble the data stream to generate a scrambled data stream, (ii) encode the scrambled data stream to generate an encoded data stream, (iii) interleave the encoded data stream, (iv) encode the interleaved data stream, (v) modulate the encoded data stream, and (vi) filter the modulated data stream.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method of transmitting digital signals generally and, more particularly, to a method and/or architecture to efficiently transmit broadband service content using low density parity code based coded modulation.  
         BACKGROUND OF THE INVENTION  
         [0002]    With the proliferation of broadband transmission media such as digital satellite television, digital cable, cable modem, and DSL, several error correcting transmission protocols have emerged. Conventional standards like Integrated Services Digital Broadcasting Satellite (ISDB-S) that deploy QuadraPhase-Shift Keying (QPSK) or 8 level Phase-Shift Keying (8PSK) based systems use conventional forward error correction techniques. Such techniques allow transmission of standard and High Definition Digital Television (HDTV) signals over satellite by using a higher bandwidth and transmitting power to be able to deliver digital television channels.  
           [0003]    The following TABLE 1 illustrates an example of a conventional target satellite system performance specification:  
                                                                 TABLE 1                                   Item   Min   Typ   Max   Unit                                    1   Payload   41     —   —   Mbps       2   Code   TBD   —   TBD       3   QEF   10E − 11   —   —       4   Symbol   20     22     23     MSps       5   Eb/No @ 10E − 1            2/3 or   —   —    4     dB           5/6 or   —   —    4.6   dB           8/9   —   —    5.2   dB       6   Dish   —   —   46     cm       7   Satellite EIRP for   +2.6   —   —   dB           8 PSK with respect to           QPSK transponders       8   C/No for QPSK 20 Msps.   —   78.9   —   dB           3/4                  
 
           [0004]    These specifications can vary based on the broadband carrier environment. Conventional QPSK based transmission systems do not achieve high definition digital television (i.e., 720 p or 1080 i) with the given constraints of bandwidth and available transmission power.  
           [0005]    It would be desirable to develop a television system specification in response to system performance goals for the design and development of a Low Density Parity Check (LDPC) code based Forward Error Correction (FEC) system for use in broadband gateways.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention concerns an apparatus comprising a first circuit and a second circuit. The first circuit may be configured to generate an MPEG packet data stream. The second circuit may be configured to (i) scramble the data stream to generate a scrambled data stream, (ii) encode the scrambled data stream to generate an encoded data stream, (iii) interleave the encoded data stream, (iv) encode the interleaved data stream, (v) modulate the encoded data stream, and (vi) filter the modulated data stream.  
           [0007]    The objects, features and advantages of the present invention include providing a system to efficiently transmit broadband service content using low density parity code based coded modulation that may (i) operate efficiently and effectively using the preexisting bandwidth allocated to television signals, and/or (ii) avoid attenuation problems when broadcast at preexisting transmission power levels. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims and drawings in which:  
         [0009]    [0009]FIG. 1 is a diagram illustrating the context of the present invention;  
         [0010]    [0010]FIG. 2 is a diagram illustrating a preferred embodiment of the present invention;  
         [0011]    [0011]FIG. 3 is a diagram illustrating an example of a MPEG-2 data payload packet;  
         [0012]    [0012]FIG. 4 is a diagram illustrating an example of a MPEG-2 data frame;  
         [0013]    [0013]FIG. 5 is a diagram illustrating a more detailed view of the data frame of FIG. 4;  
         [0014]    [0014]FIG. 6 is a diagram illustrating an example of a data frame after Reed-Solomon encoding;  
         [0015]    [0015]FIG. 7 is a diagram illustrating an example of a construction of the input to a LDPC encoder from a block interleaver output;  
         [0016]    [0016]FIG. 8 is a flow diagram illustrating an example of an encoder bit-to-symbol mapper and modulator for a nPSK/mQAM system; and  
         [0017]    [0017]FIG. 9 is a diagram illustrating an example bits-to-8PSK symbol mapping used in satellite 8PSK. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The present invention may involve a Low Density Parity Check (LDPC) based Forward Error Correcting (FEC) subsystem for digital broadcasting. The present invention may be particularly suited as part of a satellite system physical layer deployed in a consumer grade set-top box to receive Direct Broadcast Satellite (DBS) transmissions as a carrier for High Definition (HD) programming. The present invention may allow additional high definition channels to be broadcasted and decoded using the same bandwidth as conventional approaches use to deliver fewer channels. Initially, the use of the 8 Level Phase-Shift Keying (8PSK) modulated channels of the present invention may only be applied to select transponders, while the majority of transponders may continue to use QuadraPhase-Shift Keying (QPSK) in Digital Video Broadcasting/Digital Signature Standard (DVB/DSS) format. By initially introducing the 8PSK modulated channels to limited transponders, end users will have an opportunity to upgrade. Furthermore, by introducing 8PSK modulation to additional new programming choices, end users will have an incentive to implement the present invention. Furthermore, if channels that an end user is accustomed to receiving with conventional QPSK are still available during the transition, consumer satisfaction may be improved. While the digital satellite television serves as a specific example, the FEC portion of which the LDPC decoder forms a part may be suitably parameterized to be flexible enough to be used in other applications such as terrestrial or cable based broadband systems.  
         [0019]    The present invention may be designed to comply with the conventional target satellite system performance specifications discussed in the background section. The present invention may be implemented as a stand alone decoder, or as an upgrade to conventional decoders. The transmission system of the present invention may begin with channel coding. The channel coding for the class of broadband applications that the present invention is most suited for may be based on a family of iteratively decoded codes known as Low Density Parity Checks (LDPCs). Simulation results are presented for a given Finite Geometry (FG) LDPC code, but may not be restricted to this choice. However, any appropriate type of coding may be used to meet the design criteria of a particular application.  
         [0020]    Referring to FIG. 1, a diagram illustrating the context of the present invention is shown. The present invention  100  may be a circuit and/or process designed to receive an MPEG encoded digital video signal from an MPEG source encoder  50 . The MPEG encoded digital video signal may be, in one example, the raw MPEG signal read from a DVD. The signal may be provided from the encoder  50  as MPEG source input framing packets. In one example, the present invention  100  may process, encode, and/or modulate an MPEG encoded digital video signal.  
         [0021]    Referring to FIG. 2, a diagram illustrating a method (or process)  100  in accordance with a preferred embodiment of the present invention is shown. The process  100  illustrates an example of a system incorporating LDPCs. The process  100  may have six main processing stages  102 ,  104 ,  106 ,  108 ,  110 , and  112  and one optional stage  114 . The stage  102  may be implemented as a bitwise scrambling stage. The stage  102  may receive MPEG source input framing packets from a source encoder. The stage  104  may implement an outer coding process. The stage  106  may comprise a symbol or frame interleaving stage. The stage  108  may implement a variable rate LDPC inner encoding process. The stage  110  may implement a modulation process and a bit-to-symbol mapping stage. The stage  112  may implement a 8/4/2-Phase-Shift -Keying (8/4/2-PSK) modulator. The optional stage  114  may be implemented between the stages  108  and  110  and may comprise a synchronization stage. Alternatively, FIG. 2 may be viewed as a Digital Signal Processing (DSP) diagram. The seven stages of FIG. 2 may be viewed as each comprising a circuit configured to achieve the objective of the particular stage.  
         [0022]    Prior to the stage  102 ,transport stream (TS) bytes from an MPEG-2 source encoder may be packed into a packet structure. In a typical example, each packet may contain 187 data payload bytes. Two hundred of such data payload packets (e.g., 37400 bytes) may comprise one basic data frame.  
         [0023]    [0023]FIG. 3 illustrates an example of a single MPEG-2 data payload packet  150  comprising 187 bytes arranged in a contiguous block. FIG. 4 illustrates an example of a basic data frame  160  comprising 200 187 byte MPEG-2 data payload packets  150  contiguously arranged in a block. FIG. 5 is an example  170  of a more detailed view of the elements of the basic MPEG-2 data frame  160  of FIG. 4. A sync. byte (e.g., a value of 47 in hexadecimal representation) may be inserted before every packet  150  to indicate the beginning of a packet being transmitted. Before the very first packet, an inverted sync. byte (e.g., a value of b8 in hexadecimal) may be inserted to enable proper synchronization of the data frame  160 .  
         [0024]    Referring back to FIG. 2, the stage  102  may comprise energy dispersal. The stage 102 may receive the MPEG data frames  160  illustrated in FIG. 4 from the source encoder  50 . To ensure adequate transitions for proper timing recovery, bit-wise energy dispersal (e.g., randomization) may be carried out as in the Digital Video Broadcasting Satellite (DVB-S) specification. In one example, the polynomial chosen for the Pseudo-Random Binary Sequence (PRBS) generation may be given by f(x)=1+x 14 +x 15 . A bit sequence (e.g., 100101010000000) may be loaded into a shift register at the start of the MPEG source frame and subsequently, at the beginning of every 8 MPEG transport packets. The very first sync. byte position at the start of the source frame may be marked in an MPEG TS stream by the inverted MPEG sync. byte (e.g., a value of b8 in hexadecimal) as shown in FIG. 5. The scrambling operation may be disabled at the first of every 8 sync. bytes (e.g., at the beginning of each scrambling cycle comprising 8×188=1536 bit intervals). Thus, the inverted sync. byte at the beginning of the source frame may remain unaffected.  
         [0025]    Referring to FIG. 6, a complete Reed-Solomon (RS) encoded frame  180  is shown. The stage  104  may comprise outer coding (e.g., RS(200,188)). Prior to transmission, the transport bytes in each frame may be encoded by a shortened Reed-Solomon encoder of length 200 and error correcting capability t=6 (e.g., the systematic code word may contain 12 check bytes after 188 input data bytes). The RS(200,188) code defined over a Galors Field GF[2 8 ] may have the same generator and binary primitive polynomials as a DVB-S code applying RS(204,188). Thus, each RS encoded frame 180 generated by the stage  104  may then comprise ((1+187)+12)×200=200×200=40,000 bytes.  
         [0026]    The stage  106  may comprise symbol or frame interleaving. In order to decimate the error events created by the inner LDPC decoder at the receiver, a block interleaver (e.g., frame size 200×200) may be used on the output frames  180  of the Reed-Solomon encoder of the stage  104 . The interleaving operation may be synchronized by using a frame start signal aligned at the start of the inverted sync. byte from the beginning of the first RS code word of the encoded frame. The stage  106  may add parity to the data stream provided to the subsequent stage  108  to greatly reduce the probability of bit errors occurring at the receiver decoder during decoding.  
         [0027]    The following TABLE 2 illustrates a 255×175 [H] matrix that is shown to be applied in the following example:  
                                                                           TABLE 2                           1   14   23   39   46   60   88   143   144   155   163   215   221   225   251   254       0   13   22   38   45   59   87   142   143   154   162   214   220   224   250   253       12   21   37   44   58   86   141   142   153   161   213   219   223   249   252   254       11   20   36   43   57   85   140   141   152   160   212   218   222   248   251   253       10   19   35   42   56   84   139   140   151   159   211   217   221   247   250   252       9   18   34   41   55   83   138   139   150   158   210   216   220   246   249   251       8   17   33   40   54   82   137   138   149   157   209   215   219   245   248   250       7   16   32   39   53   81   136   137   148   156   208   214   218   244   247   249       6   15   31   38   52   80   135   136   147   155   207   213   217   243   246   248       5   14   30   37   51   79   134   135   146   154   206   212   216   242   245   247       4   13   29   36   50   78   133   134   145   153   205   211   215   241   244   246       3   12   28   35   49   77   132   133   144   152   204   210   214   240   243   245       2   11   27   34   48   76   131   132   143   151   203   209   213   239   242   244       1   10   26   33   47   75   130   131   142   150   202   208   212   238   241   243       0   9   25   32   46   74   129   130   141   149   201   207   211   237   240   242       8   24   31   45   73   128   129   140   148   200   206   210   236   239   241   254       7   23   30   44   72   127   128   139   147   199   205   209   235   238   240   253       6   22   29   43   71   126   127   138   146   198   204   208   234   237   239   252       5   21   28   42   70   125   126   137   145   197   203   207   233   236   238   251       4   20   27   41   69   124   125   136   144   196   202   206   232   235   237   250       3   19   26   40   68   123   124   135   143   195   201   205   231   234   236   249       2   18   25   39   67   122   123   134   142   194   200   204   230   233   235   248       1   17   24   38   66   121   122   133   141   193   199   203   229   232   234   247       0   16   23   37   65   120   121   132   140   192   198   202   228   231   233   246       15   22   36   64   119   120   131   139   191   197   201   227   230   232   245   254       14   21   35   63   118   119   130   138   190   196   200   226   229   231   244   253       13   20   34   62   117   118   129   137   189   195   199   225   228   230   243   252       12   19   33   61   116   117   128   136   188   194   198   224   227   229   242   251       11   18   32   60   115   116   127   135   187   193   197   223   226   228   241   250       10   17   31   59   114   115   126   134   186   192   196   222   225   227   240   249       9   16   30   58   113   114   125   133   185   191   195   221   224   226   239   248       8   15   29   57   112   113   124   132   184   190   194   220   223   225   238   247       7   14   28   56   111   112   123   131   183   189   193   219   222   224   237   246       6   13   27   55   110   111   122   130   182   188   192   218   221   223   236   245       5   12   26   54   109   110   121   129   181   187   191   217   220   222   235   244       4   11   25   53   108   109   120   128   180   186   190   216   219   221   234   243       3   10   24   52   107   108   119   127   179   185   189   215   218   220   233   242       2   9   23   51   106   107   118   126   178   184   188   214   217   219   232   241       1   8   22   50   105   106   117   125   177   183   187   213   216   218   231   240       0   7   21   49   104   105   116   124   176   182   186   212   215   217   230   239       6   20   48   103   104   115   123   175   181   185   211   214   216   229   238   254       5   19   47   102   103   114   122   174   180   184   210   213   215   228   237   253       4   18   46   101   102   113   121   173   179   183   209   212   214   227   236   252       3   17   45   100   101   112   120   172   178   182   208   211   213   226   235   251       2   16   44   99   100   111   119   171   177   181   207   210   212   225   234   250       1   15   43   98   99   110   118   170   176   180   206   209   211   224   233   249       0   14   42   97   98   109   117   169   175   179   205   208   210   223   232   248       13   41   96   97   108   116   168   174   178   204   207   209   222   231   247   254       12   40   95   96   107   115   167   173   177   203   206   208   221   230   246   253       11   39   94   95   106   114   166   172   176   202   205   207   220   229   245   252       10   38   93   94   105   113   165   171   175   201   204   206   219   228   244   251       9   37   92   93   104   112   164   170   174   200   203   205   218   227   243   250       8   36   91   92   103   111   163   169   173   199   202   204   217   226   242   249       7   35   90   91   102   110   162   168   172   198   201   203   216   225   241   248       6   34   89   90   101   109   161   167   171   197   200   202   215   224   240   247       5   33   88   89   100   108   160   166   170   196   199   201   214   223   239   246       4   32   87   88   99   107   159   165   169   195   198   200   213   222   238   245       3   31   86   87   98   106   158   164   168   194   197   199   212   221   237   244       2   30   85   86   97   105   157   163   167   193   196   198   211   220   236   243       1   29   84   85   96   104   156   162   166   192   195   197   210   219   235   242       0   28   83   84   95   103   155   161   165   191   194   196   209   218   234   241       27   82   83   94   102   154   160   164   190   193   195   208   217   233   240   254       26   81   82   93   101   153   159   163   189   192   194   207   216   232   239   253       25   80   81   92   100   152   158   162   188   191   193   206   215   231   238   252       24   79   80   91   99   151   157   161   187   190   192   205   214   230   237   251       23   78   79   90   98   150   156   160   186   189   191   204   213   229   236   250       22   77   78   89   97   149   155   159   185   188   190   203   212   228   235   249       21   76   77   88   96   148   154   158   184   187   189   202   211   227   234   248       20   75   76   87   95   147   153   157   183   186   188   201   210   226   233   247       19   74   75   86   94   146   152   156   182   185   187   200   209   225   232   246       18   73   74   85   93   145   151   155   181   184   186   199   208   224   231   245       17   72   73   84   92   144   150   154   180   183   185   198   207   223   230   244       16   71   72   83   91   143   149   153   179   182   184   197   206   222   229   243       15   70   71   82   90   142   148   152   178   181   183   196   205   221   228   242       14   69   70   81   89   141   147   151   177   180   182   195   204   220   227   241       13   68   69   80   88   140   146   150   176   179   181   194   203   219   226   240       12   67   68   79   87   139   145   149   175   178   180   193   202   218   225   239       11   66   67   78   86   138   144   148   174   177   179   192   201   217   224   238       10   65   66   77   85   137   143   147   173   176   178   191   200   216   223   237       9   64   65   76   84   136   142   146   172   175   177   190   199   215   222   236       8   63   64   75   83   135   141   145   171   174   176   189   198   214   221   235       7   62   63   74   82   134   140   144   170   173   175   188   197   213   220   234       6   61   62   73   81   133   139   143   169   172   174   187   196   212   219   233       5   60   61   72   80   132   138   142   168   171   173   186   195   211   218   232       4   59   60   71   79   131   137   141   167   170   172   185   194   210   217   231       3   58   59   70   78   130   136   140   166   169   171   184   193   209   216   230       2   57   58   69   77   129   135   139   165   168   170   183   192   208   215   229       1   56   57   68   76   128   134   138   164   167   169   182   191   207   214   228       0   55   56   67   75   127   133   137   163   166   168   181   190   206   213   227       54   55   66   74   126   132   136   162   165   167   180   189   205   212   226   254       53   54   65   73   125   131   135   161   164   166   179   188   204   211   225   253       52   53   64   72   124   130   134   160   163   165   178   187   203   210   224   252       51   52   63   71   123   129   133   159   162   164   177   186   202   209   223   251       50   51   62   70   122   128   132   158   161   163   176   185   201   208   222   250       49   50   61   69   121   127   131   157   160   162   175   184   200   207   221   249       48   49   60   68   120   126   130   156   159   161   174   183   199   206   220   248       47   48   59   67   119   125   129   155   158   160   173   182   198   205   219   247       46   47   58   66   118   124   128   154   157   159   172   181   197   204   218   246       45   46   57   65   117   123   127   153   156   158   171   180   196   203   217   245       44   45   56   64   116   122   126   152   155   157   170   179   195   202   216   244       43   44   55   63   115   121   125   151   154   156   169   178   194   201   215   243       42   43   54   62   114   120   124   150   153   155   168   177   193   200   214   242       41   42   53   61   113   119   123   149   152   154   167   176   192   199   213   241       40   41   52   60   112   118   122   148   151   153   166   175   191   198   212   240       39   40   51   59   111   117   121   147   150   152   165   174   190   197   211   239       38   39   50   58   110   116   120   146   149   151   164   173   189   196   210   238       37   38   49   57   109   115   119   145   148   150   163   172   188   195   209   237       36   37   48   56   108   114   118   144   147   149   162   171   187   194   208   236       35   36   47   55   107   113   117   143   146   148   161   170   186   193   207   235       34   35   46   54   106   112   116   142   145   147   160   169   185   192   206   234       33   34   45   53   105   111   115   141   144   146   159   168   184   191   205   233       32   33   44   52   104   110   114   140   143   145   158   167   183   190   204   232       31   32   43   51   103   109   113   139   142   144   157   166   182   189   203   231       30   31   42   50   102   108   112   138   141   143   156   165   181   188   202   230       29   30   41   49   101   107   111   137   140   142   155   164   180   187   201   229       28   29   40   48   100   106   110   136   139   141   154   163   179   186   200   228       27   28   39   47   99   105   109   135   138   140   153   162   178   185   199   227       26   27   38   46   98   104   108   134   137   139   152   161   177   184   198   226       25   26   37   45   97   103   107   133   136   138   151   160   176   183   197   225       24   25   36   44   96   102   106   132   135   137   150   159   175   182   196   224       23   24   35   43   95   101   105   131   134   136   149   158   174   181   195   223       22   23   34   42   94   100   104   130   133   135   148   157   173   180   194   222       21   22   33   41   93   99   103   129   132   134   147   156   172   179   193   221       20   21   32   40   92   98   102   128   131   133   146   155   171   178   192   220       19   20   31   39   91   97   101   127   130   132   145   154   170   177   191   219       18   19   30   38   90   96   100   126   129   131   144   153   169   176   190   218       17   18   29   37   89   95   99   125   128   130   143   152   168   175   189   217       16   17   28   36   88   94   98   124   127   129   142   151   167   174   188   216       15   16   27   35   87   93   97   123   126   128   141   150   166   173   187   215       14   15   26   34   86   92   96   122   125   127   140   149   165   172   186   214       13   14   25   33   85   91   95   121   124   126   139   148   164   171   185   213       12   13   24   32   84   90   94   120   123   125   138   147   163   170   184   212       11   12   23   31   83   89   93   119   122   124   137   146   162   169   183   211       10   11   22   30   82   88   92   118   121   123   136   145   161   168   182   210       9   10   21   29   81   87   91   117   120   122   135   144   160   167   181   209       8   9   20   28   80   86   90   116   119   121   134   143   159   166   180   208       7   8   19   27   79   85   89   115   118   120   133   142   158   165   179   207       6   7   18   26   78   84   88   114   117   119   132   141   157   164   178   206       5   6   17   25   77   83   87   113   116   118   131   140   156   163   177   205       4   5   16   24   76   82   86   112   115   117   130   139   155   162   176   204       3   4   15   23   75   81   85   111   114   116   129   138   154   161   175   203       2   3   14   22   74   80   84   110   113   115   128   137   153   160   174   202       1   2   13   21   73   79   83   109   112   114   127   136   152   159   173   201       0   1   12   20   72   78   82   108   111   113   126   135   151   158   172   200       0   11   19   71   77   81   107   110   112   125   134   150   157   171   199   254       10   18   70   76   80   106   109   111   124   133   149   156   170   198   253   254       9   17   69   75   79   105   108   110   123   132   148   155   169   197   252   253       8   16   68   74   78   104   107   109   122   131   147   154   168   196   251   252       7   15   67   73   77   103   106   108   121   130   146   153   167   195   250   251       6   14   66   72   76   102   105   107   120   129   145   152   166   194   249   250       5   13   65   71   75   101   104   106   119   128   144   151   165   193   248   249       4   12   64   70   74   100   103   105   118   127   143   150   164   192   247   248       3   11   63   69   73   99   102   104   117   126   142   149   163   191   246   247       2   10   62   68   72   98   101   103   116   125   141   148   162   190   245   246       1   9   61   67   71   97   100   102   115   124   140   147   161   189   244   245       0   8   60   66   70   96   99   101   114   123   139   146   160   188   243   244       7   59   65   69   95   98   100   113   122   138   145   159   187   242   243   254       6   58   64   68   94   97   99   112   121   137   144   158   186   241   242   253       5   57   63   67   93   96   98   111   120   136   143   157   185   240   241   252       4   56   62   66   92   95   97   110   119   135   142   156   184   239   240   251       3   55   61   65   91   94   96   109   118   134   141   155   183   238   239   250       2   54   60   64   90   93   95   108   117   133   140   154   182   237   238   249       1   53   59   63   89   92   94   107   116   132   139   153   181   236   237   248       0   52   58   62   88   91   93   106   115   131   138   152   180   235   236   247       51   57   61   87   90   92   105   114   130   137   151   179   234   235   246   254       50   56   60   86   89   91   104   113   129   136   150   178   233   234   245   253       49   55   59   85   88   90   103   112   128   135   149   177   232   233   244   252       48   54   58   84   87   89   102   111   127   134   148   176   231   232   243   251       47   53   57   83   86   88   101   110   126   133   147   175   230   231   242   250       46   52   56   82   85   87   100   109   125   132   146   174   229   230   241   249       45   51   55   81   84   86   99   108   124   131   145   173   228   229   240   248       44   50   54   80   83   85   98   107   123   130   144   172   227   228   239   247       43   49   53   79   82   84   97   106   122   129   143   171   226   227   238   246       42   48   52   78   81   83   96   105   121   128   142   170   225   226   237   245       41   47   51   77   80   82   95   104   120   127   141   169   224   225   236   244       40   46   50   76   79   81   94   103   119   126   140   168   223   224   235   243       39   45   49   75   78   80   93   102   118   125   139   167   222   223   234   242       38   44   48   74   77   79   92   101   117   124   138   166   221   222   233   241       37   43   47   73   76   78   91   100   116   123   137   165   220   221   232   240       36   42   46   72   75   77   90   99   115   122   136   164   219   220   231   239       35   41   45   71   74   76   89   98   114   121   135   163   218   219   230   238       34   40   44   70   73   75   88   97   113   120   134   162   217   218   229   237       33   39   43   69   72   74   87   96   112   119   133   161   216   217   228   236       32   38   42   68   71   73   86   95   111   118   132   160   215   216   227   235       31   37   41   67   70   72   85   94   110   117   131   159   214   215   226   234       30   36   40   66   69   71   84   93   109   116   130   158   213   214   225   233       29   35   39   65   68   70   83   92   108   115   129   157   212   213   224   232       28   34   38   64   67   69   82   91   107   114   128   156   211   212   223   231       27   33   37   63   66   68   81   90   106   113   127   155   210   211   222   230       26   32   36   62   65   67   80   89   105   112   126   154   209   210   221   229       25   31   35   61   64   66   79   88   104   111   125   153   208   209   220   228       24   30   34   60   63   65   78   87   103   110   124   152   207   208   219   227       23   29   33   59   62   64   77   86   102   109   123   151   206   207   218   226       22   28   32   58   61   63   76   85   101   108   122   150   205   206   217   225       21   27   31   57   60   62   75   84   100   107   121   149   204   205   216   224       20   26   30   56   59   61   74   83   99   106   120   148   203   204   215   223       19   25   29   55   58   60   73   82   98   105   119   147   202   203   214   222       18   24   28   54   57   59   72   81   97   104   118   146   201   202   213   221       17   23   27   53   56   58   71   80   96   103   117   145   200   201   212   220       16   22   26   52   55   57   70   79   95   102   116   144   199   200   211   219       15   21   25   51   54   56   69   78   94   101   115   143   198   199   210   218       14   20   24   50   53   55   68   77   93   100   114   142   197   198   209   217       13   19   23   49   52   54   67   76   92   99   113   141   196   197   208   216       12   18   22   48   51   53   66   75   91   98   112   140   195   196   207   215       11   17   21   47   50   52   65   74   90   97   111   139   194   195   206   214       10   16   20   46   49   51   64   73   89   96   110   138   193   194   205   213       9   15   19   45   48   50   63   72   88   95   109   137   192   193   204   212       8   14   18   44   47   49   62   71   87   94   108   136   191   192   203   211       7   13   17   43   46   48   61   70   86   93   107   135   190   191   202   210       6   12   16   42   45   47   60   69   85   92   106   134   189   190   201   209       5   11   15   41   44   46   59   68   84   91   105   133   188   189   200   208       4   10   14   40   43   45   58   67   83   90   104   132   187   188   199   207       3   9   13   39   42   44   57   66   82   89   103   131   186   187   198   206       2   8   12   38   41   43   56   65   81   88   102   130   185   186   197   205       1   7   11   37   40   42   55   64   80   87   101   129   184   185   196   204       0   6   10   36   39   41   54   63   79   86   100   128   183   184   195   203       5   9   35   38   40   53   62   78   85   99   127   182   183   194   202   254       4   8   34   37   39   52   61   77   84   98   126   181   182   193   201   253       3   7   33   36   38   51   60   76   83   97   125   180   181   192   200   252       2   6   32   35   37   50   59   75   82   96   124   179   180   191   199   251       1   5   31   34   36   49   58   74   81   95   123   178   179   190   198   250       0   4   30   33   35   48   57   73   80   94   122   177   178   189   197   249       3   29   32   34   47   56   72   79   93   121   176   177   188   196   248   254       2   28   31   33   46   55   71   78   92   120   175   176   187   195   247   253       1   27   30   32   45   54   70   77   91   119   174   175   186   194   246   252       0   26   29   31   44   53   69   76   90   118   173   174   185   193   245   251       25   28   30   43   52   68   75   89   117   172   173   184   192   244   250   254       24   27   29   42   51   67   74   88   116   171   172   183   191   243   249   253       23   26   28   41   50   66   73   87   115   170   171   182   190   242   248   252       22   25   27   40   49   65   72   86   114   169   170   181   189   241   247   251       21   24   26   39   48   64   71   85   113   168   169   180   188   240   246   250       20   23   25   38   47   63   70   84   112   167   168   179   187   239   245   249       19   22   24   37   46   62   69   83   111   166   167   178   186   238   244   248       18   21   23   36   45   61   68   82   110   165   166   177   185   237   243   247       17   20   22   35   44   60   67   81   109   164   165   176   184   236   242   246       16   19   21   34   43   59   66   80   108   163   164   175   183   235   241   245       15   18   20   33   42   58   65   79   107   162   163   174   182   234   240   244       14   17   19   32   41   57   64   78   106   161   162   173   181   233   239   243       13   16   18   31   40   56   63   77   105   160   161   172   180   232   238   242       12   15   17   30   39   55   62   76   104   159   160   171   179   231   237   241       11   14   16   29   38   54   61   75   103   158   159   170   178   230   236   240       10   13   15   28   37   53   60   74   102   157   158   169   177   229   235   239       9   12   14   27   36   52   59   73   101   156   157   168   176   228   234   238       8   11   13   26   35   51   58   72   100   155   156   167   175   227   233   237       7   10   12   25   34   50   57   71   99   154   155   166   174   226   232   236       6   9   11   24   33   49   56   70   98   153   154   165   173   225   231   235       5   8   10   23   32   48   55   69   97   152   153   164   172   224   230   234       4   7   9   22   31   47   54   68   96   151   152   163   171   223   229   233       3   6   8   21   30   46   53   67   95   150   151   162   170   222   228   232       2   5   7   20   29   45   52   66   94   149   150   161   169   221   227   231       1   4   6   19   28   44   51   65   93   148   149   160   168   220   226   230       0   3   5   18   27   43   50   64   92   147   148   159   167   219   225   229       2   4   17   26   42   49   63   91   146   147   158   166   218   224   228   254       1   3   16   25   41   48   62   90   145   146   157   165   217   223   227   253       0   2   15   24   40   47   61   89   144   145   156   164   216   222   226   252                  
 
         [0028]    Referring to FIG. 7, a diagram  190  illustrating the construction of the input generated by the symbol or frame interleaver stage  106  that may be provided to the LDPC encoder stage  108  is shown. The stage  108  may comprise a variable rate LDPC inner encoder. In one example, the inner encoder may use a shortened version of a 2 dimensional (255, 175) Euclidean Geometry (EG) LDPC code defined over a EG(2,2 4 ). The variable rate for a cyclic EG-LDPC code may be achieved by suitably puncturing the information and the parity bits. The resulting (239,160) shortened EG-LDPC code may be constructed by an appropriate puncturing of 15 information bits and 1 parity bit of the (255, 175) mother code. An example of the (255, 175) mother code may be represented by the [H] matrix given in Table 2.  
         [0029]    The optional stage  114  may implement synchronization. The binary LDPC code word block of the present example may comprise 160 bits. Thus, a single RS(200,188) codeword may provide for (8*200 bits)/160=10 blocks. Further, a single source frame  180  after RS encoding may comprise 200 RS encoded blocks. This may correspond to a total of 10×200=2000 input blocks  190  for the LDPC encoder  108 . With a systematic implementation of a generator matrix for both the RS and LDPC codes, the b8 hexadecimal value illustrated in FIG. 5 may still be maintained as the first input byte of the overall RS encoded frame  180  going into the systematic LDPC encoder  108 . Hence, the b8 hexadecimal value may also be the first output byte of the LDPC encoded frame. To aid in carrier recovery, n optional pilot symbols may be inserted after each LDPC encoded frame (e.g., after every 239×10×200=478,000 bits). These pilot symbols may be removed by the receiver during demodulation.  
         [0030]    Referring to FIG. 8, a block diagram of a process comprising an encoder, bit to symbol mapper and modulator for an example n-level Phase-Shift Keying/m-level Quadrature Amplitude Modulation (nPSK/mQAM) system  200  is shown. The nPSK/mQAM system  200  may be an expanded view of an example implementation of the steps  108 ,  110 , and  112  of FIG. 2. The nPSK/mQAM system may comprise a stage  202 , a stage  204 , a stage  206 , and a stage  208 . The stage  202  may apply the systemic mother code example [H] matrix of TABLE 2 to achieve inner coding. The stage  204  may perform the puncturing operation. The stage  206  may comprise a bit-to-symbol mapper that may be similar to the bit-to-symbol mapper of stage  110  of FIG. 2. The stage  208  may perform a final stage PSK/QAM modulation.  
         [0031]    Referring to FIG. 9, a bits-to-8PSK symbol mapping example used in satellite 8PSK is shown. The stage  110  of FIG. 2 may comprise modulation using bit-to-symbol mapping. An example of a bit-to-symbol gray mapping process is shown in FIG. 9. Other schemes that perform bit interleaving before the symbol mapping may also be used to improve performance under certain conditions.  
         [0032]    Referring back to FIG. 2, the final stage  112  may comprise a final stage modulator. The modulator may apply, in one example, 8/4/2-PSK modulation. The output of the final stage  112  may provide the signal to be broadcast in the digital broadband transmission system. While 8/4/2-PSK and PSK/QAM modulation have been shown, any type of modulation can be used to meet the design criteria of a particular application.  
         [0033]    The following TABLE 3 illustrates ideal channel and demodulation simulation results:  
                                                                                                                           TABLE 3                           Theoretical Linear Channel Performances                                            BER   Eb/No       linear                               Ru       after   after       channel           Inner       Inner   Outer       Useful       inner   inner   Eb/No   @ QEF            Modulation   Chan.   Code   Rs   Code   Code   Framing   Rate   Efficiency   decoder   decoder   @ Ru   C/N   C/No       Format   b/sym   Type   [Mbps]   Rate   Rate   Overhead   [Mbps]   [bits/sym]   [dB]   [dB]   [dB]   [dB]   [dB]               DVB QPSK   2   viterbi   21.5   0.750   0.922   n.a.   29.72   1.38   2.00E − 04   4.35   4.70   6.11   1.44                  
 
         [0034]    Although the proposed outer code structure was previously defined as being RS(200,188), DVB-S RS(204,188) is also considered for comparison. For a given signal byte error rate (ByteER) p supplied at an input to a RS(N, N-2T) decoder, the output byte error rate q is given by the formula:  
       q   =       ∑     i   =     T   +   1       N            C     i   -   1                   N   -   1                  p   i          (     1   -   p     )         N   -   i       .                               
 
         [0035]    Here, N is the RS codeword length and T is the correction power of the code. The estimated gain margin obtained in the example case of using an inner LDPC code may be sufficient to compensate for a higher 8PSK demodulator performance loss and also for higher distortion effects on the 8PSK constellation by the satellite transponder.  
         [0036]    The function performed by the flow diagram of FIG. 2 may be implemented using a conventional general purpose digital computer programmed according to the teachings of the present specification, as will be apparent to those skilled in the relevant art(s). Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will also be apparent to those skilled in the relevant art(s).  
         [0037]    The present invention may also be implemented by the preparation of ASICs, FPGAs, or by interconnecting an appropriate network of conventional component circuits, as is described herein, modifications of which will be readily apparent to those skilled in the art(s).  
         [0038]    The present invention thus may also include a computer product which may be a storage medium including instructions which can be used to program a computer to perform a process in accordance with the present invention. The storage medium can include, but is not limited to, any type of disk including floppy disk, optical disk, CD-ROM, and magneto-optical disks, ROMs, RAMS, EPROMs, EEPROMs, Flash memory, magnetic or optical cards, or any type of media suitable for storing electronic instructions.  
         [0039]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.