Communication decoder employing single trellis to support multiple code rates and/or multiple modulations

Abstract

Communication decoder employing single trellis to support multiple code rates and/or multiple modulations. A single trellis is employed by the decoder to decode a plurality of encoded symbols. Each of the plurality of encoded symbols is governed by a rate control. A rate control sequence, having a period, is used to decode the plurality of encoded symbols that may be arranged within a frame. Various parameters of the plurality of encoded symbols may vary on a symbol by symbol basis; these parameters may include modulation, constellation, mapping, and/or bandwidth efficiency. For example, various symbols may be encoded differently, yet they may all be decoded using the same trellis. The functionality of this decoder may be implemented within a variety of different decoder embodiments including a trellis code modulation (TCM) decoder, a turbo trellis code modulation (TTCM) decoder, and/or a parallel concatenated turbo code modulation (PC-TCM) decoder.

1 . An apparatus, comprising: 
 an input that is operable to receive a signal from a communication channel, wherein: 
 the signal includes a first symbol, that includes a first plurality of bits, that has been symbol mapped to a first modulation; and  
 the signal includes a second symbol, that includes a second plurality of bits, that has been symbol mapped to a second modulation;  
   a metric generator that is operable to: 
 for the first symbol, calculate a first plurality of metrics that is indexed by a first symbol mapping of constellation points within the first modulation;  
 for the second symbol, calculate a second plurality of metrics that is indexed by a second symbol mapping of constellation points within the second modulation;  
 transform the first plurality of metrics to a first plurality of trellis metrics, wherein the first plurality of trellis metrics is a first subset of a total plurality of trellis metrics that corresponds to a plurality of possible branch transitions within a trellis; and  
 transform the second plurality of metrics to a second plurality of trellis metrics, wherein the second plurality of trellis metrics is a second subset of the total plurality of trellis metrics; and  
   a decoder that is operable to: 
 employ the first plurality of trellis metrics during decoding processing to make a first best estimate of the first plurality of bits within the first symbol; and  
 employ the second plurality of trellis metrics during decoding processing to make a second best estimate of the second plurality of bits within the second symbol.  
   
   
   
       2 . The apparatus of  claim 1 , wherein: 
 the first symbol also includes an uncoded bit.    
   
   
       3 . The apparatus of  claim 1 , wherein: 
 the second plurality of trellis metrics is also a subset of the first plurality of trellis metrics.    
   
   
       4 . The apparatus of  claim 1 , wherein: 
 at least two metrics within the first plurality of metrics or the second plurality of trellis metrics are assigned to a single trellis metric value within the total plurality of trellis metrics.    
   
   
       5 . The apparatus of  claim 1 , further comprising: 
 a first memory, having a first size, that is operable to store the total plurality of trellis metrics; and wherein:    a second memory being operable to store the first plurality of trellis metrics would require at least a second size;    a third memory being operable to store the second plurality of trellis metrics would require at least a third size; and    because at least one trellis metric of the trellis metrics within the total plurality of trellis metrics is included within each of the first plurality of trellis metrics and the second first plurality of trellis metrics, the first size of the first memory within the apparatus is relatively less than a combined size of the second size of the second memory and the third size of the third memory.    
   
   
       6 . The apparatus of  claim 1 , wherein: 
 the first modulation and the second modulation each include a same number of constellation points;    constellation points within the first modulation are symbol mapped according to a first symbol mapping; and    constellation points within the second modulation are symbol mapped according to a second symbol mapping.    
   
   
       7 . The apparatus of  claim 1 , wherein: 
 the first modulation includes a first plurality of constellation points;    the second modulation includes a second plurality of constellation points;    constellation points within the first modulation are symbol mapped according to a first symbol mapping; and    constellation points within the second modulation are symbol mapped according to a second symbol mapping.    
   
   
       8 . The apparatus of  claim 1 , wherein: 
 the first modulation includes a first plurality of constellation points;    the second modulation includes a second plurality of constellation points; and    the second plurality of constellation points is a subset of the first plurality of constellation points.    
   
   
       9 . The apparatus of  claim 1 , further comprising: 
 a rate control sequencer that provides a rate control sequence to the metric generator and to the decoder, wherein the rate control sequence includes a first rate control and a second rate control; and wherein:    for the first symbol, the first rate control indicates the first modulation and which trellis metrics of the total plurality of trellis metrics compose the first plurality of trellis metrics to the metric generator and to the decoder; and    for the second symbol, the second rate control indicates the second modulation and which trellis metrics of the total plurality of trellis metrics compose the second plurality of trellis metrics to the metric generator and to the decoder.    
   
   
       10 . The apparatus of  claim 1 , further comprising: 
 a rate control sequencer that is operable to provide a rate control sequence to the metric generator and to the decoder, wherein the rate control sequence includes a first rate control and a second rate control; and wherein:    the first symbol has been encoded using a first code rate;    the second symbol has been encoded using a second code rate;    the first rate control indicates the first code rate of the first symbol to the metric generator and to the decoder; and    the second rate control indicates the second code rate of the second symbol to the metric generator and to the decoder.    
   
   
       11 . The apparatus of  claim 1 , wherein: 
 at least one trellis metric of the first plurality of trellis metrics is set to a predetermined maximum value or a predetermined minimum value when one bit within the first plurality of bits is estimated to be either a value of 0 or 1.    
   
   
       12 . An apparatus, comprising: 
 an input that is operable to receive a signal from a communication channel, wherein: 
 the signal includes a first symbol, that includes a first plurality of bits, that has been symbol mapped to a first modulation, wherein the first symbol has been encoded using a first code rate; and  
 the signal includes a second symbol, that includes a second plurality of bits, that has been symbol mapped to a second modulation, wherein the second symbol has been encoded using a second code rate; and  
   a decoder that is operable to: 
 employ the first plurality of trellis metrics during decoding processing to make a first best estimate of the first plurality of bits within the first symbol, wherein the first plurality of trellis metrics is a first subset of a total plurality of trellis metrics that corresponds to a plurality of possible branch transitions within a trellis; and  
 employ the second plurality of trellis metrics during decoding processing to make a second best estimate of the second plurality of bits within the second symbol, wherein the second plurality of trellis metrics is a second subset of the total plurality of trellis metrics.  
   
   
   
       13 . The apparatus of  claim 12 , further comprising: 
 a metric generator that is operable to: 
 for the first symbol, calculate a first plurality of metrics that is indexed by a first symbol mapping of constellation points within the first modulation;  
 for the second symbol, calculate a second plurality of metrics that is indexed by a second symbol mapping of constellation points within the second modulation;  
 transform the first plurality of metrics to the first plurality of trellis metrics; and  
 transform the second plurality of metrics to the second plurality of trellis metrics.  
   
   
   
       14 . The apparatus of  claim 12 , further comprising: 
 a rate control sequencer that provides a rate control sequence to the metric generator and to the decoder, wherein the rate control sequence includes a first rate control and a second rate control; and wherein:    for the first symbol, the first rate control indicates the first modulation, which trellis metrics of the total plurality of trellis metrics compose the first plurality of trellis metrics, and the first code rate to the metric generator and to the decoder; and    for the second symbol, the second rate control indicates the second modulation, which trellis metrics of the total plurality of trellis metrics compose the second plurality of trellis metrics, and the second code rate to the metric generator and to the decoder.    
   
   
       15 . The apparatus of  claim 12 , wherein: 
 the second plurality of trellis metrics is also a subset of the first plurality of trellis metrics.    
   
   
       16 . The apparatus of  claim 12 , further comprising: 
 a first memory, having a first size, that is operable to store the total plurality of trellis metrics; and wherein:    a second memory being operable to store the first plurality of trellis metrics would require at least a second size;    a third memory being operable to store the second plurality of trellis metrics would require at least a third size; and    because at least one trellis metric of the trellis metrics within the total plurality of trellis metrics is included within each of the first plurality of trellis metrics and the second first plurality of trellis metrics, the first size of the first memory within the apparatus is relatively less than a combined size of the second size of the second memory and the third size of the third memory.    
   
   
       17 . The apparatus of  claim 12 , wherein: 
 the first modulation and the second modulation each include a same number of constellation points;    constellation points within the first modulation are symbol mapped according to a first symbol mapping; and    constellation points within the second modulation are symbol mapped according to a second symbol mapping.    
   
   
       18 . The apparatus of  claim 12 , wherein: 
 the first modulation includes a first plurality of constellation points;    the second modulation includes a second plurality of constellation points;    constellation points within the first modulation are symbol mapped according to a first symbol mapping; and    constellation points within the second modulation are symbol mapped according to a second symbol mapping.    
   
   
       19 . The apparatus of  claim 12 , wherein: 
 the first modulation includes a first plurality of constellation points;    the second modulation includes a second plurality of constellation points; and    the second plurality of constellation points is a subset of the first plurality of constellation points.    
   
   
       20 . A method, comprising: 
 receiving a signal from a communication channel, wherein: 
 the signal includes a first symbol, that includes a first plurality of bits, that has been symbol mapped to a first modulation, wherein the first symbol has been encoded using a first code rate; and  
 the signal includes a second symbol, that includes a second plurality of bits, that has been symbol mapped to a second modulation, wherein the second symbol has been encoded using a second code rate; and  
   employing the first plurality of trellis metrics during decoding processing to make a first best estimate of the first plurality of bits within the first symbol, wherein the first plurality of trellis metrics is a first subset of a total plurality of trellis metrics that corresponds to a plurality of possible branch transitions within a trellis; and    employing the second plurality of trellis metrics during decoding processing to make a second best estimate of the second plurality of bits within the second symbol, wherein the second plurality of trellis metrics is a second subset of the total plurality of trellis metrics.    
   
   
       21 . The method of  claim 20 , further comprising: 
 for the first symbol, calculating a first plurality of metrics that is indexed by a first symbol mapping of constellation points within the first modulation;    for the second symbol, calculating a second plurality of metrics that is indexed by a second symbol mapping of constellation points within the second modulation;    transforming the first plurality of metrics to the first plurality of trellis metrics; and    transforming the second plurality of metrics to the second plurality of trellis metrics.    
   
   
       22 . The method of  claim 20 , wherein: 
 the first modulation and the second modulation each include a same number of constellation points;    constellation points within the first modulation are symbol mapped according to a first symbol mapping; and    constellation points within the second modulation are symbol mapped according to a second symbol mapping.    
   
   
       23 . The method of  claim 20 , wherein: 
 the first modulation includes a first plurality of constellation points;    the second modulation includes a second plurality of constellation points;    constellation points within the first modulation are symbol mapped according to a first symbol mapping; and    constellation points within the second modulation are symbol mapped according to a second symbol mapping.    
   
   
       24 . The method of  claim 20 , wherein: 
 the first modulation includes a first plurality of constellation points;    the second modulation includes a second plurality of constellation points; and    the second plurality of constellation points is a subset of the first plurality of constellation points.