Encoder Rate

• Definition:
  The encoder rate is the data rate. It specifies how much redundancy is added to message bits. The rate is entered by typing the number of message bits and the number of codeword bits in the two text boxes depicted above.
  
• Usage:
  To change the rate, enter integers in the text fields depicted above. Then press the Edit Transfer Function button to bring up a dialog box in which you can enter new FIR expressions for the codeword bits. If you enter an invalid rate the program will warn you when you try to edit the transfer function.
  
• Valid Input:
  The rate should not be less than 1/2 because a rate 1/1 code is not a code at all; it has no error correction capability and is thus not useful for the purposes of this program. In real life applications, the rate could be arbitrarily large, but in the Workshop you may not use a code with more than 4 bits per message word and 6 bits per codeword. The reason for this is that a large number of message bits makes for a cluttered trellis and thus does not serve the purpose of this program which is to elucidate the Viterbi algorithm. These are reasonable limits that allow the user to try quite a wide variety of codes and rates.
  
• Examples:
  Common rates for binary convolutional codes are 1/2, 1/3, 1/4, and 2/3.