Code Choices

• The feedback shift registers must be connected carefully to yield an error correcting code.
• Valid ways of connecting the registers have been determined by researchers and are tabulated.
• The code we have examined appears as follows in code tables:
  

  n	k	t	g
  7	4	1	13

• The column n denotes the length of the code word and the column k indicates the length of the uncoded input.
• The column t indicates the number of errors that can be corrected with this code.
• the quantity g must be interpreted as an octal number. I.e., each digit must be converted into a three bit binary number.
• E.g., Octal 13 equals 1 011.
• Now a 1 in the binary sequence indicates a feedback connection in the shift register circuit.
• Looking at the example above, you see that (from the right) connections appear in the first, third and fourth location. The second location is not connected.
• An example for a more powerful code is
  

  n	k	t	g
  127	99	4	3447023271