A type of forward error correction code using a shift register containing a number of stages to shift the input bits one at a time to produce a coded output. With the convolutional code, (a) each m-bit information symbol (each m-bit string) to be encoded is transformed into an n-bit symbol, where m/n is the code rate (n >= m) and (b) the transformation is a function of the last k information symbols, where k is the constraint length of the code.