Interleaver design for short turbo codes

We present an interleaver design approach for short turbo codes. We use the D-transform to represent the information sequence and parity sequences of a turbo code. The interleaver design method is based on the divisibility of information polynomials. Design examples are given using a short interleaver of length equal to the period of the feedback polynomial used in the turbo codes, called the optimum period interleaver. Simulation results are presented for turbo codes using our interleavers based on optimum period interleaver and sub-optimum period interleaver. It is shown that the proposed interleavers are particularly effective for short turbo codes. An order of magnitude improvement in bit error rate can be obtained for turbo codes of frame lengths in the range of 100 to 1000 compared to turbo codes using block and pseudo-random interleavers