Quadratic Permutation Polynomial Interleavers for 3gpp Lte Turbo Codes

The contention-free property of interleavers is one of the key design requirements for the parallel decoding implementations of turbo codes in order to achieve high decoding throughput. Quadratic permutation polynomial (QPP) interleavers are maximum contention-free (MCF), i.e., every factor dividing the interleaver length becomes a possible degree of parallel decoding processing without any memory access contention. Despite the desirable MCF property, the performance of QPP interleavers has been demonstrated to be excellent. The simple algebraic construction is of particular interest for practical systems as well. However, an efficient method finding good QPP interleavers needs more studies. We propose a simple method, which finds QPP interleavers maximizing the randomness, while certain minimum spreading property is guaranteed. Although the design is code-independent, turbo codes using the interleavers found by our method result in a large free distance on top of the good randomness and spreading properties. Numerical simulations show that turbo codes using these interleavers perform very well.