Design of flexible-length S-random interleaver for turbo codes

We introduce a method for generating a sequence of semi-random interleavers, intended to be optimally stored and employed in a turbo coding system that requires flexibility of the input block (i.e., interleaver) size N. A distinctive feature of this method is seen in the very simple rules for obtaining shorter/longer interleavers by pruning/adding positions to the interleaver currently used in the system. For each N, the obtained bit error rate (BER) is not higher than the BER for ordinary S-random interleaver of the same N. The method always converges and is suitable for obtaining interleavers of large lengths.