Improved decoding of woven convolutional codes via hierarchical near-EEP code structure

A hierarchically designed channel coding scheme protects a few number of input data streams, so-called layers, with a decreasing amount of redundancy from layer 0 to layer L. Such a code design clearly leads to unequal error protection, but as shown by Huettinger and Huber (see Winter School on Coding and Information Theory, Reisensburg, December 2000) it can be superior in the average bit error rate compared to an equal error protection (EEP) design, if the protection of layers is not too different. This is due to the fact, that a near-EEP hierarchical design can match the properties of the iterative decoder. We extend the result to woven convolutional codes (WCC). Based on asymptotical analysis of the convergence of iterative decoding by means of EXIT charts we show that for an infinite interleaver size the hierarchical structure is superior. Furthermore, we show that even for practical block sizes used in modern communication systems a significant improvement is possible by the hierarchical design.