Improving irregular turbo codes
The influence of the degree profile on the performance of an irregular turbo code (TC) is analysed using hierarchical EXtrinsic Information Transfer (EXIT) charts. Then, an irregular TC concatenated with a post-encoder of unity rate at its output is proposed to improve the distance properties. Through the example of 3GPP2 interleaving, the gain at low but also at high signal-to-noise ratios is illustrated.