A Simple and Efficient Method for Lowering the Error Floors of Turbo Codes that Use Structured Interleavers

A simple and efficient method for lowering the error floors of turbo codes that use structured interleavers is presented in this paper. This method identifies a set of parity bits that will be forced to take zero bit values when encoding, and exploits these known zero bit parities when decoding. The effectiveness of this method is demonstrated by its ability to significantly enhance Hamming distance spectra and thereby lowers error floors by several orders of magnitude; for example, using a rate-1/3 4-state single-binary turbo code with a packet of 1504 information bits, the packet error rate at the moderate signal-to-noise ratio (SNR) value of 1.4 dB is improved by about three orders of magnitude from 10^-4 to 10^-7.