Irregular Vector Turbo Codes with low complexity

Abstract

Abstract The term Block Turbo Code typically refers to the iterative decoding of a serially concatenated two-dimensional systematic block code. This paper introduces a Vector Turbo Code that is irregular but with code rates comparable to those of a Block Turbo Code (BTC) when the Bahl Cocke Jelinek Raviv algorithm is used. In BTC’s, the horizontal (or vertical) blocks are encoded first and the vertical (or horizontal) blocks second. The irregular Vector Turbo Code (iVTC) uses information bits that participate in varying numbers of trellis sections, which are organized into blocks that are encoded horizontally (or vertical) without vertical (or horizontal) encoding. The decoding requires only one soft-input soft-output decoder. In general, a reduction in complexity, in comparison to a BTC was achieved for the same very low probability of bit error ( $$10^{-5}$$ 10 - 5 ). Performance in the AWGN channel shows that iVTC is capable of achieving a significant coding gain of 1.28dB for a 64QAM modulation scheme, at a bit error rate of $$10^{-5}$$ 10 - 5 over its corresponding BTC. Simulation results also show that some of these codes perform within 0.49dB of capacity for binary transmission over an AWGN channel.

Keywords

• BCJR algorithm
• Block turbo code
• Extrinsic information transfer function
• Log-MAP
• Irregular coding