A New Iterative Decoder for Turbo Codes on the Nonlinear Channel with Non-uniform 16QAM Modulation

Conference: TURBO - CODING - 2006 - 4th International Symposium on Turbo Codes & Related Topics; 6th International ITG-Conference on Source and Channel Coding
04/03/2006 - 04/07/2006 at Munich, Germany

Proceedings: TURBO - CODING - 2006

Pages: 6Language: englishTyp: PDF

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Ngo, Nghia H.; Pietrobon, Steven S.; Barbulescu, S. Adrian (Institute for Telecommunications Research, University of South Australia, Mawson Lakes SA 5095, Australia)
Pietrobon, Steven S. (Small World Communications, 6 First Avenue, Payneham South SA 5070, Australia)

In conventional bit interleaved coded modulation with iterative decoding (BICM - ID), a turbo decoder is employed where extrinsic information of the data bits is exchanged between two soft input soft output (SISO) devices. For a fixed size constellation, the probability distribution and distance among signal symbols are usually assumed to be uniform. Performance of BICM-ID is determined by the code structure, the signal mapping and the iteration scheduling between the soft-demapper and the decoder. In this paper, we propose a new scheme for the turbo receiver where an extra soft-demapper is placed between the two SISO decoders. Extrinsic information is exchanged for both data and parity bits. Also, a new non-uniform probability distribution technique for 16QAM is used with this new iterative decoding structure. We simulated a parallel concatenated convolutional code (PCCC) scheme with 16QAM modulation. Over a linear channel, this new iterative decoding scheme with non-uniform 16QAM offers a gain of 0.9 dB at a bit error rate (BER) of 10-5. On a nonlinear satellite channel, we observed a gain of 1.2 dB compared to uniform 16QAM, also at a BER of 10-5.