A soft demapping technique using fuzzy logic for LDPC receiver in cooperative wireless networks

Relays in wireless networks are used to achieve cooperative diversity. Various relaying schemes such as Amplify and Forward (AF), Decode and Forward (DF), etc. exists. But in this paper, a Soft Information Relaying scheme based on a soft Decode and Forward (SDF) relay protocol is considered. In order to be efficient under poor source relay link conditions, low density parity check (LDPC) coding scheme and higher order modulation scheme called Quadrature Amplitude Modulation (QAM) are used. In the existing method, log likelihood ratio (LLR) values (soft values) are computed at the destination for LDPC decoding. Since it is a complex and probabilistic based approach, the chances of occurring errors will be more. Because of this reason, a soft computing method called fuzzy logic system is proposed. The Fuzzy logic provides more information about the transmitted data, so that perfect data can be decoded and reconstructed at the destination without error. So that the proposed system provides better performance in terms of low bit error rate (BER).