Turbo equalization using message passing methods with higher order modulation signaling
Modern digital communication systems employ some form of error-control code (ECC) to improve the system performance over intersymbol interference (ISI) channel. Since the discovery of turbo codes, iterative decoding has become a vital field of research in digital communications. The turbo equalization is a widely used iterative receiver technique which has high performance of bit error rate (BER). Many turbo equalization techniques have been proposed different BER performances and different computational complexities.
The most well-known technique is the maximum a posteriori probability (MAP)-based turbo equalization algorithm which consists of MAP equalizer and MAP decoder. However, this algorithm gives rise to an impractical computational complexity. The computational burden leads us to consider the turbo equalization based on minimum mean squared error (MMSE) linear equalizer which reduces the computational complexity extremely and improves the BER performance as much as the MAP-based turbo equalization.
In this thesis we will employ the SISO algorithm based on linear MMSE filter for the equalizer and use the SISO algorithm based on MAP/BCJR for the decoder in order for the massage passing in the turbo equalization.
The objective of this thesis is to study the proposed turbo equalization algorithm and to apply this algorithm to 16-QAM for the practical implementation. Finally, we present simulation results to compare the performances of the turbo equalization with different modulation schemes.