Optimal Soft Symbol Split Methods and Performance Analysis for Applying to Multilevel Modulation of Iterative Codes

This paper presents bit splitting methods to apply multilevel modulation to iterative codes such as turbo code, low density parity check code and turbo product code. Log-likelihood ratio method splits multilevel symbols to soft decision symbols using the received in-phase and quadrature component based on Gaussian approximation. However it is too complicate to calculate and to implement hardware due to exponential and logarithmic calculation. Therefore this paper presents Euclidean, MAX and Sector method to reduce the high complexity of LLR method. Also, this paper proposes optimal soft symbol split method for three kind of iterative codes