Robust, Low Complexity LLRs for Interference Mitigation in Reuse-1 OFDM

In this work we consider the performance of turbo coded OFDM systems in the presence of co-channel interference (CCI) in reuse-1 OFDM systems such as 802.16d/e and LTE. Because of frequency selectivity and diversity mapping, CCI does not affect all the subcarriers of the desired user. Hence CCI behaves like Narrow Band Interference(NBI) with the number of affected subcarriers ranging from 10% to 30%. The NBI in frequency domain is similar to impulsive noise in the time domain.We consider three different ǫ-mixture models,which have been used to model impulsive noise in the literature, for modelling the NBI. In this work we propose a low complexity LLR(Loglikelihood Ratio) for turbo codes which is robust under all the three model assumptions. The proposed LLR assumes the knowledge of the Signal to Noise ratio (SNR) but does not assume knowledge of the NBI power, NBI pdf and the fraction of subcarriers affected by NBI. Simulation results indicate that the proposed method performs within 0.4dB from the optimal LLR which would have complete knowledge of the pdf parameters.