A turbo receiver for wireless MC-CDMA communications using MAP-EM demodulator with LDPC codes under narrowband interference

This paper presents a turbo receiver for wireless multicarrier code division multiple access (MC-CDMA) communication systems using maximum a posteriori expectation-maximization (MAP-EM) demodulator with a son low-density parity-check (LDPC) decoder with pilotaided robust channel tracking and multiuser detection under time-varying narrowband interference (NBI). It was found that the conventional least-squares (LS) channel estimators and multiuser detectors will be significantly degraded when some sub-carrier are contaminated by narrowband interfering signals. A new weighted least M-estimate (WLM) multiuser detector, which is based on the Mestimation and weighted least square (WLS) concept, is proposed to jointly suppress the multiple access interference (MAI) and time-varying NBI. To reliably estimate the channel in NBI, a weighted recursive least Mestimate (WRLM) channel estimator is also employed to estimate the time-varying frequency-selective fading channels. Simulation results show that the proposed WLM multiuser detector significantly outperforms over the conventional linear decorrelator under NBI.