Iterative frequency-domain fractionally spaced receiver for zero-padded multi-carrier code division multiple access systems

In this study, the authors propose an improved frequency-domain fractionally spaced (FDFS) minimum mean square error (MMSE) receiver for zero-padded multi-carrier code division multiple access (MC-CDMA) systems when the guard interval is not enough to avoid the inter-symbol interference (ISI) caused by the multipath channel. The proposed novel iterative FDFS-based receivers firstly reconstruct the received symbol to reduce the ISI and then followed by the FDFS-based equalisers to minimise the effect of ISI and inter-carrier interference (ICI) caused by carrier frequency offset (CFO) and Doppler shifts. A few iterations are performed to achieve the expected bit error rate (BER) performance. To reduce the receiver complexity, the novel simplified diagonal FDFS-based receivers with a fixed noise variance are developed with slight performance degradation. The proposed iterative receivers have never been studied in the existing literature. Simulation results show that the proposed iterative FDFS-based receivers can significantly improve the BER performance of the conventional FDFS-MMSE receiver in severe multiple interferences environments caused by multipath, CFO and Doppler shift.