A multislot-interleaved turbo-coded MC-CDMA/TDD uplink system with pre-equalization using polynomial fitting and extension for uplink channel estimation

In this paper, we present a multislot-interleaved turbo-coded MC-CDMA/TDD uplink system with pre-equalization using polynomial fitting and extension (PF and E) for uplink channel estimation at a mobile transmitter. The PF and E scheme that extends the channel state information (CSI) polynomial approximated over some downlink interval to the uplink slot interval provides better uplink CSI estimates in a time-varying channel. To improve further the system performance, we propose a two-step multislot interleaving (TS-MSI) scheme that improves the decoding performance by fully randomizing burst errors near the end of the uplink slot interval due to the CSI inaccurateness when the PF and E scheme is used. In the scheme, the permutation is performed in two steps as follows: (1) the interslot group-level permutation to distribute as evenly as possible information bits in a slot over all slots in an interleaver span; and (2) the intraslot bit-level permutation to separate as distant as possible adjacent bits in a slot after group-level permutation. Computer simulations are performed to evaluate the performance of the proposed system under various system conditions and channel conditions. Simulation results show that using the PF and E scheme for uplink channel estimation at the mobile transmitter can track quite well the time variability of the uplink channel, even with some downlink CSI estimation error. We see that the system performance when using TS-MSI can be improved gradually as the interleaver size increases.