Low Complexity Iterative Receiver for Downlink MC-CDMA System in Doppler Channels

Block Iterative - generalized decision feedback equalizer (BI-GDFE) is an iterative receiver using previously made hard decisions to cancel out the multiple access interference (MAI) and inter-symbol interference (ISI). In this paper, we formulate the BI-GDFE for downlink multi-carrier code division multiple access (MC-CDMA) system under time varying channel conditions. The time varying coefficients of each channel tap over a data block is a finite length sequence whose maximum bandwidth depends on the Doppler bandwidth. This sequence can be represented using basis expansion models proposed for time varying channels. In this paper, Slepian basis expansion is used because the number of basis vectors required to represent the time varying channel is less compared with other basis expansion models and hence the number of parameters to be estimated is less. Thus less number of pilot symbols are required for channel estimation. BI-GDFE for fully loaded downlink MC-CDMA system can be formulated as a one-tap equalizer which is simple for implementation. Furthermore, the computation of the signal to interference noise ratio (SINR) value for each iteration of BI-GDFE can be simplified using matrix manipulations for the downlink MC-CDMA system. Computer simulations show that the BER performance of BI-GDFE with channel estimation is close to the single user matched filter bound (MFB).