Convolutionally Coded CI/MC-CDMA for Wireless Broadband Communications

Carrier interferometry/multicarrier code division multiple access (CI/MC-CDMA) is a promising technique for broadband wireless networks. Multiuser access interference (MAI) limits the number of users and data rate in a broadband network. Iterative receiver has been suggested in the literature to reduce MAI. But iterative receivers are complex and introduce delay. This paper suggests that complexity and delay caused by iterative multiuser interference process can be reduced by utilizing convolutional codes for CI/MC-CDMA system. Carrier interferometry (CI) codes are used to minimize the cross-correlation between different users. In this paper, the bit error rate (BER) performance of convolutionally encoded CI/MC-CDMA has been evaluated in overloaded conditions. It has been observed that by using convolutional code, the BER performance improves considerably compared to uncoded system with interference cancellation (IC) receiver. Performance of uncoded system with soft decision parallel interference cancellation (SDSub-PIC) after 8th iteration over an AWGN channel is 1e-04 while for a coded system without IC BER is 7e-06 at 10 dB SNR. In slow frequency selective channel, coded system also performs better than uncoded system with IC. Simulation results validate the improved performance of coded system compared to uncoded system with multi-stage iterative IC receiver over AWGN and multipath channel with different loading.