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Multi-carrier OFDM-CDMA has a range of advantages that are ideal for high data rate wireless access system. A two-layer carrier interferometry (CI) phase coding approach is proposed for enhancing multi-user detection of millimeter wavelength multi-carrier OFDM-CDMA based uplink broadband wireless access system (BWA). The proposed OFDM-CDMA scheme uses a two-layer CI phase coding structure, which comprises outer and inner CI modulations and is combined with iterative interference cancellation and detection to boost the system capability in high fading radio channel and strong multiple access interference environment. Orthogonal property of two-layer CI signals is exploited to enhance diversities in time, frequency and spreading code domains, as well as to mitigate peak-to-average power problem and to simplify signal processing. The proposed two-layer CI OFDM-CDMA scheme for the uplink BWA is mathematically analyzed. Effects of frequency synchronization errors to the scheme are studied. Numeric simulations are carried out to evaluate the system performance. The simulation results show the superior characteristics of the proposed two-layer CI phase coding scheme for the uplink BWA system compared to other schemes.