Block transmission CDMA schemes (Code Division Multiple Access) using FDOSS (Frequency-Domain Orthogonal Signature Sequences) have been recently proposed for the up-link transmission of broadband wireless systems providing services with substantially different data rates. As with OFDMA schemes (Orthogonal Frequency Division Multiple Access), a set of frequencies is assigned to each user and the different users' blocks remain orthogonal, even for severe time dispersive channels, provided that a perfect carrier synchronization is maintained between the BS (Base Station) and all MTs (Mobile Terminals). The impact of carrier synchronization errors on CDMA systems using FDOSS is studied in the paper. It is shown that the carrier synchronization requirements are similar to the ones of OFDMA schemes. Since the transmitted signals can have very low envelope fluctuations, these techniques present an interesting alternative to OFDMA.

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Conference 2004 IEEE International Symposium on Spread Spectrum Techniques and Applications, ISSSTA 2004
Dinis, R. (Rui), Lam, C.T. (Chan Tong), & Falconer, D.D. (2004). Carrier synchronization requirements for CDMA systems with frequency-domain orthogonal signature sequences. In IEEE International Symposium on Spread Spectrum Techniques and Applications (pp. 821–825).