Carrier synchronization requirements for CDMA systems with frequency-domain orthogonal signature sequences

Block transmission CDMA (code division multiple access) schemes using FDOSS (frequency-domain orthogonal signature sequences) have recently been proposed for the uplink transmission of broadband wireless systems providing services with substantially different data rates. As with OFDMA (orthogonal frequency division multiple access) schemes, 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. It is shown that the carrier synchronization requirements are similar to those of OFDMA schemes. Since the transmitted signals can have a very low envelope, these techniques present an interesting alternative to OFDMA.