Single-Carrier FDMA versus Cyclic-Prefix CDMA

In order to meet the data rate and quality-of-service (QoS) requirements of the future cellular systems, new air interfaces are currently under development. In this paper, we compare two air interfaces of particular interest for the uplink: cyclic-prefix code-division multiple access (CP-CDMA) proposed in the literature as an evolution of direct-sequence code-division multiple access (DS-CDMA) because it enables the low complexity equalization of the multipath channel in the frequency domain, and single-carrier frequency-division multiple access (SC-FDMA), recently proposed in the long term evolution of the 3GPP standard because it enables the easy separation of the users in the frequency domain. We demonstrate analytically that SC-FDMA is a special case of CP-CDMA, in which the CDMA codes have been optimized to minimize the symbol estimation mean square error (MSE) under a constraint of received power. Numerical results show that SC-FDMA outperforms significantly CP-CDMA at high user loads. The transmit power necessary to fulfill the received power constraint is higher in case of SC-FDMA than in case of CP-CDMA when the carrier sub-sets are allocated randomly to the users, and lower when the carrier sub-sets are allocated in an optimized way.