Single-Carrier FDMA or Cyclic-Prefix CDMA With Optimized Spreading Sequences?

To meet the data rate and quality-of-service 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: (1) cyclic-prefix code-division multiple access (CP-CDMA), which has been 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 (2) single-carrier frequency-division multiple access (SC-FDMA), which has recently been proposed in the long-term evolution of the Third-Generation Partnership Project (3GPP) standard because it enables the easy separation of users in the frequency domain. We analytically demonstrate that SC-FDMA is a special case of CP-CDMA, in which the CDMA codes have been optimized to minimize symbol estimation mean square error under a constraint of received power. Numerical results confirm that SC-FDMA significantly outperforms CP-CDMA at high user loads.