SCFDMA

SC-FDMA, or single-carrier frequency-division multiple access, is a multi-user access scheme used in wireless networks to allow multiple terminals to share the same spectrum. It is a DFT-spread OFDMA technique that combines a single-carrier signal with subcarrier-based access, producing lower peak-to-average power ratio (PAPR) than conventional OFDMA. This characteristic makes SC-FDMA well suited for uplink transmissions from battery-powered mobile devices.

In operation, the user data are first encoded into symbols, which are then subjected to a discrete Fourier transform. The resulting frequency-domain symbols are mapped onto a set of contiguous or dispersed subcarriers within a resource block. After mapping, an inverse DFT is applied, producing a time-domain signal that is sent after adding a cyclic prefix. The two main mapping options are localized SC-FDMA, where the DFT outputs occupy a contiguous block of subcarriers, and interleaved or distributed SC-FDMA, where subcarriers are spread across the band to gain frequency diversity.

In LTE, SC-FDMA is used for the uplink (user equipment to base station); the downlink uses standard OFDMA. The choice of mapping affects PAPR, spectral efficiency, and resilience to frequency-selective channels. The technique provides the benefits of single-carrier transmission while maintaining the advantages of multicarrier systems for multiple users.

SC-FDMA has influenced later wireless standards and research into efficient uplink waveforms. It remains a foundational concept in discussions of uplink design and PAPR-aware transmission strategies.