SCFDE

SCFDE, short for Single-Carrier Frequency-Domain Equalization, is a transmission technique that combines the single-carrier nature of traditional modulation with frequency-domain equalization similar to that used in multicarrier systems. The basic idea is to send data in blocks that behave like a single-carrier signal within each block, while the channel’s frequency-selective effects are mitigated by a per-tone equalizer in the frequency domain.

In operation, data symbols are arranged into blocks and optionally encoded. A cyclic prefix is added to each block to convert the linear channel convolution into a circular convolution, which enables efficient frequency-domain processing. The transmitter then moves the block to the frequency domain (via a DFT/FFT), applies a per-subcarrier equalizer (for example MMSE or zero-forcing), and converts the result back to the time domain with an inverse DFT/IDFT for transmission. At the receiver, after removing the cyclic prefix, the received block is transformed to the frequency domain, equalized on a per-subcarrier basis, and then converted back to time-domain symbols.

Advantages of SC-FDE include a lower peak-to-average power ratio than OFDM, which can improve power amplifier efficiency, and robust performance in frequency-selective channels due to effective per-subcarrier equalization. The single-carrier nature also helps in reducing sensitivity to nonlinearities. SC-FDE can be extended to multiple-antenna (MIMO) configurations, forming MIMO-SC-FDE, which combines spatial diversity with frequency-domain equalization.

Key considerations include latency and overhead from block processing and cyclic prefixes, as well as the need for accurate channel state information for the per-subcarrier equalizers. SC-FDE remains a topic of study in wireless communications as an alternative to OFDM in scenarios requiring low PAPR and effective ISI mitigation.