LTE E-UTRA UL Waveform: SC-FDM

• OFDM based UL transmission would lead to higher Peak-to- Average Power Ratio (PAPR) than the SC-FDM (TR25.814 Section 9.2.1.4).
• Single Carrier Waveform (SC-FDM or DFT-spread OFDM)
– Requires Data and control channels to be multiplexed prior to the DFT operation at the transmitter
• “Price” of maintaining Single Carrier Waveform
– 32 channel combinations == Multiplexing “rules”
» Data, ACK, CQI, SRS, SR
» No channel can be transmitted independently of the other
• Data and UL Demodulation Pilots (Reference Signals) are TDM

In OFDM each sub-carrier carries information from a specific modulation symbol and given the nature of this OFDM signal the PAPR due to the simultaneous transmission of multiple carriers can be significant.
In SC-FDM each sub-carrier carries information from all transmitted modulation symbols since the latter are spread by the DFT operation and then mapped to each sub-carrier. This single carrier transmission achieved by an IDFT operation followed by an FFT operation results in a lower PAPR. Careful multiplexing of data and control information is required for SC-FDM transmission.