In LTE OFDMA is used in Downlink.OFDMA having High PAPR.signals with high PAPR requires highly linear power amplifiers inorder to avoid excessive intermodulation distortion so,amplifiers must be operate with a large backoff from its peak value.High PAPR is particularly critical for uplink trasmissions because of power constraints at UE.
SC-FDMA is used in uplink.SC-FDMA having low PAPR.Because of low PAPR, SC-FDMA is well suited to uplink.