(
Single 
Carrier-
Frequency 
Division 
Multiple 
Access)  SC-FDMA modulation combines the low peak-to-average power ratio (PAPR or PAR) of single carrier methods, such as GSM, with OFDM's resistance to multipath.  For example, SC-FDMA is the uplink modulation in the LTE air interface, while the downlink uses OFDMA.  See 
OFDMA, 
OFDM and 
LTE architecture.