Today multi-carrier transmission and OFDM are means to allow for very high overall transmission bandwidth while still being robust to signal corruption due to radio-channel frequency selectivity. However, a drawback of OFDM modulation, as well as any kind of multi-carrier transmission, is the large variations in the instantaneous power of the transmitted signal. Such power variations imply a reduced power-amplifier efficiency and higher power-amplifier cost. This is especially critical for the uplink, due to the high importance of low mobile-terminal power consumption and cost. Several methods have been proposed on how to reduce the large power variations of an OFDM signal. However, most of these methods have limitations in terms of to what extent the power variations can be reduced. Furthermore, most of the methods also imply a significant computational complexity and/or a reduced link performance. Thus, there is an interest to consider also wider-band single-carrier transmission as an alternative to multi-carrier transmission, especially for the uplink, i.e. for mobile-terminal transmission. One of such single-carrier transmission scheme can be implemented using DFT-spread OFDM
DFT-spread OFDM (DFTS-OFDM) is a transmission scheme that can combine the desired properties for uplink transmission i.e. :
• Small variations in the instantaneous power of the transmitted signal (‘single carrier’ property).
• Possibility for low-complexity high-quality equalization in the frequency domain.
• Possibility for FDMA with flexible bandwidth assignment.
Due to these properties, DFTS-OFDM has been selected as the uplink transmission scheme for LTE, which is the long-term 3G evolution.
More detail can be accessed from here:
http://wirelesscafe.wordpress.com/2009/04/07/what-is-single-carrier-fdma-sc-fdma/