* SC-FDMA is a new concept in transmission and it is important to understand how it works
* When a new concept comes along no single explanation will work for everyone
* To help put SC-FDMA in context we will use six different ways of explaining what SCFDMA is all about
* In summary: SC-FDMA is a hybrid transmission scheme combining the low peak to average (PAR) of single carrier schemes with the frequency allocation flexibility and multipath protection provided by OFDMA
1. Explaining SC-FDMA
•The first explanation of SC-FDMA comes from the LTE physical layer “study phase” report (3GPP TR 25.814) which had the following diagram:
TR 25.814 Figure 9.1.1-1 Transmitter structure for SC-FDMA.
•Colour coding has been added here to show the change from time to frequency and back again. This diagram is not in the final specifications.
•The processing steps explain why SC-FDMA is sometimes described in the specs as Discrete Fourier Transform Spread OFDM (DFT-SOFDM)
2. Explaining SC-FDMA
•The three key processing steps shown in 25.814 are formally defined in the physical layer specification 36.211 v8.1.0 as:
| DFT |  |
| Subcarrier mapping |
 |
| IFFT |  |
•Although essential for detailed design, formal definitions like these do not provide insight to most people of the underlying concepts
3. Comparing OFDMA and SC-FDMAQPSK example using M=4 subcarriers
The following graphs show how a sequence of eight QPSK symbols is represented in frequency and time
OFDMA signal generationQPSK example using M=4 subcarriers
SC-FDMA signal generationQPSK example using M=4 subcarriers
4. SC-FDMA and OFDMA signal generation and reception
Simplified model of SC-FDMA and OFDMA signal generation and reception
5. Comparing OFDMA and SC-FDMAPAR and constellation analysis at different BW
6. Comparing OFDMA and SC-FDMAMultipath protection withshort data symbols
