uency domain equalization block at the receiver. Figure 6.25 shows the EVM results for both SC-FDMA and OFDMA air interfaces. The results for both QPSK and 16 QAM modulation are presented. SC-FDMA has better EVM performance compared to OFDMA. A change to lower modulation, QPSK, further improves the SC-FDMA performance, but this is not the case for OFDMA. These results are due to the fact that SC-FDMA has lower PAPR than OFDMA, as shown in Figures 6.4 and 6.5. The impact of the nonlinear power amplifier on SC-FDMA and OFDMA spectral efficiency is shown in Figure 6.26. These results are obtained when an input back-off (IBO) of 4 dB is assumed to maintain high-efficiency power ampli- fication and measured at a BLER target of 10%. For 16 QAM, rate 4/5, SC-FDMA has a gain of 0.7 dB over OFDMA, although only a small gain of 0.2 dB is obtained at the lower coding rate. These results confirm that the SC-FDMA is the preferred solution over OFDMA as well as in the presence of nonlinear power amplifiers. Figure 6.27 shows the impact of the nonlinear amplifier on the spectrum emission of SC-FDMA and OFDMA. An input back-off of 4 dB and 16 QAM © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology SC-FDMA OFDMA 16QAM 4/5 16QAM 3/4 16QAM 2/3 16QAM 1/2 Figure 6.26 Performance loss at 10% BLER due to the nonlinear PA. SC-FDMA OFDMA Spectrum emission mask Frequency (MHz) Figure 6.27 Spectrum emission of SC-FDMA and OFDMA. © 2009 by Taylor & Francis Group, LLC Single-Carrier Transmission for UTRA LTE Uplink modulation are assumed. It is shown that the spectrum emission of OFDMA is marginally below the spectrum emission mask, whereas a better result is obtained for the SC-FDMA transmitter, in agreement with the PAPR results. 6.13 Summary In this chapter, we have presented the key techniques for LTE uplink as well as pre- sented the baseline performance. Radio access technology is the key aspect in LTE uplink, and two radio access schemes, SC-FDMA and OFDMA, have been stud- ied. The perform