SNR (dB) Figure 6.21 BLER performance for SC-FDMA 1 X 2 MRC with and without turbo equalizer in TU 06 channel. QPSK 2/3 16QAM 1/2 16QAM 4/5 QPSK 1/2 QPSK 3/4 16QAM 2/3 SC-FDMA MMSE OFDMA SC-FDMA TEQ SNR (dB) Figure 6.22 BLER performance for SC-FDMA versus OFDMA in TU 06 channel. C 2009 by Taylor & Francis Group, LLC Single-Carrier Transmission for UTRA LTE Uplink BPSK 1/3 QPSK 1/2 QPSK 2/3 QPSK 3/4 16QAM 1/2 16QAM 2/3 16QAM 3/4 16QAM 4/5 LA MMSE LA TEQ SNR (dB) Figure 6.23 Spectral efficiency for SC-FDMA in TU 06 channel. transmission is more sensitive to the coding rate than SC-FDMA [12]. SC-FDMA takes advantage of spreading the data symbols over the transmission bandwidth, where the effect of a deep fade affecting few subcarriers will be diminished in the receiver combining all the subcarrier information. The receiver with turbo equalizer gives better performance in most cases, and in the worst case it shows the same performance as OFDMA. Therefore, the turbo equalizer makes it possible to reduce the noise enhancement due to the time domain transmission in the SC-FDMA system and makes performance the same as or bet- ter than that of OFDMA. The performance results for several MCSs in terms of spectral efficiency are shown in Figure 6.23. The figure shows the link adaptation curve for both the MMSE and the TEQ receiver. It is shown that the TEQ is effective for higher-order MCSs, whereas for BPSK it does not show any performance improvement. Therefore, in order to exploit its performance gain, the turbo equalizer receiver could be used for high-order modulation schemes, whereas the simple MMSE receiver can still be used for BPSK. In this way, the computational load for low-order modulations can be reduced. 6.12 Impact of Nonlinear Power Amplifier The selection of an air interface technique is also influenced by the RF transmitter constraints, especially the nonlinear power amplifier. The RF transmitter imper- fections create in-band performance degradation and increase the out-of-band © 2009 by Taylor & Francis G