erpolation between these two short blocks. Figure 6.18 shows the link-level simulation results with the preceding chan- nel estimation techniques and at a UE speed of 120 km/h. It is shown that the OFDMA performance is more affected by the UE speed than SC-FDMA, espe- cially at higher modulation and coding schemes (16 QAM rate 4/5). The UE at high speed has a higher Doppler frequency and creates intercarrier interference (ICI). In OFDM, each subcarrier carries different symbols and therefore OFDM is more sensitive to the ICI. Figure 6.19 illustrates the results for a speed of 200 km/h. It is shown that 16 QAM rates of 3/4 and above do not contribute to the link adaptation curve and hence the system operates at low spectral efficiency. At high speed, the subcarrier orthogonality is destroyed by the ICI. BPSK 1/3 QPSK 1/2 QPSK 2/3 QPSK 3/4 16QAM 1/2 16QAM 2/3 16QAM 3/4 16QAM 4/5 16QAM 4/5 LA OFDMA LA SC-FDMA SNR (dB) Figure 6.18 SC-FDMA and OFDMA with real channel estimation at a speed of 120 km/h. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: GPP LTE Radio and Cellular Technology 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 OFDMA LA SC-FDMA SNR (dB) Figure 6.19 SC-FDMA and OFDMA with real channel estimation at a speed of 200 km/h. 6.11 SC-FDMA with Turbo Equalization The turbo equalizer can improve SC-FDMA performance. Turbo equalization (TEQ) in the context of LTE uplink was proposed and investigated in Priyanto [11] and Berardinelli et al. [15]. Turbo equalization is an advanced iterative equalization and decoding technique that allows enhancement of the performance for the trans- mission over a frequency-selective fading channel. The turbo equalizer, however, increases the receiver complexity. Nevertheless, the implementation is performed in the base station, which does not have physical constraints and power consumption as stringent as those of the UE. The block diagram of the proposed turbo equalizer receiver is shown in Figure 6.20. It uses a soft interference c