MCSs, which typically operate at lower signal-to-noise ratios (SNRs). SC-FDMA with ZF suffers from high block error rate (BLER), and the MMSE sig- nificantly improves the performance over ZF. OFDM with MMSE is slightly better than OFDM with ZF. Basically, in this case SC-FDMA and OFDMA achieve the same performance when MMSE is selected. The results for the higher modulation schemes, 16 QAM rate 4/5, are shown in Figure 6.9, valid when the system is operated at higher SNRs. It is shown that the performance gap between SC-FDMA ZF and MMSE is getting smaller. The results in Figures 6.8 and 6.9 show that different equalization techniques do not significantly affect the OFDM system. However, they become a critical issue for SC-FDMA. The forward error correction (FEC) code used in this analysis is the © 2009 by Taylor & Francis Group, LLC Single-Carrier Transmission for UTRA LTE Uplink SC-FDMA ZF SC-FDMA MMSE OFDMA ZF OFDMA MMSE SNR (dB) Figure 6.8 BLER performance of BPSK 1/6 SC-FDMA and OFDMA with different equalization. turbo code [8]. In OFDM transmission, the FEC plays an important role in provid- ing additional diversity, especially for the transmission over frequency-selective fad- ing. Although in SC-FDMA the FEC is still important, it does not provide much additional diversity since on top of the DFT-S. Figures 6.10 and 6.11 show the SC-FDMA spectral efficiency results for both MMSE and ZF equalization. The spectral efficiency, throughput, is calculated according to (1 - BLER) X P (6.15) T X B where BLER is the block error rate; P is the subframe (block) size in bits; T is the subframe duration in seconds; and B is the bandwidth in hertz. The results are presented for all modulation schemes suitable for LTE uplink. MMSE is significantly better than ZF, especially in the low SNRs, where SC-FDMA © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology SC-FDMA ZF SC-FDMA MMSE OFDMA ZF OFDMA MMSE SNR (dB) Figure 6.9 BLER performance of 16 QAM 4/5 SC-FDMA and OFDMA with diff