ishes to transmit a sequence of eight QPSK symbols as shown in Fig. 3.16 [30]. In the OFDM case assuming NDFT = 4, four QPSK symbols would be processed in parallel, each of them modulating its own subcarrier at the appropriate QPSK phase. After one OFDM symbol period, a guard period or CP is inserted to mitigate the multi- path effects. For DFT-S-OFDM, each symbol is transmitted sequentially. With NDFT = 4, there are four data symbols transmitted in one DFT-S-OFDM symbol period. The higher rate data symbols require four times the bandwidth and SO each data symbol occupies NDFT X Af Hz of spectrum assuming a subcarrier spacing of Af Hz. After four data symbols, the CP is inserted. Note the OFDM and DFT-S-OFDM symbol periods are the same [30]. Input QPSK symbols in time (1,1) (-1,-1) (-1,1) (1,-1) (-1,-1) (1,1) (1,-1) (-1, 1) (-1,1) (1, 1) (-1,-1) (1,1) QPSK modulation Frequency NDFTX Af DFT-S-OFDM Data symbols occupy Af in frequency domain and Data symbols occupy NDFTX of in frequency domain and 1/NDFT one OFDM symbol period in time domain DFT-S-OFDM symbol period in time domain Figure 3.16 Comparison of OFDM and DFT-S-OFDM using QPSK modulation with NDFT = 4 [30]. New Radio Access Physical Layer Aspects (Part 1) 335 OFDM (16QAM) OFDM (QPSK) SC-FDMA (QPSK) SC-FDMA (16QAM) PAPR (dB) Figure 3.17 Comparison of OFDM and DFT-S-OFDM PAPRs (5 MHz bandwidth) (30,46]. As mentioned earlier, the PAPR of OFDM intrinsically is inferior to DFT-S-OFDM. Fig. 3.17 shows the comparison of complementary CDF (CCDF) of OFDM and DFT-S- OFDM PAPRs. It can be seen that the PAPR of DFT-S-OFDM is approximately 3 dB better than that of OFDM with probability of 0.99. In the case of 16QAM modulation, the PAPR of DFT-S-OFDM increases relative to that of DFT-S-OFDM with QPSK modulation, whereas in the case of OFDM, the PAPR distribution is independent of the modulation scheme because the OFDM signal is the sum of a large number of independently modulated subcarriers; thus the instantaneous power has an approximately exponential distribution, re