- order modulation schemes exhibit a higher PAPR compared to lower-order modula- tion schemes. In SC-FDMA, as a single carrier transmission, the PAPR is mainly affected by the envelope variations in each modulation scheme; thus, the higher- order modulations lead to larger dynamic range and higher PAPR. In comparison, the PAPR results for OFDMA with various modulation schemes are shown in Figure 6.5. It is observed that the PAPR is not affected by the type of modulation scheme, and all the modulation schemes have the same PAPR results. After the IFFT modulation in an OFDM system, the modulated symbols are added together to form a multicarrier signal. The addition increases the PAPR of the OFDM signal but diminishes the impact of the modulation scheme. The evaluation of SC-FDMA and OFDMA with regard to PAPR is summa- rized in Figure 6.6. SC-FDMA has an advantage in obtaining a small PAPR for the lower-order modulation schemes. For 12 BPSK, the PAPR of SC-FDMA is about © 2009 by Taylor & Francis Group, LLC Single-Carrier - Transmission for UTRA LTE Uplink pi/2 BPSK 16QAM 64QAM 10 -2 PT (dB) Figure 6.5 PAPR of OFDM for various modulation schemes. SC-FDMA pi/2 BPSK 16QAM 64QAM Figure 6.6 PAPR comparison of SC-FDMA and OFDMA. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 4 dB lower than the same modulation format in OFDM. For 64 QAM, the differ- ence is smaller than 1.6 dB in comparison to OFDMA. Link-Level Model The link-level model for the LTE uplink is shown in Figure 6.7. The left side is the transmitter, corresponding to the user equipment (UE), and the right side is the receiver, corresponding to the base station (BS). The transmission from the UE starts Base Station Input from LA Transport Block BER and BLER Generator Measurement CRC Attachment CRC Verifications Code Block Code Block Segmentation Desegmentation Channel Coding Channel Decoding L1-HARQ and Rate L1-HARQ and Matching De-Rate Matching Deinterleaver Interleaver QAM/PSK QAM/PSK Constellation Constell