QPSK 1/2 Loc QPSK 3/4 Dist QPSK 3/4 Loc 16QAM 1/2 Dist 16QAM 1/2 Loc 16QAM 2/3 Dist 16QAM 2/3 Loc 16QAM 4/5 Dist 16QAM 4/5 Loc SNR (dB) Figure 6.17 BLER performance of distributed versus localized cases in SC-FDMA. also gain the frequency diversity. Moreover, the distributed case is sensitive to the frequency error. The BLER performance of the distributed and localized case in SC-FDMA with HARQ is presented in Figure 6.17. The SIMO case is assumed, and the channel bandwidth is 10 MHz. A 2.5-MHz bandwidth is allocated for the trans- mission. For the distributed case, this configuration will allow a repetition factor of four because all the subcarriers carrying data are spread over the full 10-MHz bandwidth. It is shown that the distributed cases perform better than the localized one in most cases. For BLER 1%, it is clear that the distributed case is superior to the localized. It has about a 1-dB gain over localized in 16 QAM, rate 4/5. The dis- tributed case can maximize the frequency diversity by distributing the data in the whole bandwidth. In the real situation, when real channel estimation is taken into account, the localized case is expected to perform better than the distributed case. The reason is that, considering the limited amount of pilot signals, the distributed case has to estimate the channel transfer function (CTF) in the full bandwidth, whereas the localized case estimates the channel transfer function only in the allo- cated channel bandwidth. Thus, the distributed case is more sensitive to the error introduced by channel estimation. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 6.10 Channel Estimation For the transmission over time-varying and frequency-selective fading channels, the receiver requires an estimation of the CTF in both time and frequency domains. The receiver utilizes the received pilot signals as described in Section 6.2 to perform channel estimation. In the following, we consider a practical one-dimensional esti- mator that ope