in (3GPP 36.211). The expression for this sequence is given in Equation (3.4), where the Zadoff-Chu sequence index U can take the values 25, 29, or 34: (n) = A -jmm(1++) n=0,1,...,30 (3.4) n=31,32,...,61 Zadoff-Chu sequences (Frank, Zadoff, and Heimiller 1962, 381; Chu 1972, 531) are specially generated pseudorandom polyphase sequences with perfect correlation properties. These properties make P-SCH particularly interesting for obtaining accurate synchronization metrics. Prior to frequency domain processing of P-SCH, an initial coarse synchroniza- tion is needed in order to determine an initial position of the DFT window. This initial estimation can be extracted either from the CP of the downlink signal or from time-domain-matched filtering with the IDFT of the Zadoff-Chu sequence (Figure 3.30). Once coarse synchronization has been performed in the time domain, CFO estimation can be accurately obtained from matched filtering in the frequency domain. This process is illustrated in Figure 3.31. If necessary, it is also possible to obtain synchronization metrics from the downlink reference signal by following the method proposed in Bo, Jian-hua, and Yon (2004, 56), although such a signal is not transmitted for synchroniza- tion purposes. © 2009 by Taylor & Francis Group, LLC Radio-Interface Physical Layer H(k) = IDFT N {ZDC5EQ} r(k)*H(k) max {r(k)*H(k)} Figure 3.30 Time-domain-matched filtering for P-SCH-based time synchroni- zation. 3.4.1.2 Synchronization in SC-FDMA UL In the uplink, the signal received by the eNodeB is composed by the addition of the individual signals transmitted by the UEs. Thus, the uplink time and fre- quency synchronization becomes a complex multiparameter estimation problem. In Morelli et al. (2007, 1394), several uplink scenarios are presented that introduce some simplifications with the aim of reducing the complexity of the synchroniza- tion process. Although LTE uses SC-FDMA for uplink transmission of data and control channels, the specific physical signals used for synchronization purpo