needed in order to locate the position of the DFT window at the receiver, thus being able to decode the physical channels. The next step is the P-SCH detection, which consists of the detection of the Zadoff-Chu root, according to Equation (3.4). In this stage, the cell ID is acquired and the frame is synchronized within a 5-ms basis. Additionally, fine time and frequency synchronization can be performed, thanks to the good correlation properties of Zadoff-Chu sequences. Time and Frequency P-SCH detection S-SCH Detection BCH Detection & Search for f Synchronization Fine CFO & time (Time domain) synchronization Decoding Cell ID Cell Group ID (5 ms timing) (Radio timing) Figure 3.33 Cell search procedure. C 2009 by Taylor & Francis Group, LLC Radio-Interface Physical Layer S-SCH detection is performed, which allows completion of the frame syn- chronization process-that is, the radio timing for the downlink transmis- sion-and also obtaining the cell group ID. Finally, the cell search procedure is completed, and the UE is able to decode the broadcast channel (BCH) prior to the transmission of an uplink ran- dom access preamble. 3.4.1.4 Other Synchronization Procedures Apart from time-frequency synchronization and cell search, additional issues related to synchronization in LTE, such as radio link monitoring, intercell synchroniza- tion, or timing advance strategies, have been specified in 3GPP 36.213. The latter is particularly critical from the point of view of the synchronization algorithms for the uplink; an efficient timing advance mechanism must force the user signals to be aligned in time at the eNodeB receiver (a quasi-synchronous scenario) (Morelli et al. 2007, 1394), thus simplifying considerably the uplink reception. When the eNodeB detects that the signal from a certain UE is misaligned, the eNodeB trans- mits a timing advance command in order to force the UE to adjust its uplink trans- mission timing. This command is defined to be a multiple of 16.T (sampling time) and is relative to the previous uplink ti