e of controlling the preamble format. The bandwidth for the random access preamble is 1.08 MHz, allocated in the central subcarriers. Thus, it can be used for any transmission bandwidth in the cell. Because uplink transmission for a particular UE has not been aligned yet with the uplink timing through timing advance correction, a guard time, TG is required to avoid interfering with other UEs. Guard bands in the frequency domain are inserted on the random access preamble in order to avoid data interference at preamble edges. Additionally, a smaller frequency spacing, Afra is used to provide a higher granularity for synchronization. In order to achieve a good detection, a low false-alarm probability, and accurate time and frequency synchronization in the uplink, Zadoff-Chu sequences with zero correlation zone are used (3GPP 36.213). Zadoff-Chu sequences with zero correlation zone are generated from one of several root Zadoff-Chu sequences, defined in Expression (3.5), where the length of Zadoff-Chu sequence Nc is equal to 839 for a type-1 frame structure: (3.5) An RA preamble with a zero correlation zone is defined by a cyclic shift, given in Expression (3.6), that is applied to one of the root Zadoff-Chu sequences from Expression (3.5): (3.6) © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology eNodeB (1) Request of preamble transmission (2) Transmission of RA preamble (PRACH) (3) UL timing synchronization (4) Transmission of RA response (PDSCH) (5) DL-SCH transport block to upper layers Figure 3.37 Random access procedure from the physical layer perspective. The size of the cyclic shift, Cw must be larger than the maximum round-trip delay, SO the number of root Zadoff-Chu sequences and the number of generated Zadoff-Chu sequences with zero correlation zone are changed, depending on cell radius. That is, the required number of different root Zadoff-Chu sequences grows with the cell radius. 3.4.3.2 Random Access Procedure After downlink synchronization is acquired by the