Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

232 ApplicationsSub-frames#1 #1010 ms= Sub-frame= Primary and secondary synchronization signalFigure 5-16Synchronization signals for cell searchThe synchronization signal occupies 72 sub-carriers with a bandwidth of about 1 MHzlocated in the center of the available bandwidth. Figure 5-16 illustrates the allocation ofthe synchronization signals within one radio frame.The cell search procedure is also used to search for neighbor cells that might becandidates for a handover. The same procedure as described above is used for searchingfor neighbor cells in specific time instances. Resources have to be made available in themobile terminal for a neighbor cell search.5.2.7.2 Random Access ProcedureThe random access procedure defines how a mobile terminal (UE) can request resourcesfor data transmission. In LTE, a dedicated block of time and frequency resources isexclusively reserved for this procedure. Terminals that want to initiate a connection aretransmitting random access preambles in these reserved resources. The preambles arebased on Zadoff–Chu sequences (see Section 2.1.4.1). Each terminal selects randomlya sequence out of a set of available orthogonal Zadoff–Chu sequences. As long as nosequence is chosen twice per random access attempt, collisions can be avoided. Therandom access preamble has the duration of one sub-frame (1 ms) and occupies a bandwidthof about 1 MHz. Information about the allocation of the random access resourcesis broadcasted to all terminals. Each random access preamble of duration 0.9 ms has a0.1 ms guard time, which is needed to compensate for the different propagation times ofthe different users, which at this stage are not time-aligned. After successful detectionof a random access preamble, further information such as timing advance, schedulinginformation, and terminal identification is sent.5.2.8 Supported BandwidthsThe bandwidths supported by LTE cover narrowband 1.4 MHz up to broadband 20 MHz.The mapping of the number of resource blocks to the channel bandwidths is given inTable 5-3. The occupied bandwidth is defined as the bandwidth containing 99 % of thetotal mean power of the transmitted signal.