Transceiver working with channelization:
Frequency and time synchronisation procedure. takes place when the power is turned on in the UE. The synchronization procedure starts with downlink SCH synchronization. The UE knows the SCH primary synchronization code, which is common to all cells. The slot timing of the cell can be obtained by receiving the primary synchronization channel (P-SCH) and detecting peaks in the output of a filter that is matched to this universal synchronization code. The slot synchronization takes advantage of the fact that the P-SCH is only sent during the first 256 chips of each slot. The whole slot is 2,560 chips long. This is depicted in Figure 3.4. Thus the UE can determine when a slot starts, but it does not know the slot number yet (there are 15 slots in each frame), and thus it does not know where the radio frame boundary may be.
Figure 4.2 Structure of syncronization channel
UE correlates the received signal from the secondary synchronization channel (S-SCH) with all secondary synchronization codes (SSC), and identifies the maximum correlation value. The S-SCH is also only sent during the first 256 chips of every slot. One SSC is sent in every time slot. There are 16 different SSCs, and they can form 64 unique secondary SCH sequences. One sequence consists of 15 SSCs, and these sequences are arranged in such a way that in any nonzero cyclic shift less than 15 of any of the 64 sequences is not equivalent to some other sequence. This means that once the UE has identified 15 successive SSCs, it can determine the code group used as well as the frame boundaries (i.e., frame synchronization).An example of frame synchronization is as follows: if the UE receives a sequence of SSCs from S-SCH, it must compare it with all SSC sequences from Table 3.2 (the table is taken from ), and once a match is found, it knows the used code group for the Node B sending it and the frame boundaries. In this example the matching code group is 30, and the frame boundary is before the time slot #0, that is, before SSC 2 in code group 30 .Each code group identifies eight possible primary scrambling codes, and the correct one is found by correlating each candidate in turn over theCPICH of that cell. Once the correct primary scrambling code has been identified, it can be used to decode BCH information from the primary common control physical channel (P-CCPCH), which is covered with the cell’s unique primary scrambling code.
The CPICH also acts as a timing reference for the P-CCPCH. Note that the P-CCPCH doesn’t use the first 256 chips of each slot, whereas the P-SCH and S-SCH use only these chips.Note the important difference between the two primary codes. The primary synchronization code is common to all cells, and it is used to gain slot synchronization from the P-SCH. The primary scrambling code is unique to a cell; it is gained from the CPICH and used to demodulate common control channels. Dedicated channel synchronization is skipped here, as it is simpler than the initial synchronization.
There are three separate channel concepts in the UTRAN: logical, transport,and physical channels .Logical channels define what type of data is transferred. These channels define the data-transfer services offered by the MAC layer; that is, the concept of logical channels is used in the interface above the MAC. Transport channels define how and with which type of characteristics the data is transferred by the physical layer. These channels are used in the interface between the MAC and the PHY layers. The transport channel is a new concept if WCDMA is compared to the GSM system.
Figure 4.3 Channel realization