4.6 Basic Procedures
After the introduction of various reference signals and channels of the air interface, the following sections now give an overview of the different procedures required for communication with the network with references to the previous section for details on the channels.
4.6.1 Cell Search
When a mobile device is powered on, its first task from a radio point of view is to search for a suitable network and then attempt to register. To shorten the search process, the mobile device stores the parameters of the last cell on the SIM card before it is switched off. After the device is powered on, it can go straight to the last known band and use the last known cell parameters to see if the cell can still be found. This is the case when the mobile device has not been carried to another place while it was switched off.
In case the previous cell was not found with the information stored on the SIM card or if the SIM card does not contain information about the last used cell, the mobile device performs a full search. Voice-centric devices might start their search on GSM bands first as such networks are the most widely deployed and hence there is the highest probability to find a cell of a suitable network there. LTE devices that are more data centric might start the search by looking for LTE cells and fall back to UMTS and GSM cell search if not successful. UMTS and GSM cell search has been described in the previous chapters; so, this section focuses only on the LTE cell ...