 including intra-LTE and inter-RAT handovers, load balancing, and others. In contrast, when the UE is not connected ("idle"), it has to act (much more) autonomously, although it is possible for the network to influence this behavior, as we shall see in this section. To this end, some issues of the UE behavior need to be standardized, which indeed has some RRM-related aspects. The UE procedures in idle mode (including public land mobile network [PLMN]) and RAT selection, initial cell selection and cell reselection, cell reserva- tions and access restrictions, and the receiving of broadcast information and pag- ing) are specified by 3GPP TS 36.304 [15]. A schematic view of the UE behavior focusing on PLMN, RAT, and cell (re-)selection is depicted by Figure 4.19. During the standardization process, it was recognized that the identification of idle mobility (basically, cell reselection) drivers for scenarios in which the UE moves within the same carrier frequency (intrafrequency mobility)-as well as when it can choose between different frequency layers and even various radio access technologies (interfrequency and inter-RAT mobility)-is important because it has an impact on the preferred idle mode mobility procedures. The most important driver is, naturally, radio coverage; that is, the UE should always camp on the cell that provides the best signal strength characterized by the so-called S criterion defined by means of the RSRP (the S value) described in the measurement section of this chapter. According to 3GPP TS 36.304 [15], the S criterion is defined for cell selection as follows: - Opdeumin - P compensation 0, where Qxxlevmeas is the measured cell RSRP value, Qxxlevmin is the minimum required RSRP level in the cell in decibels of measured power (dBm), and the compensation power level (P compensation is an additional cell-specific offset value that can be set by the network operator (at the time of writing, discussed by the 3GPP). In addition to this fundamental driver, the 3GPP has agreed that, for inter- frequ