 hence, for example, with two configured inter-frequency LTE layers the time between layer search can be up to 40 DRX cycles. For 3G neighbour layers, the detection time is not defined in terms of DRX cycles, but in terms of seconds. Again, if there are, for example, two 3G layers being searched the maximum time to reselect to a suitable 3G cell would be twice the value given in Table 15.5. 3 A suitable candidate is essentially a cell with SCH and RS subcarrier power higher than -124 to -121 dBm (depending on band) and average subcarrier SNR >-4 dB [2]. Such cell is called 'detectable' in the 3GPP specification. Inter-layer Mobility Optimization 15.36 15.36 seconds seconds seconds seconds seconds seconds seconds seconds seconds seconds Figure 15.3 Example idle mode search/measurement schedule of a commercial UE. Serving cell is LTE800 The actual search procedure may be implemented in several steps over the search period or carried out as one-shot search through all PCIs or scrambling codes at once. As usual with 3GPP, only the minimum requirements are specified while the details are left to the UE implementation. It should be noted that in case GERAN cells are part of neighbour information, there is no need to search for GERAN cells since the BCCH frequency list is provided in LTE system information, or in RRC release as part of dedicated priorities, and the measurement is based on received signal strength indication (RSSI) on the given GERAN carrier frequency (i.e., there is no need to acquire radio frame timing prior to RSSI measurement). However, GERAN cells are identified by the absolute radio frequency channel number - base station identity code (ARFCN-BSIC) parameter pair, and for this reason the UE is required to decode BSIC of up to four strongest neighbour cells once every 30 seconds; this procedure still requires acquiring timing of the GERAN synchronization channel. Figure 15.3 illustrates the search and measurement implementation of a commercial LTE smartphone. In the example the following configurati