should be kept active even at high serving cell signal levels. Inter-layer cell search for higher priority layers (obtained on BCCH or from dedicated signalling) is always performed regardless of the value of sNonIntraSearch. Non-intra-layer search parameters merely define how often the UE has to search for cells on the higher priority layers. If both serving cell RSRP or RSRQ (optional) are above corresponding sNonIntraSearch level and quality thresholds then the UE has to search for higher priority layer cells at least once every 60 seconds, cyclically across the layers. Therefore, for example, if there are two higher priority layers in the list each layer would be searched at least every 120 seconds, and possibly more often depending on UE implementation. This is illustrated in Figure 15.2. The sNonIntraSearch level and quality thresholds essentially determine when the UE is in good radio conditions and is therefore allowed to schedule cell search less often. In power consumption tests with commercial UEs in the market (at the time of writing) the battery savings from disabling non-intra-layer search have been found negligible, and hence the benefit from using low sNonIntraSearch thresholds is debatable. RSRQServingCell Inside this region UE must search for higher priority layers at least once every 60 seconds Outside this region, the requirement depends on idle mode DRX cycle and RAT to search sNonIntraSearch,P as specified in 3GPP TS 36.133 sNonIntraSearch,, qRxQualMin RSRPServingCell qRxLevMin Figure 15.2 3GPP search requirement for higher priority cells when UE is camping in LTE LTE Small Cell Optimization Table 15.5 Detection time requirement per layer to search, measure and trigger reselection to a suitable cell [2] Detection time, LTE Detection time for one LTE idle mode DRX cycle intra-/inter-frequency, UTRA FDD frequency length, seconds seconds (DRX cycles) layer, seconds 11.52 (36) 17.92 (28) 32 (25) 58.88 (23) Lower priority layers are searched only if the serving cell level and quality are outside 