eriod, an eNodeB may transmit (e.g. periodically) DRS to allow for the UEs supporting the feature to discover and measure the dormant cell. Finally, at some point of time, the network can decide to turn the cell back on based on, for example, UE measurements. Configuration of an OFF-cell as a deactivated SCell at UE side allows the on/off switching to be used efficiently. When discovery signals based measurements are configured for the carrier of a deactivated SCell, the UE cannot assume that the SCell transmits any signals other than discovery signals. This allows for the network to utilize SCell activation/deactivation for ON/OFF switching, reducing the ON/OFF transition times to the timescale of few tens of milliseconds. Discovery Signal Transmission and Measurement Procedure The discovery reference signals (DRS), whose structure is shown in Figure 4.2, consist of syn- chronization and references signals introduced already in LTE Rel-8: Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), and Cell-specific Reference Signal (CRS). Additionally, Channel State Information Reference Signals (CSI-RS) standardized in Rel-10 can also be configured as part of DRS. The PSS/SSS/CRS facilitate cell discovery and RRM measurements similar to the normal LTE operation while the CSI-RS allows for dis- covery of transmission points within the cell, enabling, for example, the so-called single-cell CoMP operation via RSRP measurements. Unlike in prior LTE systems, where PSS/SSS/CRS are transmitted continuously, the Dis- covery Reference Signals are transmitted with a more sparse periodicity for the purpose of cell detection and RRM measurements. In Figure 4.11, one instance of DRS transmission is denoted as a DRS Occasion. A DRS Occasion has duration of 1-5 sub-frames and includes PSS/SSS and CRS corresponding to antenna port 0 in the same time/frequency locations as Small Cell Enhancements in Release 12/13 eNB DRS DRS occasion periodicity SSS (and for FDD also PSS) Configurable and offset are not signal