he ABS transmission periods. The LTE-based LAA defines methods for UEs in the LAA SCell coverage to provide radio resource management measurements and reporting. The Rel-12 discovery reference signals, originally designed for small cells, are being used with certain modifications in LTE-based LAA SCells. As shown in Fig. 8.15, the LTE-based LAA DRS can be transmitted within a periodically occurring time window called the DRS measurement timing configuration occasion that has a duration of 6 ms and a configurable period of 40, 80, or 160 ms. The radio frame and subframe in which DRS can be transmitted depends on the RRC parameters (dmtcOffset, dmtcPeriodicity) that are signaled to the UE. The LTE-based LAA DRS can be transmitted following a single idle observation interval of at least 25 us. To compensate for Operation in Unlicensed and Shared Spectrum Silent subframes (no CRS, PSS, SSS, PDSCH) Discovery signal sent with a 40,80, or 160 ms period in SF5 (CRS, PSS, SSS, PDCCH,/PDSCH for SIB1) Data transmitted to UE Unlicensed SCell Licensed PCell Frame in Frame n+4 Regular subframes with CRS (even when no PDSCH) DMTC periodicity (40, 80,160 ms) SFNmod T = DMTCoffset/10 T = DMTCperiodicity/10 DMTC occasion (6 ms) Subframe = DMTCoffsetmod10 DMTC offset LAA SCell 1 LAA SCell 2 Primary synchronization signal (PSS) LAA DRS occupies the first 12 OFDM symbols within a subframe Secondary synchronization signal (SSS) Cell specific reference signal (CRS) Figure 8.15 Structure and timing of discovery signals in LAA SCell [14,20]. potential DRS transmission blocking due to LBT and increase the probability of successful of DRS transmission, the network can attempt DRS transmission in any subframe within the DMTC occasion [26]. LAA operation on multiple unlicensed carriers is a key requirement for maximizing throughput. IEEE 802.11ac/ax supports transmission bandwidths of up to 160 MHz, which would span eight contiguous 20 MHz unlicensed channels in the 5 GHz band. The LAA 876 Chapter 8 multi-carrier transmission on multiple unl