oarse and fine time/frequency synchronization, although large time/frequency offset between two successive downlink bursts is unlikely due to multiple DRS transmission opportunities within a DRS measurement timing configuration (DMTC) occasion which has a duration of 6 ms. Therefore, the synchronization based on DRS in LAA systems can achieve reliable performance. The presence of downlink subframe must be detected by the LAA UE because the eNB does not always transmit in LAA scenar- ios. The exact detection method depends on UE implementation. LTE-based LAA supports transmission modes (TMs) with CRS-based CSI feedback, includ- ing TM1, TM2, TM3, TM4, and TM8, and those with CSI-RS-based CSI feedback, includ- ing TM9 and TM10 [3]. The CSI-RS/CSI-IM for CSI measurement is present in the configured periodic CSI-RS/CSI-IM subframes within downlink transmission bursts. Similar to the legacy LTE systems, both periodic and aperiodic CSI reports are supported in LAA scenarios. Unlike the legacy LTE system where the CRS/CSI-RS transmission power, or energy per resource element, is fixed, CRS/CSI-RS transmission power on LAA SCell is only fixed within a downlink transmission burst and can vary across downlink transmission bursts. Thus, the UE should not average CRS/CSI-RS measurements across different trans- mission bursts. The UE could either rely on CRS detection or common control signaling to differentiate the downlink bursts. LTE supports two different scheduling approaches, namely cross-carrier scheduling and self-scheduling. With cross-carrier scheduling, the con- trol information including scheduling indication on PDCCH and the actual data transmission on PDSCH take place on different carriers, whereas they are transmitted on the same carrier in the case of self-scheduling. Due to the uncertainty of channel access opportunities on unlicensed carriers, the synchronous uplink HARQ protocol with fixed timing relation between retransmissions was difficult to use in LAA. Thus, asynchronous HARQ protocol is used for LAA d