Methods and apparatus are provided for multiplexing DRS within a transmission burst for opportunistic spectrum access. In one novel aspect, DRS is not transmitted in a fractional subframe within a TXOP. In one embodiment, if the starting fractional subframe, which contains initial signal, occurs in a configured DMTC, DRS is transmitted in the first subframe next to the starting fractional subframe. In another embodiment, if DMTC starts from a complete subframe within a TXOP, DRS is transmitted in the first candidate position within a DMTC. In another novel aspect, in the DRS subframe, PDSCH is allocated in the PRBs outside the central PRBs (six or twenty-five PRBs). In one embodiment, the reservation signal can be used to satisfy the requirement of occupied bandwidth and continuity transmission. In another embodiment, the free REs in central PRBs carry the system information when required on the unlicensed band.