Apparatuses, methods, and systems are disclosed for uplink demodulation reference signal transmission in UpPTS. The apparatus includes a receiver that receives a configuration signal from a base unit. The configuration signal includes a reference signal configuration for a first reference signal. The apparatus includes a transmitter that transmits data in an uplink portion of a subframe on a first frequency band, the subframe containing a downlink portion, a guard period, and the uplink portion. The transmitter transmits a first reference signal in the uplink portion of the subframe on a second frequency band in response to the configuration signal. The transmitter transmits a second reference signal in the uplink portion of the subframe on the first frequency band, in response to a controller determining to transmit the second reference signal.