The disclosure is directed to a base station and a user equipment having on-demand signaling mechanism in directional wireless system. According to one of the exemplary embodiment, the present disclosure proposes a base station which includes at least but not limited to a transmitter and a receiver to transmit and receive data respectively and a processing circuit coupled to the transmitter and the receiver and is configured at least to receive through the receiver a service request to start an on-demand transmission, configure a control signaling to schedule a schedulable resource based on the service request in response to starting the on-demand transmission, and transmit through the transmitter the control signaling for triggering reference signals of an external base station to transmit the scheduled schedulable resource, wherein the reference signals are aperiodic and directional.