A computer implemented method for operating an access node includes: generating, by the access node, an initial block and a time-dependent signal for transmission in a channel occupancy time (COT) of a shared communications channel, the initial block including a time-independent initial sequence that enables the initial block to be transmitted over any slot in the COT, wherein the time-dependent signal is transmitted after the initial block; and transmitting, by the access node, the initial block and the time-dependent signal in a first slot of the COT. An access node is also described.