Disclosed is a method performed by a transmitter node of a communication system, for transmitting reference signalling. The method comprises transmitting, to one or more receiver nodes of the communication system, a reference signal sequence using a first antenna port and a carrier frequency. The method comprises transmitting, to the one or more receiver nodes, using another antenna port and the same carrier frequency, a delayed version of the reference signal sequence. The delay is non-zero and less than a symbol duration of the communication system.