A method in a radio network node for transmitting a reference signal over an antenna port includes transmitting the reference signal over a first code division multiplexing (CDM) subgroup using an orthogonal cover code. The first CDM subgroup includes a first set of resource elements in a first time slot and a second set of resource elements in a subsequent time slot. The radio network node selects a permutation of the orthogonal cover code and transmits the reference signal over a second CDM subgroup using the permutation. The second CDM subgroup includes a third set of resource elements in the first time slot and a fourth set of resource elements in the subsequent time slot. The permutation is selected to enable decoding of the reference signal in the frequency domain, by applying the orthogonal cover code to the first set resource elements and to the third set of resource elements.