Methods, a base unit and a remote unit are disclosed. A method comprises determining two or more SRS resource sets for codebook or non-codebook based UL transmission of the mobile unit in the condition that the number of antenna ports simultaneously used by the mobile unit for transmitting is smaller than the number of antenna ports simultaneously used by the mobile unit for receiving; and transmitting a trigger associated with the two or more SRS resource sets to the mobile unit to trigger resource transmissions by the mobile unit.