A method including determining whether an apparatus is to operate in a first, second or third mode of operation; wherein said first mode of operation includes a first level of activity, said second mode of operation includes a second level of activity that is lower than said first level of activity, and said third mode of operation includes a third level of activity that is lower than said second level of activity; applying a first reference signal transmission regime when in said second mode of operation; and applying a second reference signal transmission regime when in said third mode of operation.