Example embodiments describe a controller comprising means for performing i) discovering a mapping between receive analogue to digital converters, RxADCs, of a full duplex node (100) and cable modems (111-113, 121-123, 131-133, 141-143) connected to the full duplex node; and wherein the cable modems share a common communication bandwidth; and ii) determining, based on the mapping, sounding groups (152, 162) by grouping cable modems (111-131, 121-123) mapped to a same RxADC (151) into a respective sounding group (152); and wherein a sounding group is indicative for an upper bound of possible interfering cable modems.