The present invention relates to a network node and a user device. The network node comprises a transceiver configured to receive a plurality of reference signals associated with a plurality of user devices; a processor configured to group the plurality of user devices into at least one group of user devices based on the plurality of received reference signals, assign radio resources for grant-free data transmission to the group of user devices, compute a receiver filter for the group of user devices based on the plurality of received reference signals and the assigned radio resources; wherein the transceiver is configured to receive a plurality of grant-free data transmissions from user devices in the group of user devices in the assigned radio resources, wherein the processor is configured to separate the grant-free data transmissions from the user devices in the group of user devices based on the computed receiver filter.