A network node, a wireless device and methods therein, for decoding of contention based uplink transmissions of data in a cell served by the network node. The network node registers the wireless device for contention based uplink transmissions of data on a radio resource reserved for contention based uplink transmissions of data, e.g. when receiving a registration request sent from the wireless device, such that the wireless device is included in a set of wireless devices being registered for contention based uplink transmissions of data on the radio resource in the cell. The network node then performs blind decoding of uplink signals transmitted on the radio resource by considering the wireless devices in the set. In this way, the decoding is made more efficient by disregarding any other wireless devices in the cell which are not registered for contention based uplink transmissions of data on the radio resource in the cell.