A gateway device for associating the gateway device and tracking sensors as single a cargo unit: the gateway device being associable with a cargo unit, said gateway device comprising: means to detect position or movement, and short-range wireless communication means for sending out a beacon signal and connecting with nodes, characterized in that the gateway device is arranged to detect which nodes are still in short-range communications range when change of position or movement is detected and associating the nodes that are still in range with as being part of the same cargo unit as the gateway device. Corresponding arrangement and method are also presented.