A robotic lawnmower system comprising a charging station (210) and a robotic work tool (100), the charging station comprising a signal generator (240) to which a boundary cable (250) is to be connected, the signal generator (240) being configured to transmit a signal (245) through the boundary cable (250), and the robotic working tool (100) comprising a sensor (170) configured to pick up magnetic fields generated by the signal (245) in the boundary cable (250) thereby receiving the signal (245) being transmitted and a controller (110) configured to analyse the picked up signal, wherein the signal generator (240) is further configured to: prefilter the signal through an filter model； and transmit the prefiltered signal to through the boundary cable (250) by means of a current generator.
