A system, comprising: a base station including a transmitter that is configured to transmit a guide signal into a guide signal reception field spatially bounded by at least one boundary portion; a mobile robot including: a drive system configured to drive the mobile robot across a floor; two mutually adjacently disposed guide signal sensors (210a, 210b), each of which is configured to generate a reference signal that reflects its reception of the guide signal; and a controller that is operably connected to the drive system and the guide signal sensors (210a, 210b), and configured to control the drive system to move the mobile robot along the at least one boundary portion of the guide signal reception field while, based on said reference signals, maintaining a tracking state in which a first of said guide signal sensors is positioned substantially on a first side of said boundary portion, inside of the guide signal reception field, and a second of said guide signal sensors is positioned substantially on a second side of said boundary portion, outside of the guide signal reception field, characterised in that the transmitter is configured to project the guide signal onto the floor, such that the guide signal reception field is at least partly defined by a reflection of the guide signal off the floor, and in that said guide signal sensors (210a, 210b) are arranged for detecting said reflection of the guide signal off the floor. a base station including a transmitter that is configured to transmit a guide signal into a guide signal reception field spatially bounded by at least one boundary portion; a mobile robot including: a drive system configured to drive the mobile robot across a floor; two mutually adjacently disposed guide signal sensors (210a, 210b), each of which is configured to generate a reference signal that reflects its reception of the guide signal; and a controller that is operably connected to the drive system and the guide signal sensors (210a, 210b), and configured to control the drive system to move the mobile robot along the at least one boundary portion of the guide signal reception field while, based on said reference signals, maintaining a tracking state in which a first of said guide signal sensors is positioned substantially on a first side of said boundary portion, inside of the guide signal reception field, and a second of said guide signal sensors is positioned substantially on a second side of said boundary portion, outside of the guide signal reception field, a drive system configured to drive the mobile robot across a floor; two mutually adjacently disposed guide signal sensors (210a, 210b), each of which is configured to generate a reference signal that reflects its reception of the guide signal; and a controller that is operably connected to the drive system and the guide signal sensors (210a, 210b), and configured to control the drive system to move the mobile robot along the at least one boundary portion of the guide signal reception field while, based on said reference signals, maintaining a tracking state in which a first of said guide signal sensors is positioned substantially on a first side of said boundary portion, inside of the guide signal reception field, and a second of said guide signal sensors is positioned substantially on a second side of said boundary portion, outside of the guide signal reception field, the transmitter is configured to project the guide signal onto the floor, such that the guide signal reception field is at least partly defined by a reflection of the guide signal off the floor, and in that said guide signal sensors (210a, 210b) are arranged for detecting said reflection of the guide signal off the floor.