A method of selecting a frequency block includes determining a first value representing a lowest noise level of a radio channel at a first or second node, calculating a first metric representing a ratio between a first desired signal strength and the first value, determining a second value representing a lowest noise level of a radio channel at the first or second nodes, calculating a second metric representing a ratio between a second desired signal strength and the second value, selecting, on the basis of at least the first and second metrics and amongst a set of frequency blocks including at least the first and second frequency blocks, a frequency block for transmission of a message between the first and second nodes, indicating a sub-band of the selected frequency block, and causing transmission of the message on the indicated sub-band.