A millimeter-wave communication system includes a transmitter and a receiver. The transmitter is configured to be connected to a waveguide that is transmissive at millimeter-wave frequencies, the waveguide having a propagation parameter that varies with frequency at the millimeter-wave frequencies. The transmitter is configured to generate a millimeter-wave signal comprising multiple sub-carriers that are modulated with data, wherein each sub-carrier is modulated with a respective portion of the data and is subjected to only a respective fraction of a variation in the propagation parameter, and to transmit the millimeter-wave signal into a first end of the waveguide. The receiver is configured to receive the millimeter-wave signal from a second end of the waveguide, and to extract the data from the multiple sub-carriers.