two or more digital signals are encoded using two or more respective line codes . the line codes are chosen in conjunction with the data rates of the digital signals such that the encoded signals are substantially orthogonal to each other in the frequency domain . as such , the two or more encoded signals may be combined and transmitted via a single physical medium with little or no interference . a transmitter for encoding and transmitting the digital signals contains line coders for encoding the digital signals and a combiner for combining the encoded signals for transmission via a single physical medium . a receiver for receiving and decoding the combined encoded signal contains filters for extracting the individual encoded signals and line decoders for decoding the individual encoded signals to generate the original digital data signals .