Interference Avoidance and Dispersive Channels: A New Look at Multicarrier Modulation∗

The availability of software radios and application of interference avoidance may offer a new perspective on communication over dispersive channels. By both lengthening the transmission interval so that ISI is almost inconsequential and by using combinations of channel eigenfunctions to convey the bits, communications over dispersive channels becomes (not surprisingly) a multiuser detection problem where each bit is assigned its own waveform. By choosing these waveforms to meet the Welch Bound with equality – through interference avoidance or some other numerical method – a uniform maximum SINR can be achieved for each bit. In addition by using Gaussian signaling and decoding with this codeword ensemble, the channel capacity can be (theoretically) met. A trivial extension of the single user case can be used for multiple users over identical channels. Multiple users with non-identical channels is more subtle and is discussed in the interference avoidance context with suggestions for future work.