Interference Alignment for Channel-Adaptive Waveform Modulation

For communication channels with delay spreads that are longer than the symbol interval, orthogonal frequency-division multiplexing is unusable due to its redundant cyclic prefix. In this regime other techniques are therefore required to deal with inter-symbol interference. In this paper we introduce a new modulation scheme that achieves perfect immunity from inter-symbol interference and perfect diagonalization of the channel. A crucial component of this scheme is interference alignment: portions of the potential inter-symbol interference are arranged to lie in the same output subspace, thereby increasing the number of available interference-free input waveforms.