Interference Alignment for Channel-Adaptive Waveform Modulation

For communication channels with delay spreads that are longer than the symbol interval, orthogonal frequencydivision 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.