2009 Research Summary

Interference Alignment for Line-of-Sight Channels

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Leonard Henry Grokop and David Tse

The interfering nature of the wireless medium makes the design of efficient communication schemes a challenging problem, one that has received much attention in recent decades. Commonplace solutions to this problem involve either some form of reuse or orthogonalization, but all such techniques suffer from a major drawback: as the number of links in the network grows, the spectral efficiency of each link vanishes. A recently proposed technique that aligns the interfering signals in the frequency domain at each receiver has shown some promise of improving this situation for rich multipath environments, provided the power spectral density of transmissions is sufficiently high.

In this work we consider a multipath environment consisting only of a single path per link. We show that for such channels the alignment of interference has a simple time-domain interpretation. We use this insight to construct a communication scheme for which the spectral efficiency of each link is non-vanishing as the number of link grows, provided only that the bandwidth scales appropriately. Additionally, we show that scaling the bandwidth is a necessary criterion for achieving non-vanishing spectral efficiencies.