The Interference Channel Revisited: Aligning Interference by Adjusting Receive Antenna Separation

TL;DR

This paper introduces a novel interference alignment method using adjustable antenna spacing at receivers, enabling nulling of multiple interference directions while maintaining signal quality, with practical demonstrations and extensions to complex channel scenarios.

Contribution

It presents a new interference alignment scheme based on antenna spacing adjustments, applicable to various channel types, with demonstrated performance improvements in multi-user interference channels.

Findings

Significant interference suppression in multi-user channels.

Effective in low to moderate SNR regimes.

Robustness to channel estimation errors.

Abstract

It is shown that a receiver equipped with two antennas may null an arbitrary large number of spatial directions to any desired accuracy, while maintaining the interference-free signal-to-noise ratio, by judiciously adjusting the distance between the antenna elements. The main theoretical result builds on ergodic theory. The practicality of the scheme in moderate signal-to-noise systems is demonstrated for a scenario where each transmitter is equipped with a single antenna and each receiver has two receive chains and where the desired spacing between antenna elements is achieved by selecting the appropriate antennas from a large linear antenna array. We further extend the proposed scheme to show that interference can be eliminated also in specular multipath channels as well as multiple-input multiple-output interference channels where a single extra receiver suffices to align all interferers into a one-dimensional subspace. To demonstrate the performance of the scheme, we show significant gains for interference channels with four as well as six users, at low to moderate signal-to-noise ratios (0-20 dB). The robustness of the proposed technique to small channel estimation errors is also explored.