MIMO Precoding Exploiting Extra Degrees of Freedom (DoF) in the Wavenumber Domain

TL;DR

This paper introduces a novel wavenumber-domain precoding scheme for MIMO systems that enhances the number of supported data streams and overcomes traditional limitations, applicable in both near-field and far-field scenarios, with demonstrated superior performance.

Contribution

It proposes a new wavenumber-domain precoding method that exploits extra degrees of freedom in the channel, enabling multi-stream transmission beyond rank-1 constraints.

Findings

Significantly outperforms conventional spatial division schemes

Approaches the theoretical performance upper bound of SVD

Works effectively in both near-field and far-field conditions

Abstract

In this paper, we propose an emerging wavenumber-domain precoding scheme to break the limitations of rank-1 channels that merely supports single-stream transmission, enabling simultaneous transmission of multiple data streams. The proposed wavenumber-domain precoding scheme also breaks the Rayleigh distance demarcation, regardless of the far-field and near-field contexts. Specifically, by characterizing the channel response as the superposition of a series of Fourier harmonics specified by different wavenumbers, the degree of freedom (DoF) is dependent on the cardinality of the wavenumber support, based on which the extra DoF is presented. This representation is applicable for both far-field and near-field. Different wavenumber atoms, determined within this support, constitute the codebook for MIMO precoding, in which each atom allows for the transmission of a data stream. Then, to maximize the capacity, it is required to select the wavenumbers associated with the optimal transmission direction, and optimize its power allocation. Finally, our simulation results demonstrate the significant superiority in comparison to the conventional spatial division schemes, with the potential of approaching the theoretical performance upper bound achieved by singular value decomposition (SVD).