Near-field cell-free communication networks: performance analysis

Details

Supervisors

Oestges, Claude ; Vandendorpe, Luc

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

With frequencies increasing into the terahertz range and larger antenna arrays, the next generations of mobile networks are expected to operate in the near-field (NF) region, where the plane-wave approximation on the transmitted signal is no longer accurate. By taking advantage of the spherical wavefront in the NF region, beam-focusing can be performed on a single point. Furthermore, cell-free networks are currently under study to counteract the inter-cell interference and the strong path loss experienced at the cell-edge in a cellular network operating with higher frequencies. The objective of this master thesis is therefore to analyze the robustness of near-field beam-focusing to an imperfect channel state information (CSI), in a cell-free communication network. This analysis includes the estimation of the CSI, which is performed using a positioning methodology adapted for a cell-free network, where the access points are located in the near-field region of the target. The estimated position is used as focus point, and the power variation around the focus point is characterized by computing its analytical expression, when beam-focusing is performed at multiple access points. The results show that in the scenario of this work, beam-focusing is not robust to an imperfect CSI. An alternative to beam-focusing is thus proposed in this work to improve the robustness to estimation errors. This new precoding scheme is named spot-forming, and its objective is to ensure a constant and maximized power in a wider region around the estimated point, using pass-band filter design.