Metasurface for Enhanced Millimeter-Wave Communications under Imperfect Beam Alignment

In this work, we investigate the impact of beam misalignment in the performance of a wireless system employing a metasurface to improve coverage in a non-line-of-sight (NLOS) scenario. The metasurface is modeled by an array of small radiating elements each of them terminated with a complex load. An equivalent Array Factor is defined, which allows visualizing the beamsteering properties of the metasurface in far-field conditions. Angular misalignment is modeled using a truncated Gaussian distribution and an expression to evaluate signal-to-noise ratio (SNR) in the presence of misalignment is derived. Numerical results show an SNR degradation close to 8 dB for 5
^◦
error magnitude and up to 14 dB if high-gain unit cells are used. Three mechanisms are explored, which can be used to reduce SNR degradation: increasing Metasurface dimensions allows recovering SNR by 7.4 dB, low unit cell gain allows improving SNR by close to 10.5 dB when compared to a high-gain cell and base station beamwidth decrease from 25.6
^◦
to 12.7
^◦
allows recovering SNR by 4 dB thanks to the higher BS beam gain.