Near-Field Wideband Beamforming for Extremely Large Antenna Array
share
Extremely large antenna array for wideband communications is a promising technology to achieve a Tbps data rate for next-generation communications. However, due to the extremely large bandwidth and antenna array aperture, the near-field beam split effect will severely decrease the actual transmission rates, which has not been investigated in existing works. To solve this challenging problem, we first reveal the near-field beam split effect and analyze the corresponding array gain loss. Then, a piecewise-far-field model with piecewise-linear phase property is proposed to approximate the near-field channel, based on which we propose a phase-delay focusing method to effectively mitigate the near-field beam split effect. Moreover, a new metric called effective Rayleigh distance is defined, which is more accurate than the classical Rayleigh distance to distinguish the far-field and near-field regions for practical communications. Finally, theoretical and numerical results are provided to demonstrate the effectiveness of our methods.
READ FULL TEXT