  Extremely large-scale multiple-input multiple-output (XL-MIMO) is the
development trend of future wireless communications. However, the extremely
large-scale antenna array could bring inevitable nearfield and dual-wideband
effects that seriously reduce the transmission performance. This paper proposes
an algorithmic framework to design the beam combining for the near-field
wideband XL-MIMO uplink transmissions assisted by holographic metasurface
antennas (HMAs). Firstly, we introduce a spherical-wave-based channel model
that simultaneously takes into account both the near-field and dual-wideband
effects. Based on such a model, we then formulate the HMA-based beam combining
problem for the proposed XL-MIMO communications, which is challenging due to
the nonlinear coupling of high dimensional HMA weights and baseband combiners.
We further present a sum-mean-square-error-minimization-based algorithmic
framework. Numerical results showcase that the proposed scheme can effectively
alleviate the sum-rate loss caused by the near-field and dual-wideband effects
in HMA-assisted XL-MIMO systems. Meanwhile, the proposed HMA-based scheme can
achieve a higher sum rate than the conventional phase-shifter-based hybrid
analog/digital one with the same array aperture.
