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To support high throughput and massive connectivity, next-generation mobile networks are expected to utilize extremely large-scale antenna arrays. This would result in wireless communications occurring in the near-field region. Leveraging the unique channel characteristics of near-field propagation presents both opportunities and challenges, hence we critically appraise near-field communications (NFC). We commence by determining the boundary that distinguishes NFC and conventional far-field communications. Furthermore, some of the key challenges of NFC, including its spherical wavefront-based channel modeling and channel estimation, near-field beamfocusing, hardware design, as well as wireless sensing, are covered based on a comprehensive survey of existing progress. Two case studies demonstrate the potential of NFC in improving the spatial multiplexing gain and positioning accuracy in the near field. Finally, a suite of open issues are identified for motivating future research, such as dealing with spatial non-stationarity, and the potential of stacked intelligent metasurface-based transceiver design.
An et al. (Sat,) studied this question.