  Spatial division multiple access (SDMA) is essential to improve the spectrum
efficiency for multi-user multiple-input multiple-output (MIMO) communications.
The classical SDMA for massive MIMO with hybrid precoding heavily relies on the
angular orthogonality in the far field to distinguish multiple users at
different angles, which fails to fully exploit spatial resources in the
distance domain. With dramatically increasing number of antennas, extremely
large-scale antenna array (ELAA) introduces additional resolution in the
distance domain in the near field. In this paper, we propose the concept of
location division multiple access (LDMA) to provide a new possibility to
enhance spectrum efficiency. The key idea is to exploit extra spatial resources
in the distance domain to serve different users at different locations
(determined by angles and distances) in the near field. Specifically, the
asymptotic orthogonality of beam focusing vectors in the distance domain is
proved, which reveals that near-field beam focusing is able to focus signals on
specific locations to mitigate inter-user interferences. Simulation results
verify the superiority of the proposed LDMA over classical SDMA in different
scenarios.
