Spatial Division Multiple Access (SDMA)

Spatial Division Multiple Access (SDMA) is a multiple-access technique that separates users in the spatial domain, allowing multiple signals to be transmitted simultaneously on the same frequency band and time resources by exploiting differences in their spatial signatures. Separation is achieved through the use of directional antennas, multibeam coverage, beamforming, or adaptive spatial filtering, such that signals intended for different users occupy distinct spatial paths.

In satellite systems, SDMA is typically implemented using multibeam antennas and, increasingly, digital beamforming with onboard processing. By directing narrowly focused beams toward individual users or geographic regions, the satellite can reuse the same frequencies and polarizations in different spatial locations with limited mutual interference, thereby increasing overall system capacity.

The effectiveness of SDMA depends on the degree of spatial separation between users. Users with well-separated angles of arrival or beam footprints can be served concurrently with minimal interference, whereas closely spaced users with highly correlated spatial characteristics reduce the achievable performance gains. SDMA underpins many modern high-throughput satellite (HTS) architectures and is closely related to beamforming and massive MIMO concepts used in terrestrial wireless systems.