Non-orthogonal Multiple Access (NOMA)

Non-orthogonal multiple access (NOMA) is a multiple-access technique in which multiple users share the same time–frequency resources simultaneously by allowing controlled non-orthogonality between their signals. User separation is achieved primarily through power-domain multiplexing and advanced receiver processing, rather than through strict orthogonal allocation of time slots or frequency channels.

In power-domain NOMA, signals intended for different users are superimposed at different power levels. At the receiver, successive interference cancellation (SIC) is used to decode and subtract stronger signals before recovering weaker ones. This enables multiple users to be served concurrently on the same resources, potentially improving spectral efficiency and user fairness, particularly when users experience significantly different channel conditions.

In satellite communication systems, NOMA has been investigated for forward and return links in multibeam and high-throughput satellites, where it may increase capacity or improve service availability under asymmetric link conditions. However, its practical deployment is constrained by receiver complexity, sensitivity to channel estimation errors, and the stringent power and linearity requirements of satellite payloads and user terminals.