Massively Concurrent NOMA: A Frame-Theoretic Design for Non-Orthogonal Multiple Access

Abstract

We propose an original frame-theoretic design for non-orthogonal multiple access (NOMA) systems, in which the mutual interference (MUI) of a large number of users is collectively minimized. This is achieved by precoding the symbols of each user with a distinct vector in a low-coherence tight frame, constructed either given an algebraic Harmonic technique for minimum-overloaded cases or given a complex sequential iterative decorrelation via convex optimization (CSIDCO) for generic frames. As a consequence, the resulting massively concurrent non-orthogonal multiple access (MC-NOMA) enables all users to robustly and concurrently take advantage of the full orthogonal resources of the system simultaneously. The proposed strategy is therefore distinct from other coded NOMA approaches which seek to reduce the interference based exclusively on sparse access, at the penalty of limiting the resources allocated to each user. The bit error rate (BER), spectral efficiency and sum-rate gains obtained by MC-NOMA both against conventional orthogonal multiple access (OMA) and state-of-the-art NOMA systems are discussed and illustrated via numerical simulations.