Massively Concurrent Non-Orthogonal Multiple Access for 5G Networks and Beyond

We propose a new signal spreading-based non-orthogonal multiple access (NOMA) schemes that exploits the frame-theoretic design principles to enable the efficient concurrence of multiple users in both downlink (DL) and uplink (UL). In contrast to many other NOMA schemes, the proposed method does not require built-in sparsity on the usage of resources by any individual users, hence referred to as massively concurrent non-orthogonal multiple access (MC-NOMA). Instead, MC-NOMA leverages frames as vectorized ensembles of the individual complex-valued waveform signatures, optimized for low mutual coherence so as to minimize the multi-user interference. A theoretical analysis of the MC-NOMA is offered, which reveals that it can theoretically reach the capacity of the multi-user MIMO channel and outmatches the state of the art in terms of maximum achievable rate over discrete constellations. A detailed description of both the frame-based transmitter design and a newly developed low-complexity efficient decoder is given, which, via simulations, are used to demonstrate that MC-NOMA outperforms the well-established NOMA schemes, such as sparse-coded multiple access (SCMA) and pattern division multiple access (PDMA).