Abstract
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).
Highlights
non-orthogonal multiple access (NOMA) has emerged in recent years as a promising approach to improve the usage of scarce spectral resources in a seamless manner [1]–[3]
EFFECTIVENESS OF quadratic CSIDCO (QCSIDCO) FRAME DESIGN To highlight the transmitter design concepts of massively concurrent non-orthogonal multiple access (MC-NOMA) and its inherent advantages some effort is first dedicated to illustrating the structure imposed by the low-coherence tight frames used in MC-NOMA onto the channels perceived by the receivers
We considered problems of non-orthogonal multiplexing in both DL and UL, proposing a new signal spreading-based NOMA scheme which enables the efficient concurrence of multiple users in both DL and UL
Summary
NOMA has emerged in recent years as a promising approach to improve the usage of scarce spectral resources in a seamless manner [1]–[3]. In scrambling-based CD-NOMA, multiplexation is performed post-modulation by scrambling user streams with low-correlation sequences so as to aid multi-user detection (MUD) via minimum mean squared error (MMSE) with SIC or parallel interference cancellation (PIC) [16], further enhanced by error correction An example of such an approach is Qualcomm’s resource spread multiple access (RSMA) system [17]. We formulate in this sense an abstract compressive mapping between the collective active user information symbol vector, and respectively, the available REs. Some recurrent ideas are, identifiable across these related works, in light of which this article focuses on answering the following three fundamental questions: 1) CAN CD-NOMA BE ABSTRACTED UNDER A UNIFIED FRAMEWORK? This general perspective of overloaded NOMA as a Frame Theory problem requires a brief description of some of its fundamentals, which is offered in the subsection
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