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Sparse or Dense: A Comparative Study of Code-Domain NOMA Systems

Liu, Zilong and Yang, Lie-Liang (2021) 'Sparse or Dense: A Comparative Study of Code-Domain NOMA Systems.' IEEE Transactions on Wireless Communications. ISSN 1536-1276

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Abstract

This paper is focused on code-domain non-orthogonal multiple access (CD-NOMA), which is an emerging paradigm to support massive connectivity for future machine-type wireless networks. We take a comparative approach to study two types of overloaded CD-NOMA, i.e., sparse code multiple access (SCMA) and dense code multiple access (DCMA), which are distinctive from each other in terms of their codebooks having sparsity or not. By analysing their individual diversity orders (DO) in Rayleigh fading channels, it is found that DCMA can be designed with the aid of generalized sphere decoder (i.e., a nonlinear multiuser detector) to enjoy full DO which is equal to the maximum number of resource nodes in the system. This is in contrast to SCMA whose error rate suffers from limited DO equal to the codebook sparsity (i.e., the effective number of resource nodes occupied by each user). We conduct theoretical analysis for the codebook design criteria and propose to use generalized sphere decoder for DCMA detection. We numerically evaluate two types of multiple access schemes under “4 × 6” (i.e., six users communicate over four subcarriers) and “5 × 10” NOMA settings and reveal that DCMA gives rise to significantly improved error rate performance in Rayleigh fading channels, whilst having decoding complexity comparable to that of SCMA.

Item Type: Article
Uncontrolled Keywords: Non-orthogonal multiple access (NOMA), machine-type communications (MTC), massive connectivity, dense code multiple access (DCMA), sparse code multiple access (SCMA), message passing algorithm, sphere decoding, low-density parity check (LDPC) code
Divisions: Faculty of Science and Health > Computer Science and Electronic Engineering, School of
Depositing User: Elements
Date Deposited: 16 Jul 2021 14:33
Last Modified: 16 Jul 2021 14:34
URI: http://repository.essex.ac.uk/id/eprint/30740

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