Sparse and Dense: An Achievable Region for Code-Domain NOMA with Mixed Users

Benjamin M. Zaidel, Shlomo Shamai Shitz

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

3 Scopus citations


Spectrally efficient non-orthogonal multiple access (NOMA) schemes are of paramount importance for 5G and beyond wireless networks, among which code-domain NOMA is a prominent technology. Two extreme paradigms have lead to analytically tractable benchmarks for code-domain NOMA performance. The first relies on independent random dense spreading signatures (fully utilizing the available orthogonal resources) and suits settings with sporadic user activity, where signature coordination is hard to enforce. The second paradigm is regular sparse NOMA (where a small fixed number of resources is allocated to each user, and vice versa). It exhibits superior performance, while facilitating near-optimal multiuser detection using iterative message-passing algorithms. However, it also requires fully coordinated signatures and might be impractical in certain use-cases. In this paper, we investigate for the first time a mixed setting, where one class of users obeys the latter paradigm, while a second class obeys the former. The achievable ergodic class-throughput region is derived, while considering the large-system limit. Particularly, the total achievable sum-rate is characterized by means of a free additive convolution of probability measures, while relying on a recent strong representation theorem. The corresponding low-SNR characterization is further shown to admit closed-form expressions. The analysis provides insightful tools for investigating various use-cases of interest for future networks.

Original languageEnglish
Title of host publication2021 IEEE International Symposium on Information Theory, ISIT 2021 - Proceedings
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages6
ISBN (Electronic)9781538682098
StatePublished - 12 Jul 2021
Event2021 IEEE International Symposium on Information Theory, ISIT 2021 - Virtual, Melbourne, Australia
Duration: 12 Jul 202120 Jul 2021

Publication series

NameIEEE International Symposium on Information Theory - Proceedings
ISSN (Print)2157-8095


Conference2021 IEEE International Symposium on Information Theory, ISIT 2021
CityVirtual, Melbourne

Bibliographical note

Publisher Copyright:
© 2021 IEEE.


This research was supported by the ISRAEL SCIENCE FOUNDATION (grant No. 1897/19).

FundersFunder number
Israel Science Foundation1897/19


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