Fundamental limits of low-density spreading NOMA with fading
Journal article, 2018

Spectral efficiency of low-density spreading non-orthogonal multiple access channels in the presence of fading is derived for linear detection with independent decoding and optimum decoding. The large system limit, where both the number of users and number of signal dimensions grow with fixed ratio, called load, is considered. In the case of optimum decoding, it is found that low-density spreading underperforms dense spreading for all loads. Conversely, linear detection is characterized by different behaviors in the underloaded versus overloaded regimes. In particular, it is shown that spectral efficiency changes smoothly as load increases. However, in the overloaded regime, the spectral efficiency of low-density spreading is higher than that of dense spreading.

multiple access channels

non-orthogonal multiple access (NOMA)

Spectral efficiency


Mai T.P. Le

Sapienza University of Rome

Guido Ferrante

Chalmers, Electrical Engineering, Communication and Antenna Systems, Communication Systems

Massachusetts Institute of Technology (MIT)

Singapore University of Technology and Design

Tony Q.S. Quek

Singapore University of Technology and Design

Maria Gabriella Di Benedetto

Sapienza University of Rome

IEEE Transactions on Wireless Communications

1536-1276 (ISSN)

Vol. 17 7 4648-4659

Subject Categories


Communication Systems

Signal Processing



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