  5G communication systems and beyond are envisioned to support an extremely
diverse set of use cases with different performance requirements. These
different requirements necessitate the use of different numerologies for
increased flexibility. Non-orthogonal multiple access (NOMA) can potentially
attain this flexibility by superimposing user signals while offering improved
spectral efficiency (SE). However, users with different numerologies have
different symbol durations. When combined with NOMA, this changes the nature of
the interference the users impose on each other. This paper investigates a
multinumerology NOMA (MN-NOMA) scheme using successive interference
cancellation (SIC) as an enabler for coexistence of users with with different
numerologies. Analytical expressions for the inter-numerology interference
(INI) experienced by each user at the receiver are derived, where mean-squared
error (MSE) is the metric used to quantify INI. Using the MSE expressions, we
analytically derive achievable rates for each user in the MN-NOMA system. These
expressions are then evaluated and used to compare the SE performance of
MN-NOMA with that of its single-numerology counterpart. The proposed scheme can
achieve the desired flexibility in supporting diverse use cases in future
wireless networks. The scheme also gains the SE benefits of NOMA compared to
both multinumerology and single numerology orthogonal multiple access (OMA)
schemes.
