  Orthogonal Frequency Division Multiple Access (OFDMA) as well as other
orthogonal multiple access techniques fail to achieve the system capacity limit
in the uplink due to the exclusivity in resource allocation. This issue is more
prominent when fairness among the users is considered in the system. Current
Non-Orthogonal Multiple Access (NOMA) techniques introduce redundancy by
coding/spreading to facilitate the users' signals separation at the receiver,
which degrade the system spectral efficiency. Hence, in order to achieve higher
capacity, more efficient NOMA schemes need to be developed. In this paper, we
propose a NOMA scheme for uplink that removes the resource allocation
exclusivity and allows more than one user to share the same subcarrier without
any coding/spreading redundancy. Joint processing is implemented at the
receiver to detect the users' signals. However, to control the receiver
complexity, an upper limit on the number of users per subcarrier needs to be
imposed. In addition, a novel subcarrier and power allocation algorithm is
proposed for the new NOMA scheme that maximizes the users' sum-rate. The
link-level performance evaluation has shown that the proposed scheme achieves
bit error rate close to the single-user case. Numerical results show that the
proposed NOMA scheme can significantly improve the system performance in terms
of spectral efficiency and fairness comparing to OFDMA.
