Joint maximum likelihood detection in far user of non-orthogonal multiple access

Non-orthogonal multiple access (NOMA) enables multi- ple mobile devices to share the same frequency band. In a conventional NOMA scheme, the receiver of a far user detects its desired signal without canceling the signal for a near user. However, the signal for the near user acts as interference and degrades the accuracy of likelihood values for the far user. In this paper, a joint maximum likelihood detection scheme for the far user of the NOMA downlink is proposed. The proposed scheme takes the interference signal into account in calculating the likelihood val- ues. Numerical results obtained through computer simulation show that the proposed scheme improves the performance by from 0.2 dB to 3.1 dB for power allocation coefficients of 0.2 to 0.4 at a bit error rate (BER) of 10^-2 relative to the conventional scheme.