Effect of joint detection and decoding in non-orthogonal multiple access

Non-orthogonal multiple access (NOMA) can share the same frequency band with multiple mobile devices. In the conventional NOMA scheme, the possible pairs of users are limited and this limitation restricts the amount of capacity improvement. This is because the receiver only for the near user cancels the signal of the other user and then detect the desired signal. In this paper, a joint detection and decoding scheme in the far user of the NOMA downlink is proposed and its constellation constrained capacity (CCC) is evaluated through numerical analysis. The proposed scheme allows the pairing of users with the difference of the propagation losses of less than 8dB. The possible number of user pairs in the NOMA system then increases and a larger total capacity may be achievable.