Frequency-Domain NOMA With Two Sets of Orthogonal Signal Waveforms

We present a non-orthogonal multiple access (NOMA) scheme based on combining orthogonal frequency-division multiple access and multi-carrier code-division multiple access. Contrary to other NOMA architectures, the proposed approach does not require any power imbalance between user signals, making it possible to grant all users the same data rate and performance. Another major contribution concerns the receiver operation: Many papers in the recent NOMA literature refer to single-stage successive interference cancellation, where the strong user signal is first detected and subtracted from the received signal before detecting the weak user signal. While this approach may be optimal from information theoretic viewpoint, we show that this type of receiver cannot achieve performance results close to those of interference-free transmission and that, in our framework, an iterative receiver is actually required for this purpose. We investigate both hard-decision and soft-decision iterative receivers and show that a soft-decision receiver significantly improves the performance and increases the number of users.