Enhancing NOMA-OFDM with Channel Alignment

Non- orthogonal multiple access (NOMA) is a promising scheme that shares available resources among the users. Downlink power domain NOMA utilizes channel gain difference across users with superposition coding at transmitter side and successive interference cancellation at receiver side. We briefly describe the fundamental concepts of conventional hybrid orthogonal frequency division multiplexing (OFDM) NOMA scheme. Then, for downlink NOMA we propose novel null space precoding technique that aligns near user's signal into cyclic prefix portion of the far user signal. This allows the far user to benefit from interference-free reception with the CP removal at the receiver side. Simulation results are presented to show the performance improvements over conventional power domain NOMA under perfect and imperfect channel alignment scenarios.