A Low-PAPR Hybrid NOMA based on Constant Envelope OFDM

The problem of high peak-to-average-power-ratio (PAPR) is a major drawback of orthogonal frequency-division multiplexing (OFDM) technique, which is also the challenge of OFDM-based non-orthogonal multiple access (NOMA) for next-generation communications. To address this issue, this paper introduces constant envelope (CE) OFDM waveform, which is capable of achieving a PAPR of 0dB, for downlink NOMA. The proposed hybrid NOMA structure, namely CE-TF-NOMA, superposes conventional CE-OFDM and DFT spread (DFT-s)-CE-OFDM over the time-frequency domain, which significantly mitigates the time-domain fluctuation of transmitted signal and improve the power efficiency of high power amplifiers (HPA). Furthermore, two receiver schemes on the tradeoff between computational complexity and detection accuracy are presented. The system performance of the proposed TF-CE-NOMA is evaluated by comparison with the OFDM-based power-domain NOMA (PD-NOMA) and time-frequency domain NOMA (TF-NOMA), respectively. Simulation results demonstrate that CE-TF-NOMA is capable of achieving improved BER and constraint capacity with significantly reduced PAPR performance.