ASMC-NOMA: Downlink Adaptive Subcarrier Spacing Multi-Carrier NOMA for 5G Time-Varying Channels

Abstract

Non-orthogonal multiple access (NOMA) scheme has been regarded as one of the promising solutions to realize a flexible and robust multiple access scheme in next generation wireless communication system. However, the inter-carrier interference caused by time-varying fading is not considered in conventional NOMA. In this paper, a novel multi-user access scheme, adaptive subcarrier-spacing multi-carrier non-orthogonal multiple access (ASMC- NOMA), is proposed to provide robust multi-user downlink transmission in time-varying channels and support user velocities up to 500 km/h. Based on the filtered-OFDM waveform, ASMC-NOMA allows flexible power-time- frequency three-dimensional resource allocation and subcarrier spacing adaptation according to the channel state and user velocities. With the user-specific adaption and coexistence of different parameters, ASMC-NOMA is able to repel the impact of high-range Doppler effects and control the signal-to-interference ratio for every downlink user. The pre-grouped resource adaptive allocation scheme is designed with the consideration of reducing the transmission overhead and receiver-end implementation complexity. Transceiver structure and signal model are discussed in detail. Theoretical analysis on the signal properties and numerical system-level simulation results prove that the proposed ASMC-NOMA effectively enhances the transmission robustness, reduces the transmission outage due to the high mobility of users, and provides increased transmission efficiency over conventional OFDM- based NOMA and multi-carrier orthogonal multiple access.