Joint SDMA and Power-Domain NOMA System for Multi-User Mm-Wave Communications

Digital beamsteering (DBS) is an appealing technique to overcome the severe millimeter-wave path loss, with less complexity and less channel feedback. In multi-user systems, DBS generates a beam toward each user. However, in congested cells, such a system suffers from high inter-user interference causing by the neighboring beams. In this paper, a new approach of space division multiple access (SDMA) with power-domain non-orthogonal multiple access (PD-NOMA) is considered for millimeter-wave channel to significantly reduce the inter-user interference and thus enhance the overall throughput. The proposed scheme is designed by selecting the users located at the same direction to share one beam, in which PD-NOMA multiplexes the users in power domain. The proposed user clustering method built upon an interference metric, and followed by a fixed power allocation method based on the received power, makes possible the design of a low-feedback NOMA-DBS scheme. Simulation results, based on the New York university mm-wave simulator, show that the multi-user MIMO system can achieve higher sum-rate with our proposed joint SDMA and PD-NOMA scheme, with respect to only SDMA (e.g., up to 20 bps/Hz rate gain for 45 users in the cell).