User assisted cooperative relaying in beamspace massive MIMO NOMA based systems for millimeter wave communications

A novel scheme ‘user assisted cooperative relaying in beamspace massive multiple input multiple output (M-MIMO) non-orthogonal multiple access (NOMA) system’ has been proposed to improve coverage area, spectrum and energy efficiency for millimeter wave (mmWave) communications. A downlink system for M users, where base station (BS) is equipped with beamforming lens antenna structure having NRF radio frequency (RF) chains, has been considered. A dynamic cluster of users is formed within a beam and the intermediate users (in that cluster) between beam source and destination (user) act as relaying stations. By the use of successive interference cancellation (SIC) technique of NOMA within a cluster, the relaying stations relay the symbols with improved power to the destination. For maximizing achievable sum rate, transmit precoding and dynamic power allocation for both intra and inter beam power optimization are implemented. Simulations for performance evaluation are carried out to validate that the proposed system outperforms the conventional beamspace M-MIMO NOMA system for mmWave communications in terms of spectrum and energy efficiency.