Abstract
A relay-aided multi-user massive multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) downlink transmission is proposed to support simultaneous massive access for cell-edge user nodes in the same time-frequency-spatial resource block. These spatially-distributed user nodes are grouped into clusters based on their spatial directional information and long-term fading statistics. Each cluster is allocated with an orthogonal pilot sequence, while the user nodes within a cluster share the same pilot. The achievable downlink rates of this relay-aided massive MIMO NOMA are derived, and thereby, the cumulative impact of channel estimation errors, imperfect successive interference cancellation and intra-cluster pilot contamination is investigated. The achievable sum rates and the number of simultaneously served users by the proposed massive MIMO NOMA relaying are compared with the orthogonal multiple access counterpart. Consequently, the trade-offs among the sum rate gains, number of users and implementation/computational complexity are discussed, and thereby, useful insights for practically-viable system-design are obtained.
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