Abstract
The sum rate performance of simultaneous relay and direct massive multiple-input multiple-output (MIMO) downlink transmissions is investigated for the imperfect channel state information (CSI) case. In this context, a massive MIMO base-station transmits simultaneously to spatially distributed relayed and direct user nodes by using two independent zero-forcing based precoders. The uplink CSI at the base-station is estimated by using the non-orthogonal pilots transmitted by relayed and direct user nodes, and hence, the channel estimates are affected by pilot contamination. To this end, the detrimental effects of intra-cell pilot contamination are quantified by deriving the achievable sum rates when the number of antennas at the base-station is allowed to grow without bound. Furthermore, the performance degradation due to concurrent relayed and direct transmissions is quantified by analyzing the intra-cell interference effects for imperfect CSI cases. Our analysis and numerical results reveal that massive MIMO can be exploited for spectral efficient aggressive spatial multiplexing for simultaneous relayed and direct downlink transmissions.
Published Version
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