On the Uplink Transmission of Multi-user Extra-large Scale Massive MIMO Systems
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With the inherent benefits, such as, better cell coverage and higher area throughput, extra-large scale massive MIMO has great potential to be one of the key technologies for the next generation wireless communication systems. However, in practice, when the antenna dimensions grow large, spatial non-stationarities occur and users would only see a portion of the base station antenna array, which we call visibility region (VR). To exploit the impact of spatial non-stationarities, in this paper, we investigate the uplink transmission of multi-user extra-large scale massive MIMO systems by considering VRs. In particular, we first propose a subarray-based system architecture for extra-large scale massive MIMO systems. Then, tight closed-form uplink spectral efficiency (SE) approximations with linear receivers are derived.These approximations reveal that users with their VRs covering different subarrays or VRs with less overlap should be scheduled simultaneously under maximum ratio combining receiver, while as many users as possible should be selected under linear minimum mean squared error receiver. With the objective of maximizing the system sum achievable SE, we also propose schemes for the subarray phase coefficient design. In addition, two statistical CSI-based greedy user scheduling algorithms are developed. Our results indicate that statistical CSI-based scheduling algorithms achieve great performance for extra-large scale massive MIMO systems, and it is not necessary to simultaneously turn on all the subarrays and radio frequency chains to serve the users.
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