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Abstract-A multiuser dual-hop relaying system over mixed radio frequency/free-space optical (RF/FSO) links is investigated. Specifically, the system consists of m single-antenna sources, a relay node equipped with n ≥ m receive antennas and a single photo-aperture transmitter, and one destination equipped with a single photo-detector. RF links are used for the simultaneous data transmission from multiple sources to the relay. The relay operates under the decode-and-forward protocol and utilizes the popular V-BLAST technique by successively decoding each user's transmitted stream. Two common norm-based orderings are adopted, i.e., the streams are decoded in an ascending or a descending order. After V-BLAST, the relay retransmits the decoded information to the destination via a point-to-point FSO link in m consecutive timeslots. Analytical expressions for the end-to-end outage probability and average symbol error probability of each user are derived, while closed-form asymptotic expressions are also presented. Capitalizing on the derived results, some engineering insights are manifested, such as the coding and diversity gain of each user, the impact of the pointing error displacement on the FSO link and the V-BLAST ordering effectiveness at the relay.Index Terms-Decode-and-forward (DF), dual-hop communication, mixed RF/FSO systems, ordered successive interference cancellation (SIC), V-BLAST reception.

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Abstract-The performance of a multiuser communication system with single-antenna transmitting terminals and a multiantenna base-station receiver is analytically investigated. The system operates under independent and non-identically distributed rank-1 Rician fading channels with imperfect channel estimation and residual hardware impairments (compensation algorithms are assumed, which mitigate the main impairments) at the transceiver. The spatial multiplexing mode of operation is considered where all the users are simultaneously transmitting their streams to the receiver. Zero-forcing is applied along with successive interference cancellation (SIC) as a means for efficient detection of the received streams. New analytical closed-form expressions are derived for some important performance metrics, namely, the outage probability and ergodic capacity of the entire system. Both the analytical expressions and simulation results show the impact of imperfect channel estimation and hardware impairments to the overall system performance in the usage scenarios of massive MIMO and mmWave communication systems.