This paper considers a multiple-input multiple-output non-orthogonal multiple access (NOMA) downlink transmission system with different linear beamforming techniques, where the base station uses each cluster to serve a pair of users. In the considered NOMA cluster, we first derive the performance analysis of the system that uses a proposed user paring method, which exploits the different large-scale channel qualities of users to allocate the transmit power of the strong and weak users in each pair, to ensure that both users in each pair can contribute the best on the system performance. We further formulate a sum spectral efficiency (SE) maximization with a subject to the limited transmit power budget, which is emphasized to be non-convex. We have, then, proposed a framework that solves the above non-convex problem into two steps: lower bound this non-convex problem by a geometric program by using the arithmetic mean-geometric mean inequality and, then, employ the successive optimization approach to find the local Karush-Kuhn-Tucker point. Numerical results manifest that a NOMA-based network with zero forcing (ZF) beamforming gives the highest sum SE, while regularized ZF brings benefits to the SE of weak users. INDEX TERMS NOMA, OMA, spectral efficiency, optimization.
This paper proposes a flexible pilot assignment method to jointly optimize the uplink and downlink data transmission in multi-cell Massive multiple input multiple output (MIMO) systems with correlated Rayleigh fading channels. By utilizing a closed-form expression of the ergodic spectral efficiency (SE) achieved with maximum ratio processing, we formulate an optimization problem for maximizing the minimum weighted sum of the uplink and downlink SEs subject to the transmit powers and pilot assignment sets. This combinatiorial optimization problem is solved by two sequential algorithms: a heuristic pilot assignment is first proposed to obtain a good pilot reuse set and the data power control is then implemented. Numerical results manifest that the proposed algorithm converges fast to a better minimum sum SE per user than the algorithms in previous works.
This paper investigates performance of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-enabled multiple two-way full-duplex device-to-device (D2D) communication systems over Rayleigh fading channels under optimal and uncertain phase shift alignments. We derive closed-form expressions for outage probability (OP), sum throughput, ergodic capacity (EC) and energy efficiency. To gain insights, we quantify and reveal some useful guidelines for the performance behavior of the OP and the EC, such as diversity order and ergodic slope from high transmit power configuration. In addition, some critical points also deduced for the sum throughput and the system energy efficiency. Moreover, the impacts of the transmit power configurations, RIS deployments, allocating target data rate transmission, and the number of user deployments on the system performance are examined. Finally, we present some extensive simulations using Monte-Carlo method to corroborate the accuracy of the theoretical analysis.INDEX TERMS Simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs), device-to-device (D2D) communication, full-duplex, two-way communication.
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