The incorporation of user-assisted cooperative relaying into beamspace massive multiple-input multiple-output (mMIMO) non-orthogonal multiple access (NOMA) system can extend the coverage area and improve the spectral and energy efficiency for millimeter wave (mmWave) communications when a dynamic cluster of mobile user terminals (MUTs) is formed within a beam. We propose threshold-based user-assisted cooperative relaying into a beamspace mMIMO NOMA system in a downlink scenario. Specifically, the intermediate MUTs between the next-generation base station (gNB) and the cell-edge MUT become relaying MUTs after the successful decoding of the signal of the cell-edge MUT only when they meet the predetermined signal-to-interference plus noise ratio (SINR) threshold. A zero forcing (ZF) precoder and iterative power allocation are used to minimize both inter- and intra-beam interferences to maximize the system sum rate. We then evaluate the performance of this system in a delay-intolerant cell-edge MUT scenario. Moreover, the outage probability of the cell-edge MUT of the proposed scheme is investigated and an analytic expression is derived. Simulation results confirm that the proposed threshold-based user-assisted cooperative relaying beamspace mMIMO NOMA system outperforms the user-assisted cooperative relaying in beamspace mMIMO NOMA, beamspace MIMO-NOMA, and beamspace MIMO orthogonal multiple access (OMA) systems in terms of spectrum efficiency, energy efficiency, and outage probability.

We propose a Wiener filter (WF) and a combined zero forcing (ZF)/ WF precodings with ant colony optimization (ACO) algorithms as the digital precoder for millimeter wave multiple-input multiple-output (MIMO) systems. In the proposed schemes, beams are selected based on maximal magnitude (MM) criteria and the selection is optimized using ACO algorithm to achieve near optimal solution with highly reduced complexity. According to the simulation results, while ACO-WF scheme achieves higher sum rate in high inter-user interference (ISI) environments compared with conventional precoders, we confirm ACO-ZF/WF scheme can obtain a maximal sum rate in both low and high ISI environments.

<p>Millimeter-wave (mmWave) beamspace massive multiple-input multiple-output (mMIMO) system with lens antenna array can minimize transceiver hardware complexity without compromising performance. However, the number of supported portable user terminals (PUTs) cannot exceed the number of radio frequency (RF) blocks accessible at the same time, frequency, and coding resources. As a result, we propose the integration of rate-splitting multiple access (RSMA) into a beamspace mMIMO system to support a larger number of PUTs than the number of available RF blocks while minimizing intra-beam interferences. Moreover, orthogonal random precoding (ORP) is utilized in the downlink of the beamspace mMIMO system to mitigate the inter-beam interferences and extend the cell coverage area. Then, we develop an optimization problem to optimize the system's overall throughput while keeping the minimum needed throughput and power budget in consideration. The nonconvex optimization issue is then turned into a convex optimization problem using the successive convex approximation approach. Following that, we offer an alternating method to solve the approximate optimization issue and select an optimal solution. Furthermore, the suggested method's effectiveness is evaluated in terms of total throughput, energy efficiency, and cell coverage area. Finally, numerical results confirm the superior performance of the proposed method over benchmark techniques in terms of sum throughput, energy efficiency, and cell coverage area.</p>

<p>Millimeter-wave (mmWave) beamspace massive multiple-input multiple-output (mMIMO) system with lens antenna array can minimize transceiver hardware complexity without compromising performance. However, the number of supported portable user terminals (PUTs) cannot exceed the number of radio frequency (RF) blocks accessible at the same time, frequency, and coding resources. As a result, we propose the integration of rate-splitting multiple access (RSMA) into a beamspace mMIMO system to support a larger number of PUTs than the number of available RF blocks while minimizing intra-beam interferences. Moreover, orthogonal random precoding (ORP) is utilized in the downlink of the beamspace mMIMO system to mitigate the inter-beam interferences and extend the cell coverage area. Then, we develop an optimization problem to optimize the system's overall throughput while keeping the minimum needed throughput and power budget in consideration. The nonconvex optimization issue is then turned into a convex optimization problem using the successive convex approximation approach. Following that, we offer an alternating method to solve the approximate optimization issue and select an optimal solution. Furthermore, the suggested method's effectiveness is evaluated in terms of total throughput, energy efficiency, and cell coverage area. Finally, numerical results confirm the superior performance of the proposed method over benchmark techniques in terms of sum throughput, energy efficiency, and cell coverage area.</p>