Transmit Antenna Selection and Power Allocation Optimization for Non‐Orthogonal Multiple Access Systems with Statistical Channel State Information

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This paper considers a downlink multiple input single output (MISO) non‐orthogonal multiple access (NOMA) system over Nakagami‐m fading channels, where a multi‐antenna base station (BS) serves several single‐antenna users with the statistical channel state information (CSI) of each user. We propose a novel low‐complexity transmit antenna selection by head user (TAS‐head) strategy for the first time to exploit the spatial diversity of multiple antennas. Based on our proposed TAS‐head strategy, we derive a closed‐form expression of the exact outage probability (OP). We further analyse the asymptotic OP and diversity order in high signal‐to‐noise ratio (SNR) regime. Finally, we formulate a power allocation optimization problem to maximize sum throughput under outage constraints. We also design an Adam algorithm in combination with numerical differentiation method to obtain a suboptimal solution. Monte Carlo (MC) simulations verify the accuracy of our derived exact OP. Results show that our proposed TAS‐head strategy is more effective than its benchmarks (TAS‐near/far and TAS‐maj). Furthermore, we prove that PA‐TDR criterion achieves better performance than PA‐ACG in scenarios where the descending order of target data rate is the same with that of channel condition. Our designed Adam algorithm turns out to be more effective in comparison with genetic algorithm (GA) in multi‐user case. Results indicate that our proposed TAS‐head strategy is an efficient method to meet users' QoS requirements, especially in low SNR (or transmit power) regime.