This paper considers a wireless network with a base station (BS) conducting timely status updates to multiple clients via adaptive non-orthogonal multiple access (NOMA)/orthogonal multiple access (OMA). Specifically, the BS is able to adaptively switch between NOMA and OMA for the downlink transmission to optimize the information freshness of the network, characterized by the Age of Information (AoI) metric. If the BS chooses OMA, it can only serve one client within each time slot and should decide which client to serve; if the BS chooses NOMA, it can serve more than one client at the same time and needs to decide the power allocated to the served clients. For the simple two-client case, we formulate a Markov Decision Process (MDP) problem and develop the optimal policy for the BS to decide whether to use NOMA or OMA for each downlink transmission based on the instantaneous AoI of both clients. The optimal policy is shown to have a switching-type property with obvious decision switching boundaries. A near-optimal policy with lower computation complexity is also devised. For the more general multi-client scenario, inspired by the proposed near-optimal policy, we formulate a nonlinear optimization problem to determine the optimal power allocated to each client by maximizing the expected AoI drop of the network in each time slot. We resolve the formulated problem by approximating it as a convex optimization problem. We also derive the upper bound of the gap between the approximate convex problem and the original nonlinear, nonconvex problem. Simulation results validate the effectiveness of the adopted approximation. The performance of the adaptive NOMA/OMA scheme by solving the convex optimization is shown to be close to that of max-weight policy solved by exhaustive search...

中文翻译：

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通过具有自适应 NOMA/OMA 的多用户调度优化信息新鲜度

本文考虑具有基站 (BS) 的无线网络通过自适应非正交多址 (NOMA)/正交多址 (OMA) 向多个客户端及时更新状态。具体来说，BS 能够自适应地在 NOMA 和 OMA 之间切换以进行下行传输，以优化网络的信息新鲜度，其特征是信息时代 (AoI) 度量。如果BS选择OMA，它在每个时隙内只能服务一个客户端，并且应该决定服务哪个客户端；如果BS选择NOMA，它可以同时服务多个客户端，需要决定分配给服务客户端的权力。对于简单的两个客户端的情况，我们制定了一个马尔可夫决策过程 (MDP) 问题，并为 BS 制定了最佳策略，以根据两个客户端的瞬时 AoI 来决定对每个下行链路传输使用 NOMA 还是 OMA。最优策略显示出具有明显的决策切换边界的切换类型属性。还设计了具有较低计算复杂度的接近最优的策略。对于更一般的多客户端场景，受所提出的接近最优策略的启发，我们制定了一个非线性优化问题，通过最大化每个时隙中网络的预期 AoI 下降来确定分配给每个客户端的最佳功率。我们通过将其近似为凸优化问题来解决公式化问题。我们还推导出近似凸问题与原始非线性问题之间差距的上限，非凸问题。仿真结果验证了所采用的近似的有效性。通过求解凸优化的自适应 NOMA/OMA 方案的性能表明接近通过穷举搜索求解的最大权重策略的性能...