We consider a base station (BS) that receives version update packets from multiple exogenous streams and broadcasts them to corresponding users over a fading broadcast channel using a non-orthogonal multiple access (NOMA) scheme. Sequentially indexed packets arrive randomly in each stream, with new packets making the previous ones obsolete. In this case, we consider the version age of information (VAoI) at a user, defined as the difference in the version index of the latest available packet at the BS and that at the user, as a metric of freshness of information. Our objective is to minimize a weighted sum of average VAoI across users subject to an average power constraint at the BS by optimally scheduling the update packets from various streams for transmission and transmitting them with sufficient powers to guarantee their successful delivery. We consider the class of channel-only stationary randomized policies (CO-SRP), which rely solely on channel power gains for transmission decisions. We solve the resulting non-convex problem optimally and show that the VAoI achieved under the optimal CO-SRP is within twice the optimal achievable VAoI. We also obtained a Constrained Markov Decision Process (CMDP)-based solution and its structural properties. Numerical simulations show a close performance between the optimal CO-SRP and CMDP-based solutions. Additionally, a time division multiple access (TDMA) scheme, which allows transmission to at most one user at a time, matches NOMA's performance under tight average power constraints. However, NOMA outperforms TDMA as the constraint is relaxed.

翻译：我们考虑一个基站（BS），该基站从多个外部流接收版本更新数据包，并通过非正交多址接入（NOMA）方案在衰落广播信道上向对应用户广播这些数据包。每个流中的顺序索引数据包随机到达，新数据包会使先前的数据包过时。在这种情况下，我们考虑用户处的信息版本龄（VAoI），定义为基站最新可用数据包的版本索引与用户处最新可用数据包版本索引之差，作为信息新鲜度的度量指标。我们的目标是在基站平均功率约束下，通过最优调度来自不同流的更新数据包进行传输，并以足够功率保证其成功传输，从而最小化所有用户平均VAoI的加权和。我们考虑仅依赖信道功率增益进行传输决策的信道状态静止随机策略（CO-SRP）类别。我们最优地求解了由此产生的非凸问题，并证明在最优CO-SRP下实现的VAoI在最优可达VAoI的两倍以内。我们还获得了基于约束马尔可夫决策过程（CMDP）的解及其结构特性。数值仿真表明，最优CO-SRP与基于CMDP的解的性能非常接近。此外，在严格平均功率约束下，允许每次最多向一个用户传输的时分多址（TDMA）方案与NOMA性能相当。然而，当约束放松时，NOMA性能优于TDMA。