The coexistence of terrestrial networks (TN) and non-terrestrial networks (NTN) in the frequency range 3 (FR3) upper mid-band presents considerable interference concerns, as dense TN deployments can severely degrade NTN downlink performance. Existing studies rely on interference-nulling beamforming, precoding, or exclusion zones that require accurate channel state information (CSI) and static coordination, making them unsuitable for dynamic NTN scenarios. To overcome these limitations, we develop an optimization framework that jointly controls TN downlink power, uplink power, and antenna downtilt to protect NTN links while preserving terrestrial performance. The resultant non-convex coupling between TN and NTN parameters is addressed by a Proximal Policy Optimization (PPO)-based reinforcement learning method that develops adaptive power and tilt control strategies. Simulation results demonstrate a reduction up to 8 dB in the median interference-to-noise ratio (INR) while maintaining over 87% TN basestation activity, outperforming conventional baseline methods and validating the feasibility of the proposed strategy for FR3 coexistence.

翻译：地面网络（TN）与非地面网络（NTN）在频率范围3（FR3）上中频段的共存带来了显著的干扰问题，因为密集的TN部署会严重降低NTN下行链路性能。现有研究依赖于干扰归零波束成形、预编码或排他区，这些方法需要精确的信道状态信息（CSI）和静态协调，因此不适用于动态NTN场景。为克服这些限制，我们开发了一个优化框架，联合控制TN下行链路功率、上行链路功率和天线倾角，以保护NTN链路，同时保持地面网络性能。由此产生的TN与NTN参数之间的非凸耦合问题，通过一种基于近端策略优化（PPO）的强化学习方法解决，该方法制定了自适应的功率与倾角控制策略。仿真结果表明，在保持超过87% TN基站活跃度的同时，中值干扰噪声比（INR）降低了高达8 dB，优于传统基线方法，并验证了所提策略在FR3共存场景下的可行性。