Switching Cells by Meaning, Not Bits: Semantic-Aware Sleep-Mode Control in Multi-Tier Aerial-Terrestrial Networks

Integrating uncrewed aerial vehicles (UAVs) and high-altitude platform stations (HAPS) into terrestrial cellular wireless networks is central to emerging sixth-generation (6G) communication systems. However, the energy budgets of both the ground network and the power-constrained aerial platforms are a serious concern. Cell switching, which selectively places lightly loaded small base stations (SBSs) into sleep mode, is an important energy-saving mechanism, but existing feasibility criteria are typically based either on maintaining a target data rate or merely preserving coverage for the users originally served by the switched-off SBSs (i.e., displaced users). These two approaches represent opposite ends of the quality-energy tradeoff: rate-based policies require a high signal-to-interference-plus-noise ratio (SINR), limiting energy savings, whereas coverage-based policies permit more aggressive sleeping at the expense of quality of service (QoS). This work proposes a novel semantic-aware cell switching policy whose feasibility criterion is a semantic-service requirement rather than a bit-centric target: an SBS is put into a sleep mode if and only if its displaced users still satisfy an assumed semantic-service SINR criterion. The policy is tested in a multi-tier heterogeneous network comprising an always-on macro base station (MBS), switchable SBSs, a tier of UAV base stations (UAV-BSs), and a HAPS-mounted International Mobile Telecommunications (IMT) base station (HIBS), and it is solved by a greedy algorithm. For the deployment and parameter set considered, and with the HIBS present, the semantic criterion deactivates the entire SBS layer while every user continues to satisfy the assumed semantic-service SINR criterion, whereas the rate criterion deactivates none.