## 8 Conclusions  
The flying base station relies on the stationary terrestrial base station to bridge to the wired communications and connect to the cloud and Internet. Given a stationary base station's channel to the user and its SNR performance, we study the flying base station channel performance in channel capacity. The flying base station channel capacity builds on the Shannon capacity to quantify how much reliable bit transfer the channel _can_ support.  
However, in contrast to the traditional capacity analyses, the flying base station channel capacity considers both the stationary base station's channel and the mobility of the base station and assumes the ideal positioning of the flying base station. We, thus, analyze the flying base station's ideal position depending on the relative position of the stationary base station and the user. We also analyze the beneficial region and study the flying base station's transmission power requirement to become beneficial over the existing stationary base station's connectivity provision. According to our analyses, the flying base station provides multiplicative gains for the effective SNR on the user for the channel capacity where the gains are from reducing the transmission distance by half (\(2^{\gamma}\)) and the transmission power ratio (\(\eta\)). However, if the flying base station is not capable of full-duplex communication (i.e., half-duplex and cannot simultaneously transmit and receive communications), then there is a capacity decrease due to the bandwidth reduction to half. Thus, the flying base station's beneficialness over the stationary base station depends on both the stationary base station's SNR (SNR\({}_{SUI}\)) and the transmission power ratio (\(\eta\)) if the flying base station does not have the full duplex capability, while it will be beneficial independent of the stationary base stations' SNR (SNR\({}_{SUI}\)) if full-duplex capable. We introduce and analyze the flying base station's channel performance bound limit (flying base station channel capacity) to inform the flying base station R&D in the next-generation 6G and beyond-5G networking and include discussions for future directions.  
Conceptualization, S.-Y.C.; data curation, S.-Y.C.; formal analysis, S.-Y.C.; funding acquisition, S.-Y.C., J.K. ([PERSON]) and J.K. ([PERSON]); investigation, S.-Y.C. and J.K. ([PERSON]); methodology, S.-Y.C.; project administration, K.P., J.K. ([PERSON]) and J.K. ([PERSON]); resources, K.P.; software, S.-Y.C.; supervision, S.-Y.C., J.K. ([PERSON]) and J.K. ([PERSON]); validation, S.-Y.C.; visualization, S.-Y.C. and K.P.; writing--original draft, S.-Y.C.; writing--review & editing, S.-Y.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korean government (MSIT) (No.2021-0-00796, Research on Foundational Technologies for 6G Autonomous Security-by-Design to Guarantee Constant Quality of Security).  
There were no new data generated.  
This journal paper builds on and extends our previous conference paper at ACM SNTA 2024 titled _Flying Base Station Channel Capacity_[53]. In addition to the presentation and writing improvements, the extensions for this paper beyond the previous conference paper include the following: We establish stronger motivations for channel capacity and information-theoretic analyses, including decades of previous research driven by and utilizing them as the theoretical bound benchmarks in Sections 1 and 3.5. We provide greater simulation analyses and results, including those for full-duplex cases and the \(\gamma\) dependency in Section 6. We also update and add greater future-direction discussions to inform and facilitate future R&D in the flying base station in Section 7.  
The authors declare no conflicts of interest.