地面通訊網路致力於服務位於都會的用戶通訊，但較低的覆蓋率與近距離傳輸使得通道效能受干擾影響嚴重，甚至無法在環境較嚴酷的地區建立良好的通訊，例如沙漠、海洋上等等。雖然衛星通訊的營運與發射成本較高，再加上長距離傳輸所帶來的高延遲問題，但衛星的大範圍涵蓋區域特性可補足地面通訊無法服務的地區，因此地面與非地面網路的頻譜共存設計成為現今討論度極高的主題。本論文探討由一個地面基站(BS)、一個低軌衛星(LEO)與數個地面用戶(UE)所構成的地面與非地面通訊在毫米波段的共存問題，其中衛星與地面基地台皆為多天線，地面用戶為單天線之下行鏈路(downlink)設計。地面用戶設計為可自由切換選擇連線地面基站(BS)或衛星(SAT)，考慮發射功率限制與連線品質(QoS)要求下，設計聯合總系統加權傳輸速率與准入連線數最佳化問題，並搭配波束成形技術(Beamforming)設計發射向量降低傳輸干擾，以最大化系統效能。;Terrestrial communication networks are primarily designed to serve users in metropolitan areas. However, their limited coverage and short-range transmission result in channel performance being severely affected by interference. They often struggle to establish reliable communication in harsh environments such as deserts and oceans. While satellite communication incurs higher operational and launch costs, along with the high latency associated with long-distance transmission, its wide coverage area can compensate for the limitations of terrestrial networks. Consequently, the co-existence of terrestrial and non-terrestrial networks (NTNs) is a highly discussed topic. This paper investigates the co-existence of terrestrial and non-terrestrial communications in the millimeter-wave band, consisting of a terrestrial base station (BS), a low-Earth orbit (LEO) satellite, and multiple terrestrial users (UEs). Both the satellite and the terrestrial base station are equipped with multiple antennas, while the terrestrial users have single antennas in the downlink design. The terrestrial users are designed to freely switch between connecting to the terrestrial base station (BS) or the satellite (SAT). Considering transmit power constraints and quality of service (QoS) requirements, we formulate a joint optimization problem to maximize the weighted sum rate and the number of admitted connections. This is achieved by designing transmit beamforming vectors to mitigate transmission interference, ultimately maximizing system performance.
