在恆定模量限制下應用於低軌衛星通訊的寬主瓣波束成型技術

Abstract

衛星通訊在缺乏基礎通訊設施的偏遠地區因其仍能提供良好的網路連接而擁有優勢，然而因為衛星到地球的距離產生的路徑損耗，我們需要波束成型(beamforming)這個技術達成在特定方向上的接收地區有較高的訊號訊雜比(SNR)，就我們所知，這篇論文提出第一個應用於衛星通訊的寬波束設計並使用考慮恆定模量限制的均勻矩形陣列波束成型器，目的是為了可以一次服務較大的地域範圍。在最佳化問題設計中，我們確保每一個在如此寬廣的服務地區內的使用者都可以接收到足夠高的訊雜比，因此獲得良好的衛星通訊品質，在衛星通訊中，為了確保每個服務地區接收到的訊號都能維持在某個強度以上，在波束圖形設計時需要考慮一個等通量模型。在本篇論文中，我們提出應用到不同情境時需考慮的兩個波束成型器設計，第一個設計目標是在恆定模量下壓抑不在服務範圍內的波束強度，在第二個情境中，波束將覆蓋所有和和衛星之間是直線連線的地球表面，並同樣地保持恆定模量，對於這兩個兩個不是凸函數最佳化的問題，我們使用半正定鬆弛技術和Dattorro的疊代演算法來解決，最後，模擬結果顯示我們可成功地在恆定模量下產生這兩個寬波束設計。

Satellite communication (SatComm) holds the advantage of providing Internet connectivity to rural and remote areas lacking communication infrastructures. Beamformer is significant in SatComm since it plays a crucial role in enhancing the transmission signal's direction and increasing the signal-to-noise ratio (SNR) in a specific direction. To our knowledge, the first Uniform Rectangular Array (URA) beamformer for SatCom which ensures PA efficiency that can serve large areas with beam-broadening approach is proposed. The optimization problem is designed to guarantee that user equipment (UEs) can experience sufficient SNR to establish communication link with the SAT transmitter within the SAT service areas. And the isoflux radiation mask guarantees that the transmitted signal maintains nearly equal strength within the SAT service areas, regardless of the SAT elevation angle. Two scenarios of beam-broadening optimization problems are formulated. In the first scenario, we aim to suppress the maximum signal power in out-of-beam SAT service areas with the required beamwidth under constant modulus constraint (CMC). In the second scenario, we aim to achieve Earth-coverage under CMC. Both of the non-convex problems are solved with semidefinite relaxation (SDR) and Dattorro iterative algorithm. The simulation results illustrate the URA beampattern with a broadened beamwidth, ensuring the minimum received SNR in SAT service areas. Additionally, the derived beamforming coefficients satisfy the CMC.