| 摘要: | 隨著射頻元件及天線技術的突破，基於Massive MIMO和OFDM的低軌道衛星（LEO）通訊在B5G大頻寬時代中日益普及。這項技術因能夠支持高資料傳輸率並顯著降低硬體成本，而受到廣泛關注，被視為未來網絡中極具潛力的技術之一。本論文針對多用戶（MU）Massive MIMO OFDM LEO衛星通訊系統，目標是最大化上行鏈路的總系統傳輸速率，同時在滿足每個用戶的服務質量（QoS）要求，如位元錯誤率和資料傳輸速率的情況下進行優化。
在子載波配置方面，我們採用拉格朗日優化方法來有效地分配子載波，以提升頻譜效率。此方法考量了各子載波的頻譜利用率及功率分配，確保在總功率限制下達到最佳配置效果。另一方面，針對用戶選擇，我們利用每個使用者在各子通道上的通道矩陣進行奇異值分解（SVD），從眾多候選用戶中優先選取通道條件較佳的用戶進行訊息傳輸。這樣的用戶選擇策略能夠有效提升系統的整體性能和頻譜利用率。
在傳輸過程中，不同頻率上的信號可能會受到不同程度的衰減、多路徑干擾及失真，導致通道的頻率響應有所差異，因此正交分頻多工（OFDM）被廣泛應用以對抗頻率選擇性衰落。此外，拉格朗日方法不僅應用於子載波配置，還用於功率分配，確保在多用戶環境下各用戶的傳輸需求得到滿足。
綜上所述，我們評估了所提出的子載波配置與用戶選擇方案在不同參數下的性能表現，並將其與其他基準方案進行比較。模擬結果顯示，所提出的子載波配置及基於SVD的用戶選擇方案在提升系統總傳輸速率及頻譜效率方面表現優異，並且使用迭代法來調整原資料流配置的結果，可增加其總頻譜效率。
;With advancements in radio frequency (RF) components and antenna technologies, Low Earth Orbit (LEO) satellite communications based on Massive Multiple-Input Multiple-Output (Massive MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) are becoming increasingly prevalent in the B5G era characterized by vast bandwidths. This technology has garnered significant attention due to its ability to support high data transmission rates while substantially reducing hardware costs, positioning it as one of the most promising technologies for future networks. This paper focuses on designing subcarrier allocation and user selection schemes for multi-user (MU) Massive MIMO OFDM LEO satellite communication systems with the objective of maximizing the total uplink system transmission rate. The optimization is performed while ensuring that each user’s Quality of Service (QoS) requirements, such as bit error rate and data transmission rate, are met.
For subcarrier allocation, we employ a Lagrangian optimization method to efficiently distribute subcarriers, thereby enhancing spectral efficiency. This approach considers the spectral utilization and power allocation of each subcarrier to achieve optimal configuration within the total power constraints. In terms of user selection, we utilize Singular Value Decomposition (SVD) on each user′s channel matrix across subchannels, prioritizing users with superior channel conditions from a pool of candidates for data transmission. This user selection strategy effectively improves the overall system performance and spectral utilization.
During the transmission process, signals at different frequencies may experience varying degrees of attenuation, multipath interference, and distortion, leading to differences in channel frequency responses. To counteract frequency-selective fading, Orthogonal Frequency Division Multiplexing (OFDM) is widely applied. Additionally, the Lagrangian method is not only used for subcarrier allocation but also for power distribution, ensuring that the transmission needs of all users are satisfied in a multi-user environment.
In summary, we evaluate the performance of the proposed subcarrier allocation and user selection schemes under various parameters and compare them with other benchmark schemes. Simulation results demonstrate that the proposed subcarrier allocation and SVD-based user selection schemes achieve highly competitive performance, surpassing traditional fully digital designs in terms of total transmission rate and spectral efficiency. Furthermore, iterative adjustments to the original data stream configurations enhance the overall spectral efficiency. |
