在本論文中，我們考慮一個蜂窩網路連線無人機的路徑設計和基地 台連線策略問題。 為了維持可靠連線需求，無人機在飛行期間必須與 蜂窩網路保持連線。 由於地面基地台對無人機的天線增益會隨著無人 機位置而改變，因此無人機對基地台的連線策略應與飛行路徑共同考 慮，然而在現有文獻中尚未研究無人機路徑與連線策略的共同設計。 在本論文中，我們首先提出了共同規劃基地台連線策略和路徑設計的 問題，其目標為確保無人機與基地台在可容忍中斷連線的限制下最小 化任務完成時間。 然後，我們提出一個深度學習框架解決該非凸最佳 化問題。 對於無人機與基地台的連線策略，我們建構了一個在指定區 域內的信號強度無線電圖，用於訓練深度神經網路以近似無人機位置 和最佳連線基地台的非線性映射關係。 為了解決基地台連線策略和路 徑設計共同決策而導致的高複雜性問題，我們提出了一種新穎的深度 強化學習方法來學習無人機最佳路徑，在該方法中無人機可以從過去 的良好經驗中學習策略。 我們的結果顯示了在路徑長度方面，與現有 深度強化學習方法相比，所提出之改進方法更具有優勢。 此外，使用 傳統選擇離無人機最近基地台的連線策略無法提供可靠的連線品質要 求，相較之下我們所提出的方法可以確保無人機在整條路徑上與基地 台保持可靠的通訊品質。;This paper concerns the problem of trajectory design and base station (BS) association for cellular-connected unmanned aerial vehicles (UAVs). To support safety-critical functions, one primary requirement for UAVs is to maintain reliable cellular connectivity at every time instant during the flight mission. Since the antenna gain of a ground BS (GBS) changes with the position of the UAV, the UAV-GBS association strategy should be jointly considered with the trajectory design, which has not been studied in the prior arts. In this paper, we first formulate the problem of joint BS association and trajectory design with the objective of minimizing the mission completion time under a connectivity outage constraint. Then, a deep learning framework is proposed to solve the formulated non-convex optimization problem in a decoupled manner. For the UAV-GBS association strategy, the signal strength radio map of a given area is constructed, which is used to train a deep neural network (DNN) to approximate the nonlinear mapping from the UAV position to the optimal GBS. To tackle the high complexity due to the coupled decision variables of GBS association and UAV movement, a novel deep reinforcement learning (DRL) approach is developed to learn the optimal trajectory, in which the UAV can learn from its own past good experiences. Our simulation results confirm the superiority of the proposed DRL approach compared to the conventional DRL approaches in terms of trajectory length. Additionally, it is demonstrated that the nearest association scheme fails to provide reliable cellular connections, whereas our proposed approach can ensure strong connectivity with the GBS during the whole trajectory.
