In cellular networks, the performance of cell-edge users is notably deficient, especially for those receiving almost comparable signal strengths from the serving base station (BS) and interfering BS(s). To improve their performance, a cell-edge UAV deployment scheme is proposed, where the UAVs are deployed to hover over these cell-edge users to serve them. Specifically, the locations of BSs are modeled using a Poisson point process (PPP) and the Voronoi cells are formed. We consider two distinct types of cell-edge users positioned at the Voronoi vertices and boundaries, corresponding to the worst-case and boundary users, respectively. Due to the intractable spatial distribution of the interfering UAVs, we utilize the PPP and binomial point process (BPP) approximations to characterize their interference. Subsequently, we derive the success probabilities for these two types of cell-edge users. The results show the similar effectiveness of the two approximate models for the locations of the UAVs. Furthermore, we obtain the asymptotic success probabilities to analyze the performance in high-reliability regimes and propose an effective approximation based on the asymptotic behavior to simplify the analytical expressions. The results highlight the substantial performance enhancement through the proposed UAV deployment scheme for cell-edge users.

To address the poor performance experienced by cell-corner users located equidistantly to the serving base station (BS) and the nearest interfering BSs, this paper proposes a flexible and general air-ground cooperation scheme based on unmanned aerial vehicles and dynamic BS coordination in the form of BS silencing (BSS) or joint transmission (JT). To show the role of unmanned aerial vehicle (UAV) in the cooperation, we define the UAV-to-BS power ratio (UBPR) as a critical parameter to measure whether introducing the UAV can improve the user’s performance. Using stochastic geometry tools, we derive the success probability of the user located at the corner of the Voronoi diagram, called the worst-case user, in Poisson cellular networks. To facilitate the comparison between different modes of cooperation, we further analyze the cooperation gain including the diversity and power gains through the asymptotic outage probability in the high-reliability regime. Furthermore, to reflect the impact of the cooperation scheme on the overall network performance, we analyze the normalized spectral efficiency, which, unlike those adopted in existing works, accounts for the costs of both resource occupancy and data exchange. Numerical results validate the accuracy of our analytical findings and demonstrate the effectiveness of the proposed scheme for cell-corner users.

In cellular networks, the performance of cell-boundary users with almost equal distance from the serving base station (BS) and the nearest interfering BS(s) is extremely poor. In order to improve the performance of these users, this paper proposes a cell-boundary UAV deployment scheme. To quantify the performance enhancement, the locations of BSs are modeled as a Poisson point process forming Voronoi cells. Two distinct types of cell-boundary users located at the vertices and boundaries of Voronoi cells are served by a UAV-mounted BS hovering over them, and the success probabilities of these two types of users are derived with the stochastic geometry tool. Furthermore, the asymptotic success probabilities are obtained to analyze the performance in high-reliability regime and an effective approximation is proposed based on the asymptotic behavior to simplify the performance evaluation. Finally, the re-sults highlight the substantial performance enhancement achieved through UAV-assisted communication for the cell-boundary users.

To address the poor performance experienced by cell-edge users located equidistantly to the serving base station (BS) and the nearest interfering BS(s), this paper proposes an air-ground coordinated multipoint scheme assisted by unmanned aerial vehicles and the dynamic coordinated BSs selected from the sets of the serving and the equidistant interfering BSs. Using stochastic geometry tools, we derive success probabilities in a Poisson cellular network for the users located at corners of the Voronoi diagram called worst-case users served using non-coherent joint transmission. To reflect the impact of the coordinated transmission on the overall network performance, we also deduce the normalized spectral efficiency. Numerical results validate the accuracy of our analytical findings and show the superior performance of the proposed scheme for the worst-case users.