In this paper, we consider a multi-tier cellular network in which a hovering Unmanned Aerial Vehicle (UAV) assists the network in the absence of the terrestrial Macrocell base station. The orthogonal sub channels are assumed for communication between the UAV and its attached users. The Femtocell users and Device-to-Device (D2D) pairs transmit their data to the corresponding receivers in the same sub-channels. Achieving the outage probability of the ground users, is a challenge for the operators considering the dominant small scale and large scale fading over the channels, Line-of-Sight and None-Line-of-Sight conditions together. The mentioned problem becomes worse in the presence of cross-tier interferences. We investigate the outage probability of the ground UAV users to evaluate the performance of the network. Due to intractability of the calculations to derive the exact outage probability, the closed-form expressions are derived for the upper bound of outage probability under Rayleigh and Nakagami- fading. The effect of UAV altitude, density of D2Ds and corresponding transmission powers are discussed. The results verify the simulations and confirm that the proposed approach outperforms the existing upper bound methods.

中文翻译：

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衰落信道下无人机辅助蜂窝网络中断概率的上限


在本文中，我们考虑了一种多层蜂窝网络，其中悬停的无人机（UAV）在没有地面宏蜂窝基站的情况下协助网络。假设正交子信道用于无人机与其附属用户之间的通信。 Femtocell 用户和设备到设备 (D2D) 对在相同的子信道中将其数据传输到相应的接收器。考虑到信道上主要的小规模和大规模衰落、视距和非视距条件，实现地面用户的中断概率对运营商来说是一个挑战。在存在跨层干扰的情况下，上述问题变得更加严重。我们调查地面无人机用户的中断概率以评估网络的性能。由于计算得出精确的中断概率非常困难，因此导出了瑞利和 Nakagami 衰落下中断概率上限的封闭式表达式。讨论了无人机高度、D2D 密度和相应发射功率的影响。结果验证了模拟并确认所提出的方法优于现有的上限方法。