In the fractional frequency reuse (FFR) system, the bandwidth is partitioned into orthogonal subbands such that users in the cell-center region use the subbands of a frequency reuse factor (FR factor) equal to 1, whereas users in the cell-edge region exploit the subbands of an FR factor larger than 1. The distance threshold, which is used to distinguish the cell-edge region from the cell-center region, is an important factor in FFR system performance. In this paper, we study the optimal distance threshold to maximize system throughput in the downlink cellular networks, including aerial base stations. Subject to the constraint that a given target outage probability is satisfied, the optimal distance threshold is analyzed as a function of the cell size. It is proven that when the sizes of all cells in the network are scaled at the same rate, the optimal distance threshold normalized by the cell size is nondecreasing in the cell size. The analytical results in this paper provide a system design guideline for initial planning of FFR cellular networks of different sizes, including macro, pico, and femto systems. In particular, for size-scalable aerial networks comprising base stations in the sky, such as balloons or unmanned aerial vehicles, our analysis offers insight into the design of the distance threshold with regard to the cell size.

中文翻译：

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规模可扩展网络中分数频率复用的最佳距离阈值

在分数频率复用 (FFR) 系统中，带宽被划分为正交子带，以便小区中心区域的用户使用频率复用因子（FR 因子）等于 1 的子带，而小区边缘区域的用户使用频率复用因子（FR 因子）的子带利用大于 1 的 FR 因子的子带。用于区分小区边缘区域和小区中心区域的距离阈值是 FFR 系统性能的重要因素。在本文中，我们研究了在下行蜂窝网络（包括空中基站）中最大化系统吞吐量的最佳距离阈值。在满足给定目标中断概率的约束下，最佳距离阈值被分析为小区大小的函数。证明当网络中所有单元的大小以相同的比例缩放时，由单元大小归一化的最佳距离阈值在单元大小中是不减少的。本文中的分析结果为不同规模的 FFR 蜂窝网络（包括宏、微微和毫微微系统）的初始规划提供了系统设计指南。特别是，对于包含空中基站（例如气球或无人驾驶飞行器）的规模可扩展的空中网络，我们的分析提供了对与小区大小相关的距离阈值设计的深入了解。