确保与具有向上倾斜天线和干扰协调的蜂窝连接无人机的可靠连接
Ensuring Reliable Connectivity to Cellular-Connected UAVs with Up-tilted Antennas and Interference Coordination
摘要：
为了在未来的大规模部署中集成无人机（UAV），一种新的无线通信范例，即蜂窝连接的UAV最近引起了人们的兴趣。然而，视距占主导地位的空对地信道以及蜂窝地面基站（GBS）的天线方向图在蜂窝连接的UAV通信中引入了严重的干扰问题。特别是，复杂的天线方向图和来自向下倾斜天线的地面反射（GR）为空中的UAV创建了覆盖漏洞和不完整的覆盖，这导致来自底层蜂窝网络的不可靠的连接。为了克服这些挑战，在本文中，我们提出了一种新的蜂窝架构，该架构采用了一组额外的面向天空的共信道天线，以支持地面用户设备（GUE）的现有下倾天线上的无人机。为了模拟来自下倾斜天线的GR，我们提出了一个路径损耗模型，该模型同时考虑了天线的辐射方向图和配置。接下来，我们制定了一个优化问题，以最大限度地提高最小信号干扰比（SIR）的无人机通过调整向上倾斜（UT）的角度向上倾斜的天线。由于这是一个NP难问题，我们提出了一种基于遗传算法（GA）的启发式方法来优化这些天线的UT角度。在获得最佳UT角度之后，我们整合3GPP Release-10指定的增强型小区间干扰协调（eICIC）以减少源自向下倾斜天线的干扰。基于六边形小区布局的仿真结果表明，与基线方法相比，所提出的干扰抑制方法可以确保无人机具有更高的最小信干比，同时对用户设备的信干比影响最小。
英文摘要：
To integrate unmanned aerial vehicles (UAVs) in future large-scale deployments, a new wireless communication paradigm, namely, the cellular-connected UAV has recently attracted interest. However, the line-of-sight dominant air-to-ground channels along with the antenna pattern of the cellular ground base stations (GBSs) introduce critical interference issues in cellular-connected UAV communications. In particular, the complex antenna pattern and the ground reflection (GR) from the down-tilted antennas create both coverage holes and patchy coverage for the UAVs in the sky, which leads to unreliable connectivity from the underlying cellular network. To overcome these challenges, in this paper, we propose a new cellular architecture that employs an extra set of co-channel antennas oriented towards the sky to support UAVs on top of the existing down-tilted antennas for ground user equipment (GUE). To model the GR stemming from the down-tilted antennas, we propose a path-loss model, which takes both antenna radiation pattern and configuration into account. Next, we formulate an optimization problem to maximize the minimum signal-to-interference ratio (SIR) of the UAVs by tuning the up-tilt (UT) angles of the up-tilted antennas. Since this is an NP-hard problem, we propose a genetic algorithm (GA) based heuristic method to optimize the UT angles of these antennas. After obtaining the optimal UT angles, we integrate the 3GPP Release-10 specified enhanced inter-cell interference coordination (eICIC) to reduce the interference stemming from the down-tilted antennas. Our simulation results based on the hexagonal cell layout show that the proposed interference mitigation method can ensure higher minimum SIRs for the UAVs over baseline methods while creating minimal impact on the SIR of GUEs.
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