[Paper Review] Base Station Antenna Uptilt Optimization for Cellular-Connected Drone Corridors

Sung Joon Maeng, Md Moin Uddin Chowdhury+3 more|arXiv (Cornell University)|Jul 2, 2021

UAV Applications and Optimization9 references4 citations

TL;DR

This paper proposes optimizing base station antenna uptilt angles to minimize outage probability in cellular-connected drone corridors, using a 2D model with two adjacent BSs and directional antennas. The key finding is that the optimal uptilt angle minimizes SINR outage by balancing beamwidth and corridor height, with performance peaking when the entire beam covers the corridor without interference (Case 5).

ABSTRACT

The concept of drone corridors is recently getting more attention to enable connected, safe, and secure flight zones in the national airspace. To support beyond visual line of sight (BVLOS) operations of aerial vehicles in a drone corridor, cellular base stations (BSs) serve as a convenient infrastructure, since such BSs are widely deployed to provide seamless wireless coverage. However, antennas in the existing cellular networks are down-tilted to optimally serve their ground users, which results in coverage holes if they are also used to serve drones. In this letter, we consider the use of additional uptilted antennas at cellular BSs and optimize the uptilt angle to minimize outage probability for a given drone corridor. Our numerical results show how the beamwidth and the maximum drone corridor height affect the optimal value of the antenna uptilt angle.

Motivation & Objective

• Address the challenge of coverage holes in cellular networks when serving drones due to down-tilted BS antennas designed for ground users.
• Enable reliable beyond visual line of sight (BVLOS) connectivity for drones in designated corridors using additional uptilted antennas.
• Analyze how beamwidth and maximum drone corridor height affect optimal uptilt angle selection.
• Derive closed-form expressions for SINR outage probability and average SINR to evaluate system performance.
• Identify five distinct coverage cases based on uptilt angle and beamwidth, with Case 5 representing ideal beam alignment.

Proposed method

• Model a 2D drone corridor served by two adjacent base stations with directional, uptilted antennas.
• Use probability density functions to describe UAV distribution in horizontal (dx) and vertical (hx) dimensions within the corridor.
• Derive the SINR outage probability using analytical expressions based on beam alignment and interference from the neighboring BS.
• Formulate average SINR as a function of uptilt angle, beamwidth, and corridor height, with closed-form solutions for each of five coverage cases.
• Apply PDF transformation and integration techniques to compute outage probability and average SINR over the corridor area.
• Validate analytical results using Monte Carlo simulations with realistic parameters (e.g., 3 GHz, 100 MHz bandwidth, 30 dBm transmit power).

Experimental results

Research questions

• RQ1 How does the optimal antenna uptilt angle vary with beamwidth and maximum drone corridor height to minimize SINR outage probability?
• RQ2 What are the five distinct coverage scenarios that arise from different combinations of uptilt angle and beamwidth?
• RQ3 In which coverage case is the average SINR maximized, and what conditions define this case?
• RQ4 How does interference from the neighboring base station affect the SINR performance across different uptilt angles?
• RQ5 What trade-offs exist between beamwidth and performance in terms of outage probability and average SINR?

Key findings

• The SINR outage probability is a convex function of the uptilt angle, enabling global optimization via first-order derivative methods.
• Optimal uptilt angles decrease as the maximum drone corridor height increases, with performance degrading at extreme tilt values.
• Wider beamwidth reduces outage probability, while narrower beamwidth improves average SINR when the beam fully covers the corridor.
• The maximum average SINR is achieved in Case 5, where the entire beamwidth (from α to α+β) lies within the drone corridor without interference.
• For a 300 m maximum corridor height and 50° beamwidth, the optimal uptilt angle minimizes outage probability, with performance improving as beamwidth increases.
• Lower maximum corridor height (e.g., 200 m vs. 500 m) significantly improves both outage probability and average SINR across all beamwidths.