RIS-aided cooperative UAV swarm for mmWave communications in urban environments

Abstract

This paper investigates the integration of
reconfigurable intelligent surfaces (RIS) mounted on cooperative
unmanned aerial vehicle (UAV) swarms to enhance mmWave
communication in dense urban environments. While mmWave
bands offer large bandwidths for high data rates, their severe path
loss and blockage remain major obstacles in practical
deployments. UAVs provide flexible line-of-sight (LoS)
connectivity, whereas RIS enables programmable reflection to
strengthen non-line-of-sight (NLoS) links. By combining these
technologies, we develop a proposed framework that determines
UAV positions and RIS phase configurations under realistic
constraints, including quantized RIS phases, UAV, and flight
restrictions. Simulation results demonstrate that RIS-aided UAV
swarms significantly improve system reliability compared to
single-UAV or non-RIS baselines. The findings reveal that both
UAV swarm size and number of RIS elements strongly influence
performance: average signal-to-noise ratio (SNR) increases with
more UAVs, bit error rate (BER) decreases with RIS enlargement,
and outage probability exhibits a steep once the number of UAVs
and RIS elements is reached a certain limits. In particular, swarms
of four to five UAVs with 16–20 RIS elements achieve outage
probabilities below 0.05, ensuring near–ultra-reliable
communication while balancing energy and hardware costs. These
results confirm that cooperative RIS-enabled UAV swarms are a
promising solution for robust mmWave coverage in urban 6G
networks.