  In the evolving landscape of sixth-generation (6G) wireless networks,
unmanned aerial vehicles (UAVs) have emerged as transformative tools for
dynamic and adaptive connectivity. However, dynamically adjusting their
position to offer favorable communication channels introduces operational
challenges in terms of energy consumption, especially when integrating advanced
communication technologies like reconfigurable intelligent surfaces (RISs) and
full-duplex relays (FDRs). To this end, by recognizing the pivotal role of UAV
mobility, the paper introduces an energy-aware trajectory design for
UAV-mounted RISs and UAV-mounted FDRs using the decode and forward (DF)
protocol, aiming to maximize the network minimum rate and enhance user
fairness, while taking into consideration the available on-board energy.
Specifically, this work highlights their distinct energy consumption
characteristics and their associated integration challenges by developing
appropriate energy consumption models for both UAV-mounted RISs and FDRs that
capture the intricate relationship between key factors such as weight, and
their operational characteristics. Furthermore, a joint time-division multiple
access (TDMA) user scheduling-UAV trajectory optimization problem is
formulated, considering the power dynamics of both systems, while assuring that
the UAV energy is not depleted mid-air. Finally, simulation results underscore
the importance of energy considerations in determining the optimal trajectory
and scheduling and provide insights into the performance comparison of
UAV-mounted RISs and FDRs in UAV-assisted wireless networks.
