In this chapter, we have introduced existing solutions in the literature aiming to improve the performance of ambient backscattercommunication systems (ABCSs). We have first provided the reviews on several multiple access schemes that allows multiple transmitters backscatter data to the receiver. Then, solutions focusing on improving the communication range, bitrate, reliability, and robustness are presented in details. Finally, we have discussed challenges and future research directions to further improve the performance of ABCSs.

In this chapter, we focus on how wireless communication resources (spectral, temporal, and power) can be optimized and managed in wireless networks that support UAVsWestart by analyzing a very unique problem related to wireless networks supported by hovering UAV base stations: Cell association in hover time constraints. We show how the presence of hover time constraints for the UAVs will drastically change the way in which cell association is performed. Then, we generalize the problem of cell association to a fully fledged 3D cellular system that integrates both UAV base stations and UAV user equipment. Subsequently, we investigate the problem of spectrum and cache management in a wireless network supported by UAV base stations that are able to access both licensed and unlicensed spectrum resources.