In this paper, we propose a waveform design methodology for ultra high frequency radio frequency identification (UHF RFID) systems based on the quantitative analysis of the backscattered signal. This latter is leveraged to probe the wireless propagation channel, allocate power accordingly to frequency components, and design channel-adaptive multisine signals. UHF RFID system performance is evaluated based on the harvested DC voltage at the output of the rectifying circuit of the RFID tag. To this end, a flexible hybrid simulation model with modular architecture is developed via the ANSYS platform to study UHF RFID system performance. Simulation results show that the designed waveforms provide an improved energetic efficiency especially in highly reflective environments.