The objective of this dissertation research is to redesign standard backscatter modulation signaling techniques and circuitry for ultra-high-frequency (UHF) RFID technology, enabling improved communications, detection, and identification in next-generation RFID applications and systems. The functionalities hoped to be achieved by this research work are link assessment with adaptive modulation, detection and identification of tags with harmonic signature generation, and simultaneous communications with multiple tags. RFID tags use minimalist and low-power (micro-watts) circuitry. Their simple hardware design has made RFID technology and its backscatter communication techniques prime candidates to be the foundation of future energy-efficient wireless communications systems. New features, such as adaptive modulation, harmonic signature identification, and simultaneous communications, will make RFID technology more robust and versatile so that it can be used in any environment for any applications in ever-growing cyber-physical radio systems.