Enhancing passive UHF RFID communication in multipath fading channels using time-varying continuous wave signals In this paper, time-varying continuous wave (CW) signals are proposed for passive ultrahigh frequency radio frequency identification (UHF RFID) communication in multipath fading channels. The energy of the CW signals transmitted by a RFID reader is used to power up the internal circuitry of the RF tags and to backscatter their information to the reader. In this paper, three different candidates of time-varying CW signals, namely linear FM, quadratic FM, and sinusoidal FM signals, are proposed to reduce the effects of the multipath fading on the energy of the impinged signal on the RF tag. This will result in stronger backscatter signal to the reader and larger RFID system reading range. The results show that the performance of passive UHF RFID communication is considerably enhanced when the proposed signals are used.