| 摘要 |
Systems and techniques for RFID communication using a frequency shift between uplink and downlink carrier frequencies achieved by digital processing of a baseband signal before radio frequency modulation of a carrier signal occurs. Generation of the carrier signal, and modulation of the carrier signal, is accomplished using digital techniques. A digital representation of a baseband signal is modulated to create a complex baseband signal multiplied by a negative frequency shift equal to a difference between downlink and uplink carrier frequencies. This signal undergoes analog to digital conversion and modulation by a carrier signal at an uplink frequency. The complex baseband signal includes in-phase and quadrature components. During uplink communication, the in-phase component of the complex baseband signal is replaced by a constant value. The quadrature component is replaced by a zero signal. During uplink communication, therefore, an umodulated carrier signal at an uplink frequency is generated.
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