Subcarrier frequency division multiplexing of modulated backscatter signals

摘要

A communication system comprises an Interrogator (103) and one or more Tags (105). The Interrogator (103) generates a modulated carrier signal by modulating a first information signal onto a radio signal. The Interrogator transmits a downlink signal which comprises the modulated carrier signal and the radio signal. A Tag (105) receives and processes the downlink signal. Specifically, the Tag demodulates the first information signal from the modulated carrier signal and generates a second information signal typically based on the contents of the first information signal. The second information signal is used to modulate a subcarrier signal, thereby generating a modulated subcarrier signal. A Backscatter Modulator using this modulated subcarrier signal modulates the reflection of the radio signal, wherein the reflected signal is an uplink signal. The Interrogator (103) receives and demodulates the uplink signal using homodyne detection to obtain the modulated subcarrier signal, which is then demodulated using a subcarrier demodulator to obtain the second information signal. In one embodiment, frequency of the subcarrier signal is an integer multiple of the second information signal symbol rate and is up to half the sampling rate of the subcarrier demodulator. <IMAGE>