What is backscatter communication?
Backscatter communication is a wireless communication method which utilizes reflection (backscatter) of radio wave. Backscatter communication nodes realize node-to-interrogator information transmission by modulating backscatter of radio wave from interrogators. The nodes does not transmit radio wave by themselves but only modulate the backscatter, thus they can be less-power-consumption and license-free.
One of typical applications of backscatter communication is UHF-band passive RFID system. The passive RFID realizes information retrieval from battery-free nodes (passive RF tags) at 10m distance from an interrogator by energy harvesting at the tags from interrogator’s transmission. Some of RF tags can transmit not only their own ID but also sensor data measured by their embedded sensors. Fully-passive sensor-enabled RF tags, which harvest energy not only for communication but also for sensors from interrogator’s transmission, are also commercially available.
Backscatter modulation
Backscatter communication nodes, e.g. RF tags in passive RFID systems, contain RF switches which change their impedance into 2 state. The node modulates the backscatter by changing its RF switch, i.e. changing reflected power.
Frequency of modulated backscatter can be either carrier frequency, where an interrogator transmits, or frequency which is shifted from the carrier frequency by certain subcarrier frequency. In the second choice, the subcarrier is generated by adding switching of the RF switch by subcarrier frequency, i.e. multiplying carrier frequency signal by subcarrier frequency signal.