A 96 Mbit/sec, 15.5 pJ/bit 16-QAM modulator for UHF backscatter communication

We describe a low power vector backscatter modulator capable of transmitting 16-QAM at a rate of 96 Mbps while consuming only 1.49 mW (15.5 pJ/bit). While designed around a center frequency of 915 MHz, the modulator is capable of operation over the worldwide 868-950 MHz UHF band. We present experimental results from the modulator operating in 4-QAM/4-PSK, 4-PAM, and 16-QAM modes. Achieved data rates are comparable to WiFi (IEEE 802.11) with a measured tag-side power consumption over 50 times lower than a WiFi chipset. Potential applications for low power, high bit rate modulators include biotelemetry, high-bandwidth data transfer from camera tags or audio tags, uplink from mass storage tags, and exchange of large amounts of encryption or authentication data. Given a +36 dBm EIRP transmitter operating at 915 MHz, the semi-passive (battery-assisted) prototype tag is return link limited and has a theoretical maximum operating range of 17.01 m at 96 Mbps or 21.25 m at 40 Mbps.