Coded QAM Backscatter Modulation for RFID

Radio Frequency Identification (RFID) systems, presently standardized under EPC Global Class-1 Gen-2, have attracted increasing interest as the next-generation technology for tagged object identification. One of the important objectives of this work is to highlight the fact that the performance of the backscatter uplink (determined by constellation choice and forward error correction) is coupled to the downlink via the power harvesting functionality. The concept of normalized power loss per bit is introduced for such RFID communication systems to capture the consequent trade-offs, that form the crux of the results. We explore the use of higher dimensional (4-QAM) modulation schemes in future RFID systems (beyond current binary modulation in Class-1 Gen 2) as a means to improve uplink bit rate. However, this results in significantly increased normalized power loss vis-a-vis 2-PSK, suggesting a role for FEC coding. New coded modulation schemes - based on unequal error protection - are proposed that provides additional degrees of freedom (via choice of code parameters) to trade-off spectral efficiency with normalized power loss. This is explored and quantified, resulting in design recommendations.