Self-Interference Cancellation for Passive RFID

Carrier cancellation, self-interference suppression, isolation-enhancement – many names to tackle the same challenge: How to allow the receiver of an RFID reader to detect the weak back-scattered signal from a passive tag, while the collocated transmitter keeps radiating at the same carrier frequency to power the tag and allow backscattering. The strong transmit signal inevitably leaks into the reader’s receiver and causes overloading of the front-end and analog to digital converters. In this contribution we will describe the fundamental carrier leakage paths for monostatic and bi-static RFID readers, and analyze the impact of them in terms of SNR degradation and read range. Figures of merit will be introduced that allow easy comparison of different reader and antenna configurations, and indicate the importance of self-interference cancellation to avoid reverse-link limitation. We will present ways to increase isolation on the antenna and analog layer, discuss their bandwidths, and report on algorithms that can quickly adjust isolation-enhancers without expensive extra hardware.