Instantaneous, Zero-Feedback Fading Mitigation With Simple Backscatter Radio Tags

This work offers a novel, backscatter radio-based, blind beamforming technique that assists the reception of signals in multipath conditions. The technique is based on simple, assistive backscattering tags, implemented without any means of signal amplification. These tags can blindly (i.e., without feedback) modify the phase of the associated wireless channels, leading to constructive addition of the multipath components (i.e., alignment). Such alignment events offer distributed beamforming gain. Analysis is performed and an expression for the probability of alignment is offered, along with an expression for the achievable gain, corroborated by simulations and experimental results. It is shown that increased number of assistive tags offers higher beamforming gain, at the expense of increased delay. The effectiveness of the proposed beamforming technique is highlighted with experiments and measurements on the radio frequency identification (RFID) Gen2 standard. Commercial RFIDs that initially could not be interrogated due to insufficient impinged power, were successfully interrogated hundreds of times/minute with the assistance of the beamforming tags. It was experimentally shown that the proposed beamforming tags can offer power gains in the range of 0.4 – 3.7 dB. While the technique was tested on commercial RFIDs, it is not limited to a specific communication standard.