Backscatter (or simply scatter) radio is based on reflection principles, where each tag modulates information on top of an illuminating signal, by simply connecting its antenna to different loads; modulation of information is based on the modifications of the tag antenna-load reflection coefficient, requiring in principle only a switch and omitting powerconsuming signal conditioning units, such as mixers, amplifiers, oscillators, and filters. The ultralow-power nature of backscatter radio, in conjunction with the recent advances in multiple access and achieved communication ranges (on the order of hundreds of meters to kilometers), due to intelligent signal processing, elevate backscatter radio as the de facto communication principle e for nW (or less)-level consumption, last-mile connectivity, and Internet of Things (IoT) networking. This article is an update to the state-of-the-art advances in the emerging backscatter radio domain, focusing on the signal processing engine, including ambient illumination from existing signals, as well as unconventional backscatter radio-based IoT technologies that could revolutionize environmental sensing and agriculture. Finally, the offered research methodology and techniques in short-packet, channel-encoded (or not), coherent (or not) sequence detection will assist researchers in radio-frequency identification (RFID)/backscatter radio as well as other domains of the telecommunications industry.

This paper studies whether increased ranges of bistatic scatter radio communication are possible, especially when low-cost, embedded receivers, originally designed for conventional radio (and not for scatter radio) are employed. Wireless power transmission and bistatic scatter radio are closely related, and thus, this work aims to highlight a new exciting, potentially interesting, key-enabling research direction. It is found that for 13 dBm emitter transmission power, 246 meters scatter radio tag-to-reader distance is possible, with packet error rate (PER) less than 1%, while 268 meters are possible at the expense of increased PER, in the order of 10%.

This work compares different linear and nonlinear RF energy harvesting models, including limited or unlimited sensitivity, for simultaneous wireless information and power transfer (SWIPT). The probability of successful SWIPT reception under a family of radio frequency (RF) harvesting models is rigorously quantified, using state-of-the-art rectifiers in the context of commercial RFIDs. A significant portion of SWIPT literature uses oversimplified models that do not account for limited sensitivity or nonlinearity of the underlying harvesting circuitry. This work demonstrates how close to a practical scenario is the performance offered by a number of recently proposed RF energy harvesting models and concludes that for practical SWIPT studies, the inherent non-ideal characteristics of the system should be carefully taken into account; specific modeling methodology is also proposed.

This work studies the performance of two methods for providing power to an ultra-low power, ambient backscatter tag, omitting the need for any battery. RF energy harvesting from a dedicated source and energy harvesting from ambient light using a single photodiode are compared. Extensive measurement results from tests conducted under real world conditions are offered for both harvesting methods. It is concluded that for a total cost of under 7 Euros the need for a battery can be eliminated, by using a single photodiode element along with a suitable boost converter. The ultra-low power character of the utilized tag enables the use of multiple harvesting methods and paves the way towards truly battery-less wireless sensor systems.

This work exploits ultra-low cost, commodity, radio frequency identification (RFID) tags as elements of a reconfigurable intelligent surface (RIS). Such batteryless tags are powered and controlled by a software-defined radio reader, with properly modified software, so that a source-destination link is assisted, operating at a different band. Signal model includes small-scale and large-scale fading, direct link, as well as specific parameters relevant to reflection (i.e., backscatter) radio, such as antenna structural mode and reflection efficiency, typically overlooked in the literature. An algorithm is offered that computes the optimal RIS configuration with complexity of O ( M log M ) in number of elements M , instead of intractable exponential complexity of exhaustive search, while accommodating any number K ≥ 2 of loads. With the proposed algorithm, it is shown that performance gains reach a plateau for constant element spacing and increasing number of elements, suggesting that the weak, passive nature of backscattered links limits the performance gains, even with perfect channel estimation. Channel estimation with linear minimum mean squared error (LMMSE) estimator is shown to be effective, provided that there are sufficient number of pilot symbols. A concrete way is offered to design and prototype a wireless, batteryless, RF-powered, reconfigurable surface and a proof-of-concept is experimentally demonstrated.

Passive Gen2 radio frequency identification (RFID) tags work thanks to the utilization of line codes that balance their operation between two opposite states: absorbing RF (for energy harvesting) and reflecting RF (for backscattering/communications). Given the current RF harvesting technology, batteryless tags need to be located very close to an active illuminator in order to harvest sufficient energy and operate. To tackle this limitation, prior art has tried to bring the illuminator closer to the tags by designing proprietary illuminating architectures. Our solution comes in two parts. First, we offer a novel, Gen2-compliant, near-optimal, noncoherent sequence detection algorithm with linear complexity (in the sequence length) for Miller line codes. We leverage the robustness of this algorithm to overcome issues inherent in multistatic setups, such as carrier frequency offset. Second, we propose a modular multistatic architecture that makes use of low-cost commodity software defined radios (SDR) and omnipresent Ethernet infrastructure. Simulations and experimental results in a monostatic, bistatic, or multistatic SDR testbed with commercial RFIDs, corroborate the low-cost, real-time and near-optimal flavor of our solution.