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1. Multi-hop routing protocols for RFID systems with tag-to-tag communication

   https://doi.org/10.1109/MILCOM.2017.8170764  

   Liu, Chang; Haas, Zygmunt J. (October 2017, IEEE Military Communications Conference)

   Radio frequency identification (RFID) is a technology for automated identification of objects and people. RFID technology is expected to find extensive use in applications related to the Internet of Things, and in particular applications of Internet of Battlefield Things. Of particular interest are passive RFID tags due to a number of their salient advantages. Such tags, lacking energy sources of their own, use backscattering of the power of an RF source (a reader) to communicate. Recently, passive RFID tag-to-tag (T2T) communication has been demonstrated, via which tags can directly communicate with each other and share information. This opens the possibility of building a Network of Tags (NeTa), in which the passive tags communicate among themselves to perform data processing functions. Among possible applications of NeTa are monitoring services in hard-to-reach locations. As an essential step toward implementation of NeTa, we consider a novel multi-hop network architecture; in particular, with the proposed novel turbo backscattering operation, inter-tag distances can be significantly increased. Due to the interference among tags’ transmissions, one of the main technical challenges of implementing such the NeTa architecture is the routing protocol design. In this paper, we introduce a design of a routing protocol, which is based on a solution of a non-linear binary optimization problem. We study the performance of the proposed protocol and investigate impacts of several network factors, such as the tag density and the transmit power of the reader. 

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2. High Sensitivity Near-zero Power Wakeup Receiver for Backscattering RF Tags

   https://doi.org/10.1109/ISCAS48785.2022.9937291  

   Sha, Xiao; Zheng, Puyang; Stanacevic, Milutin (May 2022, 2022 IEEE International Symposium on Circuits and Systems (ISCAS))

   We present a wake-up receiver amenable to integration in a node of RF backscattering tag-to-tag network. A high input impedance of a passive envelope detector (ED) is accomplished by backward bias that improves the passive voltage gain. Two differential outputs are ac-coupled to a baseband amplifier that operates in the subthreshold region. We develop a closed-form model of the passive ED in order to predict the output and ripple voltages and therefor the receiver’s sensitivity. The wakeup receiver is implemented in 180 nm CMOS technology and consumes 2 nW with 0.8 V supply voltage while demodulating 915 MHz amplitude-shift keying (ASK) signal with data rate of 10 kbps. The receiver demonstrates -67.98 dBm sensitivity in resolving ASK modulated signal. 

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3. Receiver Selectivity Limits on Bistatic Backscatter Range

   https://doi.org/10.1109/RFID49298.2020.9244826  

   Katanbaf, Mohamad; Saffari, Ali; Smith, Joshua R. (September 2020, 2020 IEEE International Conference on RFID (RFID))

   null (Ed.)

   Backscatter communication has been a popular choice in low-power/battery-free sensor nodes development. However, the effect of RF source to receiver distance on the operating range of this communication system has not been modeled accurately. In this paper, we propose a model for a bistatic backscatter system coverage map based on the receiver selectivity, receiver sensitivity, and geometric placement of the receiver, RF source, and the tag. To verify our proposed model and simulations, we perform an experiment using a low-cost commercial BLE receiver and a custom-designed BLE backscatter tag. We also show that the receiver selectivity might depend on the interference level, and present measurement results to signify how this dependence relates the system bit error rate to the RF excitation power. 

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4. Communication by means of modulated Johnson noise

   https://doi.org/10.1073/pnas.2201337119  

   Kapetanovic, Zerina; Morales, Miguel; Smith, Joshua R. (December 2022, Proceedings of the National Academy of Sciences)

   We present the design of a passive wireless communication method that does not rely on ambient or generated RF sources. Instead, the method modulates the Johnson (thermal) noise of a resistor to transmit information bits wirelessly. By selectively connecting or disconnecting a matched resistor to an antenna, the system can achieve data rates of up to 26 bps and distances of up to 7.3 m. This communication method operates at very low power, similar to that of an RFID tag, with the advantage of not requiring a preexisting RF signal to reflect. 

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5. Leveraging RF Power for Intelligent Tag Networks

   https://doi.org/10.1145/3194554.3194621  

   Salman, Emre; Stanaćević, Milutin; Das, Samir; Djurić, Petar M. (May 2018, Proceedings of the Great Lakes Symposium on VLSI)

   A novel framework and related methodologies are described to leverage RF power for building intelligent and battery-free devices with communication and computation capabilities. These passive devices are envisioned to make significant impact for the popular vision of smart dust due to extreme low power operation. The communication framework relies on tag-to-tag backscattering with very limited energy resources. The computing framework relies on a novel AC computing methodology that facilitates local data processing with an order of magnitude less power consumption. These enabling technologies, as described in this paper, revitalize the concept of smart dust with significant impact on various application domains such as smart spaces, implantable devices, and environmental/structural monitoring. 

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