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1. 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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2. Truthful and Optimal Data Preservation in Base Station-less Sensor Networks: An Integrated Game Theory and Network Flow Approach

   https://doi.org/10.1145/3606263  

   Yu, Yuning ; Hsu, Shanglin ; Chen, Andre ; Chen, Yutian ; Tang, Bin ( October 2023 , ACM Transactions on Sensor Networks)

   We aim to preserve a large amount of data generated insidebase station-less sensor networks(BSNs) while considering that sensor nodes are selfish. BSNs refer to emerging sensing applications deployed in challenging and inhospitable environments (e.g., underwater exploration); as such, there do not exist data-collecting base stations in the BSN to collect the data. Consequently, the generated data has to be stored inside the BSN before uploading opportunities become available. Our goal is to preserve the data inside the BSN with minimum energy cost by incentivizing the storage- and energy-constrained sensor nodes to participate in the data preservation process. We refer to the problem as DPP:datapreservationproblem in the BSN. Previous research assumes that all the sensor nodes are cooperative and that sensors have infinite battery power and design a minimum-cost flow-based data preservation solution. However, in a distributed setting and under different control, the resource-constrained sensor nodes could behave selfishly only to conserve their resources and maximize their benefit.

   In this article, we first solve DPP by designing an integer linear programming (ILP)-based optimal solution without considering selfishness. We then establish a game-theoretical framework that achieves provably truthful and optimal data preservation in BSNs. For a special case of DPP wherein nodes are not energy-constrained, referred to as DPP-W, we design a data preservation game DPG-1 that integrates algorithmic mechanism design (AMD) and a more efficient minimum cost flow-based data preservation solution. We show that DPG-1 yields dominant strategies for sensor nodes and delivers truthful and optimal data preservation. For the general case of DPP (wherein nodes are energy-constrained), however, DPG-1 fails to achieve truthful and optimal data preservation. Utilizing packet-level flow observation of sensor node behaviors computed by minimum cost flow and ILP, we uncover the cause of the failure of the DPG-1. It is due to the packet dropping by the selfish nodes that manipulate the AMD technique. We then design a data preservation game DPG-2 for DPP that traces and punishes manipulative nodes in the BSN. We show that DPG-2 delivers dominant strategies for truth-telling nodes and achieves provably optimal data preservation with cheat-proof guarantees. Via extensive simulations under different network parameters and dynamics, we show that our games achieve system-wide data preservation solutions with optimal energy cost while enforcing truth-telling of sensor nodes about their private cost types. One salient feature of our work is its integrated game theory and network flows approach. With the observation of flow level sensor node behaviors provided by the network flows, our proposed games can synthesize “microscopic” (i.e., selfish and local) behaviors of sensor nodes and yield targeted “macroscopic” (i.e., optimal and global) network performance of data preservation in the BSN.

    

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3. On the Accuracy of Network Synchronization Using Persistent Hourglass Clocks

   https://doi.org/10.1145/3362053.3363497  

   Çürük, Eren ; Yıldırım, Kasim Sinan ; Pawelczak, Przemyslaw ; Hester, Josiah ( January 2019 , Proceedings of the 7th International Workshop on Energy Harvesting & Energy-Neutral Sensing Systems)

   Batteryless sensor nodes compute, sense, and communicate using only energy harvested from the ambient. These devices promise long maintenance free operation in hard to deploy scenarios, making them an attractive alternative to battery-powered wireless sensor networks. However, complications from frequent power failures due to unpredictable ambient energy stand in the way of robust network operation. Unlike continuously-powered systems, intermittently-powered batteryless nodes lose their time upon each reboot, along with all volatile memory, making synchronization and coordination difficult. In this paper, we consider the case where each batteryless sensor is equipped with a hourglass capacitor to estimate the elapsed time between power failures. Contrary to prior work that focused on providing a continuous notion of time for a single batteryless sensor, we consider a network of batteryless sensors and explore how to provide a network-wide, continuous, and synchronous notion of time. First, we build a mathematical model that represents the estimated time between power failures by using hourglass capacitors. This allowed us to simulate the local (and continuous) time of a single batteryless node. Second, we show--through simulations--the effect of hourglass capacitors and in turn the performance degradation of the state of the art synchronization protocol in wireless sensor networks in a network of batteryless devices. 

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4. Dispersed passive RF-sensing for 3D structural health monitoring

   https://doi.org/10.52953/ZQYZ8264  

   Ahmad, Abeer ; Sha, Xiao ; Athalye, Akshay ; Das, Samir R. ; Caylor, Kelly ; Glisic, Branko ; Stanacevic, Milutin ; Djuric, Petar M. ( January 2022 , ITU Journal on Future and Evolving Technologies)

   We propose a sensing system comprising a large network of tiny, battery-less, Radio Frequency (RF)-powered sensors that use backscatter communication. The sensors use an entirely passive technique to 'sense' the parameters of the wireless channel between themselves. Since the material properties influence RF channels, this fine-grain sensing can uncover multiple material properties both at a large scale and fine spatial resolution. In this paper, we study the feasibility of the proposed passive technique for monitoring parameters of material in which the sensors are embedded. We performed a set of experiments where the sensor-to-sensor wireless channel parameters are well-defined using physics-based modeling, and we compared the theoretical and experimentally obtained values. For some material parameters of interest, like humidity or strain, the relationship with the observed wireless channel parameters have to be modeled relying on data-driven approaches. The initial experiments show an observable difference in the sensor-to-sensor channel phase with variation in the applied weights. 

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5. Networkless Wireless Sensing for Bridge Structural Health Monitor

   Afonso, B. ; Liu, H. ; Yu, Z. ( September 2022 , IEEE/MIT Undergraduate Research Technology Conference (URTC))

   The recent report by American Society of Civil Engineers gave the nation's bridges an unimpressive C grade. Across the country, more than 617,000 highway bridges: 46,154 structurally deficient and 42% 50+ years old. Continuous bridge assessment is essential to protect public safety. Federal Highway Administration requires all highway bridges inspected once every 24 months. However, any drastic change on bridges within 24 months will be left undetected. Nonetheless, bridge inspection is time-consuming and labor-intensive. Civil engineers have been using bridge health monitoring (BHM) systems with wired and/or wireless sensors to measure structural response (e.g., displacement, strain, acceleration) of a bridge. The response measurements are then converted to the information related to structural health for assessment. State-of-the-art BHM technology deploys sensor networks to facilitate data connection. Installing cables is expensive and subject to extreme weather. Wireless solutions face challenges such as energy consumption. Sensors are battery-powered. Another not well-publicized problem is security threats inherited in wireless networks. Our approach to wireless BHM is to utilize sensors networkless by collecting data with a drone. Similar to a mail carrier who goes around and picks up the mail, a drone collects data from sensors throughout the bridge. A drone eliminates restrictions for civil engineers on node placement since the drone replaces sink nodes. Networkless makes BHM less prone to attacks such as Jamming and DoS. To secure access, we deploy a Needham-Schroeder authentication protocol for the drone to collect data from sensor nodes securely. Networkless sensing for BHM benefits energy efficiency. It saves battery life as the sensor nodes remain asleep until scheduled transmission or woken up by a drone. It reduces design complexity and operation energy. The system also assures security since there is no vulnerable network to be attacked. 

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