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1. NetScatter: Enabling Large-Scale Backscatter Networks

   Hessar, Mehrdad ; Najafi, Ali ; Gollakota, Shyamnath ( February 2019 , NSDI)

   We present the first wireless protocol that scales to hundreds of concurrent transmissions from backscatter devices. Our key innovation is a distributed coding mechanism that works below the noise floor, operates on backscatter devices and can decode all the concurrent transmissions at the receiver using a single FFT operation.Our design addresses practical issues such as timing and frequency synchronization as well as the near-far problem. We deploy our design using a testbed of backscatter hardware and show that our protocol scales to concurrent transmissions from 256 devices using a bandwidth of only 500 kHz.Our results show throughput and latency improvements of14–62x and 15–67x over existing approaches and 1–2 orders of magnitude higher transmission concurrency. 

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2. NetScatter: Enabling Large-Scale Backscatter Networks

   Hessar, M ; Najafi, A: Gollakota ( January 2019 , Proceedings of the 16th USENIX Symposium on Networked Systems Design and Implementation (NSDI ’19))

   We present the first wireless protocol that scales to hundreds of concurrent transmissions from backscatter devices. Our key innovation is a distributed cod- ing mechanism that works below the noise floor, operates on backscatter devices and can decode all the concurrent transmissions at the receiver using a single FFT operation. Our design addresses practical issues such as timing and fre- quency synchronization as well as the near-far problem. We deploy our design using a testbed of backscatter hardware and show that our protocol scales to concurrent transmis- sions from 256 devices using a bandwidth of only 500 kHz. Our results show throughput and latency improvements of 14–62x and 15–67x over existing approaches and 1–2 orders of magnitude higher transmission concurrency. 

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3. LeakyScatter: A Frequency-Agile Directional Backscatter Network Above 100 GHz

   Atsutse Kludze and Yasaman Ghasempour ( January 2023 , NSDI 2023: USENIX Symposium on Networked Systems Design and Implementation)

   Wireless backscattering has been deemed suitable for various emerging energy-constrained applications given its low-power architectures. Although existing backscatter nodes often operate at sub-6 GHz frequency bands, moving to the sub-THz bands offers significant advantages in scaling low-power connectivity to dense user populations; as concurrent transmissions can be separated in both spectral and spatial domains given the large swath of available bandwidth and laser-shaped beam directionality in this frequency regime. However, the power consumption and complexity of wireless devices increase significantly with frequency. In this paper, we present LeakyScatter, the first backscatter system that enables directional, low-power, and frequency-agile wireless links above 100 GHz. LeakyScatter departs from conventional backscatter designs and introduces a novel architecture that relies on aperture reciprocity in leaky-wave devices. We have fabricated LeakyScatter and evaluated its performance through extensive simulations and over-the-air experiments. Our results demonstrate a scalable wireless link above 100 GHz that is retrodirective and operates at a large bandwidth (tens of GHz) and ultra-low-power (zero power consumed for directional steering and ≤ 1 mW for data modulation). 

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4. TinySDR: Low-Power SDR Platform for Over-the-Air Programmable IoT Testbeds

   Hessar, Mehrdad ; Najafi, Ali ; Iyer, Vikram ; Gollakota, Shyamnath ( July 2019 , arXiv.org > eess > arXiv:1907.02063)

   Wireless protocol design for IoT networks is an active area of research which has seen significant interest and developments in recent years. The research community is however handicapped by the lack of a flexible, easily deployable platform for prototyping IoT endpoints that would allow for ground up protocol development and investigation of how such protocols perform at scale. We introduce tinySDR, the first software-defined radio platform tailored to the needs of power-constrained IoT endpoints. TinySDR provides a standalone, fully programmable low power software-defined radio solution that can be duty cycled for battery operation like a real IoT endpoint, and more importantly, can be programmed over the air to allow for large scale deployment. We present extensive evaluation of our platform showing it consumes as little as 30 uW of power in sleep mode, which is 10,000x lower than existing SDR platforms. We present two case studies by implementing LoRa and BLE beacons on the platform and achieve sensitivities of -126 dBm and -94 dBm respectively while consuming 11% and 3% of the FPGA resources. Finally, using tinySDR, we explore the research question of whether an IoT device can demodulate concurrent LoRa transmissions in real-time, within its power and computing constraints. 

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5. When Cryptography Needs a Hand: Practical Post-Quantum Authentication for V2V Communications

   https://doi.org/10.14722/ndss.2024.24267  

   Twardokus, Geoff ; Bindel, Nina ; Rahbari, Hanif ; McCarthy, Sarah ( February 2024 , Network and Distributed System Security Symposium (NDSS))

   We tackle the atypical challenge of supporting postquantum cryptography (PQC) and its significant overhead in safety-critical vehicle-to-vehicle (V2V) communications, dealing with strict overhead and latency restrictions within the limited radio spectrum for V2V. For example, we show that the current use of spectrum to support signature verification in V2V makes it nearly impossible to adopt PQC. Accordingly, we propose a scheduling technique for message signing certificate transmissions (which we find are currently up to 93% redundant) that learns to adaptively reduce the use of radio spectrum. In combination, we design the first integration of PQC and V2V, which satisfies the above stringent constraints given the available spectrum. Specifically, we analyze the three PQ signature algorithms selected for standardization by NIST, as well as XMSS (RFC 8391), and propose a Partially Hybrid authentication protocol—a tailored fusion of classical cryptography and PQC—for use in the V2V ecosystem during the nascent transition period we outline towards fully PQ V2V. Our provably secure protocol efficiently balances security and performance, as demonstrated experimentally with software-defined radios (USRPs), commercial V2V devices, and road traffic and V2V simulators. We show our joint transmission scheduling optimization and Partially Hybrid design are scalable and reliable under realistic conditions, adding a negligible average delay (0.39 ms per message) against the current state-of-the-art. 

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