Localization is a critical task for underwater robots, yet today's underwater localization systems are limited by their accuracy, scalability, and/or energy consumption (i.e., longevity). We present the design, implementation, and evaluation of EchoBLUE- an accurate, scalable, and low-power localization system for underwater robots.

Following the broad prospect of Radio Frequency Identification (RFID) technology is the security concern of unauthorized tag identification, which poses threats to the privacy of both objects and users. In this paper, we propose RF-Rock, the first RFID unauthorized identification attack that operates without tag activation, thereby evading almost all existing defenses. This attack exposes the vulnerabilities of current RFID networks in identification legitimacy and privacy. It is based on the intermodulation effect originating from intrinsic nonlinearity within tag circuits. To this end, we explore the distinctness and consistency of the intermodulation-based physical layer fingerprint of RFID tags with theoretical analysis and empirical validation, and optimize the attack accuracy and efficiency with delicate excitation plan. Real-world experiments show that RF-Rock achieves an attack success rate of 93.2% on average under various conditions. The entropy of our proposed fingerprint is 15.5 bits and implies sufficient capacity in practical attacks.

Underwater backscatter is a promising technology for ultra-low-power underwater networking, but existing systems break down in mobile scenarios. This paper presents EchoRider, the first system to enable reliable underwater backscatter networking under mobility.

We present the design, implementation, and evaluation of Van Atta Acoustic Backscatter (VAB), a technology that enables long-range, ultra-low-power networking in underwater environments. At the core of VAB is a novel, scalable underwater backscatter architecture that bridges recent advances in RF backscatter (Van Atta architectures) with ultra-low-power underwater acoustic networks. Our design introduces multiple innovations across the networking stack, which enable it to overcome unique challenges that arise from the electro-mechanical properties of underwater backscatter and the challenging nature of low-power underwater acoustic channels. We implemented our design in an end-to-end system, and evaluated it in over 1,500 real-world experimental trials in a river and the ocean. Our evaluation in stationary setups demonstrates that VAB achieves a communication range that exceeds 300m in round trip backscatter across orientations (at BER of 10−3). We compared our design head-to-head with past state-of-the-art systems, demonstrating a 15× improvement in communication range at the same throughput and power. By realizing hundreds of meters of range in underwater backscatter, this paper presents the first practical system capable of coastal monitoring applications. Finally, our evaluation represents the first experimental validation of underwater backscatter in the ocean.

In a modern logistics network, high-performance automation of inventory tracking and package management calls for a reliable, high-throughput and long range RFID localization system. We present RF-Chord, the first RFID localization system that simultaneously meets all these requirements. RF-Chord features a one-shot multisine-constructed wideband design that can process the RF signal with a 200 MHz bandwidth in real-time to facilitate one-shot localization at scale. In addition, multiple SINR enhancement techniques are designed for range extension. Finally, we propose a kernel-layer-based near-field localization and a multipath-suppression algorithm that reduces the 99% long-tail errors.

Conventional road signs convey very concise and static visual information to human drivers, and bear retroreflective coating for better visibility at night. This paper introduces RetroI2V - a novel infrastructure-to-vehicle (I2V) communication and networking system that renovates conventional road signs to convey additional and dynamic information to vehicles while keeping intact their original functionality. In particular, RetroI2V exploits the retroreflective coating of road signs and establishes visible light backscattering communication (VLBC), and further coordinates multiple concurrent VLBC sessions among road signs and approaching vehicles. RetroI2V features a suite of novel VLBC designs including late-polarization, complementary optical signaling and polarization-based differential reception which are crucial to avoid flickering and achieve long VLBC range, as well as a decentralized MAC protocol that make practical multiple access in highly mobile and transient I2V settings. Experimental results from our prototyped system show that RetroI2V supports up to 101 m communication range and efficient multiple access at scale.

Visible light backscatter communication (VLBC) presents an emerging low power IoT connectivity solution with spatial reuse and interference immunity advantages over RF-based (backscatter) technologies. State-of-the-art VLBC systems employ COTS LCD shutter as optical modulator, whose slow response fundamentally throttles its data rate to sub-Kbps, and limits its deployment at scale for use cases where higher rate and/or low latency is a necessity.

Current UHF RFID systems suffer from two long-standing problems: 1) miss-reading non-line-of-sight or misoriented tags and 2) cross-reading undesired, distant tags due to multi-path reflections. This paper proposes a novel system, NFC+, to overcome the fundamental challenges. NFC+ is a magnetic field reader, which can inventory standard NFC tagged objects with a reasonably long range and arbitrary orientation. NFC+ achieves this by leveraging physical and algorithmic techniques based on magnetic resonance engineering. We build a prototype of NFC+ and conduct extensive evaluations in a logistic network. Comparing to UHF RFID, we find that NFC+ can reduce the miss-reading rate from 23% to 0.03%, and cross-reading rate from 42% to 0, for randomly oriented objects. NFC+ demonstrates high robustness for RFID unfriendly media (e.g., water bottles and metal cans). It can reliably read commercial NFC tags at a distance of up to 3 meters which, for the first time, enables NFC to be directly applied to practical logistics network applications.

Grant-free non-orthogonal multiple access (NOMA) is highly expected to support massive connectivity and reduce the transmission latency for future wireless communications. In this paper, we present a joint active user and data detection with no priori knowledge of the active users relying on expectation propagation (EP) and Gaussian approximation (GA) algorithm. To detect the user activity, a structured spike and slab prior is introduced to present the sparsity of transmission signal. Further, the parameters unknown are learned via expectation maximization (EM), which improves the performance of active user detection. Specifically, the active user detection problem in NOMA is firstly formulated under EM framework by parameter learning, and then the transmission data can be detected accurately by message-passing algorithms (MPA). Simulation experiments demonstrate the superiority of our proposed EP-GA-EM algorithm both in the performance of reconstruction and the bit error rate (BER).

Visible Light Backscatter Communication presents an emerging IoT connectivity technology that offers low power and flexible angular alignment benefits. State-of-art approaches with unmodified LCD(s) as optical modulator cause flickering with a sub-kbps low data rate, which would be overcome by modulating polarization, but naive implementation requires careful Tx-Rx placement to avoid signal cancellation. To overcome such challenges, we propose a new modulation scheme called polarization-based quadrature amplitude modulation (PQAM). PQAM constructs the orthogonal basis in the polarization domain and provides 2x throughput gain with arbitrary relative orientation.

Visible light backscatter communication (VLBC) has shown great potential in IoT field. LCD, often used as optical modulator in a VLBC system, mainly limits the data rate to sub-Kbps due to its slow state transition. There is a great demand for speed improvement, to support both low latency and high throughput communication in IoT deployment. With the observation of nonlinear and time-varying characteristics of LCD, we present sys, a novel modulation scheme named Delayed Superimposition Modulation (DSM) to achieve 4kbps, which is 4x rate over the status-quo. This design is robust in the presence of LCD heterogeneity in practical setting.

Vehicle-to-anything (V2X) communications technology is an essential substrate to realize future road intelligence and autonomous driving, especially in the areas where there are no existing (radio) network infrastructure. The emerging visible light backscatter communication technique shows great potentials in enabling the massive on-road retroreflective objects to delivery dynamic information to host vehicles. In this work, we design a polarization-based differential reception scheme to suppress ambient noise and realize long range retroreflective V2X communications.