Browsing by Author "Du, Changlai"

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    Exploring the Sensing Capability of Wireless Signals
    Du, Changlai (Virginia Tech, 2018-07-06)
    Wireless communications are ubiquitous nowadays, especially in the new era of Internet of Things (IoT). Most of IoT devices access the Internet via some kind of wireless connections. The major role of wireless signals is a type of communication medium. Besides that, taking advantage of the growing physical layer capabilities of wireless techniques, recent research has demonstrated the possibility of reusing wireless signals for both communication and sensing. The capability of wireless sensing and the ubiquitous availability of wireless signals make it possible to meet the rising demand of pervasive environment perception. Physical layer features including signal attributes and channel state information (CSI) can be used for the purpose of physical world sensing. This dissertation focuses on exploring the sensing capability of wireless signals. The research approach is to first take measurements from physical layer of wireless connections, and then develop various techniques to extract or infer information about the environment from the measurements, like the locations of signal sources, the motion of human body, etc. The research work in this dissertation makes three contributions. We start from wireless signal attributes analysis. Specifically, the cyclostationarity properties of wireless signals are studied. Taking WiFi signals as an example, we propose signal cyclostationarity models induced by WiFi Orthogonal Frequency Division Multiplexing (OFDM) structure including pilots, cyclic prefix, and preambles. The induced cyclic frequencies is then applied to the signal-selective direction estimation problem. Second, based on the analysis of wireless signal attributes, we design and implement a prototype of a single device system, named MobTrack, which can locate indoor interfering radios. The goal of designing MobTrack is to provide a lightweight, handhold system that can locate interfering radios with sub-meter accuracy with as few antennas as possible. With a small antenna array, the cost, complexity as well as size of this device are reduced. MobTrack is the first single device indoor interference localization system without the requirement of multiple pre-deployed access points (AP). Third, channel state information is studied in applications of human motion sensing. We design WiTalk, the first system which is able to do fine-grained motion sensing like leap reading on smartphones using the CSI dynamics generated by human movements. WiTalk proposes a new fine-grained human motion sensing technique with the distinct context-free feature. To achieve this goal using CSI, WiTalk generates CSI spectrograms using signal processing techniques and extracts features by calculating the contours of the CSI spectrograms. The proposed technique is verified in the application scenario of lip reading, where the fine-grained motion is the mouth movements.
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    MS-PTP: Protecting Network Timing from Byzantine Attacks
    Shi, Shanghao; Xiao, Yang; Du, Changlai; Shahriar, Md Hasan; Li, Ao; Zhang, Ning; Hou, Y. Thomas; Lou, Wenjing (ACM, 2023-05-29)
    Time-sensitive applications, such as 5G and IoT, are imposing increasingly stringent security and reliability requirements on network time synchronization. Precision time protocol (PTP) is a de facto solution to achieve high precision time synchronization. It is widely adopted by many industries. Existing efforts in securing the PTP focus on the protection of communication channels, but little attention has been given to the threat of malicious insiders. In this paper, we first present the security vulnerabilities of PTP and discuss why the current defense mechanisms are unable to counter Byzantine insiders. We demonstrate how a malicious insider can spoof a time source to arbitrarily shift the system time of a victim node on an IoT testbed.We further demonstrate the harmful consequence of the attack on a real Turtlebot3 robotic platform as the robot fails to locate itself and follows a false trajectory. As a countermeasure, we propose multi-source PTP, in short, MS-PTP, a Byzantine-resilient network time synchronization mechanism that relies on time crowdsourcing. MS-PTP changes the current PTP’s single source hierarchy to a multi-source client-server architecture, in which PTP clients take responses from multiple time servers and apply a novel secure aggregation scheme to eliminate the effect of malicious responses from unreliable sources. MS-PTP is able to counter 𝑓 Byzantine failures when the total number of time sources 𝑛 used by a client satisfies 𝑛 ≥ 3𝑓 + 1. We provide rigorous proof for its non-parametric accuracy guarantee—achieving bounded error regardless of the Byzantine population. We implemented a prototype of MS-PTP on our IoT testbed and the results show its resilience against Byzantine insiders while maintaining high synchronization accuracy.
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    TriSAS: Toward Dependable Inter-SAS Coordination with Auditability
    Shi, Shanghao; Xiao, Yang; Du, Changlai; Shi, Yi; Wang, Chonggang; Gazda, Robert; Hou, Y. Thomas; Burger, Eric W.; Dasilva, Luiz; Lou, Wenjing (ACM, 2024-07-01)
    To facilitate dynamic spectrum sharing, the FCC has designated certified SAS administrators to implement their own spectrum access systems (SASs) that manage the shared spectrum usage in the novel CBRS band. As a premise, different SAS servers must conduct periodic inter-SAS coordination to synchronize service states and avoid allocation conflicts. However, SAS servers may inevitably stop service for regular upgrades, crash down, or even perform maliciously that deviate from the normal routines, posing a fundamental operation security problem — the system shall be robust against these faults to guarantee secure and efficient spectrum sharing service. Unfortunately, the incumbent inter-SAS coordination mechanism, CPAS, is prone to SAS failures and does not support real-time allocation. Recent proposals that rely on blockchain smart contracts or state machine replication mechanisms to realize faulttolerant inter-SAS coordination require all SASs to follow a unified allocation algorithm. They however face performance bottlenecks and cannot accommodate the current fact that different SASs hold their own proprietary allocation algorithms. In this work, we propose TriSAS—a novel inter-SAS coordination mechanism to facilitate secure, efficient, and dependable spectrum allocation that is fully compatible with the existing SAS infrastructure. TriSAS decomposes the coordination process into two phases including input synchronization and decision finalization. The first phase ensures participants share a common input set while the second one fulfills a fair and verifiable spectrum allocation selection, which is generated efficiently via SAS proposers’ proprietary allocation algorithms and evaluated by a customized designed allocation evaluation algorithm (AEA), in the face of no more than one-third of malicious participants. We implemented a prototype of TriSAS on the AWS cloud computing platform and evaluated its throughput and latency performance. The results show that TriSAS achieves high transaction throughput and low latency under various practical settings.