This paper presents TurboInfer, a system that enables power-efficient LLM inference on mobile devices. The core insight behind TurboInfer is that while LLMs are power-intensive due to their heavy computational demands, the model inference experiences unavoidable GPU stalls caused by tensor preparation for subsequent kernel executions at run-time. These GPU stalls arise from the unique host-controlled execution pipeline tailored to mobile phones and the significant DRAM access contention inherent to the shared memory architecture of mobile System-on-chips (SoCs). With LLM inference requiring hundreds to thousands of kernel executions, these short but frequent GPU stalls accumulate, accounting for over 74% of the token generation latency.

Wi-Fi computational imaging has emerged as a promising paradigm for non-intrusive sensing; however, its practical deployment is severely hindered by dense physical multipath clutter, hardware phase quantization errors, and the limited bandwidth of commercial Wi-Fi. Traditional beamforming-based algorithms often completely lose target focus in complex environments, resulting in severe ghosting artifacts. To overcome these fundamental limitations, we propose RISimg, a novel robust Wi-Fi imaging framework empowered by the spatiotemporal coding of Reconfigurable Intelligent Surface. We design a differential coding strategy to guarantee a well-conditioned and noise-robust sensing matrix, and propose a multi-frequency sparse reconstruction algorithm based on the Least Absolute Shrinkage and Selection Operator. By constructing a large-scale overdetermined system, this physics-driven approach effectively suppresses multipath interference and hardware errors, successfully recovering the basic morphological outlines of complex targets. To further enhance the imaging performance, we propose leveraging a Conditional Diffusion Model to refine the imaging results. By utilizing the reconstruction as a structural prior, a carefully designed Conditional U-Net progressively refines the image through a generative reverse sampling process, restoring high-fidelity continuous boundaries. Extensive evaluations using a hardware prototype built with commercial Wi-Fi devices and a low-cost metasurface demonstrate that the final cascaded CDM achieves an unprecedented Structural Similarity Index Measure of 0.9192 and a Spatial Correlation Coefficient of 0.7336, paving a robust new avenue for Wi-Fi imaging.

Deploying Tiny Deep Learning (TinyDL) on Internet of Things (IoT) devices is gaining popularity. To accommodate the limited memory, recent methods split tensors into fine-grained parts and plan memory offline to minimize its footprint. However, they fail to adapt to dynamic memory, missing the opportunity to utilize temporarily available memory for faster inference. Additionally, existing approaches focus solely on minimizing memory size while neglecting cache usage characteristics, resulting in frequent cache misses and increased latency. In this paper, we propose RAMS, an efficient framework supporting runtime adaptive memory scaling to fully utilize the dynamic memory. We also propose a cache-friendly memory management approach that minimizes cache miss times. RAMS includes an offline planner to minimize the memory footprint essential for inference and an online manager to determine memory sizes and generate layouts for size-controllable tensors based on available memory. RAMS significantly reduces inference latency while maintaining a compact memory footprint. Extensive experiments on commercial devices running RTOS and Android systems demonstrate that, compared to the state-of-the-art methods, RAMS can efficiently reduce latency by up to 1.57× and 1.48× compared to TFLM and TinyTS, respectively using a comparable memory footprint, while reducing power consumption by 67.74% and 15.97%.

With the explosive increase in wireless devices, enabling sensing between incompatible radios has become critically beneficial. Integrating diverse IoT devices enhances sensing accuracy by providing richer data, while utilizing the diverse characteristics of heterogeneous signals meets sensing needs in complex environments. However, most existing wireless sensing methods primarily focus on homogeneous signals, while research on sensing with heterogeneous signals is still in its infancy. In this paper, we proposeCrossSense, a novel Cross-Technology Sensing (CTS) framework that enables sensing between incompatible WiFi and LoRa device.CrossSenserecovers the fine-grained trajectory of a WiFi transmitter based on its emulated LoRa signals. To decompose the motion feature components of WiFi transmitter, we develop a chirp difference vector model that utilizes the energy peak within each chirp window for sensing. We model the relationship between sampling frequency offsets and oscillation frequency offsets among heterogeneous devices to guide the extraction of motion features from the emulated signal. We also propose a greedy-based peak enhancement method to calculate the optimized LoRa phases, minimizing the impact of phase discontinuity caused by cyclic prefix (CP) errors. We implement a prototype ofCrossSenseon the USRP platform. The extensive experiments demonstrate thatCrossSensecan achieve an efficient Cross-Technology Sensing with$2.92cm$distance accuracy and$0.26cm/s$speed accuracy over a$120m$sensing range.

As distributed applications increasingly span geographically distributed data centers, the demand for high-performance, long-distance transmission has been continuously growing. While intra-data-center networks have employed techniques like remote direct memory access (RDMA) to meet these design goals, extending these techniques toWANs presents unique challenges. WANs notably suffer from inherent packet losses due to buffer overflows in routers and switches, leading to decreased throughput and making distributed applications barely usable. This paper proposes Lossless Transmission (LLT), a novel buffer management scheme for enabling lossless WAN transport. LLT intelligently integrates on-chip switch buffers with an off-chip caching system to absorb traffic bursts that would otherwise cause packet loss. Its data plane logic uses a multi-level threshold system to selectively offload only critical flows during congestion. A closed-loop control protocol, managed by a stateful flow table, ensures these offloaded packets are later re-injected with guaranteed lossless and in-order delivery, effectively protecting latency-sensitive applications from retransmission overhead. We evaluate LLT using both ns-3 simulations and P4-programmable devices. The experimental results show that in typical use cases (RTT > 30ms), LLT improves link bandwidth utilization by 1.9% to 29.5% and reduces the P99 percentile tail latency by 17% to 66% in WANs compared to the state-of-the-art solutions. Overall, LLT provides a scalable, efficient, and reliable framework for long-distance data transmission, addressing critical challenges in WANs. Additionally, LLT eliminates the need for expensive WAN infrastructure modifications.

Subsea Internet of Things (IoT) networks have rapidly developed but still suffer the inefficient underwater-toair communication. Due to wireless signals exhibiting different properties in different media, it is difficult to use any single modality of signal for cross-medium communication. In this paper, we propose Exocoetus, a novel passive relay based water-to-air communication system. By taking advantage of the out-of-specification characteristics of the RF switch, Exocoetus can trigger acoustic-to-RF conversion even if the input voltage is below the standard threshold and use a clamp circuit to further maximize the efficiency of the acoustic-to-RF signal conversion. We design a dual-capacitor circuit-based pulse position modulation method to amplify the acoustic signals emitted by powerconstrained underwater nodes, ensuring reliable communication over greater distances. We implement a prototype of Exocoetus and evaluate its performance in the real environment. The results show that Exocoetus can achieve a communication distance of 6 meters above water and$\mathbf{1.25}$meters underwater.

Cross-Technology Communication (CTC) is an emerging technique that enables direct interconnection among incompatible wireless technologies. However, for the downlink from WiFi to multiple IoT technologies, serially emulating and transmitting the data of each IoT technology has extremely low spectrum efficiency. In this paper, we propose WiCast, a parallel CTC that uses IEEE 802.11ax to emulate a composite signal that can be received by commodity BLE, ZigBee, and LoRa devices. By taking advantage of OFDMA in 802.11ax, WiCast uses a single Resource Unit (RU) for parallel CTC and sets other RUs free for high-rate WiFi users. But such a sophisticated composite signal is very easily distorted by emulation imperfections, dynamic channel noises, cyclic prefix, and center frequency offset. We propose a CTC link model that jointly models the emulation errors and channel distortions. Then we carve the emulated signal with elaborate compensations in both time and frequency domains. Based on the proposed CTC scheme, a unified Media Access Control approach is introduced to discover and synchronize the heterogeneous IoT devices. We implement a prototype of WiCast using USRP N210 platform along with commodity ZigBee, BLE, and LoRa devices. The extensive experiments demonstrate WiCast can achieve an efficient parallel transmission with the aggregated goodput up to 390.24kbps.

Current WiFi imaging approaches focus on monitoring dynamic targets to facilitate easy object distinction and capture rich signal reflections for image construction. In static object imaging, massive antenna array or emulated antenna array is often necessary. We proposeWiCamera, a novel WiFi imaging prototype that utilizes vortex electromagnetic waves (VEMWs) to monitor stationary human postures using commodity WiFi, by generating human silhouettes with only$3 \times 3$MIMO. VEMWs possess a helical wavefront with different phase variations, enabling the imaging of stationary objects through different OAM (Orbital Angular Momentum) modes with time-division multiplexing.WiCameraemits three OAM modes waves from WiFi devices and utilizes their phase variations for imaging. By ray tracing the received signals to a target image plane,WiCameragenerates a wavefront image. A generative adversarial network (GAN)-based model is further utilized to refine the wavefront image and create a high-resolution human silhouette. The system's output images are evaluated using metrics such as structural similarity index measure (SSIM) and Szymkiewicz-Simpson coefficient (SSC), comparing them to ground truth images captured by cameras. The evaluation shows thatWiCameraperforms consistently well in various environments and with different users, with an SSIM reaching up to 0.89 and an SSC reaching up to 0.93.

LoRa is widely deployed for various applications. Though the knowledge of the channel occupancy is the prerequisite of many aspects of network management, acquiring the channel occupancy for LoRa is challenging due to the large number of possible channels. In this paper, we propose${\sf LoRadar}$, a novel LoRa channel occupancy acquirer based on cross-channel scanning. Our in-depth study finds that Channel Activity Detection (CAD) in a narrow band can indicate the channel activities of wide bands because they have the same slope in the time-frequency domain. Based on this finding, we design a cross-channel scanning mechanism that infers the channel occupancy states of all the overlapping channels by the distribution of CAD results. We elaborately select and adjust the CAD settings to enhance the distribution features and design a pattern correction method to cope with distribution distortions. We also design a CAD scheduler to deal with the low duty-cycle LoRa operations. We implement${\sf LoRadar}$on commercial LoRa platforms and evaluate its performance in the indoor testbed and two outdoor deployed networks. The experimental results show that${\sf LoRadar}$can achieve a detection accuracy of 0.99 and reduce the acquisition overhead by up to 90%, compared to the traversal-based methods.

Unmanned Aerial Vehicle (UAV) equipped with a gateway shows great potential for data collection in many scenarios, especially for the areas lacking of public network infrastructures. However, our in-field experiments on UAV-assisted LoRa networks show that a large throughput gap exists between the ground-to-air and ground-to-ground transmissions. We find that the misalignment of the radiation direction of transceiver antennas with height difference leads to additional signal strength loss, which is ignored by existing ground-to-ground transmissions. In this paper, we propose a directivity-aware ground-to-air link model called annulus model to quantify the impact of directivity on the ground-to-air link quality. Based on our model, a new ground-to-air channel access scheme for UAV-assisted LoRa networks,PreLoRa, is proposed. By predicting the link quality variations,PreLoRaschedules the transmission periods and adopts optimal transmission configurations for ground nodes to improve the link throughput. We implementPreLoRaon commercial LoRa platforms and extensively evaluate its performance in the wild. Experimental results show thatPreLoRacan significantly improve data collection throughput by up to 65.5% compared to baseline methods.

Remarkable advancements have been made in the field of object detection, and given its widespread application, it is of paramount importance to investigate the robustness of detection models. However, previous methods have primarily focused on models based on Convolutional Neural Networks (CNNs), seriously neglecting the Transformer-based models that develop rapidly but exhibit obvious differences in terms of information processing. Therefore, this paper aims to address this gap by exploring potential attacks arising from the self-attention mechanism inhered in Transformer. Specifically, we propose a novel adversarial attack scenario targeting Transformer-based object detection models, where only objects of specific class fail to be detected, while irrelevant objects remain undisturbed. Therefore, human perception is hard to find errors even with the detector fail. To achieve this goal, we introduce an adversarial patch generation method, termed Class-Specific Adversarial (CSAdv) patches, which simultaneously leverages class probability to attack specific objects and utilizes the output from Transformer decoder structures, Query Output, to protect irrelevant objects. Due to the long-range interactions of Transformer, the adversarial patch does not need to directly cover or closely surround the specific objects. Instead, it achieves remote targeted attacks simply by being placed in the corner of image, which greatly enhances the concealment of patches. Extensive experiments are conducted on various benchmark datasets and Transformer-based baselines, and the experimental results show that CSAdv can effectively mask certain class while keeping other classes as unaffected as far as possible.

Unlike existing studies that focus on intra-channel interference, in this paper, we reveal cross-channel interference when collided chirps with different bandwidths have the same slope in the time-frequency domain. Existing methods are inefficient in resolving this type of interference because the demodulation features they use rely on accurate time-domain distributions including the start and end time of all chirps, which is unavailable for uncompleted chirps within the limited receiving bandwidth. We propose SO-LoRa which utilizes the difference in collided chirps' time-domain distributions to identify the target chirp under interference. SO-LoRa adopts self-dechirp operation that maps the chirp's time-domain distribution to recognizable amplitude change of energy peaks that reflect the difference. However, for real received chirps, the amplitude change is unreliable due to the random phase drift and amplified channel noise. So we propose a phase correction method that uses the model between phase difference and the signal energy. We also design time-domain filtering that suppresses noise before self-dechirp. Finally, to avoid extra false energy peaks generated by self-dechirp confusing the demodulation, we separate chirps which cause peak overlapping into different groups and individ-ually perform self-dechirp. The experiments show that SO-LoRa reduces the Symbol Error Rate (SER) by up to 88.6 % compared with state-of-the-art methods.

Due to the poor indoor coverage and positioning accuracy, existing indoor GPS positioning systems leverages additional RF infrastructure as relay with known position. However, in practice, learning the relay position requires establishing an additional connection between user and relays, which is user unfriendly and even infeasible. In this paper, we propose GPSWindow, a plug-and-play indoor GPS positioning system without the prior knowledge of the relay position. By attaching optically transparent metasurfaces to windows, GPSWindow focuses the incident signal towards determined direction and provide an indoor continuous GPS signal coverage. We exploit the difference between consecutive satellite measurements and the Doppler shift measurements to recover the satellite-to-user true distance from the measured satellite-metasurface-user distance, and then locate the user using the traditional trilateration positioning method, eliminating the requirement of relay position. We also design an error correction method that leverages IMU on smartphone and the Doppler shift information to enhance GPSWindow in mobile scenarios. Extensive real-world experiments demonstrate that GPSWindow can provide continuous position service and achieve median positioning accuracy of 3.6m in indoor environments.

The Bluetooth 5.1 specification introduces the Angle of Arrival feature, which significantly enhances its applications in indoor positioning. Given the height of the target, a single BLE (Bluetooth Low Energy) base station can locate the target, thereby reducing deployment costs. However, existing methods often assume that the target's height is known in advance and remains constant, which is not always true in practice. The height can vary significantly due to user posture changes, such as when picking up a phone from a pocket, leading to positioning errors. In this paper, we propose BleHe, a novel indoor positioning system that incorporates height correction to enhance positioning accuracy in scenarios with dynamic height changes. BleHe detects height changes by utilizing on-device IMU sensor and subsequently notifies the base station of any detected height change events. To avoid altering the commodity Bluetooth protocols, rather than directly modifying application data, we create a side channel to delivery the height change information from the device to the base station by adjusting the BLE packet transmission frequency. This method allows the base station to infer the start and end times of height changes and subsequently refine the target's trajectory using a height-aware particle filtering-based positioning correction method that we propose. Experimental results demonstrate that BleHe achieves an average positioning error of 34.4cm, even in scenarios involving posture changes during walking.

In this paper, we reveal the existence of partially overlapping interference (POI) when multiple devices concurrently transmit in partially overlapping channels. Existing methods proposed for collisions in the same channel cannot achieve online decoding for target packets under POI due to unpredictable in-window distribution of interfering chirp. We instead propose PrLoRa, a novel method to achieve online LoRa decoding under POI. PrLoRa relies on the insight that only the target chirp is complete in the decoding window. Then PrLoRa adopts a novel operation named phase rotation which converts the difference in chirp's integrity to the amplitude change of energy peak after dechirp and Fast Fourier Transform (FFT). For energy peaks generated by the target chirps, their amplitude change is expected. To use phase rotation in decoding the target chirp, we first establish the theoretical model between amplitude changing and phase rotation, which can be used to infer the expected amplitude change of the target peak. In practice, the peak's amplitude suffers from the influence of channel noise, which causes decoding errors. So, we also propose a noise-aware window setting that can adaptively select the suitable window size for phase rotation according to channel noise. Furthermore, we propose the iterative phase rotation to cope with decoding errors caused by interfering chirps with confusing distributions. The Experimental results show that PrLoRa can reduce the SER by up to 0.92 compared with existing state-of-the-art methods.

WiFi imaging is an emerging technology that can overcome camera limitations like occlusion and poor lighting. Imaging static objects without antenna arrays or mobile platforms is challenging. In this paper, we use a metasurface with a single pair of WiFi transceiver to achieve high-resolution WiFi imaging for static objects. We analyze the WiFi multipath propagation model with a metasurface and propose an imaging system. This system employs diverse radiation patterns by directing the WiFi beam reflected from the metasurface to illuminate a target. We utilize an image-guided diffusion model for high resolution imaging. We prototype MAWI with commodity WiFi and evaluate its performance in real environments. Experimental results show MAWI performs well on four typical target shapes.

With the rapid growth of Internet of Things, the number of heterogeneous wireless devices working in the same frequency band increases dramatically, leading to severe cross-technology interference. To enable coexistence, researchers have proposed a large number of mechanisms to manage interference. However, existing mechanisms have severe modifications in either the physical or MAC (medium access control) layers, making them very different from the standard. In this paper, we design and implement SledZig to boost cross-technology coexistence for low-power devices through both enabling more transmission opportunities and avoiding interference. SledZig is fully compatible with the standard in both physical and MAC layers. It decreases the WiFi signal power on the channel of low-power devices while keeps the WiFi transmission power unchanged, through making constellation points on the overlapped subcarriers have the lowest power, which can be achieved by just encoding the WiFi payload. We implement SledZig on hardware testbed and evaluate its performance under different settings. Experiment results show that SledZig can effectively increase ZigBee transmissions and improve its performance over a WiFi channel under various WiFi data traffic, with as low as 6.94$\%$WiFi throughput loss.

Existing WiFi sensing systems transmit dedicated high-rate packets for accurate sensing. These “sensing packets” greatly affect the main data communication function of WiFi and significantly counteract the promised benefit of reusing WiFi communication for sensing. In this work, we propose WiImg2.0, a lightweight system which involves machine learning techniques to enable WiFi sensing under low packet rate, pushing WiFi sensing one step towards real-life adoption. The key idea is to convert the WiFi CSI samples into images and employ the Generative Adversarial Network (GAN) for CSI image inpainting, relaxing the requirement of high sample rate for sensing. We first recover the sensing data from the antenna spatial domain and then from the sample time domain. To avoid the large training overhead of GAN, we design a lightweight GAN that leverages samples of only three rates in a fixed window to recover the CSI traces of arbitrary rates and varying duration. Experiments show that with just 25 packets per second, WiImg2.0 is able to increase the recognition accuracy for hand gesture recognition and daily activity tracking from the state-of-the-art 59.1% and 65.9% to 86.7% and 96.4%, respectively.

Recent work proposes Cross-Technology Communication (CTC) from IEEE 802.11b to LoRa but has a low efficiency due to the extremely asymmetric data rates. In this paper, we propose that emulates LoRa waveform with IEEE 802.11ax. By taking advantage of the OFDMA in 802.11ax, uses only a small Resource Unit (RU) to emulate LoRa chirps and sets other RUs free for high-rate WiFi users. carefully selects the RU and adopts WiFi frame aggregation to emulate the long LoRa frame. We propose a subframe header mapping method to identify and remove invalid symbols caused by irremovable subframe headers in the aggregated frame. We also propose a mode flipping method to solve Cyclic Prefix (CP) errors, based on our finding that different CP modes have different impacts on the LoRa symbol. To cope with channel dynamics, we design an adaptation mechanism to maximize the goodput with a satisfying SER. We further extend to one-to-many transmission scenario by concurrently emulating LoRa chirps in different RUs. We implement a prototype of on the USRP platform and commodity LoRa device. Experiments demonstrate can efficiently transmit complete LoRa frames with the throughput of 40.037kbps and the SER lower than 0.1.

De-authentication attack is one of the major threats to Unmanned Aerial Vehicle (UAV) communication, in which the attacker continuously sends de-authentication frames to disconnect the UAV communication link. Existing defense methods are based on authentication by digital passwords or physical channel features. But they suffer from replay attacks or cannot adapt to the UAV mobility. In this paper, instead of enhancing the in-channel authentication, we leverage the ambient broadcasting signal to establish a low-cost additional channel for authentication. Different from methods using another dedicated secure communication channel to perform an independent authentication, we use the ambient FM radio broadcasting channel and couple the two channels by encoding parasitic bits on the host signals of the broadcasting channel, which is called parasitic coding. To further enhance the security, we propose the FM-based Parasitic Coding Authentication (FPCA) that leverages elaborate host signal processing and vector coding to ensure that the attacker cannot decode our authentication even knowing the FM receiving frequency. We implement FPCA on the embedded UAV platform. The extensive experiments show that FPCA can resist replay attacks and brute force searching, achieving reliable continuous authentication for UAVs.

With the widespread adoption of deep learning models in wireless sensing, substantial efforts have been made to develop sophisticated models that improve the accuracy and performance of sensing applications. However, the exploration of potential vulnerabilities in deep learning models has been limited, with existing studies primarily focusing on evaluating wireless adversarial performance in communication or sensing alone. Moreover, there is a lack of a comprehensive definition for attack imperceptibility. In this article, we come up with a definition of the wireless attack imperceptibility for both communication and sensing. Our objective is to create an adversarial perturbation capable of degrading WiFi sensing performance while preserving WiFi communication integrity. To achieve this, we propose WiCAM2.0 to reveal the temporal and spatial attention of a deep neural network, capturing the crucial portions of its input. Then, we design a mask to confine adversarial perturbations in the attended parts only, minimizing the impact on WiFi communication. WiCAM2.0 is a general adversarial framework that integrates adversarial methods such as the Fast Gradient Sign Method and Projected Gradient Descent to generate perturbations, capable of initiating both non-targeted and targeted attacks. We carry out experiments on three popular WiFi sensing applications, including human activity recognition, gesture recognition, and user identification. Extensive experiments are conducted on both public datasets and self-collected datasets.

LoRa is widely deploying in aquatic environments to support various Internet of Things applications. However, floating LoRa networks suffer from serious performance degradation due to the polarization loss caused by the swaying antenna. Existing methods that only control the transmission starting from the aligned attitude have limited improvement due to the ignorance of aligned period length. In this article, we propose PolarScheduler , a dynamic transmission control method for floating LoRa networks. PolarScheduler actively controls transmission configurations to match polarization aligned periods. We propose a V-zone model to capture diverse aligned periods under different configurations. We also design a low-cost model establishment method and an efficient optimal configuration searching algorithm to make full use of aligned periods. To deal with packet collisions in a multiple-node environment, we further propose an Attitude-aware Slot-allocation MAC protocol, which avoids both packet collisions and polarization loss. We implement PolarScheduler on commercial LoRa platforms and evaluate its performance in a deployed network. Extensive experiments show that PolarScheduler can improve the packet delivery rate and throughput by up to 20.0% and 15.7%, compared to the state-of-the-art method.

Long Range-Frequency Hopping Spread Spectrum (LR-FHSS) is a novel wireless communication technology to improve the coverage of Low-Power Wide-Area Network (LP-WAN). But our measurement finds that given the same set of sub-channels, different Frequency Hopping Sequence (FHS) can result in a reliability difference of up to 52.6 % in terms of Packet Reception Rate (PRR). The key observation indicates that the reliability of LR-FHSS is significantly influenced by the FHS besides the link quality. Hence, in this paper, we propose DFH that takes both link quality and FHS into consideration to improve the reliability of LR-FHSS. We first propose using the hop Signal-to-noise Ratio (SNR), a new indicator to reflect the quality of the sub-channels and establish the PRR prediction model according to hop SNR and FHS. Based on the model, we design an interleaving-based search algorithm to decide the optimal FHS. We implement and evaluate DFH on the commercial transceivers and SDR-based gateway. The results of experiments in real environments show that DFH can improve the PRR by up to 2.76x, compared to the standard LR-FHSS.

The hierarchical cooperative resource scheduling architecture provides a promising direction for efficient collaborative processing of edge computing under the dynamic and intricate landscape of the Industrial Internet of Things (IIoT). However, existing scheduling algorithms often struggle to effectively capture the intricate information features inherent in hierarchical and collaborative domains, leading to suboptimal solutions. To tackle this challenge, we introduce a novel hierarchical cooperative resource scheduling framework based on Graph Neural Networks (GNN) and Deep Reinforcement Learning (DRL). We first leverage hierarchical GNN to facilitate seamless information exchange among internal nodes and adjacent nodes between layers in the hierarchical structure and transform it into node embeddings. These meticulously designed embeddings are then input into the policy model of DRL for the iterative learning process to generate higher-quality solutions by leveraging global feature information. Experiment results unequivocally demonstrate the superiority of our approach over baselines in terms of scheduling performance. Furthermore, our model exhibits robust generalization capabilities across various scenarios.

Cross-Technology Communication (CTC) is an emerging technique that enables direct interconnection among incompatible wireless technologies. However, for the downlink from WiFi to multiple IoT technologies, serially emulating and transmitting the data of each IoT technology has extremely low spectrum efficiency. Recent parallel CTC uses IEEE 802.11g to send emulated ZigBee signal and let the BLE receiver decodes its data from the emulated ZigBee signal with a dedicated codebook. It still has a low spectrum efficiency because IEEE 802.11g exclusively uses the whole channel. Besides, the codebook design hinders the reception on commodity BLE devices. In this paper, we propose WiCast, a parallel CTC that uses IEEE 802.11ax to emulate a composite signal that can be received by commodity BLE, ZigBee, and LoRa devices. By taking advantage of OFDMA in 802.11ax, WiCast uses a single Resource Unit (RU) for parallel CTC and sets other RUs free for high-rate WiFi users. But such a sophisticated composite signal is very easily distorted by emulation imperfections, dynamic channel noises, cyclic prefix, and center frequency offset. We propose a CTC link model that jointly models the emulation errors and channel distortions. Then we carve the emulated signal with elaborate compensations in both time and frequency domains to solve the above distortion problem. We implement a prototype of WiCast on the USRP platform and commodity devices. The extensive experiments demonstrate WiCast can achieve an efficient parallel transmission with the aggregated goodput up to 390.24kbps.

Existing LoRa only supports the concurrency of orthogonal channels but ignores the large number of non-orthogonal channel concurrency opportunities. In this paper, we propose Mc-LoRa that enables LoRa concurrency for non-orthogonal overlapping channels by solving cross-channel collision that happens when chirps with different bandwidths have the same slope in time-frequency domain. Existing single-channel concurrency methods fail to resolve this new collision because the deterministic symbol offset is invalid anymore due to the asymmetric symbol duration. But we find that when wiping a part of collided signals, the amplitude change of target chirp that aligns with the decoding window is predictable, while the collided chirps experience different changes. We accordingly regard the amplitude change ratio before and after wiping as a new decoding feature. We propose a wiper selection method based on our theoretical model to obtain robust features. We also design noise-aware wiper searching and grouping mechanisms to balance the feature accuracy and computing overhead. The experiments show that Mc-LoRa efficiently decodes packets in non-orthogonal overlapping channels and improves the network throughput by up to 3.4× under cross-channel collision, compared with the state-of-the-art single-channel concurrency methods.

In the Industrial Internet of Things (IIoT) environment, time-sensitive tasks require efficient utilization of computing and network resources to ensure timely completion and fast processing. However, using existing scheduling schemes based on software-defined network (SDN), time-sensitive network (TSN), or information technology (IT) can lead to problems such as resource inefficiency, transmission delays, and task timeouts. To overcome these challenges, this paper proposes a collaborative scheduling method that combines SDN for global resource management and TSN for precise resource allocation. Additionally, a control plane algorithm is introduced to adapt task resources. This approach effectively schedules global computing and network resources, enabling timely and efficient task processing. Extensive experiments demonstrate the superiority of this method in terms of task completion rate and processing time compared to other baselines in various network environments.

We present nnPerf, a real-time on-device profiler designed to collect and analyze the DNN model run-time inference latency on mobile platforms. nnPerf demystifies the hidden layers and metrics used for pursuing DNN optimizations and adaptations at the granularity of operators and kernels, ensuring every facet contributing to a DNN model's run-time efficiency is easily accessible to mobile developers via well-defined APIs. With nnPerf, the mobile developers can easily identify the bottleneck in model run-time efficiency and optimize the model architecture to meet system-level objectives (SLO). We implement nnPerf on TFLite framework and evaluate its e2e-, operator-, and kernel-latency profiling accuracy across four mobile platforms. The results show that nnPerf achieves consistently high latency profiling accuracy on both CPU (98.12%) and GPU (99.87%). Our benchmark studies demonstrate that running nnPerf on mobile devices introduces the minimum overhead to model inference, with 0.231% and 0.605% extra inference latency and power consumption. We further run a case study to show how we leverage nnPerf to migrate OFA, a SOTA NAS system, to kernel-oriented model optimization on GPUs.

The rapid development of the Industrial Internet of Things (IIoT) provides a significant opportunity to achieve comprehensive awareness and salient event detection in manufacturing factories. However, because of the limited onboard resources of IIoT terminal devices, it remains a challenging task in the face of the processing requirements of compute-intensive and latency-critical applications. To overcome this challenge, we study the hierarchical collaboration dynamic resource scheduling problem for the IIoT cloud-edge computing model. First, we divide the network into different domains for autonomous management and hierarchical collaboration according to the dynamically available computing resources and transmission delay of edge nodes. Second, we establish a computing model of task data size and resource requirement to maximize the processing benefit of tasks and load balancing between domains, formulate the task-domain Pareto optimality matching problem and the task-node optimal matching problem, which is transformed into the 0-1 Multiple Knapsack Problem (MKP). Third, we develop a hierarchical collaboration dynamic resource scheduling algorithm to solve the above optimal matching problems and set each time slot duration according to the processing rate of the algorithm. Extensive experiments show that our method provides an efficient and reliable scheduling strategy for IIoT in various scenarios with good scalability.

Deep-learning-based (DL-based) face recognition has become an important application in the Internet of Things (IoT) environment. However, recent studies demonstrate that elaborate adversarial examples can mislead the results of DL-based face recognition on mobile and edge devices. Such vulnerability threats the robustness of face recognition systems and causes security issues. Generative adversarial defense methods can reform adversarial examples before input into the face recognition model to improve the accuracy under adversarial attacks. Unfortunately, the existing generative adversarial defense methods cannot completely remove the misleading features of adversarial examples due to the lack of robust encoding ability. In this article, we propose a local consistency generative adversarial network (LC-GAN) framework by adding the constraint of local consistency to force the encoder to mine consistent features in each local area, achieving robust encoding ability consequently. The framework includes three main novel designs. First, we present a patch-wise contrastive learning-based refinement stage with local consistency loss to encode robust identity features from nonsalient areas that are undamaged by adversarial attacks. Second, we use a powerful expert network to guide the training of LC-GAN for eliminating adversarial identity features. Third, we design a multilevel identity loss to enhance the identity preservation ability by unifying the local and global identity features. Experimental results on four widely used face data sets show that LC-GAN outperforms other generative adversarial defense methods.

The unprecedented prosperity of the Industrial Internet of Things (IIoT) promotes the traditional industry transforming into intelligent manufacturing so that the whole production process can be comprehensively controlled to achieve flexible production. Intelligent scheduling, as one of the key enabling techniques, is desired to allocate the production of several machines by an efficient solution with minimum makespan. Existing approaches adopt a fixed search paradigm based on expert knowledge to seek satisfactory solutions. However, considering the varying data distribution and large sized of the practical problems, these methods fail to guarantee the quality of the obtained solution under the real-time requirement. To address this challenge, we formulate the production scheduling problem as a Markov decision process (MDP) and specifically design a job scheduling model made up of a job batching module for the hybrid flow-shop scheduling problem on batch processing machines (HFSP-BPM). Our proposed model consists of an actor network that learns the action under different conditions and a critic network that evaluates the action of the actor. We analyze the convergence of the model under different parameter settings to determine the optimal parameter. Extensive numerical experiments on both publicly available data set and real steel plant production data set demonstrate that the proposed deep reinforcement learning (DRL) approach compared with other baselines, more than 6% average improvements can be observed in many instances.

Recent on-manifold adversarial attacks can mislead gait recognition by generating adversarial walking postures (AWP) with image generation techniques. However, existing defense methods only eliminate adversarial perturbations on each frame isolatedly but ignore the temporal correlation of gait sequence, which leads to vulnerability of robust gait recognition. In this paper, we propose GaitReload, a post-processing adversarial defense method to defend against AWP for the gait recognition model with sequenced inputs. First, GaitReload utilizes sequenced entity recognition (SER) module to detect the adversarial frames by the temporal constraints of gait sequence. Then, we apply bayesian uncertainty filtering-based (BUF-based) gait interpolation to reform adversarial gait examples. After that, we reload the reformed gait sequence and rectify the recognition results with the guidance of reloading strategy. Specifically, SER has a bi-directional frame difference attention and a temporal feature aggregation to boost the detection performance. For training SER, we apply hidden posture selective attack (HPSA) to generate training samples. The extensive experimental results on CASIA-A, CASIA-B, and OU-ISIR demonstrate that GaitReload can defend against adversarial gait by large margins in both RGB and silhouette modes.

The prosperity of Internet of Things (IoT) brings forth the deployment of large-scale sensing systems such as smart cities. To enable the collaboration tasks among distributed devices, time synchronization is crucial. However, due to the long-range and device heterogeneity, accurate time synchronization for a large-scale IoT network is challenging. Existing GPS or NTP solutions either require an outdoor environment or only have low and unstable accuracy. In this paper, we propose AirSync, a novel synchronization method that leverages the widely existed aircraft signals, ADS-B, to synchronize large-scale IoT networks with nodes even in indoor environments. But ADS-B messages have no time stamp and cannot provide a reference time. We leverage the continuity of aircraft movements to estimate the aircraft traveling time. Then devices that observe common aircraft moving segments can calculate their time offset. To obtain the time skew, we propose a combined aircraft linear regression method. We also design a transitive synchronization for devices that cannot observe common aircraft. Besides, we also design a duty-cycled ADS-B message collection method for resource-limited IoT devices. We implement a prototype of AirSync and evaluate its performance in various real-world environments. The results show that AirSync can obtain the sub-ms accuracy.

WiFi-based Long Distance (WiLD) networks are promising to cover the rural and remote regions. But the explosive short-range WiFi deployments result in the long-short coexistence. Due to CSMA is ignorance of propagation delay, its carrier sensing is too short to detect long links, leading to the temporal hidden terminal problem that causes serious performance degradation and even starvation of long links. Existing methods for traditional hidden terminal problem are inefficient to cope with this problem because of the different causes. In this paper, we propose CSMA with Protective Jamming (CSMA/PJ), a new WiLD MAC protocol that solves the temporal hidden terminal problem with the minimized influence on uncontrollable short links. The key is generating protective jamming at the WiLD receiver that is sensible to the short links. By leveraging the asymmetric propagation delay of the WiLD transmitter and receiver, we make the jamming protective rather than destructive. We precisely control the jamming right before the arrivals of WiLD packets to set aside channel time for short links. We implement and evaluate CSMA/PJ on commercial devices. The experimental results show that CSMA/PJ can improve the throughput of the WiLD link by$6\times $and$5 \times $compared with the CSMA/CA and RTS/CTS methods.

For energy constraint wireless IoT nodes, their radios usually operate in duty cycle mode. With low maintenance and negotiation cost, asynchronous duty cycle radio management is widely adopted. To achieve fast network flooding is challenging in asynchronous duty cycle networks. Recently, concurrent flooding, which allows a set of nodes (called concurrent senders ) to immediately broadcast the received packet without any backoff, is a promising approach to improve the flooding speed. We observe that selecting either large or small number of concurrent senders cannot achieve the optimal flooding speed in different deployments. There is a tradeoff between the degradation of concurrent broadcast efficiency and the missing of early receiving chance. In this article, we propose COFlood (Concurrent Opportunistic Flooding), a practical and efficient concurrent flooding protocol in asynchronous duty cycle networks. First, COFlood constructs a concurrent flooding tree in distributed manner. The non-leaf nodes are selected as concurrent senders and they can cover the entire network while reserving the most capacity of concurrent broadcast for later added opportunistic concurrent senders. Moreover, we find that exploiting both early wake-up nodes and long lossy links can speed up the concurrent flooding tree-based network flooding by increasing the early receiving chances. Then, COFlood develops a lightweight method to select the nodes that meet the conditions of these two opportunities as opportunistic concurrent senders. We implement COFlood in TinyOS and evaluate it on two real testbeds. In comparison with state-of-the-art concurrent flooding protocol, completion time and energy consumption can be reduced by up to 35.3% and 26.6%.

The massive connection of LoRa brings serious collision interference. Existing collision decoding methods cannot effectively deal with the adjacent collisions that occur when the collided symbols are adjacent in the frequency spectrum. The decoding features relied on by the existing methods will be corrupted by adjacent collisions. To address these issues, we propose Paralign , which is the first LoRa collision decoder supporting decoding LoRa collisions with confusing symbols via parallel alignment. The key enabling technology behind Paralign is tha there is no spectrum leakage with periodic truncation of a chirp. Paralign leverages the precise spectrum obtained by aligning the de-chirped periodic signals from each packet in parallel for spectrum filtering and power filtering. To aggregate correlation peaks in different windows of the same symbol, Paralign matches the peaks of multiple interfering windows to the interested window based on the time offset between collided packets. Moreover, a periodic truncation method is proposed to address the multiple candidate peak problem caused by side lobes of confusing symbols. We evaluate Paralign using USRP N210 in a 20-node network. Experimental results demonstrate that Paralign can significantly improve network throughput, which is over 1.46× higher than state-of-the-art methods.

Adversarial training can defend against universal adversarial perturbation (UAP) by injecting corresponding adversarial samples during training. However, adversarial samples used by existing methods, such as UAP, inevitably include excessive perturbations related to other categories due to its inherent goal of universality. Training with them will cause more erroneous predictions with larger local positive curvature. In this paper, we propose a curvature-aware category adversarial training method to avoid excessive perturbations. We introduce the category-oriented adversarial masks that are synthesized with class distinctive momentum. Besides, we split the min-max optimization loops of adversarial training into two parallel processes to reduce the training cost. Experimental results on CIFAR-10 and ImageNet show that our method achieves better defense accuracy under UAP with less training cost than state-of-the-art baselines.

With the rapid growth of Internet of Things, the number of heterogeneous wireless devices working in the same frequency band increases dramatically, leading to severe cross-technology interference. To enable coexistence, researchers have proposed a large number of mechanisms to manage interference. However, existing mechanisms have severe modifications in either the physical or MAC (medium access control) layers, making them hard to be deployed on commercial devices. In this paper, we design and implement SledZig to boost cross-technology coexistence for low-power devices through both enabling more transmission opportunities and avoiding interference. SledZig is fully compatible with the standard in both physical and MAC layers. It decreases the WiFi signal power on the channel of low-power devices while keeps the WiFi transmission power unchanged, through making constellation points in the overlapped subcarriers have the lowest power, which can be achieved by just encoding the WiFi payload. We implement SledZig on hardware testbed and evaluate its performance under different settings. Experiment results show that SledZig can effectively increase ZigBee transmissions and improve its performance over a WiFi channel under various WiFi data traffic, with as low as 6.94% WiFi throughput loss.

Adversarial training can boost the robustness of the model by aligning discriminative features between natural and generated adversarial samples. However, the generated adversarial samples tend to have more features derived from changed patterns in other categories along with the training process, which prevents better feature alignment between natural and adversarial samples. Unfortunately, existing adversarial training methods ignore such dynamicity of generated adversarial samples. In this paper, we propose Adversarial Contrastive Decoupling (ACD) to filter the features derived from changed patterns. Specificity, we decouple the changed patterns from adversarial samples and then extract robust representations from remaining features. First, we introduce a decoupling module with a dynamic labeling strategy to explore the dynamicity of generated adversarial samples. Then, we propose a siamese network with contrastive learning mechanism to align remaining robust representations between adversarial and natural samples. Extensive experimental results demonstrate the superior performance of ACD over baselines.

Recent studies show that image retrieval systems are vulnerable to adversarial attacks that adds imperceptible noise to the images. But the imperceptibility of noise limits the attack performance. As a commonly acceptable interference, watermark often appears in images, which can be treated as ‘‘imperceptible’’ but is unexploited. In this paper, we propose a Watermark Attack method on Image Retrieval systems (WAIR). Attacking retrieval systems is challenging due to black-box model, the absence of confidence guide, and attack failures and low efficiency caused by the randomness of traditional evolutionary algorithms. To solve these challenges, we propose a new evolutionary algorithm called Gene Joint Selecting Algorithm (GJSA) that jointly optimize the watermark parameters. We also design the Fitness Record Table (FRT), a new data structure that records the historical attack effect to guide the following evolution and avoid local optimal solutions. Thanks to FRT, WAIR can also reduce the duplicate searching caused by algorithm randomness. The extensive experiments show that WAIR can attack the black-box image retrieval system with a successful rate of 0.806, which is 12.4% higher than the traditional evolutionary algorithm. Moreover, for attacking commercial image retrieval system, we achieve 2$\times$ higher attack success rate on Baidu Image Retrieval API than the existing methods.

The Industrial Internet of Things (IIoT) is deemed a promising direction to drive a new industrial revolution. However, due to the isolation of the existing OT network and IT network, the requirements of low latency, low jitter, and high reliability for transmission and processing of industrial time-sensitive tasks data traffic in IIoT scenarios with strong dynamic and complex topology face a series of non-trivial challenges. In this paper, we propose a hierarchical computing network collaboration architecture for IIoT based on edge/fog computing. Our architecture is built upon the Time-Sensitive Networking (TSN) to flexibly support different requirements of large-scale industrial production applications by constructing the hierarchical computing network collaboration domain, combined with an improved Cyclic Queuing and Forwarding (CQF) scheduling shaper mechanism. We tackle the critical problems of architecture design by presenting three essential components. Moreover, we build and implement our simulation testbed based on Omnet++, and evaluate our design.

LoRa is widely deploying in aquatic environments to support various Internet of Things applications. However, floating LoRa networks suffer from serious performance degradation due to the polarization loss caused by the swaying antenna. Existing methods that only control the transmission starting from the aligned attitude have limited improvement due to the ignorance of aligned period length. In this paper, we propose PolarScheduler, a dynamic transmission control method for floating LoRa networks. PolarScheduler actively controls transmission configurations to match polarization aligned periods. We propose a V-zone model to capture diverse aligned periods under different configurations. We also design a low-cost model establishment method and an efficient optimal configuration searching algorithm to make full use of aligned periods. We implement PolarScheduler on commercial LoRa platforms and evaluate its performance in a deployed network. Extensive experiments show that PolarScheduler can improve the packet delivery rate and throughput by up to 20.0% and 15.7%, compared to the state-of-the-art method.

Cross-Technology Communication (CTC) is an emerging technique that enables direct interconnection among incompatible wireless technologies. Recent work proposes CTC from IEEE 802.11b to LoRa but has a low efficiency due to their extremely asymmetric data rates. In this paper, we propose WiRa that emulates LoRa waveforms with IEEE 802.11ax to achieve an efficient CTC from WiFi to LoRa. By taking advantage of the OFDMA in 802.11ax, WiRa can use only a small Resource Unit (RU) to emulate LoRa chirps and set other RUs free for high-rate WiFi users. WiRa carefully selects the RU to avoid emulation failures and adopts WiFi frame aggregation to emulate the long LoRa frame. We propose a subframe header mapping method to identify and remove invalid symbols caused by irremovable subframe headers in the aggregated frame. We also propose a mode flipping method to solve Cyclic Prefix errors, based on our finding that different CP modes have different and even opposite impacts on the emulation of a specific LoRa symbol. We implement a prototype of WiRa on the USRP platform and commodity LoRa device. The extensive experiments demonstrate WiRa can efficiently transmit complete LoRa frames with the throughput of 40.037kbps and the symbol error rate (SER) lower than 0.1.

LoRa is widely deployed for various applications. Though the knowledge of the channel occupancy is the prerequisite of all aspects of network management, acquiring the channel occupancy for LoRa is challenging due to the large number of channels to be detected. In this paper, we propose LoRadar, a novel LoRa channel occupancy acquirer based on cross-channel scanning. Our in-depth study finds that Channel Activity Detection (CAD) in a narrow band can indicate the channel activities of wide bands because they have the same slope in the time-frequency domain. Based on our finding, we design the cross-channel scanning mechanism that infers the channel occupancy states of all the overlapping channels by the distribution of CAD results. We elaborately select and adjust the CAD settings to enhance the distribution features. We also design the pattern correction method to cope with distribution distortions. We implement LoRadar on commodity LoRa platforms and evaluate its performance on the indoor testbed and the outdoor deployed network. The experimental results show that LoRadar can achieve a detection accuracy of 0.99 and reduce the acquisition overhead by up to 0.90, compared to existing traversal-based methods.

With the popularization of deep learning models in wireless sensing, researchers have made considerable efforts to construct sophisticated models to improve the accuracy of related applications. But very few studies have addressed the potential vulnerabilities of deep models, and existing works evaluate wireless adversarial performance only in communication or sensing. None of them has a comprehensive definition of attack imperceptibility. In this paper, we come up with a definition of the wireless attack imperceptibility for both communication and sensing. Our goal is to craft an adversarial perturbation, which can degrade the performance of WiFi sensing without compromising WiFi communication. To achieve this goal, we propose WiCAM to reveal the temporal and spatial attention of a DNN, capturing the crucial portions of its input. Then we design a mask to limit adversarial perturbation in the attended parts only, and thus the impact of the attack on WiFi communication is minimized. WiCAM is a general adversarial framework that can integrate existing adversarial methods such as FGSM and PGD to generate perturbations. We carry out experiments on three popular WiFi sensing applications, including human activity recognition, gesture recognition, and user identification. Extensive experiments are conducted on both public datasets and self-collected datasets. The results show that when declining the accuracy of a target model below 50%, WiCAM can reduce the impact on communication in terms of BER by up to 77.78% in QAM-64, compared to the common adversarial methods.

WiFi has achieved great success in data communication in the past two decades and WiFi signals are recently further exploited for sensing purposes. Promising progress has been achieved and diverse WiFi sensing applications have been enabled. However, one critical issue which was not paid much attention to and we believe would greatly hinder the real-life adoption of WiFi sensing is that it actually affects WiFi communication. The fundamental reason is that WiFi sensing requires high-frequency signal samples and WiFi data packets can not meet this requirement. Therefore, existing WiFi sensing systems transmit dedicated high-frequency packets (200-2000 packets per second) for sensing and these “sensing packets” greatly affect the main data communication function of WiFi. In this work, we propose WiImg, a lightweight system which involves machine learning techniques to enable WiFi sensing under low packet rate, pushing WiFi sensing one step towards real-life adoption. The key idea is to convert the CSI samples into images and improve the Generative Adversarial Network (GAN) for CSI image inpainting, relaxing the requirement of high sample rate in sensing. To avoid the large training overhead of GAN, we design a lightweight GAN that leverages samples of only three rates to recover the CSI traces of any arbitrary rates. Experiments show that with just 25 packets per second, WiImg is able to increase the recognition accuracy for hand gesture recognition and daily activity tracking from the state-of-the-art 59.1% and 65.9% to 86.7% and 96.4%, respectively.

The coexistence of heterogeneous devices in wireless networks brings a new topic on cross-technology communication (CTC) to improve the coexistence efficiency and boost collaboration among these devices. Current advances on CTC mainly fall into two categories,physical-layer CTCandpacket-level energy modulation(PLEM). Thephysical-layer CTCachieves a high CTC data rate, but with channel incompatible to commercial devices, making it hard to be deployed in current wireless networks. PLEM is channel and physical layer compatible, but with two main drawbacks of the low CTC data rate and MAC incompatibility, which will induce severe interference to the other devices’ normal data transmissions. In this paper, we propose symbol-level energy modulation (SLEM), the first CTC method that is fully compatible with current devices in both channel and the physical/MAC layer processes, having the ability to be deployed in commercial wireless networks smoothly. SLEM inserts extra bits to WiFi data bits to generate the transmitting bits, so as to adjust the energy levels of WiFi symbols to deliver CTC information. We make theoretical analysis to figure out the performance of both CTC and WiFi transmissions. We also conduct experiments to demonstrate the feasibility of SLEM and its performance under different network situations.

Low Power Wide Area Networks (LPWAN) such as Long Range (LoRa) show great potential in emerging aquatic IoT applications. However, our deployment experience shows that the floating LPWAN suffers significant performance degradation, compared to the static terrestrial deployments. Our measurement results reveal the reason behind this is the polarization and directivity of the antenna. The dynamic attitude of a floating node incurs varying signal strength losses, which is ignored by the attitude-oblivious link model adopted in most of the existing methods. When accessing the channel at a misaligned attitude, packet errors can happen. In this paper, we propose an attitude-aware link model that explicitly quantifies the impact of node attitude on link quality. Based on the new model, we proposePolarTracker, a novel channel access method for floating LPWAN.PolarTrackertracks the node attitude alignment state and schedules the transmissions into the aligned periods with better link quality. To support concurrent access of multiple LoRa nodes, an attitude-based slotted-ALOHA protocol is proposed to reduce collision. We implement a prototype ofPolarTrackeron commercial LoRa platforms and extensively evaluate its performance in various real-world environments. The experimental results show thatPolarTrackercan efficiently improve the packet reception ratio by 50.6%, compared with ALOHA in LoRaWAN.

Research on cross-technology communication ( CTC ) has made rapid progress in recent years. While the CTC links are complex and dynamic, how to estimate the quality of a CTC link remains an open and challenging problem. Through our observation and study, we find that none of the existing approaches can be applied to estimate the link quality of CTC. Built upon the physical-level emulation, transmission over a CTC link is jointly affected by two factors: the emulation error and the channel distortion. Furthermore, the channel distortion can be modeled and observed through the signal strength and the noise strength. We, in this article, propose a new link metric called C-LQI and a joint link model that simultaneously takes into account the emulation error and the channel distortion in the In-phase and Quadrature ( IQ ) domain. We accurately describe the superimposed impact on the received signal. We further design a lightweight link estimation approach including two different methods to estimate C-LQI and in turn the packet reception rate ( PRR ) over the CTC link. We implement C-LQI and compare it with two representative link estimation approaches. The results demonstrate that C-LQI reduces the relative estimation error by 49.8% and 51.5% compared with s-PRR and EWMA, respectively.

Cross-technology interference is a major threat to the dependability of low-power wireless communications. Due to power and bandwidth asymmetries, technologies such as Wi-Fi tend to dominate the RF channel and unintentionally destroy low-power wireless communications from resource-constrained technologies such as ZigBee, leading to severe coexistence issues. To address these issues, existing schemes make ZigBee nodes individually assess the RF channel's availability or let Wi-Fi appliances blindly reserve the medium for the transmissions of low-power devices. Without a two-way interaction between devices making use of different wireless technologies, these approaches have limited scenarios or achieve inefficient network performance. This paper presents BiCord, a bidirectional coordination scheme in which resource-constrained wireless devices such as ZigBee nodes and powerful Wi-Fi appliances coordinate their activities to increase coexistence and enhance network performance. Specifically, in BiCord, ZigBee nodes directly request channel resources from Wi-Fi devices, who then reserve the channel for ZigBee transmissions on-demand. This interaction continues until the transmission requirement of ZigBee nodes is both fulfilled and understood by Wi-Fi devices. This way, BiCord avoids unnecessary channel allocations, maximizes the availability of the spectrum, and minimizes transmission delays. We evaluate BiCord on off-the-shelf Wi-Fi and ZigBee devices, demonstrating its effectiveness experimentally. Among others, our results show that BiCord increases channel utilization by up to 50.6% and reduces the average transmission delay of ZigBee nodes by 84.2% compared to state-of-the-art approaches.

Low Power Wide Area Networks (LPWAN) such as Long Range (LoRa) show great potential in emerging aquatic IoT applications. However, our deployment experience shows that the floating LPWAN suffer significant performance degradation, compared to the static terrestrial deployments. Our measurement results reveal the reason behind this is due to the polarization and directivity of the antenna. The dynamic attitude of a floating node incurs varying signal strength losses, which is ignored by the attitude-oblivious link model adopted in most of the existing methods. When accessing the channel at a misaligned attitude, packet errors can happen. In this paper, we propose an attitude-aware link model that explicitly quantifies the impact of node attitude on link quality. Based on the new model, we propose PolarTracker, a novel channel access method for floating LPWAN. PolarTracker tracks the node attitude alignment state and schedules the transmissions into the aligned periods with better link quality. We implement a prototype of PolarTracker on commercial LoRa platforms and extensively evaluate its performance in various real-world environments. The experimental results show that PolarTracker can efficiently improve the packet reception ratio by 48.8%, compared with ALOHA in LoRaWAN.

Deep learning-based person re-identification (Re-ID) methods have achieved the significant performance of matching person images across camera views, which plays an important role in the construction of the smart city. Recent works of adversarial attacks have explored the serious vulnerability of deep Re-ID systems. However, existing attacks are performed with idealized conditions and ignore the real-world environments, such as occlusion caused by walking habits. In this paper, we propose a two-stage method to perform an occlusion resilient adversarial attack for better evaluation of deep Re-ID systems. Specifically, we construct the occlusion template from the observation and statics of pedestrian walking habits. Then, we design a partition training strategy for a better combination of occluded and exposed adversarial patches. During the training, we introduce contextual loss to penalize the semantic distance of attacked images with the same identity. The extensive experiments on Market1501 demonstrate the performance of our method.

Deep neural networks are easily affected by adversarial patches, causing prediction errors. However, existing adversarial patches are trained with specific model-dataset pairs and only effective for the images with the predetermined size in the dataset. The semantic information of the patch will be distorted when scaling the image, which is a common preprocessing process in practical applications. In this paper, we propose SRA Patch (Scaling-Resilient Adversarial Patch), a new adversarial patch resilient to image scaling. Specifically, we generate the patch in a block-wise way and utilize the superpixel method to resist the loss of semantic information during scaling. Further, we introduce the ensemble model as a Black-Box indicator to address the noise space shrinking issue, which is caused by the small size and the block operation of SRA patch. Finally, we leverage Class Activation Mapping to extract the region with salient features as the final patch to improve the ratio of effective semantic features on the patch to remain during scaling. Extensive experiments have demonstrated that our SRA patch has much stronger attack capability and scaling robustness than existing methods.

For energy constrained wireless IoT nodes, their radios usually operate in duty cycle mode. With low maintenance and negotiation cost, asynchronous duty cycle radio management is widely adopted. To achieve fast network flooding is challenging in asynchronous duty cycle networks. Recently, concurrent flooding is a promising approach to improve the performance of network flooding. In concurrent flooding, a key challenge is how to select a set of concurrent senders to improve both flooding speed and energy efficiency. We observe that selecting neither large nor small number of concurrent senders can achieve the optimal performance in different deployments. In this paper, we propose COFlood (Concurrent Opportunistic Flooding), a practical and effective concurrent flooding protocol in asynchronous duty cycle networks. The basic idea is based on an energy-efficient flooding tree, COFlood opportunistically selects extra concurrent senders that can speed up network flooding. First, COFlood constructs an energy-efficient flooding tree in distributed manner. The non-leaf nodes are selected as senders and they can cover the entire network with low energy consumption. Moreover, we find that exploiting both early wakeup nodes and long lossy links can speed up the flooding tree based network flooding. Then, COFlood develops a light-weight method to select the nodes that meet the conditions of these two opportunities as opportunistic senders. We implement COFlood in TinyOS and evaluate it on two real testbeds. In comparison with state-of-the-art concurrent flooding protocol, completion time and energy consumption can be reduced by up to 35.3% and 26.6%.

The advancements of AI and the exponential growth of sensory data are unlocking a wave of intelligent sensing applications. To overcome the shortcoming of centralized learning and local training, Google proposes federated learning that allows users to collectively reap the benefits of shared models trained from decentralized data. However, directly applying federated learning to intelligent sensing applications faces two deficiencies: 1) omitting personalities of local models and 2) high latency. Aiming at these limitations, in this article, we propose a new framework, Federated Sensing, to enable edge-cloud elastic collaborative learning from decentralized sensory data. We design an elastic local update algorithm that can train the personalized models by setting specific updating weights for each node based on the difference between the global and local model. Our algorithm takes both the global consistency and the personalities of the local models. We further propose an n-softsync model aggregation method that significantly reduces training time by combining the synchronous and asynchronous aggregations. Extensive experiments are conducted on two real-world data sets of air quality from Beijing and Los Angeles. Compared with existing federated learning techniques, our framework improves the model performance at least by 2.61% and 18.8% in two data sets, respectively. Besides, it reduces the cloud idle time to 25.5% of the total time, which verifies the advantages of our method in terms of both model performance and training overhead.

Cross-Technology Communication (CTC) is an emerging technique that enables direct communication across different wireless technologies. The state-of-the-art works in this area propose physical-level CTC, in which the transmitters emulate signals that follow the receiver's standard. Physical-level CTC means considerable processing complexity at the transmitter, which does not apply to the communication from a low-end transmitter to a high-end receiver. This article proposes LEGO-Fi, which supports the CTC from ZigBee to WiFi and Bluetooth to WiFi. LEGO-Fi is a transmitter-transparent CTC technique, which leaves the processing complexity solely at the receiver side and therefore, makes a critical advance toward bidirectional high-throughput CTC. The key technique inside is cross-demapping, which stems from two key technical insights: 1) a ZigBee/Bluetooth packet leaves distinguishable features when passing the WiFi modules and 2) compared to ZigBee's/Bluetooth's simple encoding and modulation schemes, the rich processing capacity of WiFi offers extra flexibility to process a ZigBee/Bluetooth packet. The evaluation results show that LEGO-Fi achieves a throughput of 213.6 Kb/s in practice, which is, respectively, 13000×, 1200×, and 7.5× faster than FreeBee, ZigFi, and SymBee, the three existing ZigBee-to-WiFi CTC approaches. For the CTC from Bluetooth to WiFi, LEGO-Fi achieves a throughput of 904.1 Kb/s.

Wi-Fi-based crowd counting is predominant because of its noninvasive and ubiquitous advantages. However, the existing Wi-Fi-based crowd counting systems have the constraint that there is always a maximum number of people counted. In order to address this issue, a Wi-Fi-based cross-environment crowd counting system, which has the capability of both estimating the walking direction and crowd counting by only one single link, called WiCrowd is proposed. WiCrowd relaxes the restriction of people number counted and demonstrates its extraordinary robustness when the environment changes. The signal change trends of the people flow are theoretically analyzed and people flow moving direction is inferred. The unique features using the eigenvalue of the convariance matrix of amplitude and phase are derived to effectively detect prominent signal changes led by the crowd movement near LoS. By adopting the augmented feature representations, the robustness of WiCrowd is improved when the environment changes. The experimental results in a typical indoor environment demonstrate the superior performance of WiCrowd. This system achieves 87.4%, 85.8%, and 79.4% recognition accuracy for the flow movement direction estimation, respectively, and 82.4% and 81.6% of the overall cross-environment accuracy for the number of subjects counted in the people flow.

Eccentricity detection is a crucial issue for high-speed rotating machinery, which concerns the stability and safety of the machinery. Conventional techniques in industry for eccentricity detection are mainly based on measuring certain physical indicators, which are costly and hard to deploy. In this paper, we propose RED, a non-intrusive, low-cost, and real-time RFID-based eccentricity detection approach. Differing from the existing RFID-based sensing approaches, RED utilizes the temporal and phase distributions of tag readings as effective features for eccentricity detection. RED includes a Markov chain based model called RUM, which only needs a few sample readings from the tag to make a highly accurate and precise judgement. The design of RED further addresses practical issues, such as parameterizing the RUM model, making it robust to dynamic and noisy environments, and considering how the doppler shift may affect our system. We implement RED with COTS RFID reader and tags, and evaluate its performance across various scenarios. The overall accuracy is 93.6 percent and the detection latency is 0.68 seconds in average.

RFID tracking attracts a lot of research efforts in recent years. Most of the existing approaches, however, adopt an orientation-oblivious model. When tracking a target whose orientation changes, those approaches suffer from serious accuracy degradation. In order to achieve target tracking with pervasive applicability in various scenarios, in this article, we propose OmniTrack, an orientation-aware RFID tracking approach. Our study presents a generic model that discribes the linear relationship between the tag orientation and the phase change of the backscattered signals. Based on this finding, we propose an orientation-aware phase model to explicitly quantify the respective impact of the read-tag distance and the tag's orientation. OmniTrack addresses practical challenges in tracking the location and orientation of a mobile tag. Our experimental results demonstrate that OmniTrack achieves centimeter-level location accuracy and has significant advantages in tracking targets with varing orientations, compared to the state-of-the-art approaches.

Operating in unlicensed ISM bands, ZigBee devices often yield poor performance due to the interference from ever increasing wireless devices in the 2.4 GHz band. Our empirical results show that, a specific interference is likely to have different influence on different outbound links of a ZigBee sender, which indicates the chance of concurrent transmissions. Based on this insight, we propose Smoggy-Link, a practical protocol to exploit the potential concurrency for adaptive ZigBee transmissions under harsh interference. Smoggy-Link maintains an accurate link model to quantify and trace the relationship between interference and link qualities of the sender's outbound links. With such a link model, Smoggy-Link can translate low-cost interference information to the fine-grained spatiotemporal link state. The link information is further utilized for adaptive link selection and intelligent transmission schedule. We implement and evaluate a prototype of our approach with TinyOS and TelosB motes. The evaluation results show that Smoggy-Link has consistent improvements in both throughput and packet reception ratio under interference from various interferers.

Cross-Technology Communication (CTC) is an emerging technique that enables direct interconnection among incompatible wireless technologies. However, CTC channels are inherently asymmetric because of either the one-way nature of emulation or the asymmetric communication range caused by the asymmetric transmission power. In this paper, we focus on establishing symmetric CTC over asymmetric CTC channels. The bottleneck is the short communication range from the low-power and narrow-band technology to the high-power and wide-band technology. To compensate the inevitable distortions, we take advantage of the channel asymmetry and construct chirps in WiFi Channel State Information (CSI) to extend the communication range from ZigBee to WiFi. We build the theoretical model of CSI chirp based CTC and design c-Chirp, a novel CTC from ZigBee to WiFi. Due to channel asymmetry and discreteness, the WiFi receiver can only observe partial and distorted CSI chirps. To cope with this issue, we design a matching based chirp decoding method as well as an adaptation algorithm to reliably decode the symbols. We further extend c-Chirp to one-to-multiple concurrent transmission scenario. The evaluation results show that c-Chirp can achieve a communication range of 60m, which is 6× longer than ZigFi, an existing representative CTC from ZigBee to WiFi.

In a large-scale wireless sensor network, hundreds and thousands of sensors sample and forward data back to the sink periodically. In two real outdoor deployments GreenOrbs and CitySee, we observe that some bottleneck nodes strongly impact other nodes’ data collection and thus degrade the whole network performance. To figure out the importance of a node in the process of data collection, system manager is required to understand interactive behaviors among the parent and child nodes. So we present a management tool BOND (BOttleneck Node Detector), which explains the concept of Node Dependence to characterize how much a node relies on each of its parent nodes, and also models the routing process as a Hidden Markov Model and then uses a machine learning approach to learn the state transition probabilities in this model. Moreover, BOND can predict the network dataflow if some nodes are added or removed to avoid data loss and flow congestion in network redeployment. We implement BOND on real hardware and deploy it in an outdoor network system. The extensive experiments show that Node Dependence indeed help to explore the hidden bottleneck nodes in the network, and BOND infers the Node Dependence with an average accuracy of more than 85%.

Cross-Technology Interference (CTI) badly harms the transmission reliability for low-power networks such as ZigBee at 2.4-GHz band. Though promising, channel hopping still faces challenges because the increasingly dense deployment of CTI leaves very few available channels. Selecting a good channel with the least overhead is crucial but challenging. Most of the existing works are heuristic methods that choose a channel far from the current one to avoid adjacent channels that may be correlatively interfered by CTI with a wider bandwidth such as WiFi. However, we observe that the correlated channels influenced by the same CTI source do not necessarily have the same channel qualities and even the opposite state, due to the uneven spectrum power density of CTI. Such channel opportunities are unexplored and wasted. In this article, we propose CoHop, a quantitative correlation-based channel hopping method for low-power wireless networks. We establish a quantitative model that describes the correlation of channel qualities to capture channel opportunities and calculate channel quality without probing, to reduce probing overhead. The probing sequence is optimized based on the Pearson Correlation Coefficient and the prediction-based probing algorithm. We implement CoHop on TinyOS and evaluate its performance in various environments. The experimental results show that CoHop can increase the Packet Reception Ratio by 80%, compared with existing methods.

Cross-Technology Communication (CTC) is an emerging technique that enables the direct communication across incompatible wireless technologies. Without modifying any hardware, CTC establishes mutually sensible side channel by manipulating the packet transmissions and encodes information by constructing transmission patterns in terms of signal strength, packet interval, and etc. However, the transmission patterns are prone to the coexisting interference, leading to the unreliability of CTC. Most of the existing methods deal with the reliability problem by reactive retransmission of the corrupted packets, which incurs large delay. In this paper, we propose RCTC, a rateless-coding based CTC that proactively copes with the unreliability. Since the computation ability of low-power ZigBee nodes is limited, we carefully design the coding combination with proper degree distribution to balance the trade-off between reliability and decoding latency. We also propose a coding adaptation algorithm to adapt to the channel dynamics. We implement a prototype on commercial WiFi and ZigBee platforms. The experiment results show that RCTC can reduce the BER by up to 92.6%, compared to existing CTC methods.

Research on Cross-technology communication (CTC) has made rapid progress in recent years, but how to estimate the quality of a CTC link remains an open and challenging problem. Through our observation and study, we find that none of the existing approaches can be applied to estimate the link quality of CTC. Built upon the physical-level emulation, transmission over a CTC link is jointly affected by two factors: the emulation error and the channel distortion. We in this paper propose a new link metric called C-LQI and a joint link model that simultaneously takes into account the emulation error and the channel distortion in the process of CTC. We further design a light-weight link estimation approach to estimate C-LQI and in turn the PRR over the CTC link. We implement C-LQI and compare it with two representative link estimation approaches. The results demonstrate that C-LQI reduces the relative error of link estimation respectively by 46% and 53% and saves the communication cost by 90%.

Opportunistic forwarding seizes early forwarding opportunities in duty-cycled networks to reduce delay and energy consumption. But increasingly serious Cross-Technology Interference (CTI) significantly counteracts the benefits of opportunistic forwarding. Existing solutions try to reserve the channel for low-power networks by implicit avoidance or explicit coordination but ignore the potential of high-power CTI's superior capability. In this paper, we propose a new paradigm for low-power opportunistic forwarding in CTI environments. Instead of keeping high-power CTI devices silent, we directly involve them into the forwarding, as cross-technology forwarders. We design Portal to solve the challenges of realizing cross-technology opportunistic forwarding. To be transparent to the low-power networks, Portal adopts cross-technology rebroadcasting to enable the fast overhearing and forwarding of cross-technology data. To maximize the performance gain of using heterogeneous forwarders while minimizing the influence on legacy high-power traffic, we propose a post-forwarding forwarder selection and a traffic scheduling method. We also propose a feature-based ACK recognition method and a jamming-based ACK replying mechanism to forward the unreliable ACKs from asymmetric regions. Extensive experiments demonstrate that Portal not only avoids the CTI but also breaks through the existing performance limit.

As a new type of highly collaborative and shared intelligent network between producers and production environments, Industrial Internet of Things (IIOT) has been taken an important part of the fourth industrial revolution. IIOT generates large amounts of sensory data which need to be processed rapidly. However, the cloud-based data processing method consumes a long time and huge network overhead, which further affects the quality of service. On the other hand, the emerging edge computing also cannot process data efficiently because of limited compute and network resource. In this paper, we propose a four-layer network architecture based on SDN for the industrial internet of things scenario. Through effective transmission and computation coupling, the processing response efficiency is improved. We present a three-level computation offloading method to realize the optimization of network delay and power consumption. Theory and experiments show that the method proposed in this paper can effectively reduce the computation power consumption and response time.

Thanks to Industrial Internet of Things (IIoT), traditional industry is transforming to the fine and flexible production. To comprehensively control the dynamic industrial processes that includes marketing and production, accurate productivity is a vital factor that can reduce the idle operation and excessive pressure of the equipment. Due to increasing requirements of flexible control desired by IIoT, the productivity forecast also demands finer granularity. However, due to the neglect of multiple related factors and the ignorance of the multi-frequency characteristics of productivity, existing methods fail to provide accurate fine-grained productivity forecasting service for IIoT. To fill this gap, we propose a multivariate and multi-frequency Long Short-Term Memory model (mmLSTM) to predict the productivity in the granularity of day. mmLSTM takes equipment status and order as new supporting factors and leverages a multivariate LSTM to model their relationship to productivity. mmLSTM also integrate a multi-level wavelet decomposition network to thoroughly capture the multi-frequency features of productivity. We apply the proposed method in a real-world steel factory and conduct a comprehensive evaluation of performance with the productivity data in nearly two years. The result shows that our method can effectively improve the prediction accuracy and granularity of industrial productivity.

The coexistence of heterogeneous devices in wireless networks brings a new topic on cross-technology communication (CTC) to improve the coexistence efficiency and boost collaboration among these devices. Current advances on CTC mainly fall into two categories, physical-layer CTC and packet-level energy modulation (PLEM). The physical-layer CTC achieves a high CTC data rate, but with channel incompatible to commercial devices, making it hard to be deployed in current wireless networks. PLEM is channel and physical layer compatible, but with two main drawbacks of the low CTC data rate and MAC incompatibility, which will induce severe interference to the other devices’ normal data transmissions. In this paper, we propose symbol-level energy modulation (SLEM), the first CTC method that is fully compatible with current devices in both channel and the physical/MAC layer processes, having the ability to be deployed in commercial wireless networks smoothly. SLEM attaches the CTC bits to one WiFi data packet through adjusting the energy levels of WiFi symbols, achieving concurrent CTC and WiFi transmissions. We make theoretical analysis to figure out the performance tradeoff between CTC and WiFi, and also conduct experiments to demonstrate the feasibility of SLEM and its performance under different network situations.

Cross-Technology Interference (CTI) badly harms the transmission reliability for low-power networks such as ZigBee at 2.4GHz band. Though promising, channel hopping still faces challenges because the increasingly dense deployment of CTI leaves very few available channels. Selecting a good channel with the least overhead is crucial but challenging. Most of the existing works are heuristic methods that choose a channel far from the current one to avoid adjacent channels that may be correlatively interfered by CTI with a wider bandwidth such as WiFi. However, we observe that the correlated channels influenced by the same CTI source do not necessarily have the same channel qualities and even the opposite state, due to the uneven spectrum power density of CTI. Such channel opportunities are unexplored and wasted. In this paper, we propose CoHop, a quantitative correlation based channel hopping method for low-power wireless networks. We establish a quantitative model that describes the correlation of channel qualities to capture channel opportunities and calculate channel quality without probing, to reduce probing overhead. We implement CoHop on TinyOS and evaluate its performance in various environments. The experimental results show that CoHop can increase the Packet Reception Ratio (PRR) by 80%, compared with existing methods.

Cross-Technology Communication (CTC) is an emerging technique that enables direct interconnection among incompatible wireless technologies. However, CTC channels established by existing methods are inherently asymmetric because of either the one-way nature of emulation in physical-level CTC or the asymmetric communication range caused by the asymmetric transmission power. In this paper, we focus on establishing symmetric CTC over asymmetric CTC channels. The bottleneck is the short communication range from the low-power and narrow-band technology to the high-power and wide-band technology because the asymmetric bandwidth and transmission power lead to serious symbol distortions. To compensate the inevitable distortions, we take advantage of the channel asymmetry and construct chirps in WiFi Channel State Information (CSI) to enhance the patterns used for conveying data. In this way, we can extend the communication range from ZigBee to WiFi. We theoretically build the model of CSI chirp based CTC and design c-Chirp, a novel CTC from ZigBee to WiFi. Due to channel asymmetry and discreteness, the WiFi receiver can only observe partial and distorted CSI chirps. To cope with this issue, we design a matching based chirp decoding method as well as an adaptation algorithm to reliably decode the symbols. We conduct extensive experiments to evaluate c-Chirp. The results show that c-Chirp can achieve a 60m communication range from ZigBee to WiFi, which is 6× longer than ZigFi, an existing representative CTC from ZigBee to WiFi.

The prosperity of Internet of Things (IoT) brings forth the deployment of large-scale sensing systems such as smart cities. The distributed devices upload their local sensing data to the cloud and collaborate to fulfill the large-area tasks such as pollutant diffusion analysis and target tracking. To accomplish the collaboration, time synchronization is crucial. However, due to the long range and device heterogeneity, accurate time synchronization for a large-scale IoT network is challenging. Existing GPS or NTP solutions either require an outdoor environment or only have low and unstable accuracy. In this paper, we propose AirSync, a novel synchronization method that leverages the widely existed aircraft signals, ADS-B, to synchronize large-scale IoT networks with nodes even in indoor environments. But ADS-B messages have no time stamp and cannot provide a reference time. We leverage the continuity of aircraft movements to estimate the aircraft traveling time. Then devices that observe common aircraft moving segments can calculate their time offset. To obtain the time skew, we propose a combined aircraft linear regression method. We also design a transitive synchronization for devices that cannot observe common aircraft. We implement a prototype of AirSync and evaluate its performance in various real-world environments. The results show that AirSync can obtain the sub-ms accuracy.

In this article, we propose WiSign that recognizes the continuous sentences of American Sign Language (ASL) with existing WiFi infrastructure. Instead of identifying the individual ASL words from the manually segmented ASL sentence in existing works, WiSign can automatically segment the original channel state information (CSI) based on the power spectral density (PSD) segmentation method. WiSign constructs a five-layer Deep Belief Network (DBN) to automatically extract the features of isolated fragments, and then uses the Hidden Markov Model (HMM) with Gaussian mixture and Forward-Backward algorithm to recognize sign words. In order to further improve the accuracy, WiSign also integrates the language model N-gram, which uses the grammar rules of ASL to calibrate the recognized results of sign words. We implement a prototype of WiSign with commercial WiFi devices and evaluate its performance in real indoor environments. The results show that WiSign achieves satisfactory accuracy when recognizing ASL sentences that involve the movements of the head, arms, hands, and fingers.

The proliferation of IoT applications brings the demand of ubiquitous connections among heterogeneous wireless devices. Cross-Technology Communication (CTC) is a significant technique to directly exchange data among heterogeneous devices that follow different standards. By exploiting a side-channel like frequency, amplitude, or temporal modulation, the existing works enable CTC but have limited performance under channel noise. In this article, we propose WiZig, a novel CTC technique from WiFi to ZigBee that employs modulations in both the amplitude and temporal dimensions to optimize the throughput over a noisy channel. We establish a theoretical model of the energy communication channel to clearly understand the channel capacity. We then devise an online rate adaptation algorithm to adjust the modulation strategy according to the channel condition. Based on the theoretical model, WiZig controls the number of encoded energy amplitudes and the length of a receiving window, so as to optimize the CTC throughput. We implement a prototype of WiZig on a software radio platform and a commercial ZigBee device. The evaluation shows that WiZig achieves a throughput of 153.85bps with less than 1% symbol error rate in a real environment.

Cross-technology communication (CTC) is a technique that enables direct communication among different wireless technologies. Recent works in this area have made substantial progress, but CTC from ZigBee to WiFi remains an open problem. In this paper, we propose ZigFi, a novel CTC framework that enables communication from ZigBee to WiFi. ZigFi carefully overlaps ZigBee packets with WiFi packets. Through experiments we show that Channel State Information (CSI) of the overlapped packets can be used to convey data from ZigBee to WiFi. Based on this finding, we propose a receiver-initiated protocol and translate the decoding problem into a problem of CSI classification with Support Vector Machine. We further build a generic model through experiments, which describes the relationship between the Signal to Interference and Noise Ratio (SINR) and the symbol error rate (SER). Moreover, we extend ZigFi to multiple-to-one concurrent transmissions. We implement ZigFi on commercial-off-the-shelf WiFi and ZigBee devices. We evaluate the performance of ZigFi under different experimental settings. The results demonstrate that ZigFi achieves a throughput of 215.9bps, which is 18X faster than the state of the arts.

Low Earth Orbit (LEO) satellite networks play an indispensable role in global communications. To cope with the dynamic nature of the LEO networks, a flexible management architecture that can provide low-latency configuration and routing services is desired. Recent advances of Software Defined Networks (SDN) inspire researches using geostationary satellites, GEO, as the controllers to build the SDN solutions for LEO satellite networks. However, GEO-based solutions inevitably face the bottleneck problem because all the routing requests have to be processed and forwarded by a limited number of GEO satellites. In this paper, we propose HTCA, a Hierarchical Terrestrial Controllers Architecture based on SDN that reuses the ground stations instead of dedicated GEO satellites to establish a more scalable control plane. But the limited coverage of a ground station brings about design challenges for consistent network management and seamless routing service. HTCA adopts an online network view integration method to support flexible and consistent management. A load-aware routing method is also designed for HTCA to provide seamless and low-latency routing service. The experiment results demonstrate that HTCA can achieve agile configuration and reduce the instruction update time by 86.87%, compared with the GEO-based solution.

Cross-Technology Communication (CTC) is an emerging technique that enables direct communication across different wireless technologies. The state-of-the-art works in this area propose physical-level CTC, in which the transmitters emulate signals that follow the receiver's standard. Physical-level CTC means considerable processing complexity at the transmitter, which doesn't apply to the communication from a low-end transmitter to a high-end receiver, e.g. from ZigBee to WiFi. This paper presents transmitter-transparent cross-technology communication, which leaves the processing complexity solely at the receiver side and therefore makes a critical advance toward bidirectional high-throughput CTC. We implement our proposal as LEGO-Fi, the communication from ZigBee to WiFi. The key technique inside is cross-demapping, which stems from two key technical insights: (1) A ZigBee packet leaves distinguishable features when passing the WiFi modules. (2) Compared to ZigBee's simple encoding and modulation schemes, the rich processing capacity of WiFi offers extra flexibility to process a ZigBee packet. The evaluation results show that LEGO-Fi achieves a throughput of 213.6Kbps, which is respectively 13000× and 1200× faster than FreeBee and ZigFi, the two existing ZigBee-to-WiFi CTC approaches.

Cross-Technology Communication (CTC) is an emerging technology to support direct communication between wireless devices that follow different standards. In spite of the many different proposals from the community to enable CTC, the performance aspect of CTC is an equally important problem but has seldom been studied before. We find this problem is extremely challenging, due to the following reasons: on one hand, a link for CTC is essentially different from a conventional wireless link. The conventional link indicators like RSSI (received signal strength indicator) and SNR (signal to noise ratio) cannot be used to directly characterize a CTC link. On the other hand, the indirect indicators like PER (packet error rate), which is adopted by many existing CTC proposals, cannot capture the short-term link behavior. As a result, the existing CTC proposals fail to keep reliable performance under dynamic channel conditions. In order to address the above challenge, we in this paper propose AdaComm, a generic framework to achieve self-adaptive CTC in dynamic channels. Instead of reactively adjusting the CTC sender, AdaComm adopts online learning mechanism to adaptively adjust the decoding model at the CTC receiver. The self-adaptive decoding model automatically learns the effective features directly from the raw received signals that are embedded with the current channel state. With the lossless channel information, AdaComm further adopts the fine tuning and full training modes to cope with the continuous and abrupt channel dynamics. We implement AdaComm and integrate it with two existing CTC approaches that respectively employ CSI (channel state information) and RSSI as the information carrier. The evaluation results demonstrate that AdaComm can significantly reduce the SER (symbol error rate) by 72.9% and 49.2%, respectively, compared with the existing approaches.

Consumer Virtual Reality (VR) has been widely used in various application areas, such as entertainment and medicine. In spite of the superb immersion experience, to enable high-quality VR on untethered mobile devices remains an extremely challenging task. The high bandwidth demands of VR streaming generally overburden a conventional wireless connection, which affects the user experience and in turn limits the usability of VR in practice. In this paper, we propose FoVR, attention-based hierarchical VR streaming through bandwidth-limited wireless networks. The design of FoVR stems from the insight that human's vision is hierarchical, so that different areas in the field of view (FoV) can be served with VR content of different qualities. By exploiting the gaze tracking capacity of the VR devices, FoVR is able to accurately predict the user's attention so that the streaming of hierarchical VR can be appropriately scheduled. In this way, FoVR significantly reduces the bandwidth cost and computing cost while keeping high quality of user experience. We implement FoVR on a commercial VR device and evaluate its performance in various scenarios. The experiment results show that FoVR reduces the bandwidth cost by 88.9% and 76.2%, respectively compared to the original VR streaming and the state-of-the-art approach.

Backscatter communication, due to its low energy consumption, attract a broad range of applications. The throughput of such low-power communication is however limited. Parallel backscatter is deemed as a promising technique for improving the overall throughput by enabling concurrent transmissions of the backscattering tags. The state-of-the-art approaches for parallel backscatter assume that all the states of the collided signals are distinguishable in the In-phase and Quadrature (IQ) signal plane. In this paper, we disclose the superclustering phenomenon that makes the assumption untenable and significantly degrades the overall performance. Moreover, we observe that the indistinguishable states at different channels are not the same due to the intrinsic channel diversity. Motivated by the observation, we propose Canon, an approach that exploits the channel diversity of the backscatter tags for reliable parallel decoding. In Canon, we address two critical challenges: (i) designing the Multi-Carrier Backscatter (MCB) module to extract the collided signals simultaneously from multiple channels, (ii) designing the Multi-Channel Cluster Union (MCCU) algorithm to distinguish each state of the collided signals. The experiments demonstrate that Canon can achieve over 10 times higher throughput than the state-of-the-art approaches.

Cross- Technology Communication (CTC) is an emerging technique to enable the direct communication among different wireless technologies. A main category of the existing proposals on CTC propose to modulate packets at the sender side, and demodulate them into 1 and 0 bits at the receiver side. The performance of those proposals is likely to degrade in a densely coexisting environment. Solely judged according to the received signal strength, a symbol 0 that is modulated as packet absence is generally indistinguishable from dynamic interference. In this paper, we propose StripComm, interference-resilient CTC in coexisting environments. A sender in StripComm adopts an interference-resilient coding scheme that contains both presence and absence of packets in one symbol. The receiver strips the interference from the interested signal by exploiting the self-similarity of StripComm signals. We prototype StripComm with commercial WiFi, ZigBee devices and a software radio platform. The theoretical and experimental evaluation demonstrate that StripComm offers a data rate up to 1.1K bps with a SER (Symbol Error Rate) lower than 0.01 and a data rate of 0.89K bps even against strong interference.

Cross-technology communication (CTC) is a technique that enables direct communication among different wireless technologies. Recent works in this area have made positive progress, but high-throughput CTC from ZigBee to WiFi remains an open problem. In this paper, we propose ZigFi, a novel CTC framework that enables direct communication from ZigBee to WiFi. Without impacting the ongoing WiFi transmissions, ZigFi carefully overlaps ZigBee packets with WiFi packets. Through experiments we show that Channel State Information (CSI) of the overlapped packets can be used to convey data from ZigBee to WiFi. Based on this finding, we propose a receiver-initiated protocol and translate the decoding problem into a problem of CSI classification with Support Vector Machine. We further build a generic model through experiments, which describes the relationship between the Signal to Interference and Noise Ratio (SINR) and the symbol error rate (SER). We implement ZigFi on commercial-off-the-shelf WiFi and ZigBee devices. We evaluate the performance of ZigFi under different experimental settings. The results demonstrate that ZigFi achieves a throughput of 215.9bps, which is 18X faster than the state-of-the-art.

Eccentricity detection is a crucial issue for highspeed rotating machinery, which concerns the stability and safety of the machinery. Conventional techniques in industry for eccentricity detection are mainly based on measuring certain physical indicators, which are costly and hard to deploy. In this paper, we propose RED, a non-intrusive, low-cost, and realtime RFID-based eccentricity detection approach. Differing from the existing RFID-based sensing approaches, RED utilizes the temporal and phase distributions of tag readings as effective features for eccentricity detection. RED includes a Markov chain based model called RUM, which only needs a few sample readings from the tag to make a highly accurate and precise judgement. We implement RED with commercial-of-the-shelf RFID reader and tags, and evaluate its performance across various scenarios. The overall accuracy is 93.59% and the detection latency is 0.68 seconds in average.

RFID tracking attracts a lot of research efforts in recent years. Most of the existing approaches, however, adopt an orientation-oblivious model. When tracking a target whose orientation changes, those approaches suffer from serious accuracy degradation. In order to achieve target tracking with pervasive applicability in various scenarios, we in this paper propose OmniTrack, an orientation-aware RFID tracking approach. Our study discovers the linear relationship between the tag orientation and the phase change of the backscattered signals. Based on this finding, we propose an orientation-aware phase model to explicitly quantify the respective impact of the read-tag distance and the tags orientation. OmniTrack addresses practical challenges in tracking the location and orientation of a mobile tag. Our experimental results demonstrate that OmniTrack achieves centimeterlevel location accuracy and has significant advantages in tracking targets with varing orientations, compared to the state-of-the-art approaches.

The development of Internet-of-Things (IoT) technologies in recent years brings us unprecedented opportunities for innovations in the power industry. This demo abstract introduces our research and practice with Pavatar - IoT for the power industry. Pavatar includes a series of system deployments in the core sections of Global Energy Internet (GEI), for the purposes of automatic surveillance and remote diagnosis of ultra-high-voltage converter stations (UHVCSs). Pavatar incorporates technologies like lower-power or battery-free sensing, cross-technology communication, edge computing, machine learning, and enhances the user experience with 3D virtual reality. The deployed system significantly reduces the manpower cost and enhances the operational efficiency of the UHVCS.

Software-defined networking (SDN) is deemed as a promising direction to offer generalizability of wireless sensor networks (WSN). To introduce SDN into WSNs, however, means a series of non-trivial challenges due to the wireless and ad-hoc nature of WSNs. In this paper, we present our study towards a software-defined architecture for multi-function wireless sensor networks. Our proposal called Pangu is built upon the opportunistic routing protocol stack and introduces the concept of modality properties of sensor nodes. It enables centralized network control over a WSN while preserving the flexibility of underlying ad-hoc routing. We tackle the critical problems of the architecture design by presenting three essential components of Pangu. Moreover, we implement Pangu on a real-world testbed and evaluate it with various experiments.

The proliferation of loT applications drives the need of ubiquitous connections among heterogeneous wireless devices. Cross-Technology Communication (CTC) is a significant technique to directly exchange information among heterogeneous devices that follow different standards. By exploiting a side-channel like frequency, amplitude or temporal modulation, the existing works enable CTC but have limited performance under channel noise. In this paper, we propose WiZig, a novel CTC technique that employs modulation techniques in both the amplitude and temporal dimensions to optimize the throughput over a noisy channel. We establish a theoretical model of the energy communication channel to clearly understand the channel capacity. We then devise an online rate adaptation algorithm to adjust the modulation strategy according to the channel condition. Based on the theoretical model, WiZig can accurately control the number of encoded energy amplitudes and the length of a receiving window, so as to optimize the CTC throughput. We implement a prototype of WiZig on a software radio platform and a commercial ZigBee device. The evaluation show that WiZig achieves a throughput of 153.85 bps with less than 1 % symbol error rate in a real environment. The results demonstrate that WiZig realizes efficient and reliable CTC under varied channel conditions.

To save energy, wireless sensor networks often run in a low-duty-cycle mode, where the radios of sensor nodes are scheduled between ON and OFF states. For nodes to communicate with each other, low power listening (LPL) and low power probing (LPP) are two types of rendezvous mechanisms. Nodes with LPL or LPP rely on signal strength or probe packets to detect potential transmissions, and then keep the radio-ON for communications. Unfortunately, in co-existing environments, signal strength and probe packets are susceptible to interference, resulting in undesirable radio ON time when the signal strength of interference is above a threshold or a probe packet is interfered. To address the issue, we propose ZiSense, a low duty cycling mechanism resilient to interference. Instead of checking the signal strength or decoding the probe packets, ZiSense detects the ZigBee signals and wakes up nodes accordingly. On sensor nodes with limited information and resource, we carefully study and extract short-term features purely from the time-domain RSSI sequence, and design a rule-based approach to efficiently identify the existence of ZigBee. We theoretically analyze the benefit of ZiSense in different environments and implement a prototype in TinyOS with TelosB motes. We examine ZiSense performance under controlled interference and office environments. The evaluation results show that, compared with the state-of-the-art rendezvous mechanisms, ZiSense significantly reduces the energy consumption.

Asynchronous duty cycle is widely used for energy constraint wireless nodes to save energy. The basic flooding service in asynchronous duty cycle networks, however, is still far from efficient due to severe packet collisions and contentions. We present Chase, an efficient and fully distributed concurrent broadcast layer for flooding in asynchronous duty cycle networks. The main idea of Chase is to meet the strict signal time and strength requirements (e.g., Capture Effect) for concurrent broadcast while reducing contentions and collisions. We propose a distributed random inter-preamble packet interval adjustment approach to constructively satisfy the requirements. Even when requirements cannot be satisfied due to physical constraints (e.g., the difference of signal strength is less than a 3 dB), we propose a lightweight signal pattern recognition-based approach to identify such a circumstance and extend radio-on time for packet delivery. We implement Chase in TinyOS with TelosB nodes and extensively evaluate its performance. The implementation does not have any specific requirement on the hardware and can be easily extended to other platforms. The evaluation results also show that Chase can significantly improve flooding efficiency in asynchronous duty cycle networks.

Even though indoor smoking ban is being put into practice in civilized countries, existing vision or sensor-based smoking detection methods cannot provide ubiquitous detection service. In this paper, we take the first attempt to build a ubiquitous passive smoking detection system, Smokey, which leverages the patterns smoking leaves on WiFi signal to identify the smoking activity even in the non-line-of-sight and through-wall environments. We study the behaviors of smokers and leverage the common features to recognize the series of motions during smoking, avoiding the target-dependent training set to achieve the high accuracy. We design a foreground detection-based motion acquisition method to extract the meaningful information from multiple noisy subcarriers even influenced by posture changes. Without the requirement of target's compliance, we leverage the rhythmical patterns of smoking to detect the smoking activities. We also leverage the diversity of multiple antennas to enhance the robustness of Smokey. Due to the convenience of integrating new antennas, Smokey is scalable in practice for ubiquitous smoking detection. We prototype Smokey with the commodity WiFi infrastructure and evaluate its performance in real environments. Experimental results show Smokey is accurate and robust in various scenarios.

Shopping behavior data is of great importance in understanding the effectiveness of marketing and merchandising campaigns. Online clothing stores are capable of capturing customer shopping behavior by analyzing the click streams and customer shopping carts. Retailers with physical clothing stores, however, still lack effective methods to comprehensively identify shopping behaviors. In this paper, we show that backscatter signals of passive RFID tags can be exploited to detect and record how customers browse stores, which garments they pay attention to, and which garments they usually pair up. The intuition is that the phase readings of tags attached to items will demonstrate distinct yet stable patterns in a time-series when customers look at, pick out, or turn over desired items. We design ShopMiner, a framework that harnesses these unique spatial-temporal correlations of time-series phase readings to detect comprehensive shopping behaviors. We have implemented a prototype of ShopMiner with a COTS RFID reader and four antennas, and tested its effectiveness in two typical indoor environments. Empirical studies from two-week shopping-like data show that ShopMiner is able to identify customer shopping behaviors with high accuracy and low overhead, and is robust to interference.

Asynchronous duty cycle is widely used for energy constraint wireless nodes to save energy. The basic flooding service in asynchronous duty cycle networks, however, is still far from efficient due to severe packet collisions and contentions. We present Chase, an efficient and fully distributed concurrent broadcast layer for flooding in asynchronous duty cycle networks. The main idea of Chase is to meet the strict signal timing and strength requirements (e.g., Capture Effect) for concurrent transmission while reducing contentions and collisions. We propose a distributed random inter-preamble packet interval adjustment approach to constructively satisfy the requirements. Even when requirements cannot be satisfied due to physical constraints (e.g., the difference of signal strength is less than a 3 dB), we propose a light-weight signal pattern recognition based approach to identify such a circumstance and extend radio-on time for packet delivery. We implement Chase in TinyOS and TelosB platform and extensively evaluate its performance. The implementation does not have any specific requirement on the hardware and can be easily extended to other platforms. The evaluation results also show that Chase can significantly improve flooding efficiency in asynchronous duty cycle networks.

Operating in unlicensed ISM bands, ZigBee devices often yield poor throughput and packet reception ratio due to the interference from ever increasing wireless devices in 2.4 GHz band. Although there have been many efforts made for interference avoidance, they come at the cost of miscellaneous overhead, which oppositely hurts channel utilization. Our empirical results show that, a specific interference is likely to have different influence on different outbound links of a ZigBee sender, which indicates the chance of concurrent transmissions. Based on this insight, we propose Smoggy-Link, a practical protocol to exploit the potential concurrency for adaptive ZigBee transmissions under harsh interference. Smoggy-Link maintains an accurate link model to describe and trace the relationship between interference and link quality of the sender's outbound links. With such a link model, Smoggy-Link can obtain fine-grained spatiotemporal link information through a low-cost interference identification method. The link information is further utilized for adaptive link selection and intelligent transmission schedule. We implement and evaluate a prototype of our approach with TinyOS and TelosB motes. The evaluation results show that Smoggy-Link has consistent improvements in both throughput and packet reception ratio under interference from various interferer.

Even though indoor smoking ban is being put into practice in civilized countries, existing vision or sensor-based smoking detection methods cannot provide ubiquitous smoking detection. In this paper, we take the first attempt to build a ubiquitous passive smoking detection system, which leverages the patterns smoking leaves on WiFi signals to identify the smoking activity even in the non-line-of-sight and through-wall environments. We study the behaviors of smokers and leverage the common features to recognize the series of motions during smoking, avoiding the target-dependent training set to achieve the high accuracy. We design a foreground detection based motion acquisition method to extract the meaningful information from multiple noisy subcarriers even influenced by posture changes. Without requirements of target's compliance, we leverage the rhythmical patterns of smoking to reduce the detection false positives. We prototype Smokey with the commodity WiFi infrastructure and evaluate its performance in real environments. Experimental results show Smokey is accurate and robust in various scenarios.

To guarantee reliability, bulk data dissemination relies on the negotiation scheme in which senders and receivers negotiate transmission schedule through a three-way handshake procedure. However, we find negotiation incurs a long dissemination time and seriously defers the network-wide convergence. On the other hand, the flooding approach, which is conventionally considered inefficient and energy-consuming, can facilitate bulk data dissemination if appropriately incorporated. This motivates us to pursue a delicate tradeoff between negotiation and flooding in the bulk data dissemination. We propose SurF (Survival of the Fittest), a bulk data dissemination protocol which adaptively adopts negotiation and leverages flooding opportunistically. SurF incorporates a time-reliability model to estimate the time efficiencies (flooding versus negotiation) and dynamically selects the fittest one to facilitate the dissemination process. We implement SurF in TinyOS 2.1.1 and evaluate its performance with 40 TelosB nodes. The results show that SurF, while retaining the dissemination reliability, reduces the dissemination time by 40 percent in average, compared with the state-of-the-art protocols.

Due to the constraint of energy resource, the radio of sensor nodes usually works in a duty-cycled mode. Since the sleep schedules of nodes are unsynchronized, a sender has to send preambles to coordinate with its receiver(s). In such contexts, opportunistic forwarding, which takes the earliest forwarding opportunity instead of a deterministic forwarder, shows great advantage in utilizing channel resource. The multiple forwarding choices with temporal and spatial diversity increase the chance of collision tolerance in concurrent transmissions, potentially enhancing end-to-end network performance. However, the current channel contention mechanism based on collision avoidance is too conservative to exploit concurrency. To address this problem, we propose COF, a practical protocol to exploit the potential Concurrency for low power Opportunistic Forwarding. COF determines whether a node should concurrently transmit or not, by incorporating: (1) a distributed and light-weight link quality measurement scheme for concurrent transmission and (2) a synthetic method to estimate the benefit of potential concurrency opportunity. COF can be easily integrated into the conventional unsynchronized sender-initiated protocols. We evaluate COF on a 40-node testbed. The results show that COF can reduce the end-to-end delay by up to 41% and energy consumption by 18.9%, compared with the state-of-the-art opportunistic forwarding protocol.

In distributed networks such as wireless ad hoc networks, local and lossy logs are often available on individual nodes. We propose REFILL, which analyzes lossy and unsynchronized logs collected from individual nodes and reconstructs the network behaviors. We design an inference engine based on protocol semantics to abstract states on each node. Further we leverage inherent and implicit event correlations in and between nodes to connect interference engines and analyze logs from different nodes. Based on unsynchronized and incomplete logs, REFILL can reconstruct network behavior, recover the network scenario and understand what has happened in the network. We show that the result of REFILL can be used to guide protocol design, network management, diagnosis, etc. We implement REFILL and apply it to a large-scale wireless sensor network project. REFILL provides a detailed per-packet tracing information based on event flows. We show that REFILL can reveal and verify fundamental issues, like locating packet loss positions and root causes. Further, we present implications and demonstrate how to leverage REFILL to enhance network performance.

Shopping behavior data are of great importance to understand the effectiveness of marketing and merchandising efforts. Online clothing stores are capable capturing customer shopping behavior by analyzing the click stream and customer shopping carts. Retailers with physical clothing stores, however, still lack effective methods to identify comprehensive shopping behaviors. In this paper, we show that backscatter signals of passive RFID tags can be exploited to detect and record how customers browse stores, which items of clothes they pay attention to, and which items of clothes they usually match with. The intuition is that the phase readings of tags attached on desired items will demonstrate distinct yet stable patterns in the time-series when customers look at, pick up or turn over desired items. We design ShopMiner,, a framework that harnesses these unique spatial-temporal correlations of time-series phase readings to detect comprehensive shopping behaviors. We have implemented a prototype of ShopMiner, with a COTS RFID reader and four antennas, and tested its effectiveness in two typical indoor environments. Empirical studies from two-week shopping-like data show that ShopMiner, could achieve high accuracy and efficiency in customer shopping behavior identification.

Crossroad is among the most dangerous parts outside for the visually impaired people. Numerous studies have exploited navigating systems for the visually impaired community, providing services ranging from block detection, route planning to realtime localization. However, none of them have addressed the safety issue in crossroad and integrated three key factors necessary for a practical crossroad navigation system: detecting the crossroad, locating zebra patterns, and guiding the user within zebra crossing when passing the road. Our CrossNavi application responds to these needs, providing an integrated crossroad navigation service that incorporates all the essential functionalities mentioned above. The overall service is fulfilled by the collaboration of built-in sensors on commodity phones, and requires minimal human participation. We describe the technical aspects of its design, implementation, interface, and further improvements to make the system practical on a wider basis. Experimental results from three visually impaired volunteers show that the system exhibits promising behavior in both urban and rural areas.

To save energy, wireless sensor networks often run in a low duty cycle mode, where the radios of sensor nodes are scheduled between ON and OFF states. For nodes to communicate with each other, Low Power Listening (LPL) and Low Power Probing (LPP) are two types of rendezvous mechanisms. Nodes with LPL or LPP rely on signal strength or probe packets to detect potential transmissions, and then keep the radio-on for communications. Unfortunately, in many cases, signal strength and probe packets are susceptible to interference, resulting in undesirable radio on time when the signal strength of interference is above a threshold or a probe packet is interfered. To address the issue, we propose ZiSense, an energy efficient rendezvous mechanism which is resilient to interference. Instead of checking the signal strength or decoding the probe packets, ZiSense detects the existence of ZigBee transmissions and wakes up nodes accordingly. On sensor nodes with limited information and resource, we carefully study and extract short-term features purely from the time-domain RSSI sequence, and design a rule-based approach to efficiently identify the existence of ZigBee. We theoretically analyze the benefit of ZiSense in different environments and implement a prototype in TinyOS with TelosB motes. We examine ZiSense performance under controlled interference and office environments. The evaluation results show that, compared with state-of-the-art rendezvous mechanisms, ZiSense significantly reduces the energy consumption.

Data dissemination is a building block of wireless sensor networks (WSNs). In order to guarantee the reliability, many existing works rely on a negotiation scheme, making senders and receivers negotiate the schedule of transmissions through a three-way handshake procedure. According to our observation, however, negotiation incurs long dissemination time and seriously defers the network wide convergence. On the other hand, the flooding approach, which is conventionally considered to be inefficient and energy-consuming, may facilitate data dissemination if appropriately designed. This motivates us to pursue a delicate tradeoff between negotiation and flooding in the data dissemination process. In this paper, we propose SurF (Survival of the Fittest), a data dissemination protocol which selectively adopts negotiation and leverages flooding opportunistically. How to capture and utilize the opportunities when negotiation should be used is a challenging issue. SurF incorporates a time-reliability model to estimate the time efficiencies of the two schemes (flooding vs. negotiation) and dynamically selects the fittest one to facilitate the dissemination process. We implement SurF based on TinyOS 2.1.1 and evaluate its performance with 40 TelosB nodes. The results show that SurF, while retaining the dissemination reliability, reduces the dissemination time by 40% in average, compared with the state-of-the-art protocols.