Publication

Vision-based machine learning (ML) methods offer a scalable and non-invasive solution to gait analysis, but face challenges in correctly detecting and analyzing prosthesis, due to their unique appearances and new movement patterns. In this paper, we aim to bridge this gap by introducing a multi-purpose dataset, namely ProGait, to support multiple vision tasks including Video Object Segmentation, 2D Human Pose Estimation, and Gait Analysis (GA). ProGait provides 412 video clips from four above-knee amputees when testing multiple newly-fitted prosthetic legs through walking trials, and depicts the presence, contours, poses, and gait patterns of human subjects with transfemoral prosthetic legs. Alongside the dataset itself, we also present benchmark tasks and fine-tuned baseline models to illustrate the practical application and performance of the ProGait dataset.

While recent studies show performance improvements in wireless sensing tasks by incorporating synthetic data from generative models into training sets, the quality of synthetic data remains unpredictable and the resulting performance gains are not guaranteed. To address this gap, we propose tractable and generalizable metrics to quantify quality attributes of synthetic data - affinity and diversity. Our assessment reveals prevalent affinity limitation in current wireless synthetic data, leading to mislabeled data and degraded task performance. We attribute the quality limitation to generative models’ lack of awareness of untrained conditions and domain-specific processing. To mitigate these issues, we introduce SynCheck, a quality-guided synthetic data utilization scheme that refines synthetic data quality during task model training. Our evaluation demonstrates that SynCheck consistently outperforms quality-oblivious utilization of synthetic data.

Personalization of Large Language Models (LLMs) is important in practical applications to accommodate the individual needs of different mobile users. Due to data privacy concerns, LLM personalization often needs to be locally done at the user’s mobile device, but such on-device personalization is constrained by both the limitation of on-device compute power and insufficiency of user’s personal data. In this paper, we address these constraints by fine-tuning an already personalized LLM with user’s personal data, and present XPerT, a new technique that ensure proper selection of such already personalized LLMs based on explainability about how they were being fine-tuned. We implemented and evaluated XPerT on various smartphone models with mainstream LLMs, and experiment results show that XPerT reduces the computation costs of on-device LLM personalization by 83%, and improves its data efficiency by 51%.

Federated Artificial Intelligence of Things (AIoT) uses distributed data on IoT devices to train AI models. However, in practical AIoT systems, heterogeneous devices cause data heterogeneity and varying amounts of device staleness, which can reduce model performance or increase federated training time. Existing FL frameworks improperly consider device delays as independent from data heterogeneity. Our work explore a scenario where device delays and data heterogeneity are closely correlated, and propose FedDC, a new technique to mitigate the impact of such device delays. Our basic idea is to use gradient inversion to learn knowledge about device’s local data distribution and use such knowledge to compensate the impact of device delays on devices’ model updates. Experiment shows that FedDC can improve the FL performance by 34% with high amounts of device delays, without impairing the devices’ local data privacy.

Text-to-video (T2V) generative AI could revolutionize many current and emerging application and industry domains. However, the capabilities of today’s T2V generative models are mostly data dependent. While they perform well in domains covered by the training data, they usually fail to obey the real-world common knowledge and physical rules with out-of-distribution prompts. Expanding the model’s capabilities, on the other hand, relies on large amounts of real-world data and is hence not scalable. Our recent work aims to address this limitation of data dependency, by fully unleashing the current T2V models’ potential in scene generation given proper and detailed prompts. Our approach, namely PhyT2V, is a training-free technique that leverages the LLM’s capabilities of chain-of-thought and step-back reasoning in the language domain, to logically identify the deficiency of generated videos and iteratively refine the current T2V models’ video generation by correcting such deficiency with more precise and well articulated prompts.

Illegally using fine-tuned diffusion models to forge human portraits has been a major threat to trustworthy AI. While most existing work focuses on detection of the AI-forged contents, our recent work instead aims to mitigate such illegal domain adaptation by applying safeguards on diffusion models. Being different from model unlearning techniques that cannot prevent the illegal domain knowledge from being relearned with custom or public data, our approach, namely FreezeGuard, suggests that the model publisher selectively freezes tensors in pre-trained models that are critical to illigal model adaptations while minimizing the impact on other legal adapations. Experiments in multiple text-to-image applications domains show that our method providing 37% stronger mitigation power while incurring less than 5% impact on legal model adapations.

Multimodal reasoning by LLMs is critical to autonomous mobile systems, but the growing diversity of input data modalities prevents incorporating all modalities into LLMs. Instead, only the useful modalities should be adaptively involved at runtime, based on the current environmental contexts and task requirements. Existing work on runtime modality adaptation uses fixed connections between data encoder and LLM’s input layer, but results in high training costs and ineffective cross-modal interaction. In this paper, we present MPnP, a new modality adaptation technique that connects data encoders to a flexible set of last LLM blocks and makes such latent connections fully trainable at runtime. Evaluation results show that MPnP has high compute and data efficiency, with 3.7× FLOPs reduction and 30% memory usage reduction compared to best baselines. It requires only few hundreds of training samples at runtime, and completes modality adaptation within few minutes on weak devices.

Federated Learning (FL) can be affected by data and device heterogeneities. Traditional schemes consider these heterogeneities as two separate and independent aspects, but this assumption is unrealistic in practical FL scenarios where these heterogeneities are intertwined. In these cases, traditional FL schemes are ineffective. We introduce a novel FL framework with the idea of estimating the distributions of clients’ local training data from their uploaded stale model updates, and use these estimations to compute unstale client model updates. Experiments on comparison with existing FL strategies on mainstream datasets and models showed that our approach can improve the trained model accuracy by up to 25% and reduce the number of required training epochs by up to 35%.

Image super-resolution (SR) is widely used on mobile devices to enhance user experience. However, neural networks used for SR are computationally expensive, posing challenges for mobile devices with limited computing power. A viable solution is to use heterogeneous processors on mobile devices, especially the specialized hardware AI accelerators, but the reduced arithmetic precision on AI accelerators can lead to degraded perceptual quality in upscaled images. To address this limitation, we present a novel image SR technique that enhances the perceptual quality of upscaled images when using heterogeneous processors for SR computations. It strategically splits the SR model and dispatches different layers to heterogeneous processors, to meet the time constraint while minimizing the impact of AI accelerators on image quality. Experiment results show that our method outperforms the best baselines, improving perceptual image quality by up to 2×, or reducing SR computing latency by up to 5.6× with on-par image quality.

Being different from model compression that requires expensive retraining, sparse activation can effectively reduce neural network models’ inference cost at runtime without any prior retraining or adaptation efforts. Although sparse activation has been proved to be effective on Large Language Models (LLMs) that are usually redundant (e.g., OPT and BLOOMZ models), its applicability on recent Small Language Models (SLMs) with higher parameter efficiency remains questionable. Our recent work verified such possibility by using gradient-based attribution scores to evaluate neurons’ importance in inference, in both analytical and experimental perspectives. Our results show that we can achieve up to 80% sparsity in major SLM models, including Phi-1.5/2 and MobiLlama-0.5B/1B, with less than 5% model accuracy loss on QA tasks.

The growing need of fine-tuning large language models (LLMs) can lead to significant energy consumption and environmental impact. To address this issue, we introduce GreenTrainer, a novel LLM fine-tuning technique. GreenTrainer assesses the backpropagation costs and contributions of different tensors to model accuracy, allowing for the selection of the most efficient set of tensors. This selection is guided by a user-defined objective, which can adapt to energy supply considerations and Green AI goals. Experimental results demonstrate that GreenTrainer can reduce FLOPs by up to 64% without compromising model accuracy, and outperforms existing techniques like LoRA while maintaining comparable FLOPs reduction.

The first mobile health system that turns a commodity smartphone into a fully functional pulmonary examination device to measure the internal physiological conditions of human airways, such as airway caliber, obstruction and possible inflammation. Information about these airway conditions could provide vital clues for precise and objective pulmonary disease evaluation.

The first on-device AI technique that achieves full elasticity of on-device training on resource-constrained mobile and embedded devices. By leveraging the principle of eXplainable AI (XAI) and evaluating the importance of different tensors in training, we allow fully flexible adaptation of the trainable neural network portion at runtime, according to the current training needs and online data patterns, to minimize the training cost without accuracy loss.

This work prsents AWARE, a new sensing and AI system that supports accurate and reliable pulmonary function tests (PFT) using commodity smartphones. AWARE uses a smartphone to transmit acoustic signals and reconstructs the profile of human airway based on the analysis of reflected acoustic waves captured from the smartphone’s microphone. The subject’s pulmonary condition is then evaluated by a multi-task learning model to detect airway obstruction and inflammation and identify pulmonary diseases like asthma or COPD.

This work applies on-device AI techniques to interference cancellation in WiFi networks and enables generalizable interference cancellation on commodity WiFi devices without any extra RF hardware. By using neural network models to mimic WiFi network’s PHY-layer operation, AiFi can be generally applied to different types of interference signals ranging from concurrent WiFi transmissions, ZigBee/Bluetooth to wireless baby monitors or even microwave oven, and improves the MAC-layer frame reception rate by 18x.

AgileNN is the first work that achieves real-time inference (<20ms) of mainstream neural network models (e.g., ImageNet) on extremely weak MCUs (e.g., STM32 series with <1MB of memory), without impairing the inference accuracy. The usage of eXplainable AI (XAI) techniques allows >6x improvement of feature compressibility during offloading and >8x reduction of the local device’s resource consumption.

TransFi realizes fine-grained signal emulation and allows commodity WiFi devices to emulate custom wireless physical layer, including but not limited to, custom PHY-layer preambles and new ways of agile spectrum usage. It could also improve the performance of cross-technology communication and many other wireless applications by up to 50x, enabling high-speed data communication on par with commodity WiFi.

A new backscatter system of precise, adaptive and lightweight power adaptation towards energy-efficient backscatter readers. It learns the entangled correlation between backscatter channel conditions, transmit RF power and goodput by designing a modular neural network to avoid redundancy and any confusion in training. Experiment results show improvement in energy efficiency at readers by 3.5× and reduces power consumption by up to 80%.

FaceListener transforms the commodity headphone into an acoustic sensing device, which captures the face skin deformations caused by fa-cial muscle movements with different facial expressions. To ensure the recognition accuracy, FaceListener leverages the knowledge distillation technique to learn the subtle correlation between face skin deformation and the acoustic signal changes.

This is one of the few works that demonstrate critical security vulnerabilities of mainstream GPUs (QualComm Adreno GPU on Snapdragon SoCs) on smartphones, which allow an unprivileged attacker to eavesdrop the user’s sensitive credentials such as app username and password.

We present a new technique to mimic an active sonar system with the smartphone’s built-in microphone and speaker, and use this sonar system to evaluate muscle fatigue from the muscle’s surface characteristics that can be measured from the transmitted acoustic signal.

We present MagHacker, a new sensing system that realizes such eavesdropping attack over commodity mobile devices, which monitor and analyze the magnetic field being produced by the stylus pen’s internal magnet. It divides the continuous magnetometer readings into small segments that represent individual letters, and then translates these readings into writing trajectories for letter recognition.

The first work that allows commodity smartphones to be used as a portable spirometer and provide accuracy lung function test results on par with clinical-grade spirometers. This is a collaborative work with the Children’s Hospital of Pittsburgh, and could also potentially contribute to in-home evaluation of COVID-19 risks by allowing convenient out-of-clinic lung function evaluation.

StarLego is a wireless system that can produce custom wireless signals over commodity devices without hardware modification. It is showcased by implementing a custom WiFi PHY preamble, and exhibits great promise to facilitate penetration of new wireless PHY techniques to existing wireless systems.

EasyPass exploits the excessive SNR margin in a wireless channel as a dedicated side channel for IoT traffic, and allow multiple access to the side channel by separating signals from different transmitters on the air. It allows multiple IoT devices to simultaneously transmit data over a congested wireless link without being delayed.

Device-free acoustic motion tracking allows a commodity mobile device to precisely track the human user’s motion, without applying any extra hardware tracker on the human body. We present a new system that ensures precise motion tracking over large targets by correctly interpreting the reflected acoustic signal and extracting the phase from the signal.

EmBee is designed to exploit the diversity of different wireless technologies’ spectrum utilization, so as to adaptively reserve occupied spectrum from the strong devices for weak wireless devices’ concurrent data transmissions. It is a new wireless PHY technique that enables cross-technology coexistence at zero cost or performance loss to these extremely weak wireless devices.

We present a novel design of high-throughput wireless side channel, which operates concurrently with the existing wireless network channel over the same spectrum but dedicates to real-time traffic. Our key idea of realizing such a side channel is to exploit the excessive SNR margin in the wireless network to encode data as patterned interference. We design such patterned interference in the form of energy erasure over specific subcarriers in an OFDM-based wireless network, and achieve a data rate of 1.25 Mbps in the side channel without affecting the existing wireless network links.

This work leverages the unique characteristics of image warping used in current VR applications, and fundamentally expand the scope of image warping to the entire VR lifespan to precisely capture the fluctuations of VR scene due to VR dynamics. We implemented our design over Android OS and Unity VR application engine, and demonstrated that our design can maximize the mobile VR performance over highly dynamic VR scenarios with 95% less amount of VR frame data being transmitted.

MUVR aims to remove the performance constraint of highly dynamic VR appliations by adaptively reusing the redundant VR frames being rendered for different VR users. The redundancy in each frame is decided at run-time by the edge cloud, which further reuses its redundant pixels compared with other frames. The design implementation over Android OS and Unity VR demonstrated that the design can reduce edge computation burden and transmitted VR frame data.

This work presents vMod, a lightweight and practical solution towards maximum wireless network throughput by redesigning the wireless link rates from discrete to continuous. The key idea of vMod is to modulate a fractional number of data bits into each symbol by employing the Variable-Length Code (VLC), which is able to statistically yield any link rate.