Image and Video Processing · Cross-listed from cs.CV
Downstream Task Inspired Underwater Image Enhancement: A Perception-Aware Study from Dataset Construction to Network Design
Bosen Lin, Feng Gao, Yanwei Yu et al. (+2 more)
In real
underwater environments, downstream image recognition tasks such as semantic
segmentation and object detection often face challenges posed by problems like blurring and color inconsistencies.
Underwater image enhancement (UIE) has emerged as a promising preprocessing approach, aiming to improve the recognizability of targets in
underwater images. However, most existing UIE methods mainly focus on enhancing images for human visual perception, frequently failing to reconstruct high-frequency details that are critical for task-specific recognition. To address this issue, we propose a Downstream Task-Inspired
Underwater Image Enhancement (DTI-UIE) framework, which leverages human visual perception model to enhance images effectively for
underwater vision tasks. Specifically, we design an efficient two-branch network with task-aware
attention module for feature mixing. The network benefits from a multi-stage training framework and a task-driven perceptual loss. Additionally, inspired by human perception, we automatically construct a Task-Inspired UIE
Dataset (TI-UIED) using various task-specific networks. Experimental results demonstrate that DTI-UIE significantly improves task performance by generating preprocessed images that are beneficial for downstream tasks such as semantic
segmentation, object detection, and instance
segmentation. The codes are publicly available at https://github.com/oucailab/DTIUIE.
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All authors Bosen Lin, Feng Gao, Yanwei Yu, Junyu Dong, Qian Du
Systems and Control · Cross-listed from cs.RO
Shape-Interpretable Visual Self-Modeling Enables Geometry-Aware Continuum Robot Control
Peng Yu, Xin Wang and Ning Tan
Continuum
robots possess high flexibility and redundancy, making them well suited for safe interaction in complex environments, yet their continuous deformation and nonlinear dynamics pose fundamental challenges to perception, modeling, and control. Existing
vision-based control approaches often rely on end-to-end learning, achieving shape regulation without explicit awareness of
robot geometry or its interaction with the environment. Here, we introduce a shape-interpretable visual self-modeling framework for continuum
robots that enables geometry-aware control.
Robot shapes are encoded from multi-view planar images using a Bezier-curve representation, transforming visual observations into a compact and physically meaningful shape space that uniquely characterizes the
robot's three-dimensional configuration. Based on this representation, neural ordinary differential equations are employed to self-model both shape and end-effector dynamics directly from data, enabling hybrid shape-position control without analytical models or dense body markers. The explicit
geometric structure of the learned shape space allows the
robot to reason about its body and surroundings, supporting environment-aware behaviors such as obstacle avoidance and self-motion while maintaining end-effector objectives. Experiments on a cable-driven continuum
robot demonstrate accurate shape-position regulation and tracking, with shape errors within 1.56% of image resolution and end-effector errors within 2% of
robot length, as well as robust performance in constrained environments. By elevating visual shape representations from two-dimensional observations to an interpretable three-dimensional self-model, this work establishes a principled alternative to
vision-based end-to-end control and advances autonomous, geometry-aware manipulation for continuum
robots.
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Signal Processing
Detection of weak signals under arbitrary noise distributions
J. Zschetzsche, M. Weimar, O. Lang et al. (+7 more)
Detecting weak signals buried in complex, non-Gaussian noise is a fundamental challenge in science and engineering, with applications ranging from radar systems and communications to industrial monitoring and gravitational wave detection. The Rao detector, a key concept in this domain, achieves asymptotically optimal performance as the number of measurements increases, but requires precise knowledge of the data's statistical properties, often relying on simplified noise models. We propose a hybrid framework that combines a lightweight neural network with the Rao detection framework to address this limitation. The neural network, trained on noise-only data, learns the optimal multivariate nonlinearity, transforming noisy data to enhance signal detectability. The newly introduced LRao detector then fully extracts the signal information, achieving asymptotically optimal performance even under challenging noise conditions. Validated on both simulated and real-world
magnetic sensor data, our method significantly outperforms conventional approaches. By bridging data-driven techniques with model-based signal processing, it offers a robust and interpretable solution for signal detection across diverse applications.
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All authors J. Zschetzsche, M. Weimar, O. Lang, S. Schuster, A. Haberl, S. Schertler, B. Lehner, J. Reisinger, M. Huemer, S. Rotter
Signal Processing
Cramer-Rao Bounds for Target Parameter Estimation in a Bi-Static IRS-Assisted Radar Configuration
Sanjeeva Reddy S and Vinod Veera Reddy
The use of Intelligent Reflective Surfaces (IRS) to assist communication and sensing has proven cost-effective in challenging scenarios. For sensing, IRS is shown to sense non-line-of-sight (NLOS) and stealth targets, albeit with significant loss due to the four-hop path model. Amongst the available IRS-assisted configurations, we consider a three-hop model in which the IRS redirects the scattered target response towards the mono-static radar. With the IRS spatially displaced from the radar, this configuration mimics a bi-static radar. While target detection has been studied in this configuration, parameter estimation has not been investigated to date. To this end, we first develop the signal model for this configuration and derive the CRB for target parameters. The dependence of CRB on system parameters such as SNR, number of snapshots, number of IRS elements and their weights is brought forward through extensive simulations. This study can enable a designer to customize the system parameters to meet the requirements. It also serves as a
benchmark for parameter estimation techniques developed for this configuration.
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Signal Processing · Cross-listed from cs.LG
Transform-Invariant Generative Ray Path Sampling for Efficient Radio Propagation Modeling
Jérome Eertmans, Enrico M. Vitucci, Vittorio Degli-Esposti et al. (+3 more)
Ray tracing has become a standard for accurate
radio propagation modeling, but suffers from exponential computational complexity, as the number of candidate paths scales with the number of objects raised to the interaction order. This bottleneck limits its use in large-scale or real-time applications, forcing traditional tools to rely on heuristics that reduce path candidates at the cost of potentially reduced accuracy. To overcome this limitation, we propose a machine-learning-assisted framework that replaces exhaustive path searching with intelligent sampling via Generative Flow Networks. Applying these generative models to this domain presents challenges, particularly sparse rewards due to the rarity of valid paths, which can lead to convergence failures and trivial solutions when evaluating high-order interactions in complex environments. To ensure robust learning and efficient exploration, our framework incorporates three key components. First, an experience replay buffer captures and retains rare valid paths. Second, a uniform exploratory policy improves generalization and prevents overfitting to simple geometries. Third, a physics-based action masking strategy filters out physically impossible paths before the model considers them. Validated on idealized street-canyon scenarios, our model achieves substantial speedups over exhaustive search – up to $10\times$ faster on GPU and $100\times$ faster on CPU – while maintaining high coverage accuracy and successfully uncovering complex propagation paths. However, out-of-distribution evaluations on real-world Manhattan street geometries reveal that generalizing to substantially different urban morphologies requires further advancement in model capacity or alternative training strategies. Source code, tests, and a tutorial are available at https://github.com/jeertmans/sampling-paths.
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All authors Jérome Eertmans, Enrico M. Vitucci, Vittorio Degli-Esposti, Nicola Di Cicco, Laurent Jacques, Claude Oestges
Systems and Control
Predictive Lane-Change and Routing Coordination in Bus-Priority Mixed Traffic Corridors
Tanlu Liang, Ting Bai and Andreas A. Malikopoulos
In this paper, we investigate the coordination of vehicle maneuvers in mixed-traffic corridors where connected and automated vehicles, human-driven vehicles, and buses interact under dedicated bus lane operations. We develop a segment-based network coordination framework that jointly optimizes lane-change and routing decisions of connected and automated vehicles to improve dedicated lane utilization while preserving bus priority. The proposed framework incorporates a predictive bus-protection mechanism that restricts vehicle access to protected lane segments within a monitoring horizon, together with a utility-driven lane-change strategy that accounts for anticipated travel time gains, downstream routing feasibility, and lane-change stability. By explicitly coupling network-level routing decisions with lane-level interaction control, the method proactively mitigates conflicts on dedicated lanes before congestion effects materialize. The proposed approach is evaluated through microscopic traffic simulations in SUMO using a realistic urban corridor. Simulation results demonstrate that the framework enhances bus schedule adherence and reduces average travel times for both automated and human-driven vehicles, while maintaining stable lane-change behavior without increasing maneuver frequency.
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Signal Processing
A Block Least Mean Square Method for Fiber Longitudinal Power Profile Monitoring
Paolo Serena, Chiara Lasagni, Alberto Bononi et al. (+2 more)
We propose a block least mean square (LMS)
algorithm to monitor the longitudinal power profile of a fiber-optic link through receiver-based digital data from a coherent detector. Compared to the
benchmark least squares (LS) method, the proposed
algorithm does not require large
matrix inversions or batch processing, thus allowing the received data to be processed in blocks of minimum size by an overlap-save
algorithm, reducing complexity and latency. We propose an efficient implementation of the method with a
stochastic gradient update leveraging a key computation in the frequency domain, offering computational savings over state-of-the-art monitoring techniques. We test the proposal in different scenarios by means of numerical simulations.
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All authors Paolo Serena, Chiara Lasagni, Alberto Bononi, Fabien Boitier, Joana Girard-Jollet
Systems and Control
Battery Discharge Modeling for Electric Vehicles: A Hybrid Physics-based Residual Learning Approach
Praharshitha Aryasomayajula, Ting Bai and Andreas A. Malikopoulos
The growing integration of electric vehicle (EV) fleets into transportation services and energy systems requires accurate modeling of battery discharge and state-of-charge (SoC)
evolution to ensure reliable vehicle operation and grid coordination. Existing approaches face a trade-off between interpretable but simplified physics-based models and data-driven methods that demand large
datasets and may lack physical consistency. In this paper, we propose a hybrid physics-based residual learning framework for EV battery discharge modeling. A vehicle dynamics model based on force-balance equations provides an interpretable baseline estimate of energy consumption and SoC
evolution, capturing aerodynamic drag, rolling resistance, and regenerative braking. A neural network residual learner then corrects discrepancies caused by complex factors such as traffic conditions and driver behavior. Experimental results on $1,500$ trip scenarios demonstrate that the proposed approach reduces the mean absolute percentage error to approximately $0.8\%$, significantly outperforming physics-only models while preserving physical interpretability and computational efficiency.
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Image and Video Processing
MR-Compass: Inertial Navigation-Driven Motion Correction for Brain MRI
Musa Tunc Arslan, Fatih Calakli, Joshua Auger et al. (+3 more)
Inertial sensors can track object kinematics, however, unbounded drift from integrating noisy signals makes them impractical for MRI motion correction at millimeter resolution and minute-long scans. We introduce MR-Compass, which exploits the MRI system's static
magnetic and gravitational fields to estimate 3-DOF orientation at 2 kHz directly, without integration, eliminating random-walk. The remaining 3-DOF translation is recovered via phase correlation from the MRI data. We experimentally validate the efficacy of the method retrospectively using a 3D radial koosh-ball sequence and prospectively using 2D EPI fMRI during large volunteer motions. MR-Compass followed by phase-correlation achieved a mean accuracy of 0.6$^o$ and 0.4 pixels across all experiments. Image quality improved when motion correction was applied in all volunteer scans for both retrospective and prospective correction cases. MR-Compass was effective in measuring head motion in the MRI scanner with high accuracy at unprecedented sample rates, and enabled both retrospective and prospective reconstruction to improve image quality by aligning the k-space data appropriately and by reducing the motion related artifacts.
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All authors Musa Tunc Arslan, Fatih Calakli, Joshua Auger, Hongli Fan, Alan J Macy, Simon K Warfield
Audio and Speech Processing
Investigating Group Relative Policy Optimization for Diffusion Transformer based Text-to-Audio Generation
Yi Gu, Yanqing Liu, Chen Yang et al. (+1 more)
Text-to-audio (T2A) generation has advanced considerably in recent years, yet existing methods continue to face challenges in accurately rendering complex text
prompts, particularly those involving intricate audio effects, and achieving precise text-audio
alignment. While prior approaches have explored data augmentation, explicit timing conditioning, and reinforcement learning, overall synthesis quality remains constrained. In this work, we experiment with reinforcement learning to further enhance T2A generation quality, building on
diffusion transformer (DiT)-based architectures. Our method first employs a large
language model (LLM) to generate high-fidelity, richly detailed audio captions, substantially improving text-audio semantic
alignment, especially for ambiguous or underspecified
prompts. We then apply Group Relative Policy Optimization (GRPO), a recently introduced reinforcement learning
algorithm, to fine-tune the T2A model. Through systematic experimentation with diverse reward functions (including CLAP, KL, FAD, and their combinations), we identify the key drivers of effective RL in audio synthesis and analyze how reward design impacts final audio quality. Experimental results demonstrate that GRPO-based fine-tuning yield substantial gains in synthesis fidelity and
prompt adherence.
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All authors Yi Gu, Yanqing Liu, Chen Yang, Sheng Zhao
Audio and Speech Processing · Cross-listed from cs.CL
Geometric Alignment without Functional Equivalence: A Layer-wise Analysis of the Speech-Text Modality Gap
Ming-Hao Hsu, Xiaohai Tian, Jun Zhang et al. (+3 more)
End-to-end
speech large
language models (LLMs) often answer the same question less accurately from
speech than from text, even when the spoken content matches the text
prompt. Existing analyses study this modality gap through the geometry of representations and measure how closely
speech representations align with text.
Geometric alignment gives the gap a measurable form, but it does not show whether the model uses aligned representations in the same way. This work connects representation geometry with answer formation and asks whether
geometric alignment implies functional equivalence. We compare cross-layer Centered Kernel
Alignment (CKA) with layer-wise answer margins for four open-weight
speech LLMs on SpeechMMLU and VoiceBench BBH. In Qwen2.5-Omni and MiniCPM-o,
speech and text representations align in middle layers while their late-layer answer margins still differ, so mid-layer
alignment does not imply functional equivalence. Qwen2-Audio instead shows weak
alignment, which indicates a different failure mode. An
attention intervention at fixed input and
token count identifies a causal effect of late
attention allocation on answer-code separation, a quantity distinct from answer correctness. Compressing the
speech signal or its
token sequence repairs a subset of the errors that occur only with
speech.
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All authors Ming-Hao Hsu, Xiaohai Tian, Jun Zhang, Lu Lu, Yuxuan Wang, Zhizheng Wu
Signal Processing
A Unified Fractional Spectral Framework for Spatiotemporal Graph Signals: Bi-Fractional Transform and Geodesic Coupling
Mingzhi Wang, Manjun Cui, Feiyue Zhao et al. (+2 more)
Graph signal processing extends spectral analysis to data supported on irregular domains. Existing fractional transforms for two-dimensional graph signals, including the two-dimensional graph fractional
Fourier transform (GFRFT), typically impose a shared fractional order across dimensions, which limits adaptivity to heterogeneous spatiotemporal spectra. To address this limitation, we propose the two-dimensional graph bi-fractional
Fourier transform, which assigns independent fractional orders to the factor graphs of a Cartesian product, enabling decoupled spectral control while preserving separability, unitarity, and invertibility. To further resolve the basis ambiguity in temporal fractional analysis, we develop a geodesic-coupled GFRFT by constructing a coupling path along the principal geodesic on the
unitary manifold, thereby unifying graph-induced and discrete temporal bases with guaranteed unitarity and a closed-form inverse. Building on these transforms, we derive a differentiable Wiener-type filtering framework with a hybrid optimization strategy: the fractional orders are learned end-to-end from data, while the coupling parameter is fixed as a structural regularizer. Experiments on real-world time-varying graph
datasets and dynamic image restoration tasks demonstrate consistent gains over state-of-the-art fractional transforms and competitive learning-based baselines.
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All authors Mingzhi Wang, Manjun Cui, Feiyue Zhao, Yangfan He, Zhichao Zhang
Audio and Speech Processing
A SUPERB-Style Benchmark of Self-Supervised Speech Models for Audio Deepfake Detection
Hashim Ali, Nithin Sai Adupa, Surya Subramani et al. (+1 more)
Self-supervised learning (SSL) has transformed
speech processing, with
benchmarks such as SUPERB establishing fair comparisons across diverse downstream tasks. Despite it's security-critical importance, Audio deepfake detection has remained outside these efforts. In this work, we introduce Spoof-SUPERB, a
benchmark for audio deepfake detection that systematically evaluates 20 SSL models spanning generative, discriminative, and spectrogram-based architectures. We evaluated these models on multiple in-domain and out-of-domain
datasets. Our results reveal that large-scale discriminative models such as XLS-R, UniSpeech-SAT, and WavLM Large consistently outperform other models, benefiting from
multilingual pretraining, speaker-aware objectives, and model scale. We further analyze the robustness of these models under acoustic degradations, showing that generative approaches degrade sharply, while discriminative models remain resilient. This
benchmark establishes a reproducible baseline and provides practical insights into which SSL representations are most reliable for securing
speech systems against audio deepfakes.
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All authors Hashim Ali, Nithin Sai Adupa, Surya Subramani, Hafiz Malik
Audio and Speech Processing
Entropy-Guided GRVQ for Ultra-Low Bitrate Neural Speech Codec
Yanzhou Ren, Noboru Harada, Daiki Takeuchi et al. (+6 more)
Neural audio codec (NAC) is essential for reconstructing high-quality
speech signals and generating discrete representations for downstream
speech language models. However, ensuring accurate semantic modeling while maintaining high-fidelity reconstruction under ultra-low bitrate constraints remains challenging. We propose an
entropy-guided group residual vector quantization (EG-GRVQ) for an ultra-low bitrate neural
speech codec, which retains a semantic branch for linguistic information and incorporates an
entropy-guided grouping strategy in the acoustic branch. Assuming that channel activations follow approximately Gaussian statistics, the variance of each channel can serve as a principled proxy for its information content. Based on this assumption, we partition the encoder output such that each group carries an equal share of the total information. This balanced allocation improves codebook efficiency and reduces redundancy. Trained on LibriTTS and VCTK, our model shows improvements in perceptual quality and intelligibility metrics under ultra-low bitrate conditions, with a focus on codec-level fidelity for communication-oriented scenarios.
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All authors Yanzhou Ren, Noboru Harada, Daiki Takeuchi, Siyu Chen, Wei Liu, Xiao Zhang, Liyuan Zhang, Takehiro Moriya, Shoji Makino
Audio and Speech Processing
Conversational Speech Naturalness Predictor
Anfeng Xu, Yashesh Gaur, Naoyuki Kanda et al. (+6 more)
Evaluation of conversational naturalness is essential for developing human-like
speech agents. However, existing
speech naturalness predictors are often designed to assess utterances from a single speaker, failing to capture conversation-level naturalness qualities. In this paper, we present a framework for an automatic naturalness predictor for two-speaker, multi-turn conversations. We first show that existing naturalness
estimators have low, or sometimes even negative, correlations with conversational naturalness, based on conversational recordings annotated with human ratings. We then propose a dual-channel naturalness
estimator, in which we investigate multiple pre-trained encoders with data augmentation. Our proposed model achieves substantially higher correlation with human judgments compared to existing naturalness predictors for both in-domain and out-of-domain conditions.
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All authors Anfeng Xu, Yashesh Gaur, Naoyuki Kanda, Zhicheng Ouyang, Katerina Zmolikova, Desh Raj, Simone Merello, Anna Sun, Ozlem Kalinli
Image and Video Processing
Revisiting Global Token Mixing in Task-Dependent MRI Restoration: Insights from Minimal Gated CNN Baselines
Xiangjian Hou, Chao Qin, Chang Ni et al. (+3 more)
Global
token mixing, implemented via self-
attention or state-space sequence models, has become a popular model design choice for MRI restoration. However, MRI restoration tasks differ substantially in how their degradations vary over image and k-space domains, and in the degree to which global coupling is already imposed by physics-driven data consistency terms. In this work, we ask the question whether global
token mixing is actually beneficial in each individual task across three representative settings: accelerated MRI reconstruction with explicit data consistency, MRI super-resolution with k-space center cropping, and denoising of clinical carotid MRI data with spatially heteroscedastic noise. To reduce confounding factors, we establish a controlled testbed comparing a minimal local gated CNN and its large-field variant, benchmarking them directly against state-of-the-art global models under aligned training and evaluation protocols. For accelerated MRI reconstruction, the minimal unrolled gated-CNN baseline is already highly competitive compared to recent
token-mixing approaches in public reconstruction
benchmarks, suggesting limited additional benefits when the forward model and data-consistency steps provide strong global constraints. For super-resolution, where low-frequency k-space data are largely preserved by the controlled low-pass degradation, local gated models remain competitive, and a lightweight large-field variant yields only modest improvements. In contrast, for denoising with pronounced spatially heteroscedastic noise,
token-mixing models achieve the strongest overall performance, consistent with the need to estimate spatially varying reliability. In conclusion, our results demonstrate that the utility of global
token mixing in MRI restoration is task-dependent, and it should be tailored to the underlying imaging physics and degradation structure.
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All authors Xiangjian Hou, Chao Qin, Chang Ni, Xin Wang, Chun Yuan, Xiaodong Ma
Systems and Control · Cross-listed from math.OC
On the Stability Connection Between Discrete-Time Algorithms and Their Resolution ODEs: Applications to Min-Max Optimisation
Amir Ali Farzin, Yuen-Man Pun, Philipp Braun et al. (+1 more)
This work establishes a rigorous connection between stability properties of discrete-time
algorithms (DTAs) and corresponding continuous-time dynamical systems derived through $ O(s^r) $-resolution ordinary differential equations (ODEs). We show that for discrete- and continuous-time dynamical systems satisfying a mild error assumption, exponential stability of a common
equilibrium with respect to the continuous time dynamics implies exponential stability of the corresponding
equilibrium for the discrete-time dynamics, provided that the step size is chosen sufficiently small. We extend this result to common compact invariant sets. We prove that if an
equilibrium is exponentially stable for the $ O(s^r) $-resolution ODE, then it is also exponentially stable for the associated DTA. We apply this framework to analyse the limit point properties of several prominent optimisation
algorithms, including Two-Timescale Gradient Descent–Ascent (TT-GDA), Generalised Extragradient (GEG), Two-Timescale Proximal Point (TT-PPM), Damped Newton (DN), Regularised Damped Newton (RDN), and the Jacobian method (JM), by studying their $ O(1) $- and $ O(s) $-resolution ODEs. We show that under a proper choice of hyperparameters, the set of saddle points of the objective function is a subset of the set of exponentially stable
equilibria of GEG, TT-PPM, DN, and RDN. We relax the common Hessian invariance assumption through direct analysis of the resolution ODEs, broadening the applicability of our results. Numerical examples illustrate the theoretical findings.
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All authors Amir Ali Farzin, Yuen-Man Pun, Philipp Braun, Iman Shames
Audio and Speech Processing
The USTC-NERCSLIP Systems for the CHiME-9 MCoRec Challenge
Ya Jiang, Ruoyu Wang, Jingxuan Zhang et al. (+19 more)
This report details our submission to the CHiME-9 MCoRec Challenge on recognizing and clustering multiple concurrent natural conversations within indoor social settings. Unlike conventional meetings centered on a single shared topic, this scenario contains multiple parallel dialogues–up to eight speakers across up to four simultaneous conversations–with a
speech overlap rate exceeding 90%. To tackle this, we propose a
multimodal cascaded system that leverages per-speaker visual streams extracted from synchronized 360 degree
video together with single-channel audio. Our system improves three components of the pipeline by leveraging enhanced audio-visual pretrained models: Active Speaker Detection (ASD), Audio-Visual Target
Speech Extraction (AVTSE), and Audio-Visual
Speech Recognition (AVSR). The AVSR module further incorporates Whisper and LLM techniques to boost transcription accuracy. Our best single cascaded system achieves a Speaker Word Error Rate (WER) of 32.44% on the development set. By further applying ROVER to fuse outputs from diverse front-end and back-end variants, we reduce Speaker WER to 31.40%. Notably, our LLM-based zero-shot conversational clustering achieves a speaker clustering F1 score of 1.0, yielding a final Joint ASR-Clustering Error Rate (JACER) of 15.70%.
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All authors Ya Jiang, Ruoyu Wang, Jingxuan Zhang, Jun Du, Yi Han, Zihao Quan, Hang Chen, Yeran Yang, Kongzhi Zheng, Zhuo Chen, Yanhui Tu, Shutong Niu, Changfeng Xi, Mengzhi Wang, Zhongbin Wu, Jieru Chen, Henghui Zhi, Weiyi Shi, Shuhang Wu, Genshun Wan, Jia Pan, Jianqing Gao
Systems and Control
Koopman-based Estimation of Lyapunov Functions: Theory on a Reproducing Kernel Hilbert Space
Wentao Tang and Xiuzhen Ye
Koopman operator provides a general linear description of nonlinear systems, whose estimation from data (via extended dynamic mode decomposition) has been extensively studied. However, the elusiveness between the Koopman spectrum and the stability of
equilibrium point poses a challenge to utilizing the Koopman operator for stability analysis, which further hinders the construction of a universal theory of Koopman-based control. In our prior work, we defined the Koopman operator on a reproducing kernel
Hilbert space (RKHS) using a linear–radial product kernel, and proved that the Koopman spectrum is confined in the unit disk of the complex plane when the origin is an asymptotically stable
equilibrium point. Building on this fundamental spectrum–stability relation, here we consider the problem of Koopman operator-based Lyapunov function estimation with a given decay rate function. The decay rate function and the Lyapunov function are both specified by positive operators on the RKHS and are related by an operator algebraic Lyapunov equation (ALE), whose solution exists uniquely. The error bound of such a Lyapunov function estimate, obtained via kernel extended dynamic mode decomposition (kEDMD), are established based on statistical learning theory and verified by a numerical study.
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Signal Processing · Cross-listed from cs.IT
GNN Based Joint Beamforming Design for Extremely Large-Scale RIS Assisted Near-Field ISAC Systems
Jiahao Chen, Feng Wang, Guojun Han et al. (+2 more)
This paper investigates an extremely large-scale reconfigurable intelligent surface (XL-RIS) assisted near-field integrated sensing and communication (
ISAC) system, where a multi-
antenna base station (BS) simultaneously sends unicast data to multiple single-
antenna communication users (CUs) and senses multiple targets (TGTs). The BS, CUs and TGTs are all assumed to be located in the near-field region of the XL-RIS. We aim to maximize the weighted sum rate (WSR) of all CUs, subject to the sensing beampattern gain constraint for each TGT, the transmit power constraint for the BS, and the unit modulus constraints on the XL-RIS phase shift. First, we develop a fractional programming (FP) based block coordinate descent (BCD)
algorithm to obtain a locally optimal solution for such a non-convex joint design problem. Secondly, to address the high-dimensional spatial correlations and scalability of the XL-RIS near-field channels, we propose a customized graph neural network (GNN) scheme to generate the BS transmit beamforming variables and the XL-RIS reflecting coefficient vector for
ISAC, where the near-field
ISAC system is modeled as a heterogeneous graph comprising XL-RIS/CU/TGT nodes. The proposed GNN scheme can effectively learn the near-field channel state information (CSI) features, in which the message passing mechanism is employed to exchange CSI among these directly connected nodes in the graph. Furthermore, each XL-RIS/CU/TGT node maintains a feature vector for mapping to the BS transmit beamforming variables or the XL-RIS reflecting coefficient vector. Numerical results show that the proposed GNN-based beamforming design scheme achieves a better performance than the existing baselines, in terms of computational efficiency, feasibility, robustness, and the ability of generalization.
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All authors Jiahao Chen, Feng Wang, Guojun Han, Xin Wang, Vincent K. N. Lau
Systems and Control · Cross-listed from cs.LG
Align and Filter: Improving Performance in Asynchronous On-Policy RL
Homayoun Honari, Roger Creus Castanyer, Michael Przystupa et al. (+3 more)
Distributed training and increasing the gradient update frequency are practical strategies to accelerate learning and improve performance, but both exacerbate a central challenge: policy lag, which is the mismatch between the behavior policy generating data and the learning policy being updated. Policy lag can hinder the scaling of on-policy learning
algorithms to larger problems. In this paper, we identify the sources of policy lag caused by distributed learning and high update frequency. We use the findings to propose total Variation-based Advantage aligned Constrained policy Optimization (\methodacronym) as a practical approach to mitigate policy lag. We empirically validate our method and show that it offers better robustness to policy lag in classic RL tasks and a modern RL for LLM math
reasoning task.
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All authors Homayoun Honari, Roger Creus Castanyer, Michael Przystupa, Michael Noukhovitch, Pablo Samuel Castro, Glen Berseth
Systems and Control
Operational Modal Analysis of Aeronautical Structures via Tangential Interpolation
Gabriele Dessena, Marco Civera and Oscar E. Bonilla-Manrique
Over the last decades, progress in modal analysis has enabled increasingly routine use of modal parameters for applications such as structural health monitoring and finite element model updating. For output-only identification, or Operational Modal Analysis (OMA), widely adopted approaches include
Stochastic Subspace Identification (SSI) methods and the Natural Excitation Technique combined with the Eigensystem Realization
Algorithm (NExT-ERA). Nevertheless, SSI-based techniques may become cumbersome on large systems, while NExT-ERA fitting can struggle when measurements are contaminated by noise. To alleviate these, this work investigates an OMA frequency-domain formulation for aeronautical structures by coupling the Loewner Framework (LF) with NExT, yielding the proposed NExT-LF method. The method exploits the computational efficiency of LF, due to the effectiveness of tangential interpolation, together with the impulse response function
retrieval enabled by NExT. NExT-LF is assessed on two experimental
benchmarks: the eXperimental BeaRDS 2 high-aspect-ratio wing main spar and an Airbus Helicopters H135 bearingless main rotor blade. The identified modal parameters are compared against available experimental references and results obtained via SSI with Canonical Variate Analysis and NExT-ERA. The results show that the modes identified by NExT-LF correlate well with
benchmark data, particularly for high-amplitude tests and in the low-frequency range.
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