LYRA: Label-Free Structural Synchronization and Resource Allocation for UAV Edge Networks
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LYRA: Label-Free Structural Synchronization and Resource Allocation for UAV Edge Networks Feng He∗† , Alireza Furutanpey† , Paolo Bellavista∗ , Yu Qiu‡ , Jiangchuan Liu§ , Jiannong Cao¶ , Schahram Dustdar† ∗ University of Bologna, † TU Wien, ‡ City University of Hong Kong, § Simon Fraser University, ¶ Hong Kong Polytechnic University,
arXiv:2608.07392v1 [cs.NI] 7 Aug 2026
Email: feng.he2@unibo.it, a.furutanpey@dsg.tuwien.ac.at, paolo.bellavista@unibo.it, csqiuyu@mail.scut.edu.cn, jcliu@sfu.ca, jiannong.cao@polyu.edu.hk, dustdar@dsg.tuwien.ac.at
Abstract—While deploying hierarchical vision models to process mission-critical tasks, UAV edge systems must adaptively update the models to sustain inference reliability under low-level environmental corruption. However, existing work has overlooked the optimal timing for model updates, the impracticality of relying on real-time expert labels, and the significant bandwidth and energy constraints of UAVs. This paper proposes a joint model update scheduling and resource allocation framework, aiming to maximize long-term semantic fidelity and resource efficiency of UAV edge intelligence systems. To address the challenge of label-free semantic evaluation, we formulate the Online Semantic Disagreement Rate (OSDR) as a proxy for timely update triggering, thereby enabling fine-grained Sensitivity-Aware Structural Synchronization (SASS). Furthermore, to overcome the curse of dimensionality in hybrid action spaces and effectively bound longterm energy budgets, we propose a Lyapunov-guided discrete reinforcement learning algorithm that performs action space dimensionality reduction and transforms constraints into virtual queue stability problems. The reported experimental results, based on real traffic traces, demonstrate that the proposed framework consistently outperforms representative baselines in semantic recovery efficiency and update triggering precision, by satisfying long-term energy budget and by reducing average risk backlog by up to 33.3% in the dynamic environmental corruption scenario. Index Terms—UAV edge intelligence, model update scheduling, resource allocation, Lyapunov optimization, deep reinforcement learning.
I. I NTRODUCTION MEC-enabled unmanned aerial vehicle (UAV) systems have emerged as a pivotal paradigm for mission-critical visual tasks, ranging from autonomous infrastructure inspection to real-time disaster response. To maintain high-level perception, these UAV edge nodes typically deploy sophisticated vision models characterized by hierarchical architectures [1]–[3]. However, the operational reliability of these systems is frequently compromised by low-level environmental corruptions, such as fog or abrupt illumination variations, encountered during continuous flight. These environmental stressors primarily corrupt low-level physical pixels, which, due to the feed-forward nature of hierarchical deep neural networks (DNNs), can trigger a significant degradation of semantic fidelity. Consequently, ensuring the continuous reliability of edge intelligence against such unpredictable stressors, while effectively bounding the
system operational energy and bandwidth budgets, constitutes a primary challenge for resilient autonomous inspection. Despite the critical need for timely model maintenance, existing paradigms struggle to reconcile semantic reliability with resource efficiency under dynamic stressors. On the one hand, current frameworks predominantly rely on communication-intensive and full model synchronization [4]– [19], which incurs substantial overhead on the limited bandwidth of UAV-to-ground links. Moreover, these conventional trigger mechanisms are ill-suited for tracking inference degradation caused by dynamic environmental stressors. In fact, existing trigger mechanisms, whether time-driven (e.g., AoI, periodic schedules) or state-driven (e.g., resource utilization, data accumulation) [4], [5], [8], [9], [11]–[17], [19]–[26], are content-agnostic, relying solely on elapsed time or system states without perceiving the non-linear semantic degradation caused by abrupt visual corruptions. On the other hand, recent semantic-aware scheduling approaches attempt to incorporate task-level feedback, but typically assume the realtime availability of ground-truth labels to compute inference accuracy or loss as feedback [6], [7], [10], [18]. In autonomous inspection flights, streaming visual data cannot be annotated by ground experts in real time, making label-dependent feedback physically unrealizable mid-flight, thus generating a relevant operational issue: the UAV cannot afford bandwidth-heavy full updates over air-to-ground links, yet lacks a label-free proxy to evaluate semantic degradation. To address these open challenges, we propose LYRA, which, to the best of our knowledge, is the first joint update scheduling and resource allocation framework tailored for UAV edge inference. LYRA specifically optimizes synchronization efficiency under low-level environmental corruptions to maintain the semantic fidelity and resource efficiency of hierarchical vision models. To achieve these conflicting objectives, we introduce three interconnected innovations. First, we develop SASS, transitioning from communicationintensive full-model synchronization to fine-grained and partial updates. By adaptively regulating synchronization depth via dynamic sensitivity thresholds, SASS achieves bandwidthefficient maintenance tailored to DNN hierarchical vulnerability. Second, to circumvent the unavailability of expert feed-
back, we formulate OSDR as a label-free proxy to quantify real-time semantic fidelity. Crucially, simply combining these mechanisms introduces non-trivial optimization challenges: dynamically coupling proxy-driven update triggers with SASS structural thresholds and continuous resources inherently creates an intractable hybrid continuous-discrete optimization problem. To resolve this integration complexity, we develop a Lyapunov-guided DRL that mathematically unifies these components, by performing action space dimensionality reduction and by decoupling long-term physical constraints to facilitate efficient exploration within the complex action space. Therefore, the main original contributions of the paper can be summarized as follows: • Novel Hierarchical Synchronization Mechanism: We introduce SASS, which replaces conventional and communication-intensive full-model updates. By leveraging dynamic sensitivity thresholds to regulate synchronization depth, SASS executes fine-grained partial structural updates, by significantly reducing bandwidth consumption while accelerating semantic recovery. • Label-Free Semantic Performance Proxy: We formulate OSDR to dynamically evaluate the Value of Update (VoU). This metric circumvents the reliance on real-time ground-truth labels, by providing a physically realizable label-free proxy to quantify inference degradation under dynamic environmental corruptions. • Joint Optimization and Algorithm Design: We formulate the joint model update scheduling and resource allocation problem as a highly non-convex Mixed-Integer Non-Linear Programming (MINLP) model. To solve this, we propose the LYRA framework, which originally integrates Lyapunov optimization with DRL. This approach decouples long-term hard physical constraints and performs action space dimensionality reduction, thereby mitigating the curse of dimensionality and satisfying long-term energy and resource compliance. • Trace-driven system evaluation: Extensive experiments have been conducted to validate LYRA effectiveness. The reported quantitative results demonstrate that LYRA reduces average semantic risk backlog by 33.3% over state-of-the-art baselines. Furthermore, SASS reduces average communication overhead by 80.5% compared with conventional back-to-front updates, while achieving superior semantic recovery efficiency. II. R ELATED W ORK Edge AI Models and Continuous Maintenance. Recent advancements in MEC have catalyzed the development of continuous edge learning and cloud-edge collaborative model maintenance to support dynamic inference tasks. However, predominant model update mechanisms typically rely on either full-model fine-tuning or back-to-front partial updates, i.e., retraining only deep semantic layers or classifier heads [27], [28]. These conventional paradigms are tailored for addressing label shifts or task variations. When subjected to low-level environmental corruptions, such as dynamic fog or illumination drops commonly encountered by UAVs, these strategies exhibit significant inefficiency. Full-model synchronization is
impractical over bandwidth-constrained air-to-ground links. Furthermore, back-to-front updates are inherently informationlimited when faced with significant low-level corruptions, as deep-layer refinements cannot recover information discarded by degraded shallow representations. This motivates SASS, which prioritizes front-to-back synchronization to better align with asymmetric sensitivity of hierarchical neural blocks. Model Update Triggers and Scheduling Metrics. To optimize resource allocation in MEC networks, conventional update triggers generally fall into three categories: time-driven (e.g., periodic triggers [4], [5], [20], [24], [25] or AoI [8], [11], [14], [20]–[23]) to minimize model staleness, internal system state-driven heuristics (e.g., resource utilization [12], [15]– [17], [19], updated DT data accumulation [9], [13]–[15], [17], [19], [26]) to control system overhead, or model-driven metrics (e.g., loss or accuracy [6], [7], [10], [18]) to maximize model fidelity. Concurrently, emerging semantic-aware scheduling frameworks [28]–[33] attempt to prioritize transmissions based on downstream task utility rather than mere bit-level metrics. Nevertheless, both state- and time-driven metrics are contentagnostic; they track elapsed time or system states, failing to capture the non-linear inference degradation caused by these environmental corruptions. Furthermore, SOTA semantic scheduling mechanisms often operate under the assumption of the real-time availability of ground-truth labels at the edge node to compute inference accuracy or loss as feedback. In realistic autonomous UAV operations, real-time visual streams are unlabelled, rendering such label-dependent feedback loops impractical to deploy online. To solve this challenge, we formulate the OSDR. By addressing the limitations of state/timedriven mechanisms and the label-dependence of model-driven approaches, this proxy drives the VoU evaluation. DRL for Joint Scheduling and Model Updates. DRL have been extensively adopted to tackle dynamic resource allocation and trajectory planning in UAV-assisted MEC networks [34]– [42]. However, directly applying conventional DRL to our joint update scheduling and resource allocation problem encounters specific optimization challenges. The formulation is a highly non-convex MINLP problem featuring a hybrid action space: discrete update decisions coupled with continuous layer sensitive threshold, bandwidth and power allocations. To handle such hybrid spaces, existing DRL frameworks typically resort to either coarse discretization of continuous variables, leading to a curse of dimensionality and precision loss, or utilizing soft reward penalties that lack theoretical guarantees for longterm physical constraints, i.e., energy budgets. To address this convergence instability, our proposed Lyapunov-guided hierarchical architecture, which decouples long-term hard constraints and resolves the complex MINLP by mapping coupled hybrid decision variables into a unified discrete structural action space, paired with exact closed-form physical execution. III. E MPIRICAL O BSERVATIONS AND M OTIVATIONS This section presents a series of trace-driven empirical observations using ResNet-18 and CIFAR-10-C in order to reveal the physical failure mechanisms of edge vision models under
A. Vulnerability of edge vision model to low-level corruptions UAVs serving as MEC edge nodes frequently encounter highly dynamic environments, i.e., sudden fog or illumination drops, during continuous flight, inducing severe visual corruptions that directly degrade vision model reliability. To quantify this vulnerability, we expose a pre-trained baseline model to varying severities of fog and contrast corruptions. As depicted in Fig. 1(a), inference accuracy decreases nonlinearly under environmental stress: fog corruption significantly destroys high-frequency spatial features, causing an immediate degradation (from 92.1% to 47.4%) at Severity 1, whereas contrast corruption remains initially stable before crashing below 20% at Severity 5. Insight 1: This unpredictable, non-linear degradation invalidates static deployments and periodic, AoI-based updates, necessitating a dynamic, on-demand update trigger (αt ∈ {0, 1}) tailored to real-time stress. B. Asymmetric layer sensitivity and trade-off Given strict UAV energy and bandwidth constraints, continuous full-model updates are impractical. To explore the optimal balance between communication cost and accuracy recovery, we investigate SASS. Unlike traditional back-to-front fine-tuning for task shifts, these environmental corruptions primarily corrupt low-level physical pixels. If shallow receptive fields fail to extract reliable spatial features, deep semantic layers cannot recover the lost information, a phenomenon supported by Data Processing Inequality I(Y ; Ŷ ) ≤ I(Y ; Hk ). Therefore, front-to-back synchronization is generally more resource-efficient than back-tofront updates under significant low-level physical corruptions. So, we propose the Front-to-Back Cumulative Update strategy. This mechanism inherently demands a sensitivity-aware threshold τ (see Section IV.B), where only the neural blocks most vulnerable to current environmental shift are selected for synchronization. Fig. 1 (b) reveals two critical physical properties of DNNs: (1) Diminishing marginal returns: Updating only the shallowest block (Conv1+Blk1) requires a minimal static patch size (0.574 MB) yet generates significant accuracy recovery (25.14%). Conversely, extending updates to the deepest layers hits an accuracy ceiling (65.78%) but incurs an exponential physical patch size explosion (42.662 MB). (2) Block-wise physical topology: CNN architectures inherently introduce discrete boundaries for feature transmission. Insight 2: Block-wise structure and tradeoff curve legitimize continuous physical patch-size functions in Section IV and inspire our Action Space Dimensionality Reduction (Section VI), which maps complex continuous optimization into discrete macro-block actions to guarantee DRL convergence.