Research
My current project is about multi-model federated learning (MMFL): local clients can handle multiple unrelated FL models concurrently.
For example, a smartphone user can generate data for both keyboard prediction and speech recognition models.
Instead of building two single-model FL systems, we build one MMFL system and solve system-level optimization problems to make it more efficient.
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My research at CMU: Federated Learning and Optimization
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Towards Optimal Heterogeneous Client Sampling in Multi-Model Federated Learning
Haoran Zhang,
Zejun Gong,
Zekai Li,
Marie Siew,
Carlee Joe-Wong,
Rachid El-Azouzi
arXiv, 2025
This work extends our preliminary result (Best Poster Award at ICDCS), which focused on minimizing update variance to stabilize training in MMFL. While reducing variance is beneficial, our new analysis shows that it is only part of the picture. We revisit the convergence behavior of MMFL and reveal that optimizing solely for variance ignores other critical factors that significantly impact convergence—especially under heterogeneous system constraints. In response, we propose new solutions that not only achieve better performance but also come at a much lower cost, paving the way for practical and scalable MMFL deployments.
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Group-based Client Sampling in Multi-Model Federated Learning
Zejun Gong*,
Haoran Zhang*,
Marie Siew,
Carlee Joe-Wong,
Rachid El-Azouzi
VTC, Spring 2025. *Equal contribution
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Poster: Optimal Variance-Reduced Client Sampling for Multiple Models Federated Learning
Haoran Zhang,
Zekai Li,
Zejun Gong,
Marie Siew,
Carlee Joe-Wong,
Rachid El-Azouzi
ICDCS, 2024 [Best Poster Award]
[Poster]
Supplementary material
This paper explores an MMFL scenario where each client is restricted to training only one model per global round due to limited computational resources.
We propose a client sampling and task assignment method that theoretically minimizes the variance of global updates. The method achieves a 30% higher accuracy than the baseline.
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Fair Concurrent Training of Multiple Models in Federated Learning
Marie Siew,
Haoran Zhang,
Jong-Ik Park,
Yuezhou Liu,
Yichen Ruan,
Lili Su,
Stratis Ioannidis,
Edmund Yeh,
Carlee Joe-Wong
arXiv, 2024
Supplementary material
In the real-world scenario, clients could contribute to multiple federated learning models' training at the same time.
For example, a company may update their keyboard prediction model, speech recognition model, and other more federated learning models on your phone.
In this paper, we propose a client-task assignment strategy to preserve the fairness across multiple training tasks.
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My research at HKUST: Medical AI
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Efficient 3D Transformer with cluster-based Domain-Adversarial Learning for 3D Medical Image Segmentation
Haoran Zhang, Hao Chen
ISBI, 2023
We proposed a pyramidally downsampled 3D Transformer to boost efficiency and maintain high segmentation accuracy.
This paper also discussed the domain generalization problem, and
proposed a cluster-based domain-adversarial learning method to exploit available domains at a fine-grained level.
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About Me
I was born in Xinxiang, China.
My family name is 张 (Zhang), which is one of the most common family names in China.
And my given name is 皓然 (Haoran), 皓(Hao) means "the color of the moon", 然(Ran) doesn't have a specific meaning, maybe it means "yeah, uh-huh".
As the first in my family to attend college, I am deeply grateful for the support from my parents, mentors, and friends.
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