Important Notice:

This code was our class project years ago, which means we are not the authors of this paper nor continue to maintain this project. We are so sorry, but we cannot provide further help with this code.

Self-Balancing Federated Learning With Global Imbalanced Data in Mobile Systems

Group Member:

Mingyue Tang: Read Literatures and looking for baseline code, implemented z-score calculation, implemented mediator based stochastic gradient descent, relative part of the research report

Xinrui Li: Read Literatures and looking for baseline code, implemented z-score calculation, implemented mediator based stochastic gradient descent, relative part of the research report

Zhige Li: Literature review on distributed deep learning framework; Implemented three different imbalance evaluation and generation; Implemented data augmentation and down sampling algorithm; Implemented greedy mediator selection algorithm; System design on coding; Relative part of the research report

Xinhe Yang: Learn about framework of federated learning and distributed system. Looking for baseline code. Implemented data separation and processing and relative part of the research report

Goal: Try to solve data imbalance problem in Federated Learning

Background:

Federated Learning:

Federated learning (also known as collaborative learning) is a machine learning technique that trains an algorithm across multiple decentralized edge devices or servers holding local data samples, without exchanging them. This approach stands in contrast to traditional centralized machine learning techniques where all the local datasets are uploaded to one server, as well as to more classical decentralized approaches which often assume that local data samples are identically distributed.

Data imbalance:

1. Size Imbalance, where the data size on each device (or client) is uneven;
2. Local Imbalance, i.e., independent and non-identically distribution (non-IID), where each device does not follow a common data distribution;
3. Global Imbalance, means that the collection of data in all devices is class imbalanced

Proposed solution:

Paper Link: https://ieeexplore.ieee.org/document/9141436

Model Framework:

Algorithm Framework:

Workflow:

1. Initialization: The FL server initializes the weights and the optimizer of the neural network model and collects the local data distribution of participants;
2. Rebalancing: First, we perform the z-score-based data augmentation and downsampling to relieve the global imbalanced of training data. Then, we propose the mediator which asynchronouly receives and applies the updates from clients to averaging the local imbalance;
3. Training: First, each mediator sends the model to the subordinate clients. Then each client trains the model for E local epochs and returns the updated model to the corresponding mediator. Loops this process Em times. Finally, all the mediators send the updates of models to the FL server;
4. Aggregation: The FL server aggregates all the updates using the FedAvg algorithm

Benchmark and Dataset:

https://github.com/chaoyanghe/Awesome-Federated-Learning#Benchmark-and-Dataset

Baseline Code (just examples):

• https://github.com/shaoxiongji/federated-learning

• https://github.com/ivishalanand/Federated-Learning-on-Hospital-Data

• https://github.com/AshwinRJ/Federated-Learning-PyTorch

Steps:

• Replicate Baseline Code
• Run evaluation pipeline
• Improve the baseline by https://docs.google.com/document/d/1qa0Cv-axRw9ZSVDB-C5YZMp9lEd6qp3d1FmzX7D8Mgg/edit methods
• Propose our own method (optional)

Experiment:

Experiment Setup:

We ran three groups of experiments with three different imbalanced conditions, size-imbalance, local-imbalance, and global-imbalance. Each group contained two experiments, one is for the baseline model and another one is for our proposed self-balanced model.

Global Parameters:

All the default parameters are in utils/options.py, for the seek of fairness we have the same set of global parameters for all the running experiments

Imbalanced Dataset Parameters setup:

To ensure each group of experiment is running on a same distributed imbalance dataset, we wrote our own dataset generation method in DataBalance.py and DataProcessor.py. Different imbalance type has different set of parameters need to be set.

Size Imbalance:

• list_size: list_size is a size indicates the size of each device

Local Imbalance:

• num_device: num_device indicates the number of the devices
• device_size: device_size is the size of each device (it's an integer, not a list, as each device should have the same size)
• alpha: Alpha = 0 means full random sampling, totally balanced, Alpha = 1 means no sampling, each device takes only one class, totally imbalanced

Global Imbalance:

• num_device: num_device indicates the number of the devices
• device_size: device_size is the size of each device (it's an integer, not a list, as each device should have the same size)
• num_each_class: num_each_class is a list indicating the number for each class

Result:

Running Parameter: --size_balance(local_balance/global_balance) --confusion_matrix --epochs 10 --gpu -1

Test Set Comparison Result

Imbalance Type	Baseline Model Test Set Accuracy	Self-balanced Model Test Set Accuracy
Size Imbalance	81.22%	87.05%
Local Imbalance	88.42%	89.46%
global Imbalance	84.08%	87.03%

The self-balance model outperformed the baseline model in all three conditions with a 10 epochs training. There are 5.83% improvement on the size imbalance situation, 1.04% on local imbalance, 2.92% on global imbalance with the same experiment setup.

From the result, we can observe that the augmentation and down sampling method plays a significant role for size balance and global balance problem. However, the greedy mediator selection method does not give much support. However, from the experiment we do observe that each mediator successfully has the similar distribution with the global. So It could be caused by the sequential training of the mediator selection. So we can leave it as a future work to discuss how to better improve the result with the balanced mediator.

Detailed breakdown:

Size-Balance

Figure. Baseline Model Test Confusion Matrix on Size Imbalance

Figure. Self-balance Model Test Confusion Matrix on Size Imbalance

From the confusion matrix, it's clear to see the self-balance model have better classification result on almost every class(9/10). Better in both precision and recall. So overall, it has a better F1 score than the baseline model.

Local Balance:

Figure. Baseline Model Test Confusion Matrix on Local Imbalance

Figure. Self-Balance Model Test Confusion Matrix on Local Imbalance

From the confusion matrix, the self-balance model do not have significant improvement accourding to the classes (6/10 are outperformed). It narrowly beats the baseline function on both accuarcy and f1 scores.

Global Balance:

Figure. Baseline Model Test Confusion Matrix on Global Imbalance

Figure. Self-Balance Model Test Confusion Matrix on Global Imbalance

From the confusion matrix, the self-balance model has better classification result almost in every class (9/10) which can be observed clearly in the figure. So it has higher f1 score and test accuracy than baseline model.