
Split Federated Learning on Micro-controllers: A Keyword
Spoing Showcase
Jingtao Li
ASU
Tempe, USA
Runcong Kuang
ASU
Tempe, USA
ABSTRACT
Nowadays, AI companies improve service quality by aggressively
collecting users’ data generated by edge devices, which jeopardizes
data privacy. To prevent this, Federated Learning is proposed as a
private learning scheme, using which users can locally train the
model without collecting users’ raw data to servers. However, for
machine-learning applications on edge devices that have hard mem-
ory constraints, implementing a large model using FL is infeasible.
To meet the memory requirement, a recent collaborative learning
scheme named split federal learning is a potential solution since it
keeps a small model on the device and keeps the rest of the model
on the server. In this work, we implement a simply SFL framework
on the Arduino board and verify its correctness on the Chinese
digits audio dataset for keyword spotting application with over 90%
accuracy. Furthermore, on the English digits audio dataset, our SFL
implementation achieves 13.89% higher accuracy compared to a
state-of-the-art FL implementation.
KEYWORDS
TinyML, Federated Learning, Keyword Spotting
ACM Reference Format:
Jingtao Li and Runcong Kuang. 2022. Split Federated Learning on Micro-
controllers: A Keyword Spotting Showcase. In Proceedings of Make sure to
enter the correct conference title from your rights conrmation emai (Con-
ference acronym ’XX). ACM, New York, NY, USA, 5 pages. https://doi.org/
XXXXXXX.XXXXXXX
1 INTRODUCTION
Increasing accessibility of edge computing devices has shown great
impact on our daily life, and at the same time, their generated
data powers up machine learning applications such as computer
vision and voice recognition. However, as these devices are close
to our living environment, it starts to raise concern on the data
privacy. General Data Protection Regulation (GDPR) that is recently
approved by European Union imposes a strong limitation on col-
lecting data from users. In this context, how to utilize these valuable
data while comply with GDPR is still a challenge for AI community.
In fact, private schemes such as multi-party computation (MPC)[
2
]
and homomorphic encryption (HE) can enable provable privacy
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while handling users’ data. However, the large overhead of computa-
tion and communication of these private methods are not practical
for public use (though they can be good for cross-silo use case).
Thus, companies start to investigate cheap but privacy-preserving
learning schemes. Google presents Federated Learning (FL) [
4
] as
one of these schemes and deploy it in its Google assistant and
Google Keyboard applications.
The key idea of FL is to prevent users’ data from leaving the
device. In its design, each user acquires a local copy of the model,
train it on user’s own private data, and send the updated parameters
to the server periodically. Server, once collecting updated parame-
ters from all users, perform an average (as in FedAvg[
4
]) to get the
global model updated and transfer to user for training in the next
round. For the rst time, [
3
] brings the Federated Learning idea to
the TinyML community, where they are able to demonstrate the
successful implementation of FL in a tiny micro-controller for a
2-layer MLP model in a binary keyword classication problem.
A clear limitation of using FL is that it requires user have the
ability to train the entire model locally on the device. For embedded
systems which are extremely constrained by memory and power,
training locally is not possible for an industry-scale model. Thus,
[
3
] uses a tiny 2-layer MLP of 16K parameter, mostly in the concern
of the limited SRAM of the micro-controller.
For more complex datasets and use cases, model has to be larger.
Thus, we investigate the realization of Split Federated Learning
(SFL) [
5
] as an edge-friendly version of FL on a micro-controller.
SFL, splits the model into two parts, client-side model and server-
side model. Client-side model is designed to be small enough to run
on the device and server-side model can be very large to achieve a
good accuracy. As a split version of Federated Learning, the raw
data is also protected in SFL since it is processed pure in local
devices. Moreover, SFL allows users to have only a small part of
the model which can relieve the hardware requirement.
In the scope of our project, we implemented SFL on Arduino
Nano BLE 33 sense for a multi-class keyword classication task,
where an audio dataset of digits pronounced in Chinese and English
is classied respectively. By SFL, We are able to use very large
model in training because server does not have memory limitation
and has fast training speed. We compared dierent model sizes
(FL’s and SFL’s) in terms of the model’s classication accuracy,
and gave a proof-of-concept example of using SFL can achieve
better performance than using FL in practice. We also demonstrated
that SFL enables using bigger model to enhance the accuracy. SFL
shows 13.89% better accuracy using a large CNN model compared
to Federated Learning where only a small MLP can be used. After
training, we compressed the entire model and put it back to the
device. Then, the device can perform inference without dependence
arXiv:2210.01961v1 [cs.LG] 4 Oct 2022