MorpheusNet: Resource efficient sleep stage classifier for embedded
  on-line systems
Ali Kavoosi Morgan P. Mitchell Raveen Kariyawasam John E. Fleming Penny Lewis Heidi Johansen-Berg Hayriye Cagnan Timothy Denison
Sleep Stage Classification (SSC) is a labor-intensive task, requiring experts
to examine hours of electrophysiological recordings for manual classification.
This is a limiting factor when it comes to leveraging sleep stages for
therapeutic purposes. With increasing affordability and expansion of wearable
devices, automating SSC may enable deployment of sleep-based therapies at
scale. Deep Learning has gained increasing attention as a potential method to
automate this process. Previous research has shown accuracy comparable to
manual expert scores. However, previous approaches require sizable amount of
memory and computational resources. This constrains the ability to classify in
real time and deploy models on the edge. To address this gap, we aim to provide
a model capable of predicting sleep stages in real-time, without requiring
access to external computational sources (e.g., mobile phone, cloud). The
algorithm is power efficient to enable use on embedded battery powered systems.
Our compact sleep stage classifier can be deployed on most off-the-shelf
microcontrollers (MCU) with constrained hardware settings. This is due to the
memory footprint of our approach requiring significantly fewer operations. The
model was tested on three publicly available data bases and achieved
performance comparable to the state of the art, whilst reducing model
complexity by orders of magnitude (up to 280 times smaller compared to state of
the art). We further optimized the model with quantization of parameters to 8
bits with only an average drop of 0.95% in accuracy. When implemented in
firmware, the quantized model achieves a latency of 1.6 seconds on an Arm
CortexM4 processor, allowing its use for on-line SSC-based therapies.