DCT-SNN: Using DCT to Distribute Spatial Information over Time for Learning Low-Latency Spiking Neural Networks

Isha Garg, Sayeed Shafayet Chowdhury, Kaushik Roy

Keywords: Spiking Neural Networks, Input Encoding, Low Latency, Discrete Cosine Transform, Temporal Information, Frequency Domain

Abstract:

Spiking Neural Networks (SNNs) offer a promising alternative to traditional deep learning frameworks, since they provide higher
computational efficiency due to event-driven information processing. SNNs distribute the analog values of pixel intensities into binary spikes over time. However, the most widely used input coding schemes, such as Poisson based rate-coding, do not leverage the additional temporal learning capability of SNNs effectively. Moreover, these SNNs suffer from high inference latency which is a major bottleneck to their deployment. To overcome this, we propose a scalable time-based encoding scheme that utilizes the Discrete Cosine Transform (DCT) to reduce the number of timesteps required for inference. DCT decomposes an image into a weighted sum of sinusoidal basis images. At each time step, a single frequency base, taken in order and modulated
by its corresponding DCT coefficient, is input to an accumulator that generates spikes upon crossing a threshold. We use the proposed scheme to learn DCT-SNN, a low-latency deep SNN with leaky-integrate-and-fire neurons, trained using surrogate gradient descent based backpropagation. We achieve top-1 accuracy of 89.94%, 68.3% and 52.43% on CIFAR-10, CIFAR-100 and TinyImageNet, respectively using VGG architectures. Notably, DCT-SNN performs inference with 2-14X reduced latency compared to other state-of-the-art SNNs, while achieving comparable accuracy to their standard deep learning counterparts. The dimension of the transform allows us to control the number of timesteps required for inference. Additionally, we can trade-off accuracy with latency in a principled manner by dropping the highest frequency components during inference.

One-sentence Summary: We propose a new scheme that utilizes DCT to encode pixel information across timesteps, enabling us to learn deep spiking neural networks that can perform inference with lower number of timesteps compared to other state-of-the-art SNNs.

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Community Implementations: [ 1 code implementation](https://www.catalyzex.com/paper/arxiv:2010.01795/code)

Reviewed Version (pdf): https://openreview.net/references/pdf?id=TZNVkTFnQ9