Spectrum Attention Mechanism for Time Series Classification

Time series classification(TSC) has always been an important and challenging research task. With the wide application of deep learning, more and more researchers use deep learning models to solve TSC problems. Since time series always contains a lot of noise, which has a negative impact on network training, people usually filter the original data before training the network. The existing schemes are to treat the filtering and training as two stages, and the design of the filter requires expert experience, which increases the design difficulty of the algorithm and is not universal. We note that the essence of filtering is to filter out the insignificant frequency components and highlight the important ones, which is similar to the attention mechanism. In this paper, we propose an attention mechanism that acts on spectrum (SAM). The network can assign appropriate weights to each frequency component to achieve adaptive filtering. We use L1 regularization to further enhance the frequency screening capability of SAM. We also propose a segmented-SAM (SSAM) to avoid the loss of time domain information caused by using the spectrum of the whole sequence. In which, a tumbling window is introduced to segment the original data. Then SAM is applied to each segment to generate new features. We propose a heuristic strategy to search for the appropriate number of segments. Experimental results show that SSAM can produce better feature representations, make the network converge faster, and improve the robustness and classification accuracy.

A Spike Learning System for Event-driven Object Recognition

Event-driven sensors such as LiDAR and dynamic vision sensor (DVS) have found increased attention in high-resolution and high-speed applications. A lot of work has been conducted to enhance recognition accuracy. However, the essential topic of recognition delay or time efficiency is largely under-explored. In this paper, we present a spiking learning system that uses the spiking neural network (SNN) with a novel temporal coding for accurate and fast object recognition. The proposed temporal coding scheme maps each event's arrival time and data into SNN spike time so that asynchronously-arrived events are processed immediately without delay. The scheme is integrated nicely with the SNN's asynchronous processing capability to enhance time efficiency. A key advantage over existing systems is that the event accumulation time for each recognition task is determined automatically by the system rather than pre-set by the user. The system can finish recognition early without waiting for all the input events. Extensive experiments were conducted over a list of 7 LiDAR and DVS datasets. The results demonstrated that the proposed system had state-of-the-art recognition accuracy while achieving remarkable time efficiency. Recognition delay was shown to reduce by 56.3% to 91.7% in various experiment settings over the popular KITTI dataset.

Spiking Neural Networks with Single-Spike Temporal-Coded Neurons for Network Intrusion Detection

Spiking neural network (SNN) is interesting due to its strong bio-plausibility and high energy efficiency. However, its performance is falling far behind conventional deep neural networks (DNNs). In this paper, considering a general class of single-spike temporal-coded integrate-and-fire neurons, we analyze the input-output expressions of both leaky and nonleaky neurons. We show that SNNs built with leaky neurons suffer from the overly-nonlinear and overly-complex input-output response, which is the major reason for their difficult training and low performance. This reason is more fundamental than the commonly believed problem of nondifferentiable spikes. To support this claim, we show that SNNs built with nonleaky neurons can have a less-complex and less-nonlinear input-output response. They can be easily trained and can have superior performance, which is demonstrated by experimenting with the SNNs over two popular network intrusion detection datasets, i.e., the NSL-KDD and the AWID datasets. Our experiment results show that the proposed SNNs outperform a comprehensive list of DNN models and classic machine learning models. This paper demonstrates that SNNs can be promising and competitive in contrast to common beliefs.

Temporal Pulses Driven Spiking Neural Network for Fast Object Recognition in Autonomous Driving

Accurate real-time object recognition from sensory data has long been a crucial and challenging task for autonomous driving. Even though deep neural networks (DNNs) have been successfully applied in this area, most existing methods still heavily rely on the pre-processing of the pulse signals derived from LiDAR sensors, and therefore introduce additional computational overhead and considerable latency. In this paper, we propose an approach to address the object recognition problem directly with raw temporal pulses utilizing the spiking neural network (SNN). Being evaluated on various datasets (including Sim LiDAR, KITTI and DVS-barrel) derived from LiDAR and dynamic vision sensor (DVS), our proposed method has shown comparable performance as the state-of-the-art methods, while achieving remarkable time efficiency. It highlights the SNN's great potentials in autonomous driving and related applications. To the best of our knowledge, this is the first attempt to use SNN to directly perform object recognition on raw temporal pulses.

Deep SCNN-based Real-time Object Detection for Self-driving Vehicles Using LiDAR Temporal Data

Real-time accurate detection of three-dimensional (3D) objects is a fundamental necessity for self-driving vehicles. Traditional computer-vision approaches are based on convolutional neural networks (CNN). Although the accuracy of using CNN on the KITTI vision benchmark dataset has resulted in great success, few related studies have examined its energy consumption requirements. Spiking neural networks (SNN) and spiking-CNNs (SCNN) have exhibited lower energy consumption rates than CNN. However, few studies have used SNNs or SCNNs to detect objects. Therefore, we developed a novel data preprocessing layer that translates 3D point-cloud spike times into input and employs SCNN on a YOLOv2 architecture to detect objects via spiking signals. Moreover, we present an estimation method for energy consumption and network sparsity. The results demonstrate that the proposed networks ran with a much higher frame rate of 35.7 fps on an NVIDIA GTX 1080i graphical processing unit. Additionally, the proposed networks with skip connections showed better performance than those without skip connections. Both reached state-of-the-art detection accuracy on the KITTI dataset, and our networks consumed an average (low) energy of 0.585 mJ with a mean sparsity of 56.24%.

Direct training based spiking convolutional neural networks for object recognition

Direct training based spiking neural networks (SNNs) have been paid a lot of attention recently because of its high energy efficiency on emerging neuromorphic hardware. However, due to the non-differentiability of the spiking activity, most of the related SNNs still cannot achieve high object recognition accuracy for the complicated dataset, such as CIFAR-10. Even though some of them can reach the accuracy of 90%, the energy consumption in those networks is very high. Considering this, we propose a direct supervised learning based spiking convolutional neural networks (SCNNs) using temporal coding scheme in this study, aiming to exploit minimum trainable parameters to recognize the object in the image with high accuracy. The MNIST and CIFAR-10 datasets are used to evaluate the performance of the proposed networks. For the MNIST dataset, the proposed networks with noise input are able to reach the high recognition accuracy (99.13%) as the other state-of-art models but use the much less trainable parameters than them. For CIFAR-10 dataset, the proposed networks with data augmentation step can reach the recognition accuracy of 80.49%., which is the state-of-art high accuracy in the field of direct training based SNNs using temporal coding manner. In addition, the number of trainable parameters used in such networks is much less than that in the conversion based SCNNs reported in the literature.

Object Detection based on LIDAR Temporal Pulses using Spiking Neural Networks

Neural networks has been successfully used in the processing of Lidar data, especially in the scenario of autonomous driving. However, existing methods heavily rely on pre-processing of the pulse signals derived from Lidar sensors and therefore result in high computational overhead and considerable latency. In this paper, we proposed an approach utilizing Spiking Neural Network (SNN) to address the object recognition problem directly with raw temporal pulses. To help with the evaluation and benchmarking, a comprehensive temporal pulses data-set was created to simulate Lidar reflection in different road scenarios. Being tested with regard to recognition accuracy and time efficiency under different noise conditions, our proposed method shows remarkable performance with the inference accuracy up to 99.83% (with 10% noise) and the average recognition delay as low as 265 ns. It highlights the potential of SNN in autonomous driving and some related applications. In particular, to our best knowledge, this is the first attempt to use SNN to directly perform object recognition on raw Lidar temporal pulses.