Human activity recognition using multi-input CNN model with FFT spectrograms

An activity recognition method developed by Team DSML-TDU for the Sussex-Huawei Locomotion-Transportation (SHL) recognition challenge was descrived. Since the 2018 challenge, our team has been developing human activity recognition models based on a convolutional neural network (CNN) using Fast Fourier Transform (FFT) spectrograms from mobile sensors. In the 2020 challenge, we developed our model to fit various users equipped with sensors in specific positions. Nine modalities of FFT spectrograms generated from the three axes of the linear accelerometer, gyroscope, and magnetic sensor data were used as input data for our model. First, we created a CNN model to estimate four retention positions (Bag, Hand, Hips, and Torso) from the training data and validation data. The provided test data was expected to from Hips. Next, we created another (pre-trained) CNN model to estimate eight activities from a large amount of user 1 training data (Hips). Then, this model was fine-tuned for different users by using the small amount of validation data for users 2 and 3 (Hips). Finally, an F-measure of 96.7% was obtained as a result of 5-fold-cross validation.