# Pedestrian Counting Based on Piezoelectric Vibration Sensor
###### Abstract  
Pedestrian counting has attracted much interest of the academic and industry communities for its widespread application in many real-world scenarios. While many recent studies have focused on computer vision-based solutions for the problem, the deployment of cameras brings up concerns about privacy invasion. This paper proposes a novel indoor pedestrian counting approach, based on footstep-induced structural vibration signals with piezoelectric sensors. The approach is privacy-protecting because no audio or video data is acquired. Our approach analyzes the space-differential features from the vibration signals caused by pedestrian footsteps and outputs the number of pedestrians. The proposed approach supports multiple pedestrians walking together with signal mixture. Moreover, it makes no requirement about the number of groups of walking people in the detection area. The experimental results show that the averaged F1-score of our approach is over 0.98, which is better than the vibration signal-based state-of-the-art methods.  
vibration signal; pedestrian counting; pattern recognition; deep learning; privacy protection; piezoelectric sensor +
Footnote †: journal: Medical  
In this paper, we present a novel infrastructure-based approach based on piezoelectric sensors. The piezoelectric sensor is much cheaper than the geophone sensor [22] used in previous studies [14; 15; 23], which is advantageous from a cost perspective. Meanwhile, our approach does not require high-density sensor deployment [24]. Furthermore, different from the existing studies, our approach can be applied to many real-life scenarios where multiple people are in the same room.  
While the identity authentication-based approaches [23; 25; 26] requires that the signals should not mix or there is only one person in the area, our approach can handle scenarios where signals from different people are mixed together. Our approach does not require that only one group of people should be in the monitored area [15]. Our system can detect the number of pedestrians in many possible cases where groups of people may walk with different walking speed, frequency, and directions. In this work, we consider the cases from 0 person to 4 persons in a 3 m by 3 m area. Our system can be treated as a minimal functional unit and be scaled out to support more people in a larger area. In future products, sensors can be embedded in floor tiles to unify the physical transmission characteristics of vibration signal.  
The major contributions of our work are as follows:  
* We propose a novel approach that can count the number of people with vibration signals from the piezoelectric sensors while protecting privacy.
* Our approach supports the situations where multiple people walk together with the signals mixed.
* Our approach does not require that only one group of people should be in the detection area.
* Different from the room-level approach [14], our approach is a step-level pedestrian counting approach, making it more appropriate for many real-world applications.
* Our approach uses piezoelectric sensors, which are much cheaper than geophone sensors, making our solution economically viable.
* Experimental evaluation shows that our approach outperforms the vibration signal based state-of-the-art methods in accuracy for similar pedestrian counting task.  
This paper is structured as follows. In Section 2, we discuss previous works regarding infrastructure-based pedestrian counting approaches from different perspectives, which motivates our approach. In Sections 3 and 4, we introduce and present our systematic approach and methodology. In Section 5, we present the experimental evaluation of our system. We conclude the work in Section 6 and discuss potential future directions.