A Multi-Path Compensation Method for Ranging in Wearable Ultrasonic Sensor Networks for Human Gait Analysis.

Karalikkadan Ashhar,Mohammad Khyam,Cheong Soh

doi:10.3390/s19061350

Karalikkadan Ashhar, Mohammad Khyam + Show 1 more

Open Access

https://doi.org/10.3390/s19061350

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Abstract

Gait analysis in unrestrained environments can be done with a single wearable ultrasonic sensor node on the lower limb and four fixed anchor nodes. The accuracy demanded by such systems is very high. Chirp signals can provide better ranging and localization performance in ultrasonic systems. However, we cannot neglect the multi-path effect in typical indoor environments for ultrasonic signals. The multi-path components closer to the line of sight component cannot be identified during correlation reception which leads to errors in the estimated range and which in turn affects the localization and tracking performance. We propose a novel method to reduce the multi-path effect in ultrasonic sensor networks in typical indoor environments. A gait analysis system with one mobile node attached to the lower limb was designed to test the performance of the proposed system during an indoor treadmill walking experiment. An optical motion capture system was used as a benchmark for the experiments. The proposed method gave better tracking accuracy compared to conventional coherent receivers. The static measurements gave 2.45 mm standard deviation compared to 10.45 mm using the classical approach. The RMSE between the ultrasonic gait analysis system and the reference system improved from 28.70 mm to 22.28 mm. The gait analysis system gave good performance for extraction of spatial and temporal parameters.

Highlights

Gait analysis is an important clinical tool to assess disorders due to neurovascular or musculoskeletal diseases and to study relations between gait and falls in the elderly population [1]
The amplitude of signal after attenuation in air was modeled as A = A0 e−γ×δd, where A0 and δd are the originally transmitted amplitude and the distance traveled through the medium respectively
The results show that the performance of the linear chirp was better than the logarithmic and quadratic chirp signals

Summary

Introduction

Gait analysis is an important clinical tool to assess disorders due to neurovascular or musculoskeletal diseases and to study relations between gait and falls in the elderly population [1]. The gold standard system for human motion capture and gait analysis is an optical system with high-speed infrared cameras [2]. Non-traditional methods developed for human motion tracking include magnetic sensors [4], laser sensors [5,6], inertial measurement units [7,8], ultrawideband (UWB) ranging sensors [2,9], ultrasonic sensors [1,10]. Inertial sensors are affected by the drift during integration and fluctuating offset values and require sensor fusion to obtain accurate results [14]. UWB sensors demand high accuracy clock synchronization and high-cost ADCs to provide accurate ranging measurements [1]. Ultrasonic sensors can provide high accuracy time of flight (ToF) measurements without using expensive hardware as the wave travels much slower

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