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

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.

Wearable wireless ultrasonic sensors for human gait analysis

“…The Empirical CDF calculated for ranging error in meters (X) using half-peak detection method and conventional peak detection method. 73 5.6 The mobile node and camera marker attached to left lower limb [4]. 75 5.7 The anchor nodes attached on a vertical board along with the anchor nodes [4].…”

“…73 5.6 The mobile node and camera marker attached to left lower limb [4]. 75 5.7 The anchor nodes attached on a vertical board along with the anchor nodes [4].…”

“…Results and Discussion The anchor nodes attached on a vertical board along with the anchor nodes[4].Doppler shift affects the performance of the system. We took the average of the range estimated from linearly increasing and decreasing chirp signals to offset these errors as explained in Section 5.2.2[7].…”