Quantitative gait measurement with pulse-Doppler radar for passive in-home gait assessment

Abstract

In this paper, we propose a pulse-Doppler radar system for in-home gait assessment of older adults. A methodology has been developed to extract gait parameters including walking speed and step time using Doppler radar. The gait parameters have been validated with a Vicon motion capture system in the lab with 13 participants and 158 test runs. The study revealed that for an optimal step recognition and walking speed estimation, a dual radar set up with one radar placed at foot level and the other at torso level is necessary. An excellent absolute agreement with intraclass correlation coefficients of 0.97 was found for step time estimation with the foot level radar. For walking speed, although both radars show excellent consistency they all have a system offset compared to the ground truth due to walking direction with respect to the radar beam. The torso level radar has a better performance (9% offset on average) in the speed estimation compared to the foot level radar (13%-18% offset). Quantitative analysis has been performed to compute the angles causing the systematic error. These lab results demonstrate the capability of the system to be used as a daily gait assessment tool in home environments, useful for fall risk assessment and other health care applications. The system is currently being tested in an unstructured home environment.

Fig. 1

(a) Human walk illustration and (b) associated Doppler radar spectrogram (blue line: torso motion, black circle: leg swing).

Fig. 2

Extracted frequency shift from torso motion (black line) shown in a spectrogram.

Fig. 3

Spectrogram after background noise subtraction with time-domain signal F(t) in blue line and extracted steps (o).

Fig. 4

Walking speed comparison: Vicon versus radar. Dashed line: velocity threshold selected.

Fig. 5

Foot velocity obtained from Vicon markers attached to the shoes (black lines), and steps recognized (blue dash line).

Fig. 6

Walking speed comparison for the single radar setting: Vicon versus Foot radar. Blue dashed line: v_radar = 0.87* v_vicon.

Fig. 7

Angle θ and φ affect the walking speed estimated by the radar: (a) θ estimation: walk paths (dash line: fitting line) and radar beam projected on the ground plane (red), (b) φ estimation and experiment setup, and (c) cosφ as a time variant parameter.

Fig. 8

Foot radar walking speed comparison in the dual radar setting: (a) Vicon versus Floor radar. Dashed line: v_foot__radar = 0.82* v_vicon. (b) Vicon versus Foot radar with angle φ corrected. (c) Vicon versus Foot radar with both angles φ and θ corrected.

Fig. 9

Torso radar walking speed comparison in the dual radar setting: (a) Vicon versus Torso radar. Dashed line: vtorso_radar = 0.91* v_vicon. (b) Vicon versus Torso radar with angle θ corrected.

Fig. 10

Step time comparison: Vicon versus Foot radar including both single radar and dual radar setting.