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Indoor RFID Gait Monitoring System
for Fall Detection Yung-Chin Chen*, Member, IEEE, Vi-Wen Lin
Asia University
ycchen@asia.edu.tw, gamepeare@hotmail.com
Abstract�Due to home accidents occurring within the
world's aging population, especially with the accidental stumble
and falling of the elderly, mortality and morbidity from falls
have become one of the major issues in the health care system.
In most developed countries, most frequent stumbles and falls
occur in and around the community or at home. A number of
wearable devices integrated with accelerometers have been
tested to detect accidental stumbles and falls. Of those tested
using waist or chest-attached devices, however, were not only
user unfriendly but also deficient in 100% detection accuracy. In
this paper, a RFID-based gait monitoring system (RGMS) is
proposed, which helps caregivers detect stumbles and falls of
the elderly without any restriction to time and place. The
proposed RGMS consists of a pair of slippers with a dual band
RFID module, several readers and a computing system. The
RGMS provides quantitative and graphical feedback to
caregivers for gait monitoring and the assessment of gait
abnormality by tracking the elder's cadence, stride length, and
gait. This gait tracking system is responsive, accurate, and most
of all user friendly.
Index Terms�RFID, aging, falls, stumbles, gait.
1. INTRODUCTION
Home accidents occurring within the world's aging
population, especially with the accidental stumble
and fall, have become one of the major causes of
mortality and morbidity in the elderly[I]. Consequently,
leading to an ever increasing care burden with the burden
of disease [2,3]. According to the data provided by
Department of Health, accidental stumbles and falls
death in Taiwan over the past few years [4]. Injuries due
to falls have been ranked second highest of the leading
reasons. In the United States alone, the percentage of fatal
home accidents from stumbles and falls have also been on
the rise. More than 86% of the victims are 65 years old or
older. An estimated 30% of persons who are 65 years or
older have been affected by a serious fall. In addition,
elderly persons residing in nursing home facilities,
hospitals, and elderly care centers have a higher
probability of stumbles and falls than that at home [5].
According to a study released by the Centers for
Disease Control and Prevention's Morbidity and
Mortality Weekly Report (MMWR), fall-related death
rates among Americans ages 65 and older increased
greatly from 1993 to 2003. More than 13,700 seniors died
from falls in 2003, making falls the leading cause of
injury-related deaths among elderly persons. Fall-related
fatalities increased by 55% from 1993 to 2003. In 2003
nearly 1.8 million elderly persons received treatment in
emergency rooms for fall-related injuries and 460,000
were hospitalized. The costs for fall-related care among
seniors in 2000 totaled approximately $19 billion.
"Fall-related death rates have increased faster than that of
fall-related injury rates" [6]. On the other hand, the
leading causes for increasing elderly death rates may no
longer be dominated by chronic diseases, such as heart
disease, cancer, and diabetes, but by fatal falls as well.
According to researchers in the United States, elderly
people are obviously prone to stumbles and falls due to
the progressive deterioration in their balancing
leading to injury occurring with people ages from 65 reflexes[7]. Besides, behaviors of trying to get up and
years and above are ranked 7th as the leading causes of walking on a slippery surface such as wet bathroom floor
978-1-4244-8314-3/10/$26.00 ©20l0 IEEE 207
are also among the main causes of elderly falls.
According to one survey, one in three elderly people
living within a community are at risk of likely falling one
or more times in a year; with one in four falling ending up
with serious or fatal injuries. Moreover, stumble and falls
constitutes a significant portion of health care cost [8,9].
On the other hand, aging population and public health
care services are the driving factors for moving toward
the adoption of a home tele-care system.
During the last decade, technological advances in
microcontrollers, wireless communication, and sensor
miniaturization have provided for the development of
wearable devices for home-based healthcare monitoring
systems. A number of wearable sensor devices integrated
with a two-axis accelerometer [10-11] or a three-axis
accelerometer [12-25] have been widely developed to
detect stumble and fall activities by measuring the
changes in instantaneous acceleration values and attitude
angles. Sensor devices already in the market which were
designed either to be attached to their wrists or waist were
not only user unfriendly but also lacked 100% detection
accuracy.
We therefore propose a novel RFIO-based gait
monitoring system for stumble and fall detection without
any restriction to time and place. The ROMS consists of a
pair of slippers with dual-band RFID module built inside,
several readers, and a computing system that provides
quantitative and graphical feedback for gait monitoring
and the assessment of gait abnormality. This system is
designed to adjust stumble and fall activities by tracking
the elder's gait and stride length.
2. RFID GAIT MONITORING SYSTEM
As far as the RFID-based positioning or tracking
technology is concerned, there have been several
investigations involved in the localization and tracking
applications for various purposes [26-33], while paying
insignificant amount of observation to track the elderly
person's gait and stride length for fall detection have been
made. The possible reasons for lack of attention to this
208
area of research are as follows; (l) The accuracy of such
proposed RFIO-based indoor positioning systems have
been insufficient to measure and mark the stride length.
(2) Indoor RFID positioning accuracy highly depends on
the signal strength, which is easily dissipated by way of
mUlti-path fading. (3) And, the relatively high number of
active readers which are required leading to high capital
costs.
Therefore, we propose a ROMS system that consists
of several 2.450Hz active readers, a pair of slippers
attached with dual-band RFID module incorporated
internally and a computing system. Thus, the degree of
gait abnormality is quantified based on the measured
stride length.
The 2.450Hz active reader is shown in Figure 1. The
reading range is up to five meters and its specification is
listed in Table 1.
Fig 1. 2.450Hz active reader
Table 1 Specification of Active Reader
Feature Description
Frequency 2.4�2.45 OHz
Size 92(W)X66(H)X20(D) (mm)
Interface USB Vl.1
Antenna Built-in 1 dBi omnidirectional antenna
The dual-band RFID module combines a 2.450Hz
active tag and a 13.56MHz passive reader (ISO 15693),
see Figure 2. Power supply for the 13.56MHz passive
reader is an ER2450 3.6V battery. A motion sensor is also
built-in for power saving. The dual-band RFID module is
designed to be attached inside the slipper as shown in
Figure 3.
I I
I I I I I \ \ \
'- '" ..... _- ,
U.56 MHz ..... e<
I I
I Battet')'
3.6V
Fig 2. RFID dual-band module
The function of the dual-band RFID module is to read
the low-cost 13.56MHz passive tags mounted on the floor
for measuring stride length while transmitting the signal
to the 2.45GHz active reader through the 2.45GHz active
tag. The system will then be able to calculate the possible
stumble and fall activity as a result of gait abnormality.
The architecture of the indoor RFID gait monitoring
system is shown in Figure 4.
Fig 3. A slipper attached with a fitted dual-band module
RFlO 2.45G Tag & 13.56 Reader
•
Active Moving path
Fig 4. Indoor RFID gait monitoring system
For precise stride length measurement, many
13.56MHz passive tags are to be mounted onto the floor
using a triangular array separated by 20cm, as illustrated
in Figure 5. By taking advantage of the unique ID-(x. y
• z) axes correspondence, we can not only track elder
person's position but also measure their stride length.
The RGMS allows elders to take advantage of the gait
209
monitoring slippers in their daily lives in an unconscious
and responsive manner. A decision algorithm for real-time
stride length monitoring embedded in the RGMS is
illustrated in Figure 6. It is able to measure various stride
length and just gait useful for stumble and fall detection.
The algorithm developed is based on normal stride length
of >50cm and abnormal stride length of <25cm for
elderly people. The system will be alerted once the stride
length falls below 25cm. Stride lengths ranging from
25cm to 50cm will then be calculated by averaging ten
read times to find these values. If the average value is less
than 35cm, system will alert and inform care givers
through the visual feedback information displayed on the
RGMS.
Fig 5. Triangular array
Fig 6. An algorithm for real-time stride length monitoring
3. EXPERIMENTAL RESULTS
The performance of RGMS have been tested within a
living room with a triangular tag array separated by 20cm
while mounted on the floor (see Figure 7). Read rate of
the mounted tags were tested first by wearing slippers
while walking around the living room. Test resulted in a
relatively high read rate as listed in Table 2.
Fig 7. Triangular tag array mounted on the floor
Table 2. Read rate of the mounted triangular tags
time read successful read rate
interval No times read times (%)
(min:sec)
1 100 86 86% 4:09 2 100 95 95% 4:05 3 100 100 100% 2:33 4 100 91 91% 3:09 5 100 98 98% 2:50
As we can see from the main interface of the RFID gait
monitoring system (see Figure 8), it shows a layout for
the living room, a list table for those mounted tags, some
control buttons, a list table for measured stride length, and
two ID numbers used in the identification of both left: and
right foots.
Figure 9 demonstrates the quantitative and graphical
feedback for gait monitoring for both left: and right foot.
If the stride length of the mounted tags read by the slipper
is less than 25cm, the gait monitoring system will be
alerted and caregivers will be informed to give aid, see
Figure 10.
210
Table 3 shows that this monitoring system can also
provide physical activity information by collecting their
overall daily stride length. This table is helpful for in
physical activity health care monitoring.
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--:Leftfoot 0016001608329001
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Fig 8. Main System Interface
.J '.' '.' , .. '" ,., " ". ,�
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(,:dc u latu w:llklnjt distancf's lilt' ",",f ... Lui
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Fig 9. Gait Monitoring Interface
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6115 6116 6117
C :tlCllhllt'.'I w � lki n � disl:lIlct'.'I VIO Cl>IMl(ts leul "'1',(�)";(II'�Qo."'1 I" ;lI.§ O{ol.tX'I" ��0)(1';:'� Z":8
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Fig 10. Abnormal Gait Warning Interface
Table 3. Physical activity
stride length Average velocity time interval (cm) (cmls) (5:1' : fj))
5823 34.85 2:47 6234 33.69 3:05 5689 37.18 2:33
4. CONCLUSION
Since there are very few resesarch focusing on RFID
gait monitoring system for indoor tracking to detect
stumbles and falls, aRFID-based gait monitoring system
(RGMS) consisting of a dual-band RFID module built
into a pair of slippers, several readers, and a computing
system is proposed. The RGMS provides quantitative and
graphical feedback to caregivers for gait monitoring and
the assessment of gait abnormality by tracking the
elderly's stride length and gait. The RGMS is not only
helpful for caregivers to detect stumbles and falls of the
elderly, but also to possibly predict stumbles and falls in a
responsive, accurate, and most of all user friendly
manner.
ACKNOWLEDGMENT
This work was supported by National Science
Council, Republic of China, under Grant NSC98-2221
-E-468-0 14.
[1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
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