Effectivity_of_Sports_Timing_RFID_System_Field_Study

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Effectivity of Sports Timing RFID System,
Field Study
1st Jan Kolaja
Institute of New Technologies and Applied Informatics
Technical University of Liberec
Liberec, Czech Republic
jan.kolaja@tul.cz
2nd Jana Kolaja Ehlerova
Institute of New Technologies and Applied Informatics
Technical University of Liberec
Liberec, Czech Republic
jana.kolaja.ehlerova@tul.cz
Abstract—This study summarises experiences obtained while
using the UHF RFID system for sports timing (of the shelf RFID
hardware and custom software designed by authors). The system
uses four basic layouts of RFID reader/tags for four groups of
sports. Data from several events were resumed into statistics
where read probability and inaccuracy are monitored.
Index Terms—UHF RFID, sports timing
I. INTRODUCTION
Sports timing for mass outdoor events such as running or
cycling races is more often using technology providing results
in real time. There are several industrial tools and technologies
which are used for online sports timing these days. Some of
these technologies are commonly used by a broad range of
timers some are unique such as Bluetooth [3].
RFID technology became common in the world of timing.
A broad spectrum of this technology is used for timing in its
full range beginning with NFC, through LF, HF, UHF to MW.
The MicroWave frequency with active RFID tags is probably
the most accurate solution for contactless timing system on
the other hand it is as well the most expensive way especially
in case of large amount of tracked sportsmen.
RFID systems are widely used for mass events with no need
for great precision where the timing is still essential but has no
ambition to change the world record tables. Therefore even the
best possible RFID system isn’t reliable enough to meet IAAF
regulations so it cannot be used for track running competitions
[4].
From several points of view UHF RFID system with passive
tags have the best value for the price. This is the list of main
benefits of this technology for sports timing:
• a rich supply of RFID readers, antennas and tags on the
market,
• low tag price — no need for returnable timing chip,
• tags in the form of stickers — can be easily attached to
the start number,
• read range is good enough for reading without racer’s
interaction,
• availability
• effectivity
Apart from all the benefits, there are also some limitations
which appears when RFID UHF based timing system is used
in real worlds condition. RFID systems of the shelf are tuned
to meet specifications needed for reliable identification [2],
[5].
Based on years of experience in the field of RFID sport’s
timing the main reason of troubles is simply that humans are
individuals, not uniform parts in the production process. That
is the reason why they
• make RFID tag not working before the use (bend, shock),
• wear start bib with RFID tag in various (not recom-
mended) way,
• swap their start bib with colleagues.
Apart from this user’s distractions, there are also limitations
which are not racer’s fault like
• various read probability depending on the weather (atmo-
spheric distractions), tag clearance (mud, sweat),
• RSSI (Relative Signal Strenght Identifier) is not always
accurate,
• the first seen tag is not always the first one on the finish
line.
II. USED TECHNOLOGY AND SETTINGS
Fig. 1. Sportchallenge gate, two antennas, and reader overhead
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2019 IEEE International Conference on RFID Technology and Applications (RFID-TA)
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Fig. 2. Scheme of Sportchallenge timing system.
Sportchallenge timing system’s basic hardware consists of
custom antennas connected to Impinj reader (see Fig. 1) and
DogBone tags (Impinj Monza 4D), see specification in Tab. I
[1] as transponders. Speedway Connect software as a part of
Impinj reader sends all read data to a Linux server which runs
custom Sportchallenge software. This software based on PHP
and MySQL is responsible for the final data interpretation into
race results, see Fig. 2.
TABLE I
TAG SPECIFICATION, DOGBONE IMPINJ MONZA 4D
Operating Frequency 860 - 960 MHz
Antenna size 86 x 24 mm
Die-cut size 97 x 27 mm
Memory EPC memory up to 496 bit
user memory up to 512 bit
Serialized TID
A. Hardware layout
Basic hardware layout of RFID timing gate is adjustable
frame made of square steel profiles. Reader and 2 horizontal
antennas are mounted on the top part of the frame. Antennas
are usually leveled approx. 2.3m above the ground, oriented
in 45◦ angle. The reader is placed between these 2 antennas.
Such a layout provides shortest antenna cables possible and
the possibility to keep the reader and antennas set together
without a need of disassembly with each transport.
The gate described above is the same for the variety of
sports such as running, inline skating, road cycling, cyclocross
or MTB. The difference between each discipline is where the
start bib is worn. From this point of view, the task of racer’s
inventory may be divided into 4 groups named by the most
typical example of such a discipline, see Fig. 3.
• MTB - bib on bicycle’s handlebar, aproaching the anten-
nas.
• Run - bib on runner’s chest, aproaching the antennas.
• CX, inline - bib on rider’s bendt back (45◦) appearing
suddenly in antennas view and becoming more distant.
• OCR, XC skiing - bib on rider’s back (not ideal angle)
appearing suddenly in antennas view and becoming more
distant.
B. Specifics of different sports
1) MTB: Tag included in bib number is worn on handle-
bars. Bib number is usually from harder material (firmer than
Fig. 3. Position of the tag and antenna, different sports.
bib for running) and is not likely to be destroyed. Sweat
is also not a problem and even hard rain doesn’t affect the
reading. Mud can create a barrier strong enough to reduce read
probability but in the usual case, the mud is sprayed from the
opposite side.
2) Run: For practical and historical reasons runners are
used to wear start numbers at their chest so the tag included
in bib number is worn at the chest. This setting introduces a
problem for an RFID system. The antenna has to be angled
forward so the read range is not strictly bordered.
Another problem of this setting is water: racers can easily
sweat over the tag and make a barrier for the antenna. This
problem is quite successfully prevented by using a spacer -
piece of foam stuck under the tag, that keeps tag away from
runners body.
Finally, the next problem connected with sweating or rainy
weather is the material of the bib number, which is strained
and can be manually destroyed, destroying the tag as well.
3) Cyclocross/Road cycling: Bib number is very same as
the one used for road racing or obstacle race. Due to CX rules,
the bib should not be worn in the middle of riders back as it
is the first place to be sprayed in muddy conditions. Usually,
the bib is worn on the riders left side of the back.
4) OCR, XC skiing: Obstacle race is a specific kind of
running event. The key problem is that participants have to
crawl in the mud which limits wearing the bib on the chest.
The possibility is to wear the bib on the back. Scratching the
participants back is much less probable than scratching his
chest.
Wearing the tag on riders back appeared to be convenient for
XC skiing as well. Especially with the double pole technique,
the skiers back is the only part that is visible from height in
every sequence of the movement. Thats why this layout has
been successfully applied to XC skiing on snow as well as on
road. It has replaced previously tested ankle bibs as it is much
more comfortable for the racer as well as for the person who
has to sort, clean and store tags.
III. RESULTS PROCESSING
When processing results there are two sources of informa-
tion. The first one is data obtained by RFID reader filtered by
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the timing system (start number and time). Filtering means the
system recognizes whether the number should be in the race,
whether the racer is in his first, second or final lap, whether
this tag was already recorded, whether the result is valid, etc.
The second source of data is the ordered list of start numbers
given by the referee on the finish line. As referees cannot
know all the data about each number (category, lap number,
start time), the RFID system cannot provide accurate data for
the finish line for various reasons. Therefore RFID data must
be verified to follow the referee list.
TABLE II
STATISTICS
discipline events readings added swapped
MTB 17 3528 22 (0.62%) 130 (3.68%)
Run 19 4656 27 (0.58%) 492 (10.57%)
CX/ROAD 10 812 13 (1.6%) 5 (0.62%)
OCR/SKI 16 3003 6 (0.2%) 1 (0.03%)
In Tab. II is an overview of processed data collected by
Sportchallenge system.
• Discipline defines the hardware layout specified in Fig.
3.
• The column called Events stands for the number of events
collected using this layout.
• The column called Readings is the number of readings
on the finish line. Each tag is classified in statistics only
once (on the finish line), even if the race setting provides
more than one lap (more going through the finish gate).
It prevents multiple errors for one malfunction tag or the
fact that only final laps are verified.
• The column called Added is the number of tags missed
by the RFID system.
• The column called Swapped is the number of tags that
were read in reverse order by the referee. It affects two
numbers but they were considered as one malfunction.
Tables III to VI show detailed statistics of swapping the
racers position according to verification with the referee’s list.
• The column called Diff means the rounded difference in
seconds between two items that were read.
• The column called Readings means the total amount of
processed results with indicated time difference.
• The column called Swapped means amount of one-to-
one replacements that had to be done in indicated time
difference.
• The column called Correct means percentage of how the
system was successful in position estimation.
Data in tables and chart were obtained in the season 2018
and half of the 2019 season by authors. The reason why older
events weren’t included is there wasn’t any rule given to store
the recorded data.
A. MTB
As shown in Tab. II MTB layout is quite powerful in reading
probability and compared to RUN layout it has fewer needs to
TABLE III
STATISTICS OF MTB IN DETAIL
diff [s] readings swapped correct
0 217 56 74.19%
1 305 47 84.59%
2 204 19 90.69%
3 164 7 95.73%
4 134 2 98.51%
5 110 0 100%
6 105 1 99.05%
7 82 1 98.78%
8 76 0 100%
9 71 0 100%
swap. This is given by the speed the racers pass the finish gate
so they spend only a short time in the gate. Tab. III shows in
detail that time difference is recognized quite well even though
there are some exceptions which are mostly cased by races of
children when these small racers usually pass the finish line
very slowly and seldom stops in the finish area.
B. RUN
TABLE IV
STATISTICS OF RUN IN DETAIL
diff [s] readings swapped correct
0 541 177 67.28%
1 725 154 78.76%
2 503 91 81.91%
3 389 39 89.97%
4 305 20 93.44%
5 229 6 97.38%
6 158 7 95.57%
7 151 1 99.34%
8 140 0 100%
9 94 0 100%
According to Tab. II RUN layout has almost the same read
probability as MTB but it has the worst statistics in accuracy.
Also, Tab. IV shows many swaps in further distances. This
is given by the speed, runners pass the finish line and also
sudden changes within a few meters before the finish line are
common. Small children races have a much bigger impact on
bad statistics compared to other layouts.
Eventually, special running layouts are being tested. Tab. V
shows 2 unique tests in comparison with the common RUN
layout.
TABLE V
SPECIAL TESTS WITH RUNNERS
layout events readings added swapped
Run 19 4656 27 (0.58%) 492 (10.57%)
Run no spacer 1 248 8 (3.23%) 17 (6.85%)
Run 90◦ 1 294 6 (2.04%) 24 (8.16%)
The first one (called “no spacer”) was the test with RUN
layout without spacer on the back side of start number (no
isolation between tag and runners wear). Results of this test
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has shown how big the impact of spacers is and it has proved
it’s benefits. In the second one (“90◦”) antennas radiation
angle was changed so they radiated from above down to the
ground. This solution was supposed to make the reading border
sharper although overlapping by participant’s head would have
a significant impact. This again is possible to solve by added
secondary RFID gate which would make the system more time
demanding to assemble and disassemble. Anyway this isolated
test was burdened by use of returnable start bib set which was
in use for the fourth season in the time of the event. This bib
set is used in low-cost events constantly and it shows signs of
wear.
C. CX/ROAD
TABLE VI
STATISTICS OF CX/ROAD IN DETAIL
diff [s] readings swapped correct
0 26 3 88.46%
1 45 0 100%
2 27 0 100%
3 34 0 100%
4 30 0 100%
5 27 0 100%
6 23 0 100%
7 17 0 100%
8 18 0 100%
9 27 0 100%
Tab. VI shows excellent results for this layout. This statistics
is worsen by the use of reversible start bibs that are used in
the only real road race in the season. As these bibs are used
for several times they might suffer from degradation and their
read probability is getting worse.
Speed and density (overlap) make it harder to read in road
races as well.
D. OCR/SKI
TABLE VII
STATISTICS OF OCR/SKI IN DETAIL
diff [s] readings swapped correct
0 119 2 98.32%
1 190 0 100%
2 116 0 100%
3 95 0 100%
4 49 0 100%
5 71 0 100%
6 47 0 100%
7 49 0 100%
8 41 0 100%
9 47 0 100%
Although this layout states the best statistical results (Tab.
VII) the method doesn’t seem to be the best for obstacle
races. Especially in difficult conditions, many racers lost their
numbers. For statistic purposes the lost numbers were not
given into consideration as it has nothing to do with RFID
reading. Statistical results of this layout used for timing of ski
events showed only a positive impact without problems with
losing start numbers.
Fig. 4. Statistics of different sports.
Finally Fig. 4 shows all data from Tables III to VI. Discrete
time difference points are interleaved by a polynomial to show
the trend.
IV. CONCLUSION
A UHF RFID system with passive tags is an effective and
easy system for sports timing. The limits of the system such as
high speed (cyclists), overlaps, etc. were processed statistically
and data has been shown in the text above. According to
the statistics, the biggest problem seems to be reading from
the racer’s chest (RUN layout) because the better the tag
responds the faster the racer seems. To solve this problem
it is possible to take all read values (including RSSI) into
account when evaluating each number’s result. This may lead
to using hundreds of records for one simple line passing. In
case of a crowded finish line, this causes extraordinary data
traffic with most of the data being redundant. The solution (in
perspective) would be a processing of the RFID data inside
the RFID reader with a custom filter. This filter would return
only the record when the item starts to lower it’s RSSI. Such
an algorithm provided on data transferred by the reader to the
server didn’t show much improvement yet.
ACKNOWLEDGMENT
This publication was supported by the institutional support
of The Faculty of Mechatronics, Informatics and Interdisci-
plinary Studies, Technical University of Liberec.
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