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Real-time Locating Service. Japanese security
company Secom has commercialized a real-time
locating service to deal with social problems such
as kid napping, theft of cars and motorcycles,
wandering aged people, and so on. The service
utilizes a GPS terminal connected to a server
through cell phone networks. The user can locate
wandering people with the terminal through the
Internet. This service works only online.
Table 1 shows a comparison of GPS applications
for walkers. There are differences on how the digital
maps are stored on terminals, who are the target users,
and the quality of the communication environment.
Handy GPS’s are developed for users who enjoy
outdoor activities like mountain climbing, trekking,
and so on and are supposed to be used offline. The
digital maps have been installed manually in advance.
Handy GPS’s are stand alone systems that do not need
communication to the servers.
On the other hand, Walking Navigation Systems
suppose good communication environment and al-
ways work online. They are normally connected to
the servers, and they can download the digital maps
in need at any time.
The target users of Real-time Locating Service are
not ones who have the GPS terminal but the ones who
search for the one with the GPS terminal. The GPS
terminal does not have a display to show digital maps.
The system works in the good communication envi-
ronment because communication links between ter-
minals and servers should be stable to know the loca-
tion of the terminals.
The conventional systems mentioned above are
not suitable in PCEDHandy GPS’s caninform the cur-
rent location to the climber but they cannot inform it
to the rescue party when the climber gets lost. Walk-
ing Navigation Systems and Real-time Locating Ser-
vice suppose the good communication environment
and they cannot work properly in the PCE like the
mountain areas. We propose a new walking naviga-
tion system that navigates the user as a stand alone
system even when the Internet access is unavailable
and sends walking records to the server, when the In-
ternet access is available, to inform the location of the
climber to the rescue party in need.
It is difficult to estimate the location of the climber
when the Internet access is unavailable for a long
time. As a remedy, we utilize opportunistic commu-
nication based on the P2P access between the termi-
nals. When a terminal encounters another, they ex-
change the walking records with each other. When
the terminal reaches an area where the Internet access
is available, it sends not only the walking record of
the terminal but also ones of the other terminals that
it has encountered. This leads to a better location es-
timation of the climbers.
3 TREKKING NAVIGATION
SYSTEM IN PCE
We are developing a new trekking navigation system
that works on a smartphone. It works without the In-
ternet access in PCE like the mountain area, because
digital maps have been installed in it. It measures
the latitude, the longitude, and the altitude of the cur-
rent location in a constant interval by using GPS and
displays the current location on the digital map. It
also measures the signal strength of mobile phone net-
works.
The terminal records the walking trajectory and
sends it to the server when the Internet access is avail-
able. It exchanges the record with the other terminal
through Bluetooth when it encounters the other ter-
minals. When the climber with the terminal gets lost,
the rescue party gets access to the server to estimate
the location of the climber referring to the walking
record.
We performed a simulation experiment to show
how opportunistic communication improve the trace-
ability of climbers. We model walking routes as a grid
world shown in Figure 3. Climbers repeat to walk
between S and G at a constant speed. It takes 200
steps to go to G and to return to S. When a climber
reaches a branch, he/she takes a route closer to the
destination. If there is a tie between two routes, he/she
chooses one at random. We record the history of en-
counters among climbers and calculate the traceabil-
ity of climbers depending on the number of climbers
in the area. Figure 4 shows a result of the simula-
tion. X-axis shows the location on route and Y-axis
shows the estimation of the location. Climbers start
from S(0%), go to G(50%), and return to S(100%).
“Ideal” means the estimation when the Internet access
is always available, and it is correct at every location
on the route. When we assume the Internet access is
available only at S, the estimation becomes incorrect
except at S. The difference becomes large when the
number of climbers is few.
4 SUMMARY AND FUTURE
WORK
We proposed a new trekking navigation system that
works even in the poor communication environment
where communication links are frequently disrupted.
TrekkingNavigationSystemusingOpportunisticCommunication
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