Vol.10 No.1, 2008

Original Paper

Proposal of Pedestrian-Oriented Wearable GPS with the New
Scalable Capability of Instantaneous Azimuth Limitation
Masato TAKAHASHI∗1 ∗2 , Susumu TACHI∗1
Abstract– A pedestrian would find it difficult to steadily acquire his bearings justusing a Global Positioning System (GPS). This paper proposes a novel practical method
for acquiring azimuth instantaneously with a new wearable GPS user segment that works
even when the user is stationary. This is suitable for timely decision making out-of-doors.
Possible systems are also proposed using this method. The device using this method canwork both by itself and in combination; when multiple devices are connected, the azimuth
limitation capability is improved. Improvements due to scalability are quantitatively confirmed with computer simulation.

Keywords : Global Positioning System, Azimuth, Elevation, Orientation, Guiding

2.
1.

Introduction

Conventional Approaches

user’s stationary or rotating status, rather than only
in walking status (3) azimuth information should be

Historically, GPS was designed as a maritime orairborne vehicle navigation system at the initial
phase [2 ] . Therefore it is quite natural that the required accuracy is at a level suitable for marine or
air vehicles. Such vehicles have room to install otherequipment to compensate for deficits of GPS azimuth
information.
However, GPS is now being used by pedestrians.
As its conventional user segment for vehicles is simply appropriated for pedestrians who want azimuth
information, this has led to usability problems. Unlike the maritime or airborne vehicles, pedestrians
have the following special characteristics.
(1) Pedestrians are small, less than one-tenth ofthe location accuracy (2) They carry out frequentrotations around the vertical body axis (3) They cannot afford to have heavy or large equipment and find
it difficult to give heed to repetitive calibrations (4)They sometimes walk in areas full of artificial andprovided in the form of a sector of about 30 degrees
with certainty, rather than a single value with lim-

geological magnetism.
Due to (1), “GPS differentiation by setting two

itless uncertainty (4) this azimuth acquisition functionality should have scalability. These design con-

GPS units at a sufficient distance” is denied. Thismethod was suitable for ships or airplanes.

cepts are based one of the author’s experience of
mountaineering. (5) it should be wearable and hands

Due to (2), “GPS location differentiation by trial
walking” is denied. This method is very effective forfree use. Based on the above considerations, we propose a new portable GPS unit, with instantaneousvehicles that do not rotate around their vertical axes.
However, a pedestrian may turn around the axis of

azimuth limitation ability and scalability.

the body, which invalidates azimuth by this method.
Due to (3), “rate gyro” [3 ] and “GPS carrier wave

*1：The University of Tokyo*2：The National Institute of Information and Communications Technology

detection” are denied. Rate gyro requires frequentcalibration. “GPS carrier wave detection” is ex-

Generally speaking, low usability is responsible forthe discrepancy between the contexts of use conceived of by the user and the designer [1 ] . In otherwords, human-centric design is not carried out. From
this viewpoint, the low usability is discussed regarding current portable GPS units for pedestrians. The
fundamental framework of the GPS user segment was
initially designed for maritime and airborne vehicles.
It would inevitably score low usability if it were simply used for pedestrians
To improve the low usability, we propose new requirements that reflect the context of use of a GPSunit for pedestrians as follows; (1) the same device
should be able to provide azimuth information andlocation, rather than requiring multiple equipment(2) azimuth information should be given even in theThe Transactions of Human Interface Society Vol.10, No.1, 2008

tremely expensive.
Due to (4), “geomagnetism compass” is denied [3 ] .
A pedestrian’s environment is not free from artificial or geological magnetisms, which are practically
unpredictable, being entirely different from the situation on the ocean or in the air. A geomagnetic
compass may easily become unreliable in such anenvironment and should not be used when a critical decision must be made.
We have to make an invention of a device whichkeeps its usability even in the environment for pedestrians.
3.

Human-Centric Design Process

ISO 13407 ”Human-centered design processes forinteractive systems” [4 ] defines the steps as follows:(1) understand and specify the context of use. (2)specify the user and organizational requirements. (3)produce designs and prototypes. (4) carry out userbased assessment.
First, we attempted to understand and specify thecontext of use. It includes a pedestrian’s or party’s
acquiring reliable information on both the positionand orientation quickly even when motionless in order to support timely decision making in critical situations such as on a mountain in bad weather conditions.
In the context of use, the most important requirements are considered to be as follows; (1) Azimuth and location information are simultaneously
provided by the same low-cost device. (2) The acquisition requires no task such as user’s walking, which
may raise some risks including falling off a mountainridge in bad weather conditions. (3) The azimuth

After that, we carried out semi user-based assessment on the performance of the proposed design bysimulations.
4.

GPS: Global Positioning System

GPS (Global Positioning System) consists ofspace, management and user segments. [2 ] ．The
space segment of GPS includes the GPS satellites
that fly in circular orbits at an altitude of 20,200
km and with a period of 12 hours. The orbits aretilted to the Earth’s equator by 55 degrees to ensure coverage of the Polar Regions. Each of the 24
satellites, positioned in 6 orbital planes, circles the
Earth twice a day. These orbital planes are illustrated in Figure 1. As of September 2007, there are
31 actively broadcasting satellites in the GPS constellation. Additional satellites improve the precision of the GPS receiver calculations by providing
redundant measurements.

Fig. 1 GPS satellites orbits

The exterior of a GPS satellite has a variety ofantennas. The signals generated by the radio transmitter are sent to GPS receivers via L-band anten-

information has to be suitable for timely decision
making. The azimuth information should be pre-nas. Another component is the radio transmitter,
which generates the signal. Each of the 24 satellites

sented not in a single value but in sector form. (4)The acquisition should be carried out both by a sin-transmits its own unique code in the signal.
The Control Segment of GPS consists of the Mas-

gle device alone and by multiple devices connected,
for individual and group (party) uses respectively.

ter Control Station, Six Monitor Stations. The master control station is responsible for overall man-(5) The device should be wearable for hands-free use
in bad weather conditions. In addition, it should beagement of the remote monitoring and transmission
sites. Each of the monitor stations checks the exact

light-weight and low profile.
Based on these requirements, the new design wasaltitude, position, speed, and overall health of the orbiting satellites. The control segment uses the mea-

produced. In the process, many inventions weremade and registered for patents in the United States,

surements collected by the monitor stations to predict the behavior of each satellite’s orbit and clock.

Great Britain, Australia, Germany, and France aswell as in Japan.

Noted variations, such as those caused by the gravityof the Moon, Sun and the pressure of solar radiation,

Proposal of Pedestrian-Oriented Wearable GPS with the New Scalable Capability of Instantaneous Azimuth Limitation

are passed along to the master control station.
At the position calculation phase, 4 times and locations (x1 , y1 , z1 ), (x2 , y2 , z2 ), (x3 , y3 , z3 ), (x4 , y4 , z4 )at 4 navigational messages from 4 satellites and light
speed c are used known values, to build as 4 elements simultaneous equations. 4 unknown values are
the current position and time of the user (x, y, z), t.
Solving the 4 elements simultaneous equations, thecurrent position of the user and the time can be specified.
p(t − t1 )c = (x − x1 )2 + (y − y1 )2 + (z − z1 )2p(t − t2 )c = (x − x2 )2 + (y − y2 )2 + (z − z2 )2p(t − t3 )c = (x − x3 )2 + (y − y3 )2 + (z − z3 )2p(t − t4 )c = (x − x4 )2 + (y − y4 )2 + (z − z4 )2

Fig. 2 Configuration of the antennas and thesky hemisphere

The principle of the azimuth limitation of thepresent invention is explained with reference to Figure 2. Near the middle of Figure 2 are disposed afirst planar patch antenna 1a and a second planar
patch antenna 1b. The first planar patch antenna
1a and second planar patch antenna 1b are disposed
back-to-back and parallel with each other. Both antennas are perpendicular to the ground. The direction in which an observer faces when standing on thepatch antenna 1a or the second planar patch antenna1b) extends coincides with half of the sky divided in
two by a great circle 7, as shown in Figure 2. This
great circle 7 forms the boundary between the coverage area 6a of the first planar patch antenna 1aand the coverage area 6b of the second planar patch
antenna 1b. In other words, the coverage area 6a of
the first planar patch antenna 1a is the sky quartersphere in which the GPS satellite A is present andthe coverage area 6b of the second planar patch antenna 1b is the sky quarter-sphere in which the GPS
satellite B is present.
The signal of standard positioning services transmitted by a GPS satellite has a microwave band frequency of 1575.42 MHz and, therefore, exhibits excellent linear propagation property like light. Whenobserved by the first planar patch antenna 1a, a distinct difference arises between the receiving status
for the signal from the GPS satellite A in the coverage area 6a and the receiving status for the signal
from the GPS satellite B not in the coverage area 6a.

ground and looking down on the antennas arranged
with the first planar patch antenna 1a on the left andAs shown in Figure 3, the first planar patch antenna 1a is connected to the first GPS receiver 2athe second planar patch antenna 1b on the right isdefined as measurement direction 5.

and the second planar patch antenna 1b is connectedto the second GPS receiver 2b.

The first and second patch antennas 1a, 1b are provided with hemispherical beam patterns with respect

Considering Figure 2 and Figure 3 together, thesignal from the GPS satellite C in Figure 2 can beto the Right Hand Circularly Polarized (RHCP) Lband signal known as L1 at 1575.42 MHz used byreceived by the first GPS receiver 2a and the second
GPS receiver 2b in Figure 3.

the standard positioning service of the GPS satellite
system.

In the present invention, when signals are received
simultaneously by both GPS receivers in this man-

When two such planar patch antennas are disposed
back-to-back in parallel with both standing perpen-

ner, it becomes possible to discriminate the directionof the GPS satellite C as the measurement direction

dicular to the ground, the coverage area to which
the antenna sensitivity of each (i.e., the first planar

5 or as the direction opposite the measurement direction, and, by using the satellite azimuth of GPS

Besides the current position and the time, all satellite azimuths are acquired. This is because the almanac data can be extracted from any one navigational message. Thus，at the same time as the position calculation, all the satellite azimuths are to be
known. This is exploited by the proposed GPS unit
for pedestrians in this paper.
5.

New Proposed GPS Unit to Provide
Both Azimuth and Location

The Transactions of Human Interface Society Vol.10, No.1, 2008

satellite C and the aforesaid satellite azimuth information of the GPS satellite A or the GPS satellite
B and the result of the area discrimination, to determine the azimuth of the measurement direction
5.

Fig. 3 Block diagram of the azimuth acquisition device

solid angle shape comes out somewhat broader thandesired, the antenna can still be used as it is. In thiscase, the great circle in Figure 2 is not a line but is aband of small width (small visual angle as seen by anobserver). The slight spread imparts a small width
to the measurement direction 5 and the direction opposite the measurement direction and increases theprobability of catching a satellite with these directions by chance, which enables azimuth determination immediately fortuitously even when intending
azimuth limitation.
The first GPS receiver 2a and second GPS receiver
2b shown in Figure 3 can have the same functionalfeatures and specifications as the GPS receivers included in widely-used compact mobile positioning
devices employing L1 signals. This makes it possible
to take advantage of technologies developed for the
production of small, lightweight civilian GPS positioning devices, most notably size reduction and easeof volume production. Thanks to the size and weight
reduction achieved in civilian GPS positioning devices, GPS receivers are abundantly available in sizes
commensurate with planar patch antennas. They arealso easy to manufacture. Moreover, these GPS receivers have planar patch antennas formed integrallywith the receiver case, and inexpensive palm-sizedmodels are already available.

The easiest way to create hemispherical beam pattern planar patch antenna is to block the extra sensitivity of a planar patch antenna having a wider
beam pattern than the hemisphere using shield material. In the actual fabrication of a planar patch
antenna, the completed antenna may have a solid
angle slightly broader than the hemisphere of thewidth theoretically calculated at the time of design.
This occurs because the result of the design assuming
an infinite ground plate in the theoretical calculationdiffers from the actual situation [5 ] . A typical GPS
antenna beam pattern of the plane patch antenna is
illustrated for example in [6 ] . Using electro-magnetic
wave absorption and shield sheet in the back of theantenna, the hemispherical antenna pattern is eas-

Fig. 4 Satellites and the antennas in azimuth
limitation

ily created [7 ] . The technique for correcting such
beam shape deviation by slightly modifying the sub-

The first GPS receiver 2a attempts to synchro-strate size, patch size or the like to obtain the desired
antenna pattern is known as antenna pattern shap-

nize with and decode satellite signals through thefirst planar patch antenna 1a and to determine theing [5 ] .
In this invention, however, even when a beam of

position. Similarly, the second GPS receiver 2b attempts to synchronize with and decode satellite sig-

Proposal of Pedestrian-Oriented Wearable GPS with the New Scalable Capability of Instantaneous Azimuth Limitation

nals through the second planar patch antenna 1b andto determine the position. In other words, the firstGPS receiver 2a and the second GPS receiver 2b conduct a search for the signals from all GPS satellites
expected to be present in the sky, just as does the
GPS receiver of an ordinary mobile satellite positioning device, in exactly the same way as if connectedwith antennas whose coverage areas are the sky hemisphere.
The only difference at this point, between the GPS
receivers in an embodiment of the device for acquiring azimuth information according to this invention
and the GPS receiver of an ordinary mobile satellite
positioning device, is the fact that the GPS receiver
1a cannot synchronize with the signals from GPS
satellites not being in the coverage area in the sky
6a and the GPS receiver 1b cannot synchronize withthe signals from GPS satellites not being in the coverage area in the sky 6b while the GPS receiver ofan ordinary mobile satellite positioning device placed
horizontally can synchronize with the signals from all
GPS satellite in the sky.

Fig. 5 An example of the data table in azimuth limitation

other GPS satellite. Equipment that outputs suchinformation already exists.
Although all GPS satellites transmit signals at exactly the same frequency, owing to the utilization ofa technology called the spread spectrum communication system made possible by Pseudo Random Noise
coding, signal interference does not occur even whenusing the same frequency. Each GPS satellite is assigned a unique Pseudo Random Noise code, which
is a different digital signal sequence wherein 0 and
1 appear to alternate irregularly. This enables thesignals from the satellites to be distinguished andseparately received. In other words, the principle of
Pseudo Random Noise coding makes it easy to discriminate the signal from each GPS satellite present
at an angle of elevation of greater than 0 degrees asviewed from the current location.
Figure 4 is an example of satellite constellation
where the azimuth limitation function is available.
Figure 5 is an example of the data table that theazimuth limitation module creates from the received
signals. Figure 6 is an example of the azimuth extraction from Figure 5.

Fig. 6 An example of the azimuth extraction
from the data table in azimuth limitation

The signal transmitted from every GPS satellite
contains information on the orbits of all GPS satellites (almanac data). Every satellite transmits thisThe configuration of the 2 planer patch antenna
has already been discussed. However, a single an-data. Therefore, in the case of a satellite present in
the sky at an angle of elevation of greater than 0

tenna type device is also configurable. Takahashi [8 ]discuss it in detail. The configuration illustrated indegrees viewed from the current location but whose
signal is blocked by a building or the topography, orFigure 7 illustrates the concept. In this case, one
antenna is both location device and azimuth device;of a satellite not in the antenna coverage area whose
signal is not synchronized with, i.e., in the case of ain the latter case, the single unit serves as if there
were two units.

GPS satellite in a state preventing reception of its
radio wave, the angle of elevation and azimuth of
the satellite concerned can be computed and output
by a simple calculation from data received from an-

6.

Usability Discussion

In the previous section, a new GPS user segmentthat provides both location and azimuth is proposed

The Transactions of Human Interface Society Vol.10, No.1, 2008

Figure 8 and 9 show that the expected value of
azimuth limitation depends on the time, i.e. thesatellite constellation. This proposed system takes
full advantage of the plurality of GPS satellites. The
transformation of latent capability in the existing infrastructure to a new form close to the new user context is a usability improvement.

Fig. 8 Azimuth limitation width dependency
on GPS constellation (Single unit)
Fig. 7 Proposed GPS unit deployment on ahelmet or cap (Single antenna unit
type)

in a cost-effective fashion. When placed horizontal
as usual, it works as a standard GPS user segment.
When placed vertical, it works as a completely new
GPS user segment with azimuth limitation ability.
In this section, usability is discussed in more detail.
6. 1

Basic and Simple Functions: Azimuthand Location Only

As seen so far, this proposed device has double
functionality both of location and azimuth. None of
the conventional low-cost devices are able to achieve
this feature alone. (The carrier wave detection
method of GPS can achieve this, but it is extremely
expensive and is a combination of GPS units itself.)
6. 2

Quickness to Find Azimuth with No
Task

Fig. 9 Azimuth limitation width dependency
on GPS constellation (Double units
parallel deployment)

6. 3

This proposed device can immediately provide azimuth information on its power-on. The user is not

Azimuth Provision in Sector Form
Suitable for Critical Decisions
The conventional low-cost azimuth presentation
method is subject to erroneous features; a geomag-

required to walk or to suppress turning around the
body axis. This proposed method is superior to the

netism compass is subject to other magnetisms, rategyro is subject to errors accompanied with rate de-conventional GPS location differentiation method inthis point.

tection accumulation. The range is indicated by two
azimuths. These azimuths are quite certain as en-Proposal of Pedestrian-Oriented Wearable GPS with the New Scalable Capability of Instantaneous Azimuth Limitation

dorsed by a high self-correlation feature at synchronization and matching between original and replica
1024 C/A chip code. The true azimuth value is always between the two in a clockwise manner. This
capability is specific to the proposed device.
6. 4

Azimuth Acquisition by Units with
Scalability

The explanation is based on the configuration of
back-to-back 2 GPS units and a single GPS unit described so far. However, any number of GPS units
work when placed at the sides of a polygon. Figure 10 shows examples of how such GPS units canbe placed on the sides of regular polygons; triangles, squares, pentagons, hexagons, heptagons andoctagons. For multiple units to function together, it
is sufficient that an angle detector of the adjacentunit is provided.
Figure 11 shows the simulation results of the expected azimuth limitation width. The date and timeis selected at 24 timings, 1 hour interval, from 0:00 to
23:00 of February 20th, 2000. 10,000 trials at 24 discrete timings were carried out. In total, 240,000 data
were obtained to draw a point on the graph. The
location selected was Hibiya Park, Chiyoda-ward,
Tokyo.
Using a normal GPS unit, a user cannot detect any
azimuth information without walking, which is associated with high cost and risk. However, according
to the graph, if a user has even one GPS unit, he/she
can immediately acquire azimuth information about
60 degrees. If a mountaineering party has two GPS
units, they can immediately acquire azimuth information about 30 degrees. With more of the proposed

Fig. 11 GPS scalability: azimuth limitation
width and number of proposed GPSunits

GPS units, a narrower (better) azimuth limitation
width is acquired.
For practical purposes, two or three units might
be sufficient to acquire meaningful results outdoors.
Interestingly, even with only one proposed GPS unit,
it can be used as if it were two, as shown in Figure
7. It is important for portable devices for use in outdoor activities to be light weight and small volume;
scalability is also preferable and contributes to highusability.
A computer simulation was conducted to determine what level of azimuth limitation values can beacquired in the case of on-the-spot azimuth limitation using the device for acquiring azimuth information in an embodiment of the method for acquiring
azimuth information of the present invention. The
results are as follows.
The computer simulation was conducted using
real-time GPS satellite orbital parameters of actuallyoperating GPS satellites on February 17, 2000 in thesky over the center (latitude N35 40’ 14.9”, longitude
E139 45’ 33.4”) of Hibiya Park in Tokyo (located ina middle latitude area in the northern hemisphere).
Evaluation was conducted with respect to fixed time
points between midnight (0) and 23 (0, 1, 2, ... 22,

Fig. 10 Alignment Example of Multiple use
by proposed GPS unit(s)23) o’clock, i.e. with respect to 24 separate fixed
time points spaced at regular time intervals. The

The Transactions of Human Interface Society Vol.10, No.1, 2008

evaluation was conducted at different time points inorder to accurately reflect the fact that the numberof available satellites and the satellite constellationin the sky hemisphere vary depending on the time ofday.
In order to obtain realistic results, the angle of elevation region of 5 degrees and lower, which is affectedby ground feature signal blocking, was defined as being unavailable, and control was effected to exclude
high elevation satellites (85 degrees and higher satellites) from azimuth computation due to the possibility of such high elevation satellites contaminating theazimuth limitation result by the possible existenceof the unit’s slant in real use of context. Figure 11
can be interpreted as the expected azimuth limitation width at one of the least obstacle environmentsof sufficient reality.
The spread spectrum communication method is resistant to affects of multipath or fading effects bynature, compared to other communication methods
such as time division multiple access for the following two reasons; (1) When a long delay multipath isconsidered where the delay time is longer than thechip width (about 300 meters or 1 micro second at
C/A code), the self-correlation function of Gold code
invalidates its effect [9 ] . (2) When a short delay multipath is considered where the delay time is shorter
than the chip width, the multipath effect on the azimuth is so small (about 10−3 ) that it is negligible.
Assuming the multipath whose amplitude is weakened by 12 dB compared to the direct wave, thelength measurement error would be about 35 meters [10 ] or 4 meters [11 ] when a correlator width of
1.0 or 0.1 is taken advantage of respectively. The
effects on the azimuth limitation affected by theselength measurement errors are to be found 2.0×10−3
or 1.6 × 10−3 degrees at most respectively, and are
negligible [12 ] .
The arbitrary (random) setting of the measurement direction 5 in actual use was emulated by making random numbers (0-359) to select the measurement direction 5 on every trial in the whole simulation.
One-hundred-thousand random trials were conducted at each time point to enhance the evaluation
results and enable consistent assessment.
As 100,000 random simulations were conducted ateach of the 24 time points, the total number of trials

was 2,400,000.
A maximum of 12 directions at intervals of 30 degrees are commonly used in human daily activities:
north, north-northeast, east-northeast, east, eastsoutheast, south-southeast, south, south-southwest,
west-southwest, west, west-northwest and northnorthwest. The method of this invention enables
azimuth limitation of this level even by random measurement with no rotation. This demonstrates thatthe invention provides a simple azimuth informationacquisition method with great practical utility.
The number of available GPS satellites in the skyhemisphere viewed from a middle latitude area isusually as many as 9 to 12. This largeness of thenumber of available satellites in the sky hemisphereis believed to be the main factor for the high efficiency of the device for acquiring azimuth information, which is an embodiment of the method for acquiring azimuth information of the present invention.
In the proposed framework, the greater the numberof synchronized satellite signals, the narrower the azimuth limitation width. It, however, is notable that,even when only 6 to 8 satellite signals can be received
on a forested mountain, the azimuth limitation ability still remains. If a simple situation is considered
where signals from only 6 satellites evenly scatteredin the sky hemisphere are available, the expected azimuth limitation width is to be 60 degrees or the
like. This kind of simple thought experiment makes
clear the potential validity of the proposed methodin the variety of different situations that pedestrians
encounter outdoors.
6. 5

Fitness to Wear with Minimized Load

The exemplified configuration, i.e., the headband
configuration, can be embodied in various similar
configurations, such as headphone-like (illustrated in
Figure 12) and hat-like configurations, having thefollowing advantages: (1) The measurement direction 5 of the device always coincides with the direction in which the user faces, which is very convenient
because it provides the user with a direct operation
to point the measurement direction to the orientation in which the user is interested and an intuitive
understanding of how to utilize the numerical values representing the result of the acquired azimuth
information. (2) Wearing the device for acquiring
azimuth information on the head maximizes the vertical projection distance between it and the groundProposal of Pedestrian-Oriented Wearable GPS with the New Scalable Capability of Instantaneous Azimuth Limitation

and, as such, minimizes the effect of signal blockage by ground and topographical features. (3) The
user is likely to feel at ease about the appearanceof the device when worn because wearing of headbands, other ornaments, headphones, earmuffs andother functional devices on the head is commonplace.

Such ideas are expected to make GPS user segments more familiar to pedestrians, including mountaineers, and to contribute to making pedestrians’
outdoor activities safer and more secure. A prototype is currently being developed, the details of
which are to be reported as well in the future.
7.

Conclusion

In this paper, we discuss the low usability of conventional azimuth acquisition devices, especially theFig. 12 An example of the wearable application on the head (Double unit type)(4) The user is likely to feel at ease about how heor she looks when turning in order to carry out azimuth determination because the action can be performed naturally in the manner of looking at something in the distance without any specific behavior
that would appear strange to other people in daily
life situations . This is an important point for visionimpaired persons in using this device.

GPS differentiation method for pedestrians.
We made a new design step-by-step according to
ISO 13407 in 1999, Human-centered design processes
for interactive systems. As a result, the most important requirements are considered to be as follows;(1) Functionalities should be limited to basic andsimple ones. (2) Important information should beacquired quickly, with no task required (3) The important information should be useful for user’s timely
decision making. In order to be so, the information
should be presented not in a single value, which theuser cannot easily tell how far the true value possibly
locates, but in sector form, which the user can haveconfidence to make a decision based on the fact thatat least it is true as a sector. (4) Outdoors, scalability is desirable so that both group activities andindividual activities can be supported by the samedevices. (5) It should be wearable for hands-free use
There are many studies on interaction systems forindoor use. However, there are few studies on systems for outdoor use. This study is an importantcase study of an electric device for outdoor use, including a significant new invention, which is registered for patent in many countries.
We carried out a semi user-based assessment on
the performance of the proposed design by simulations. Firstly, we made it clear that the average valueof azimuth limitation width is about 34 degrees, forthe back-to-back 2 unit configuration. Secondly, we
found that the average value varies from about 22

Fig. 13 Example of the wearable applicationon the body (Double unit type)

degrees to 58 degrees, depending not on the numberof trials but on the GPS satellites constellation at thetime. Finally, we quantitatively evaluated the scalability of the proposed method. Even a single unit

It is also possible to attach the planar patch antennas on the outer sides of the shoulders or limbs as

can ease a situation of orientation loss as it can easily
limit an orientation up to about 60 degrees on aver-illustrated in Figure 13 as well as on the chest andback in parallel, back-to-back orientation.

age. With only two or three units, the averages ofazimuth limitation widths are dramatically improved