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					              A Comparison of Direct and Indirect URI Sensing Technologies
                  for use in Context-Aware Mobile Service Applications

                                               Michael J. Cavallari

Abstract                                                         series of pieces throughout an exhibit. These bookmarks
                                                                 can then be used to gain further information about each
Context-aware computing in mobile devices is considered          piece and may even provide assistance in the museum gift
at present to be an emerging technology. The use of              shop. Such information could truly enhance visitors’
semantic location could revolutionize the way people             experiences at museums and have the potential to provide
interact with mobile devices by providing a much greater         similar benefits to a wide variety of both public and
personalized and customized response to everyday                 commercial installations.
situations (driving directions/maps, assistance with
train/bus schedules, aid to shoppers in a grocery store).        A computing environment that enables users to interact
Direct sensing (active) and indirect sensing (passive) are       with semantic locations is often referred to as a context-
the main approaches to provide mobile devices with               aware system. Another example of the use of semantic
context or location sensitive information. This paper            location involves a shopper using a Personal Digital
contains in-depth analysis comparing direct and indirect         Assistant (PDA) in a bookstore. Upon seeing a book of
URI discovery via mobile devices equipped with sensors by        interest the shopper is able to sense the uniform resource
identifying the benefits and cost of the hardware and            identifier (URI) associated with the item and then a book
technologies available to implement such a solution. The         review appears on the shoppers PDA screen. Palm Pilots,
results demonstrate direct URI discovery to be the overall       Windows CE devices and other mobile devices are a few
superior technology.                                             of the types of hardware that can interact with context-
                                                                 aware environments. The labels or URIs in a context-
Keywords                                                         aware environment can interact with the user directly or
                                                                 indirectly. Direct sensing URIs actively push the
Context-aware computing, semantic location, location             information to the users where as indirect sensing is
awareness, ubiquitous computing                                  passive and requires user activation. Although the
                                                                 information received from a URI can vary, the object is to
1. Introduction                                                  acquire a label in a manner that software running on a
                                                                 mobile device can display information particular to that
The number of mobile computing devices continues to              semantic location.
grow each year [14]. These wireless devices are offering
progressively more types of services to users at growing         2. Setting the Scene / Background
numbers of office, retail, education, and even residential
locations. A recent technological advancement with mobile        A context-aware computing environment consists of three
phones has been the integration of Global Positioning            main components: a mobile device in the hands of an end
Systems (GPS) capabilities to determine the physical             user, a label (URI storage) installed in a physical location,
location of the individual using the device. Enhanced ‘911’      and a communication protocol to transmit the URI. Each
emergency coverage is an example of how physical                 mobile device is equipped with different types of sensors
location has improved services for mobile device users. In       that allow it to communicate with a URI storage location
addition to physical location information, mobile devices        over a given communication protocol. In order to process a
can now take advantage of geographical location                  URI, the mobile device must have context-aware software
information to provide a richer set of user services.            that enables the device to decode and interpret the URI.
Geographical location implies much more than just the            URI storage components can be divided into two types
physical latitude and longitude provided by GPS. It can          active (direct) and passive (indirect). Direct URI sensing
include additional semantic information, such as the ability     technologies utilize active URI storage devices that
to determine that the user is located on a bus, which could      transmit or “push” a URI over some communication
then be used to supply the estimated time of arrival to the      protocol. Using powerless tags or labels, indirect URI
chosen destination [5].                                          sensing technologies require the device to acquire or “pull”
                                                                 the URI from the tag or label. The transmission of the URI
Semantic locations are uniquely identifiable physical            from the URI storage device to the mobile device takes
locations that have the additional properties of being user      place over one of many available communication
definable, extendable, and machine- as well as human-            protocols; this research will analyze four such
readable [5]. The use of semantic location could                 communication protocols. To illustrate the interaction in a
revolutionize the way people interact with mobile devices        context-aware environment, figure 1 depicts an end-user
by providing a much greater personalized and customized          holding a handheld device (A), obtaining a URI from a
response to everyday situations (driving directions/maps,        URI storage location (C) over some communication
assistance with train/bus schedules, aid to shoppers in a        protocol (B).
grocery store). One recent prototype [7] has included a
self-guided museum tour that allows users to bookmark a
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                                                                      ·    Is there a URI discovery method that supports
                                                                           powerless beacons or tags?
                                                                      ·    Which type of URI discovery (direct or indirect)
                                                                           provides a better solution to handling multiple
                                                                           simultaneous users?
                                                                      ·    What URI discovery solution is better suited for
                                                                           outdoor use?

                                                                  This paper will attempt to provide an in-depth comparison
                                                                  of direct and indirect URI sensing technologies for use in
                                                                  context-aware mobile service applications. This research
                                                                  could provide assistance to end-users, developers and
Figure 1. Context-aware computing environment                     organizations in understanding the best URI discovery
(Illustration by and courtesy of Paula J. O’Keefe)                method for use in context-aware mobile computing.
Context-aware computing in mobile devices is considered           4. Methodology and Research Design
to be an emerging technology. Consequently, there are
very few solutions currently being offered to consumers or        The approach used in comparing direct and indirect URI
organizations. Although there has been some recent                sensing technologies was to perform the evaluation based
research activity [5,6,7,12,15,16] on this topic from the         on data obtained from published sources. The external data
academic community, very little has focused on the                that was used in this study was collected from recognized
techniques available to current mobile devices in receiving       sources that included researchers, open standards
the semantic location information in a given context-aware        organizations, and specifications from public and private
computing environment. It is my intention to provide an           corporations. The data can be categorized into three areas
in-depth analysis comparing direct and indirect URI               representing the three main components of a context-aware
discovery via mobile devices equipped with sensors.               system: communication protocols, mobile computing
                                                                  devices, and URI storage (beacons and tags).
3. Research Question
                                                                  A total of four communication protocols were chosen for
Does direct or indirect URI discovery provide a better            evaluation: Bluetooth, and IrDA (Infrared Data
solution for context-aware computing based upon cost,             Association) represent direct URI sensing, and RFID
range/communication protocol(s), physical size and                (Radio Frequency Identification), and barcode reading
usability?                                                        represent indirect URI sensing.
Recent research efforts [5,7] have demonstrated that              The mobile computing device selections were a
context-aware computing environments are not only                 combination of four stand-alone units capable of
theoretically possible but have been physically established       participating in a context-aware environment along with
both in labs and on project sites. While there has been           four add-on units that could provide context-aware support
research     on     context-aware      mobile     computing       to an otherwise unsupported mobile device. The stand-
[5,6,7,12,15,16], very little has focused on the use of direct    alone devices included traditional handhelds (Tungsten T2
or indirect URI discovery. What advantages and                    running Palm OS, IPAQ h1945 running PocketPC, Symbol
disadvantages do direct or indirect URI discovery have for        PPT 2800 running PocketPC) as well as one mobile phone
end-users, developers, and organizations that are looking         (Nokia 3600). Add-on devices for both the Palm (Palm
to use, develop, or promote a context-aware environment?          Bluetooth Card, XP700) and PocketPC (Symbol SPS 3000,
                                                                  XP600) devices were selected due to their prevalence in
End-users looking to participate in context-aware mobile          the marketplace where many lack the inherent ability to
computing environments might ask the following types of           participate in a context-aware computing environment.
    · Do mobile devices available today; have the                 The data needed for comparison purposes associated with
         ability to use direct and indirect URI discovery?        the URI storage that included beacons and tags was very
    · Does one of the URI discovery methods offer                 limited due to the lack of commercially available products,
         better security controls over the other?                 presumably because context-aware computing is still in its
    · What is the cost of mobile devices equipped to              infancy. Nonetheless, data was acquired from working
         support URI discovery?                                   research prototypes for each of the four types of URI
                                                                  storage (Bluetooth beacon, IrDA beacon, RFID tag and
Developers interested in building hardware or software            barcode label).
components for a context-aware system could benefit from
knowing the answers to these questions:                           The criteria that were selected as the basis of the
   · Are there differences in the availability of API             evaluation were cost, range/communication protocols,
       support for direct and indirect type systems?              physical size, and usability. This set of criteria was chosen
   · Which type of system (direct or indirect) is more            in an attempt to analyze the key characteristics in which
       prevalent in mobile devices available on the               end-users, developers, and organizations might be
       consumer market?                                           interested in when making decisions related to context-
                                                                  aware mobile computing. Following are detailed
Organizations that are considering installing a context-          discussions of each criterion.
aware computing system in their facility might want know
answers to these questions:

                                                 20th Computer Science Seminar
Cost is a key factor in the evaluation of direct and indirect    Measurements
URI sensing technologies both on the side of the end-user
who needs to purchase a supported device and with the            The following characteristics were used in the comparison
implementer or organization that needs to build a context-       of direct and indirect URI sensing technologies:
aware system. Cost data for the hardware of the mobile
devices and add-ons were obtained directly from the              Cost – MSRP or list price of the device in U.S. dollars.
manufactures where MSRP or list price was used. Due to           Range – The distance in meters of the range of the
the current lack of commercially available beacons or tags,      communication protocol as documented by it’s
it was impossible to collect specific cost information           specification.
associated with URI storage.                                     Height – The height of the device in inches, as documented
                                                                 in its specification.
Range/communication protocols is an important factor to          Width - The width of the device in inches, as documented
consider in the evaluation process because it will               in its specification.
determine the maximum proximity between the end-user             Thickness - The thickness or depth of the device in inches,
and the beacon or tag and may also play a role in the            as documented in its specification.
usability of the system. The range associated with each          Weight - The weight of the device in ounces, as
communication protocol was determined from looking up            documented in its specification.
the documented distances reported in the standards
specification.                                                   In addition to the measurements described above, two
                                                                 additional columns were added (where applicable) to help
Physical size/weight is another important criterion in the       clarify the results. The URI Sensing (direct or indirect)
evaluation process because mobile devices are increasingly       column provides a way to group the data as related to
becoming smaller and smaller and acceptance of context-          either the direct or indirect approach. The Type (stand-
aware enabled devices may be contingent on URI sensing           alone or add-on) column was added to distinguish mobile
technology not adding to a handheld’s weight or size.            devices that have built-in support for URI sensing versus
When selecting beacons or tags for use in context-aware          add-on devices that provide URI sensing features to an
systems, physical characteristics may play a role in             otherwise unsupported device.
determining how or where URI storage can be placed. The
size and weight data for the mobile devices was acquired         Range/communication protocol
from manufacturers’ specifications. Due to the fact that
beacons and tags are not currently commercially available,       Table 1. Range Results [1, 2, 4, 13]
this data had to be obtained from previous research                                                          Range
references involving working prototypes.                         URI Sensing     Communication Protocol      (m)
                                                                 Direct          Bluetooth                   10
Usability is a vital factor in the evaluation process of
direct and indirect URI sensing technologies because end-        Direct          IrDA                        1.5
users, developers, and system implementers are interested        In-direct       RFID                        1
in using a URI sensing technology that provides the              In-direct       Visual / Barcodes           .5
features that best meet their needs. Due to the subjectivity
of usability, the methodology used here will be based on
the results of a series of statements where one of the two       Data collected on range/communication protocol are
approaches (direct URI sensing or indirect URI sensing)          shown in Table 1. The communication protocols
will be chosen as the more effective technology for a given      supporting indirect URI sensing technologies provide a
statement/user requirement.                                      much shorter range, offering at best a distance of 1 meter,
                                                                 as compared to protocols used in direct URI sensing
5. Results / Analysis                                            systems that can achieve a 10-meter range. The indirect
                                                                 approach of utilizing visual barcodes as a URI storage
The results of the study based on the methodology and            device offers the shortest range of .5 meters. One
criteria described in section 4 are presented below.             explanation for the short ranges attributed to the indirect
Although the majority of the data was acquired from              approach lies with the fact that the communication
published specifications and research articles, it is            happens between a device and passive and powerless
important to provide some context to aid with the                RFID tag or barcode label. If the direct approach of using
interpretation of these results. Notice that the data            the Bluetooth protocol with a 10-meter range was not
presented for the communication represents the accepted          sufficient for a given context-aware environment, other
range of the protocol standard, while the practical range        direct communication protocols such as WiFi could be
may slightly differ due to any limitations associated with       explored as potential candidates. While communication
the hardware device that’s communicating using a given           protocols that support the indirect approach are inherently
protocol. In addition, due to an absence of commercially         limited to close proximities, protocols that are direct in
available URI storage mechanisms (beacons and tags), it          nature don’t have this limitation and can offer much
was not possible to present specific cost information for        greater distances.
the various types of URI storage devices. The basis for
determining the price of each hardware device was to use
the manufacturer’s suggested retail price (MSRP), thus the
actual price is expected to be somewhat lower, especially
as time goes on.

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Physical size/weight                                             Cost
Table 2. Size and Weight Results [3, 8, 9, 10, 11, 13]           Table 3. Cost results [3, 8, 9, 10, 11, 13]
                                                      Thick                                                        MSRP
URI Sensing/                 Weight Height      Width -ness      URI Sensing Type             Device Name          (US$)
Type            Device       (oz)   (in)        (in)   (in)
                                                                 Direct         Stand-alone   Tungsten T2         329.00
Mobile Devices                                                   Direct         Stand-alone   IPAQ h1945          299.00
                                                                 Direct         Stand-alone   Nokia 3600          399.00
Stand-alone   Tungsten T2 5.60         4.00     3.00 0.60
                                                                 Direct         Add-on        Palm bluetooth card 129.00
Stand-alone   IPAQ h1945 4.37          4.46     2.75 0.50        In-direct      Stand-alone   Symbol PPT 2800     1,695.00
Direct/                                                          In-direct      Add-on        Symbol SPS 3000     499.00
Stand-alone   Nokia 3600 4.59          5.10     2.24 1.00        In-direct      Add-on        xp600               600.00
Direct/       Palm                                               In-direct      Add-on        xp700               398.00
Add-on        bluetooth
              card        0.13         1.60     0.94 0.08        Data collected on cost is shown in Table 3. In comparing
                                                                 the cost of the stand-alone mobile devices, it was
Indirect/     Symbol                   7.00                      discovered that on average a mobile device with built-in
Stand-alone   PPT 2800 12.90                    3.63 1.00        support for indirect URI sensing technologies costs five
Indirect/     Symbol                                             times more than similar devices that support the direct
Add-on        SPS 3000 2.55            4.46     0.74 0.50        method of obtaining a URI. Similarly, the cost of add-on
Indirect/                                                        devices for use with indirect URI storage were found to be
                                                                 four times more expensive than their direct URI storage
Add-on        xp600       8.84         6.50     2.99 1.50        equivalents. One reason for this large discrepancy in price
Indirect/                                                        may be that the devices supporting indirect URI sensing
Add-on        xp700       4.82         5.98     2.99 0.98        are almost exclusively being marketed for industrial or
Labels / Beacons                                                 commercial use as opposed to being made available to the
                                                                 mass market.
na            beacon      9.65         4.60     3.46 1.26        Usability
na            IrDA beacon 6.00         3.75     2.50 1.50
na            RFID tag    0.10         0.25     0.25 0.10        Table 4. Usability results
na            label       0.00         0.75     1.50 0.00
                                                                                                   Advantage   Advantage
The results from assessing the physical size and weights of      Statement                         Direct      Indirect
devices shown in Table 2 indicate that mobile devices that       Consumers
support indirect URI sensing are considerably larger and         Ability to prevent unwanted
heavier than those equipped with the direct approach. In
comparing the stand-alone type mobile devices, the               URIs                                                X
indirect variety weighed on average 250% more than those         Built-in URI reading support of
stand-alone devices equipped with direct URI sensing             off-the-shelf mobile devices             X
capabilities. The average weight of the add-on devices had       Overall Ease in obtaining URI            X
similar results, with indirect URI sensing add-ons much
heavier than add-ons supporting the direct technologies.         Ability to obtain URI in a
Interestingly, the exact opposite was discovered when            crowd                                    X
comparing the physical weight and sizes of the tags and          Developers
beacons. Tags and labels supporting indirect URI sensing
technologies were shown to be much smaller and lighter           API (Application Programming
than the beacons associated with direct URI storage. It is       Interface) Support                       X
not that direct URI storage devices were large, but rather       Open source API available                X
the indirect tags and beacons were shown to be extremely         Organizations
                                                                 Ability to serve a number of
                                                                 simultaneous users                       X
                                                                 Supports outdoor use                                X
                                                                 Ability to move the location
                                                                 of the URIs (tags)                                  X
                                                                 Works without power                                 X
                                                                 Ability to connect to a network          X
                                                                 Ability to manage URIs
                                                                 remotely                                 X
                                                20th Computer Science Seminar
Data collected on usability appears in Table 4. The                Findings as they relate to consumers
usability results for consumers show direct URI sensing
technologies offer a greater level of usability as compared        Consumers will find direct URI discovery provides a better
to indirect based solutions. For consumers the usability           solution to their context-aware mobile computing needs by
advantages of direct URI sensing technologies start with           offering:
the fact that many mobile devices purchased today are                   · Mobile devices and add-ons with lower cost
equipped to support direct sensing. While devices that                  · Mobile devices and add-ons with less weight and
support indirect URI sensing are available, they are                         smaller form factor
currently of commercial grade and have not yet hit the                  · Longer range (up to 10m)
mass consumer market. While overall the direct URI                      · Ease of use in obtaining a URI
sensing technologies offer a more usable solution for the
consumer, because the direct technique pushes the URI to           Findings as they relate to developers
the device, there exists the very real possibility for the end-
user to receive unwanted URIs. These concerns of direct            Developers will find direct URI discovery provides a
URI sensing technologies “pushing” unwanted URIs to an             slightly better solution (albeit only modest improvements
end-user would have to be addressed as a hardware or               over the indirect approach) to their context-aware mobile
software setting on the device. Indirect URI sensing               computing needs by offering:
technologies do not have these same issues because they                 · Well developed set of APIs
require the end-user to “pull” the URI storage by actively              · Availability of open-source APIs as opposed to
reading a tag or label. Software developers of context-                     vendor-specific
aware computing applications for mobile devices must
interact with an API (application programming interface)           Findings as they relate to organizations
associated with a given communication protocol. Direct
URI sensing technologies including the Bluetooth and               Organizations interested in developing a context-aware
IrDA protocols offer several well-developed APIs for               system for mobile devices will find direct URI discovery
developers use, and there is at least one open source API          provides a better solution by offering:
available for Bluetooth. API support for the indirect URI               · Ability to serve multiple users (even
sensing technologies is not as widely available and must                    simultaneously)
usually come directly from sensing device manufacturers.                · Ability to connect URI storage devices to a
Organizations interested in building a context-aware                        network
system will find many other advantages to the direct URI                · Ability to manage URI beacons remotely
sensing technologies, including the ability to send URIs to
a large number of devices in a short period of time.               7. Summary and Future Work
Additionally, direct URI sensing technologies have the
ability to connect the URI beacon to a network, thus,              This research compared direct and indirect URI discovery
allowing for real-time feedback and administration.                for use in context-aware mobile computing environments.
Indirect URI sensing technologies may provide a better             Data was collected from a combination of sources
solution for organizations requiring the ability to move           including research materials and industry specifications.
URIs easily from location to location or for installations         Analysis was performed with respect to cost,
where power sources are not available.                             range/communication protocol, size and weight, and
                                                                   usability. Direct URI discovery proved to be the overall
6. Findings and Impact of Work                                     superior technology based on these characteristics. The
                                                                   direct URI sensing approach was shown to have the
This study has shown a number of differences between               advantages of greater range, lower cost, and availability of
direct and indirect URI sensing technologies when                  supporting consumer grade mobile devices. Indirect URI
comparing cost, range/communication protocols, physical            sensing technologies, while in many respects less
size and weight, and usability. Direct URI discovery is            advantageous, might still be the preferred solution when
available in mobile devices that are both smaller, less            there is a need for URI storage to be moved easily or
expensive, offer a longer range, and are easier to use.            operate without power. While context-aware mobile
While direct URI sensing technologies offer an overall             computing is considered to be an emerging technology [7],
better solution in implementing a context-aware mobile             it’s important to note that it is still in the very early stages
computing environment, indirect URI approaches may be              of development. One potential area of future research
preferable under certain circumstances. The URI storage            would be to examine ways to add security restrictions that
using tags and labels associated with indirect URI sensing         provide an end-user with control over receiving unwanted
technologies are as small as a grain of rice [16] and in the       URIs.
case of barcodes can be easily created. This allows an
organization to have a wide range of flexibility with their        References
use and placement of URI storage locations. Given that an
organization needs to be able to move URI storage                  [1]      Association for Automatic Identification and Data
locations easily from one location to another (even                         Capture Technologies, “Radio Frequency
outdoors) or has a need to apply beacons to consumer                        Identification (RFID) Homepage”,
goods, indirect URI sensing technology may be a better            
option. Taking a closer look at how these findings affect          [2]      Bluetooth Inc., “The Specification”,
the consumer, developer, and organizations we have the            

                                                  20th Computer Science Seminar
[3]    Hewlett-Packard Development Company, “hp
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[10]   Northern Apex Solutions Integrator, “Northern
[11]   PalmOne Inc., “PalmOne”,
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[13]   Symbol Technologies, “Symbol Technologies
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                                            20th Computer Science Seminar

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