Wireless communication and computing at the construction jobsite

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.
Automation in Construction 7 1998 327±347
Wireless communication and computing at the
construction jobsite
Jesus M.de la Garza
a,)
,Ivan Howitt
b,1
a
Virginia Tech,200 Patton Hall,Blacksburg,VA 24061-0105,USA
b
UniÍersity of Wisconsin,P.O.Box 784,Milwaukee,WI 53201,USA
Abstract
For many years,the walkie-talkie has been synonymous with the construction industry.During jobsite project execution,
there are three variables which can either hinder or facilitate successful results,namely,quality,quantity,and timing of
information.Wireless data communications technology is capable of delivering just-in-time information within the`last
mile'between the trailer and a desired location on the jobsite.This paper reports on a study which surveyed information
needs at the jobsite,emerging wireless data communications technology,and assessed the extent to which wireless data
w
technology can fulfill the information needs of the jobsite J.M.de la Garza,I.Howitt,Wireless communication and
x
computing at the jobsite,Research Report 136-11,Construction Industry Institute,Austin,TX,1997.We have organized
...
jobsite information needs into the following ten categories:a requests for information,b materials management,c
....
equipment management,d cost management,e schedule and means and methods,f jobsite record keeping,g
...
submittals,h safety,i QCrQA,and k future trends.Each category was analyzed in terms of its appropriateness to take
..
advantage of wireless technology.The four formats considered to transmit information wirelessly were:a live voice,b
..
live video,c batched data,and d live data.Current wireless communication technology has been classified into the
..
following five classes:a circuit-switched wireless data systems,b packet-switched wireless data systemsÐthis class was
.
further subdivided into specialized mobile radio systems and cellular digital packet data systems,c wireless local area
..
networks,d paging systems,and e satellite-based data communications.A primer for wireless communications covering
both fundamental and advanced communications concepts has also been included to enable a better understanding of the
issues involved in making trade-offs while configuring a wireless jobsite communication system.The example presented in
this paper shows how a contractor can define a subset of information needs by choosing from those already articulated
herein and determine if a given wireless technology should even be considered as a viable way of meeting the information
needs that such company has.q1998 Elsevier Science B.V.All rights reserved.
Keywords:Wireless communication;Construction;Walkie-talkie
Abbreviations:AMPS,advanced mobile phone system;AMSC,American Mobile Satellite Corporation;bps,bits per second;CDPD,
cellular digital packet data;FCC,Federal Communication Commission;GEOS,geostationary earth orbit satellite;kbps,kilobits per second;
LEOS,low earth orbit satellite;Mbps,mega bits per second;MEOS,medium earth orbit satellite;PCS,personal communications service;
PSTN,public-switched telephone network;QOS,quality of service;SMR,specialized mobile radio;WLAN,wireless local area network;
WLL,wireless local loop
)
Corresponding author.E-mail:chema@vt.edu
1
E-mail:howitt@cae.uwm.edu
0926-5805r98r$19.00 q 1998 Elsevier Science B.V.All rights reserved.
.
PII S0926- 5805 98 00050- 8
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347328
1.Introduction
For many years,the walkie-talkie has been synonymous with the construction industry.As a result,wireless
voice communication between members of the construction team at the jobsite is a well-established technology.
However,in the last few years,remarkable progress in wireless data communications technology has made
possible the provision of new wireless information services within the jobsite.
During jobsite project execution,there are three variables which can either hinder or facilitate successful
results,namely,quality,quantity,and timing of information.Current paper-based jobsite construction processes
are becoming obsolete as they are unable to deliver just-in-time information.The paper-based pipeline of
information is clogged,hence,creating an information deficit.A shift to an electronic-based exchange of
information can help alleviate the timely delivery and access of relevant amounts of information.
For the most part,the wireless portion of the communications link will serve as the`last mile'from a
network connection within the trailer to the desired location on the jobsite.Wired telephone and ror internet
links would still carry data traffic from the jobsite to desired off-site locations.Because timely access to
information is what keeps relevant information from becoming irrelevant,applications of wireless data
communications technology have the potential of reaping more productivity benefits than the ones achieved
already by applications of wireless voice communications technology,e.g.,walkie-talkies.
The manufacturing,trucking,and package-delivering industries have already incorporated wireless data rvoice
communication systems into their respective work places.The construction industry faces both similar and
different challenges from those found within these industries.However,generic concepts can be learned by
studying them and following their lead.All parties involved in a constructed facility are suppliers and
consumers of information.Hence,owners,designers,contractors,suppliers,and construction managers will
benefit substantially from having the means to deliver and access to information wherever and whenever they
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need to 1.
.
This paper reports on a study sponsored by the Construction Industry Institute CII to assess the imminent
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applicability spectrum of wireless data communication technology at the jobsite 2.The objectives of this paper
.
are to show the results of:1 a survey of information needs at the jobsite with a focus on type,amount,quality,
..
and timeliness;2 a survey of emerging wireless data communications technology;and 3 an assessment of the
extent to which wireless data technology can fulfill the information needs of the jobsite.
Although the CII study was limited in scope in that it was concentrated primarily on the jobsite information
needs of the industrial process construction sector,our findings are logically extendable to other sectors of the
.
construction industry.The Lyondell rCitgo Refinery LCR revamprexpansion project in the Houston-Texas
area was targeted for visits with the purpose of eliciting and articulating information needs as well as to assess
the impact that the typical construction environment may have on the effectiveness of wireless data communica-
tion technologies.Concurrent to the articulation of information needs,a survey of wireless technology that was
available off-the-shelf was conducted.This survey examined several different formats of wireless communica-
tion from several different manufacturers.Once the information needs at a construction jobsite and the wireless
products that were currently available were identified,a framework for determining and ror eliminating wireless
products for a given set of information needs was developed.This paper included an example to illustrate the
use of this framework.
2.Cost-benefit considerations
It is important to consider the trade-off between the Íalue of transmitting the information wirelessly on
demand against the cost of transmitting it.Wireless communication is not an inexpensive technology.There are
initial equipment expenses,expenses associated with service fees and maintenance,and indirect expenses that
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 329
Fig.1.Cost-benefit example 1.
.
need to be considered.Some of the costs of investing in wireless technology that need to be considered are:1
.
the purchase of hardware and software,a one-time cost;2 the maintenance and upgrading of hardware,an
..
on-going cost;3 the upgrading and licensing of software,an on-going cost;4 the fees of wireless service
..
providers,an on-going cost;5 the salaries of in-house technical support personnel,an on-going cost;6 the
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training of the users,an on-going cost;and 7 the fees to a specialized wireless consultant,an on-going cost.
Fig.1 is a graph that shows the Íalue and cost of information versus the time of day that the information is
sent.In this example,a foreman has information that he needs to send to the trailer at 8:00 AM.The Íalue of
this information at 8:00 AM is V1.If the foreman had access to a wireless information system,he could
immediately download that information to the trailer at a cost of C1.If he did not have access to wireless
information,he might have to wait until the end of his shift to bring the information to the trailer.The Íalue of
the information has decreased as depicted by V2,because of the 9-h time delay.The cost of delivering the
information has also decreased,as shown by C2.The company must decide if the additional cost of transmitting
the information wirelessly is worth the added Íalue of the information.This example examines the cost-benefit
comparison by looking at the decrease of the Íalue of the information over time.The question is:is Value
Added 1)Value Added 2?
The next example depicted in Fig.2 examines the productivity that is lost if the foreman needs to leave the
field to deliver information to the trailer.If the foreman had access to wireless communication he could
download the information at 8:00 AM,at a cost of C1.If the foreman did not have wireless communication
capabilities,he would have to leave the field and bring the information to the trailer at 8:30 AM.The Íalue of
the information has not changed much between V1 and V2.However,when the foreman leaves the field,his
crew's productivity could decrease and,hence,the cost of transmitting the information increases from C1 to C2.
The question again is:is Value Added 1 )Value Added 2?
Assessment of the value-added by delivering information just-in-time is as quantifiable as the cost of the
technology if we think in terms of throughput.By delivering information just-in-time,a contractor can reduce
work-in-progress inventory,and thus,working capital.Reduction of cycle times and flow variation are
.
additional benefits derived since resources materials,equipment,and labor will spend less time in queues
waiting to be processed.
Fig.2.Cost-benefit example 2.
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347330
3.Jobsite information needs
We use tables to articulate and organize the content within each of the information needs categories.Herein,
we use Table 1 to describe the meaning of each of the tables'headings.
There are four formats that are considered to transmit the information wirelessly.The first two,voice and
video,are`live'transfers of information.This means that there is no latency in the data transfer.The third
format is batched data.The fourth format is`live data'.The different types for each format are as follows:
.
¯ Voice is defined by quality of service QOS as low,medium or high.
.
¯ Video is defined by quality of service QOS as low,medium or high.
¯ Batched data files are divided by file size as follows:
.
1.Small:-5 kilobytes;included are e-mail,short text messages,and simple line drawings.
.
2.Medium:)5 kilobytes,-100 kilobytes;included are medium resolution graphics,large text docu-
ments and medium resolution digital pictures.
.
3.Large:)100 kilobytes,-1 Megabyte;included are high-resolution compressed graphics or pictures,
moderate to high resolution video,CAD files and multimedia applications.
The Delay column defines how much of a delay in information transfer is allowable for a given format.The
delay scale is as follows:
.
5ÐData can be transmitted within 0.01 min no latency.
.
4ÐData can be transmitted within 0.1 min minimal latency.
3ÐData can be transmitted within 1 min.
2ÐData can be transmitted within 10 min.
NFÐTime is not a factor.
The Importance column gives a rating as to the usefulness of the information being transferred.This scale
..
ranges from a value of 5 very important to a value of 1 unimportant.The Simplex rDuplex column defines
whether one-way or two-way communication is necessary for a given application.If an application is simplex
..
then the table defines whether the originating point of the information is the field SF or the trailer ST.For
each information subcategory,a transmission data rate is determined.It is based on the amount of information to
be transmitted and on the allowable delay.The following formula was used to determine transmission data rates
.
of batched files.The data rate is expressed in kilobits per second kbps.
Max.File Size in kilobytes 1024bytesrkilobyte 8bitsrbyte 1kilobitr1000bits
....
.
Data Rate kbps s
.
Time in s
.
.
The jobsite information needs have been organized into the following ten major categories:a requests for
....
information,b materials management,c equipment management,d cost management,e schedule and
.....
means and methods,f jobsite record keeping,g submittals,h safety,i QCrQA,and k future trends.
Table 2 provides a general classification of jobsite information needs and Table 3 examines in detail the request
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for information category.All other information needs'tables are found in Refs.2,3.
Although these tables were obtained from a single,but fairly large,jobsite and from a handful of contractors,
the categories and subcategories are fairly generic,hence,extensible to other jobsites and ror firms.The entries
in these tables,which show company-specific preferences,i.e.,format type,importance of information,delay in
Table 1
Information needs charts headings
Information Explanation Formats of information Type Delay Importance Simplex r Data rate
..
subcategory transfer min duplex kbps
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 331
Table2
Classificationofjobsiteinformationneeds
RequestforMaterialsEquipmentCostScheduleandJobsiterecordSubmittalsSafetyQCrQAFuture
informationmanagementmanagementmanagementmeansandkeepingtrends
.
Table3methods
DesignintentAccesstoma-Equipmentlo-BudgetScheduleup-RecordingTestresultsAccidentInitiateinspec-Positio-
andclarifica-terialmanage-cationdatestimesheetsreportingtionsningdata
tionment
SubcontractorMaterialloca-Fuelmonitor-MaterialcostDelayrecord-ProgressRevisionstoReportingvio-ReportSensory
informationtioningaccountingingreportingsubmittalslationsQCrQAprob-data
lems
Contractspec-MaterialorderEquipmentAs-builtExceptionReportinspec-
ificationsstatuscostaccount-recordsreportingtionresults
ing
ContractRequestmate-ProductivityVisitor's
drawingsrialstositeinformationlog
WorkpackagePlacematerial
informationorders
Meansand
methods
Implementa-
tionproblems
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347332
Table3
Informationcategory:requestsforinformation
.
InformationExplanationFormatsofTypeDelayminImportanceSimplexrduplexDatarate
.
subcategoryinformationinkbps
transfer
.
1DesignandConsultationwithengineersrdesignersforVoice-0.015D8±32
intentclari-questionsregardingdesignandintent.
ficationVideo-0.011SF128±10,000
BatcheddataSmall-14D0.68
Medium-14D13.65
Large-103D13.65
.
2Subcon-AccesstoanyinformationthattheprimeVoice-0.013D8±32
tractorinfor-contractorhasaboutanyoftheir
mationsubcontractor's.Also,informationaboutasub-
contractor'sactivitiesatanygiventime.
Video-0.011SF128±10,000
BatcheddataSmall-13D0.68
MediumNF1D)1
LargeNF1D)1
.
3ContractAccesstospecificationsorinformationVoice-0.015D8±32
specificationregardingspecifications.
Video-0.011SF128±10,000
BatchedDataSmall-13D0.68
Medium-12D13.65
LargeNF1D)1
.
4ContractAccesstocontractorshopdrawingsandifVoice-0.013D8±32
drawingsnecessarypersonnelthatcananswerquestions
regardingthedrawings.
Video-0.011SF128±10,000
BatcheddataSmall-13D0.68
Medium-14D13.65
Large-104D13.65
.
5WorkAccesstoworkpackageinformationincludingVoice-0.015D8±32
packageinfor-scopeofwork,materialsandequipmentre-
mationquired,etc.
Video-0.011SF128±10,000
BatcheddataSmall-15D0.68
Medium-103D1.37
LargeNF1D)1
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 333
.
6MeansandShouldfieldpersonnelneedtoverifyorconsultVoice-0.015D8±32
methodsques-abouttheplannedmeansandmethods.
tions
Video-0.011SF128±10,000
BatcheddataSmall-15D0.68
Medium-14D13.65
Large-103D13.65
.
7Implemen-ForconsultationwhenfieldpersonneldiscoverVoice-0.015D8±32
tationprob-thatanitemcannotbeinstalledaccordingtothe
lemsowner'splansorcontractor'smethods.
Video-0.011SF128±10,000
BatchedDataSmall-14D0.68
Medium-13D13.65
Large-103D13.65
AverageAverageDefiningvalue
..
inminskbps
SummaryforcategoryVoice-0.014.438±32
Video-0.011.00128±10,000
BatcheddataSmall-13.860.68
Medium-2.53.0013.65
Large-102.2913.65
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347334
transmission and data rate,by necessity need to be recomputed for each jobsite rcompany pair combination.The
process of addingrremoving information categories andror of reassessing preference-based inputs is simple and
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explained with a full example in Ref.2.
4.Wireless communications:an overview
Wireless communications have sustained a tremendous growth rate over the past decade.Significant strides
have been made in the technology and by the communication community to provide reliable services.To date
the services have focused primarily on voice communication,but there has been a recent trend to providing
mobile data services.There are many in the communication field who feel this trend will become a strong area
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for mobile communications in the near future 4±7.
The current challenge for the mobile user,especially in the area of mobile computing,is to identify the
information flow needs and obtain the wireless service and ror wireless technology which best meets the
companies'requirements.As in any fast growing and emerging market,the more the consumer knows about the
technology,the better prepared they are to make decisions.
Prior to delving into the communications details,let us revisit the jobsite problem.The underlying problem is
to first identify the requirements for a wireless solution and next to narrow the field of wireless technologies
available.The problem involves providing a method to communicate data between the field operation and the
field office.Typically the field office is located in a trailer within close proximity to the field operation.The
foreman or supervisor in the field needs to be free to roam within the boundaries of the field operation.Also,the
information needs under consideration are time critical to assist in maintaining or improving the efficiency at the
jobsite.The combination of these two factors indicates a benefit for a mobile computing platform with a
wireless link to the field office.The wireless technologies studied are:circuit-switched cellular modems,
specialized mobile radio utilizing packet-switched wireless data systems,packet-switched cellular modems,
wireless local area networks,paging systems,and satellite-based data communications.
Based on the geometry and obstructions of typical jobsites,two major wireless technologies are not viable
options.These technologies are microwave links and cordless telephones.Microwave links would be attractive
due to their capability to maintain high data rate communicationsÐtens to hundreds of mega bits per second
.
Mbps.Microwave links typically require line of sight and fixed locations for both transmitter and receiver
antennas;therefore,making them unsuitable for the typical jobsite application.They may still provide a good
method for linking field offices,if a company needs to support multiple field offices at a construction site.
Cordless telephones could also be considered an attractive solution since they are being used as wireless local
.
loops WLL in office buildings.A WLL is a wireless implementation of the traditional wired connection
between the switching exchange and the user,i.e.,the local loop.As an example,a single wireless base station
could be used to support several cordless telephones on a single floor of an office building.This would
eliminate the need to provide a wire to each telephone and provides each user the ability to roam around the
office floor and remain in communication with the base station.The base station would then be tied into the
private branch exchange for the building or it could be tied directly into the public-switched telephone network
.
PSTN.Therefore,through the base station each user can be linked to the outside world.The difficulty with
using this technology is that the current availability of commercial cordless telephones to support data
communications in a severe multipath and shadowed environment is questionable.Therefore,cordless telephone
technology is not suggested as a possibility at this time,even though it may be a strong alternative in the future.
4.1.Circuit-switched cellular modems
A simple form of wireless data communication in common use now is data transmission using modems over
analog cellular telephone system.This involves the mobile user to simply accede access a cellular channel just
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 335
Fig.3.Analog cellular circuit-switched data communications.
as would be done for making a standard voice call over the cellular network.The modem is then operated in the
same fashion as it would be for a standard wireline phone on the PSTN.A typical connection is illustrated in
Fig.3.The mobile user is using a laptop which is connected via a wireless cellular link to the mobile telephone
.
switching office interface point between the local cellular network to the PSTN.At this point,the signal is
routed to the wireline modem connected at the desktop computer.The laptop modem is normally based on a PC
card format and currently most new PC card modems can be used with cellular telephones with the purchase of
the correct cable.
The advantage of circuit-switched wireless data transmission is the capability of using the existing
communication software developed for wireline modems.Another advantage involves the geographic coverage.
Since this method uses the existing cellular infrastructure,wherever a cell phone call can be placed data
transmissions can be conducted.There is a caveat to this statement,i.e.,voice communication can occur over
channels that are more severely corrupted then those required for reliable data communication.There is no
additional hardwarersoftware requirements placed on the service provider.The disadvantage is that the service
is based on a circuit-switched connection,which means the communication link remains dedicated to the
modem-to-modem link independent of the amount of data being transmitted.Therefore,this approach may not
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be cost effective for sending intermittent data,such as a number of short messages 8.
4.2.Specialized mobile radio using packet-switched wireless data systems
.
The specialized mobile radio SMR service was first established by the Federal Communications Commis-
.
sion FCC in 1979 to provide land mobile communications on a commercial basis.The growth of SMRs has
been significant.For example,at the end of 1994,approximately 1.8 million vehicles and portable units were
served by SMR systems.A traditional SMR system consists of one or more base station transmitters,one or
more antennas,and end-user radio equipment that usually consists of a mobile radio unit either provided by the
end-user or obtained from the SMR operator for a fee.Typical SMR customers using dispatch communications
include construction companies with several trucks at different jobs or on the road with a dispatch operation in a
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central office 9.The SMR analog circuit-switched service is the traditional service used by the construction
industry to support voice communication over`walkie-talkies'.
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347336
Although SMRs are primarily used for voice communications,systems are also developed for data and
facsimile services.The use of the SMR for data communication typically involves the use of a proprietary
interface and software between the radio and the end-user's computer.Typical data applications include
two-way acknowledgement paging and inventory tracking,credit card authorization,automatic vehicle location,
fleet management,remote database access,and voicemail.
4.3.Packet-switched cellular modems
.
The cellular digital packet data CDPD system was designed to provide packet data services as an overlay to
the existing analog cellular telephone network.The goal of the CDPD system is to provide data services on a
non-interfering basis with existing analog cellular telephone services.This is accomplished in one of two ways.
First,a few analog cellular channels may be dedicated to handling packet-switched data via CDPD.Second,
CDPD is designed to make use of cellular channels that are temporarily not being used for voice traffic and to
jump to an alternative cellular channel when it is allocated to voice service.In other words,CDPD uses the dead
time between voice phone calls to transmit and receive data.Based on the 30 kHz channels allocated for cellular
.
communications,CDPD has been designed to have a radio frequency RF channel data rate of 19.2 kbps.The
effective rate due to the nature of packet switching and error correction requirements is typically between 5 to
10 kbps.As of mid-1995 CDPD service has been implemented in more than a dozen major market areas and an
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additional deployment in 55 markets were planned by the end of 1995 8.
4.4.Wireless local area networks
.
Wireless local area networks WLAN are unlike the other technologies discussed.All the other methods for
providing wireless communications are based on obtaining services from a provider,i.e.,a service provider has
obtained a portion of spectrum from the FCC and is providing a specified service in a given geographic region.
WLANs operate in the unlicensed bands.In the United States,this means the WLANs must comply with the
FCC's part-15 rules which governs operation of systems transmitting in the unlicensed bands.Therefore the
WLAN user does not need to obtain a license,the only requirement is to ensure the system operates in
.
compliance with the FCC or other governing body rules.The compliance with FCC regulations is normally the
responsibility of the wireless system manufacturer.
WLANs typically provide the following services:low-mobility,relatively high data rates,and small coverage
regions.The configuration,coverage,type of system,and maintenance are the responsibility of the end-user.
There are two overall network architectures pursued by WLAN designers.One is a centrally coordinated and
.
controlled network that resembles other wireless systems e.g.,cellular telephone networks,see Fig.4.In the
.
WLAN infrastructure network,there are base stations access points that exercise overall control over channel
access.In these architectures,roaming is generally supported.In other words,the WLAN system has been
designed to allow a mobile station to move from being serviced by one access point,to being reassociated with
another access point.
An alternative network architecture is the self-organizing and distributed controlled network where every
terminal has the same function as every other terminal,see Fig.5.Networks are formed on an adhoc basis by
communication exchanges among stations.
A primary difficulty with maintaining reliable WLAN performance is the potential interference from other
users in the band.This interference can occur from other users of the same network or other users from a
different WLAN system,but one which uses the same frequency and is co-located in the same region.Another
source of interference is from non-WLAN devices operating in the frequency band.As an example,in the 2.4
.
GHz unlicensed personal communications service PCS band,interference is possible from conventional
kitchen microwaves.
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 337
Fig.4.WLAN network with access points.
4.5.Paging systems
Radio paging has been a means for handling one-way wireless communications for many years.In general,

paging can be categorized as one-way messaging over wide areas.The information content of the page i.e.,
.
message is typically brief.Depending on the type of service the message may be either numeric,alphanumeric,
or voice.The communication link is optimized to utilize the one-way communication path and to provide robust
coverage to the subscriber independent of the subscribers location.The paging system is designed with high
antennas at the base stations and with high transmitter power,hundreds to thousands of watts.Using these
Fig.5.WLAN adhoc network.
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347338

communication parameters at the transmitter and in conjunction with low data rates several thousand bits per
.
second,the receiver carried by the subscriber can be designed with low complexity and high battery life.
Paging systems vary widely in their complexity and coverage area.Simple paging systems may only cover
the area within an individual building as compared to wide-area paging systems which provide worldwide
.
coverage.Wide-area paging systems simultaneously broadcast a page from each base station simulcasting in
order to ensure the reception of the page by the subscriber.
A relatively new and emerging service is two-way paging.With two-way paging the subscriber will be able
to respond to inquiries posed in the original message.The replies are typically prearranged responses,so the
data rate in the reverse direction is on the order of one to ten bits per second.
4.6.Satellite-based data communications
Satellite-based systems provide an alternative wireless communication system.Satellite-based systems can be
viewed as expensive base stations providing wide-area coverage.The systems can provide services similar to
those provided by cellular or paging systems.These services typically include limited quality two-way voice,
circuit-switched or packet-switched data,and paging.A fundamental advantage of satellite-based systems over
the other wireless systems is its capability to cover a widespread area.Often with the use of multiple satellites
global coverage is possible.Hence even though the cost may be several times more expensive than a cellular
service,it may be the only choice if the jobsite is located in a remote location and a wireless service provider is
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deemed necessary 10.
.
Proposed satellite systems range from low earth orbit satellites LEOS having tens to hundreds of satellites,
..
through medium earth orbit satellites MEOS,to geostationary earth orbit satellites GEOS having fewer than
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ten satellites.Some of the fundamental trade-offs in designing the satellite-based system are as follows 11.
Coverage area:in general,the further the satellite is from the earth the larger the coverage region or foot
print,this decreases the user capacity within a given spectrum allocation,but also decreases the number of
satellites required to cover a given geographical location.
Transmission delays:the difference in transmission delay between the location of the satellite can be upwards
of two orders of magnitude,large transmission delays impact the quality of two-way voice communications.
.
American Mobile Satellite Corporation AMSC was the first service provider for terrestrial mobile radio
services in North America.Their first satellite was launched into geosynchronous orbit in April 1995.Their
current system is a dual mode system providing the user with both cellular and satellite-based services.The size
and weight of the mobile users'system lend itself to a vehicle-based terminal,but not a handset at this time.The
service provides both satellite-based voice telephony and circuit-switched asynchronous data using a built-in
.
modem.The circuit-switched modem provides transmission rates of between 1200±4800 bits per second bps
for data.
4.7.Restriction of wireless technology based on data rate requirements
This section shows how to eliminate different types of wireless communication technology from considera-
tion based on the data rates that have been identified for the information needs.This section is not intended to
validate the use of any particular wireless technology but to show which ones will not work based on data rate
requirements alone.Table 4 presents a number of issues which influence the wireless technology assessment.
Each of the wireless technologies are then evaluated with respect to these criteria.
Table 5 is presented as a tool for eliminating different types of wireless communication from consideration.
The left most columns of this table identify different formats of information transfer.For voice and video,the
three levels of quality of service are identified,and for batched files three different ranges of data rates are
identified.The top row identifies several categories of wireless technology that are currently available.Inside
the table,a notation of`NrA'means that currently the given technology will not support the data rates required
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 339
Table4
Wirelesstechnologyoverview
FactorsinfluencingCircuit-switchedcellPacket-switchedSMRCDPDWLANPagingSatellite
assessmentmodem
.
Dataratekbps14.49.69.612002.44.8
GeographiccoverageExtensivecoverageinMajorcitiesandLimitedavailabilityLimitedtoaccessNationwideforoneNationwidecoverage.
US.RuralareasmaytownsinUSpointlocation.Accesswaypaging.TwowayInternationalcover-
havelimitedQOSpointlocationsdeter-pagingreportedoper-agereportedinnext2
minedbyend-userationalin1300cities.to5years.
ServicerequirementsServiceproviderServiceproviderServiceproviderInstallationandmain-ServiceproviderServiceprovider
tenancedetermined
byend-user.
FactorsinfluencingTypicalhardware:Typicalhardware:Typicalhardware:Typicalhardware:Typicalhardware:Typicalhardware:
costmodem,cable,cellspecialmodem.Ser-modem,cable,cellmodem,accesspoint.pager,cablerinter-specialmodem,an-
phone.Service:vice:monthlysub-phone.Service:Installationandmain-face.Service:monthlytenna.Service:
monthlysubscription,scription,perusemonthlysubscription,tenancesubscription,perusemonthlysubscription,
perusecharge.charge.perusecharge.charge.perusecharge.
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347340
Table 5
Framework for elimination of wireless communication from consideration
Voice QOS Required data Circuit-switched Packet-switched CDPD WLAN Paging Satellite
.
rate kbps cellular modem SMR
a a a b
Low 8 U U U U NrA U
a a a b
Medium 16 U U U U NrA NrA
b
High 32 NrA NrA NrA U NrA NrA
Video QOS
b
Low 128 NrA NrA NrA U NrA NrA
Medium 1500 NrA NrA NrA NrA NrA NrA
High 10,000 NrA NrA NrA NrA NrA NrA
Batched Data rate
Low -1 U U U U U U
c,d c e
Medium )1,-14.4 U U U U NrA U
High )14.4 NrA NrA NrA U NrA NrA
U:Commercially available;NrA:not currently available.
a
Analog voice using standard voice service.
b
Possible but not implemented.
c
Covers up to medium end of defined data rate range.
d
Location is a major consideration.
e
Covers up to low end of defined data rate range.
for the given application.A check mark indicates that there is technology available that will support the data
rate required for the given application.However,a check mark is not an endorsement of the technology for that
application.
For example,if one were to examine the CDPD column in Table 5,one can see that CDPD could support
low and medium quality live voice communications,but not high quality.Looking further down the column,it
can be seen that CDPD cannot support any live video applications.For batched data,the table shows that CDPD
can support low data rates.By looking at footnote c,it can be seen that CDPD can only support medium data
rates to the middle of the defined data rate range.Finally,it can be seen that CDPD cannot support high data
rates.
Continuing with the example,let us assume it is required to use batched file communication capable of
achieving a data rate of 12 kbps.This data rate falls into the medium batched file category.Starting at the left
side of Table 5,one can see that the circuit-switched cellular modem technology will support this format of
wireless transfer.Moving to the right of the table,it can be seen that the packet-switched SMR format will only
support data rates to the middle of the defined range.Therefore,on this basis,they should not be considered as
an option.The same is true for CDPD.WLAN will support the required data rate.Paging and satellite will not
support the required data rate.
4.8.Implementation considerations when using wireless technology
When wireless technology is being considered for communication at a jobsite,there are a number of
technical issues which need to be considered.These issues have been addressed in this document and are
w x
addressed in greater detail in the source document 2.There are other issues which have less to do with the
technical feasibility of using wireless technology and more with implementation feasibility.Three primary
considerations under this category are information security,the potential for electromagnetic interference to
other jobsite equipment,either the company's or the client's,and the interaction among signals resulting from
transmitting in a cluttered environment.
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 341
All communications systems are vulnerable to being breached and the information transmitted being received
by an undesired listener.Wireless systems are inherently more susceptible to unintentional listeners since the
signal is transmitted into free space and not contained in a conduit connecting the transmitter and receiver.If the
information is sensitive then steps need to be taken to safeguard it.The wireless industry recognizes this concern
.
and in some technologies WLAN encryption techniques are built in to provide secure communications.If the
wireless technology being considered does not have sufficient security for the application being considered,then
in most cases additional software andror hardware can be incorporated to provide the needed security.As an
example,if the system is being used to transmit sensitive data from a jobsite computer to the trailer,then the
data can be encrypted at the jobsite computer,transmitted and then decrypted at the intended receiver.If
clandestine activity is occurring and an unintended listener receives the encrypted data,the unintended listener
does not have the`key'to unlock the content in the encrypted data,so the received data is meaningless.
Wireless systems transmit electromagnetic energy,therefore,there may be concern for electromagnetic
interference to other equipment,either the company's or the client's.If the wireless system is working correctly,
then the energy should be predominately contained in a narrow frequency band with typically low transmit
power.These two factors imply the chance for interference is limited.As an example,wireless systems based on
.
a service provider cellular,SMR,paging,etc.are licensed by the FCC and operate in a specific frequency
band.Therefore,if the jobsite is located in a region where the wireless service is provided,radio frequency
energy is already present to support other wireless service customers in the area.The operation of a WLAN may
require additional coordination between the company and client.It would be prudent to verify that its operation
does not adversely affect other communication systems already at the site.Since WLANs operate in the
unlicensed frequency band,there is little or no coordination between users of different communication systems.
The WLANs manufacturers understand this and provide alternate setup procedures for minimizing interference
between different communication systems,but the setup may require coordination with the system being used
by the client.Both the security and electromagnetic interference issues require the owner's approval and should
not be assumed acceptable.
Wireless signals are governed by electromagnetic wave propagation mechanisms.A visual analogy corre-
sponds to tossing a rock into a pool of water.If the pool of water has no obstructions,then there are concentric
ripples emanating from the center.This would correspond to free space signal propagation.On the other hand,if
the pool contains obstructions,then a wave is reflected and ror diffracted when it strikes an obstruction.The
resulting waves then constructively or destructively combine in certain regions of the pool.This corresponds to
the interaction of multipath components resulting from transmitting a signal in a cluttered environment.Due to
the presence of buildings,terrain or other obstructions multiple reflections are generated.Each of the resulting
electromagnetic waves travels along a different path,combining with a specific resulting power at different
locations.The received power is therefore dependent on where the receiver's antenna is located in relationship
to the transmit antenna and the obstructions in the environment.
5.Example
.
This hypothetical example is based on the construction of a sulfur recovery unit SRU inside the confines of
an operating crude oil refinery.The refinery is located near a small city.An SRU is used to extract excess sulfur
from the oil,and it is usually located near the outside of the refinery complex or at least near a road.An SRU
has steel towers and holding vessels that can be between three and four stories in height.There are steel pipes
and pipe racks throughout an SRU.
The SRU that is being considered in this example is 150 ft in width and 300 ft in length.The job trailers are
located approximately 900 ft away from the SRU.There are pipe racks with 6
Y
to 24
Y
pipes in them that are in
the line of sight between the trailers and the construction jobsite.The area is shown in Fig.6.The owner of the
facility has design and quality control representatives that are located in the trailers at this jobsite throughout the
( )
J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347342
Fig.6.Layout of site for hypothetical SRU example.
day.Most of the materials for use on this project are stored in a warehouse and laydown yard in another area of
the refinery approximately one mile from the site.
The contractor has approximately fifty people working on this project in five crews per shift.The contractor
wants the foremen of each of these crews to have access to the wireless communication system.The contractor
.
would like to meet information needs in the following categories with wireless technology:1 requests for
...
information RFI's,2 materials management,3 jobsite record keeping,and quality control rquality
assurance.Table 6 is a listing of all of the information needs,by subcategory that this contractor has identified.
This contractor estimates that only the jobsite record keeping information need will be used on a regular basis
.
two to three times per shift per foreman and the rest will be used on an as-needed basis.
Based on the information from Table 6,a summary chart for each of the information categories can be
formulated.This information is presented in Table 7.
Table 7 shows that the maximum data rate required for batched data is 13.65 kbps,for a variety of medium
and large file transfers.Additionally,this contractor has decided that medium quality voice will serve his
purposes.
With this information,the contractor can then consult Table 5 and eliminate certain types of technology from
consideration.Table 5 shows that the following wireless communication formats can support the information
...
needs that the contractor has identified:1 circuit-switched cellular modem,2 packet-switched SMR,3
.
CDPD,and 4 WLAN.
Because packet-switched SMR's and CDPD are based on packet-switched technology,they would be able to
marginally support the data rates dictated by the information needs summarized in Table 7.Furthermore,even if
the data rate that was required had been low enough for these two methods to support it,they would still be
eliminated as viable options because it was stated that this SRU was being built near a small city.Service for
packet-switched SMR's and CDPD are only typically available in large metropolitan areas.Therefore,the
service to support these two wireless communication techniques would not be available at this construction site.
Now that packet-switched SMR's and CDPD have been eliminated from consideration,the contractor will
..
see in Table 5 that he can only use the following:1 circuit-switched cellular modem,and 2 WLAN.
5.1.Circuit-switched cellular method
The circuit-switched cellular method requires that standard cellular phone service be available.Since this site
is near a small city,it is likely that there is cellular service available.However,the contractor must be sure of
this before he considers this technology further.For the purpose of this example,it will be assumed that cellular
service is available.The next step that a contractor should take is to find the cost of service from the cellular
provider.The hypothetical case explanation indicated that the contractor would have five different users at any
given time.The number of users may affect the pricing that he receives for the service from the cellular
provider.
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 343
Table 6
Information needs that have been identified for the hypothetical case
...
Information category Information subcategory Formats of Type file size Delay min Importance Data rate kbps
information transfer
.
Requests for information 1 Design and intent Voice -0.01 5 8±32
clarification Video -0.01 1 128±10,000
Batched data Small -1 4 0.68
Medium -1 4 13.65
Large -10 3 13.65
.
3 Contract specifications Voice -0.01 5 8±32
Video -0.01 1 128±10,000
Batched data Small -1 3 0.68
Medium -1 2 13.65
Large NF 1 )1
.
4 Contract drawings Voice -0.01 3 8±32
Video -0.01 1 128±10,000
Batched data Small -1 3 0.68
Medium -1 4 13.65
Large -10 4 13.65
.
Materials management 1 Access to company's Voice -0.01 4 8±32
material management Video -0.01 1 128±10,000
information Batched data Small -1 5 0.68
Medium -1 3 13.65
Large NF 1 )1
.
2 Material location Voice -0.01 4 8±32
Video -0.01 1 128±10,000
Batched data Small -1 5 0.68
Medium -1 3 13.65
Large NF 1 )1
.
Jobsite record keeping 1 Recording timesheets Voice -0.01 2 8±32
Video -0.01 1 128±10,000
Batched data Small -1 5 0.68
Medium NF 1 )1
Large NF 1 )1
.
2 Progress reporting Voice -0.01 2 8±32
Video -0.01 1 128±10,000
Batched data Small -1 4 0.68
Medium -1 2 13.65
Large NF 1 )1
.
Quality controlrquality 1 Reporting QCr Voice -0.01 3 8±32
assurance QA results Video -0.01 1 128±10,000
Batched data Small -1 5 0.68
Medium -10 4 13.65
Large NF 1 )1
The number of users that the contractor has on his wireless system may also affect the data transmission.The
.
advanced mobile phone system AMPS that is currently used in the United States in analog cellular systems
allows only 118 channels per cell.Since this contractor has only five users this limitation should not be a
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347344
Table 7
Summary of information needs and maximum data rate
..
Information category Formats of information transfer Type file size Data rate kbps
.
1 Requests for information Batched files Small 0.68
Medium 13.65
Large 13.65
.
2 Materials management Batched files Small 0.68
Medium 13.65
Large )1
.
3 Jobsite record keeping Batched files Small 0.68
Medium 13.65
Large )1
.
4 QCrQA Batched files Small 0.68
Medium 13.65
Large )1
tremendous consideration.However,if the contractor were working on a much larger site and needed several
hundred foremen to be able to have access,this limitation would become important.
Another issue that the contractor needs to consider for his batched communication is that this method is
circuit-switched and,therefore,may not be cost effective to send short batched files.Since most of the cellular
service providers in the country charge by the minute,it might become expensive for the contractor to send
short batched files.
The contractor would need to invest in hardware in order to be able to use the circuit-switched method.He
would need to purchase a laptop or pen-tab computer for each of his foremen.In addition,he would need to
purchase a cellular modem for each computer.For example,one of the modem listed is the Motorola Montana
w x
28.8 2.This modem has a data rate of 28.8 kbps,which exceeds the 13.65 kbps that is the maximum that
contractor identified.The only other hardware that the contractor will be required to purchase is a data
compatible cellular telephone and the cable to connect the modem to the phone.
To meet his live voice needs the contractor has two options.First,since the circuit-switched cellular method
already requires a service agreement with the cellular provider,the contractor could use this agreement and use
cellular phone service to meet his live voice needs.There are cellular modems available that allow simultaneous
transmission of data and voice.The contractor must also be aware that because of the rugged environment,the
large scale propagation issues need to be taken into consideration.Pipe racks,large metal towers and some of
the other items that are on this hypothetical site might cause propagation problems.Before the contractor
purchases equipment for the circuit-switched cellular option,he may want to walk through his site as well as
other parts of the refinery with a cellular phone and data device to get an idea how well it will perform in the
site's environment.The contractor's second option to meet his live voice needs would be to get a voice SMR
service.This could be as simple as a walkie-talkie.
5.2.The WLAN method
The WLAN method is the second technology that will be discussed.WLAN operate in the unlicensed bands
of the spectrum.Therefore,no service providers are needed and there are no service fees.A drawback to the
WLAN method is that it requires additional initial investment in equipment.In addition to the computers,the
contractor will need to purchase WLAN cards for each foreman.The contractor will also need to purchase
access points to the WLAN.Due to the size of the site that was described in the example,the contractor will
need to purchase at least two access points.Additional access points or repeaters may be necessary to provide
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347 345
adequate coverage,depending on environmental conditions.One other on-going expense that the contractor will
need to consider is that he will need to have someone who is responsible for the WLAN and its on-going
maintenance.
Propagation issues need to be considered with the WLAN as well.If the contractor had problems,he could
move the WLAN access points to minimize the interference that might be caused by the material and equipment
on the site.Also,since WLAN operate in an unlicensed band,there is the potential to have interference from
other users in the band.
WLAN currently do not have the capability to transmit live voice.Therefore,as with the circuit-switched
cellular option,another means of live voice will need to be used.The same two options,cellular phone service
or a SMR,are available to augment the WLAN option.
w x
There are seven different WLAN that are currently available 2.One is the AiroNet ArLAN 630-2400.This
model is capable of a data rate of 1r2 Mbps or 500 kbps.This data rate greatly exceeds the 13.65 kbps that the
contractor has identified as his maximum requirement.
One final issue that will be discussed is cost.For the circuit-switched cellular modem method,in addition to
.
the computers for each foremen,the contractor will be required to purchase a cellular modem;US$200±300,
..
a connection cable;US$50 and a harsh environment cellular telephone;US$400±500.Therefore,the
hardware cost range for adding circuit-switched cellular modems to the five foremen at the jobsite would be:
From:5 200q50q400 sUS$3250
.
To:5 300q50q500 sUS$4250
.
For the WLAN method,in addition to the computers for each foreman,the contractor will need to purchase a
..
WLAN card;US$400,as well as access points to the WLAN;US$1500 each.Based on the simple
geometry of the jobsite and location of field trailers,a minimum of two access points would be required.Due to
the variability in the propagation effects possible from the pipes blocking the line of sight between the field
trailer and jobsite,it is difficult to determine precisely the number of base stations required.To obtain reliable
.
communication service throughout the jobsite if this is required may take three to four base stations or
.
repeaters.Therefore,the hardware cost range for adding WLAN to the five foremen at the jobsite would be:
From:5
)
400 q 2
)
1500 sUS$5000
..
) )
To:5 400 q 4 1500 sUS$8000
..
For both the circuit-switched cellular modem and WLAN approaches,these cost estimates represent just an
approximation of the hardware expenses at the time of this publication.It is important to note that there will be
software,setup,on-going maintenance and WLAN support expenses to consider that will probably greatly
outweigh the initial hardware expenses for any of the wireless communication systems that have been discussed.
6.Conclusions
There are many ways that the construction industry might benefit from incorporating wireless communication
technology onto its jobsites.First,wireless communication technology will permit information to flow in a
faster,more timely manner between the field and the trailer.Wireless communication techniques will allow the
parties to communicate without leaving their respective locations.This alone will make it more convenient for
the parties to communicate with one another.Additionally,the speed with which information can be
communicated can be increased through the use of wireless communication technology.
Second,wireless communication has the potential to provide the personnel in the field with information
while they are actually performing work.This means that if a crew in the field has a problem,the foreman has
the means to consult with the trailer for a solution without having to actually go to the trailer.The faster the
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J.M.de la Garza,I.Howitt rAutomation in Construction 7 1998 327±347346
answers to problems can be received,the less likely it is that a crew will need to stand idle waiting for
information.
One final consideration is that if supervisory personnel,foremen and ror superintendents need to leave the
field less often,their crews will be unsupervised less often.Wireless communication technology is a means to
allow the supervisory personnel at a construction site to stay in the field,and hence affect productivity.
Notwithstanding the subjectivity involved in ranking the information needs of Table 2 with respect to payoff,
it is reasonable to assume that materials management,equipment management,requests for information,and
jobsite record keeping would be included in the first tier,while the rest of the information needs would belong
in the second tier.
If a company is considering using wireless communication technology on its jobsite it should examine
carefully the applications that are being considered for wireless use.An application that is being considered for
wireless technology should have two important components.First,it needs to be an application that is time
critical.If time is not a major consideration,then the information could be transmitted between the trailer and
the field,using traditional methods.Second,it should be an application that cannot be done using hardwired
means.If it is an application that needs to be performed in the field,it generally cannot be done using hardwired
methods.
The primary reason for mentioning these two criteria is financial.Many of the wireless technologies that
have been considered require a service fee that must be paid when they are in use.If a given transfer of
information can be done using hardwired or conventional means it will be less expensive than using wireless
means.If the information is not time critical,then it can wait until a break or the end of a shift when a foreman
would normally be going to the trailer.The task of designing and deploying wireless communications
technology at the jobsite is as technical and complex as the task of configuring a multi-functional fleet of earth
moving equipment.Hence,it should be assigned to individuals possessing the necessary technical background in
digital communications as well as possessing the wisdom to recognize their technical competence limits and the
circumstances warranting the advise of third-party communications consultants.
The construction industry at-large will profit from leveraging walkie-talkie wireless Íoice communication
with wireless data communication.Wireless technology like cellular modems,WLAN,CDPD modems,pagers,
and satellites can do it now.For a given construction firm,what is important is to understand that there is a
trade-off between the Íalue of information and the cost of obtaining itÐboth Íalue and cost are time-depen-
dent variables.The marginal benefit of obtaining the information wirelessly must exceed the marginal benefit of
conventional practice.
Acknowledgements
The Construction Industry Institute sponsored this project.The views,findings,and conclusions expressed in
this paper are those of the authors and do not necessarily represent those of the sponsor.We would like to
express our appreciation to the people who helped in this study.They are Mr.John Bennett,H.B.Zachry;Jason
Gagnon,Virginia Tech Graduate Student;Mr.Mikkel Hansen,Texaco;Mr.Joseph St.Julien,H.B.Zachry;Dr.
.
William Stone,National Institute of Standards and Technology NIST;Mr.Alan R.Waldbusser,Research
Team Chairman,TPA.
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