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Towards hybrid GPS/RFID positioning
G
PS and RIFD-based real
Container termi-
these systems typically cost over
time location systems US$500 per unit of container han-
(RTLS) are two leading
nal automation
dling equipment. Even with
technologies in automated con- DGPS, terminals have found sub-
tainer and equipment tracking sys-
can benefit from
stantial interference problems un-
tems at container terminals.
hybrid solutions
der quay cranes or in the stacks.
Initially all position detection With RFID, several locating
systems (PDS) used Differential
leveraging the
options are possible. Simple zone
GPS (DGPS) systems on container reads will give 10-100m accuracy
handling equipment to track its
advantages of
dependent upon antenna systems.
position and record container lo- With full RTLS, and without in-
cations. RTLS is a newer technol-
GPS and RFID*
terference (ie clear line of sight to
ogy based on multiple RFID read- a reader) ±3m accuracy can be
ers “reading” active RFID tagged expected. This is acceptable for
equipment and a software engine minal generally focuses on discrete rough tracking like chassis locat-
* This article was written by
Michael Dempsey, president,
calculating position based on time operational areas (gate, yard, rail ing ,but not for container posi-
Radiantwave Consulting, a
distance of arrival (TDOA) of the and the wider port community) tioning or other applications.
consultancy focused on marine and
RFID signals. An accurate loca- and the benefits realised in each. GPS has the accuracy advan-
intermodal process automation
tion requires a tag to be “visible” Comparing the “best fit” tech- tage, but it is generally not easily
to three or four readers. nology for any area involves a
Container handlers with RFID antennae mounted high on the mast to reduce
solutions
signal interference from container stacks
leveraged by multiple stakeholders.
matrix of analysis points with four Terminals need DGPS but the optimisation software at a lower
Evaluating the options key criteria: infrastructure costs; cost of infrastructure. RFID on a poles to support dense arrays of wider transport community does infrastructure cost than RTLS.
The question for terminal opera- accuracy; cost per tracked asset; localised basis is generally low readers, RTLS can be expensive not need or want to pay for this Tracking street trucks in the
tors is which technologies will and “leveragability.” The latter re- cost (for example zonal readers at and more impractical to deploy level of accuracy. yard is more challenging. Full vis-
best address the need of their con- fers to how easily the system can a gate lane), but where full RTLS than GPS. RFID, on the other hand, is ibility requires handing out DGPS
tainer terminal today and in the deliver a benefit to other stake- capabilities are required, the cost While GPS is now cheap and highly leveragable inside and out- receivers at the gate or a full RTLS
future and how do they evaluate holders in the supply chain. of covering a large terminal can ubiquitous on the consumer mar- side the terminal. Active tags are system with active tags on every
systems on the market? Process The popularity of GPS has become prohibitive. If high fibre ket, container terminals need much cheaper and there is a wide truck. The PierPass program took
automation in the container ter- been based on the generally low optic cabling has to be run to light DGPS for sub-metre accuracy and range of deployment options. Pas- the latter approach but many ter-
sive tags can provide simple truck minals today are moving away
ID at very low cost but they se- from RTLS to more localised
verely limit the ability of con- RFID solutions. They lose real
tainer terminals to use the tag for time “snail trail” visibility of street
automating processes at the gate trucks, but enjoy reduced infra-
or in the yard. structure costs.
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a71 Chassis, general cargo and ro-ro track-
Clear preferences ing: Terminals which handle one or
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Looking at the way container ter- more of these assets must deal with
minals have implemented GPS high quantities of tracked assets. Tra-
and RFID technology to date re- ditional RTLS has been the answer
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veals that there are clear prefer- to date as the high infrastructure
ences across different parts of the cost can be amortised across the
terminal: large asset base.
a71 Port Community: Active RFID a71 On the quay: Using DGPS to lo-
is the standard for road truck tag- cate container handling equip-
ging programmes, including ment under quay cranes is diffi-
PierPass in the Port of Los Ange- cult as the signal is lost or “fuzzy”
les/Long Beach, Georgia Port and lane discrimination is difficult.
Authority (GPA) and DPW Jebel Until recently, RTLS deployed
Ali. The tags are low cost, provide across the terminal was also prob-
better accuracy for security gating lematic as readers located on the
and can be used in a variety of landside of the quay could not
applications external to the port. produce the accuracy needed un-
In some cases, active RFID is der the hook.
being used to gain greater visibil- What is emerging is the con-
ity into container movements out- cept of RTLS within the “quay
side the terminal. The GPA, for crane box,” effectively creating a
example, uses solar-powered mo- mini-RTLS coverage area under
bile readers on feeder roads to each crane. The container han-
monitor inbound gate traffic, dling equipment is equipped with
while in Alaska, Horizon Lines is a low cost tag (US$75) and an
involved in a project using read- RTLS reader set costing around
ers at key points on the highways US$10,000 per crane provides
to send messages to retailers of in- highly accurate container handling
coming containers. equipment lane positions.
Some port authorities have
considered GPS combined with Hybrid applications
cellular systems for drayage trucks. Most recently a range of hybrid
Conceptually, if the exact location solutions have emerged to over-
of a truck can be determined and come some of the issues associ-
data can be communicated to the ated with a single technology ap-
driver, the port can control the proach. “Localised” RFID can
flow of trucks into the terminals provide a solution in areas where
from longer distances. However, DGPS has visibility problems
the cost burden of equipping dray without the infrastructure cost of
trucks with GPS and cell systems full scale RTLS.
remains beyond the funding Austria-based Identec Solu-
reaches of most ports. tions has developed Intellifind, a
a71 Gates: Again active RFID ap- system for chassis, general cargo
pears to be the logical choice. Ac- and ro-ro applications. Assets are
tive tags can be read at discrete “tagged” with a low cost active tag
positional markers in a gate proc- at the gate or in the yard. When
ess (OCR portal, weigh scale, ped- the asset is placed in the yard, the
estal), providing high accuracy tag is scanned and associated with
without the need for full RTLS. a GPS position from an RDT ter-
Moreover, if the tags can be minal with a GPS card.
leveraged within the terminal for Alternately, container handling
other automation processes, then equipment can be equipped with
all stakeholders benefit. an RFID reader and GPS device
GPS at the gate does not pro- and the asset locations automatically
vide the lane and positional accu- mapped to a geo-spatial location by
racy required. A ±10m accuracy the Intellifind application.
could be three lanes difference. Another example is Symeo’s
a71 Yard: Mixed technology domi- Local Positioning Radar system
nates. DGPS remains the most ef- that uses frequency modulated
fective method for tracking con- continuous wave technology to
tainer handling equipment in transmit electromagnetic signals
terms of accuracy, infrastructure from container handling equip-
cost and leveragability. Exact ment to “echo” units on STS and
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equipment locations can gener- RTG cranes. SYMEO’s technol-

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ate accurate yard inventory and ogy is also used in Kalmar’s Smart-
data input for equipment Spot tractor positioning system. a74
28 February 2009
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