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101
dramatically reduced when compared to the other
identification methods
[7].
RFID is an automatic identification system that carries
information around using radio waves
[7]. This technology is
emerging as the ultimate tool to help supply chain automation.
The impact of that automation in shelf replenishment policy is
really significant
[8]. It eases the replenishment processes
minimizing human periodic verifications and it also allows
reduced shelf dimensions and a faster and more accurate
backroom and store inventories
[9].
C. Frequency Ranges
Four frequency ranges are adopted in RFID: LF (Low
Frequency, 125-133 kHz), HF (high Frequency, 13.56 MHz),
UHF (Ultra-High Frequency, 862-870 MHz) and microwaves
(2.5 GHz / 5.8 GHz)
[10].
D. Main Components
The main specific components of a RFID system are:
electronic label (called tag), the reader and its associated
antennas, besides the computer which runs the application
software. These are the main components located in the front
end of an identification system, like a shop, for instance.
There are two basic types of chip used in RFID tags: read-
only and read-write. Depending on the power source, tags can
be classified as active, passive or semi-passive [11].
Each type of tag presents a minimum power requirement to
respond properly to the reader. Depending on the type and the
standard they belong, there is a specification for this
parameter. For instance, 10 dBm is the minimum power level
required to read EPC tags [12].
The readers use antennas to send digital coded information
in a waveform using amplitude modulation or load modulation
[10]. The readers can be found in handhelds, mounted in
support brackets or fixed in furniture or walls.
A RFID reader can have one or more antennas connected to
it. The typical parameters of a reader are: transmission and
reception mode and polarization. Transmission modes are:
monostatic, bistatic and multistatic [13]. In monostatic mode,
the same antenna transmits and receives signals during the
reading cycle. The bistatic type has antennas working in pairs:
one always transmits and another always receives. The
multistatic system is a mix of the monostatic and the bistatic
configurations. Similar to a bistatic interrogator, the
multistatic has their antennas working in pairs, but like the
monostatic systems, both antennas send and receive signals in
an alternated mode.
The polarization of an antenna can be linear or circular. A
linear polarized antenna irradiates the signal only in the
propagation direction plane. Linear propagation can be
horizontal, where the propagation runs in parallel to the earth
plane, or it can be vertical, where the signal propagates
perpendicularly to the earth plane [14]. If the direction of the
electrical component spins around the propagation axis, the
antenna is circular polarized [15].
E. EPCglobal
Regarding the issues concerned with RFID, there are two
main organizations defining the standards (conflicting
sometimes): ISO and Auto-ID Centre, which is now
controlled by EPCglobal.
EPCglobal, Inc. (http://www.epcglobalinc.org) was created
aiming to establish and support the Electronic Product Code
(EPC) Network as a global specification to keep a unique
identification standard for every item manufactured.
EPC is a 96 bit number composed of a header and three
data sets. Depending on the application specification, there
may be many iterations of EPC
[11]. A typical EPC code is
shown on the Table I.
TABLE I
EPC
FORMAT
Electronic Product Code Type 1
02 0000A69 00012D 000112DE1
HEADER
(8 bits)
EPC MANAGER
(28 bits)
OBJECT CLASS
(24 bits)
SERIAL NUMBER
(36 bits)
II. O
BJECTIVES
The main objective of this paper is to verify the feasibility
of using a smart shelf system with RFID as a core technology
for a lean supply system. The focus is on retailers supply
chain automation, intending to increase shelf replenishment
efficiency, avoiding out-of-stock situations.
The current analysis involves the arrangements of RFID
equipments and the definitions of a prototype layout. As the
underlying technology is radiofrequency (RF), lots of issues
regarding interference and performance arise, because each
kind of material can affect the RF signal in a different way.
The whole methodology of design and the tests applied to
validate the smart shelf prototype are also explained. No
software solution is evaluated.
III. S
MART SHELF SYSTEM
A smart shelf application allows a very accurate inventory
of products by means of automated processes. If any item is
removed from or added to the shelf, some action of
replenishment or expiration date verification, for instance, can
be applied instantly. A simulation shows that the shelf lost
sales quantity decrease up to 99 percent with a RFID
automated shelf
[8].
In short, the scanning cycle of tagged objects occurs when a
computerized system requests the reader to communicate with
the tags in the read zone. The reader emits a RF signal through
its antennas to the tags attached on items. The tags send a
response with their unique numbers back to the reader, so
those objects can be identified.
A. Initial Specifications
After a deep analysis of the RFID market, some decisions
had to be made in order to limit the number of variables
involving any RFID item-level application. It was decided to
use only UHF GEN2 equipments to be tested, instead of the
HF inductive coupling systems. This choice was supported by