ETSI TR 102 436 V1.2.1 (2008-02)

Technical Report
Electromagnetic compatibility
and Radio spectrum Matters (ERM);
Short Range Devices (SRD) intended for operation
in the band 865 MHz to 868 MHz;
Guidelines for the installation and commissioning
of Radio Frequency Identification (RFID) equipment at UHF

2 ETSI TR 102 436 V1.2.1 (2008-02)

Reference
RTR/ERM-TG34-005
Keywords
ID, radio, short range, terrestrial
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3 ETSI TR 102 436 V1.2.1 (2008-02)
Contents
Intellectual Property Rights.5
Foreword.5
1 Scope.6
2 References.6
2.1 Informative references.6
3 Definitions, symbols and abbreviations .7
3.1 Definitions.7
3.2 Symbols.7
3.3 Abbreviations.8
4 Principles of operation.8
4.1 Characteristics of RFID at UHF .9
4.1.1 Antennas.9
4.1.2 Data Rates.10
4.1.3 Intermodulation Products.10
4.1.4 De-tuning and absorption .10
4.1.5 Shielding.11
4.1.6 Transparent materials.12
4.2 Operation in the band 865 MHz to 868 MHz according to EN 302 208 .12
4.2.1 Dense interrogator mode.12
4.2.2 4 channel plan.13
4.2.3 Multiple interrogators.13
4.2.4 Sharing the spectrum with SRDs .13
4.2.5 Fixed and portable readers.14
4.2.6 Near field systems.14
4.3 Operation in the band 868 MHz to 870 MHz under EN 300 220 .14
4.3.1 Hand held readers .15
4.3.2 Vehicle mounted readers.15
4.3.3 Proximity printers.15
5 Preliminary considerations.16
5.1 Acceptance Tests.16
6 Site considerations.16
6.1 Site survey.16
6.2 Basic principles.17
6.3 Antenna configurations.17
6.4 Configurations for near field systems at UHF.18
6.5 Tags using E.M. transmissions.19
6.6 Near field tags .20
6.7 Sources of interference.20
7 Recommendations for installation.20
7.1 Antenna fixtures.20
7.2 Selection of antennas.21
7.3 Positioning of the antenna .21
7.4 Outside antennas .21
7.5 Cabling.21
7.6 Earthing (Fixed Interrogators).22
7.7 RFID and Short Range Devices operating within the same area.22
8 Commissioning.22
8.1 Setting to work.22
8.2 Site records.22
9 Maintenance .23
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4 ETSI TR 102 436 V1.2.1 (2008-02)
Annex A (informative): Conversion of units of measurement.24
A.1 Measurements of power .24
Annex B (informative): Earthing systems.25
B.1 Earth System Minimum Requirements .25
B.2 Typical electrode and array characteristics .25
B.2.1 Vertical rod.25
B.2.2 Buried ring.26
B.2.3 Buried grid.26
B.2.4 Measurement of soil resistivity .26
B.3 Earthing of support structures and buildings.28
B.3.1 Ancillary equipment external to buildings .28
B.3.2 Metal support poles on buildings .28
B.3.3 Metal security fences.28
B.4 Interconnection of lightning protection systems with power supply earthing arrangements .28
Annex C (informative): Prefabricated portals.29
Annex D (informative): Commissioning procedure .30
Annex E (informative): Bibliography.31
History .32

ETSI
5 ETSI TR 102 436 V1.2.1 (2008-02)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://webapp.etsi.org/IPR/home.asp).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Electromagnetic compatibility and Radio
spectrum Matters (ERM).
Every TR prepared by ETSI is voluntary. This text should be considered as guidance only and does not make the
present document mandatory.
The present document has been produced by ETSI in response to a perceived need by RFID manufacturers, installers
and end users for general guidance on the installation and commissioning of RFID systems operating at UHF.
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6 ETSI TR 102 436 V1.2.1 (2008-02)
1 Scope
The present document provides recommendations to system integrators and installers on good practice for the
installation and commissioning of RFID systems operating at UHF at power levels up to 2 W e.r.p. Guidance is given
on making best use of the available spectrum as envisaged within the ETSI standard EN 302 208 [1]. In addition the
present document covers the use of reduced power RFID devices at UHF, such as hand held readers and proximity
printers, operating in accordance with EN 300 220 [2]. This includes operation in the sub-bands 869,40 MHz to
869,65 MHz at power levels of 500 mW and 869,7 MHz to 870,0 MHz at power levels of 5 mW. In particular the
present document considers the practices necessary to minimize interference in situations where multiple interrogators
are co-located in close proximity. Failure to take the necessary precautions could lead to degradation in system
performance. The present document also endeavours to cover the approaches necessary to ensure that the operational
requirements of the end-user are met.
The present document concerns itself with radio matters only. It does not provide any guidance on computer hardware
and software that may be used to process the data recovered from tags.
Many of the techniques recommended in the present document have been subject to practical tests in a working
distribution centre. However each application is different and the techniques recommended in the present document
may not be applicable in all situations.
End users may wish to make use of the present document as a general guide.
The present document does not cover matters related to Health and Safety. End-users and system integrators should
familiarise themselves with the relevant national and international standards.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• Non-specific reference may be made only to a complete document or a part thereof and only in the following
cases:
- if it is accepted that it will be possible to use all future changes of the referenced document for the
purposes of the referring document;
- for informative references.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
For online referenced documents, information sufficient to identify and locate the source shall be provided. Preferably,
the primary source of the referenced document should be cited, in order to ensure traceability. Furthermore, the
reference should, as far as possible, remain valid for the expected life of the document. The reference shall include the
method of access to the referenced document and the full network address, with the same punctuation and use of upper
case and lower case letters.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
2.1 Informative references
[1] ETSI EN 302 208 (Parts 1 and 2): "Electromagnetic compatibility and Radio spectrum Matters
(ERM); Radio Frequency Identification Equipment operating in the band 865 MHz to 868 MHz
with power levels up to 2 W".
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7 ETSI TR 102 436 V1.2.1 (2008-02)
[2] ETSI EN 300 220 (Parts 1 and 2): " Electromagnetic compatibility and Radio spectrum Matters
(ERM); Technical characteristics and test methods for radio equipment to be used in the 25 MHz
to 1 000 MHz frequency range with power levels up to 500 mW".
[3] CEPT ERC/REC 70-03: "Relating to the use of Short Range Devices (SRD)".
[4] CEPT ECC Report 037: "Compatibility of planned SRD applications in 863 - 870 MHz".
[5] ISO 18000-6: "CD Information Technology RFI for item management Part 6 Parameters for air
interface communications at 860 - 960 MHz".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
assigned frequency band: frequency band within which the device is authorized to operate
dense-interrogator mode: RFID operating mode in which multiple, nearby interrogators can transmit simultaneously
in a channel without incurring noticeable performance degradation
frequency agile technique: technique used to determine an unoccupied sub-band in order to minimize interference
with other users of the same band
interrogator: equipment that will activate an adjacent tag and read its data
NOTE: It may also enter or modify the information in a tag.
link frequency: frequency offset of the tag backscatter with respect to the centre frequency of the interrogating signal
load: collection of tagged items that are carried on a transportable device
listen before talk: action taken by an interrogator to detect an unoccupied sub-band prior to transmitting (also known
as "listen before transmit")
preferred channel: channel assigned to an interrogator which, provided it is available, is selected automatically as the
channel of first choice
radiated measurements: measurements which involve the absolute measurement of a radiated field
reading range: maximum range at which a tag may be read by an interrogator
secondary channel: channels assigned to an interrogator, which is selected in the event that use of the primary
preferred channel is not possible
tag: transponder that holds data and responds to an interrogation signal
3.2 Symbols
For the purposes of the present document, the following symbols apply:
dB decibel
dBm power in decibels relative to 1 mW
d distance
λ wavelength
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8 ETSI TR 102 436 V1.2.1 (2008-02)
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AFA Adaptive Frequency Agility
AM Amplitude Modulated
CEPT European Conference of Postal and Telecommunications Administrations
E.M. ElectroMagnetic
e.r.p. effective radiated power
ECC Electronic Communications Committee
EMC ElectroMagnetic Compatibility
ERC European Radio communication Committee
FM Frequency Modulated
LBT Listen Before Talk
PIB PolyIsoButylene
PM Phase Modulated
R&TTE Radio and Telecommunications Terminal Equipment
RCD Residual Current Devices
RF Radio Frequency
RFID Radio Frequency IDentification
SRD Short Range Device
UHF Ultra High Frequency
4 Principles of operation
A basic RFID system comprises an interrogator with its associated antennas and a collection of tags. The antennas are
arranged to transmit their signal within an interrogation zone. Tags are attached to either animate or inanimate objects
that are to be identified. When a tag enters an interrogation zone, it is activated by the transmitted signal from the
interrogator. Typically the tag will respond by sending its identity and possibly some associated data. The identity and
data from the tag is validated by the receiver in the interrogator and passed to its host system. A block diagram of the
principle is shown in figure 1.
To Host
To Host
Tag Interrogator
Tag Interrogator
System
System
Figure 1: Principle of RFID
A sophisticated protocol is used to handle the transfer of data between the interrogator and tags. This ensures the
integrity of data transfer and may include error checking and correction techniques. In addition the protocol handles the
process for writing data to the tag and controls the procedure for reading multiple tags that may be present
simultaneously within the same interrogation zone.
Across the whole of the radio spectrum three different forms of communication are used for the transfer of information
between interrogators and tags. These are:
• Electrostatic.
• Inductive.
• Electromagnetic waves.
The present document confines itself solely to electromagnetic waves and near field techniques since they are the only
forms of communication that are relevant for RFID at UHF.
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9 ETSI TR 102 436 V1.2.1 (2008-02)
To transfer information between an interrogator and a tag it is necessary to superimpose the data on a carrier wave. This
technique is known as modulation. Various schemes are available to perform this function. They each depend on
changing one of the primary features of an alternating sinusoidal source in accordance with the transmitted data. The
most frequent choices of modulation are amplitude (AM), frequency (FM) and phase (PM).
Tags exist in a range of shapes and sizes to satisfy the particular needs of their intended application. Many tags are
passive and derive the power for their operation from the field generated by the interrogator. However some tags are
fitted with batteries, which may provide additional features (e.g. sensors) and may enable them to operate at
significantly greater ranges.
4.1 Characteristics of RFID at UHF
UHF transmission takes place by means of electromagnetic (E.M.) waves. At these frequencies E.M. waves have
properties that have many similarities to light. Transmissions travel in a straight line and the power of the received
signal is a function of the inverse square of the distance from its source. For example if the distance from a transmit
antenna is doubled the received power drops to one quarter. This property means that it is possible with UHF systems to
achieve significant reading ranges. Operation in the UHF band also makes it possible to transfer information at high
data rates. Both of these characteristics make UHF systems well suited for use in applications where tags are moving at
speed or in which there are multiple tags present in an interrogation zone.
UHF can present the installer with a number of challenges. Electromagnetic transmissions at UHF are readily reflected
from many surfaces. The reflections can cause the activation of unwanted tags and can also give rise to an effect known
as standing wave nulls. These can produce points within the interrogation zone where there are very low levels of
signal. UHF signals also experience significant levels of attenuation in the presence of water. In applications where
water may be present, system integrators must therefore make suitable provision for a reduction in reading range during
the design and configuration of the installation.
Operation is also possible using near field coupling between an interrogator and tags. This technique is useful in
situations where there are many tags in a confined area and it is necessary to control the transmitted field. Near field
systems generate magnetic fields that attenuate in accordance with the inverse cube of distance. Their properties
therefore make them useful for reading tags at close range while avoiding activation of tags outside the area of interest.
Near field techniques require the use of special antennas that are configured in the shape of a loop. Some tags have
antennas that are capable of operating with both E.M. transmissions and near field coupling.
4.1.1 Antennas
At UHF the shape of the interrogation field generated by the E.M. antennas of an interrogator will typically be in the
form of a cone. The angle subtended between the half power (or 3 dB) points of this cone is known as the beamwidth.
Often beamwidth is specified in both horizontal and vertical values, which need not necessarily be the same. In many
installations the long reading ranges possible at UHF mean that tags outside the wanted interrogation zone are
inadvertently activated. The use of antennas with a narrow beamwidth provides one means by which it is possible to
limit the area where tags may be read.
The most common type of antenna used at UHF is the patch antenna. This typically has a beamwidth of the order of
70 degrees. The patch antenna is fully satisfactory for many short to medium range applications where there are no
other interrogators and unwanted tags in the immediate vicinity. In applications where longer reading ranges are
required it may be necessary to control the extent of the interrogation zone more precisely. A first order of improvement
may be achieved by using a variant of the standard patch antenna that is physically larger. This makes it possible to
produce antennas with a horizontal beamwidth down to 30 degrees. Other types of antenna exist with narrower
beamwidths. One of these is the helical antenna, which can have a beamwidth of as little as 10 degrees. This narrow
beamwidth makes it possible to generate an interrogation zone that is very directional.
As the beamwidth of an antenna is reduced the transmitted power is compressed into a smaller volume, which produces
increased field intensity. This effect is quantified by the term "antenna gain". Since the radio regulations limit the
maximum field level that is permitted, it is necessary to reduce the level of power generated by the interrogator to
compensate for the increased gain of the antenna. Where the use of different antennas is allowed by the manufacturer,
details of how this adjustment should be carried out should be included within the product manual for the interrogator.
Generally transmissions from the antenna of the interrogator will be circularly polarized. This eliminates differences in
the reading range of tags caused by their orientation in the x and y planes (but not the z plane, which is the direction of
travel of the radio wave). The variation of reading range with orientation in the z plane is considered under
"Recommendations for mounting tags" in clause 6.5.
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10 ETSI TR 102 436 V1.2.1 (2008-02)
4.1.2 Data Rates
The maximum data rate of the communication link from the interrogator to the tag (sometimes called the downlink) is
determined by the size of the permitted channel of operation of the interrogator. The size of the channel is specified in
ERC/CEPT 70-03 [3] and is effectively a fixed parameter. For channels of 200 kHz channel spacing as defined in
annex 11 of ERC/CEPT 70-03 [3] the maximum possible data rate is of the order of 40 kbits per second. However the
protocol used for transferring the information includes error checking and other features, which reduce the effective
speed of information transfer. Details of the agreed standard data rates are included in ISO 18000-6 [5].
In most situations the response from the tag (sometimes called the uplink) will lie in the same, or adjacent channels as
the downlink. This will place a practical limit on the achievable data rate. Where interrogators operate in accordance
with the 4 channel plan as specified in EN 302 208 [1], the tag may be set to operate at link frequencies of
approximately 300 kHz. In such circumstances data rates of 75 kbits per second are achievable.
However EN 302 208 [1] also permits the wanted signal from the tag to occupy the entire designated band from
865 MHz to 868 MHz provided that the levels specified in the spectrum mask are met. For some applications this
provides scope for manufacturers to create systems with substantially faster uplinks, which could provide significant
benefits. Where this technique is used, system designers must ensure that any transmissions from other nearby
interrogators do not block the response from the tag. This implies the need for some form of system planning to manage
either the timing of transmissions or the permissible sub-bands of operation.
4.1.3 Intermodulation Products
Where two or more devices are sited close to each other and are transmitting at similar frequencies, they may interfere
with each other. This can arise through the generation of intermodulation products. These are unwanted transmissions
that occur at frequencies that are at multiples of the sums and difference of the transmitting frequencies.
Intermodulation products can adversely affect the performance of both interrogators and tags.
The effect of intermodulation products may be reduced to an acceptable level by reducing the power received from
adjacent transmitters. This may be achieved either by the introduction of shielding or by increasing the physical
separation between transmitters. As a general guide for acceptable operation the power received by an interrogator or
tag from an adjacent transmitter should be at least 20 dB less than the power received from the wanted transmission.
An alternative mitigation technique is to arrange for adjacent transmitters to operate on different channels. The
frequencies must be sufficiently spaced apart that any intermodulation products do not degrade the performance of the
device. From practical tests and measurements it has been determined that for adjacent interrogators and their tags to
operate satisfactorily, the frequency separation between them should be at least 1 MHz.
4.1.4 De-tuning and absorption
The proximity of certain materials to UHF tags may cause a significant reduction in their reading range. This effect is
due predominantly to de-tuning of the resonant frequency of the tag. Spacing the tag a small distance away from the
material can significantly reduce this effect. However the application may impose a restriction on the extent to which
spacing is acceptable. Alternatively where the material to be tagged is known in advance, it may be possible to adjust
the tuning of the tag to compensate. Nevertheless recovery of the full free space reading range is unlikely to be
achieved. This difference is due to power absorption by the material.
In situations where an electromagnetic wave meets a boundary between two dissimilar materials, some of the energy is
reflected at the surface and some of the energy passes into the material. The proportion of the energy that passes into the
material is a function of its physical properties (known as its dielectric constant). This process is repeated at each
boundary between two dissimilar materials.
Where a tag is read through an object the consequent reduction in the level of signal reaching the tag will reduce its
reading range. Some indication of the scale of reduction in reading range caused by different materials is given in
table 1. The figures in the table are based on some informal tests and are illustrative only.
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11 ETSI TR 102 436 V1.2.1 (2008-02)
Table 1: Typical effect of materials on performance
Reference Distance (cm) Range (cm) (R/Rref)**2 Loss dB
Scenario
Air 200 200 1,00 0,00
Tag on front of plastic case 200 180 1,23 0,90
Tag on front of plywood sheet 200 131 2,33 3,68
Tag on front of wood block 2,5 cm deep 200 120 2,78 4,44
Tag on front of paper 3 cm thick 200 108 3,43 5,35
Tag on front of empty plastic jug 200 149 1,80 2,56
Tag on rear of empty plastic jug 200 138 2,10 3,22
Tag on front of plastic jug filled with tap water 200 46 18,90 12,77
Tag on rear of plastic jug filled with tap water 200 31 41,62 16,19
Tag behind metal mesh 10 x 10 cm 200 28 51,02 17,08
Tag behind metal mesh 1 x 1 mm 200 10 400,00 26,02

NOTE: For the purpose of making these measurements the transmit level from the interrogator was set to a
constant value.
An associated effect, which can also reduce the reading range of a tag, is its proximity and orientation with respect to
other adjacent tags. The effect is greatest where tags are parallel with each other since this produces the highest level of
mistuning and absorption. A similar situation arises where a second tag is positioned a short distance behind the first
one and in line with the transmission path from an interrogator. The tag nearest to the interrogator creates a "shadow",
which reduces the field available to power the tag that is further away.
It is important for end-users to understand and assess the impact of all of the above effects on their application.
In applications in which near field techniques are used the above effects will be significantly reduced.
4.1.5 Shielding
A particular difficulty with systems operating at UHF is that the E.M. signal transmitted by an antenna may extend over
a significant distance. Situations may therefore arise where tags outside the wanted interrogation zone may
inadvertently be activated. The responses from these unwanted tags may be read by the interrogator and passed to its
host. It is important for installers to be aware of this problem and ensure that the size of the interrogation field is the
minimum necessary and does not extend into areas that may contain unwanted tags. This requirement may create
particular difficulties in situations where adjacent interrogation zones and storage areas are physically close to each
other. One technique that may be used to contain the interrogation zone is shielding. There are two possible approaches,
which are:
• Reflection of the transmitted signal.
• Absorption of the transmitted signal.
The reflective approach involves placing an electrically conductive surface in the path of the transmitted signal. The
radio signal is unable to pass through the conductive surface but instead is reflected off it in a similar manner to light
reflected by a mirror. While this stops the transmitted signal from passing into the unwanted area, consideration must be
given to the path of the reflected signal. Since very little power is dissipated in the reflection process, the reflected
signal may bounce off yet further surfaces and end up in unwanted areas. It has also to be remembered that reflections
may create holes in the field (due to standing wave nulls), which may prevent the activation of wanted tags. Not all
situations are therefore amenable to the use of reflective materials.
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12 ETSI TR 102 436 V1.2.1 (2008-02)
Materials with good properties of electromagnetic absorption may assist in overcoming the problems of unwanted
reflections. As the transmitted signal passes into the absorptive material its energy is largely dissipated. What energy
remains either passes through the material or is reflected by it to emerge at much reduced levels. If electromagnetic
absorption materials are used, it is important that the material selected is of the correct thickness and suitable for the
intended frequency. Materials with phase shifting properties may also provide a means to reduce field levels but they
should be used with great care. Correctly applied, E.M. absorbent materials will help overcome the problem of reading
unwanted tags outside the interrogation zone. The reduced reflections will also lower the ambient signal level within the
installation, which will assist the operation of multiple interrogators.
Reflective materials have the advantage that they are low cost. A thin metal sheet works well although it is also possible
to achieve a very acceptable performance using wire mesh materials. Absorption materials are significantly more
expensive and less robust. Furthermore in outdoor applications it may be necessary to protect them from the
environment, which may reduce their efficiency. However in situations where the presence of reflected waves is not
acceptable, absorption materials may provide the most satisfactory technical solution.
4.1.6 Transparent materials
Transparent materials permit radio frequency waves to pass through them at the frequency of interest with very low
loss. An example of where transparent materials can perform an important role is as a means of physical protection.
This may be particularly relevant in the case of antennas and E.M. absorbent materials, which may be exposed to the
elements and to possible physical damage. Note that if a transparent material is permanently mounted in front of an
antenna, it may be beneficial to increase the power supplied to the antenna to compensate for any loss through the
transparent material.
4.2 Operation in the band 865 MHz to 868 MHz according to
EN 302 208
4.2.1 Dense interrogator mode
To enable multiple interrogators to transmit simultaneously in the same geographic space, EN 302 208 [1] specifies the
use of a 4 channel plan. To obtain maximum benefit from this arrangement, it is recommended that RFID systems
operate in the dense interrogator mode.
The principle of the dense interrogator mode is shown in the diagram at figure 2 and is illustrative only.
2 W e.r.p.
in 200 kHz
channel
Tag response
< -20 dBm e.r.p.
Figure 2: Principle of dense interrogator mode
The transmit signal from an interrogator may be at a power level of up to 2 W e.r.p. and is shown in figure 2 as
occupying the centre channel of 200 kHz. The two channels on each side of the transmit channel are reserved for the
backscatter response from the tag. Typically tags will respond at link frequencies of approximately 200 kHz or
300 kHz, which is set by the configuration of the interrogator. The power level of the response from a tag will be
-20 dBm e.r.p. or less depending on its distance from the interrogator and the nature of the material to which it is
attached. The dense interrogator mode separates the high power transmission of the interrogator from the low power
signals of the tags, which improves system performance. It also permits transmissions from multiple interrogators on
the same channel. In fact provided that an adequate minimum working distance is maintained between adjacent
interrogators (see guidelines in clause 4.1.3), there is no upper limit to the number of interrogators that may
simultaneously operate at the same frequency.
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13 ETSI TR 102 436 V1.2.1 (2008-02)
4.2.2 4 channel plan
Using the principle of the dense interrogator mode illustrated in figure 2, EN 302 208 [1] has specified four channels for
high power use. A diagram of the four channel plan is shown in figure 3.
Interrogator
signal
Tag response
2 9 13 Channels
1 34 5 678 10 11 12 14 15
865 MHz 868 MHz
Figure 3: Diagram of four channel plan
Interrogators may operate on any of the four specified high power channels within the band 865 MHz to 868 MHz at
power levels up to 2 W e.r.p. The band width of each high power channel is 200 kHz and the centre frequency of the
lowest channel is 865,7 MHz. The remaining three high power channels are spaced at equal intervals of 600 kHz. Tags
should preferably respond in the dense interrogator mode within the adjacent low power channels.
4.2.3 Multiple interrogators
In practice some sites may require the simultaneous use of more than one channel. For example where two or more
interrogators are operated in close proximity to each other, it may be beneficial for them to occupy different channels
To avoid undesirable intermodulation products the frequencies of the two channels should be separated by at least
1,0 MHz. (see clause 4.1.3) One example of where this may be necessary is at a distribution centre with a row of
adjacent dock doors. Typically the system would be configured so that odd numbered doors would be assigned one
channel (say channel 4), while even numbered doors would be on the other (say channel 10). The remaining two
channels could be designated as secondary channels and may be used in the event that a preferred channel is not
available. It would be normal practice to assign each interrogator with one preferred channel and one or more secondary
channels.
4.2.4 Sharing the spectrum with SRDs
It should be noted that the sub-band 865,0 MHz to 868,0 MHz is also designated for use by generic Short Range
Devices (SRDs), which therefore have same rights as RFID. (For details see EN 300 220 [2]).
To ensure equitable sharing between users of this sub-band, EN 302 208 [1] (RFID) and EN 300 220 [2] (SRDs) impose
a number of rules. For example an interrogator may not transmit continuously on the same channel for more than
4 seconds. Once the interrogator has stopped transmitting it may not re-transmit on the same channel for a further
100 ms. However an interrogator may switch immediately to another high power channel.
The standard EN 302 208 [1] also requires that interrogators transmit for no longer than is necessary to perform the
intended operation. This clause is included to ensure that maximum productive use is made of the available spectrum by
all users of the band.
SRDs operating in the sub-band are subject to the use of either LBT with AFA or Duty Cycle RFID operating in
accordance with the 4 channel plan may co-exist with generic SRDs using LBT with AFA. SRDs (without LBT )
srd srd
operating under the Duty Cycle spectrum access technique may also occupy the band. However for acceptable operation
in the high power channels they may have to observe adequate separation distances. This may vary from 918 m (indoor)
to 3,6 km (rural outdoor). In the remaining 2,2 MHz, where tags at -20 dBm e.r.p. occupy the spectrum, this may vary
from 24 m (indoor) to 58 m (rural outdoor).
ETSI
14 ETSI TR 102 436 V1.2.1 (2008-02)
Where RFID and SRDs are deployed in the same area, appropriate precautions should be observed to ensure the
satisfactory operation of both applications. If SRDs and RFID are in close proximity it may be preferable to operate
SRDs in the alternative designated sub-band 868 MHz to 870 MHz.
Some SRDs operating in the sub-band 868,0 MHz to 868,6 MHz may experience interference when sited in close
proximity to RFID systems. This applies particularly to certain industrial and home automation products. To minimize
the possibility of interference, wherever possible interrogators should be configured to operate on those high power
channels furthest removed from 868,0 MHz.
4.2.5 Fixed and portable readers
Interrogators are often fixed devices that are connected to an antenna array configured to cover a defined interrogation
zone. Portable devices also exist, which are frequently referred to as hand held readers. A further example of a portable
device is where readers are fitted to forklift trucks. There will frequently be situations where end users will wish to
operate com
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