ETSI TR 102 436 V2.1.1 (2014-06)

Technical Report
Electromagnetic compatibility
and Radio spectrum Matters (ERM);
Short Range Devices (SRD) intended for operation
in the bands 865 MHz to 868 MHz and 915 MHz to 921 MHz;
Guidelines for the installation and commissioning
of Radio Frequency Identification (RFID) equipment at UHF

2 ETSI TR 102 436 V2.1.1 (2014-06)

Reference
RTR/ERM-TG34-22
Keywords
ID, radio, short range, terrestrial
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3 ETSI TR 102 436 V2.1.1 (2014-06)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 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 lower and upper bands according to EN 302 208 . 12
4.2.1 Dense interrogator mode . 12
4.2.2 4 channel plan . 13
4.2.3 Benefits of band at 915 - 921 MHz . 14
4.2.4 Multiple interrogators . 14
4.2.5 Sharing the spectrum with SRDs . 14
4.2.6 Flags and the "Select" command . 15
4.2.6.1 Session Flags . 15
4.2.6.2 Selected Flag . 16
4.2.6.3 Select Command . 16
4.2.6.4 Use of flags and select commands . 16
4.2.7 Fixed and portable interrogators . 18
4.2.8 Near field systems . 18
4.3 Operation in the band 868 - 870 MHz under EN 300 220 . 18
4.3.1 Hand held readers . 19
4.3.2 Vehicle mounted interrogators . 19
4.3.3 Proximity printers . 19
4.4 CE Marking . 19
5 Preliminary considerations . 20
5.1 Acceptance Tests . 20
6 Site considerations . 20
6.1 Site survey . 20
6.2 Basic principles . 21
6.3 Antenna configurations . 21
6.4 Configurations for near field systems at UHF . 23
6.5 Tags using E.M. transmissions . 23
6.6 Near field tags . 24
6.7 Sources of interference . 24
7 Recommendations for installation . 25
7.1 Antenna fixtures . 25
7.2 Selection of antennas . 25
7.3 Positioning of the antenna . 25
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4 ETSI TR 102 436 V2.1.1 (2014-06)
7.4 Outside antennas . 25
7.5 Antennas for GSM-R receivers . 26
7.6 Cabling . 26
7.7 Earthing (Fixed Interrogators) . 26
7.8 RFID and Short Range Devices operating within the same area . 27
8 Commissioning . 27
8.1 Setting to work . 27
8.2 Site records . 27
9 Maintenance . 27
Annex A: Conversion of units of measurement . 29
A.1 Measurements of power . 29
Annex B: Earthing systems . 30
B.1 Earth System Minimum Requirements . . 30
B.2 Typical electrode and array characteristics . 30
B.2.1 Vertical rod . 30
B.2.2 Buried ring. 31
B.2.3 Buried grid. 31
B.2.4 Measurement of soil resistivity . 31
B.3 Earthing of support structures and buildings . 33
B.3.1 Ancillary equipment external to buildings . 33
B.3.2 Metal support poles on buildings . 33
B.3.3 Metal security fences . 33
B.4 Interconnection of lightning protection systems with power supply earthing arrangements . 33
Annex C: Prefabricated portals . 34
Annex D: Commissioning procedure. 35
Annex E: Bibliography . 36
History . 37

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5 ETSI TR 102 436 V2.1.1 (2014-06)
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://ipr.etsi.org).
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.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "may not", "need", "need not", "will",
(Verbal forms
"will not", "can" and "cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules
for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
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6 ETSI TR 102 436 V2.1.1 (2014-06)
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 4 W e.r.p. Guidance is given
on making best use of the available spectrum as envisaged within the ETSI standard EN 302 208 [i.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 [i.2]. This includes operation in the sub-bands 869,40 - 869,65 MHz
at power levels of 500 mW and 869,7 - 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
familiarize 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 specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
2.1 Normative references
The following referenced documents are necessary for the application of the present document.
Not applicable.
2.2 Informative references
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.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".
[i.2] ETSI EN 300 220 (Parts 1 and 2): "Electromagnetic compatibility and Radio spectrum Matters
(ERM); Short Range Devices (SRD); Radio equipment to be used in the 25 MHz to 1 000 MHz
frequency range with power levels ranging up to 500 mW".
[i.3] CEPT ERC/REC 70-03: "Relating to the use of Short Range Devices (SRD)".
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7 ETSI TR 102 436 V2.1.1 (2014-06)
[i.4] Void.
[i.5] ISO/IEC 18000-6, Information technology - Radio frequency identification for item management -
Part 6: Parameters for air interface communications at 860 MHz to 960 MHz General.
[i.6] ETSI TS 102 902 (V1.2.1): "Electromagnetic compatibility and Radio spectrum matters (ERM);
Methods, parameters and test procedures for cognitive interference mitigation towards ER-GSM
for use by UHF RFID using Detect-And-Avoid (DAA) or other similar techniques".
[i.7] TCAM (21)36: "Passive RFID tags at the stage of placing on the market and the R&TTE
Directive".
[i.8] Directive 1999/5/EC of the European Parliament and of the Council of 9 March 1999 on radio
equipment and telecommunications terminal equipment and the mutual recognition of their
conformity (R&TTE Directive).
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 interrogators can transmit simultaneously in the
same channel while tags respond in the adjacent channels
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
lower band: frequency range 865,0 - 868,0 MHz designated for use by RFID
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
upper band: frequency range 915 - 921 MHz designated for use by RFID
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 V2.1.1 (2014-06)
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AFA Adaptive Frequency Agility
AM Amplitude Modulated
BCCH Broadcast Control Channel
CE Conformité Européenne
CEPT European Conference of Postal and Telecommunications Administrations
DAA Detect and Avoid
E.M. ElectroMagnetic
e.r.p. effective radiated power
ECC Electronic Communications Committee
EMC ElectroMagnetic Compatibility
EPC Electronic Product Code
ERC European Radio communication Committee
ER-GSM Extended Railways GSM
FM Frequency Modulated
GSM-R Railway GSM
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
SNMP Simple Network Management Protocol
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.
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9 ETSI TR 102 436 V2.1.1 (2014-06)
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.
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 should 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.
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10 ETSI TR 102 436 V2.1.1 (2014-06)
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 known 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.
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 [i.3] and is effectively a fixed parameter. For channels of 200 kHz channel spacing as defined for the
lower band in annex 11 of ERC/CEPT 70-03 [i.3] the maximum possible data rate is of the order of 40 kbits per second.
For the upper band the channel width is 400 kHz and the data rate is 80 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/IEC 18000-6 [i.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 in the lower band as specified in EN 302 208 [i.1], the tag may be set to operate at link
frequencies of approximately 300 kHz. The upper band uses a link frequency of 600 kHz. This leads to data rates of
75 kbits per second and 150 kbits per second respectively.
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 sum 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 should 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.
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11 ETSI TR 102 436 V2.1.1 (2014-06)
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.
Table 1: Typical effect of materials on performance
Scenario Reference Distance (cm) Range (cm) (R/Rref)**2 Loss dB
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 should
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 V2.1.1 (2014-06)
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 lower and upper bands 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 [i.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. The values given in the diagram apply
to the lower band and are 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 in the lower band 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 in the lower band 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 in the lower band 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 V2.1.1 (2014-06)
For the upper band power interrogators are permitted to transmit at levels up to 4 W e.r.p. in a high power channel with
a width of 400 kHz.
4.2.2 4 channel plan
Using the principle of the dense interrogator mode illustrated in figure 2, the standard EN 302 208 [i.1] has specified
four channels for high power use in each band. Diagrams of the four channel plan for both the lower and upper bands
are shown in figure 3 and figure 4a respectively.
Interrogator
signal
Tag response
1 2 34 5 678 9 10 11 12 13 14 15 Channels
865 MHz 868 MHz
Figure 3: Diagram of four channel plan for lower band
For the lower band interrogators may operate on any of the four specified high power channels 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 in the adjacent low power channels.

Figure 4a: Four channel plan for the upper band
For the upper band the centre frequency of the lowest channel is 916,3 MHz and the band width of each high power
channel is 400 kHz. The remaining three high power channels are spaced at equal intervals of 1,2 MHz. Tags should
preferably respond in the dense interrogator mode in the adjacent low power channels.
A number of member states have allocated the upper sub-band 918 - 921 MHz to the railways for use by ER-GSM.
RFID systems may share this sub-band with ER-GSM provided that they operate in accordance with an agreed
mitigation technique. This is described in clause 8.7 and annex B of EN 302 208-1 V2.1.1 [i.1] and clause 6 of
TS 102 902 [i.6].
In some member states the lower sub-band 915 - 918 MHz or all of the band 915 - 921 MHz is allocated to the military
and government services. Where this applies the use by RFID of the lower sub-band is not permitted. Informa
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