The WLAN EMC Immunity Testing for Mobile Devices in EU
T. A. Alasuvanto*
* Oulu University of Applied Sciences, School of Engineering, Oulu, Finland,
t8alto00@students.oamk.fi
Abstract
The aim of this paper was to find the definition of the
European requirements and performance criteria for
WLAN EMC verification and testing according the
EMC standards. In more detail, the aim was to define
the need of the measurements, the limit values as well as
performance criteria. The definition was based on the
European Telecommunication Standard Institute (ETSI)
EN 301489-17 standard and the Institute of Electrical
and Electronics Engineers (IEEE) 802.11 specifications.
According to these references, the limit values and the
performance criteria for minimum setup consists of
immunity tests, test site and monitoring of the WLAN
data.
Keywords: EMC, EMS, immunity, susceptibility, EUT
1
Introduction
Electromagnetic compatibility (EMC) is the branch
of electrical sciences, which studies the unintentional
generation,
propagation
and
reception
of
electromagnetic energy with reference to the unwanted
effects (Electromagnetic Interference, EMI) that such
energy may induce. Electromagnetic compatibility can
be divided to two main aspects such as immunity and
emission or some cases susceptibility. Immunity
compatibility means the ability of equipment to function
satisfactorily in its electromagnetic environment with
certain
limitations.
Introducing
intolerable
electromagnetic disturbances to other sensitive
equipment in that environment is called emission
compatibility. [1] These aspects require preventive
measures against emission and measures for immunity
(Electromagnetic Susceptibility, EMS). In this work,
immunity (EMS) aspects are more closely studied such
as test cases and performance criteria, but emission will
be ruled out. The motivation for this study is that
currently there are no ready-made testing systems
available, which are dedicated to WLAN EMC testing
in a mobile device (EUT) perspective.
Wireless LAN is that the devices communicate via
radio waves instead of wires. The original 802.11
WLAN standard (ISO/IEC 8802-11) which supports 1
Mbps to 2 Mbps data rates has gradually evolved to 14
sub-standards. The most common commercial WLAN
standards are b and g (including a and n in near future)
because 802.11b/g WLANs provide adequate
performance for today's networking applications. All
these wireless LAN devices are operating in 2.4 GHz
frequency range which is known as the industrial,
scientific, and medical (ISM) band. [3] Devices in
Europe which are using 2.4 GHz WLAN transceiver
must fulfill EMC requirements specified by European
Telecommunication Standard Institute (ETSI).
2
Test Requirements
Standard EN 301 489-17 together with EN 301 489-1,
covers the assessment of the 2,4 GHz wideband
transmission systems and 5 GHz high performance
RLAN (including HIPERLAN 1 and 2) equipment, in
respect of electromagnetic compatibility. Standard EN
301 489-17 belongs to the series of telecommunications
standards where part 17 defining specific conditions for
2.4 GHz wideband transmission systems and 5 GHz
high performance RLAN equipments such as test
conditions, performance assessment and performance criteria
[4].
2.1
Test definitions
Test conditions, which actually mean that equipment,
should be tested under normal test conditions according to the
relevant product and basic standards. According to the
applicable EN 301 489 standard all EMC tests are
port-related. The applicability of EMC tests depends on
the actual type of radio and associated ancillary
equipment. Typically portable or stand alone devices can
be used together with AC- or DC- power cable and there
might have some control and data cables as well.
Any connection point of that equipment, which is
intended for connection of cables to that equipment, is
considered as a port including enclosure port, which is
physical boundary of the equipment. Common interfaces of
the specified equipment which interact with the electromagnetic
environment are listed [5]:
fixed station equipment [4].
2.3
•
•
•
•
•
•
•
AC power port
DC power port
Enclosure port
Earth port
Antenna port
Control port
Telecommunication port
Equipment classification such as equipment purpose of
use should be taken into account when defining
applicable tests. Some devices are intended for different
kind of use like fixed, vehicular or portable use. Fixed
use, such as base station equipment, are intended for
operation at a fixed location and powered directly or
indirectly by the AC- or DC mains network. Mobile
equipment are intended for installation and use in a
vehicle, and powered by the main battery of the vehicle.
Portable such as handheld equipment are intended for
portable operation, powered by its own integral battery.
Moreover telecommunication equipment, which
includes one or more radio transceivers, can be used in
fixed, mobile or portable applications. [4]
Performance assessment refers to the information how
the equipment is operating during and after EMC
exposure including equipment normal intended
operations. This information is usually provided by the
manufacturer and that information can be found in the test
report. [4]
Applicable immunity tests
The applicability table below gives a comprehensive
overview about all immunity EMC tests for radio and
associated ancillary equipment. [4]
Table 1. Immunity tests for radio and
associated ancillary equipment [4]
Ports
Phenomenon
Equipment test requirement
AC-
DC-
Internal
powered
powered
battery
powered
Enclosure
RF
Valid*
Valid*
Valid*
Valid*
Valid*
Valid*
Valid*
N/A
N/A
Valid*
Valid*
N/A
Valid*
N/A
Valid*
N/A
N/A
Valid*
N/A
Electromag.
Field 80–
2000 MHz
Electrostatic
Discharge
Signal,
Fast
Telecom-
Transients
munication
Common
and
Mode
Control,
RF
DC and
Common
AC power
mode 150
#
#
#
kHz-80
2.2
Immunity test cases
Immunity, also called as susceptibility is a measure of
the ability of an electronic product to tolerate the
influence of electrical energy (radiated or conducted)
from other electronic products and electromagnetic
phenomena. In the case of the immunity tests,
transceiver can be tested as a system, which allows
simultaneous testing for transmitter and receiver of the
equipment. [4]
In this case, mobile phone or mobile device, which is
equipped with WLAN transceiver, refers to handheld
equipment. The term handheld; according ETSI EN
301 489-17, refers hand-portable station or portable
equipment, equipment (commonly called as EUT,
equipment under test), which is powered by its own
integral battery and to the equipment, which can be
carried by a person. Furthermore accordingly ETSI EN
301 489-17 document sub clause 5.5 equipment
classification, defines that hand portable equipment, or
combinations of equipment as capable of being powered
for intended use by the main battery of a vehicle, is
additionally considered as vehicular mobile equipment,
or a device capable of being powered for intended use
by AC mains should be additionally considered as a
MHz
AC mains
Voltage Dips
power
and
input
Interruptions
Surges, Line
#
#
#
N/A
#
to Line and
Line to
Ground
DC power
Transients
input
and Surges
#
N/A
#
* Valid = Applicable test
#
N/A = Not applicable test
2.4
Practical aspects of testing
Radio field electromagnetic field testing requires EUT
protection from a radiated RF field interference, which is
amount of disturbance that EUT can tolerate. Disturbing
AM modulated RF field is swept from 80 – 2000 MHz
with a step size not exceeding 1% of fundamental signal
and with sufficient dwell time to allow the EUT to respond
to the RF field (stress level). Conducted immunity or
susceptibility tests are mainly for cables (accessories),
which are connected via EUT’s interface to EUT. In this
case, disturbing AM modulated RF signal is injected or
coupled directly to the AC- or DC mains or other I/Ocables. Frequency range is from 150 kHz to 80 MHz and
sweep step size is 1% including sufficient dwell time as in
radiated RF field testing. Fast transients, surges, voltage
dips and interruptions are AC- DC-mains network normal
characteristics and therefore these tests are applied to AC-,
DC- and some cases signal/control ports of the equipment.
The main idea of fast transients, surges, voltage dips and
interruption phenomena (known as electro-magnetic
interferences) are that the ability of the EUT to operate as
intended in the event of these phenomena on the mains of
power and signal/control input/output ports. The wave
shape, number of pulses, their frequency and length
including repetition frequency of the signals can be natural
or man-made phenomena. The ESD test method consists
of indirect discharge to vertical and horizontal coupling
plane and direct discharge to EUT. The direct discharge is
divided to air and contact discharges, which are applied to
conductive points to EUT. Voltage levels start from 1 kV
ending up to the 8 kV, or even higher levels. Both voltage
polarizations, negative and positive, must be applied to the
test, which will increase numbers of individual discharges
to the EUT. These phenomena involve short duration such
as nanosecond or microseconds events that have enough
amplitude to disrupt the operation of electronic circuits and
in some cases have energy to destroy or damage the whole
system. [2]
The main concern with these different immunity tests
cases is that all individual tests should be long enough that
any coincidence with sensitive states of the EUT has been
explored. [5]
2.5
Performance criteria
The performance criteria are used to take a decision
when equipment passes or fails immunity test or tests.
The performance criteria are applied either to transmitter
or receiver the case of phenomena. [4]
•
•
Continuous or transient phenomena
applied to transmitter
Continuous or transient phenomena
applied to receiver
Table 2. Nature of phenomena [4]
Phenomenon
Nature of phenomena
applied to transmitter
and receiver
RF Electromagnetic Field 80–2000 MHz
Electrostatic Discharge
Fast Transients Common Mode
RF Common mode 150 kHz-80 MHz
Continuous
Transient
Transient
Continuous
Voltage Dips and Interruptions
Transient
Surges, Line to Line and Line to Ground
Transient
Transients and Surges
Continuous and
Transient
According applicable radio standard EN 301 489-17
the performance criteria for immunity tests are [4]:
•
•
•
A with phenomena of a continuous nature
B with phenomena of a transient nature
C with power interruptions exceeding
certain time
Equipment under test (EUT) should be monitored
during test and after test, which means that EUT must be
constantly monitored during the test and EUT status
should be also checked after the test. The criteria A is the
most demanding level of performance, which basically
requires that EUT operates as intended in all cases and
there will be no loss of function, but may show some
degradation of performance. Performance criteria B
allow EUT to have one or more loss of function and
show degradation of performance, but it should be
self-recoverable after EMI exposure. Performance
criteria C is similar with criteria B, such as allow to EUT
to have one or more loss of function, but after EMI
exposure EUT is allowed to be recovered by action of
the operator. [4]
2.6
WLAN data monitoring
Wireless devices which operate 2.4 GHz frequency
range should operate in case of EMI as intended.
WLAN data transmission and data receiving can be
used for monitoring WLAN transceiver functionality.
WLAN systems operate with a positive
acknowledgement-based technique. When a frame is
sent, it incorporates extra data to allow the receiver to
determine if any bit errors have occurred. This is the role
of the Cyclic Redundancy Check (CRC) and Frame
Check Sequence (FCS). A receiver uses the payload
data it recovers to calculate a CRC, employing exactly
the same algorithm as the transmitting device. The two
CRCs are then compared. Any differences between
them mean that one or more bit errors have occurred in
the payload data. If this is the case, the ‘ACKnowledge’
frame is not sent. The CRCs are themselves
error-protected, so they will not suffer bit errors unless
the performance of the data content of the frame is very
poor. IEEE 802.11g also use a frame-based receiver
performance test called Packet Error Rate (PER). Unlike
Frame Error Rate in 802.11b, CRCs are not used, but
there is a frame check sequence after the user data, by
which the receiver determines if the data was corrupted
or not. [6]
Test setup for WLAN data testing can be done by
using similar equipment than EUT or specified WLAN
protocol tester. Data testing with two similar EUT
requires ad-hoc connection between these two EUT,
where the one equipment is sending data and the other
one is receiving. This testing method creates more test
cases because EUT transmitter and receiver must be
tested separately and this requires special test software as
well. Instead of two EUT the best solution could be
specified protocol tester, where tester can simulate real
WLAN network access points (AP) such as basic
service set (BSS) or extended basic service set (EBSS).
When using access point created by tester, the situation
is exactly same as in real WLAN network, and in this
way there is no need to create any extra test software for
EUT or to the system. This data monitoring could be
done with following settings based on WLAN protocol
testing requirements. Some of the basic network settings
should be considered as compulsory settings like
transmission levels, length of the data packets and data
rates (see Table 3). These three settings according
specification of IEEE 802.11b and IEEE 802.11g are the
only one needed for minimum setup for PER
measurement. [6, 7]
Table 3. Minimum network settings for PER
measurement. [6, 7]
Settings
IEEE 802.11b IEEE 802.11g
Length of Data 1024 bytes
1000 bytes
Packets
Data Rate
11 Mbit/s
54 Mbit/s
Transmission
–76 dBm
–65 dBm
Level
Other settings that might be very useful to change or to
be noticed during network establishment are listed:
•
•
•
•
•
•
Service set identifier (SSID) / MAC
Channel number
Beacon interval
Preamble
Payload
Number of Packets
The clear limits for packet errors (PER) for both
specifications, types b and g are set in ideal or normal
conditions. These conditions must be verified first is at
the level of errors are in suitable level or that this level is
totally free from errors. Since faulty packets occur
randomly, measured PER values are as a rule difficult to
reproduce. The number of packets tested directly
influences measurement accuracy. Receiver minimum
input level sensitivity and error rates are listed in Table 4
[6, 7].
Table 4. Sensitivity and error rates [6, 7]
Data rate
Input level
PSUD
Error rate
1
2
5.5
11
6
9
12
18
22*
24
33*
36
48
54
-76 dBm
-76 dBm
-76 dBm
-76 dBm
-82 dBm
-81 dBm
-79 dBm
-77 dBm
-76 dBm
-74 dBm
-74 dBm
-70 dBm
-66 dBm
-65 dBm
1024
1024
1024
1024
1000
1000
1000
1000
1024
1000
1024
1000
1000
1000
8 % FER
8 % FER
8 % FER
8 % FER
10 % PER
10 % PER
10 % PER
10 % PER
8 % FER
10 % PER
8 % FER
10 % PER
10 % PER
10 % PER
* Optional data mode
2.7
Conclusions
A basic idea behind all of these immunity tests is that
all wireless devices (electronic equipments) are tested as
they are and operate in the real life situation. Some
equipment during these tests may suffer loss of
operational functions (change state or jam), hardware
damages or even complete failures. On the other hand,
the ability of the equipment to handle or tolerate EMC
immunity tests are some cases references as the quality
of the equipment.
One very promising solution for this kind of WLAN
data testing could be a PC with common ADSL-modem.
The ADSL-modems are capable of same kind of test
configurations like some very expensive WLAN
protocol testers in EMC perspectives. Only one special
experiment concerning packet error rate at minimum
input level, which is measured at the antenna connector,
must be carried out more carefully or study further. The
antenna connector point refers to conducted
measurements where the RF-cable is connected directly
to the device antenna connector switch inside device.
This cable connection situation is not suitable for the
needed purposes, because of all devices are mobile, and
some cases if connecting cable directly to the device
might lead too good test results compared to the real
situation.
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systems, 5 GHz high performance RLAN equipment and
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