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Conformance Test for GSM/UMTS Phones
by Ian Poole and Phil Medd, Racal Instruments Wireless Solutions Division, an
Aeroflex company
The overall certification process may seem very long and involved, but it
does provide a high level of uniformity across the industry.
The expectations for quality of service provided by mobile-phone systems are very high these days. Users anticipate that when they turn on their phones they will obtain flawless
service. For GSM, they expect to roam across the globe and receive the same
level of service that they do at home. Or, they will be able to drop a SIM card
into any phone and experience no problems, regardless of the network. It is the
successful operation of these features and many more that has lead to the
phenomenal success of GSM that now has more than a billion subscribers
worldwide.
The high levels of quality are by no means easy to achieve, especially when the
degree of complexity of mobile phones and mobile-phone networks is considered.
As an indication of the complexity, the original specifications for the GSM
system consisted of many thousands of pages, and since then, further features
have been added.
 This documentation is required because essential operations such as registration
require many transactions between the phone and the network. As a call proceeds,
the network and phone have to communicate with one another to ensure that the
call is maintained.
Handoff and other scenarios must be defined very precisely and operate
correctly. For UMTS, intersystem handoff needs to be accommodated so mobiles can
revert to the 2G or 2.5G systems when no 3G system is available and vice versa.
Ensuring that all the facilities work correctly before a phone is introduced
into the market is essential. Adopting a test methodology that enables phones to
operate on any network in any country means that they have to be tested to
ensure they conform to the standards. This conformance testing is at the heart
of the success of the GSM system.
Following on from GSM, a very similar approach has been adopted by the 3G UMTS
or the WCDMA system. It is anticipated that a similar degree of success will be
achieved.
Testing
Several different areas comprise the overall testing of a new mobile phone.
Safety, RF absorption, protocols, RF performance, SIM or USIM, and audio
performance are essential elements that need to be included in the overall
program of tests.
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Any piece of electrical equipment must be safe to use and operate. Mobile phones
are no exception and must undergo rigorous safety tests to ensure that they will
not cause harm or injury in any way. Although there have been a few reports of
occurrences such as exploding batteries, these are very few and usually are
attributed to third-party replacement batteries. Problems of this type are very
rare and show how well the systems and individual devices work.
Another form of safety testing is undertaken to ensure that the level of RF
absorption falls below the maximum permitted levels. The testing, known as SAR
testing, involves the use of an anatomically correct model of the human head.
Inside the model are sensors to measure the temperature rise.
The figures obtained can be related to the levels of RF radiation that are being
absorbed at different places on the head. With the continuing awareness and
concern of possible harmful effects of radiation, this is a key test.
Protocol testing determines the overall operation of the phone. If the phone
protocol software operates incorrectly, then it is likely that the phone will
not operate properly on a network. There even have been instances when the
incorrect operation of phones has caused problems with a network.
In view of the complexity of the protocols that are used, this testing can be
very involved and requires the use of specialized network simulators. These
testers emulate a variety of network entities, such as BTS, BSC, or in the case
of UMTS, Node Bs and RNC. In this way, a host of scenarios from registering to
terminating a call and all the different forms of handoff can be simulated. In
fact, any situation that can be encountered needs to be fully tested.
The RF performance of the phone also must be checked. Many measurements of the
transmitter and receiver performance are carried out in a variety of areas
including the out-of-band emissions. Measurements of the RRM are carried out to
ensure that the control capability of the phone is operating correctly. The RRM
is the entity used to control the physical or RF layers in accordance with the
requirements of the protocols from the higher layers.
There are, for instance, very tight limits on the transmitter output power as it
is controlled to meet conditions such as variations in signal strength. This
ensures that the phone only transmits sufficient power to maintain a reliable
circuit under the prevailing conditions, and as a result, the overall level of
noise in the phone bands is reduced to the minimum level.
 To achieve RF performance testing, a protocol tester often is used to control
the phone and set up the relevant scenarios along with RF measurement and
generation equipment. This equipment may include signal generators, power
meters, analyzers, and noise generators. Additionally, to check operation of the
phone with multipath and fading, special fading simulators are used.
Another critical area of testing involves the SIMs used in GSM phones or the
USIMs used in UMTS. These cards are interchangeable between phones, and it is
essential that the interface is checked rigorously to ensure that it will work
with any SIM or USIM.
It also is vital to check the security aspects since any lapses could compromise
elements of the network security. A SIM simulator or USIM simulator is required
to emulate the operation of the SIM, and tests on the phone then can be run
using a protocol tester.
Finally, audio checks need to be completed. These ensure that the audio aspects
of the phone meet the required standards both in terms of the microphone and
earphone. A wide variety of checks is performed to ensure that audio
characteristics are satisfactory under all conditions.
Test Cases
All testing performed on a mobile must be repeatable and conform to the
specifications regardless of the test equipment being used. To achieve this,
formal test cases are written for each test. For GSM, these originally were
defined by ETSI but now are controlled by 3GPP.
A variety of processes can be adopted for writing test cases. For GSM, test
cases are written in prose, describing in detail the test setup, the stimuli
that need to be applied, the way in which the test is carried out, and the pass
and fail criteria. To ensure that each test is a true representation of the
original intent of the test, a validation and certification process has been set
in place.
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Once the manufacturer is satisfied that the test operates correctly, it then is
given to an independent validation organization to test for conformance with the
original test specification and check for proper operation. Once it has passed
this test, it can be submitted to the relevant industry body for certification.
After certification, it can be used in formal handset testing.
The 3GPP has overall control of the test cases for GSM and UMTS. Changes,
however, are handled by the GERAN Working Group for GSM. For UMTS, changes are
addressed by the T1 Group. The validation and approval of the implemented test
cases then are handled by the GCF.
The North American version of GSM running in the 1,900-MHz band often is
referred to as PCS, and now there is another allocation at 850 MHz. A group
known as PVG handles the approvals, and its results are ratified by the PTCRB.
Phones then are tested against the test cases that, if successful, are certified
by the CTIA. To achieve CTIA certification, it is necessary for phones to be
tested in CTIA-approved laboratories.
UMTS Test Cases
The experiences and lessons learned through GSM have resulted in a number of
changes to the way in which test cases are generated for UMTS. Protocol test
cases for UMTS were written in prose and then converted into TTCN code. This
language enables the test cases to be compiled by a computer into a format that
can be run directly on the target test equipment.
This approach saves time for the industry as a whole and reduces costs because
generating the test cases is far easier. It also gives far more consistency
across the industry because tests no longer are open to the same level of
interpretation that they were before. As a result, time is saved during the
validation process.
The TTCN test cases have been prepared by a team of industry experts based at
ETSI working on behalf of the 3GPP. The team developed the basic TTCN code that
was reviewed within the 3GPP community using e-mail reflectors. By reviewing the
software at the beginning of the process, the individual test cases do not need
to be reviewed each time they are submitted by a test-equipment manufacturer for
validation.
To test a new handset, the manufacturer generally approaches a qualified test
house. The test house will run the required certified test cases and state that
the handset is suitable for use on the available networks.
Summary
Although the overall certification process may seem very bureaucratic and long,
it has resulted in an exceedingly high level of uniformity across the industry.
This has been part of the success of the GSM system and, no doubt, will be part
of the success of UMTS.
Phone manufacturers have shared in this success because, once certified, their
phones should operate on any network. This greatly increases the markets that
are open to them.
About the Authors
Ian Poole, a consultant at Aeroflex, is a chartered engineer and fellow of the
Institution of Electrical Engineers. He obtained his degree from University
College London. Mr. Poole also has authored more than 18 books and many articles
worldwide for which he has won awards. e-mail:
ian_poole@lineone.net
Phil Medd is a product manager for Racal Instruments Wireless Solutions,
supporting the 3G mobile protocol test products. Mr. Medd graduated from
Nottingham University in 1977 with a degree in electrical and electronic
engineering and since then has worked in the test-equipment industry. e-mail:
phil.medd@aeroflex.com
Racal Instruments Wireless Solutions, an Aeroflex company, 480 Bath Rd.,
Burnham, Berkshire SL1 6BE UK, 011 44 (0) 1628 604455
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