| Cellular Phone Conformance Testing |
Cellular Phone Conformance Testing
An overview or tutorial about the basics of cellular phone conformance test
and the way that GSM and UMTS testing is handled by organisations such as GCF,
PTCRB, TIA, etc.
Today, vast numbers of mobile phones are in use around the
globe. 2006 saw in well excess of 2 billion subscribers connected and over 1
billion phones manufactured. When users buy phones they expect that the system
will work. They are not interested in the reasons why there may be problems,
often blaming the phone itself. Poor service, for whatever reason will result in
users choosing a different network, and adding to the rate of churn.
Ensuring that cell phones operate correctly when deployed is
no easy task. Testing of the design is required at all stages of the
development. It is necessary to check the hardware, and software. Once the cell
phone is assembled, full testing of the complete "system" is required, testing
it against its requirements and specification. Then prior to deployment it must
undergo formal testing and be "approved" before it can be used.
Dependent upon the type of cellular network, i.e. GSM / UMTS,
or CDMA (cdmaOne / cdma2000) this formal "approval" may take one of two forms:
- Conformance test
- Interoperability test
Once the formal approval has been gained, the cell phone can
then be manufactured in quantity, sold and deployed on the cellular network.
In many respects cell phone conformance test and
interoperability test perform the same function but they have some significant
differences between them. A conformance test tests for conformance to a
particular specification, whereas an interoperability test checks that the phone
will work on a given network. Both conformance test and interoperability tests
have the advantages and disadvantages. However a conformance test is required
for GSM, UMTS cell phones and generally interoperability tests are required for
phones for many of the CDMA networks.
Conformance and interoperability tests
To ensure that a mobile phone meets its required standards it
has to undergo a variety of types of test. These are often categorised into
different areas. In order to undertake these tests different test house may be
required.
- Basic safety testing This is a form of test that every
piece of equipment, whether mobile phone or otherwise has to undergo to
ensure that it is intrinsically safe to use and no injury will be inflicted
for example from sharp edges, etc..
- SAR, Specific Absorption Rate This test
involvesmeasuring the amount of radio frequency power that a human head will
absorb when the cell phone is transmitting. The test uses an anatomically
correct model of the human head. Inside the model temperature sensors are
set up to measure the temperature rises to ensure that the heating effects
caused by the cell phone fall below acceptable limits.
- Protocol testing One of the major areas of cellular
conformance testing is the protocol testing of the cell phone. With the
complicated protocols used in mobile phones this is a critical area. If the
phone protocol software operates incorrectly then it could result not only
in problems experienced by the phone, but also on the network. In view of
the complexity of the protocols that are used this testing can be very
involved. Specialised network simulators are used. These testers emulate a
variety of network entities, i.e. base stations or Node B's (in the case of
UMTS), RNCs (Radio Network Controller and the like. In this way a host of
scenarios from registration to handover, and in fact any situation that can
be encountered can be simulated.
- RF testing Conformance testing also includes testing
of the RF signal. Many measurements of the transmitter and receiver
performance are undertaken in a variety of areas such as the out of band
emissions. Measurements of the Radio Resource Management (RRM) are
undertaken to ensure that the control capability of the phone is operating
correctly. There are for instance very tight limits on the control of the
transmitter output power to ensure that the cell phone radiates only as much
as is needed under any given conditions and noise in the phone bands is
reduced to the minimum level. To achieve this testing a protocol tester is
often used to control the phone and set up the relevant scenarios. In
addition to this an RF measurement and generation equipment is required.
This is often in the form of additional signal generators, power meters,
analysers, noise generators, etc. To check operation of the phone with
multi-path and fading, special fading simulators are required.
- SIM card testing Another very important area of
cellular conformance or interoperability testing is the operation of the SIM
card, or in the case of UMTS the USIM. As SIMs are interchangeable between
phones it is necessary to rigorously check the interface. It is also vital
to check the security aspects of the operation of the SIM, as lapses in
security could compromise elements of the network security. To undertake
this testing a SIM simulator (or USIM simulator) is required. This simulator
emulates the operation of the SIM, and tests on the phone can then be run
using a protocol tester to set up the variety of scenarios that are needed.
- Audio tests Finally audio checks of the cell phone are
undertaken. These check the correct operation of the audio aspects of the
cellular phone, both in terms of the microphone and the earphone. Checks of
audio levels, quality and much more are measured using a variety of audio
equipment to ensure they conform to the requirements laid down.
Test cases
It is obviously necessary to ensure that each stage in the
testing is repeatable regardless of the test equipment is used and the
organisation performing the testing.
To achieve uniformity a large number of what are termed "test
cases" are defined. These may be expressed in a number of ways, but typically
they may be in prose, or they may be in a form of computer notation called TTCN
(Tree and Tabular Combined Notation). In the latter format they can often be
compiled directly into code that can be run on a given test system.
For any given standard, i.e. GSM UMTS, cdma2000, etc there
are many hundreds of test cases that need to be run. They are prepared under the
auspices of the governing body, e.g. 3GPP for GSM and UMTS. Manufacturers of
conformance test equipment are then able to take these test cases and convert
them to run on their test equipment. Often the test cases must be ratified on a
given test system before they can be used towards approval of a phone.
Summary
The process of conformance testing and interoperability
testing can be time consuming and expensive. However it is essential because the
cost of releasing a phone that does not operate correctly is very much higher.
As a result network operators and phone manufacturers alike see the importance
of conformance testing and interoperability testing.
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