| WiMAX testing including conformance testing |
WiMAX testing including conformance testing
- an overview, summary or tutorial about WiMAX testing, conformance test,
and WiMAX test equipment, including conformance test equipment.
WiMAX is a broadband wireless data communications technology
based around the IEE 802.16 standard that is capable of providing high speed
data communications (70 Mbps) over a wide area. The letters of WiMAX stand for
Worldwide Interoperability for Microwave Access (X), and it is a technology for
point to multipoint wireless networking. The technology is being deployed in a
variety of applications from providing "the last mile" communications to users
to supplying the backbone communications networks required in many developing
countries.
Types of WiMAX testing
With many manufacturers now developing and supplying equipment, it is essential
that they operate to their individual specifications and that they also
interoperate with each other. To ensure that this can happen, manufacturers need
to perform a variety of different types of test:
- Development testing
- Verification and Validation testing
- Conformance testing
- Production testing
Each of these types of test has its place in the development
of any product, and in this case in the development of WiMAX.
Development testing
During the development of any product, test equipment is required to ensure that
all the circuitry operates as it should. The test equipment that will typically
be required will include items such as oscilloscopes, as well as RF measuring
equipment including spectrum analyzers, RF power meters and the like. In
addition to this test equipment will be needed to aid debugging the software.
This is likely to include emulators of various types.
During the development testing stage it is always wise to
undertake testing of the product against the conformance tests (see later) as
these will have to be undertaken later. By using the conformance test equipment
along with the conformance test cases, the product can be made to work correctly
and any bugs removed at this stage. Often the conformance test equipment will
enable the test cases to be modified to enable development testing to be
undertaken.
Verification and Validation testing
Once the design of the product has been completed, in this case a WiMAX unit, it
will be necessary to ensure that it meets its requirements the requirements set
down in the development specification, and that it also operates satisfactorily.
These tests need to be performed formally to ensure that the development has
been satisfactorily completed. Test equipment here will include any equipment
needed to test the interfaces to the overall unit. Typically the test equipment
will include items from spectrum analyzers and power meters to check the RF
performance to data communications analyzers to check the data interfaces.
To ensure that some of this testing can be undertaken more
easily, because the overall operation of WiMAX involves many complicated
protocols, specialised WiMAX testers or WiMAX test equipment may be used. These
items are supplied by a number of test equipment manufacturers and have been
developed specifically for WiMAX testing. They are able to interface to both the
RF and data interfaces of the unit, and provide a comprehensive test of its
operation.
WiMAX Conformance Testing
One of the major concerns for any organisation such as the WiMAX Forum, is that
of ensuring that devices from a variety of different manufacturers operate
satisfactorily together. With the size of specifications for standards such as
WiMAX increasing along with their complexity, there is the possibility of areas
being interpreted in different ways, or bugs being present that will prevent
their interoperability. In addition to this, the 802.16 standard only specifies
the Physical and MAC layers of the standard and this leaves many aspects open to
the individual vendors. The WiMAX Forum seeks to address this, and ensure that
interoperability issues do not arise. A large number of problems in this area
would lead to a lack of confidence in the technology as a whole and would
significantly decrease sales for all vendors.
To ensure that interoperability issues do not occur, products
must be run against a validated set of conformance test cases on a set of
conformance test equipment that has been validated by the WiMAX Forum. Products
that pass conformance and interoperability testing are able to claim they are:
"WiMAX Forum Certified" and they can display this mark on their products and
marketing materials. Some vendors may claim that their equipment is
"WiMAX-ready", "WiMAX-compliant", or "pre-WiMAX", if they are not officially
WiMAX Forum Certified. These products may not have been fully tested against the
test cases and as a result they may have interoperability problems.
There are two types of WiMAX conformance test equipment:
- Base Station Emulator (BSE): - used for testing a mobile
station (MS)
- Mobile Station Emulator (MSE): - used for testing a base
station (BS).
There are also other distinctions between the testers. There
are those that address the radio signal itself, and those that address the
protocols. The radio tests typically take longer to perform as they look for the
radio signal performance, addressing parameters such as the spectrum of the
signal, power levels and the like. The protocol tests address the manner in
which the WiMAX equipment communicates with other units, sending the messages
and establishing a link.
Although conformance test equipment will be able to run the
conformance tests for WiMAX equipment, in view of the different bands that are
in use, the conformance test equipment may need different options to enable it
to cover the relevant bands.
One major area of importance is the development of the test
cases that are used for the certification process. The model used follows a
similar process to that used for test cases for UMTS. The basic test procedures
are written by the WiMAX Forum and these procedures describe the functionality
to be tested and the test method. They also provide a priority for them. ETSI
then take the test procedures and write the code in TTCN-3. This code is
released to the test equipment vendors who analyse, integrate and if necessary
raise "changes requests" if necessary. Once test cases are passing on real
equipment, they can be submitted for validation. Only then can vendor equipment
be tested for certification in a WiMAX Forum accredited test lab. New test cases
are often developed as technologies evolve and the older ones can change.
Production WiMAX testing
Once an item is in production, testing needs to be performed on it to ensure
that each item leaving the production line performs correctly. The testing
undertaken at this point in the process is aimed at checking that the unit is
built correctly. As this testing adds no value, but only ensure things are
correct, the testing needs to be as fast as possible while still ensuring that
no faulty product leaves the factory. Accordingly this form of WiMAX testing
should not include any development , verification, validation or conformance
testing. Instead it should only concentrate on the tests needed to ensure the
product has been correctly assembled.
The type of test equipment used for production testing is
quite different to that needed for, say, conformance testing. Tests need to be
performed very quickly, and therefore the test equipment is honed to ensure that
it can undertake a limited number of tests very quickly.
Summary
WiMAX testing is an essential element of the WiMAX rollout. WiMAX products need
to be correctly designed, verified and validated and then conformance tested.
Once in production, they need to undergo the correct level of production
testing. Although this testing can be costly, it is an essential element of the
development and production process.
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