WiMAX testing and WiMAX conformance test

- 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.

WiMAX development test

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:

  1. Base Station Emulator (BSE):     - used for testing a mobile station (MS).

  2. 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.

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.

By Ian Poole

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