How to effectively validate new RF technologies
With the advent of new technologies such as high-speed downlink packet access and high-speed uplink packet access, RF verification has rapidly evolved to address the complex RF interfaces found in today's telecom standards.
Intensive mathematical analysis is required to correctly understand and verify these interfaces. Most sectors of the telecoms industry have defined validation processes and procedures that laboratories must adhere to.
In the mobile-phone segment, groups such as the Global
Certification Forum and the PCS
Type Certification Review Board use validation as the fundamental
basis to determine test cases for mobile-phone validation.
Note that a validation organization must be ISO 17025-accredited, be independent of test-system manufacturers, and have acquired solid industry expertise.
Validation of a new technology begins as soon as an appropriate industry body decides that the technology is stable, and that there are enough manufacturers and operators ready to use it.
The validation organization is required to write a specification before starting any verification, after which it produces a validation report.
Similarly, in case of problems during test implementation, the manufacturer must be alerted immediately. Generally, a laboratory verification procedure entails the following steps:
1. Confirm that the manufacturer uses the correct version of the industry specifications.
2. Check that the protocol message sequences comply with relevant test specifications.
3. Ensure that the correct pass, fail or inconclusive verdicts are given.
4. Verify that the implementation is stable and will run reliably in different scenarios.
5. Assess the calibration methodology.
6. Evaluate the manufacturers' test-system uncertainties.
7. Assess the accuracy of the test system's RF path-compensation procedures.
8. If a new hardware is added to the platform, perform rigorous testing to ensure that its RF characteristics suit its intended purpose.
Meanwhile, a validation report must detail all software, firmware
and hardware used, along with the version of the industry specification
and any amendments to it.
Any deviations done and the rationale for such must also be noted. However, a detailed description of the device-under-test (DUT) may prove difficult to make due to commercial confidentiality agreements.
Non-compliance with a test case is something that manufacturers would not want to admit to their competitors. The test platform manufacturer identifies a target test case. Several DUTs from different manufacturers that can run appropriate test cases are then acquired.
Often, this means approaching the manufacturers directly because off-the-shelf devices do not support special test modes required for testing. Nonetheless, non-compliance is not an issue as it helps determine how a test platform behaves with failing user equipment. In fact, large failure data can crash a test platform if the manufacturer has not allotted sufficient memory for it.
Several technologies require the manufacturer to complete an
implementation conformance statement to determine the suitability of a
test sample. However, the surest and fastest way to do so is to run the
test case on a test sample. A protocol trace log records the full test.
Cellular technologies use DUT and test system logs, while WLAN technologies often use over-the-air "sniffers." Basic RF parameters are easily verified using standard test measurement instrumentation. Meanwhile, some test sample modes and settings are only verified using debug facilities within the DUTs or with trace logging tools.
To reduce test times, some technologies use statistical analysis. Keeping the test time at a minimum without compromising the accuracy of the overall pass-fail verdict is a paramount consideration.
A simple but time consuming method of assessing the accuracy of the statistical test method requires comparing the measurements done with and without statistical analysis. Generally, the industry committees write and develop the standards.
The task of validation laboratories is to ensure compliance with these specifications. However, labs can also point out errors to industry representatives.
Reviewing the manufacturer's system uncertainty calculations is vital. Often, the applicable industry will have issued guidelines on how to calculate uncertainties.
For mobile radio equipment, an industry body such as the European Telecommunications Standards Institute issues technical reports that detail the methodology for calculating and applying uncertainties.
System uncertainties are a combination of systematic and random components, the suitability of detectors to measure modulated signals, the operation of test instrumentation in linear measuring range and mismatch of RF connections.
A huge amount of data can be gathered from manufacturers' data sheets and from calibration certificates, while repeatability of measurements can be quickly checked by practical measurements.
Independent validation laboratories help manufacturers keep abreast of evolving applicable standards. They develop and maintain relevant skills in both consultancy and verification testing, while advising manufacturers on test specifications and generating accurate test reports.
More importantly, they help expedite the launch of RF products in the market, matching new technologies with consumer needs and prevailing standards.
Stuart Thomas is Manager of
Cellular Technology Development at RFI
Global Services Ltd.
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