By Rob Johnson, Anite

Working with TTCN

3G is happening. As the broader market reconciles the overly optimistic expectations of the last several years, the wireless industry is, in fact, proceeding with the launch of next-generation wireless services. The momentum and commitment behind 3G network deployment and terminal development remains strong. It is the overblown 3G "hype"— not the underlying technology and market forces — that has subsided, allowing carriers and handset manufacturers to focus on the challenge of implementing the next step in wireless communications. Top order of business remains the migration of wireless subscribers to new, 3G-based applications and services. This critical transition is dependent on the integrity and operability of 3G infrastructures and handsets; delivery must be seamless, ensuring profitable adoption by discerning subscribers.

As operators pursue their timeline for 3G deployment, however, they face a quandary along with their handset suppliers: How to meet roll-out objectives and jumpstart the market with advanced 3G handsets, while simultaneously avoiding the operability issues capable of scuttling the entire transition process. A successful transition will depend in large part on the availability of rigorously tested, 3G-capable handsets, handsets that must also function properly across multiple technologies, i.e. GSM, GPRS, and EDGE. Handset performance, in turn, is ensured through compliance testing that uses comprehensive test suites to rigorously exercise complex 3G protocol stacks.

The 3G Testing Regime

An effective test strategy needs to thoroughly exercise 3G device designs and functionality across a range of normal and abnormal operating conditions. In complex communications structures such as 3G systems, this requires explicit testing of protocol stacks in hundreds of different specific and repeatable situations. And, given the increasing complexity of 3G systems, providers cannot afford to rely solely on operational testing as they introduce new products and services. The only viable solution is to conduct comprehensive pre-deployment testing of handsets using Third Generation Partnership Project (3GPP) -defined test specifications, which entail the high-level definition of hundreds of industry-standard test cases for 3G products.

The 3GPP - a broad-based consortium that generates globally-applicable specifications and reports for a 3rd generation mobile system — has assumed the task of translating high-level "core specifications" for mobile devices into "prose test specifications" that ultimately will be translated into TTCN test cases. (See sidebar: Working with TTCN) In parallel, the Global Certification Forum (GCF) is also evaluating the test specifications and prioritizing them in the context of an overall implementation scheme that will provide operators with standard test regimes to support introduction of 3G handsets.

Conformance test cases that have been "tuned" or optimized for execution on a specific hardware platform provide handset manufacturers and wireless operators a consistent, more accurate 3G test and measurement regime.

Examples of 3GPP test coverage required by Global Certification Forum (GCF) include:

• Idle mode

• Basic procedures

     MO call (mobile originated call)

     MT call (mobile terminated call)

     Packet and Circuit Switched data

• Lower Layer Protocol RLC, MAC

• Cell selection and re-selection

• Handovers

• Simultaneous services, Speech + Data

• Interoperation between 3G and 2/2.5G

With the need to address both existing and evolving standards within multi-mode 3G handsets, the volume of required test cases represents a massive undertaking. For example, more than 800 GSM/GPRS tests have already been specified to cover operation across the 850 MHz, 900 MHz, 1800 MHz and 1900 MHz bands — and if you include each band, the number scales up to ~1,500 tests. In addition, over 700 specified W-CDMA test cases have been selected from the many thousands of possible W-CDMA functions. As W-CDMA and its feature-rich handsets come to market, its many different data rates and coding schemes will all need testing, requiring test cases to include multiple paths, e.g., repeating the same test at 9.6 kbit/s and 64 kbit/s. As a result, producing a combined, multi-mode W-CDMA/GSM/GPRS handset will likely require developers to perform thousands of conformance tests. Additionally, test cases are written to Known Pass and Known Fail conditions, which requires the testing of multiple paths of failure to ensure handsets function properly across varied operating conditions.

Although the abstract nature of TTCN provides a good environment for creating "ideal" test cases, these test cases must still be able to run efficiently on the testing hardware. In order to provide optimal performance, the test processes must take into account specific resources and capabilities available in the target test platform(s). Given the overall complexity of 3G wireless technology and importance of subtle timing issues, it is vital that the test cases and testing hardware be "tuned" or optimized to maintain a consistent, repetitive testing environment. Otherwise, developers run the risk of uncontrolled variables in the test environment generating variations in test results, thereby masking errors or creating false error conditions in the device under test.

Putting Test Development on a "Faster Path"

Some 3G handset manufacturers and test and measurement providers continue to be very concerned over the amount of effort remaining to create and debug the detailed TTCN code, as well as the inherent risks of not having sufficient test cases available to support the growing market need for 3G deployments.

As a result, one strategy being implemented is an independent and more aggressive schedule to develop TTCN test case code that conforms explicitly to the 3GPP prose definitions, with the target of providing a critical mass of test cases to support full-scale 3G rollouts as soon as possible. This comprehensive initiative is focused not only on producing TTCN code, but also includes independent third-party validation of the test cases as well as optimization for real-world testing on target test system platforms.

In this regard, a key advantage of a test and measurement solutions provider like Anite in delivering 3G test cases is its ability to tune the TTCN code to mesh with specific hardware. A solutions provider is able to optimize the hardware's efficiency to provide better cost, features and performance than can be achieved by overlaying abstract TTCN code on to generic hardware. Instead of treating the development of 3G TTCN test case code as an end in itself, this development process is aimed at providing comprehensive test platforms that target the real-world testing requirements of 3G manufacturers and operators, thus providing a faster path to actual 3G deployment.