By Michael Lawton, Product marketing engineer, Wireless division, Agilent
When people talk about the digital life, they usually refer to mobility and content. But neither of these benefits is possible without a reliable and feature-rich wireless device. It is the test engineer who makes sure that all the software and hardware components in these complex devices work together. The role of the test equipment supplier is to make the work of these engineers as easy and productive as possible.
Delivering digital services in a mobile environment is challenging, and the demand for multimedia applications is driving technology to ever higher data rates. Modulation formats such as 1xEV-DO, EDGE, WCDMA, and HSDPA are becoming the norm.
In the R&D lab, engineers have to verify that their implementations of these technologies meet industry standards before releasing a new wireless device into manufacturing. They also have to thoroughly test the many applications now embedded in the device and ensure that it performs well at maximum data rates, even if these rates are unlikely to ever be achieved in an operating commercial network.
Test challenges
Traditionally, design engineers test software and hardware separately. They use scripting solutions to develop the protocols and RF-based tools to test physical-layer components. Everything comes together at the integration and verification stage, however, when the complex inter-workings of software and hardware must be tested as realistically as possible in a network running data traffic.
According to engineers, integration can be a painful business. Each problem they identify must be solved before they can move on to the next step. Solving one problem often leads to uncovering another. Test engineers can't just verify part of a chipset, for example, when they know that an elusive problem still exists. And whenever they modify firmware or software for any reason, they have to do regression testing to measure the effects of the change.
A range of commercial test equipment, specifically scripting engines, RF parametric testers, and stack-based signaling testers, address the various aspects of integration and verification testing. A particularly useful tool for engineers is a bench-top test set that combines capabilities of the three major instrument types. The test set emulates an operating base station and other critical parts of the network to make real-world performance testing possible in the lab.
Control of the test environment
With "network in a box" capability, engineers can establish a call between a wireless device and the test set, send IP data traffic at maximum data rates, and apply controlled signal degradation to stress-test their product.
The air interface, which can distort or attenuate a data signal, is always a complicating factor in a wireless call. So is mobility. Data applications don't like lost connections, delays, or sudden drops in throughput as a caller changes location in relation to the base station.
By using a test set to emulate these real-world conditions in the controlled lab environment, engineers can identify potential problems in a wireless device earlier in the development cycle when problems are less costly to fix.
Advanced features in the test set will help simplify the job of testing. A data throughput monitor, for example, can recognize significant reductions in data flow. Protocol logging software can capture and analyze messages related to the data recovery and flow control.
Engineers can use two test sets together to emulate the cells involved in a handover, testing complex scenarios such as cell selection and reselection or dual transfer mode. They may also run multiple data transfers simultaneously, start and stop data transfer tasks, and run tasks over long periods of time to check for memory leaks or other management issues in their wireless device.
Consistency throughout the life cycle
A test set that incorporates a real-time, stack-based architecture with RF measurements and protocol analysis gives engineers what they need for integration and verification testing. It also gives them a way of assessing their compliance to industry standards prior to formal conformance testing.
Engineers can run selected RF and protocol conformance tests from their bench in the lab, an easier approach than trying to gain access to a full-scale conformance test system.
The same test set may even be a key component of RF and protocol conformance test systems, systems used in manufacturing test, and equipment used for interoperability testing and field trials. In such cases, the test engineers will benefit from a consistent approach to the measurements across the product life cycle. When test equipment vendors provide consistent test methodologies and platforms, they help lighten the load on engineers and pave the way for the production of new wireless devices. That brings everyone another step closer to the promise of the digital life.