Design and test links help support multistandard radios from design to production

As wireless communications standards evolve, engineers must contend with multiple RF standards addressing cellular, WLAN, geopositioning, Bluetooth, and other connectivity applications. The “Special Report: Applications” in our March issue highlights hardware and software offerings that can address multistandard radio implementations. In this Online Exclusive companion article, industry experts elaborate on the tools they offer, with particular attention to their applicability from design verification though manufacturing test. In addition, they comment on the increasing importance of links between design and test.

Spanning the lifecycle

Martha Zemede, applications expert in Agilent Technologies' Microwave and Communications Division, said, “Agilent offers an extensive range of test equipment for a wide range of wireless technologies covering the lifecycle from early design and development through volume manufacturing, to conformance test and field service.” Agilent's 89600 VSA, Signal Studio, and SystemVue software products, she said, are targeted at physical-layer testing in R&D, system integration, or design validation for base stations, user equipment, modules, or components that go into the various devices. Agilent covers more than 75 radio standards and modulation types, she said, with recent additions being LTE-Advanced and 802.11ac WLAN.

All three software products, she said, can be used with multiple Agilent products. “For example, 89600 VSA supports more than 40 measurement platforms including signal analyzers, oscilloscopes, and logic analyzers, allowing users to choose hardware based on performance, bandwidth, and number of channels needed.” With the 89600 VSA's multimeasurement capability, she said, users can analyze multiple radio standards (any of the 2G, 3G, 4G cellular or wireless connectivity standards such as WLAN and Bluetooth) simultaneously and with no restriction, and they can analyze signal quality along the signal path from baseband to RF. Users can also analyze uplink and downlink signals simultaneously. Similarly, she said, “SystemVue can be used to combine any of the radio formats (cellular and non-cellular) into a single MSR waveform,” enabling a combination of 89600 VSA and SystemVue to address high-level design and verification of MSR devices.

A Tektronix spokesperson said, “We have solutions for the entire RF value chain—chipsets/components, embedded systems, radios, and mobile devices—in R&D, testing and validation, integration, compliance, and troubleshooting. We know that as standards evolve and designs become more complex it becomes increasingly difficult to keep the cost of testing down.” One approach taken by Tektronix has been to introduce mixed-domain instruments. “By leading the way in mixed-domain products such as our MDO4000,” the spokesperson said, “Tektronix ensures that customers can test their designs effectively without investing in a great deal of additional equipment. Whether customers need a solution that crosses time and frequency domains, correlates digital and RF events, or looks at multiple radio standards across a wide frequency range, we provide a solution that can be easily upgraded to keep total cost of ownership concerns at bay.” In addition, the spokesperson said, “with SignalVu software running on the instrument or on a PC, modern VSA functionality no longer requires a dedicated spectrum analyzer if a scope can do the job.”

Design and test

The Tektronix spokesperson also commented on design and test. “The collaboration between design and test is always important but has grown more so in recent years. As we talk about multistandard devices and RF embedded in even the most nontraditional places, the potential for interference, EMI, self-jamming, and other performance limiting situations grows. Tektronix provides a number of tools to work within wireless standards or in custom applications to catch potential problems before going to final testing and conformance stages of the lifecycle—thus ensuring product success and shortening time to market.

“A notable example of this link between design and test is our EMI diagnostic solution on the RSA series spectrum analyzers. Not only does the RSA let you view the most transient events in the frequency range of interest, but our spurious search function and DPX-powered spectrum processing enables a full range of diagnostics to be performed quickly and confidently. Having the confidence that designs will pass full EMI compliance before leaving the lab means reduced time to market, lower testing costs and less complexity the lifecycle.”

Zemede at Agilent also addressed design and test. “Collaboration between design and test is very important as it helps accelerate development and minimizes risk throughout the product development cycle,” she said. “The complexities of devices with multiple radio access technologies along with time-to-market pressures make it critical to minimize system integration risk to avoid costly design turns and product delivery delays.”

She added that simulation tools such as Agilent's EDA tools help minimize integration risk throughout the product development lifecycle, from the initial design through R&D hardware testing. RF/baseband integration is prone to risk, she said, and simulating and verifying RF and baseband designs together can help mitigate the integration risk and unexpected behavior late in the system testing phase.

“As the design cycle transitions to the hardware testing stage,” she said, “Agilent’s design software can be combined with test equipment to verify system-level performance. With this approach, some portions of the design are modeled in simulation, and other portions are represented as hardware device under test (DUT). The simulated signals can be downloaded to an arbitrary waveform signal generator to turn simulated signals into real world physical test signals.”

She said the test signals then serve as stimuli for hardware DUTs during R&D testing. “The 89600 VSA software can capture digital and RF DUT outputs using a variety of different instruments (X-Series signal analyzers for RF DUT output or logic analyzers for digital DUT outputs) and transfer the data into Agilent’s design software for simulation post-processing,” she said. “The ability to integrate EDA tools with instruments to stimulate, measure, and emulate hardware subsystems extends the reach of simulation tools further into the design lifecycle. The ability to use the 89600 VSA software for both design simulation and testing of real hardware provides unique measurement-algorithm and user-interface consistency across the entire product development cycle.

Haydn Nelson, product marketing manager, RF and wireless at National Instruments, said, “Traditionally, we’ve observed a substantial organizational divide between design and test groups developing wireless products. However, one of the ways we’re bridging the gap is by enabling design and test tools—and therefore data—to be shared between both groups. For example, a new feature in AWR’s (A National Instruments Company) Visual System Simulator (VSS) software is co-simulation abilities with NI LabVIEW system design software. This feature enables engineers to use measurement algorithms developed in LabVIEW inside their EDA tools. As a result, design and test engineers are better able to correlate measurement results between simulations and measured performance of a DUT.”

Manufacturing Challenge

Zemede at Agilent also elaborated on a manufacturing challenge. “3GPP Release 9 introduced multistandard radio-base station conformance testing in a new TS37 series standard,” she said. The standard covers five radio formats (LTE-FDD, LTE-TDD, GSM, WCDMA, and TD-SCDMA), which are divided into three band categories. “The standard defines MSR RF test requirements such as channel power, modulation quality (EVM), frequency error, spurious emissions, and spectrum emissions mask (SEM) under MSR multicarrier allocating scenarios,” she said. “For base station manufacturers, the challenge is in verifying their MSR base station against the TS37 standard and doing so under fast measurement speed.” She added, “The N9083A MSR measurement application addresses this challenge by providing fast, one-button standard compliance transmitter measurement in accordance to 3GPP TS37 standard. Transmitter tests can be performed on any combination of LTE FDD, W-CDMA/HSPA/HSPA+ and GSM/EDGE/EDGE Evolution multi-RAT signals.”

For testing MSR components such as a base-station power amplifier, she said, “The test challenge is to determine how a multistandard signal affects a base-station power amplifier. The Agilent Signal Studio software for LTE-FDD or TDD (N7624B or N7625B) allows a creation of any combination of 2G, 3G, and 4G waveforms using a single signal generator as a stimulus MSR signal for power amplifier testing. The software includes built in tools to assess amplifier compression for different signal configurations.”