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RF test aims at wireless standards

Posted: 16 May 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Ron Harrison? RF Test? rf? opinion? national instruments?

Wireless standards are inundating the market, placing tremendous demands on the test engineer and on the tools necessary to test these new integrated devices. There are two realities in device manufacturing. First, assembly complexity is inversely proportional to the level of integration. Second, functional test complexity is proportional to the number of features and wireless standards to test.

This challenge is compounded, because RF measurements and tests for a particular standard often require specific firmware personalities or modes of operation for the test instrument. Testing multiple wireless standards on a single device requires either purchasing another RF test instrument for that standard (increasing test costs) or reconfiguring the instrument firmware or mode for the next standard (increasing test time and cost for new firmware).

The solution to these challenges is to take a different approach to the architecture for RF test instruments. The two biggest hurdles in building a software-defined RF test system are the processing power necessary to demodulate, decode and analyze acquired waveforms, and the bandwidth necessary to transfer a large enough waveform from the measurement circuitry to the processing circuitry.

Engineers can overcome these hurdles by using a modular, PC-based architecture with a high-throughput bus interconnecting the measurement and processing circuitry. An example of an ideal software-defined architecture is the rugged, CompactPCI-based PXI platform for test, measurement and control. PXI leverages commercial off-the-shelf computer components, such as the latest Intel processors and large memories, and a PCI-based high-throughput bus that links this controller to the measurement module.

The measurement module uses a modular architecture, incorporating a downconverter unit to transfer a block of frequency spectrum to an IF acquired by a digitizer unit, which then transfers this large waveform to controller memory using the 132Mbps bus in the PXI backplane.

An example of software-defined, modular instrumentation is the development of a MIMO-OFDM system. The combination of MIMO and OFDM lies behind many of the latest wireless and data standards emerging, including 4G mobile cellular communications and 802.11n Wi-Fi data networking, designed to increase the number of subscribers and data throughput on cellphones and computers, respectively.

The Wireless Networking and Communications Group (WNCG) at the University of Texas at Austin studied the characteristics of this system to validate the research and benefits of MIMO-OFDM. The WNCG study involved simulation and full hardware integration components, and took six weeks to complete. This was made possible by the high degree of reuse of MIMO-OFDM software simulations and models in the software used to define the PXI-based modular RF vector signal generators and analyzers from National Instruments.

The result of using a modular, PC-based architecture such as PXI is a universal, software-based RF test system that can adapt to any type of measurement and wireless standard. The system also has the ability to test multiple wireless standards and protocols, and adapt to emerging communication standards.

- Ron Harrison
Product Marketing Manager, RF and Communications
National Instruments Corp.

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