Electronic Design

UWB Gets Put To The Test

Designers have their work cut out for them, but products are available to make wireless test easier.

Testing any wireless system or device is a challenge, but Ultra-Wideband (UWB) offers more than the usual tribulations. The orthogonal frequency-division multiplexing (OFDM), low power, protocols, frequency hopping, and other physical- layer (PHY) and media access controller (MAC) conditions all add up to the need for a pretty sophisticated test setup. Furthermore, you have to be sure that your chip or box meets WiMedia certification standards. But despite the difficult requirements, you do have some choices.

ANALYZE THIS
The 89600 vector signal analyzer (VSA) software with option BHB from Agilent Technologies analyzes multiband OFDM (MB-OFDM) UWB signals such as WiMedia-based Wireless USB. Using the Agilent Infiniium scopes, including the Agilent 90000 series, the software analyzes all band groups, including BG6, and all time frequency codes (TFCs), including TFI2 hopping modes. It includes all tests required for WiMedia PHY certification, plus multiple error analysis traces and tables, allowing detailed packet, payload, and header characterization.

Users can take advantage of auto-setup features or manually adjust parameters such as time scaling, tone nulling, and hopping status to make measurements even in early design phases. User macros easily automate repetitive measurements like those needed for compliance testing or silicon validation. Signal analysis setup is easy with auto detection of data rate, TFC, and preamble type. Using these automatic measurement selections, the software automatically detects and demodulates the signal even if the parameters change.

Control of advanced setup parameters lets users adjust a wide range of parameters, like time scaling, which is useful for running initial design implementations at slower clock rates whether hopped or not. Users can also set the threshold value for considering subcarriers nulled by enabling tone nulling. Frame check sequence (FCS) information and decoded payload bits are available for analysis of packet and frame structure.

MISTER POPULARITY
The WEX300 analyzer/generator from Ellisys Corp. is one of the most widely used UWB test products available (Fig. 1). The analyzer captures over-the-air traffic and presents it chronologically in terms of frames, full decodes of these frames, protocol error detection, statistical analyses (such as frame sizes, payload sizes, error rates, and throughput), and various timing analyses, all delivered to the user’s screen in real time. It also “understands” not just the WiMedia frames, but also the Wireless USB stack or Bluetooth stack that may sit on top of the WiMedia platform by providing protocol decoding specific to these upper-layer protocols.

Developers can use the WEX300G WiMedia traffic generator to emulate a WiMedia device, generally for testing another device. They also can employ its scripting interface to precisely control the traffic the generator hardware sends. A compliance test suite uses the generator hardware to run automated scripts through a separate application to confirm a device’s compliance with WiMedia specifications.

COST-EFFECTIVE COMBINATION
LitePoint’s IQultra-300 UWB error vector magnitude (EVM) test system combines a special-purpose VSA with an attenuator for UWB receiver testing (Fig. 2). It handles all band groups up to 10.6 GHz and all TFCs from 1 to 10. Its 1.5-GHz bandwidth can cover a three band capture. The single-band IQultra-100 version is also available. Available tests include EVM, mask measurements, adjacent channel leakage power ratio (ACLR), transmitter power, and receiver sensitivity.

These products come with the IQsignal for WiMedia graphical user interface, which controls the unit and support signal analysis. With IQultra’s C++ software applications program interface (API), users can quickly and easily create automated test programs. If the fullblown generic test instrument setup isn’t necessary, this product is excellent for WiMedia production testing. It is one of the most cost-effective UWB test products around.

MEETING THE SPEC
The WiMedia Ultra Wideband Transmitter Measurement Software Package from LeCroy Corp. works with the company’s SDA13000 and SDA11000 serial data analyzers. Designated the QPHY-UWB, it provides a concise set of validation, verification, and debug tools written in accordance with the WiMedia PHY Compliance and Interoperability Test Specification.

With this package, users can measure power spectral density (PSD), perform mask testing of the bands in use in any of the band groups (1-6), observe a constellation display, and measure EVM. The software provides six analysis views: power spectral density, or PSD (mask and adjacent channel power ratio, or ACPR), EVM/constellation, magnitude/phase, spectrogram (spectrum changes over time), common phase error (CPE) versus time, and power.

THE TOTAL PACKAGE
Tektronix has a full-blown test setup for UWB. For receiver testing, developers need a signal generator like the arbitrary waveform generator AWG7122B or AWG7062B (Fig. 3). Add to that the RFX100 test software, and you have a generator that can produce UWB signals in all band groups up to the 10.6-GHz upper limit. All TFC rates are generated. Users also can add real-world impairments to test the design and determine receiver sensitivity and immunity to in-band and out-of-band interference. And, users can validate the Detect and Avoid function.

For transmitter testing, developers need a scope like the Tek DPO/DSA 71254. Add the optional UWB software, and you have a full test platform. Using Tek’s DPX technology, users can quickly identify idle and packet traffic information to determine proper PHY functioning. The scope has deep memory for long capture analysis, and users can trigger on data packets. Other possible measurements include PSD, auto rate detection, time frequency coding, EVM, constellation, and EVM versus time. The Tek RSA6114A spectrum analyzer also can help with UWB RF troubleshooting.

A UWB SIGNAL GENERATOR
The Rohde & Schwarz AFQ100B UWB signal generator and I/Q modulation generator stores waveforms in its 256-Msample, 512-Msample, or 1-Gsample memory. Such long signals are required, for example, for biterror- rate measurements. It also can clock the output over a 1-kHz to 300-MHz range or 600-MHz rate. The generator has two bandwidth options, 200 MHz and 528 MHz, which is ideal for UWB generation.

Balanced and unbalanced outputs are both available. The spurious-free dynamic range (SFDR) is typically 78 dBc. Interfaces include USB 2.0, IEEE 488, and Gigabit Ethernet. The unit includes a 160-Gbyte removable hard drive as well.

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