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New Insights into Varying RF Phenomena with Live RF

March 24, 2008
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The rapid expansion of digital RF applications has driven the measurement needs of many applications including mobile communications and spectrum management beyond the capabilities of swept spectrum and vector signal analysis. To address these new requirements, Tektronix has developed Digital Phospor Technology (DPX™) with live RF that first became available in the RSA6100A performance series introduced in 2006. This technology is now being offered in the mid-range RSA3000B Series of real-time spectrum analyzers, enabling detailed RF signal discovery capability for a broad range of digital RF applications including RFID, radio communications and spectrum management. DPX transforms volumes of real-time data, and produces a live RF spectrum display that reveals previously unseen RF signals and signal anomalies.


DPX waveform image processor technology in the new RSA3300B Series and RSA3408B models displays the live spectrum by processing > 48,000 spectrum updates per second, similar to the previously announced RSA6114A model. This is over 500 times more information than is shown by spectrum analyzers without DPX, minimizing the analysis gaps inherent in swept spectrum and vector signal analyzers. To achieve > 48,000 spectrum measurements per second, DPX makes use of dedicated, real-time hardware to process the incoming signal.

DPX can be used to find illegal jammers captured off-the-air. Figure 1 displays an example on an intentional jammer of GSM signals captured by a spectrum management agency using Tektronix Real-time Spectrum Analyzer (RTSA) using DPX.

In addition to live RF, the waveform image processor also provides an intensity-graded persistence display that holds anomalies until the eye can see them to show the history of occurrence for dynamic signals and immediate feedback on signal variations over time. This provides engineers the ability to rapidly see on screen both transients and signals that ordinarily could not be seen, either because they are masked by other signals or could only be deduced after time-consuming offline analysis. DPX waveform imaging will enhance productivity by quickly capturing elusive anomalies and transient events, improving accuracy and insight, and accelerating design debug.

Digital RF Changes RF World

The explosion of digital RF has created a highly complex spectral environment. In a crowded RF spectrum, signals must use time varying techniques to avoid interference and ensure seamless operation. To improve performance and spectral efficiency, digital RF devices employ signals that change from one instant to the next, including some that hop frequencies, while others use signals that quickly pulse on and off. With numerous devices transmitting simultaneously within a limited radio frequency spectrum, frequent collision and interference problems occur. This makes it important to ensure these devices do not transmit RF energy at unwanted times or unwanted frequencies and are able to function correctly in the presence of interference.

Common to all of the new digital RF technologies is the dimension of time. Enabled by the power of computing in the time-domain world, powerful DSP applied to the RF (frequency-domain) world has necessitated the analysis of spectrum over time. Digital RF technologies can exhibit frequency-domain and modulation changes that occur over time—sometimes milliseconds, sometimes microseconds, or even faster. The limited architecture of traditional RF tools is not able to fully characterize frequency events over time, and time can no longer be ignored. Digital RF creates new requirements for tools whose capabilities mirror the time-varying nature of today’s signals. RF engineers need real-time instruments that can discover how their device operates over time, trigger on intermittent events that occur in frequency, capture them seamlessly and analyze accumulated data representing the passage of time.

The RSA3000B allows engineers to discover the unexpected problems with DPX live RF that are commonplace in digital RF, and selectivity trigger and capture these signals into memory. Once captured into memory, this enables complete time-correlated, multi-domain analysis without the need to recapture the signal.

DPX Makes the Difference

Using a parallel processing architecture, DPX technology produces greater than 500x improvement in the spectrum processing rate. Conventional swept spectrum analyzers typically do not exceed 50 spectrum measurements per second. The RSA3000B Series with DPX technology delivers over 48,000 spectrum measurements per second, with a 100 percent probability of detecting RF spectrum events with minimum signal duration as fast as 31 microseconds (RSA3408B).

By continuously converting time domain signals into the frequency domain, as shown in Figure 1, DPX technology provides a means of displaying both frequent and infrequent events, distilling real-time computing discrete Fourier transform (DFT) at frame rates far above what is perceivable by the human eye and converting them into an intuitive, full motion display.

The RSA3000B Series is able to display live RF signals that have never been visible before, except by using the high performance Tektronix RSA6100A Series. With variable color-graded persistence that holds anomalies until they can be seen, these analyzers help reveal elusive glitches and other transient events, as demonstrated in Figure 2. With each update, the power level values at each frequency across the capture bandwidth are recorded, and the incidence of power over time at each frequency is shown by varying colors on the display. This gives the DPX display a translucent quality that reveals spectral information below the peak amplitude of the time-varying spectral envelope (see Figure 1).

As shown in Figure 3, the figure on the left is a typical display of a signal that can be seen with the fastest swept-spectrum analyzer technology. The Tektronix DPX display on the right shows complex signals and pulses that change frequency and level over time, and can be immediately identified with DPX persistence.

Capture Elusive RF Events in Real Time

To improve capacity and performance, modern RF signals often employ sophisticated combinations of RF techniques such as bursting, frequency hopping and adaptive modulation. The intricacy and prevalence of these time varying RF signals create challenges for designers to capture and analyze. This leads to a need to detect and characterize RF signals and events over a wide range of strengths, durations and environments. Traditional spectrum analyzers and vector signal analyzers are limited to power level or external event triggering. However, since many time varying transients do not increase the signal amplitude when they happen, and signals do not always tell you where they are going, these triggers do not always satisfy the need to isolate spectrum events efficiently for analysis.

This need is addressed by the Frequency Mask Trigger (FMT) in the RSA3000B Series that allows the user to trigger a measurement based on the occurrence of a unique pattern of events in the frequency domain. The high dynamic range of the FMT also allows triggering on weak transient signals while ignoring strong known signals. Operating across either the 15 or 36 MHz real-time bandwidth, the FMT reliably captures elusive RF signals or frequency abnormalities.

The FMT is useful for finding short duration or time varying signals while troubleshooting RF circuits. It can detect sporadic signals, the presence of intermodulation products and transient spectrum containment violations. The FMT is also appropriate for surveillance and radio communications applications, with the ability to capture a spectrally interesting event, such as a weak signal pulse under complex spectral conditions.

Mid-range Fits Many Applications

The RSA3300B Series and RSA3408B, with DPX Spectrum, provide 100 percent probability of intercept for transients as brief as 31 microseconds on the RSA3408B and 41 microseconds on the RSA3300B Series models. This is combined with the ability to trigger on transient signals in both the time and frequency domains for troubleshooting and debugging of a wide variety of digital RF designs and for use in many different application areas.

The RSA3300B Series is available with either DC to 3 GHz or DC to 8 GHz frequency coverage. With a 15 MHz capture bandwidth and 70 dB spurious free dynamic range (SFDR), the RSA3300Bs are well-suited for use in the design and debugging of 3G mobile systems, near-field systems (such as RFID and Bluetooth), and narrow to medium bandwidth communications systems.

The RSA3408B with DC to 8 GHz frequency coverage, a 36 MHz capture bandwidth and 73 dB SFDR is tailored for higher bandwidth and dynamic range applications including 3G mobile components and system debugging, WLAN (IEEE 802.11 a/b/g/n), MIMO and WiMAX system design, demanding spectrum management applications and general purpose digital RF debug.

Comprehensive RFID/NFC Standards Support

Adding to an already extensive support of RFID industry standards, Tektronix now supports ISO 18000-7 and ISO 15693 RFID standards. With this support, the RSA3000B Series provides integrated analysis for the most comprehensive set of RFID/NFC standards in the industry: ISO 18000-4 (Mode 1); ISO 18000-6 (Type A, B, C); ISO 1444-3-2 (Type A/B); ePC Global Gen 1 and Gen 2; and ISO 18092 (424k). These are performed using simplified standards-based measurements for timing, frequency, modulation, decoding and bit-rate measurements for the RFID standards.

Active and passive RFID are part of a much larger hierarchy to tag and track everything in the supply chain. Though adequate infrastructure has not yet been deployed, retailers would like to see a supply chain developed so every piece of merchandise could be managed from the manufacturing origin through the point of sale.

Testing is required for standards compliance, design verification and troubleshooting during chip design, tag integration with the antenna and system integration. More complete testing is required for full compliance and interoperability testing at independent testing labs. Testing is also needed to ensure interoperability between tag and interrogator manufacturers throughout the RFID value chain.

For RFID measurements, the RSA3000B goes beyond the conventional compliance tester. It functions as a field interoperability tester for real-time interference troubleshooting. The DPX live RF capability sees and measures interrogator-tag transactions live to debug problems such as tag confusion caused by adjacent interrogators, high power tag interference with low power tags and listen-before-talk bugs, as shown in Figure 4.

Conclusion

Tektronix real-time spectrum analyzers are designed specifically to solve problems created by digital RF technologies. The addition of DPX technology with live RF from the high performance RSA6100A Series combined with a broad range of application-specific measurements make the mid-range RSA3300B Series and RSA3408B well-suited for tough RF discovery and debug problems, and for use as an everyday spectrum analysis and system characterization tool.

Tektronix Inc.
Beaverton, OR
(800) 833-9200
www.tektronix.com

RS No. 301

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