Inside Track

Dec. 16, 2011
With David Erisman, Chief Technology Officer, X-COM Systems
NF: For many people in the microwave industry, the announcement of your Wideband Acquisition Record and Playback (WARP) system introduced them not just to this product, but to the company as well.

DE: That's probably a fair assessment, although I formed the company in 1996. Our first commercial products were introduced in 1997. Because most of our early efforts were for a specific customer or customers, however, we've kind of flown under the radar. WARP has certainly changed that, and I hope it will bring more attention to our other systems and software. I'd call WARP the culmination of our development efforts in high-speed analog-to-digital conversion, error-free digital recording on solid-state media, field-programmable-gate-array (FPGA) programming, signal generation, timing and control, and signal-analysis software. So WARP is certainly our most comprehensive product because it has 15 times the bandwidth of any other commercial RF signal capture and recording system. But it is far from our only one.

NF: How has your product line evolved?

DE: Our product line today covers three key areas. The first is signal capture. In the case of WARP, it can be either directly from an antenna or from frequency-downconverted signals. In our IQC-2110 RF capture and storage product, it is from a baseband signal provided by a high-performance signal analyzer. The second area is spectrum playback, which is exemplified by our CPG-2110 continuous playback generator. It converts digital spectrum fileswhich were either recorded by the IQC-2110 or created using, for example, our Wave CAF program or MATLAB from The MathWorksback to the analog domain. They can then be played back through a vector signal generator (VSG) at their original frequency or at a different frequency. All of the instruments are supported by disk arrays of various capacities with redundancy. The technology required to store data at high rates is really another key development area, although we don't sell these storage systems alone.

The IQC-2110 and CPG-2110 have a maximum capture bandwidth of 150 MHz, which exceeds the output bandwidths of current signal analyzers. We will be increasing this shortly to accommodate instruments that have just been introduced. WARP differs from the IQC-2110 and CPG-2110 in that it captures data directly from an antenna or downconverter and needs no spectrum analyzer to serve as its front end. The third area is software, which includes the following: Spectro-X, which allows spectrum to be parsed and signals to be identified and visualized among many other functions; RF Editor, which allows in-phase (I) and quadrature (Q) files to be modified or rearranged much like an audio or video editing system; and WaveCAFE, which allows custom waveforms to be created.

NF: How does the WARP system work?

DE: WARP captures RF signals with an instantaneous bandwidth to 6 GHz, which can be DC to 6 GHz or 6 GHz of spectrum downconverted from a higher-frequency band. This requires an exceptionally capable analog-to-digital converter (ADC)in this case, a 12-GSample/s device. Once the analog signals are captured and digitized, WARP distributes them to a RAID array of solid-state drives with total capacity of 32 TB. If you're sampling at the full 6 GHz of bandwidth, this translates into about 44 minutes of continuous recording or nearly 3 hours at 1500 MHz. FPGAs also are extensively used for processing and moving data around the system. So you can see how the technologies that I mentioned work together to enable continuous capture and recording without losing data. However, this capability and such massive amounts of data would be useless if we didn't develop a way to use it for solving problems. This is why we've worked so hard on our software.

NF: What are the specific benefits of having all of this capability?

DE: Current real-time signal analyzers are incredibly powerful instruments, but they essentially capture a snapshot in timeand a very short time at that. Once the real-time analyzer receives a trigger, its operation ceases being real time until that acquisition is completely post-processed. There are many instances when an interferer appears randomly or very infrequentlywhether it's a jammer, the spurious or harmonic content of a system at a lower frequency, or some other errant signal that's degrading a system's performance. Without the ability to continuously capture and store every bit of signal activity over a long period of time, finding that interferer is highly unlikely.

Probably the most impressive capability of Spectro-X is that it can find a signal or signals of interest among millions of samples over long periodseven if the transmission is only a few microseconds long. It lets you see where the suspect signal was before it appeared in your band of interestwhether it hopped in, swept in, or simply appeared and disappeared. Spectro-X will search the entire file for a signal that matches what you've found based on numerous user-defined parameters. This correlation capability is truly unique among software tools. Once a signal of interest has been found, Spectro-X allows you to clip and save only that portion of the much larger file. You can then export the smaller file to tools like MATLAB or X-MIDAS for more detailed analysis. Because they are limited in memory to the RAM in a workstation, those tools cannot work on terabyte-sized files.

NF: Who are the most likely candidates for this hardware and software?

DE: Generally speaking, any organization that needs to view the signal content in a large swath of spectrumover a period of time from minutes to hours or days and then analyze it in minute detailcan benefit from the WARP system. For example, some radar systems today have signal bandwidths of 1 GHz or more. So if you record their output over a specific period, you can evaluate it to see if they are stable. To judge a system's performance in radar, EW, ECM, ESM, and other defense applications, you can play back an RF spectrum file at its original frequency rangewith its original characteristics, or those modified with RF Editor or other software. If there is a problem, you can create a countermeasure for it and transmit the spectrum again to see if the fix worked.

Military test ranges and development laboratories are excellent candidates for WARP. In a single system, they have the ability to record and play back a very large amount of spectrum. They can apply techniques to the signals, insert new signals, rearrange them, and do a variety of other things to evaluate new or existing designs. It gives them immense flexibility without resorting to cobbling together an array of broadband tuners and a rat's nest of cables, and finding some way to make sense of the results. We also have found considerable interest from spectrum managers in government and military organizations, whose job it is to monitor and control spectrum usage. This is a truly enormous challenge, as the signal environment is incredibly dense and getting even more congested. WARP lets them record the entire contents of the most densely populated portion of the spectrumDC to 6 GHzand look for variations between samples taken at different times.

NF: Now that you have set the RF-acquisition bandwidth record, what's next?

DE: We just introduced the 4CH-VSG2000, which is a 2U rack unit that is only 3.5 in. high. It contains four phase-coherent, arbitrary-waveform vector signal generatorseach with a bandwidth of 110 MHz and output of 50 MHz to 2 GHz, a 1-TB solid-state drive for waveform storage, control software, and assorted interfaces. It's small enough for mobile field testing or jamming applications and can be easily integrated into an ATE system via Ethernet. We designed it for people who need to simulate complex signal environments and evaluate multiple-input multiple-output (MIMO) systems and devices like smartphones, which have multiple receivers. But the applications are actually much broader than that.

Unlike some other systems, the 4CH-VSG2000 is not limited to using standards-based waveforms, such as 3GPP Long Term Evolution (LTE). It will accept any waveform sequence constructed of various waveform segmentswhether it was created in tools like MATLAB, Signal Studio from Agilent Technologies, RFXpress from Tektronix, our own WaveCAFE software, or recorded over the air. It's extremely flexible. The outputs of the generators can be phase locked, independently varied in phase, or completely independent of each other in phase and frequency. It's a powerful system in a small package, which has already received a warm welcome from our beta customers.

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