Multichannel Spectrum Monitoring

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"National Instruments has a proven track record of releasing new VSA hardware on a regular basis, including new bandwidth capabilities, FPGA coprocessing functions, and improved RF sensitivity. With NI’s commitment to maintain a common programming interface even across these new hardware releases, and the driver abstraction layers built into Spectrum Defender’s software architecture, the user of this spectrum monitoring system enjoyed a clear system upgrade path, and a long system lifecycle."

- Sean Wallace, Acquired Data Solutions, Inc.

The Challenge:
Building compact system for spectrum monitoring of multiple satellite transponders to ensure compliance with FCC-mandated power and spectral mask limits, and detect any intermittent spurious transmissions or anomalous events.

The Solution:
Using Acquired Data Solutions, Inc. (ADS) Spectrum Defender™ platform with Surveyor™ module, configured for four-channels, with the NI PXI Express vector signal analyzer (VSA) and high-speed disk recording.

Author(s):
Sean Wallace - Acquired Data Solutions, Inc.

About ADS

ADS is foremost a data acquisition and control company spanning a variety of operational, environmental, and technical domains. These domains range from RF spectrum, vision, acoustics, and vibration to testers and systems that emulate environments and capture responses for development and operational test.

Typical Industry Requirements and Limitations

Systems specifically designed for spectrum monitoring applications typically acquire RF signals from a reference antenna or downlink, analyze the shape (or mask) of the acquired signals, and compare the mask of the acquired signals to some user-supplied reference mask or power level. These are the foundational requirements for nearly any spectrum monitoring system in service today. However, since the industry for spectrum monitoring equipment is not high volume, many of these systems are unfortunately built using standard spectrum analyzers originally designed for an entirely different purpose (such as R&D or production testing). The size of the spectrum monitoring marketplace has not supported highly specialized spectrum monitoring functions at a budget-friendly price point. Often, the software or firmware that runs the spectrum analyzer hardware was not designed with off-air spectrum monitoring as a driving use case for the instrument, which resulted in a clumsy user interface with poor productivity and significant gaps in functionality.

Fortunately, the combination of a high-volume PXI Express VSA with the lower volume Spectrum Defender software suite ends this industry paradigm. Users can now enjoy the benefits of a highly specialized and capable spectrum monitoring solution within budget. This powerful high-volume hardware and low-volume software combination is a natural fit in this application area.

System Solution

Recently, ADS took advantage of these benefits for a key customer engaged in satellite operations for the military/aerospace industry. As ADS dug into the project during the requirements discovery phase, we realized that a few additional capabilities would extend the system’s value proposition to real-world users. These additional capabilities fell into two categories: productivity enhancements and signal analysis insights.

Productivity Enhancements

The underlying PXI Express hardware and Spectrum Defender software suite could easily manage four channels of simultaneous spectrum monitoring across multiple satellite transponders/polarities, but we quickly determined that a single operator could probably not carefully monitor all four channels simultaneously. An operator could certainly not recognize if very short duration/intermittent anomalous events exhibited time correlation across multiple spectrum monitoring channels. This wetware limitation led to a newly identified requirement for raw IQ signal recording and synchronized slow motion playback of anomalous events across multiple channels. We added high-speed disk array hardware and a license for Spectrum Defender’s Recorder option to enable slow-motion replay of anomalous events for further investigation, troubleshooting, and interference source identification.

Also during requirements discovery, we found that users faced a large number of operational tasks in a network operating center (NOC) environment. It seemed unlikely that even one operator could check in on RF mask compliance on more than an occasional basis. This pragmatic use case scenario indicated that we needed a fully autonomous spectrum monitoring solution with push notifications of anomalous events. We implemented push notifications through email and SNMP traps. SNMP is a health monitoring technology common in IT-centric environments. A higher-level system health monitoring package (such as Nagios) would receive and log SNMP traps and OIDs automatically.

Signal Analysis Insights

Unlike traditional spectrum monitoring solutions, the PXI Express VSA and Spectrum Defender software can deliver access to real-time streaming IQ data with no acquisition dead time. In practice, this permits signal analysis not only in the frequency/spectral domain, but also in the time domain, modulation domain, and joint time-frequency domains. A wide range of new analysis capabilities and signal insight become possible when RF signals are captured as a raw IQ series, instead of just conventional frequency domain snapshots.

With access to raw IQ data, users could postprocess anomalous event recordings to increase resolution bandwidth in the frequency domain, demodulate signals, add band-limiting filters, and test compliance against a variety of different spectral masks in an iterative fashion.

Continued Evolution

Finally, adopting the PXI Express platform and Spectrum Defender software gave the user a clear migration path to higher frequency bands (such as the K and Ka band), up to 765 MHz instantaneous capture bandwidths, and advanced analysis features. The NI PXIe-5668R 26.5 GHz VSA delivers a migration path to these features. Figure 1 shows a block diagram of the final system configuration. Note the addition of RF capture capability and push notifications through email and SNMP.

National Instruments has a proven track record of releasing new VSA hardware on a regular basis, including new bandwidth capabilities, FPGA coprocessing functions, and improved RF sensitivity. With NI’s commitment to maintain a common programming interface even across these new hardware releases, and the driver abstraction layers built into Spectrum Defender’s software architecture, the user of this spectrum monitoring system enjoyed a clear system upgrade path, and a long system lifecycle.

Figure 1. System Architecture

Summary Conclusions

  • Operation with fewer NOC technicians
  • Size optimized to fit four channels into the space of one legacy instrument
  • New analysis modes including event correlation across multiple channels
  • Higher productivity with autonomous email reporting and SNMP monitoring
  • Software code base that easily ports with new NI VSA hardware releases

NI Hardware (varies by implementation)

Author Information:
Sean Wallace
Acquired Data Solutions, Inc.
sean.wallace@acquiredata.com

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