A Good Scout™

An SwRI-developed tool enables signal analysts to scan an area’s radio spectrum and locate signal sources

James H. Nixon     image of PDF button

image of Jim Nixon

James H. Nixon is director of the SIGINT Solutions Department in SwRI’s Signal Exploitation and Geolocation Division. He leads the design, development and deployment of modern radio communications intelligence solutions. His expertise includes wideband and narrowband signal acquisition and direction-finding systems.

image SCOUT logo  
image of stored display of radio frequency activity.

One aspect of the Scout system is an SwRI-developed function known as “Prospector,” whose user interface allows the operator to select from a stored display of radio frequency activity over the past 24 hours. An operator can select a single RF signal (photo above) for analysis by Scout software (photo below).

image of a Scout software interface  
image of usage allocation chart.

Scout operates across the RF spectrum, as shown in this usage allocation chart.

image of engineer at Scout system

An SwRI engineer prepares a Scout system for operation. The unit is much more compact than earlier systems.

Tourists who find themselves in an exotic locale typically spend some time taking in the local sights and sounds to get a better sense of the place and its people. Likewise, before military specialists can operate safely in some remote and potentially hostile part of the world, they also need a sense of the local environment’s electronic sights and sounds.

An almost universal facet of modern communications is the unseen and silent chatter of wireless communications, both friendly and hostile. Unlike normal broadcast radio or TV stations, the sources of this chatter don’t advertise their broadcast frequencies. It is up to signal intelligence, or SIGINT, specialists to detect the signals, locate their source and interpret their significance to the mission at hand. Engineers at Southwest Research Institute (SwRI) have been conducting research in antennas and geolocation for more than 60 years. A newly developed system — dubbed Scout — is a portable, yet highly capable system for supporting radio frequency (RF) survey teams deploying to uncharted geographic regions.

Reading the signals

Scout comprises a family of wideband radio frequency survey and direction-finding systems that operate in the high, very high and ultra-high (HF, VHF and UHF) frequency ranges. It provides a view into the types of communications transmissions employed in the geographic region of interest. If a network of Scouts is deployed, the locations of these transmitters can be determined using direction finding and radiolocation techniques. Such surveys are an important first step in understanding an adversary’s modes of communication and preparing military and intelligence sources for the electronic battlefield.

SIGINT is derived from electronic signals and systems used by adversaries for communications systems, radars and weapons systems. It provides a vital window into the capabilities, actions and intentions of adversaries. A category of SIGINT called communications intelligence, or COMINT, focuses on exploiting an adversary’s communications signals. These types of signals include voice, Morse code and many digitally coded signals, such as those used by cell phones and data modems.

Scout includes a radio antenna, special radio signal tuners and a number of high-performance servers similar to those used by information technology data centers and for scientific research. Once the radio spectrum is digitally converted to ones and zeros by the special wide-bandwidth radio receiver hardware, the digitized radio spectrum is transferred over a high-capacity local area network to an array of computer servers. SwRI-developed software running on these servers performs a number of signal processing steps needed to take the raw RF environment and transform it to useful information. The first step in this process is to automatically detect signal events occurring anywhere within the frequency coverage of the system. Once such energy has been detected, the system builds a software radio receiver that filters and isolates the new energy into a narrow-band channel.

Adding a sense of direction

The Scout system can construct hundreds of these channels simultaneously. Once the new energy has been channelized, it is routed to one of many mission prosecutor software services. Within these mission prosecutors, the channel is automatically analyzed by SwRIdeveloped modulation recognition software to determine the general type of modulation employed and ascertain whether the energy comes from a voice, Morse code or digital modem signal, and what kinds of digital modulation techniques are being employed. Additional processing is applied to digitally modulated signals to further refine the identification process, ultimately resulting in a determination of the specific type of modem employed, and in some cases, the underlying data protocols in use.

If the digital signal is recognized by the system, it is then demodulated and decoded to extract the underlying data being communicated. Even signals that are not part of the Scout signal-ofinterest library are catalogued. This information can help the user discover new signals of interest. If the unit is equipped with the radio direction-finding option, a line of bearing is computed from the Scout’s location to the radio transmitter. Moreover, a number of Scouts can be networked together and the various lines of bearing can be triangulated so that the radio transmitter’s estimated location can be computed. The final results are stored in a database. Web browser-based tools are provided with the system to allow any authorized user on the Scout network access to the collection results.

Record now, playback later

Scout also supports manual search and user-driven signal discovery operations. The automatic RF environment cataloguing operation requires that the user already know many details about the signals of interest. In many cases the types of signals are known, and the automatic search capability will confirm that they exist in the geographic region of interest. However, if an adversary deploys a newly invented signal waveform, the automatic system may not identify those emissions or characterize them in enough detail to assist the user. For these situations, the SwRI team developed a graphical user interface (GUI) tool, called Prospector, which is deployed with Scout to enable the operator to visualize the RF environment and search for interesting and unique signal activity. This is accomplished by storing the last 24 hours of RF spectrum on Scout’s internal hard drive. An operator who sees an interesting signal event can simply draw a box around the signal and Scout constructs a software radio on the spot that channelizes the signal and presents the waveform in another SwRI-developed tool called Tass. Tass provides a multitude of signal analysis tools that enable the breakdown of signal structures, including demodulation of fundamental modulation schemes. Scout’s ability to store the entire radio-frequency environment on disk and channelize any part of the spectrum at will is akin to having “TiVo® on steroids” — except that instead of storing only your favorite channels, Scout stores everything on the RF spectrum, enabling the operator to reconstruct any kind of signal event after the fact.

Combining capabilities of earlier systems

Originally developed to replace a now-retired system, Scout not only exceeds its predecessor’s capabilities in automatic detection of known signals of interest, but also has a fully integrated direction-finding capability. The way signals are described in Scout is compatible with U.S. Department of Defense formats, enabling Scout to leverage new signals as they are developed by others. Additionally, 24 hours of RF environment storage and a GUI enable the user to manually scour the last 24 hours of RF activity and reconstruct and locate a signal event. This capability was previously performed by other systems that were separate from Scout’s predecessor.

Scout does a job that previously required a number of systems from multiple vendors. By combining automatic search and signal identification functions with a manual search tool, Scout reduces the hardware resources required to support RF survey missions and also reduces the cost.

Scout is based on commercially available, high-performance servers widely used in data centers across the globe. All of the signal processing required to support the operating modes consists of software rather than expensive special-purpose processing components such as those developed for the aerospace industry. This combination of commodity hardware and a software-defined framework gives Scout an unprecedented level of scalability and expandability. Leveraging the commercial computer market allows the use of the latest computer technology with minimal risk of obsolescence and keeps costs economical, while taking advantage of the latest breakthroughs in the globally driven computer market.

Although Scout’s primary application is in support of U.S. and allied military, law enforcement and intelligence communities, potential commercial applications could include surveying other types of radio spectrum signals, such as electromagnetic interference emissions from industrial and power distribution sources.

Questions about this article? Contact Nixon at (210) 522-2619 or jim.nixon@swri.org.

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