JED - August 2014 - 29

with HF

As observed by Wollesen, the difficulty is not due to a shortage of smart
people to address the challenge, but
rather that "the problem they are trying
to attack is itself very hard. And, the
other thing about the military domain
versus the civil domain, is that you're
not working in a permissive environment; people are actively trying to deceive you and are actively trying to deny
your ability to receive their information. These are challenges that remain
constant, whether you're working with
SDR or dedicated analog electronics."

CALLING SYSTEMS
An additional challenge facing both
the modern HF SIGINT system designer
and the SIGINT analyst is the use of
advanced calling systems in the HF
arena. Similar in some ways to the way
cell phone communication links are established, these are sophisticated and
automated communication connection
systems that establish a link between
communication stations in milliseconds,
while taking into consideration numerous factors such as antenna type, range,
propagation inversions, ionosphere and
atmospheric conditions, noise and other
factors (such as jamming) prior to even
transmitting message signals. (For more
on the HF region, see "HF SIGINT Battles
the Ionosphere" on p. 32.)
Calling systems have been in use in
HF for nearly 20 years now, with some
extremely advanced versions now available that can frequency hop and adapt
to changing parameters in the middle
of a transmission, switching to a different channel and reestablishing the link
right where they left off. As observed
by Kilgallen, "You can imagine the problems this can pose. For example, if you
don't know who called who, how do you
know what modem got set up after-

wards? Sure, you might stumble into the
modem, but you won't have a full understanding of how that network works."

WIDEBAND VS. NARROWBAND
Not unique to HF, but certainly a
major factor for SIGINT system designers, is whether to focus on wideband
or narrowband collection systems.
Obviously, wideband systems can collect signals over a wider bandwidth,
and for that reason they are primarily
used to broadly survey an operational
environment to determine what is out
there. Narrowband systems with higher-quality processing are then used to
examine specific channels of interest
in more detail.
As described by Wollesen, there are
some very fundamental tradeoffs between wideband and narrowband approaches with a tight mathematical
relationship between bandwidth and
processing of dynamic range. From his
personal experience, Wollesen says he believes it's generally more difficult to design wideband systems. "For narrowband
systems, there are a great number of specialized components that are perfectly
tailored for very particular military communications bands and that offer amazing value and performance. Achieving
this same performance with wideband
components is an ongoing challenge.
Still, having said that, there are systems
out there that can act as both a broadband and narrowband platform."
Some wideband collection systems
are in fact themselves also capable of a
fair degree of the higher-level processing
found in their narrowband counterparts.
These "digital drop" receivers are essentially software-implemented narrowband
receivers that automatically select individual channels and "drop them down"
for further processing. Says Kilgallen,

The Journal of Electronic Defense | August 2014

platform together with an application
or applications that turn that platform
into something more specialized. Just as
depending on their processing technology requirement, some users will invest
in a more powerful computer or server to
run their applications, the majority of
users can get away with a less expensive
generic system, while the application(s)
can run across all of the platforms."
Very much related to this, one particular technology development posing
challenges for SIGINT systems operating across the entire spectrum is the
widespread use of Software Defined
Radio (SDR). Noting that while there
are many different architectures called
SDR, Wollesen says they define it as, "a
separation, as best as possible between
the digitization and tuning of a radio
signal and the processing or information extraction method of that signal."
As such, Wollesen says, "SDR gives you
the freedom to do things, at least conceptually, that would be traditionally
impossible using dedicated silicon and
dedicated processing."
Of course, like most things in the
EW/SIGINT world, the SDR technology sword cuts both ways, making the
signal detection and processing challenge exponentially greater even for extremely sophisticated SIGINT systems.
Says Kilgallen, "today anyone can write
software to create a modem that can
be uploaded into some firmware, and
all of a sudden, there's a new mode on
the network. Imagine what the arrival
of systems that completely reprogram
themselves in milliseconds does to the
intercept challenge. And, then there
are networks now that will implement a
mode, use it for a few days to do an operation, and then it goes away and we'll
never see it again. We have no response
to that."

SIGINT

29



JED - August 2014

Table of Contents for the Digital Edition of JED - August 2014

The View From Here
Conferences Calendar
Courses Calendar
From the President
Letters
The Monitor
Washington Report
World Report
Back to the Future With HF SIGIHT
HF SIGIHT Battles the Ionosphere
Technology Survey: Solid-State Power Amplifiers
Book Reviews
EW 101
Index of Advertisers
JED Quick Look
JED - August 2014 - cover1
JED - August 2014 - cover2
JED - August 2014 - 3
JED - August 2014 - 4
JED - August 2014 - 5
JED - August 2014 - The View From Here
JED - August 2014 - 7
JED - August 2014 - Conferences Calendar
JED - August 2014 - 9
JED - August 2014 - Courses Calendar
JED - August 2014 - 11
JED - August 2014 - From the President
JED - August 2014 - 13
JED - August 2014 - Letters
JED - August 2014 - The Monitor
JED - August 2014 - 16
JED - August 2014 - 17
JED - August 2014 - 18
JED - August 2014 - 19
JED - August 2014 - 20
JED - August 2014 - 21
JED - August 2014 - Washington Report
JED - August 2014 - 23
JED - August 2014 - World Report
JED - August 2014 - 25
JED - August 2014 - 26
JED - August 2014 - 27
JED - August 2014 - Back to the Future With HF SIGIHT
JED - August 2014 - 29
JED - August 2014 - 30
JED - August 2014 - 31
JED - August 2014 - HF SIGIHT Battles the Ionosphere
JED - August 2014 - 33
JED - August 2014 - 34
JED - August 2014 - 35
JED - August 2014 - 36
JED - August 2014 - Technology Survey: Solid-State Power Amplifiers
JED - August 2014 - 38
JED - August 2014 - 39
JED - August 2014 - 40
JED - August 2014 - 41
JED - August 2014 - 42
JED - August 2014 - 43
JED - August 2014 - 44
JED - August 2014 - Book Reviews
JED - August 2014 - EW 101
JED - August 2014 - 47
JED - August 2014 - 48
JED - August 2014 - Index of Advertisers
JED - August 2014 - JED Quick Look
JED - August 2014 - cover3
JED - August 2014 - cover4
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