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This Defense Intelligence Reference Document, DIA-08-1004-005, is dated 6 April 2010. The Defense Intelligence Agency's Defense Warning Office prepared it under the Advanced Aerospace Weapon System Applications program. It reviews proposed laboratory generators and detectors for high-frequency gravitational waves. It favors a piezoelectric approach for proof-of-concept tests, IR-excited molecules for an operational transmitter and the Li-Baker detector as the receiver. It estimates about 1.9 million bits per second over 7,000 km through the Earth and discusses timing standards and interplanetary navigation uses.
From the source:Release of 2026-09-18 Incident: 4/6/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD examines whether high-frequency gravitational waves could serve as a communications medium while avoiding the attenuation that limits radio-frequency systems. The report surveys proposed transmitter and detector concepts, argues that gravitational-wave communications could support secure point-to-point links, timing standards, and interplanetary navigation, and gives particular attention to laboratory generator concepts and the Li-Baker detector as possible building blocks for such a system. The document makes clear, however, that the entire concept depends on capabilities that had not been demonstrated in practice, including laboratory-scale generation and reliable detection of usable high-frequency gravitational-wave signals. It is an exploratory systems-oriented review built around a future communications concept.
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3.3.4 The Impact of Frequency Noise Improvements on FDMA and
FHSS
The very low noise frequency standard that would be supplied by an HFGW FTS system
would allow for much more efficient use of reserved frequency bandwidth. Frequency
noise limits the type of modulation and manner of encoding that can be performed in
frequency space, such as Frequency Division Multiple Access (FDMA) or Frequency
Hopping Spread Spectrum (FHSS). HFGW can reduce frequency noise by providing a
frequency reference with outstanding stability. For example, guard bands can be shrunk
in FDMA, and frequency slices can be smaller and more stable in FHSS.
A frequency space representation of the FDMA and FHSS noise improvements are
depicted in Figure 22.
High Freq Noise
Case
Low Freq
Case
oise High Freq Noise
Case
Low Freq Noise
Case
Larger Guard Bands Smaller Guard Bands
t
~~;.~ .- r- ~ r- -- -
I II
Fewer Freq
Symbols ,,,-·
t ~~
Frequency-;--+Frequency~
(a) Frequency Division Multiple Access. (b) Frequency Hop Spread Spectrum .
Figure 22. The Impact of Frequency Noise Improvements on FDMA and FHSS
Efficiencies in guard-band structure can be defined as in Equation (14).
Guard band BW Efficiency = (Total Bandwidth - {Sum of Guard BW} )/Total Bandwidth
(14)
Guard bands often consume 30 to 50 percent of assigned frequency space. While guard
bands would still be required to allow for the side lobes of signals, the frequency error
component would be eliminated. Similar efficiencies may be gained in the FHSS
approach. A better knowledge of absolute frequency allows better frequency coding
efficiencies, as seen in Equation (13) and depicted in Figure 21.
3.4 POSSIBLE FUTURE UPGRADES TO THE FTS DEVICES
Per the 9 Feb 2009 issue of New Scientist, optical lattice clocks are under development
that will lead to a dramatic improvement over the current standard Cesium atomic
oscillation clocks that now provide frequency time standard references. Optical lattice
clocks vibrate at optical frequencies rather than microwave frequencies, with the
reference frequency mixed down via frequency combs to allow measurements back
down in the microwave regime. Strontium lattice clock are already operating with
measurement precisions of 1 part in 10 16 , and theoretical performance approaches 1
part in 1018 . At this precision one could measure the time delay caused by changing
once centimeter in height in the Earth's gravitational field.
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30 Not linked to a story yet.
Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 57 pages are in the text index: search them above, or from the library's search.